Ran HAN

Peking University

For PHENIX

The Polarization of Anti-Lambda Produced In sqrt(s)=200GeV

Polarized Proton-Proton Collision

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

Proton Spin Structure

self analyzing via its weak decaysBelong 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

%30~ q

Lambda production in e+e- and SDIS

Lambda polarization in e+e- annihilation at the Z-resonanceBut: 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, Ee=30GeV, x=0.3 and Q2 =10GeV2)

DIS experiment at CERN, DESY, JLab and SLAC continue to gain some new insight

Expect a lot to be achieved by means of RHIC!

Lambda production in PP collision

PP collision at High luminosity and High c.m.s energyLambdas 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

The PHENIX Experiment

LB DPP

00

Pbackward forward ..vsP

The Polarization of outgoing anti-lambda

This can help us to understand where the lambda (anti-lambda) from:

uduud

uudss

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

Extract the Signal from PHENIXCentral 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 )

Extract the Signal from PHENIXData 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?

How to determine the Polarization

• How to determine polarization ?

dN / d cos = 1/2 (1 + cos )

Fit to decay distribution returns polarization

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 RHIC3:How to Subtract the Background Influence

In Real Analysis:

The angle between p momentumdirection and lambda polarization direction in lambda rest frame

)cos,()cos1(0

pp

kPd

d

d

d

Pcan be analyzed through its dominant decay channel

p

In anti-lambda rest frame

LddddN )/(/

pP

RNN

RNNcos

12

3

LLRPRNN

RNN

p/,cosConsider 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 AcceptanceThe four spin pattern at RHIC make it possible

The Way to Build Beam Polarization Balance

0 BB PNPN

Invariant mass

PB

PB

0 BP

Reminder: no one-one correlation between anti-lambdas event and hadron pairs

Opt 1: to drop randomly has nothing to do with anti-lambda eventsOpt 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

Nvsp

..cos

)()(coscoscos

BGppBGpr

1:BackgroundCorrection

2:BackgroundSubtraction

“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

Nvsp

..cos

Subtract the Background

The Costheta distribution when the beam forward and backward polarized

The Costheta Distribution

• 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