Studies of hadronization in nuclei at HERMES

Document Sample
Studies of hadronization in nuclei at HERMES Powered By Docstoc
					Studies of hadronization in
   nuclei at HERMES
          H.P. Blok (VU/NIKHEF)
  (on behalf of the HERMES collaboration)


               • Why?
               • How?
               • What?
               • Next?

          Hadronization workshop Trento, Oct. 2005   1
Motivation
Hadronization is a non-perturbative QCD phenomenon
  Want to know space-time evolution of the hadron
  formation process
  Use nuclei as time/length-scale probe

Hadronization in relativistic heavy-ion collisions possible
  probe of different state of matter
  Nuclei (cold nuclear matter) reference point

Experimental data needed to gauge calculations
  HERMES offers suitable energy range, set of nuclear
  targets, and hadron identification; clean initial state


                 Hadronization workshop Trento, Oct. 2005   2
Method
Semi-Inclusive Deep Inelastic Scattering (SIDIS)

                                                     Variables:
                                                        ν = E − E'
                                                    − Q 2 = q 2 = ( p − p' )2
                                                       z = Eh / ν
                                                         pt2



In free space described by          σ        ∑ f
                                              e 2 q f ( x) D h ( z )
                                               f
                                                             f



                  Hadronization workshop Trento, Oct. 2005                      3
Hadronization (in a nucleus)

quark ‘production’

quark energy loss

(pre)hadron formation

reactions (absorption) of
produced (pre)hadrons




                     Hadronization workshop Trento, Oct. 2005   4
Models
Phenomenological
 A. Bialas and T. Chmaj, PhL 133B (1983) 241
 A. Bialas and M. Gyulassy, NPh B291 (1987) 793
one or two time scales plus corresponding cross sections




Energy loss type
 X. Guo and X.N. Wang, PRL 85 (2000) 3591
 E. Wang and X.N. Wang, PRL 89 (2002)162301
 F. Arleo EPJ C30 (2003) 213
gluon radiation and quark-quark interaction
                                                    h
effective (increased) z in fragmentation function D f ( zeff )
                    Hadronization workshop Trento, Oct. 2005   5
Models
Energy loss and absorption
 A. Accardi, V. Muccifora, H.J. Pirner, NPh A720 (2003)131
 B.Z. Kopeliovich, J. Nemchik, E. Predazzi, A. Hayashigaki,
                                                NPh A740 (204) 211
nuclear absorption cross sections after ‘formation’ time


‘Full FSI’
 T. Falter, W. Cassing, K. Gallmeister, U.Mosel, PR C70 (2004) 054609
coupled-channel treatment of FSI
by means of BUU transport model




                     Hadronization workshop Trento, Oct. 2005        6
Studying hadronization in nuclei

 Measure nuclear attenuation in (e,e’h) SIDIS reaction

                              ⎧ N hSIDIS (ν , z , Q 2 , pt2 ; φ ) ⎫
                              ⎨                                   ⎬
                              ⎩        N h (ν , Q )
                                          DIS          2
                                                                  ⎭A
   RA (ν , z , Q , pt ; φ ) =
    h           2   2

                              ⎧ N hSIDIS (ν , z , Q 2 , pt2 ; φ ) ⎫
                              ⎨                                   ⎬
                              ⎩        N h (ν , Q )
                                          DIS         2
                                                                  ⎭D

 Depending on the size of the nucleus different length
 scales probed

                       Hadronization workshop Trento, Oct. 2005        7
                    HERMES at DESY
HERMES studies the spin structure of the nucleon … but not only..

                                                                E=27.5 GeV e+ (e-)
                                                                     I ~ 30 mA
                                                                 p beam of 920 GeV,
                                                                not used by HERMES




     Internal target polarized and unpolarized gas.
   Last part of the fill:high-density unpolarized runs.




                     Hadronization workshop Trento, Oct. 2005               8
            HERMES Spectrometer




• e+ identification: >99% efficiency, <1% contamination
• Particle IDentification: RICH (< ‘98 Čerenkov), TRD,
                           Preshower, e.m. Calorimeter
                  Hadronization workshop Trento, Oct. 2005   9
HERMES experiments
SIDIS on nuclei: A(e,e’h) with h = π+, π–, π0, K+, K–, p, p

Studied in D, He, N (only all h or π), Ne, Kr (1997-2000)
           D, Kr, Xe (2004)

Ee = 27.6 GeV; some 12 GeV data on N and Kr

       2 (5) < ν < 23.5 GeV
       0.1 (0.2) < z < 1.1
       Q2 > 1.0 GeV2
       W > 2 GeV


                    Hadronization workshop Trento, Oct. 2005   10
Analysis

Calculate RA (ν , z , Q 2 , pt2 ; φ ) for all h
           h




Corrections (largely cancel in double ratio):
      radiative effects
      exclusive ρ production




                      Hadronization workshop Trento, Oct. 2005   11
Hadron attenuation vs transfer energy ν
                                     HERMES, EPJ C 20 (2001) 479.
                                     HERMES, Ph.L. B 577 (2003) 37.
                                     EMC Coll. Z.Phys. C52 (1991) 1.
                                     SLAC PRL 40 (1978) 1624.

                              • Increase of R with ν consistent
                              with the EMC data at higher
                              energy.

                              • Discrepancy with SLAC mainly
                              due to the EMC effect

                              • HERMES kinematics optimal
                              to study medium effects.

           Hadronization workshop Trento, Oct. 2005             12
12 GeV




Data on N and Kr

Average Q2 lower
 at 12 GeV

Good agreement


                   Hadronization workshop Trento, Oct. 2005   13
Target fragmentation
Investigate by looking at xF

For pions very strong correlation of xF with z

Suggestion from data for proton that value of R
stable when xF > 0




                    Hadronization workshop Trento, Oct. 2005   14
 xF coverage/dependence

     Correlation between z and xF for pions and protons




↑
xF




                                                             →z
                  Hadronization workshop Trento, Oct. 2005        15
First data and analysis EJP C20 (2001) 479
Results for N (all hadrons or pions)

‘Time scale’ analysis and comparison with gluon
Bremsstrahlung model

     1.1
               z > 0.5                                                     ■
 π                                                           h/π           ❍
RM                                                         RM      1


      1

                                                                0.9


     0.9

                                                                0.8


     0.8
           8        10   12   14   16     18   20    22                0       0.2   0.4       0.6   0.8    1

                              ν (GeV)                                                      z

                                        Hadronization workshop Trento, Oct. 2005                           16
More detailed studies                                                                               PhL B577 (2003) 37

Kr data with PID from RICH
      h
  R       1
   M
      0.9

      0.8

      0.7

      0.6

      0.5

      0.4
        1

      0.9

      0.8

      0.7

      0.6

      0.5

      0.4
              0   0.1   0.2   0.3   0.4   0.5   0.6   0.7   0.8   0.9   1
                                                                        z




                                                             Hadronization workshop Trento, Oct. 2005             17
ν and z dependence




                 Hadronization workshop Trento, Oct. 2005   18
Comparison of published data with models: ‘Arleo’




                   Hadronization workshop Trento, Oct. 2005   19
Comparison of published data with models: ‘Kopeliovich’




                   Hadronization workshop Trento, Oct. 2005   20
Comparison of published
data with models: ‘Falter’




                    Hadronization workshop Trento, Oct. 2005   21
Results for He, Ne, Kr: pions
         RAπ
   1.1                                                                1.1




                                                                      +
                                                                 π                                                             π-
               4              20               84
                He                 Ne                  Kr
 1.01                                                                  1




                                                                                                                                                1


   0.9                                                                0.9




                                                                                                                                           0.8
 0.8
   0.8                                                                0.8




   0.7                                                                0.7




                                                                                                                                           0.6
 0.6
   0.6                                                                0.6




                                          HERMES PRELIMINARY
   0.5                                                                0.5




                                                                                                                                                    5         10      15         20
                   5          10          15                20                       5          10          15           20                                                           ν(GeV)
         0         5          10          15                20              25
                                                                            0        5          10          15            20         25




                                                                                                                         ν, GeV
   1.1
         RAπ                                                          1.1




                                                                      +
 1.01
                                                                 π     1
                                                                                                                               π-          1

   0.9                                                                0.9




 0.8
   0.8                                                                0.8




                                                                                                                                          0.8
   0.7                                                                0.7




 0.6
   0.6                                                                0.6




             sys. uncer. Ne(He) - 3.3 %                                          sys. uncer. Ne(He) - 3.3 %                               0.6

             sys. uncer. Kr - 3.9 %                                              sys. uncer. Kr - 3.9 %
   0.5                                                                0.5




 0.4
   0.4                                                                0.4




                                                                                                                                                0       0.2    0.4   0.6   0.8          1
                   0.25            0.5         0.75              1.0                 0.25            0.5         0.75          1.0
         0             0.25         0.5         0.75              1         0            0.25         0.5         0.75          1




                                                                                                                                                                                            z
                                                                                                                                     z

                                                                                   Hadronization workshop Trento, Oct. 2005                                                                     22
π+/π- ratio
Based on 3,4He data some more π+ produced on protons
compared to neutrons

Nuclear effects: at lower pπ R(π-) < R(π+) for Ne (N≈Z)

Overall very little difference between R(π-) and R(π+) for
same nucleus




                   Hadronization workshop Trento, Oct. 2005   23
 He, Ne, Kr:                                                                                                                   other hadrons
        RAK                                                                                                                                            RAp
                                                                                                                                             1.4
                                                                                                                                                                                                                              sys. uncer. Ne(He) - 4.5 %
                                                                                                                                               1.4                                                                 1.4




  1.1                                                                   1.1




                                                                                                                                                                                                                                                                           p-
                 4                20              84                    +                                                           -
                     He                Ne           Kr             K                                                           K               1.3
                                                                                                                                                           4
                                                                                                                                                               He
                                                                                                                                                                                20
                                                                                                                                                                                  Ne
                                                                                                                                                                                                84
                                                                                                                                                                                                        Kr    p    1.3




                                                                                                                                                                                                                              sys. uncer. Kr - 7.2 %
1.01                                                                     1




                                                                                                                                             1.2
                                                                                                                                               1.2                                                                 1.2




                                                                                                                                               1.1                                                                 1.1




  0.9                                                                   0.9




                                                                                                                                             1.0   1                                                                1




0.8
  0.8                                                                   0.8
                                                                                                                                               0.9                                                                 0.9




                                                                                                                                             0.8
                                                                                                                                               0.8                                                                 0.8




  0.7                                                                   0.7




                                                                                                                                               0.7                                                                 0.7




                                                                                                                                             0.6
                                                                                                                                               0.6                                                                 0.6




0.6
  0.6                                                                   0.6




                                                                                                                                               0.5                                                                 0.5




                                             HERMES PRELIMINARY                                                                                                                            HERMES PRELIMINARY
  0.5                                                                   0.5




                                                                                                                                             0.4
                                                                                                                                               0.4                                                                 0.4




             5               10              15               20                    5           10          15           20
                                                                                                                                                           5               10              15            20              25     5           10          15            20         25
             5               10              15               20              25    5           10          15            20            25




                                                                                                                                                           5               10              15            20                     5           10          15           20
                                                                                                                         ν, GeV                                                                                                                                      ν, GeV
        RAΚ                                                                                                                                            RAp
                                                                                                                                             1.4
                                                                                                                                                                                                                                                                           p-
  1.1                                                                   1.1                                                                    1.4                                                                 1.4




                                                                        +                                                           -
1.01
                                                                   K     1
                                                                                                                               K               1.3                                                            p    1.3




                                                                                                                                             1.2
                                                                                                                                               1.2                                                                 1.2




  0.9                                                                   0.9




                                                                                                                                               1.1                                                                 1.1




0.8
  0.8                                                                   0.8
                                                                                                                                             1.0   1                                                                1




                                                                                                                                               0.9                                                                 0.9




  0.7                                                                   0.7




                                                                                                                                             0.8
                                                                                                                                               0.8                                                                 0.8




0.6
  0.6                                                                   0.6
                                                                                                                                               0.7                                                                 0.7




            sys. uncer. Ne(He) - 3.0 %                                             sys. uncer. Ne(He) - 3.5 %
                                                                                                                                             0.6
                                                                                                                                               0.6




                                                                                                                                                               sys. uncer. Ne(He) - 4.4 %
                                                                                                                                                                                                                   0.6




            sys. uncer. Kr - 4.2 %                                                 sys. uncer. Kr - 4.2 %
  0.5                                                                   0.5




                                                                                                                                               0.5




                                                                                                                                                               sys. uncer. Kr - 3.9 %                              0.5




0.4
  0.4                                                                   0.4




                                                                                                                                             0.4
                                                                                                                                               0.4                                                                 0.4




                     0.25          0.5            0.75             1.0                  0.25         0.5         0.75          1.0                              0.25             0.5            0.75          1.0                   0.25         0.5         0.75          1.0
        0             0.25             0.5             0.75         1         0          0.25         0.5         0.75          1




                                                                                                                                                       0            0.25             0.5         0.75          1         0           0.25         0.5         0.75          1




                                                                                                                                        z                                                                                                                                        z



                                                                                                     Hadronization workshop Trento, Oct. 2005                                                                                                                        24
pt2 distribution
    1.5
      1.4                                               1.4




                                                    +
h                   4
                     He
                                   20
                                        Ne Kr π                                  π-
R     1.2                                               1.2




A
    1.0
                                                                                                          • Large increase of the
       1                                                 1




      0.8                                               0.8




      0.6
                   sys. uncer. Ne(He) - 3.3 %
                   sys. uncer. Kr - 3.5 %    HERMES
                                                        0.6




                                                                   PRELIMINARY
                                                                                                            multiplicity ratios with
    1.5
      1.4
            10-2




                              K+
                              10
                              -1                1




                                                        1.4
                                                              -2
                                                              10




                                                                                 K-
                                                                                10-1              1




                                                                                                            pt2
      1.2                                               1.2




    1.01                                                 1
                                                                                                          • Nuclear pt2 broadening;
      0.8




                   sys. uncer. Ne(He) - 3.0 %
                                                        0.8




                                                                                                            Cronin effect.
      0.6                                               0.6




                   sys. uncer. Kr - 2.9 %
    2.02                                                 2




                                                                                ⎯
            10-2




                              p
                              10
                              -1                1             10
                                                              -2




                                                                                 p
                                                                                10-1              1




    1.5
      1.5                                               1.5




    1.01                                                 1




                   sys. uncer. Ne(He) - 3.5 %                        sys. uncer. Ne(He) - 3.7 %
                   sys. uncer. Kr - 3.0 %                            sys. uncer. Kr - 3.5 %
    0.5
      0.5                                               0.5




            10-2




                             0.1
                              10
                              -1




                                                1
                                                1             10
                                                              -2




                                                                               0.1
                                                                                10-1




                                                                                                  1
                                                                                                  1




                                                                                              2       2
                                                                                            p (GeV )
                                                                                              t


                                                                    Hadronization workshop Trento, Oct. 2005                     25
Q2 dependence
               RAπ
        1.1                                                                1.1                                                            1.1




                                     +
                                 π                                        HERMES PRELIMINARY                                                                                        20
1.05   1.05




                                 π
                                   -                                      1.05                                                           1.05




                                                                                                                                                                                                Ne
         1                                                                  1                                                              1




0.95   0.95                                                               0.95                                                           0.95




        0.9                                                                0.9                                                            0.9




0.85   0.85                                                               0.85                                                           0.85




                                                                                                                                                                                                                 Q2 dependence weak,
        0.8                                                                0.8                                                            0.8




0.75
                              2 < ν < 8 Gev                                                      8 < ν < 12 Gev                                                 12 < ν < 16 Gev
       0.75                                                               0.75                                                           0.75




                                                                                                                                                                                                                 little or not dependent on ν
        0.7                                                                0.7                                                            0.7


        1.1                                                                1.1                                                            1.1




              0.8   0.9   1      2       3   4   5   6   7   8   9   10          0.8   0.9   1      2   3   4   5   6   7   8   9   10          0.8   0.9   1      2    3       4   5   6   7   8   9   10




1.05   1.05                                                               1.05                                                           1.05




         1                                                                  1                                                              1




0.95   0.95                                                               0.95                                                           0.95




        0.9                                                                0.9                                                            0.9




0.85   0.85                                                               0.85                                                           0.85




                                                                           0.8                                                            0.8
        0.8




0.75
                              16 < ν < 20 Gev                                                    20 < ν < 24 Gev                                                2 < ν < 24 Gev
       0.75                                                               0.75                                                           0.75




        0.7                                                                0.7                                                            0.7




              0.8   0.9   1      2       3   4   5   6   7   8   9   10          0.8   0.9   1      2   3   4   5   6   7   8   9   10          0.8   0.9   1      2    3       4   5   6   7   8   9   10




                     1                                           10                     1                                       10                     1                                            10
                                                                                                                                                                            2                                2
                                                                                                                                                                       Q (GeV )


                                                                                                                                         Hadronization workshop Trento, Oct. 2005                                                        26
Double-hadron attenuation




  Additional way to study hadronization
  R2h sensitive to model assumptions :
     – Partonic energy loss: slight A dependence of double-hadron to
       single-hadron ratio on a nuclear target (correlated (?))
     – Absorption in final state: the ratio decreases with A (uncorrelated)




                       Hadronization workshop Trento, Oct. 2005               27
Double-hadron attenuation
       1.4
 R2h




       1.3                                                       •    Ratio is generally below unity
                                                                 •    No significant difference
       1.2
                                                                      between nuclei
       1.1                                                       •    Mass dependence substantially
                                                                      smaller than for single-hadron
        1
                                                                      case
       0.9                                                       •    Double-hadron ratio: new way
                                                                      to differentiate contributions of
       0.8                                                            different mechanisms
       0.7

       0.6
             0   0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5
                                                         z2




                                       Hadronization workshop Trento, Oct. 2005                    28
A-dependence
Try fit:   RA = exp[-βAα] ≈ 1 – βAα

Globally α ≈ 0.55 - 65 (0.05) (for pions)

Caveats:
     - RA = MA/MD: attenuation in D?
     - Simple formula’s such as
             1 − RA ∼ L2 ∼ A2/3 (energy loss models)
             1 − RA ∼ L ∼ A1/3 (absorption models)
         too simple!


                     Hadronization workshop Trento, Oct. 2005   29
a) L ∼ A1/3 ?
Based on nucleus as a hard sphere
With realistic matter distribution (diffuse surface) Leff ∼ A0.45

b) Including distribution of formation length, also in absorption
models, 1 − RA ∼ A2/3 (for hard sphere)
                                  (Accardi et al., hep-ph/0502072)


- And: if more than one mechanism, depending on traversed
  distance, A-dependence will be more complicated than
  ‘simple’ Aα .




                     Hadronization workshop Trento, Oct. 2005        30
Summary

• Substantial nuclear attenuation depending on
  the kinematic variables ν, z, pt2 and Q2
• Attenuation increases with atomic mass A
• Decrease of attenuation with higher ν
• Increase of attenuation with higher z
• Weak dependence on Q2
• Broadening of pt2 distribution


               Hadronization workshop Trento, Oct. 2005   31
Outlook


 • Increased statistics on Krypton, as well as new data
   on Xenon to be released very soon
 • Detailed analysis (2-dimensional) of the high-
   statistics data samples (especially for pions)
 • Global A-dependence as function of ν and z for
   various hadrons




                Hadronization workshop Trento, Oct. 2005   32

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:5
posted:4/8/2011
language:English
pages:32