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Measurement of Single Transverse-Spin Asymmetry of Neutrons in p-p Collisions at RHIC-PHENIX

This study focuses on the measurement of the single transverse-spin asymmetry of forward neutrons in p-p collisions at RHIC-PHENIX. Motivation, setup, neutron asymmetry at different energies, simulation study, and estimation of asymmetry error are discussed. The first measurement of neutron asymmetry at sqrt(s) = 410GeV is presented, and its implications are discussed.

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Measurement of Single Transverse-Spin Asymmetry of Neutrons in p-p Collisions at RHIC-PHENIX

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

  2. Outline • Motivation • PHENIX neutron measurement • Setup • Neutron asymmetry at sqrt(s)=200GeV • Simulation study • Estimation of asymmetry error at 2005 RUN • First measurement of neutron asymmetry at sqrt(s)=410GeV • 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 sqrt(s)=30~63GeV, cross section of forward neutron production at low pT was measured to be larger than at high pT. [left pict.] • In the RHIC IP12 experiment, pp sqrt(s)=200GeV. We found large single transverse-spin asymmetry AN (-10%) [right pict.] • PHENIX data can shed new light to understand the production mechanism.

  4. Eur.Phys.J.A7:109-119,2000 xF dependence sqrt(s) >= 200GeV - cross section - asymmetry pT dependence sqrt(s) >= 200GeV - 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 amplitude with other’s one. • Twist-3 model • It can explain asymmetries of forward pion (E704). • Based on pQCD, does it work in such forward kinematics?

  5. GeV Forward neutron measurement at PHENIX At 2005 RUN, sqrt(s) = 200, 410GeV polarized proton beams. scintillator ～1800cm PHENIX Collision Point 10cm blue beam yellow beam Dxmagnet ±2.8mrad Typical energy distribution sqrt(s)=200GeV 100GeV To calculate asymmetry, use square root formula. GeV * Energy calibration was done by CuCu data. (1 neutron peak)

  6. 100 5 150 Hadron shower unit:mm ZDC (Zero Degree Calorimeter) and SMD (Shower Max Detector) Hadron Calorimeter (sampling by Tungsten and fiber plates.) 5.1λT 149X0 (3 ZDCs) ～1800cm PHENIX Collision Point 10cm blue beam yellow beam Dxmagnet ±2.8mrad Energy resolution ~20% @ 100GeV Position resolution ~1cm @ 50GeV (sim). beam beam

  7. Detector Raw asymmetry Raw asymmetry Backward Forward f f Neutron asymmetry at PHENIX from RUN5 data (200GeV) Using square root formula.

  8. GeV s ~ 20% s ~ 21% GeV Simulation study • ZDC and SMD have not been measured energy and position resolution less than 100GeV. • In the test experiment, energy resolution was measured 100 and 160GeV by proton beam. • It is necessary to study the response by simulation. • Asymmetry is smeared by position resolution Simulation is based on geant3. Real data (1 neutron @ CuCu data) Simulation out (neutron 100GeV input)

  9. Error reach ~ 10-3 order simulation study Estimation of asymmetry error - energy dependence - Asymmetry definition • A has energy dependence ? • Flat at IP12 experiment. • In this forward region,

  10. detector pT distribution at sqrt(s) = 200GeV (x,y) (0,0) n r pT(GeV) Error reach ~ 10-3 order simulation study Estimation of asymmetry error - pT dependence - Max x and y : ~5 cm r ~ 1800 cm 0.1GeV

  11. Analysis cut effect is uncorrected. pT(GeV) First measurement Asymmetry at 410GeV • Asymmetry remains in higher energy region. • pT is larger compared with 200GeV. • Local polarimeter needs this asymmetry until 500GeV in RHIC spin program.  it is expected to remain at 500GeV ! Raw asymmetry Raw asymmetry Forward Backward f f

  12. Summary • We took forward neutron data at sqrt(s)=200 and 410 GeV in 2005 RUN at RHIC-PHENIX. • The expected asymmetry error at 2005 RUN were estimated. • Asymmetry will be obtained with 10-3 accuracy. • Energy and pT resolution were estimated by simulation. • Neutron asymmetry at sqrt(s)=410GeV was measured for the first time. • It remains in such high energy. • It is expected that asymmetry will remain when go to sqrt(s) = 500GeV.

  13. Back up

  14. How to measure how longitudinal? Parity violation : allow by weak decay  unconvincing Basic idea is from FNAL704 (AN of forward pion) The E704 experiment at Fermilab pp p0X Sqrt(s)=19.4GeV pT=0.2~2.0GeV/c

  15. Electro Magnetic Cal-based System -performance- Calibrated with the beam experiment at SLAC. DE/E ~ 10/sqrt(E) % Noise ~ 1.4GeV Dx = Dy ~ 0.15cm for g Dx = Dy ~ 0.5cm for N Particle ID logic

  16. EMCal based results Succeed in p0 reconstruction DM/M ~ 9.3% Average beam pol. ~ 11% Calculate asymmetry using sqrt root formula.

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

  18. Shower MAX Detector • 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). 100 5 SMD 150 Hadron shower For x-pos : 7 For y-pos : 8 1 ZDC Unit : mm

  19. Looking neutron peak SOUTH NORTH After subtract pedestals and apply calibration constant. To match 1 neutron peak is 100. (should be 100 GeV)

  20. ZDC shape BLUE : SOUTH RED : NORTH Very agree both shape after calibration. GeV

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

  22. Square root furmula

  23. Bunch Fittinig Pol derection • Calculate for each bunch. • As a fit function, Fit for all bunch as D,AB,AY variables. (55 bunch mode at RUN3) Our measurement NL(R) : Number of Left(Right) D : detector asymmetry AB : BLUE asymmetry AY : YELLOW asymmetry PB : BLUE polarization PY : YELLOWpolarization Measured by CNI polarimeter

  24. Neutron energy (sim)neutron put to center Output energy Input energy Energy resolution Input energy

  25. Position resolution (sim)neutron put to center Xpos Input line Neutron energy Ypos * Position resolution is defined as RMS. Neutron energy

  26. Neutron energy (sim)neutron put to edge * Resolution is defined as RMS/Energy

  27. Asymmetry as function of ZDC2 cut Gamma  stop at ZDC1. Neutron  hadron shower goes to ZDC2. beam

  28. Reducing asymmetry valueby energy and position smearing Input : neutron with flat energy distribution, 10 ~ 100GeV input positions are flat for x and y.

  29. Hadron Cal based results EMCal based results <AN>=-0.1090.0072 <AN>=-0.1090.0072 Detector <AN>=-0.1080.0087 Calibrated for the photon only.

  30. RHIC（Relativistic Heavy Ion Collider） CNI polarimeter BRAHMS PHOBOS PHENIX STAR Siberian Snakes Spin Rotators As a local polarimeter system • 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)

  31. AT A q AL RUN5(2005) result. Through the RUN5, longitudinal component : <pL/p> BLUE = 99.54 ± 0.12 ± 0.03 (%) <pL/p> YELL = 98.78 ± 0.24 ± 0.06 (%)

  32. Fill by fill analysisby sqrt formula

  33. Bunch shuffling : sqrt formula (sim with 1% asymmetry) Forward LR Forward UD Backward LR Backward UD

  34. Bunch shuffling : sqrt formula (forward region) BLUE LR BLUE UD YELLOW LR YELLOW UD

  35. Bunch shuffling : sqrt formula (backward region) BLUE LR BLUE UD YELLOW LR YELLOW UD

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