The Longitudinal Polarization of Anti-Lambda Produced in sqrt(s)=200GeV Polarized P-P Collision

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The Longitudinal Polarization of Anti-Lambda
Produced in sqrt(s)200GeV Polarized P-P Collision

• Ran HAN
• Peking University

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Outline

• Motivation
• Spin Physics Via the Polarization of
  Lambda/Anti-Lambda
• The Polarization Measurement of Anti-lambda in
  PHENIX
• Experiment Issues
• Summary

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Proton Spin Structure
Hyperon Polarization phenomena studied for many
years 1 The Nucleon Spin Structure 2The
Strange Quark Distribution 3 The
Fragementation Process Lambda/Anti-Lambda is
escpecially suit for this purpose
1 Self analyzing via its weak decays 2 Belong
to Octect-states is the same as proton 3 Larger
cross section The lambda/anti-lambda can give us
an idea tool to study the spin structure and
fragmentation process.
What we have learnt so far about
lambda/anti-lambda polarization
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Lambda production in ee- and SDIS
Semi-Inclusive DIS useful to study the polarized
up down quark distribution functions up and down
quark is the dominant channel for Lambda (e-p
scattering, Ee30GeV, x0.3 and Q210GeV2 Pe50)
Lambda polarization in ee- annihilation at the
Z-resonance But A flavor separation is
impossible Dominated by the fragmentation of
strange quarks
SDIS experiment at CERN, DESY, JLab and SLAC
continue to gain some new insight
We expect a lot to be achieved by means of RHIC
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Lambda production in PP collision
The polarization can be studied for the first
time(lognitudinal) in PP collision at High
energy At large rapidity, expect lambda mainly
from fragmentation of up and down quraks
What will do for Polarization of
lambda/anti-lambda in PHENIX
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The PHENIX Experiment
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What we Measured in PHENIX
The Polarization of outgoing anti-lambda
-
DL spin transfer the probability that the
polarization of the beam is transferred to
anti-lambda
This measurement can help us to understand where
the lambda (anti-lambda) from
PHENIX collected a large sample of anti-lambdas
The Anti-Lambda is found to be sensitive to the
polarization of the anti-strange sea of the
nucleon(hep-ph/0511061)
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Extract the Signal from PHENIX
Reconstructed via its weak decays
Central Arm Tracking Drift Chamber, Pad
Chambers, Time Expansion Chamber Calorimeter
PbGl and PbSc, Muon Piston Calorimeter Particl
e Id Muon Identifier, RICH, TOF, TEC,
EMC In the future we will use the TOF as PID
selection For now The time information from
PbSc to do PID selection ( The time resolution of
PbSc500ps )
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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?
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How to determine the Polarization

• How to determine polarization ?

The angle between p-bar momentum direction and
lambda-bar polarization direction in lambda-bar
rest frame
Fit to decay distribution returns polarization Ã
In Analysis
1Detector Acceptance 2Beam Polarization
Balance (as both beams are polarized, but
Asymmetry is measured respective to one beam only
at RHIC) 3Background subtraction
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How to Account for the Acceptance
The four spin pattern at RHIC make it possible
can be analyzed through its dominant decay channel

In anti-lambda rest frame
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2
Consider a small decay angle theta and Two
anti-lambda sample from opposite polarized beam
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How to build the beam polarization balance?
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Build Beam Polarization Balance
Build Blue Beam to be unpolarized
Reminder no one-one correlation between
anti-lambda event and hadron pairs
PB
Opt 1 The hatched area are consider as hadron
pairs which could be spin-independent
area (no-antilambda) Opt2 The
hatched area are selected and the
distribution of beam are plotted Opt 3 From
left side, enhance negative polar. events?
From right side, enhance positive polar.
events? Opt 4 From both sides and carefully
maintain, Then we can get the
balance Not a big influence
PB
Next Step To Subtract the Background
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Subtract the Background
1Background Correction
2Background Subtraction
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The Distribution of Costheta
Fit the distribution of (c1-Rc2)/(c1Rc2) will
get the polarization of anti-lambda To study the
systematic error and wait for more data
The Costheta distribution when the beam forward
and backward polarized
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Summary

• The polarization of lambda/anti-lambda is a good
  probe connecting to spin physics
• To measure the polarization of lambda/anti-lambda
  in PHENIX experiment is feasible
• The anti-lambda polarization can be measured by
  decay distribution of proton
• Further detailed study is in progress

Thank You!
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• Backup

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Some New Results from Other Experiment