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Manabu Togawa for the PHENIX collaboration. Kyoto University / RBRC

Measurement of the cross section and the single transverse spin asymmetry of forward neutrons from p-p collisions at RHIC-PHENIX. Manabu Togawa for the PHENIX collaboration. Kyoto University / RBRC. Outline. Physics motivation Measurement of forward neutron at PHENIX Experimental setup

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Manabu Togawa for the PHENIX collaboration. Kyoto University / RBRC

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  1. Measurement of the cross section and the single transverse spin asymmetry of forward neutrons from p-p collisions at RHIC-PHENIX Manabu Togawa for the PHENIX collaboration. Kyoto University / RBRC

  2. Outline • Physics motivation • Measurement of forward neutron at PHENIX • Experimental setup • Analysis procedure • Result of the cross section. • Very forward case. • Results of the single transverse spin asymmetry • xF-dependence • Comparing tagged with/without charged particles • Summary

  3. Kinematics ±2.8mrad Forward region xF <AN>=-0.1090.0072 Nucl. Phys. B109 (1976) 347-356 Motivation • In the forward neutron production, there are some interesting behaviors. • In ISR experiment, pp √s=30~63GeV, cross section of forward neutron production at low pT was measured to be larger than at high pT. [left figure] • In the RHIC IP12 experiment, pp √s=200GeV. We found large single transverse-spin asymmetry AN (-10%) [right figure] • PHENIX data can shed new light to understand the forward neutron production mechanism.

  4. Eur.Phys.J.A7:109-119,2000 xF dependence √s >=200 GeV - cross section - asymmetry pT dependence √s >= 200 GeV - asymmetry xF • Does Feynman scaling hold when going to RHIC energy? • From the ISR result, C.S. are well scaling by xF at 30<sqrt(s)<63 GeV.. • Forward neutron C.S. has peak structure and it is well described by pion exchange model. • What is the mechanism of neutron asymmetry ? • pion exchange model • Asymmetry can be appeared by interference of spin flip. • Twist-3 model, Siverse, Collins…

  5. ZDC 10*10cm  2.8 mrad 3 module 150X0 5.1λI SMD Dx magnet Forward counter SMD Neutron position can be decided by centroid method. veto Proton shower event (In case of proton mom = 50GeV/c) 1 ZDC Setup Schematic view from simulation. - GEANT3 (Geisha) - From the pythia simulation, Main backgrounds are gamma and proton. 1800 cm Collision point BBC

  6. Analysis outline • Data set • In this analysis, √s=200 GeV data which was took from 2003 to 2005 is used. The data is corrected by single neutron trigger with/without MinBias trigger. • MinBias is defined as detecting charged particles in BBC(3.0<|h|<3.9) • Calibration • ZDC : Looking the 1 neutron peak at heavy ion data. • SMD : Relative gain correction is done by cosmic-ray data. • Simulation ( GEANT3 with pythia v.6220 or single particle generator ) • Background and efficiency after neutron ID cut. • Unfold the neutron energy. • Smearing effect of asymmetry caused by position cut and resolution.

  7. pT distribution is assuming ISR result Cross section Integrated pT area : 0<pT<0.11xF GeV/c in each point. Cross section result is consistent with ISR data and xF scaling holds at such higher energy.

  8. charged particles neutron neutron ypos Single transverse spin asymmetry • Smearing effect is evaluated by simulation. • For asymmetry calculation, square root formula is used. xpos Expected mean pT (Estimated by simulation assuming ISR pT dist.) 0.4<|xF|<0.6 0.088 GeV/c 0.6<|xF|<0.8 0.118 GeV/c 0.8<|xF|<1.0 0.144 GeV/c preliminary * Cut is not same

  9. How about charged particles at BBC ? • Asymmetry is 0 when data is selected by BBC only. • Finite asymmetries are shown tagged with forward neutron. 4s • Opposite direction as neutron (2.28±0.55±0.10)*10-2 • Same direction as neutron (-4.50±0.50±0.22)*10-2 9s  Neutron analyzing power can be large with charged particles. preliminary Top view pion exchange model Y : charged particles Y polarized proton proton Y n (neutron) Y’ pol direction N*(D*)  n+Y’ ?? AN(X) < 0, AN(Y) > 0,AN(Y’) N* ???  will be analyzed with high statistics and good polarization data.

  10. Summary • The cross section and the single transverse spin asymmetries of forward neutron production in √s=200GeV polarized p-p collision are measured at RHIC-PHENIX. • Cross section • It is consistent with ISR data at pT ~ 0 (GeV/c). xF scaling holds in this high energy. • Single transverse spin asymmetry • xF-dependence looks flat, negative polarity. • Analyzing power of forward neutron tagged with charged particles are lager than without them. • Prefer the pion exchange model and like diffractive process(?).  Theoretical calculation is very welcome.

  11. Future analysis • pT dependence • Important parameter same as xF. • Charged particle asymmetry tagged with forward neutron. • with high statistics and good polarization data.

  12. Horizontal scan We can see finite asymmetry in other energy RUN ! -5cm 5cm √s=62.4 GeV √s=410 GeV

  13. backup

  14. Cross section calculation Input pT shape • The total cross section with PHENIX neutron cut. is estimated. • pT is not evaluated from our data. As simulation input, ISR result is assumed. • In this analysis, radius<2cm from the collision point (1800cm) is calculated.  1.1 mrad : 0<pT<0.11xF GeV/c。 Assumed Simulation input pT=A*exp(-4.8pT) PHENIX data. comparing ISR data is converted to current cut. (0<pT<0.11xF GeV/c) 

  15. charged particles neutron neutron Asymmetry with different trigger • Smearing effect is evaluated by simulation. • For asymmetry calculation, square root formula is used. Without MinBias With MinBias

  16. Summary • The cross section and the single transverse spin asymmetries of forward neutron production in √s=200GeV polarized p-p collision are measured at RHIC-PHENIX. • Cross section • It is consistent with ISR data at pT ~ 0 (GeV/c). xF scaling holds in this high energy. • with 2cm radius cut in ZDC region (~1.1 mrad) • Integrated pT range is 0~0.11xF (GeV/c) • Single transverse spin asymmetry • xF-dependence looks flat, negative polarity. • Integrated pT range is 0.03xF~0.22xF (GeV/c) • Analyzing power of forward neutron tagged with charged particles are lager than without them. • Prefer the pion exchange model and like diffractive process(?).  Theoretical calculation is very welcome.

  17. t-range p (mp,0,0,Ep) t p (mn,pT,0,En) ISR pT distribution is assuming.

  18. Red/Black ~ 0.47 Red/Black ~ 0.71 Mean pT : 0.030 Mean pT : 0.048 Mean pT : 0.043 Mean pT : 0.070 Red/Black ~ 0.75 Red/Black ~ 0.73 Mean pT : 0.058 Mean pT : 0.089 Mean pT : 0.072 Mean pT : 0.102

  19. Systematic error for C.S. • Systematic error in calibration • Energy calibration ~5% • SMD relative calibration (it is including in SMD cut eff) • Trigger bias correction.< 10% • Systematic error in simulation • Acceptance few % from pt distribution by SMD pos cut. • SMD cut eff. ~3% • Neutron ID • SMD shape match. ~ 3% • Forward counter match. ~5% • Background estimation. apply 100% error for BG ratio. • Mainly from K0 and proton • For cross section 8% • 2 particle in 1 event ~ 5% • Systematic error in luminosity • Cross section error 13% (22.9 mb * 0.591) for NoVtxCut • In total • For shape after cut : ~11.6%For scaling of cross section : 17.1%

  20. Systematic error for phi-asym. • Measurement : 1% • Bunch shuffling result is ~2% of statistics, RUN5 local pol analysis note. (AN462) • Center scan ~ 1% • Beam gas BG at ZDCN|S trigger : 0.2% • Simulation uncertainty 4.1% • Simulation stat 2% • pT match : few% • BG estimation 3% • Center cut scan 2% • Total : 4.2% • Online polarization 20%  scaling error.

  21. Systematic error for xF-asym. • Estimation from measurement : 2% • ~4% of statistics, by bunch shuffling. • Center scan ~ 2% • Beam gas BG at ZDCN|S trigger : 0.2% • Unfolding : calibration (bin by bin  18p) • xF : 0.4~0.6 : 2.1% 0.6~0.8 : 0.3% 0.8~1.0 : 0.3% • Simulation uncertainty 7.8% • BG estimation 3% • Position smearing estimated by center cut scan (Differences between PHENIX and flat xF inputs) 7.2% • Unfolding : linearity (bin by bin  17p) • xF : 0.4~0.6 : 12.1% 0.6~0.8 : 2.1% 0.8~1.0 : 2.1% • Total : 8.1% of asymmetry value (not including blue term)

  22. Calibration (ZDC) • Neutron cainbration is done by 1 neutron peak from heavy ion run. We can see 100 GeV peak in CuCu event Select “coulomb” event by BBC ZDC detector Black : all event Red : select center region. 10cm pp event after calibrated. 10cm

  23. Calibration (SMD) Relative gain of each channels are matched by cosmic ray data. Cosmic peak Took by Alexei. Compared with simulation data. See simulation term.

  24. nID study using pythia input. ZDC threshold is ~5GeV n g p Black : sum Green : gamma Blue : neutron Red : proton

  25. Correction of BG (estimation) • With SMD cut and center cut (r<0.5), BG are mainly K0 and proton • From ISR paper, Pythia out. Pythia out is agree K0 ration with ISR data. I used BG distribution after cut from the pythia. Error will be added 100% of this value

  26. Neutron measurement stability Stability = 7.65762e-06/4.76148e-03*sqrt(315.5/95) = 0.3 %.

  27. BBCLL1 bias study. RUN5 pp MB looking 22.9 ± 9.7mb For neutron C.S. correct BBCLL1 cut efficiency. Red : BBCLL1(>0 tube) Blue : BBCLL1(noVtxCut) BBCLL1/NoVtxCut cm 0.591 ± 0.05 (for maximum error)  8.46%

  28. Stability of neutron peak after cut This peak

  29. NORSH vs. SOUTH (nID num) nID number are agree with SOUTH and NORTH after SMD cut efficiency  Amplitude of C.S. will be same

  30. BG estimation from pythia • With BBC trigger • K0 : 1.16% proton : 1.60% sum : 2.76% • Without BBC trigger • K0 : 0.97% proton : 2.27% sum : 3.24%  correction assuming A of K0 and p = 0. if 3%, asymmetry is smeared as 1.0/1.03 = 0.97

  31. Radius distribution for calculating asymmetry Center cut by r>0.5cm real data sim : C.S. is flat sim : C.S. is pT ~ 0 * () means ration to cut radius = 0.5. Differences of ratio will be systematic error : 2%

  32. 前方中性子測定

  33. xF Nucl. Phys. B109 (1976) 347-356 ISR実験 ○重心系エネルギー 30~63 GeV ○STAC検出器 40*40*80 cm3 (iron) 5.5lI res. 26%@20GeV 19%@30GeV ○They were placed in 0o,20o,66o,119o,(±1)mrad(56m for 0o) 前方ピーク xFスケーリング

  34. Eur.Phys.J.A7:109-119,2000 xF One pion exchange model B. Kopeliovich et al. Z.Phys.C73:125-131,1996 レッジェポール メソンクラウドモデル

  35. 3枚の charge veto counter (70*50*2 cm3) ZEUS測定 106m Leading neutron spectrometer Beam pipe Neutron exit window Lead plates sampling cal. (7 lI) 30 GeV 電子　920 GeV 陽子

  36. ZEUS results C.S. of neutron-tagged D*± Forward neutron epでの重クォーク生成はgg融合 もし交換されたパイオンと仮想光子との反応ならパイオン内部のグルーオン構造関数が見えるはず Scaling is unreliable S. Chekanov et al. nuclear Physics B 637 (2002) 3–56 S. Chekanov et al. physics Letters B 590 (2004) 143–160

  37. Eur.Phys.J.A7:109-119,2000 xF • 生成断面積に関して • 今のところパイオン交換モデルでよく記述できている。 • 横偏極非対称度 • パイオンはスピンフリップなので、記述できるだろう。 PHENIXでの新しいデータが重要だ。

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