Selected Recent Results from HERMES

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					                     Selected Recent Results from HERMES
                                 Seattle Spin Symposium, August 4-7, 2003

                                                         Wolf-Dieter Nowak
                                                          DESY Zeuthen
                                                     Wolf-Dieter.Nowak@desy.de




                                           For the                           Collaboration




Wolf-Dieter Nowak (DESY), HERMES Collaboration                                    Seattle Spin Symposium, August 4-7, 2003   – p.1
                                                  Table of Contents
This talk:
           HERA polarized e± beam,
           HERMES forward spectrometer & polarized internal target
           First measurement of the tensor structure function b1
           Deeply Virtual Compton Scattering on nuclei (D, Ne, Kr)
           Observation of f0 (980) scalar meson in electroproduction


   Most other HERMES physics topics covered in parallel talks
   ⇒ list will be given at the end of this talk




 Wolf-Dieter Nowak (DESY), HERMES Collaboration                  Seattle Spin Symposium, August 4-7, 2003   – p.2
                                            Polarized Beam at HERA
                                                              Beam                                                   transverse
                                                             Direction                                              Polarisation

                                                                                                 Transverse
                                                                                  HERA B         Polarimeter



                                                ZEUS                        HERA Electron Ring                                      H1



                                                                            Longitudinal   Longitudinal
                                                                            Polarimeter    Polarisation


                                                                  Spin Rotator                       Spin Rotator
                                                                                      HERMES
                                 Comparison of rise time curves
                   80
Polarization [%]




                        Transverse Polarimeter
                        Longitudinal Polarimeter                                            27.5 GeV e+ /e− beam
                   60

                                                                                            Self-polarizing through
                   40
                                                                                            Sokolov-Ternov-Effect
                   20                                                                       Average beam polarization
                   0
                                                                                            of about 55%
                             6            6.5          7    7.5           8
                                                                       Time [hours]



     Wolf-Dieter Nowak (DESY), HERMES Collaboration                                                            Seattle Spin Symposium, August 4-7, 2003   – p.3
                                The HERMES Experiment
                                              FIELD CLAMPS                        TRIGGER HODOSCOPE H1
m
                         FRONT                                   DRIFT CHAMBERS               270 mrad
2                        MUON
                                                                                                                                                 170 mrad
                         HODO
                                                                                                   PRESHOWER (H2)




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                                      CHAMBERS                                                                                                                              27.5 GeV
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0
                                                                                                          MONITOR
                                                                                                                                                                            e+




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        TARGET                            MC 1-3
         CELL




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                  HODOSCOPE H0




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-1                                                           BC 1/2




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                                                                                   BC 3/4    TRD        CALORIMETER                                                         140 mrad




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                  STEEL PLATE




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                                                                          RICH                                              IRON WALL
-2                                                                                                                                                                170 mrad
                                                                                             270 mrad
                                                                                     WIDE ANGLE
                                                                                                                    MUON HODOSCOPES
                                                                                   MUON HODOSCOPE
                                                                 MAGNET

              0             1             2           3      4            5           6            7           8             9                            10 m

           Forward spectrometer: 40 mrad ≤ Θ ≤ 220 mrad
           Tracking: O(50) tracking planes per half spectrometer:
            δp/p ∼ 1% (2%), δΘ ≤ 0.6 (1) mrad
           PID: e± , π ± , K ± , p by Cherenkov (RICH ≥ 1998), TRD, Preshower, Calorimete
     Wolf-Dieter Nowak (DESY), HERMES Collaboration                                                       Seattle Spin Symposium, August 4-7, 2003                                     – p.4
                   HERMES Internal Gas Target
                                                                                          gas injection
                                                     target
                                                 vacuum chamber
                                                                                    G

                                           C2                                       G
                                                                                          wake field
                                           fixed                                   G
                                                                                         suppressors
                                           collimator                                                      thin walled
                                                                                    G                     beam pipe
                                                                    G    G    G    G G   G
                                                                              G                G
                                                                        G         G G G GG  GG
                                                                             G         G G GG G G


                                                                                                                                                 Polarized
                                                                        G     G        G
                                                                    G             G

                                                                G
                                                                         Storage Cell               G
                                                                                                          thin exit
                                                                                                                                                 deuterium
                                                        G                                      G
                                                                                                           window
               movable                                          G

              collimators C1
                                                                                                                                                 hyper-fine
                                                        G                                          G

                                                                                               G




                                                                                                                                                 splittings
                                                            G

                                                                to pump                            to pump


                                                                                                                                                        ⇓
                                                                                                                                   4




                                                                                                                          E/EHFS
                                                                                                                                          mF                                     mI          mS

  Pure gas target ⇒ no dilution


                                                                                                                          D
                                                                                                                                                                                      }
                                                                                                                                         +3/2                             |1 >   +1
                                                                                                                                         +1/2                             |2 >    0         +1/2
                                                                                                                                   2     -1/2                             |3 >   -1

  90 s cycling time ⇒ low systematics
                                                                                                                                         -3/2
                                                                                                                         F = 3/2
                                                                                                                                   0

  Polarized gases: H,D (Storage cell                                                                                     F = 1/2


  fed by Atomic Beam Source)                                                                                                       -2
                                                                                                                                         -1/2
                                                                                                                                         +1/2
                                                                                                                                                                          |4 >
                                                                                                                                                                          |5 >
                                                                                                                                                                          |6 >
                                                                                                                                                                                 -1
                                                                                                                                                                                  0
                                                                                                                                                                                 +1
                                                                                                                                                                                      }      -1/2



  Unpolarized: H, D, He, N, Ne, Kr                                                                                                 -40                      2                         4
                                                                                                                                                                                          x = B/B
Wolf-Dieter Nowak (DESY), HERMES Collaboration                                                                                     Seattle Spin Symposium, August 4-7, 2003                  – p.5
                   Vector and Tensor Polarization
                               Spin- 1
                                     2                           Nucleon   Spin-1                     Deuteron

                                                                              m= −1 0            +1
                                      m= −1/2                +1/2

                                                                                           .

                                                                    z            n−                                z
                                               n−                                               n+
                                                            n+                        n0

 Vector
                                                           n+ −n−                            n+ −n−
olarisation                                 Pz =           n+ +n−             Pz =         n+ +n− +n0
                                                   |Pz |      1                     |Pz |             1
 Tensor
                                                                                        (n+ +n− )−2n0
olarisation                                                                  Pzz =       n+ +n− +n0
                                                                               −2              Pzz < 1

  Wolf-Dieter Nowak (DESY), HERMES Collaboration                                      Seattle Spin Symposium, August 4-7, 2003   – p.6
       Polarized Atomic Deuterium Target
                    Spin states can be separately chosen
                    Target ‘mode’: combine 2 spin states

                                                 hyperfine states   injected no.
                              target mode        injected by ABS   of particles   Pz            Pzz
                                 vector +          |1 > +|6 >          n+         +1             +1
                                 vector –          |3 > +|4 >          n−         −1             +1
                                 tensor ±          |3 > +|6 >       n + + n−       0             +1
                                 tensor 0          |2 > +|5 >          n0          0             −2
                                                                                  ( ideal values)


            ⇒ Large Pzz ≈ 1.665 (at tiny Pz ≈ −0.01) accomplished

                    6 weeks of special data taking in ‘tensor operation’
                    2.4 Mio. DIS events recorded for the extraction of bd
                                                                        1
Wolf-Dieter Nowak (DESY), HERMES Collaboration                                    Seattle Spin Symposium, August 4-7, 2003   – p.7
     DIS Structure Functions in the QPM
  hD           q                                 q           q0
                 hq




              Spin- 1
                    2                            Nucleon     Spin-1                     Deuteron

              p,n                1                                    1
             F1 =                2          e2 q ↑ +q ↓
                                           q q
                                                            d
                                                           F1 =       3        e2 q ↑ + q ↓ +q 0
                                                                              q q

               p,n              1                                         1
              g1 =              2          e2 q ↑ −q ↓
                                          q q
                                                               d
                                                              g1 =        2      e2 q ↑ −q ↓
                                                                                q q

                                                                  1
                                                           bd =
                                                            1     2        e2 2q 0 −(q ↑ + q ↓ )
                                                                          q q


          bd measures nuclear effects that make the deuteron look
           1
          different from just the most simple proton-neutron system
Wolf-Dieter Nowak (DESY), HERMES Collaboration                                    Seattle Spin Symposium, August 4-7, 2003   – p.8
             Extraction of Tensor Asymmetry
                           d2 σmeas   d2 σunpol                1
                                 2
                                    =        2
                                                1 − Pz PB DA1 + Pzz Azz
                           dxdQ        dxdQ                    2
          σunpol = σ ↑↑ + σ ↑↓ + σ 0                                    vector term                 tensor term
                                                           |
          Pzz =            n+ +n− −2n0                     |     σ ↑↑   +|Pz · PB |                           0
                                                                                                            +Pzz
                           n+ +n− +n0
                                                           |     σ ↑↓   −|Pz · PB |                           0
                                                                                                            +Pzz
                                                           |
                                                                  σ0      < 0.01                             0
                                                                                                          −2Pzz
                         (σ ↑↑ + σ ↑↓ ) − 2σ 0             |
             Azz       =                0
                              3σunpol Pzz                  |             |Pz · PB | = 0.45 ± 0.04
                                                           |                  0
                                                                            Pzz = 0.83 ± 0.03

          Use vector+, vector– and tensor0 modes to calculate Azz
          for 6 bins in xBj (tensor± mode only for cross check):

                                                   1   N ↑↑ + N ↑↓ − 2 · N 0
                                           Azz   = 0 ·
                                                  Pzz   N ↑↑ + N ↑↓ + N 0
Wolf-Dieter Nowak (DESY), HERMES Collaboration                            Seattle Spin Symposium, August 4-7, 2003   – p.9
                     Result: Tensor Asymmetry Azz
                                                               gd
   AT (10-2)


                                                                1
               2
                                                               Fd
                                                                1   0.4   HERMES PRELIMINARY
                                                                          (’00 data, no smearing correction)


                                                                    0.3
               0                                                          exp. systematic uncertainty

                                                                    0.2   uncertainty due to R



                                                                    0.1
               -2

                                                                     0


               -4                                                               -2                          -1
                           -2                         -1                   10                          10
                      10                         10        x
                                                                                                                          x

                    |Azz | of O(1%) over measured range                                         Note: Azz ≡ AT
                    At small xBj : |Azz | ≈ |A1 |                                                                g1
                                                                                                                 F1   ≈ A1

                    At larger xBj : little impact on g1 determination
                                                      d

Wolf-Dieter Nowak (DESY), HERMES Collaboration                            Seattle Spin Symposium, August 4-7, 2003       – p.10
                              Model Calculations for b1
        0.2
b1




       0.15
                                                               Theory work < 1997:
                                                                 binding & Fermi motion effects at x ≥ 0.2
        0.1

                                                               Theory ≥ 1997: Double scattering
       0.05
                                                                 diffr. nucl. shadowing + pion excess mech
            0
                                                                 Nikolaev et al., PLB 398, 245 (1997)
       -0.05
                                                                 coherent double scattering
       -0.1                                                      Edelmann et al., PRC 57, 3392 (1998)
       10
<Q2>




                                                                 double scattering through VMD
        1

            -1
                                                                 Bora & Jaffe, PRD 57, 6906 (1998)
       10
                             -2                       -1
                        10                       10        x


         → observe significant enhancement of b1 at small xB :
                 Close-Kumano sum rule                            dx b1 (x, Q2 ) = 0 violated ??
                 interpretable as tensor polarization of the quark sea ?
Wolf-Dieter Nowak (DESY), HERMES Collaboration                                 Seattle Spin Symposium, August 4-7, 2003   – p.11
         Deeply Virtual Compton Scattering
Generalized Parton                                    Unified theoretical description of
Distributions:                                        inclusive and (hard) exclusive processes

                           DVCS: ep → epγ                   (γ ∗ p → γp) in Bjorken limit
                                                                                             γ

                                                 γ∗                 γ   l                         l’
                                                                                                              Bethe-Heitler
 dominant subprocess
                                                                                                              (BH) process
 for DVCS in pQCD:
                                                                                                              has identica
 ‘hand-bag’ diagram
                                                  P            P’           P                    P’           final state

                            dσ ∼ |τBH + τDV CS |2 = |τBH |2 + |τDV CS |2 + I
                                         ∗                   ∗
                                    I = τBH τDV CS + τBH τDV CS

           DVCS dominated by BH in most of HERMES kin. region
           Interference term: access to DVCS amplitudes
           ⇒ Use BH as an ‘amplifier’ to study DVCS
Wolf-Dieter Nowak (DESY), HERMES Collaboration                                  Seattle Spin Symposium, August 4-7, 2003   – p.12
                     φ-dependence of Asymmetries
                                                             dσ ↑ (φ)−dσ ↓ (φ)
Beam Spin Asymmetry                              ALU (φ) =   dσ ↑ (φ)+dσ ↓ (φ) ∝            sin φ · Im(I)
(Long. pol. beam, unpol. target)

                                                            dσ + (φ)−dσ − (φ)
Beam Charge Asymmetry                            AC (φ) =   dσ + (φ)+dσ − (φ) ∝             cos φ · Re(I)
(Unpol. beam, unpol. target)


⇒ Real and imaginary
                                                                                                        γ      φ
part of a linear combi-
nation of DVCS ampli-                                        e’
                                                                                                    θγ∗γ
                                                                        γ*
tudes separately accessi-
                                                        e
ble through ALU and AC

    NOTE: Measuring ALU and AC probes predominantly GPD H .


Wolf-Dieter Nowak (DESY), HERMES Collaboration                      Seattle Spin Symposium, August 4-7, 2003   – p.13
                               DVCS on Nuclear Targets
 Proton                  Probe nucleon                ˜
                                                  Hq, Hq   for t → 0: ordinary PDFs
 Target                  GPDs                         ˜
                                                  Eq, Eq   do not exist in DIS

 Nuclear Probe convolution of nucleon GPDs with nucleon
 Targets momentum spectra inside nucleus
            at large -t: Incoherent scattering ⇒ again nucleon GPDs
            at small -t: Coherent scattering, overlap with incoherent
            (incoherent sample causes dilution of nuclear effect !)

⇒ Problem: Need a model to relate nuclear to nucleon GPDs
⇒ Question: What do we learn about the nucleus’ structure ?

            Polyakov, PL B555 (2003), 57: Large idealized nucleus with ‘skin’
            ⇒ may probe deviations of the distributions of energy, ‘pressure’ and
            ‘shear forces’ (on quarks w.r.t. nucleus) from that of electric charge
 Wolf-Dieter Nowak (DESY), HERMES Collaboration                   Seattle Spin Symposium, August 4-7, 2003   – p.14
                 Nucleus vs. Proton Asymmetry Ratios
                  Anucleus (φ)                                              dx IP V (x±ξ) [H p (x,ξ,0)+(A/Z−1)H n (x,ξ,0)]                                     A
                   C
                  Aproton (φ)
                                                  ∝                                     dx IP V (x±ξ) H p (x,ξ,0)
                                                                                                                                                        ∝      Z     >1!
                   C


                  Anucleus (φ)                                H p (ξ,ξ,0)−H p (−ξ,ξ,0)+(A/Z−1)[H n (ξ,ξ,0)−H n (−ξ,ξ,0)]                                                              A
                   LU
                  Aproton (φ)
                                                  ∝                             H p (ξ,ξ,0)−H p (−ξ,ξ,0)                                                                         ∝    Z   >1
                   LU
                                                        ALU(Neon)/ALU(p)
AC(Neon)/AC(p)




                 2.4                                                       2.4                                            Impulse approximation (xBj ≥ 0.05
                           coh. only                                                    x=0.1, Q=1.58 GeV
                 2.2                                                       2.2                                            Guzey/Strikman, hep-ph/0301216
                  2                                                         2        coh. only
                           Neon/Krypton
                 1.8                                                       1.8



                 1.6                                                       1.6
                                                                                     Neon/Krypton                      ⇒ Nucl. effect only at −t < 0.05
                                         AC
                 1.4                                                       1.4
                                                                                               ALU                        (diluted by incoh. contrib.)
                 1.2                                                       1.2
                                                                                                                          better t-resolution crucial
                  1                                                         1



                 0.8
                       0
                           coh.+incoh.
                           0.02   0.04   0.06   0.08   0.1
                                                                           0.8
                                                                                 0
                                                                                     coh.+incoh.
                                                                                     0.02   0.04   0.06   0.08   0.1
                                                                                                                          Now: use average kinematics
                                                -t, GeV                                                   -t, GeV



Wolf-Dieter Nowak (DESY), HERMES Collaboration                                                                                             Seattle Spin Symposium, August 4-7, 2003       – p.15
      Nuclear Targets - Beam Spin Aymmetry
                                                                0.3                                                                   0.3




                                                                                                                                                                                                     sinφ
                                                                                                                                                                                                                         →+
                                                                                                                                                                                                                         e Kr→e+γX




                                                         φ




                                                                                                                               φ




                                                                                                                                                                                                            LU
                                                          LU




                                                                                                                                LU
                                                         Asin




                                                                                                                               Asin
        →+                                                                    →+                                                                    →+                                                       0.4
        e p → e+ γ X                                                          e d → e+ γ X                                                          e Ne → e+ γ X




                                                                                                                                                                                                     A
                                                                0.2                                                                   0.2                                                                                HERMES PRELIMINARY
        HERMES PRELIMINARY 2000                                               HERMES PRELIMINARY                                                    HERMES PRELIMINARY
                                                                                                                                                                                                             0.2
        (refined analysis)                                      0.1                                                                   0.1

                                                                 0                                                                     0                                                                         0

                                                             -0.1                                                                  -0.1
                                                                                                                                                                                                             -0.2
                                                             -0.2                                                                  -0.2
                                                                                                                                                                                                             -0.4
                                                             -0.3                                                                  -0.3

                                                             -0.4                                                                  -0.4                                                                      -0.6
                                                                                                                                                                                                                     sinφ
    φ                                                                     φ                                                                     φ                                                                    A        |Mx< 1.7GeV=-0.17±0.07(stat.)±
Asin M < 1.7 GeV
 LU                = -0.18 ± 0.03 (stat) ± 0.03 (sys)                 Asin M < 1.7 GeV
                                                                       LU                = -0.15 ± 0.03 (stat) ± 0.03 (sys)                 Asin M < 1.7 GeV
                                                                                                                                             LU                = -0.22 ± 0.03 (stat) ± 0.03 (sys)                    LU
      x                                                                     x                                                                     x
                                                             -0.5                                                                  -0.5                                                                                        2                2
                                                                                                                                                                                                             -0.8 <-t>=0.09 GeV , <xBj>=0.08, <Q >
                   2                    2            2                                   2                    2            2                                   2                    2            2
<-t > = 0.18 GeV , <xB> = 0.12, <Q > = 2.5 GeV                        <-t > = 0.20 GeV , <xB> = 0.10, <Q > = 2.5 GeV                        <-t > = 0.13 GeV , <xB> = 0.09, <Q > = 2.2 GeV
                                                             -0.6                                                                  -0.6
 -1     0      1       2      3     4        5   6                     -1     0      1       2      3     4        5   6                     -1     0      1       2      3     4        5   6                           -1      0     1     2      3       4

                                            Mx (GeV)                                                              Mx (GeV)                                                              Mx (GeV)                                                             M




                             Anucleus
                              LU                                Guzey/Strikman                                          Kirchner/Müller                                           HERMES result
                             Aproton
                              LU                             hep-ph/0301216                                            hep-ph/0302007                                            for sin φ moment
                           Deuteron                                                —                                                        1.15                                         0.83 ± 0.29
                                  Neon                                1.05 ± 0.01                                                           1.31                                         1.22 ± 0.32
                             Krypton                                  1.18 ± 0.01                                                           —                                            0.94 ± 0.44

                       ⇒ Present statistical accuracy not sufficient
      Wolf-Dieter Nowak (DESY), HERMES Collaboration                                                                                                                    Seattle Spin Symposium, August 4-7, 2003                                        – p.16
  Future DVCS Measurements at HERMES
            0.25
                                                                                                   Construct & install RECO
∆t (GeV )




             0.2                                                                                   DETECTOR ( 2004/05)
            0.15
                                                                                                   Reduce non-exclusive
                                                                                                   background to below 1%
             0.1
                                                                                                ⇐ Significant improvement
            0.05                                                                                  of t-resolution at low -t
                                             Silicon                           Spec, DVCS

                                             SciFi                             Spec, rho
                                                                                                   Measure t-dependence
                0
                    0    0.25     0.5     0.75         1     0   0.25   0.5   0.75    1
                                                                                            2
                                                                                                   AC and ALU precisely
                                                                               -t (GeV )


                                 Measurements on nuclear targets possible in 2005/06
                                 Statistics on nuclear target will concentrate on low -t
                        ⇒ Good chance to challenge model builders
                                 (need predictions at exact kinematics of measurements !)
            Wolf-Dieter Nowak (DESY), HERMES Collaboration                                            Seattle Spin Symposium, August 4-7, 2003   – p.17
   Meson Nonets in Const. Quark Model
           SU(3)c q¯ representations:
                   q
                     Vector (J P C = 1−− , L = 0): ρ0 , ω, φ,J/ψ; ρ± , K ∗
                     Pseudo-scalar (J P C = 0−+ , L = 0): π 0 , η, ηc , η ; π ± , K
                     Scalar (J P C = 0++ , L = 1) with masses below 2 GeV:
                             I=0 candidates: σ(400 − 1200), f0 (980), f0 (1370), ...
                             I=1 candidates: a0 (980), a0 (1450)
            ⇒ light scalars problematic: may not be q¯ states, but
                                                     q
                               ¯
                             K K bound states (molecules: (qq)(¯q ))
                                                               q¯
                             multiquark (q qg) hybrid states
                                            ¯
                             mixed glueball state - vacuum scalar state
                     Decay modes: f0 (980) dominant ππ; a0 (980) dominant ηπ
            ⇒ field of controversy for almost 40 years
Wolf-Dieter Nowak (DESY), HERMES Collaboration                          Seattle Spin Symposium, August 4-7, 2003   – p.18
                      Scalar Mesons at HERMES ?
           HERMES (non-)capabilities to look for scalar mesons:
                     difficult to separate from background, as in other
                     scattering exp’s
                     can not do phase shift analysis, but Breit-Wigner fit
                     can study kinematic (Q2 , xBj , p2 , t) dependences
                                                      t

                     different targets available: H, 2 H, 20 Ne, 84 Kr

           HERMES data analysis to extract f0 (980):
                     data: 1996-2000; unpolarized hydrogen
                     DIS cuts: W2 > 4 GeV2 , y < 0.85
                     reaction: e A → e π + π − h X (non-exclusive !)
                     2.5 < pπ > 15 GeV (dual RICH: C4 F10 /Aerogel)
Wolf-Dieter Nowak (DESY), HERMES Collaboration               Seattle Spin Symposium, August 4-7, 2003   – p.19
        Identification of f0(980) at HERMES
1400
                                                  HERMES Preliminary (`96, `97, `00)
1200
                                                           ep → ef0(980)X                    top: after cuts
1000
 800                                                                                         bot: after background
 600                                                                                              subtraction
 400
                                                                                                    fit using 3rd order
 200
    0
                                                                                                    polynomial +
        0      0.2       0.4       0.6       0.8      1       1.2    1.4   1.6    1.8    2
                                                                                 M2π (GeV)
                                                                                                    Breit-Wigner shape
150
                                                                    Mf0 = 980±7 MeV
                                                                                                    only in the region
125
                                                                    Γf0 = 39±15 MeV                 0.9 - 1.1 GeV to
100                                                                 signf. = 4.1σ
  75                                                                                                exclude ρ-region
  50
  25
                                                                                              ⇒ peak seen at book
    0                                                                                           mass 980 MeV
 -25
                                                                                              ⇒ narrow width favore
              0.9      0.925 0.95 0.975                   1   1.025 1.05 1.075 1.1
                                                                            M2π (GeV)
                                                                                                (39 ± 15 MeV)
 Wolf-Dieter Nowak (DESY), HERMES Collaboration                                                 Seattle Spin Symposium, August 4-7, 2003   – p.20
                        Kinematic dependences for f0(980)
                             HERMES PRELIMINARY [ep → ef0(980)X]
                                              0.7                                                        points: data (in acceptance
Norm. Yield




                                                               Norm. Yield
              0.6                               - -
                                      PYTHIA6 (uu+dd)                        0.6
              0.5                     PARJ(15)=0.08
                                                                             0.5                         bands: PYTHIA6: u¯ + dd
                                                                                                                             u    ¯
              0.4
                                                                             0.4                                 + full HERMES cha
              0.3                                                            0.3
              0.2                                                            0.2
              0.1                                                            0.1
                                                                                                           MC- data comparison:
               0                                                              0
                    0       2          4      6     8                          0.3 0.4 0.5 0.6 0.7 0.8
                                               2  2
                                            Q (GeV )                                               z         ⇒ supports q q
                                                                                                                          ¯
              0.8                                                                                              hypothesis
Norm. Yield




                                                               Norm. Yield




              0.7                                                            0.5
              0.6                                                            0.4
                                                                                                            (no other MC exists yet
              0.5
                                                                             0.3
              0.4
              0.3                                                            0.2
              0.2
                                                                                                                     Q2 , Pt2 , ν : ok
                                                                             0.1
              0.1
                0                                                             0
                                                                                                                     peak at z = 0.5
                    0           0.2        0.4
                                           Pt
                                                    0.6
                                              2 (GeV2)
                                                                                   10   15    20
                                                                                              ν (GeV)
                                                                                                                     stronger in data
              Wolf-Dieter Nowak (DESY), HERMES Collaboration                                                  Seattle Spin Symposium, August 4-7, 2003   – p.21
Acceptance-corrected data on Hydrogen
   Acc. Corr. Yield (a.u.)




                              1
                                                         HERMES Preliminary [ep → ef0(980)X]
                                                              (1/Q2)α α=1.6±0.2 (all Q2)
                                                                                   2       2
                                                                                                         DIS: α = 2
                                  -1                                  α=1.8±0.3 (Q >1.0 GeV )
                             10
                                                                                                      ⇒ not inconsistent with
                             10
                                  -2
                                                                                                        f0 (980) produced by
                                       0   1         2         3   4     5         6      7
                                                                                           2
                                                                                               8
                                                                                         Q (GeV)
                                                                                                        DIS fragmentation



                                                                                                         Pt2 -slope consistent
   Acc. Corr. Yield (a.u.)




                              1                          HERMES Preliminary [ep → ef0(980)X]
                                                                 exp(-b.Pt2) b=4.4±1.2 GeV-2
                                  -1
                                                                                                         with NOMAD result
                             10
                                                                                                         (b=5.3 ± 0.2)
                                  -2
                             10
                                       0       0.1       0.2       0.3       0.4       0.5      0.6
                                                                                           2    2
                                                                                         Pt (GeV )




Wolf-Dieter Nowak (DESY), HERMES Collaboration                                                            Seattle Spin Symposium, August 4-7, 2003   – p.22
                               Summary & Conclusions
               First measurement of tensor structure function b1 :
                       significant enhancement of b1 with decreasing xBj
                       suggests significant tensor polarization of the quark sea
                       qualitative agreement with coherent double scattering models


               Deeply Virtual Compton Scattering on Nuclei (D, Ne, Kr)
                       beam-charge (1st time) & single beam-spin asymmetry measured
                       Exply : separation of coherent sample not easy; more data needed
                       Theorly : more work on interpretation highly appreciated


               Observation of f0 (980) in electroproduction (1st time)
                       kinematics consistent with f0 (980) being a q¯ state
                                                                    q
                       produced in DIS fragmentation
Wolf-Dieter Nowak (DESY), HERMES Collaboration                    Seattle Spin Symposium, August 4-7, 2003   – p.23
         Parallel Talks on HERMES Results
                   Monday, August 4, 16:30-16:50 (Room A114)
                   P. Liebing:
                   Double Spin Asymmetries in 1- and 2-Pion Production at
                   HERMES
                   Monday, August 4, 14:55-15:20 (Room C520)
                   R. Kaiser:
                   Exclusive Measurements at HERMES
                   Tuesday, August 5, 14:50-15:15 (Room A114)
                   T.-A. Shibata:
                   Experimental Results on Polarized Quark Distributions
                   from HERMES
                   Thursday, Aug. 7, 11:25-11:50 (Room A114)
                   G. Schnell:
                   Transversity measurements at HERMES
Wolf-Dieter Nowak (DESY), HERMES Collaboration        Seattle Spin Symposium, August 4-7, 2003   – p.24

				
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