1. First measurement and future prospects for measurements of single spin asymmetries in W production with the PHENIX experiment at RHIC
Young Jin Kim
for the
PHENIX Collaboration
SPIN-Praha-2010

2. Single spin asymmetry of W bosons RHIC Accelerator PHENIX experiment
Outline
Physics motivation
Proton spin
Single spin asymmetry of W bosons
RHIC
Accelerator
PHENIX experiment
Single spin asymmetry of W bosons from RHIC Run-9
PHENIX forward moun trigger upgrade
MuTRG
RPC
Projection
Summary
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3. Physics Motivation
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4. Proton Structure With three valance quarks: We understand Charge
Proton = 3 valance quarks + sea quarks + gluons
Momentum: carried by both quarks and gluons
What about proton spin?
Quark spin = ½
Spin Crisis:
Quark Spin  = 0.24  0.12  0.01
EMC: Phys. Lett. B 206, 364 (1988); Nucl. Phys. B 328, 1 (1989) u d
quark spin
gluon spin
orbital angular momentum
Spin ½ quarks
Spin ½ anti-quarks
Spin 1 gluons
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5. Quark and Gluon Distribution Functions
Spin dependent quark distribution functions by the QCD analysis of DIS data
: well known
: only known with large uncertainties
Spin dependent gluon distribution function by the QCD analysis of DIS data
G=0.471.08 (largely unknown)
The latest extraction of polarized parton distributions (DSSV):
D. de Florian, R. Sassot, M. Stratmann, W. Vogelsang, Phys. Rev. D 80, (2009)
M. Hirai, S. Kumano, N. Saito, Phys. Rev. D 74, (2006)
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6. Semi-Inclusive DIS: e+p  e+ h +X Quark & Anti-Quark Helicity Distributions
How well do we know hadron
fragmentation functions ?
new analysis of e+e- data,
Hirai, Kumano, Nagai, Sudo
hep-ph/ , INPC 2007
Extraction based on LO-QCD inspired QPM at low Q2
Unspecified uncertainties from possible QCD NLO contributions and/or sub-leading twist
Large uncertainties from fragmentation functions
SPIN-Praha-2010

7. Semi-Inclusive DIS: e+p  e+ h +X Quark & Anti-Quark Helicity Distributions
How well do we know hadron
fragmentation functions ?
new analysis of e+e- data,
Hirai, Kumano, Nagai, Sudo
hep-ph/ , INPC 2007
Recent progress on fragmentation functions (DSS):
D. de Florian, M. Stratmann, R. Sassot, Phys. Rev. D76, (2007)
For the first time: Inclusion of e+e-, SIDIS and pp data in global analysis
Still significant uncertainties in s, heavy flavor and gluon fragmentation function
Several data sets at low Q2: validity of analysis at leading twist OPE and NLO QCD
Extraction based on LO-QCD inspired QPM at low Q2
Unspecified uncertainties from possible QCD NLO contributions and/or sub-leading twist
Large uncertainties from fragmentation functions
SPIN-Praha-2010

8. Parity Violating W Production
W boson production in p-p collision
Large scale (~mW)
flavor combination is almost fixed
flavor separated measurement
helicities of interacting partons are fixed
spin measurement
W → lepton decay includes no fragmentation process
direct and clean measurement
Important to control hadron decays and beam backgrounds
Asymmetry measurement of W boson production is ideal method
High luminosity and longitudinally polarized p+p collisions at 500 GeV (integrated L = 300 pb-1, polarity = 70%)
lefthanded quarks and righthanded antiquarks
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9. Single Spin Asymmetry of W
Forward/backward region selects valance/sea quark helicity contribution
Flavor decomposed proton quark polarization can be probed using the single spin asymmetry of W+ and W- in longitudinally polarized p+p collisions
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10. Relativistic Heavy Ion Collider (RHIC) and PHENIX
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11. Relativistic Heavy Ion Collider (RHIC)
STAR
PHENIX
PHOBOS
BRAHMS
RHIC, lenght: 3.83 km
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12. Relativistic Heavy Ion Collider (RHIC)
Bunch crossing 106 ns ~ 9MHz
RHIC is world’s unique polarized proton collider
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13. PHENIX Detector e+/- μ+/- Philosophy (initial design):
High rate capability & granularity
Good mass resolution & particle ID
Sacrifice acceptance
e+/-
Central Arms:
hadrons, photons, electrons
|η| < 0.35
Δφ = π (2 arms x π/2)
Global Detectors:
Beam-Beam Counter (BBC)
Zero Degree Calorimeter (ZDC)
μ+/-
Muon Arms:
muons
1.2 < |η| < 2.2
Δφ = 2π
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14. Expected Single Spin Asymmetry of W in the PHENIX Acceptance
Central Arms: W measurement at RHIC Run-9
Muon Arms: Forward muon trigger upgrade is ongoing and ready for RHIC Run-11
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15. W measurement at PHENIX Central Arms
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16. e  W  e RHIC Run-9: First 500 GeV Run, March 17 - April 13, 2009
EMCal (x~0.01x0.01) 4x4 tower sum trigger
±30 cm vertex cut
High energy EMCal clusters matched to charged track
Loose timing cut to reduce cosmic ray background
Loose E/p cut e
Fully efficient at 12 GeV/c 
Delta p/p = 40% at 40 GeV/c, high collision rate (~ 2 MHz): Multiple collisions and pile up effects (Luminosity determination) & BBC z-vertex position (calculated from the arrival times) is affected
RHIC Run-9: First 500 GeV Run, March 17 - April 13, 2009
Machine development in parallel with physics running to increase luminosity, polarization , reduce backgrounds
Integrated luminosity (with vertex cut) = 8.57 pb-1
Polarization is <P> = 0.39±0.04 (scale uncertainty)
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17. Effect of Cuts
Clusters
Good track match
TOF cut
E/p
Smooth spectrum of EMCal clusters after removing bad towers
Have a good track pointing to an EMCal cluster
Timing within start time of collision
Reduces out of time backgrounds (cosmics) by ~80%
E/p cut
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18. Expected W  e Decay Signal
positive
negative
RHICBOS: Nadolsky and Yuan, Nucl. Phys. B 666:31-55,2003
QCD provides the most obvious background (W. Vogelsang)
Not shown here but very important
Cosmics and photons (from meson decays and direct), which can have accidental matches to tracks or conversions
c/b relatively small above 30 GeV, calculated at FONLL (Matteo Carciari)
Z/* background is estimated from PYTHIA (~1 count is expected in Run09).
We is also small
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19. + - + Comparison To Measured Spectra Data and MC driven BG estimation:
EMCal cluster distribution after subtracting cosmic background
 (Conversion + Accidental)
 Tracking Acceptance
(NLO Hadrons thru Geant + FONLL c/b)
Normalization from fit to GeV + + -
The same scale factor for PYTHIA was used for W/Z shape
W-  e- signal has fewer counts than W+  e+ signal as expected
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20. + - Isolation Cut Signature of a W event is that it is isolated
Sum up energy in a cone around electron and in cone on opposite hemisphere
E < 2GeV + -
90+% of signal is kept (red histograms)
Factor ~5 reduction in jet dominated region
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21. Raw Asymmetries (e+) Background Signal 12-20 30-50 0.0350.047
pT Range (GeV/c)
12-20
30-50
Raw Asymmetry
0.0350.047
-0.290.11
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22. PHENIX AL(W+  e+) ALW+ = -0.83 ± 0.31
Using average polarization 0.39±0.04, we get
Asymmetry is corrected for dilution by Z and QCD backgrounds
ALW+ = ± 0.31
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23. PHENIX Forward Muon Trigger Upgrade
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24. Current PHENIX Muon Arms
Muon ID
(MuID)
Acceptance
1.2 < |η| < 2.2
Δφ = 2π
MuTr
80 cm of steel & Copper absorber
3 stations of cathode strip chamber
3gap + 3 gap + 2 gap
Each gap has non-stereo and stereo strip plane
Total 16 cathode strip planes
MuID
5 gaps of larocci tube in x and y directions
Total 80 cm of steel plates
Muon Tracking and triggering
Tracking uses hit positions from each station
Most hadrons are absorbed before reaching MuID last gap
Rejection power of the current MuID based first level trigger ~ 100
Absorber
Muon
Muon Magnet
Hadron
Muon Tracker (MuTr)
SPIN-Praha-2010

25. Current Muon Trigger at PHENIX
PHENIX Muon Arms
simulated muons into Muon Arms
(2000 pb-1, with PYTHIA 5.7)
Design Luminosity
√s = 500 GeV σ=60mb
L = 1.5x1032cm-2s-1
(L = 3.0x1032cm-2s-1, after luminosity upgrade)
Total interaction rate = 9MHz (18 MHz)
DAQ LIMIT = 2kHz (for Muon Arm)
Required RF = 4500 (9000)
MuID LL1 (trigger) = RF < 100 W
Current Muon Trigger at PHENIX
SPIN-Praha-2010

26. Current Muon Trigger at PHENIX
PHENIX Muon Arms
In order to measure W at 500 GeV, we need a first level rejection factor 9000
The current muon trigger accepts muons above 2 GeV/c and current DAQ cannot take full rate at 500 GeV
We need a momentum sensitive muon trigger and fast readout electronics for muon tracker
NSF funded trigger RPC stations
JSPS funded MuTr front end electronics
Additional RPC and MuTr information in the trigger makes it possible to measure the sagitta of charged particles online
The upgraded first level trigger will select events with muons of high transverse momentum pt  20 GeV/c from W boson decay
simulated muons into Muon Arms
(2000 pb-1, with PYTHIA 5.7) W
Current Muon Trigger at PHENIX
SPIN-Praha-2010

27. PHENIX Muon Trigger Upgrade
RPC 1
RPC 3
MuTRG
MuTRG
Adding 35 cm Fe absorber:
reduce the lower momentum hadron punch through
(S/B=3:1 instead of 1:3 without absorber)
RPC1: 16 RPC detector modules (384 read-out channels), RPC3: 96 RPC detector modules (11488 read-out channels)
MuID Trigger (existing):
Selecting momentum above 2 Gev/c
MuTRG (fully installed):
Fast selection of high momentum tracks
RPC (being installed):
Provide timing information and rough position information
SPIN-Praha-2010

28. PHENIX Muon Trigger Upgrade
RPC3
RPC1
LL1 decision: within 40 BCLK (4 microsec.)
Momentum selectivity through online sagitta measurement
Uses MuTr station 1, 2, 3 and RPC station 1, 3
Implement trigger using fast, parallel logic on FPGA’s
Beam related background rejected by RPC timing information
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29. PHENIX Muon Trigger Board Upgrade (MuTRG) Resistive Plate Counter
(RPC) (Φ segmented) B
Trigger events with straight track
(e.g. Dstrip <= 1)
Level 1
Trigger
Board
Trigger
RPC
FEE
MuTRG
Data
Merge
Amp/Discri.
Transmit
Trigger 5%
Optical
MuTRG
MRG
MuTRG
ADTX
1.2Gbps
2 planes
Trigger
RPC / MuTRG data are
also recorded on disk
MuTr
FEE
95%
Interaction Region
Rack Room
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30. PHENIX MuTRG Installation
MuTRG Rack
MuTRG ADTX
Completed MuTRG installation and commissioned MuTRG
Evaluation of commissioning data is in progress
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31. MuTRG Efficiency for Track
0.939
0.874
 = (# of MuTRG)/(# of MuTr hits)
Red : Δs=1
Black : Δs=0
8.5
GeV/c
12.2
GeV/c
Sufficient efficiency can be achieved in MuTRG
Turn on point is enough low with Δs=0
(12.2 GeV/c in p, ~6 GeV/c in pT)
SPIN-Praha-2010

32. PHENIX Muon Trigger RPC
Characteristics of double gap RPC in avalanche mode
Fast response: Suitable for the trigger device
Good time resolution: ns for M.I.P
Good spatial resolution: typically ~ cm
→ Determined by the read-out strip width and cluster size
Efficiency: > 95 % for M.I.P
Rate capability: kHz/cm2
Low cost: bakelite (resistivity cm)
Noise rate: Hz/cm2 for 1010 cm
Typical strip multiplicity:
Typical gas mixture
95% C2H2F4 (Tetrafluoroethane, R134A, base gas for avalanche mode RPC) + 4.5% i-C4H10 (isobutane, photon quencher) + 0.5% SF6 (electron quencher)
20 – 40% relative humidity
PHENIX RPC Detector Requirement
Time resolution
 3 ns
Average cluster size
 2 strips
Efficiency
 95%
Rate capability
0.5 kHz/cm2
Number of streamers
 10 %
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33. PHENIX Muon Trigger RPC
station
RPC1(a,b)
RPC3
Use already established CMS Bakelite RPC technology and expertise
half octant
RPC 1A
RPC 3A
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34. PHENIX RPC Module QA RPC test stand event display
cosmic ray trigger scintillators
RPC readout strip planes
cosmic ray trajectory
Raw TDC :
1 unit = 100 ns/44 = 2.41 ns
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35. PHENIX RPC Module Noise Rate
# of strips vs. noise rate
all 48 modules
H.V = 9.5 kV
FEE Threshold = 160 mV
<noise rate> = 0.52 Hz/cm2
7 strips are over 10 Hz/cm2
# of strips vs. noise rate
Individual module
H.V = 9.5 kV
FEE Threshold = 160 mV
Black = module A
Blue = module B
Red = module C
All results are compliant with PHENIX RPC requirements
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36. PHENIX RPC Half Octant Assembly
RPC half octant placed on half octant assembly table at the RPC factory in BNL
All half octant parts are made of aluminum
Half octant contains three RPC modules
Final cable routing during half octant QA
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37. PHENIX RPC Half Octant Noise Rate
<noise rate> = 0.37 Hz/cm2
Modules are in Faraday cage
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38. PHENIX RPC-3 North Installation
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39. PHENIX RPC-3 North Installation Completed
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40. PHENIX RPC-3 North Integration Completed
RPC Integration completed
RPC TDC Rack
RPC-3 north was commissioned in Run-10
Evaluation is in progress
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41. Partially installed MuTRG
PHENIX RPC Prototypes during RHIC Run-9
MuTRG
Prototype
RPCs
Absorber Prototype
RPC Prototypes
Partially installed MuTRG
SPIN-Praha-2010

42. Timing Information from PHENIX RPC Prototype
 ~ 5.3ns
 ~ 4.1ns
No correction for collision vertex 30 cm ~ 2nsec.
Muon cuts: tracks close to RPCs, at least 3 GeV momentum
The peak below zero: tracks coming from the collision or the outgoing beam
The other peak above zero: background generated by incoming beam
Separation of the peaks: ~ 12 ns
Width for each peak: 3 ns
Individual RPC timing results required a timing correction from reference detector
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43. PHENIX Muon Trigger Upgrade Schedule
RPC Installation for Station 3 South
by October
+Absorber Installation
RPC Installation for Station 3 North by October
RPC Production for Station 1 North by December
RPC Installation for Station 1 during shutdown
PHENIX RPC-3 south production completed
PHENIX RPC-3 south half octant QA is underway
PHENIX will be ready for W measurement for RHIC Run-11
Completion of RPC Project expected in 2011
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44. RHIC Run-11 AL of W Projection
Exceptive
Conservative
For RHIC Run-11, asking 10 weeks 500 GeV p+p collisions with 50% of polarization
Expecting integrated luminosity L = 50 pb-1
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45. RHIC Run-11+12 AL of W Projection
Exceptive
Conservative
For RHIC Run-12, asking 8 weeks 500 GeV p+p collisions with 50% of polarization
Expecting integrated luminosity L = 150 pb-1 (together RHIC-11 and 12)
SPIN-Praha-2010

46. Summary PHENIX observed W  e decay in the mid-rapidity region
First attempt to measure single spin asymmetry has detected a parity violating asymmetry leading to a preliminary value of AL
AL(W+  e+) at |ye| < 0.35 has been measured to be
Within errors, it is consistent with the predictions.
While the data sample is small, we got a first significant result
Gained experience on the backgrounds to the W in the PHENIX central arm
Learned how to handle multiple collisions from high luminosity
Learned how to handle very high momentum particles
Working on finalizing cross-sections, AL(W+), and AL(W-)
Goal of the RHIC W program is 300 pb-1 and 70% polarization
Order of magnitude improvement in the error bars
Forward muon measurements in PHENIX will contribute significantly starting next year with MuTRG, RPC, and absorber
ALW+ = ± 0.31
SPIN-Praha-2010