W physics PHENIX

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W physics _at_ PHENIX

• 2009/06/01
• Kyoto Univ. / RIKEN
• Kenichi Karatsu

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Contents

• Proton Spin Structure
• Probe Proton Spin with W boson
• W detection _at_ PHENIX
• Summary

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1. Proton Spin Structure
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Parton polarization function

• Proton Spin ½ ½?? ?G L
• lt about ?? gt
• The polarization of valence quark (u, d) are well
  understood but, that of sea quark (anti-u,
  anti-d, anti-s) are not well constrained
• This talk is about the extraction of sea quark
  polarization by W-boson production

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2. Probe Proton Spin with W boson
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Probe proton spin with W boson

• Extract the sea polarization by measuring the
  Single Spin Asymmetry of W-boson production
• W is produced through pure V-A
• - Chirality is fixed ? ideal for spin structure
  studies
• W couples to weak charge flavor
• - Flavor is (almost) fixed ? ideal for flavor
  structure studies
• No fragmentation for the final state

• Asymmetry of W -gt ?u, ?d-bar
• Asymmetry of W- -gt ?d, ?u-bar

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3. W detection _at_ PHENIX
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The PHENIX Experiment

• Philosophy (initial design)
• High rate capability granularity
• Good mass resolution particle ID
• Sacrifice acceptance

Central Arm
e/-
Muon Arm Muon Tracking Detector (MuTr), Muon
Identifier (MuID)
Rapidity 1.2 lt ? lt2.2 (2.4) ?f 2 p
Muon Arm
Rapidity h lt 0.35 ?f 2 (p/2)
µ/-
Central Arm Drift Chamber (DC), Pad Chamber
(PC), Ring Imaging Cherenkov Counter (RICH),
Electromagnetic Calorimeter (Emc), HBD, TOF, TEC
RPCs
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Expected Asymmetry of W production in the PHENIX
Acceptance
(l- pTgt20 GeV)
(l pTgt20 GeV)
Muon Arms trigger upgrade is ongoing ? will be
ready for next 500 GeV run
Central Arms ready for W measurement
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W in the PHENIX Muon Arms
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W in the PHENIX Muon Arms
Muon pT spectra in the Muon Arms (2000 1/pb,
from PYTHIA5.7)
recorded luminosity ? 300 pb-1
Forward AL µ
Forward AL µ-
W is dominant (pTgt20 GeV/c)
W
Backward AL µ
Backward AL µ-
Right plot expected asymmetry of W (assuming
60 polarization, backgrounds and detector
resolution included) from RHICBOS
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W in the PHENIX Muon Arms
Design Luminosity vs 500 GeV s60mb L
2x1032/cm2/s
Muon pT spectra in the Muon Arms (2000 1/pb,
from PYTHIA5.7)
MuID LL1 pmuongt1.5 GeV/c
Total interaction rate 12MHz
New Trigger
DAQ LIMIT 2kHz (for Muon Arm)
W
Required RF 6000
BUT

• Need Momentum Selectivity in the LVL-1 Trigger!

MuID LL1 (trigger) RF lt 200
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PHENIX Muon Trigger Upgrade
Rapidity 1.2 lt h lt2.2 (2.4)

• New MuTr FEE was installed fully in North Arm and
  partially in South Arm
• Prototype RPC was installed in South Arm
• Prototype Pb absorber was installed in South Arm
• -gt part of South Arm has the full configuration
  (MuTRGRPCPb) in 2009 RHIC Run!
• -gt Evaluate the performance with beam of ?s500
  GeV _at_ 2009 RHIC Run

• MuID
• - only existing trigger
• no momentum selectivity..

• ltMuon Trigger Upgradegt
• MuTr FEE Upgrade (MuTRG)
• Install RPC (Resistive Plate Chamber)
• Install additional Pb absorber

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Current Status - Muon Arms

• Performance of New MuTr FEE (MuTRG)

• Turn on Point of Efficiency Curve 4 (arb.
  unit)
• Most Probable Value of MIP 20 (arb. unit)
• MuTRG and MuTr have matching properly
• Efficiency for MIP is 97.5 (Yellow / Blue)
• Study of rejection factor is ongoing

Trigger Emulation (offline analysis)
Collision Point
Red MuTRG Hit, Blue Accepted Track
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Current Status - Muon Arms

• Performance of Prototype RPC

Peak (lt0) Tracks coming from collision or
outgoing beam Peak (gt0) Background by incoming
beam Width of each peak 3 ns -gt good timing
resolution!
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W in the PHENIX Central Arms
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W in the PHENIX Central Arms
pions NLO pQCD calculation from W. Vogelsang W
RHICBOS (Nadolsky, Yuan)
Upper plot cross section of e/- from W p/-
in the PHENIX acceptance
Rapidity h lt 0.35
ltCharged hadron rejectiongt EMCal intrinsic
50-150 Shower profile 2-4 Isolation cut
10 Total 1000-6000
Lower plot expected asymmetry of W (assuming 70
polarization, no background or detector
resolution included)
recorded luminosity ? 300 pb-1 ? 70 pb-1
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Current Status - Central Arms

• Brief summary of 2009 RHIC Run (Run9)
• Polarization 35
• (from RHIC pol-group)
• recorded luminosity _at_ PHENIX 10 pb-1
• (with vertex cut)
• The aim of Run9 analysis
• -gt measure cross section of W boson!
• (W?e W-?e-)

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Current Status - Central Arms
Emc Energy calibration -gt Done Invariant mass
v.s. total energy of 2 photons

• ltTo dogt
• estimate detector eff. acceptance
• estimate backgrounds
• isolation cut
• estimate charge contamination
• etc..
• -gtlots of things are work in progress now

eta
pi0
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Event Display of High energy events
Energy v.s. Inclination of the track
Found W candidates. Analysis is under way!
Energy dist. (Black , Red -)
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4. Summary

• W bosons provide possibilities for flavor
  separated measurements -gt sensitive to the
  polarization of sea quark!
• Upgrades are ongoing to measure W boson in the
  PHENIX Muon Arms. They have been partially
  installed tested at 2009 RHIC Run
• -gt Ready for the next 500 GeV run!
• W boson measurements in the PHENIX Central Arms
  is possible and analysis is under way on 2009
  RHIC data
• -gt W candidates are seen!

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Back up
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W production

• We can extract the sea polarization from
  Single Spin Asymmetry of W production!!

• No fragmentaion for the final state!

• W is produced from left-handed q and right-handed
  q-bar
• No W founded to coupled to right-handed current