1. 1 Single spin asymmetry of forward neutron at PHENIX. 2005/06/02 RBRC workshop "Single-Spin Asymmetries" Manabu Togawa Kyoto-University, RIKEN

2. 2 Outlook Motivation –First motivation for the PHENIX Local Polarimeter Test experiment at IP12 collision point. –Setup, –Asymmetry for pi0,gamma and neutron. Neutron production at forward region. Local Polarimeter for PHENIX experiment –Setup, asymmetry. Summary

3. 3 Motivation One of the main program of RHIC experiment is that the determination of the polarized parton distribution function. –It needs longitudinally polarized proton-proton collision. Polarimeter at the collision point is necessary to confirm “beam is longitudinal”. (Local polarimeter) PHOBOS BRAHMS STAR PHENIX Spin Rotators Siberian Snakes RHIC （ Relativistic Heavy Ion Collider ） CNI polarimeter In RHIC, proton is stored with transverse polarization.  Measured by CNI polarimeter Spin rotator magnets rotate the proton to longitudinal direction. They are put at PHENIX and STAR collision points.

4. 4 How to measure how longitudinal? Parity violation : allow by weak decay  unconvincing Basic idea is from FNAL704 (A N of forward pion) The E704 experiment at Fermilab pp    X Sqrt(s)=19.4GeV p T =0.2~2.0GeV/c

5. 5 IP12 experiment. (EMCal) Blue beamyellow beam ～ 1800cm 10cm ±2.8mrad pp collision in sqrt(s) = 200GeV : IP12 Collision Point D x magnet Neutron veto (plastic scinti.) Charged veto (plastic scinti.) EM Cal hodoscope To measure Collision point 400cm

6. 6 Electro Magnetic Cal-based System -performance- Calibrated with the beam experiment at SLAC.  E/E ~ 10/sqrt(E) % Noise ~ 1.4GeV  x =  y ~ 0.15cm for   x =  y ~ 0.5cm for N Particle ID logic

7. 7 EMCal based results Succeed in  0 reconstruction  M/M ~ 9.3% Average beam pol. ~ 11% Calculate asymmetry using sqrt root formula.

8. 8 EMCal based results Average beam pol. ~ 11% Calculate asymmetry using sqrt root formula. Calibrated for the photon only. =-0.109  0.0072

9. 9 Neutron asymmetry  distribution Average beam pol. ~ 11% Calculate asymmetry using sqrt root formula. =-0.108  0.0087  dependence is consistent with sin  We measured ~10% level neutron L-R asymmetry. To confirm this, we installed one more detector. Detector

10. 10 IP12 experiment. (HadronCal) Blue beamyellow beam ～ 1800cm 10cm ±2.8mrad pp collision in sqrt(s) = 200GeV : IP12 Collision Point D x magnet EM Cal Neutron veto (plastic scinti.) Charged veto (plastic scinti.) hodoscope To measure Collision point Steel Hadron Cal Post shower counter Gamma veto (plastic scinti.) Lead block

11. 11 Hadron Cal-based system (1 ZDC) -performance- Energy is calibrated by using cosmic-ray data and simulation. Flat response E>20GeV  E/E ~ 40 to 50 % at E>20GeV  x ~ 3 to 4cm (post shower) Particle ID logic

12. 12 Hadron Cal-based result =-0.110  0.015 Average beam pol. ~ 18% Calculate asymmetry using sqrt root formula. We also measured ~10% level neutron L-R asymmetry in hadron based calorimeter.

13. 13 Summary of IP12 experiment. We measured single transverse-spin asymmetry in forward production of photons and neutrons in pp collision at sqrt(s)=200GeV. –  o : consistent with 0 within error. –Inclusive  : small. –Neutron : observed and its analyzing power is -0.109  0.0072 for EM Cal -0.110  0.015 for Hadron Cal

14. 14 Neutron production in forward region. In ISR experiment, cross section for forward neutron production was measured to be larger than at mid- rapidity. Our understanding of these effects is based on pion exchange. Large A N asymmetry is expected from  and  P(pomeron) interference. (talked by Boris Kopeliovich 2002 Sep. @ spin discussion) Forward neutron CS. Mid-rapidity CS. Nucl. Phys. B109 (1976) 347-356

15. 15 PHENIX Local polarimeter PHENIX has already ZDC (Zero Degree Calorimeter) in the same region. We upgraded to measure the position of neutrons. ZDC region

16. 16 ZDC(Zero Degree Calorimeter) ～ 1800cm 10cm ±2.8mrad beam -Hadron Calorimeter (sampling calorimeter is made of Tungsten plate and fibers) 5.1λ T 149X 0 (3 ZDCs) Energy resolution ~ 20% @ 100GeV PHENIX Collision Point D x magnet blue beamyellow beam SOUTH ZDCNORTH ZDC

17. 17 Shower MAX Detector For x-pos : 7 For y-pos : 8 150 Unit : mm For measuring neutron position, SMD (Shower Max Detector) was installed btw ZDC1 and ZDC2. –Arrays of plastic scintillators –Obtain the position by calculating the center of gravity of shower generating in first ZDC. –Position resolution ~1cm @ 50GeV neutron (simulation study). 1 ZDC SMD 100 5 Hadron shower

18. 18 Asymmetry with transverse (vertical) beam (RUN3) øø (Raw Asymmetry) / (beam pol.) BLUEYELLOW

19. 19 Asymmetry with transverse (radial) beam (RUN3) ø (Raw Asymmetry) / (beam pol.) ø BLUEYELLOW

20. 20 Asymmetry with longitudinal beam (RUN3) ø (Raw Asymmetry) / (beam pol.) ø BLUEYELLOW

21. 21 Through the spin RUN. RUN3 – BLUE = 99.3+0.5 -(1.4  1.8) – YELL = 97.4+(1.3  0.5) -(3.2  2.5) RUN4 – BLUE = 99.68+(0.21  0.13) -0.65 – YELL = 99.82+0.16 -0.75% RUN5 –Now we are taking.  p pTpT pLpL

22. 22 PHENIX BBC 2 identical parts (BBC-north and -south) Quartz Cherenkov counter 64 segments each. NorthSouth 144.35 cm ⊿ φ = 2π

23. 23 BBC Asymmetry Forward neutron, forward BBC, left-right -  9  ! Forward neutron, backward BBC, left-right - No significant asymmetry in backward ZDC tagged data or in top-bottom asymmetry. Systematic error doesn’t include A N CNI error. K.Tanida et al. p N*(  *)  n+X Y Diffractive-like process A N (X) 0 p n X kick-out/recoil picture A N (X) > 0, A N (Y)??

24. 24 Summary We found a large neutron single spin asymmetry (A N =-10%) in forward production of pp collision at IP12 experiment (2001-2002). Local polarimeter motivation, “check that the proton is longitudinally polarized at collision point” was achieved using this neutron asymmetry. –“How longitudinal” of both beams are measured to be ~99%. New neutron asymmetry measurements are coming. –410GeV pp collision will start tonight. Inputs from theorists are welcome.

25. 25 Backup slides

26. 26 Gluon polarization To understand the spin structure in the nucleon -> 1/2(proton) = 1/2DS(quark) + DG + L γ For ex. gq -> qγ Measured in DISCalculated by pQCD The experiment of longitudinal polarized proton collide had been started from this year by introducing the spin rotator.

27. 27 Square root furmula

28. 28 Calculate for each bunch. As a fit function, Fit for all bunch as D,A B,A Y variables. (55 bunch mode at RUN3) N L(R) : Number of Left(Right) D : detector asymmetry A B : BLUE asymmetry A Y : YELLOW asymmetry P B : BLUE polarization P Y : YELLOWpolarization Measured by CNI polarimeter Our measurement Bunch Fittinig Pol derection

29. 29 PHENIX A N Effective A N = (raw asymmetry) / polarization Blue : 6.21 +- 0.50% Yellow : 6.39 +- 0.55% Raw asymmetry is just measured values, not corrected smearing effect or so.

30. 30 PHENIX Pioneering High Energy Nuclear Interaction eXperiment PHENIX Detector 1 Central Arm e, g, Charged Hadrons detection | h |<0.35, Df = p 2, Muon Arm m detection 1.2<| h |<2.4, 2 p in f 3, Forward detectors Luminosity Monitoring Local polarimetery Good particle identification High Rate and High Detector granularity. Limited geometrical coverage