STAR Spin Analysis Update

1
STAR Spin Analysis Update

Stephen Trentalange
2
Beam-Beam Counters
- scintillator annulus installed around the beam
pipe, on the east and west poletips of STAR
magnet at 3.74m from IR for detection of
charged particles in forward region 2
Small hexagonal annulus
18 pixels (16 PMT) covering 3.30
- azimuthal segmentation !
2m
A coincidence condition between BBC East and West
- suppresses beam-gas background and used for
- triggering in pp (minimum bias, jet
triggers), - (relative) luminosity measu
rements - local polarimetery
0.5m
ADC (PMT Sum)
Data MC
BBC cross section s(BBC) 50 of ?
tot (pp) 26 mb Large! - Van der Meer scans at
RHIC ( Run2 and Run3 data) are consistent with
Geant simulations for STAR
Data and MC agree
3
Transverse Single Spin Asymmetries
Asymmetries measured for pp - A X, where A
hit(s) in the BBC (small tiles, 3.3







Number of coun
ts from the BBC (L,R,T,B) sorted by beam
polarization states


Example Polarized Yellow beam (sum over Blue
beam polarization states)
heads towards BBC East
RHIC CNI polarimeter
Zero at RHIC (Vertical pol)
N L(R,T,B) -nr of counts from BBC East or West
in Left, Right, Top, Bottom part counted every
bunch crossing by scaler system


Top
Left
Right
X
Bottom
Interaction Vertex
BBC East
BBC West
4
Local Polarimetry
Rotators
OFF ON CNI polarimeter
non-zero
non-zero BBC Left-Right ( vertical )
NON_ZERO ZERO BBC Top-Bottom ( rad
ial ) zero zero

e CNI (ON-LINE) eLR BBC 0.13(2)
eTB BBC -0.24(2)
e CNI (ON-LINE) eLR BBC - 0.07(2)
eTB BBC - 0.04(2)
Blue beam, BBC West
Yellow beam, BBC East
CNI
CNI
Measured asymmetry
drop
drop
BBC
BBC
Run
Run
Rotators ON
OFF
OFF
Rotators ON
Spin rotators worked as designed and stable,
BBC worked very well as a local polarimeter
- vertical and radial
polarization components smaller than 3
Longitudinal polarization for the first time!

Joanna Kiryluk
5
Transverse Single Spin Asymmetries
Preliminary Results
Blue Beam
Yellow Beam
BBC East
BBC West
e (BBC)
e (BBC)
Ratio e (BBC East)/e (CNI) consistent with e
(BBC West)/e (CNI) We get AN(BBC)0.0066(8)
Stat. error only! using AN(CNI) 0.0118
(10) from CNI online analysis
Left-Right BBC asymmetry ( Vertical Pbeam compo
nent )
P24
P24
e (CNI)
e (CNI)
Blue Beam
Yellow Beam
BBC East
BBC West
e (BBC)

• 5 s effect
• may be a result of a broken snake?

Consistent with zero - as expected for vertical p
olarization
e (BBC)
Top-Bottom BBC asymmetry ( Radial Pbeam compone
nt )
Joanna Kiryluk
e (CNI)
e (CNI)
6
Relative Luminosity - Motivation
Double spin longitudinal asymmetry (e.g. pp
- jet X ) is defined as
P1,2 beam polarization, from CNI polarimeter at
RHIC N i where i, - are spin depende
nt yields - r
elative luminosity of bunch crossings with
different spin directions
Assumption ALL 0.01
0.07
Relative luminosity - one of the dominant
systematic errors in ALL measurement It must be
known at (least) 10-3 level
R0.7
dALL / ALL
Requirements for a luminosity process/detector
- high rates - small background - no
(or small) spin dependence
R1.3
0.01
10-4
10-3
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Relative Luminosity - Measurement
- RHIC filled with 55 - transversly polarized
- proton bunches, - spin orientation related
to the bunch crossing number 1-120,
polarization pattern at STAR
Spin Up Spin Down Unpolarized
Relative Luminosity
abort gaps (beam-gas background)
and time dependent!
Run 4150010
BBC E.W coincidence counts
1.0
Blue Yellow
05/16/03
05/30/03
bunch crossing
Time Run Number

• integrated luminosity (number of BBC E.W counts
  ) recorded every 5 minutes - scaler board
  system
  
• relative luminosities calculated for each STAR
  run, which typically lasts from a few minutes to
  hour
  
• statistical uncertainty d Rstat 10-4 10-3

Joanna Kiryluk
8
Relative Luminosity Systematics
Beam-Gas Background Contribution
Yellow beam-gas bg Blue beam-gas bg
Bg/2
0.2
Run
Contribution to systematic uncertainty on R d
R(sys) 0.004 x 0.2 8 x 10-4
- must correct for background
Joanna Kiryluk
9

• Summary
• Single transverse spin asymmetry measured with
  the Beam Beam Counters in 2003 were found to be
  AN(BBC)0.0066(8) using AN(CNI)0.0118(10) from
  CNI online analysis. Systematic studies in
  progress.
• The BBC was used to tune spin rotators needed to
  get longitudinally polarized beams at STAR IP
  and to monitor on-line transverse and radial beam
  polarization components. They are found to be
  small Prad(vert)
• 3. The BBC in STAR is a good luminosity
  monitoring detector. The relative luminosity is
  known at the level of 3 x10-3
  
• - statistical uncertainty 10-4 10 -3
  
  
  
• - (conservative) systematic uncertainty
  (BBC and ZDC comparison) 3 x 10-3
  
• This needs further studies
  (background contribution)
  

Joanna Kiryluk
10
2003 Detector Configuration
STAR
EMC (Half) Barrel
EMC Full Barrel 2005
Full EndCap 2004
TPC
BBC East
BBC West
EndCap EMC (1/3)
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Leading Jet Asymmetries are Sensitive to Gluon

• Simulation based on Pythia
• Use Fast TPC and EMC Simulators
• EMCTPC Jets Reconstructed using Cone Algorithm
• Includes Jet-Patch Trigger ( ET 5) covering
  the Full Half Barrel Calorimeter
  
• ALL includes all jet processes (not a direct
  measure of delta G)
  

Max Allowed Gluon Polarization
Best Fit to DIS Data
Simulations by Les Bland
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pp Longitudinal Data Set
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Jet Finder (Mike Miller/Thomas Henry)
For this Analysis, Jets are defined as a grouping
of one or more (charged) Tracks measured in the
TPC and satisfying
the following requirements

• Using an Iterative, Midpoint, Cone Algorithm
• Cone Angle 0.7 in eta-phi
• Seed Energy 0.5 GeV
• pT Track 0.1 GeV
• Track Range /- 1.6
• pT Jet 5 GeV
• Z /- 75 cm

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TPC Jet Characteristics EMC Trigger
Ratio of EMC to Charged Et

• Select 0.2

Total
TPC Tracks
EMC points

• Strong Trigger Bias at low ET

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Longitudinal Spin Asymmetries
momentum
spin
Does Not Violate Parity
Violates Parity
REQUIRES luminosity ratios to be measured much
more accurately than desired asymmetry
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TPC-Jet, Single-Spin Asymmetries
Blue Beam
Run (time)
Yellow Beam
Parity-Violating Asymmetries are Consistent with
Zero
Dylan Thein
17
2003 Outlook