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 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 p T was measured to be larger than at high p T. [left pict.] –In the RHIC IP12 experiment, pp sqrt(s)=200GeV. We found large single transverse-spin asymmetry A N (-10%) [right pict.] –PHENIX data can shed new light to understand the production mechanism. =  Kinematics ±2.8mrad Forward region xFxF Nucl. Phys. B109 (1976)

4 Does Feynman scaling hold when going to RHIC energy? From the ISR result, C.S. are well scaling by x F 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? Eur.Phys.J.A7: ,2000 xFxF x F dependence sqrt(s) >= 200GeV - cross section - asymmetry p T dependence sqrt(s) >= 200GeV - asymmetry

5 Forward neutron measurement at PHENIX ～ 1800cm 10cm ±2.8mrad PHENIX Collision Point Dx magnet blue beamyellow beam To calculate asymmetry, use square root formula. Typical energy distribution GeV * Energy calibration was done by CuCu data. (1 neutron peak) scintillator 100GeV sqrt(s)=200GeV At 2005 RUN, sqrt(s) = 200, 410GeV polarized proton beams. Trigger setsqrt(s)=200sqrt(s)=410 NORTH or SOUTH12M11M (NORTH or SOUTH) & Minbias 90M72M NORTH & SOUTH30M20M GeV

6 ZDC (Zero Degree Calorimeter) and SMD (Shower Max Detector) beam ～ 1800cm 10cm ±2.8mrad PHENIX Collision Point Dx magnet blue beamyellow beam 150 unit:mm 100 Hadron shower 5 Hadron Calorimeter (sampling by Tungsten and fiber plates.) 5.1λ T 149X 0 (3 ZDCs) Energy resolution 100GeV Position resolution 50GeV (sim).

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

8 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 GeV  ~ 21%  ~ 20% Real data (1 CuCu data) Simulation out (neutron 100GeV input) Simulation is based on geant3.

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

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

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

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 accuracy. –Energy and p T 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 (A N of forward pion) The E704 experiment at Fermilab pp    X Sqrt(s)=19.4GeV p T =0.2~2.0GeV/c

15 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

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

17 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

18 Shower MAX Detector For x-pos : 7 For y-pos : 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 50GeV neutron (simulation study). 1 ZDC SMD Hadron shower

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

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

21 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.

22 Square root furmula

23 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

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

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

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

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

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

29 EMCal based results Calibrated for the photon only. =  =  Detector Hadron Cal based results = 

30 As a local polarimeter system PHOBOS BRAHMS STAR PHENIX Spin Rotators Siberian Snakes RHIC （ Relativistic Heavy Ion Collider ） CNI polarimeter 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 RUN5(2005) result.  A ATAT ALAL BLUE9.5 ± 2.2 (%) YELLOW15.5 ± 2.4 (%) Through the RUN5, longitudinal component : BLUE = ± 0.12 ± 0.03 (%) YELL = ± 0.24 ± 0.06 (%)

32 Fill by fill analysis by sqrt formula

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

34 Bunch shuffling : sqrt formula (forward region) BLUE LRBLUE UD YELLOW LRYELLOW UD

35 Bunch shuffling : sqrt formula (backward region) BLUE LRBLUE UD YELLOW LRYELLOW UD

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