Spin Physics with the PHENIX Detector

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Spin Physicswith the PHENIX Detector
Mickey Chiu University of Illinois at Urbana
21st Winter Workshop on Nuclear Dynamics,
Breckenridge
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Nucleon Spin Physics
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Polarised PDFAsymmetry Analysis Collaboration
M. Hirai, S. Kumano and N. Saito, PRD (2004)

• Valence Dists are determined well
• Sea Distribution poorly constrained
• Gluon can be either pos, 0, neg!

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RHIC Spin Evolution
RHIC pC CNI Polarimeter
BRAHMS PP2PP
PHOBOS
RHIC
PHENIX
STAR
Siberian Snakes
Partial Siberian Snake
LINAC
BOOSTER
Pol. Proton Source 500 mA, 300 ms
AGS
AGS Internal Polarimeter
Rf Dipoles
200 MeV Polarimeter
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What Do We Measure at RHIC?

• We measure spin asymmetries for cross sections
• ALL double helicity asymmetry
• Useful in extracting Dg(x), Dq(x) etc.

ANTwist-3 etc
ATT Transversity
ALParity Violation
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RHIC Spin L and P Progress

• Run 2 AN
• 7 nb-1/day
• (0.15/pb),PB15
• Run-3ALL
• 10 nb-1/day 0.35/pb,PB26
• (AGS) 40
• Run-4ALL
• Only Machine Studies
• 30nb-1/day
• 0.12/pb,PB40
• (AGS) 50
• Run-5 ALL
• 11 weeks

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Mid-Rapidity ?0 and charged hadron Production in
pp at ?s 200 GeV

• NLO QCD Calculation Cross-sections consistent
  with Data
• CTEQ5M pdf
• KKP and Kretzer Fragmentation Fcns
• Necessary Confirmation that pQCD can be used
  successfully at RHIC to extract spin dependent
  pdfs.
• Same comparison fails for lower energies

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Getting Polarization Information
preliminary
AN ?0.1080.0087

• Large Neutron AN was discovered at IP12
• Cause not yet well understood
• A possible diffractive process?
• Charge Exchange?
• ZDC/SMD can make a local polarimetry measurement
  at PHENIX
• Allows us to measure independently the
  polarization

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Measuring ALL

• To determine ?g, look at ALL
• R is the relative luminosity, and can be measured
  (to some accuracy) at PHENIX using the BBC or
  ZDC.
• Our Goal dR/R lt 0.1 for each fill
  ? dALL lt 210-3(expected ALL for
  pions 310-3 _at_pT3 GeV/c)

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Constraints on Dg(x) w/ p0 Production

• pp ? p0 X is sensitive to gg?gg and gq?gq

PHENIX Results from Run-3 To Appear in PRL
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Other Probes of ?g
GS95
hadrons
DG(x)
prompt photon
cc?eX
bb?e?X
J/????
x
See Talks by Takao Sataguchi, Youngil Kwon,
Sergey Butsyk
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Single Transverse SpinAsymmetries

• Fermilab E-704 reported Large Asymmetries AN in
  pion productions

left
right

• Transversity x Spin-dep fragmentation (Collins
  effect), or
• Intrinsic-kT imbalance (Sivers effect) , or
• Higher-twist effects
• Sterman and Qiu Initial State Twist 3
• Koike Final State Twist 3
• Or combination of above

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Calculating AN

• Look for left-right asymmetry with respect to
  beam spin and direction
• OR look either on left or right side and compare
  p0 production for and - spin states
• Two methods provide important check of systematic
  errors

Racc relative acceptance of left and right
detectors
Rlumi relative luminosity of and - spin states
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AN of Neutral Pions and Non-Identified Charged
Hadrons
Data taken 0.15 pb-1 and 15 beam polarization
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Sivers and Why it is Interesting
J1/2
ltLZgt ?

• Non-Zero Sivers function means that there is a
  left/right asymmetry in the kT of the partons in
  the nucleon
• Probes space-time structure of nucleon
  wave-function
• Testable kT dependence of nucleon wave-function
  testable
• Sivers requires quark orbital angular momentum
• Centrality dependent effects
• Quark Shadowing in central region causes kT
  asymmetry?
• Red Shift/Blue Shift effects in peripheral
  regions?
• ST ? (P ? kT) is T-odd and naively thought to
  vanish
• FSI effects found by Brodsky et.al. that allow
  T-odd function to be non-zero

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Sivers Fcn from Back2Back Analysis
Boer and Vogelsang, Phys.Rev.D69094025,2004,
hep-ph/0312320

• Boer and Vogelsang find that this parton
  asymmetry will lead to an asymmetry in the ??
  distribution of back-to-back jets
• There should be more jets to the left (as in
  picture to the left).
• Should also be able to see this effect with
  fragments of jets, and not just with fully
  reconstructed jets?
• Take some jet trigger particle along ST axis
  (either aligned or anti-aligned to ST)
• Trigger doesnt have to be a leading particle,
  but does have to be a good jet proxy
• Then look at ?? distribution of away side
  particles

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Unpolarized Results from Run03 pp
Boer and Vogelsang, PRD69094025,2004
Run03 ?-charged dn/d??
anti-aligned
aligned
1/Ntrig dN/d?? (au)

• Asymmetry
• numerator is difference between aligned and
  anti-aligned ?? dists, where aligned means
  trigger jet and spin in same direction
• denominator is simply unpolarized ?? distribution
• On left are some theoretical guesses on expected
  magnitude of AN from Sivers
• On right are gamma-charged hadron ?? dists from
  Run03 pp
• 2.25 GeV gammas as jet trigger, 0.6-4.0 GeV
  charged hadrons to map out jet shape
• Dotted lines are schematic effect on away side ??
  dist due to Sivers Fn (not to scale)

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Estimated AN from Run03 pp
parametrized AN
??-?

• Parametrized AN with
  , A0.08,
  ?0.8
• Used this to calculate AN using unpolarized
  gamma-charged Run03 pp dN/d??
• Put asymmetry into distribution and then
  calculate AN
• On right shows statistical significance from
  Run03 pp (0.35/pb).
• Assumed Poisson statistics (but k factor only
  10 different?)
• Note that area around ??0 can be used as a
  systematic check (it should be flat)
• Also note that AN from Boer/Vogelsang paper is
  idealized, and the real signal will be reduced

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AN Reduction 1 Polarization

• Polarization P lt 1 just reduces AN by P

• Besides that, most of the time the jet is not
  aligned exactly along the polarization axis,
  which means ANAN(?j1,??) and also the
  polarization is reduced by cos(?j1)

• We can make a simple (though wrong) estimate for
  this effect by calculating the average
  polarization from a jet spread of ?/2 around the
  polarization axis

j1
ST
j2
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AN Reduction 2 Di-Hadron vs. Di-Jets
AN
away side parton
up down unpolarized
di-hadron di-jet

• Since we dont reconstruct jets fully, we have to
  use di-hadron correlations to measure jet ??.
  This smears out the di-hadron AN relative to the
  di-jet AN, with smearing function g (assumed here
  to be a gaussian, with ?jT0.35).
• The effect broadens and lowers (by just a little
  bit) the asymmetry

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Combined Effects
Full di-jet Sivers Reduced by lower ltPgt,
di-hadron smearing Run03 pp gamma-charged,
0.35/pb

• Given 0.35/pb of data, we should be able to get
  1 statistical significance in AN using
  gamma-charged measurements of jet dphi
• Expected raw AN could be 3.5
• Could also be as low as 0.5, or as large as 10
• Effects from P0.5, jet angle not aligned with
  transverse polarization, and fragmentation to
  dihadrons reduces raw AN to 1.0
• Have not evaluated systematic errors yet
  (underlying event)
• Can also do this in Longitudinal collisions
  (Collins effect?)

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Some Future Measurements

• Upgrades
• Muon Trigger for W Bosons (Wei)
• Measure sea quark polarization
• Nose Cone Calorimeter (Vasily)
• ? jet ? ?G, extends x-range
• Silicon Vertex Tracker (Gerd)
• heavy flavor and jet reconstruction

• Searches for new physics (RHIC can become a
  polarized parton collider)
• Anomalous Parity Violation in Jet Production
• Contact Interaction (Scale ? 3.3 GeV at RHIC)
• New Gauge Boson Z

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Summary

• There are a variety of QCD phenomena that are not
  well understood in our most basic QCD object, the
  proton
• QCD is complicated
• PHENIX Has Measured ?0 ALL out to pt 5 GeV/c
• Demonstration of ability to do spin physics
• First constraints on ?g(x)
• 10 times statistics for ?0, h, ?, c, b ALL
  expected in upcoming run
• ?0 and charged AN at xF 0 is 0
• Start of transverse physics program
• Have access to Sivers function via back-to-back
  di-hadrons
• Possibly probes orbital angular momentum

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Backup Slides
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AN Systematic Errors
In addition to calculating the asymmetry using
more than one method, potential systematic errors
have been investigated in the following ways

• Measured asymmetry of background
• Immediately outside the p0 mass peak
• In the mass region between the p0 and the h
• Compared independent measurements for two
  polarized beams
• Compared results for left and right sides of
  detector
• Compared minimum bias and triggered data samples
• Examined fill-by-fill consistency of asymmetry
  values
• Used the bunch shuffling technique to check for
  systematic errors
• Randomly reassign the spin direction to each
  bunch in the beam
• Recalculate the asymmetry
• Repeat many times (1000) to produce a shuffled
  asymmetry distribution centered around zero
• Compare width of shuffled distribution to
  statistical error on physics asymmetry

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AN of Neutral Pions and Non-Identified Charged
Hadrons at Midrapidity
Mainly sensitive to g-g and g-q interactions