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					STAR      Forward Physics at RHIC
                   Transverse Spin Effects and
                      Probing Low-x Gluons


                              OUTLINE
  • Transverse single spin effects in p+p collisions at s=200 GeV
  • Towards understanding forward p0 cross sections
  • Probing low-x gluon densities
  • Plans for the future




                                               L.C. Bland
                                               Brookhaven National Laboratory
                                               The Partonic Structure of Hadrons
                                               ECT*, Trento 9 May 2005
             Transverse Spin Effects




9 May 2005          L.C.Bland, ECT* Workshop   2
                            A Brief History…
    p  p  p  X                 • At leading twist and with collinear factorization, the
                                   chiral properties of QCD predict small analyzing
    s=20 GeV, pT=0.5-2.0 GeV/c    powers for particle production with transversely
                                   polarized protons colliding at high energies.


                                   • The FermiLab E-704 experiment found strikingly
                                   large transverse single-spin effects in p+p fixed-target
                                   collisions with 200 GeV polarized proton beam.

                                   • Theoretical models were developed to explain these
                                   effects using spin and transverse-momentum
                                   dependent distribution or fragmentation functions or
                                   higher-twist effects.

                               • Large transverse single-spin effects were observed
p0 – E704, PLB261 (1991) 201. in semi-inclusive electroproduction experiments.
•




p+/- - E704, PLB264 (1991) 462.
•




      9 May 2005                    L.C.Bland, ECT* Workshop                             3
Two Models for Transverse Single-Spin Effects
                                  p +p→p0+Х
• Sivers effect [Phys Rev D41 (1990) 83; 43 (1991) 261]:
    Flavor dependent correlation between the proton spin (Sp),
   momentum (Pp) and transverse momentum (k) of the unpolarized
   partons inside. The unpolarized parton distribution function fq(x,k)
   is modified to:
                                                                              
                                          1 N            
                                                               S P  ( Pp  k q )
       ƒ q (x, k q , S P )  ƒ q (x, k q )  Δ q ƒ q (x, k q )               
                                            2                    S P PP k q

• Collins effect [Nucl Phys B396 (1993) 161]:
   Correlation between the quark spin (sq), momentum (pq) and
   transverse momentum (k) of the pion. The fragmentation function
   of transversely polarized quark q takes the form:
                                                                         
                                           1 N               sq (pq  k π )
                          ˆ                            
      Dp/q (z, k , s q )  Dp/q (z, k p )   Dp/q (z, k p )
                π                                                      
                                           2                    pq  k π

9 May 2005                      L.C.Bland, ECT* Workshop                            4
                     Questions
  • Do transverse single spin effects persist to RHIC
  energies (200<s<500 GeV)?


  • Do we understand the unpolarized cross section
  where transverse single spin effects are large?


  • Can we disentangle the dynamics?




9 May 2005            L.C.Bland, ECT* Workshop          5
                Installed and commissioned during run 4
                Planned to be commissioned during run 5
                Installed in run 5 and to be commissioned in run 5
Developments for runs 2 (1/02), 3 (3/03  5/03) and 4 (4/04  5/03)
• Helical dipole snake magnets                         • b*=1m operataion
• CNI polarimeters in RHIC,AGS                         • spin rotators  longitudinal polarization
   fast feedback                                      • polarized atomic hydrogen jet target
   9 May 2005                          L.C.Bland, ECT* Workshop                             6
                          Run-5 Status
                 Longitudinal Polarization at STAR/PHENIX
                   Transverse Polarization at BRAHMS




                              L dt = 0.8 pb1



                         Scheduled to run until 6/25/05
     Original STAR goals: Pbeam > 0.4, L dt = 14 pb1 (long) / 4 pb1 (trans)
9 May 2005                     L.C.Bland, ECT* Workshop                          7
             STAR detector layout

                                             •   TPC: -1.0 < h < 1.0

                                             •   FTPC: 2.8 < h < 3.8

                                             •   BBC : 2.2 < h < 5.0

                                             •   EEMC:1 < h < 2

                                             •   BEMC:0 < h < 1

                                             •   FPD: |h| ~ 4.0 & ~3.7




9 May 2005        L.C.Bland, ECT* Workshop                             8
     STAR Forward Calorimetry
                    Recent History and Plans


•       Prototype FPD proposal Dec 2000
    –        Approved March 2001
    –        Run 2 polarized proton data (published
             2004 spin asymmetry and cross section)
•       FPD proposal June 2002
    –        Review July 2002
    –        Run 3 data pp dAu (Preliminary An
             Results)
•       FMS Proposal Submitted Jan 2005.
        Near full Forward EM Coverage.
        (hep-ex/0502040).


9 May 2005                   L.C.Bland, ECT* Workshop   9
     First AN Measurement at STAR
                             prototype FPD results
 STAR collaboration                      Similar to result from E704 experiment
 Phys. Rev. Lett. 92 (2004) 171801         (√s=20 GeV, 0.5 < pT < 2.0 GeV/c)

                                         Can be described by several models
                                           available as predictions:
                                              Sivers: spin and k correlation in
                                              parton distribution functions (initial
                                              state)
                                              Collins: spin and k correlation in
                                              fragmentation function (final state)
                                              Qiu and Sterman (initial state) /
                                              Koike (final state): twist-3 pQCD
                                              calculations, multi-parton correlations


   √s=200 GeV, <η> = 3.8

9 May 2005                     L.C.Bland, ECT* Workshop                                10
                  Single Spin Asymmetry
                                           Definitions

                            d   d                    Two measurements:
     • Definition:     AN 
                            d    d           • Single arm calorimeter:
                                                           1  N   RN          L
     • dσ↑(↓) – differential cross                  AN                
                                                                N  RN      R 
       section of p0 then incoming                       PBeam                   L
       proton has spin up(down)                      R – relative luminosity (by BBC)
                                                     Pbeam – beam polarization
                     Left
                                                 • Two arms (left-right) calorimeter:
       π0, xF<0                 π0, xF>0
                                                          1  NL  NR  NR  NL 
                                                                                 
                                                   AN                              
                                                        PBeam  N   N   N   N  
p                                              p                L     R     R     L 

                                                     No relative luminosity needed

                     Right                               positive AN: more p0 going
                                                           left to polarized beam
     9 May 2005                    L.C.Bland, ECT* Workshop                           11
Caveats:
 -RHIC CNI Absolute polarization
  still preliminary.
 -Result Averaged over azimuthal
  acceptance of detectors.
 -Positive XF (small angle
  scattering of the
  polarized proton).


    Run 2 Published Result.

    Run 3 Preliminary Result.
     -More Forward angles.
     -FPD Detectors.
    Run 3 Preliminary
     Backward Angle Data.
     -No significant Asymmetry
     seen.
     (Presented at Spin 2004: hep-ex/0502040)




     9 May 2005                        L.C.Bland, ECT* Workshop   12
STAR
xF and pT range of FPD data




9 May 2005             L.C.Bland, ECT* Workshop   13
Forward p0 Cross Sections at RHIC




9 May 2005   L.C.Bland, ECT* Workshop   14
                        Hard Scattering
                        Hard scattering hadroproduction
        p
                                      Factorization theorems state that the
                                      inclusive cross section for p+p  p +X
                                      can be computed in perturbative QCD
                                      using universal PDF and fragmentation
                                                    p
                                      functions, Dc (z ) and perturbatively
                                      calculated hard-scattering cross sections,
                                      d ab , for partonic process a+bc. All
                                        ˆc
                                      such processes are summed over to yield
                                      the inclusive p production cross section.




d p           dxa  dxb  dzc                              p
                                        f a ( xa ) f b ( xb ) Dc ( zc )dˆ   c
                                                                             ab
             a ,b , c



9 May 2005                 L.C.Bland, ECT* Workshop                         15
  Why Consider Forward Physics at a Collider?
                                        Kinematics
Deep inelastic scattering                               Hard scattering hadroproduction




              Can Bjorken x values be selected in hard scattering?
Assume:
1. Initial partons are collinear
2. Partonic interaction is elastic
                                            
      pT,1  pT,2
   Studying pseudorapidity, h=-ln(tanq/2), dependence of particle production
   probes parton distributions at different Bjorken x values and involves different
   admixtures of gg, qg and qq’ subprocesses.
    9 May 2005                       L.C.Bland, ECT* Workshop                    16
              Simple Kinematic Limits
Mid-rapidity particle detection:                                   NLO pQCD (Vogelsang)
                                                       1.0
                                                                 p+p  p0+X, s = 200 GeV, h=0
    h10 and <h2>0                                    0.8
                                                                                   qq
     xq  xg  xT = 2 pT / s




                                            fraction
                                                       0.6

                                                       0.4                              qg

                                                       0.2            gg
Large-rapidity particle detection:
                                                       0.0
    h1>>h2                                                   0         10        20       30
                                                                                   pT,p(GeV/c)
     xq  xT eh1 xF (Feynman x), and
         xg  xF e(h1h2)
   Large rapidity particle production and correlations involving large
  rapidity particle probes low-x parton distributions using valence quarks
 9 May 2005                L.C.Bland, ECT* Workshop                                      17
How can one infer the dynamics of particle production?
     Particle production and correlations near h0 in p+p collisions at s = 200 GeV
       Inclusive p0 cross section
                                                        Two particle correlations (h)


                                                        STAR



                                             STAR, Phys. Rev. Lett. 90 (2003), nucl-ex/0210033


                                        At √s = 200GeV and mid-rapidity, both
                                        NLO pQCD and PYTHIA explains p+p
                                        data well, down to pT~1GeV/c, consistent
                                        with partonic origin
                                                       Do they work for
Phys. Rev. Lett. 91, 241803 (2003)
        hep-ex/0304038
                                                      forward rapidity?
  9 May 2005                         L.C.Bland, ECT* Workshop                                    18
     Forward p0 production in hadron collider
                                                                        Q 2 ~ pT
                                                                               2               2E p
                                                                                          xF 
                                                Ep         p0           s  2E N                s
p                                                                                             E
  E
d N                        qq                        qp                            q    z p
                                                                        h  ln(tan( ))       Eq
                                     xgp                     p                       2
                xqp                                                                             p h
                                                             Au         xq  xF / z
                             qg                  EN                                      xg  T e g
                                                                             (collinear approx.) s

• Large rapidity p production (hp~4) probes asymmetric partonic collisions
                                                        
                                                             p  p  p 0,hp 3.8, s  200GeV
                                                                            
• Mostly high-x valence quark + low-x gluon                       <z>

    • 0.3 < xq< 0.7
                                                                                 <xq> NLO pQCD
    • 0.001< xg < 0.1
                                                                        Jaeger,Stratmann,Vogelsang,Kretzer

• <z> nearly constant and high 0.7 ~ 0.8                                           <xg>

• Large-x quark polarization is known to be large from DIS
• Directly couple to gluons = A probe of low x gluons
   9 May 2005                      L.C.Bland, ECT* Workshop                                        19
But, do we understand forward p0 production in p + p?
                    At s << 200 GeV, not really….
         √s=23.3GeV                        √s=52.8GeV
                Data-pQCD
               difference at
                pT=1.5GeV
                                                                     2 NLO
                                                                    collinear
                                                                  calculations
                                                          q6o   with different
                                                                      scale:
                   q15o                      q10o
                                                                  pT and pT/2



    q22o                                     q53o
                               xF                                 xF
 Bourrely and Soffer (hep-ph/0311110, Data references therein):
  NLO pQCD calculations underpredict the data at low s from ISR
   data/pQCD appears to be function of q, √s in addition to pT
  9 May 2005                   L.C.Bland, ECT* Workshop                   20
       Time/luminosity dependent
    PMT Gain Matching
Di-photon Mass Reconstruction and calibration
           gain shift corrections
            Pb-glass reconstruction with STAR FPD
            FTPC-FPD
      p0 reconstruction matching                  Track in
                                                                   FTPC
                                 Cluster categorization
                    • Clusteringconversionanalysis
                      Photon and moment in beam pipe
                 efficiency
              Luminosity
                vs p (+ X)  g MC  e e
                                   (+ g)
         p + p  PMTwith parametrized shower shape
                       0
                • Fitting gain                + -
                                          & Data comparison
                                      2 photon cluster example Hit in
                • Number of photons found >= 2 20MeV
          Beam pipe Mass resolution ~                          FPD
                    • Fiducial volume > 1/2 cell width from edge
                   • Energy sharing zggE1E2/(E1 ~2%
                   We understand gainE2) < 0.7level
             h
                     • Absolute gain determined from p0 peak
                     position for each tower almost
                      Efficiencies is
                   Limit with zgg<0.5 cut correction) purely
                      Gain stability (before
                                   Try both
                       geometrically determined
                    • Energy dependent gain correction
                   • Run/luminosity
               from reconstructiondependent gain correction
                      Energy




                   • Checking1gCluster f
             of MC(PYTHIA+GEANT) (PYTHIA+GEANT) h
                              with MC
                                          FPD position known
                     Gain stability (after correction)
                        Geometrical limit
                                     f
                                relative to STAR
                                              2gCluster
      High tower sorted mass distributions
9 May 2005                         L.C.Bland, ECT* Workshop               21
                               2nd moment of cluster (long axis)
     ppp0X cross sections at 200 GeV
                                                The error bars are point-to-point
                                                systematic and statistical errors added
                                                in quadrature

                                                The inclusive differential cross section
                                                for p0 production is consistent with NLO
                                                pQCD calculations at 3.3 < η < 4.0

                                                The data at low pT are more consistent
                                                with the Kretzer set of fragmentation
                                                functions, similar to what was observed
                                                by PHENIX for p0 production at
                                                midrapidity.



D. Morozov (IHEP),
XXXXth Rencontres de Moriond - QCD,               NLO pQCD calculations by Vogelsang, et al.
March 12 - 19, 2005
9 May 2005                       L.C.Bland, ECT* Workshop                                 22
STAR -FPD
Preliminary
Cross Sections


Similar to ISR analysis
J. Singh, et al Nucl. Phys.
B140 (1978) 189.



 d 3
E 3  (1  xF ) pT
               N   B

  dp
N 5
B6
    9 May 2005                L.C.Bland, ECT* Workshop   23
            PYTHIA: a guide to the physics
    Forward Inclusive p0 Cross-Section:            Subprocesses involved:




                                                                                      q+g
                                                               g+g and
                                                               q+g  q+g+g



                                                                                  STAR FPD
                                                                 Soft processes




• PYTHIA prediction agrees well with the inclusive p0 cross section at h3-4
• Dominant sources of large xF p0 production from:                p0
●   q + g  q + g (22)  p0 + X          q                g
                                                                                  p0
●   q + g  q + g + g (23)  p0 + X                       q            g
       9 May 2005                     L.C.Bland, ECT* Workshop                    g          24
       Probing low-x gluon densities

    Forward inclusive particle production in p+p and d+Au

             Particle correlations in p+p and d+Au




9 May 2005             L.C.Bland, ECT* Workshop             25
                Parton Densities in the Proton
                               Deep inelastic scattering (DIS) of electrons and
                               muons is the primary source of information about the
                               quark and gluon structure of the proton.
Deep inelastic scattering




Kinematics defined for
electron(muon) scattering
from a fixed proton target.    Global analyses use world data from DIS, neutrino
                               scattering, Drell-Yan,… to determine parton
                               distribution functions (PDF).

   9 May 2005                 L.C.Bland, ECT* Workshop                       26
             Determining the gluon density
                                   The gluon density is determined by
                                   applying QCD evolution equations to
                                   account for the Q2 dependence (scaling
                                   violations) of structure functions
                                   measured in DIS.
                                   At low-x, the full QCD evolution
                                   equations can be simplified to
                                   approximate the gluon distribution by


                                                F2 ( x, Q )    2
                                      g (2 x) 
                                                  (ln Q 2 )
                                   i.e., determine g(2x) by measuring the
                                   lnQ2 slope of F2(x,Q2) at fixed x.
                                   K. Prytz, Phys. Lett. B311 (1993) 286


9 May 2005            L.C.Bland, ECT* Workshop                         27
                    Gluons in the Proton

• DIS results from HERA ep collider
provide accurate determination of xg(x)
for the proton in the range 0.001<x<0.2
• the low-x gluon density is large and
continues to increase as x0 over the
measured range




                                           J. Pumplin, D.R. Stump, J. Huston, H.L. Lai, P.
                                           Nadolsky, W.K. Tung JHEP 0207 (2002) 012.

 9 May 2005                   L.C.Bland, ECT* Workshop                              28
                 Nuclear Gluon Density
    e.g., see M. Hirai, S. Kumano, T.-H. Nagai, Phys. Rev. C70 (2004) 044905
                             and data references therein




         World data on nuclear DIS constrains nuclear modifications to
         gluon density only for xgluon > 0.02


9 May 2005                   L.C.Bland, ECT* Workshop                      29
New Physics at high gluon density

1. Shadowing. Gluons hiding
   behind other gluons. Modification
   of g(x) in nuclei. Modified distributions
   needed by codes that hope to calculate
   energy density after heavy ion collision.


2. Saturation Physics. New phenomena
   associated with large gluon density.
    • Coherent gluon contributions.
    • Macroscopic gluon fields.
    • Higher twist effects.
    • “Color Glass Condensate”          Figure 3 Diagram showing the boundary
                                        between possible “phase” regions in the
                                        t=ln(1/x) vs plane
  Edmond Iancu and Raju Venugopalan, review for Quark Gluon Plasma 3,
                                    .
  R.C. Hwa and X.-N. Wang (eds.), World Scientific, 2003 [hep-ph/0303204].
 9 May 2005                   L.C.Bland, ECT* Workshop                    30
             FPD Detector and pº reconstruction




                                                   • robust di-photon
                                                   reconstructions with FPD
                                                   in d+Au collisions on
                                                   deuteron beam side.
                                                   • average number of
                                                   photons reconstructed
                                                   increases by 0.5
                                                   compared to p+p data.




9 May 2005              L.C.Bland, ECT* Workshop                       31
   h Dependence of RdAu                                                 Ed 3
                                                             inelastic       dp3 dAu      1  dAu
                                                  RdAu        pp
                                                                                      
                                                         N binary  dAu Ed 3
                                                                    inelastic
                                                                                        2  197  pp
                                                                              dp3 pp

                                                                            y=0

                                                                            As y grows


                         1  dAu
     G. Rakness (Penn State/BNL),                         Kharzeev, Kovchegov, and Tuchin,
               RdAu 
                      2 197  Moriond - QCD,
     XXXXth Rencontres de pp
                                                          Phys. Rev. D 68 , 094013 (2003)
     March 12 - 19, 2005
                                                          See also J. Jalilian-Marian,
                                                          Nucl. Phys. A739, 319 (2004)

   • From isospin considerations, p + p  h is expected to be suppressed relative to d
   + nucleon  h at large h [Guzey, Strikman and Vogelsang, Phys. Lett. B 603, 173 (2004)]
   • Observe significant rapidity dependence similar to expectations from a “toy
   model” of RpA within the Color Glass Condensate framework.

9 May 2005                         L.C.Bland, ECT* Workshop                                  32
Constraining the x-values probed in hadronic scattering
     Guzey, Strikman, and Vogelsang,
     Phys. Lett. B 603, 173 (2004).
                                                                                      For 22 processes




                                                   Log10(xGluon)
                                                                         FTPC         TPC       FTPC
                                                                        FPD       Barrel EMC       FPD
                    Log10(xGluon)

     Collinear partons:                                                                            hGluon
        +
     ● x = p /s (e
                    +h1 + e+h2)
        
            T
     ● x = p /s (e
                   h1 + eh2)                                     • FPD: |h|  4.0
            T
                                                                   • TPC and Barrel EMC: |h| < 1.0
 CONCLUSION: Measure two
 particles in the final state to constrain                         • Endcap EMC: 1.0 < h < 2.0

 the x-values probed                                               • FTPC: 2.8 < h < 3.8
  9 May 2005                        L.C.Bland, ECT* Workshop                                              33
         Back-to-back Azimuthal Correlations
                               with large h
 Beam View         Top View
                                                                          Fit ffpfLCP normalized
                                     Trigger by                               distributions and with
   f                             ] forward p0
                                                                                Gaussian+constant

                                     • Ep > 25 GeV




                                                     Coicidence Probability
                                     • hp  4




                                                           [1/radian]
                       ]


Midrapidity h tracks in TPC
    • -0.75 < h< +0.75
Leading Charged Particle(LCP)
    • pT > 0.5 GeV/c                                                            ffpfLCP
               S = Probability of “correlated” event under Gaussian
               B = Probability of “un-correlated” event under constant
               s = Width of Gaussian
9 May 2005                     L.C.Bland, ECT* Workshop                                            34
                                    STAR
                                                 PYTHIA (with detector
                                                 effects) predicts
                                                 • “S” grows with <xF>
                                                 and <pT,p>
                                                 • “s” decrease with
                                                 <xF> and <pT,p>
      25<Ep<35GeV


                                                 PYTHIA
                                                 prediction agrees
                                                 with p+p data
                                                 Larger intrinsic kT
                                                 required to fit data
      45<Ep<55GeV
                       Statistical errors only
9 May 2005          L.C.Bland, ECT* Workshop                            35
                                               Expectation from HIJING
                                               (PYTHIA+nuclear effects)
                                               X.N.Wang and M Gyulassy, PR D44(1991) 3501

                                                                 with detector effects



                                                      • HIJING  predicts
                                                      clear correlation in
                                                      d+Au
      25<Ep<35GeV
                                                      • Small difference in “S”
                                                      and “s” between p+p
                                                      and d+Au
                                                      • “B” is bigger in d+Au
                                                      due to increased particle
                                                      multiplicity at
                                                      midrapidity

      35<Ep<45GeV


9 May 2005          L.C.Bland, ECT* Workshop                                      36
   dAu Correlations: probing low x

                                        “Mono-jet”                       p0
                                                                      PT is balanced by
                                         Dilute parton
                                            system                      many gluons
                                          (deuteron)

                                                              Dense gluon field
                          25<Ep<35GeV                               (Au)


                                              Beam View   Top View


                                                 f                          p0
           STAR                                                      • Ep > 25 GeV
         Preliminary   35<Ep<45GeV                                   • hp  4

Statistical errors only
  9 May 2005                   L.C.Bland, ECT* Workshop                            37
        dAu Correlations: probing low x

                                          Large h p0+h± correlations
                                         • Suppressed at small <xF> , <pT,p>
                                                  Consistent with CGC picture


                          25<Ep<35GeV
                                                                  Fixed has
                                                                 E & pT grows




                                         •Consistent in d+Au and p+p at larger <xF>
          STAR                           and <pT,p>
        Preliminary   35<Ep<45GeV
                                               More data are needed…
Statistical errors only
  9 May 2005                   L.C.Bland, ECT* Workshop                         38
             Plans for the Future




9 May 2005        L.C.Bland, ECT* Workshop   39
   STAR Forward Meson Spectrometer
     NSF Major Research Initiative (MRI) Proposal
              -submitted January 2005
                  [hep-ex/0502040]




9 May 2005           L.C.Bland, ECT* Workshop       40
     Three Highlighted Objectives In FMS Proposal
                          (not exclusive)
1.   A d(p)+Aup0p0+X measurement of the
     parton model gluon density distributions xg(x)
     in gold nuclei for 0.001< x <0.1. For 0.01<x<0.1,
     this measurement tests the universality of the
     gluon distribution.

2.   Characterization of correlated pion cross sections
     as a function of Q2 (pT2) to search for the onset of
     gluon saturation effects associated with
     macroscopic gluon fields. (again d-Au)

3.   Measurements with transversely polarized
     protons that are expected to resolve the origin of
     the large transverse spin asymmetries in
     reactions for forward p0 production.
     (polarized pp)
9 May 2005            L.C.Bland, ECT* Workshop          41
                  FMS Design
                                       • FMS increases areal coverage of
                                       forward EMC from 0.2 m2 to 4 m2
                                       • FMS to be mounted at roughly the
                                       same distance from the center of the
                                       STAR interaction region as the FPD,
         FPD Calorimeters              and would face the Blue beam
                                       • Addition of FMS to STAR provides
                                       nearly continuous EMC from -1<h<+4




9 May 2005         L.C.Bland, ECT* Workshop                           42
         STAR detector layout with FMS

                                             TPC: -1.0 < h < 1.0

                                             FTPC: 2.8 < h < 3.8

                                             BBC : 2.2 < h < 5.0

                                             EEMC:1 < h < 2

                                             BEMC:-1 < h < 1

                                             FPD: |h| ~ 4.04.0~3.7
                                             FMS: 2.5<h< &




9 May 2005        L.C.Bland, ECT* Workshop                43
       FMS MRI Proposal Details

• Full azimuthal EM coverage 2.5<h<4.0
    – Extending STAR coverage to -1<h<4.0
• 684 3.8 cm  3.8 cm  45 cm lead glass inner
  cells (IHEP, Protvino).
• 756 5.8 cm  5.8 cm  60 cm Schott F2 lead
  glass outer cells (FNAL-E831).
• New Photinis XP2202 (outer cells)
• Cockroft Walton Bases.
• Readout Electronics
9 May 2005          L.C.Bland, ECT* Workshop     44
Frankfurt, Guzey and Strikman,
J. Phys. G27 (2001) R23 [hep-ph/0010248].




• constrain x value of gluon probed by high-x quark
by detection of second hadron serving as jet surrogate.
• span broad pseudorapidity range (-1<h<+4) for
second hadron  span broad range of xgluon
• provide sensitivity to higher pT for forward p0 
reduce 23 (inelastic) parton process contributions
thereby reducing uncorrelated background in f
correlation.
    9 May 2005                    L.C.Bland, ECT* Workshop                       45
                                                             Pythia Simulation
d+Au  p0+p0+X, pseudorapidity correlations with forward p0
                              HIJIING 1.381 Simulations

• increased pT for forward p0 over run-3 results is
expected to reduce the background in f correlation
• detection of p0 in interval -1<h<+1 correlated with
forward p0 (3<h<4) is expected to probe
0.01<xgluon<0.1  provides a universality test of
nuclear gluon distribution determined from DIS
• detection of p0 in interval 1<h<4 correlated with
forward p0 (3<h<4) is expected to probe
0.001<xgluon<0.01  smallest x range until eRHIC
• at d+Au interaction rates achieved at the end of
run-3 (Rint~30 kHz), expect 9,700200 (5,600140)
p0p0 coincident events that probe 0.001<xgluon<0.01
for “no shadowing” (“shadowing”) scenarios.




    9 May 2005                     L.C.Bland, ECT* Workshop   46
             Disentangling Dynamics of Single Spin
                         Asymmetries
                     Spin-dependent particle correlations

Collins/Hepplemann mechanism
                                              Sivers mechanism asymmetry is
 requires transversity and spin-
                                                 present for forward jet or g
    dependent fragmentation




Large acceptance of FMS will enable disentangling dynamics of spin asymmetries


9 May 2005                  L.C.Bland, ECT* Workshop                         47
     Timeline
     Completion
         By
      Fall 2006




9 May 2005        L.C.Bland, ECT* Workshop   48
       Other Possible Applications of FMS

• forward p0/g reconstruction in heavy-ion collisions                 Reconstruction of
                                                                 HIJING/GSTAR simulations
• direct photon detection at large rapidity
• reconstruction of other mesons decaying to g or e
produced in p+p or d(p)+Au (and heavy-ion?)
collisions
     hgg
     wp0g
     Kshort  p0p0  4g
     hgg?
                                                             Limited sample of events obtained
     J/  e+e?                                          in Cu+Cu run with good view of
                                                             interaction region



   9 May 2005                     L.C.Bland, ECT* Workshop                             49
                       Summary / Outlook

 • Large transverse single spin asymmetries are observed for large rapidity p0
 production for polarized p+p collisions at s = 200 GeV
       AN grows with increasing xF for xF>0.35
       AN is zero for negative xF
 • Large rapidity p0 cross sections for p+p collisions at s = 200 GeV is in
 agreement with NLO pQCD, unlike at lower s. Particle correlations are
 consistent with expectations of LO pQCD (+ parton showers).
 • Large rapidity p0 cross sections and particle correlations are suppressed in
 d+Au collisions at sNN=200 GeV, qualitatively consistent with parton
 saturation models.
 • Plan partial mapping of AN in xFpT plane in RHIC run-5
 • Propose increase in forward calorimetry in STAR to probe low-x gluon
 densities and establish dynamical origin of AN (complete upgrade by 10/06).


9 May 2005                   L.C.Bland, ECT* Workshop                          50
New FMS Calorimeter
Lead Glass From FNAL E831            Loaded On a Rental Truck for Trip To BNL




9 May 2005                  L.C.Bland, ECT* Workshop                       51

				
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