1. Ran HAN Peking University For PHENIX The Polarization of Anti-Lambda Produced In sqrt(s)=200GeV Polarized Proton-Proton Collision

2. Why Spin Physics Spin Physics Via the Polarization of Lambda/Anti-Lambda The Polarization Measurement of Anti-lambda in PHENIX Issues During the Measurement Summary Outline

3. Proton Spin Structure self analyzing via its weak decays Belong to Octect-states is the same as proton Hyperon Polarization phenomena studied lots of years: 1: The Nucleon Spin Structure 2:The Strange Quark Distribution 3: The Fragementation Process Information Lambda/Anti-Lambda is escpecially suit for this study DIS : What we have for the polarization of lambda/anti-lambda until now

4. Lambda production in e+e- and SDIS Lambda polarization in e+e- annihilation at the Z-resonance But: A flavor separation is impossible Dominated by the fragmentation of strange quarks Semi-Inclusive DIS: to study the polarized up down quark distribution functions (e-p scattering, E e =30GeV, x=0.3 and Q 2 =10GeV 2 ) DIS experiment at CERN, DESY, JLab and SLAC continue to gain some new insight Expect a lot to be achieved by means of RHIC!

5. Lambda production in PP collision PP collision at High luminosity and High c.m.s energy Lambdas are mainly fragmentation productis of up and down at large rapidity What will do for Polarization of lambda/anti-lambda in PHENIX Lambda Polarization with rapidity

6. The PHENIX Experiment

7. backward forward The Polarization of outgoing anti-lambda This can help us to understand where the lambda (anti-lambda) from: u d uud ss s Phenix has more anti-lambda sample for ERT-Trigger Data The Anti-Lambda is found to be sensitive to the polarization of the anti-strange sea of the nucleon(hep-ph/0511061) What we Measured in PHENIX

8. Extract the Signal from PHENIX Central Arm Tracking Drift Chamber, Pad Chambers, Time Expansion Chamber Calorimeter PbGl and PbSc, Muon Piston Calorimeter Particle Id Muon Identifier, RICH, TOF, TEC …………………… In the future we will use the TOF as PID selection For now: The time information from PbSc is used to do PID selection ( The time resolution of PbSc~500ps )

9. Extract the Signal from PHENIX Data from PHENIX 2003  s = 200 GeV longitudinal-spin run with beam polarization 26% The data sample consider here is 180nb -1 How to determine the Polarization?

10. How to determine the Polarization How to determine polarization ? dN / d cos q = 1/2 (1 + a à cos q ) Fit to decay distribution returns polarization à Need large analyzing power 1:How to Cancel the Acceptance Influence 2:How to Build the Beam Polarization Balance (only one polarized beam needed) at RHIC 3:How to Subtract the Background Influence In Real Analysis: The angle between p momentum direction and lambda polarization direction in lambda rest frame

11. can be analyzed through its dominant decay channel In anti-lambda rest frame 1 2 3 Consider a small decay angle theta and Two anti-lambda sample from opposite polarized beam How to build the beam polarization balance How to Cancel the Acceptance The four spin pattern at RHIC make it possible

12. The Way to Build Beam Polarization Balance Invariant mass PBPB PBPB Reminder: no one-one correlation between anti-lambdas event and hadron pairs Opt 1: to drop randomly has nothing to do with anti-lambda events Opt 2: From left side, enhance negative polar. events? Opt 3: From right side, enhance positive polar. events? Opt 4: From both sides and carefully maintain Not a big influence Build Blue Beam to be unpolarized Next Step: To Subtract the Background

13. 1:Background Correction 2:Background Subtraction “Background Subtraction”: 1: Divided costheta to five bins, have similar statistics in each bin 2: Obtained the number of anti- lambda 3: Normalized number of anti- lambda by the bin width 4: Draw the Subtract the Background

14. The Costheta distribution when the beam forward and backward polarized The Costheta Distribution

15. The Polarization of Lambda/Anti-Lambda Will Give Us Lots of Interesting Spin Physics Introduce How to Measure the Polarization of Lambda/Anti-Lambda in Experiment The Study Status in PHENIX Experiment Thank you ! Summary