spin physics with phenix (an overview, but mainly g) abhay deshpande stony brook university riken...
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Spin Physics with PHENIX (an overview, but mainly
DG)
Abhay DeshpandeStony Brook University
RIKEN BNL Research Center
July 28, 2011
Abhay L. Deshpande, Nucleon spin studies with PHENIX at RHIC 2
Outline Introduction
Relativistic Heavy Ion Collider as a polarized p+p collider
A brief overview of the RHIC Spin program
Spin Physics with PHENIX Recent measurements leading to DG: Impact &
limitations
Prospects of improvement in DG @ PEHNIX in near future
The question of anti-quark polarization
Summary & outlook7/28/11
Abhay L. Deshpande, Nucleon spin studies with PHENIX at RHIC 3
Complementary techniques
Polarized DIS discovered and established the nucleon spin crisis: quarks carry a small fraction of nucleon’s spin. Do gluons carry the remaining spin?
Previous talk by COMPASS experiment at CERN
Protons are mostly gluons. Why not explore the gluon’s contribution to the nucleon spin by colliding polarized protons? A complementary approach!
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pDIS p+p
Abhay L. Deshpande, Nucleon spin studies with PHENIX at RHIC 4
RHIC as a polarized Collider
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BRAHMS & now ANDY
STAR
PHENIX
AGS
LINACBOOSTER
Pol. H- Source
Spin Rotators(longitudinal polarization)
Siberian Snakes
200 MeV Polarimeter
Internal Polarimeter
pC PolarimetersAbsolute Polarimeter (H jet)
pC Polarimeter
10-25% Helical Partial Siberian Snake
5.9% Helical Partial Siberian Snake
PHOBOS
Spin Rotators(longitudinal polarization)
Spin flipper
Siberian Snakes
Without Siberian snakes: nsp = Gg = 1.79 E/m ~1000 depolarizing resonances
With Siberian snakes (local 180 spin rotators): nsp = ½ no first order resonances
Two partial Siberian snakes (11 and 27 spin rotators) in AGS
Abhay L. Deshpande, Nucleon spin studies with PHENIX at RHIC 5
The RHIC Spin Program Determination of polarized gluon distribution via multiple probes
( , p g, c-cbar,… production)
Measurement of double longitudinal spin asymmetry ALL
THIS TALK (for PHENIX) & C. Gagliardi (STAR)
Determination of anti-quark polarization using production and decay of W+/- [ maximal parity violation]
Measurement of single longitudinal spin asymmetry AL
TALKS BY E. Kistenev (PHENIX) & J. Balewski (STAR)
Systematic study of transverse spin phenomena & their connections to transverse momentum and spatial distribution of partons
Measurement of single transverse spin asymmetries AN
TALKS BY D. Kleinjan (PHENIX) and R. Fatemi (STAR)
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Probes available at RHIC
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LuminosityLow
High
500 GeVCM
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Measuring ALL in a collider
(N) Yield (R) Relative Luminosity(P) Polarization
Bunch spin configuration alternates every 106 ns Data for all bunch spin configurations are collected at the same time Possibility for false asymmetries are greatly reduced
Message: Spin measurements at a collider enable exquisite control over false asymmetries due to ultra fast rotations
of the target and probe spin.
Abhay L. Deshpande, Nucleon spin studies with PHENIX at RHIC 8
DG program at PHENIX
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PHENIX in 2011 Design philosophy: high resolution in limited acceptance, high rate capability DAQ, excellent trigger and DAQ system
Central Arms (|h| < 0.35)Tracking: Drift, Pad Chambers
EM Calorimetry: Df x Dh ~ 0.01 x 0.01
Particle ID: RICH, TOF
Si VTX tracker (|h| < 1)
Forward arms:Mu trackers and identifier (1.2 < h < 2.4)
Global detectors: Beam-Beam collisions counters, Zero Degree Calorimeters
Muon Piston Calorimeter (3.1 < h < 3.9)
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Abhay L. Deshpande, Nucleon spin studies with PHENIX at RHIC 10
Access to DG in p+p collisions:
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From ep (& pp)(HERA mostly) NLO pQCD
From e+e-(& SIDIS,pp)
pp hX
Spin dependence
Df : Dq from pDIS DG to be measured
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p0s in PHENIX Large cross section, predominantly g-g interactions
2-g invariant mass reconstructed using high pT photon triggers
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Partonic contribution to 0
s=200GeV, ||<0.35
0 pT wBG
2 20%5 8%10 5%
pT (GeV/c) vs.
Background fraction
under signal
PRD 76, 051106 (2007)
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p0 cross section & ALL
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PRL 103, 012003 (2009)PRD 76, 051106 (2007)
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Impact: Early studies by PHENIX
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PRL 103, 012003 (2009)
at m2 = 4 GeV2
Abhay L. Deshpande, Nucleon spin studies with PHENIX at RHIC 14
p0 cross section & ALL
Lower CM Energy: accesses higher x
No evidence of significant asymmetry,
Consistent within uncertainties with asymmetry measurements at 200 GeV
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0
PRD 79, 012003 (2009)
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Impact: Global analysis at NLO (I)
NLO pQCD + Data from RHIC (p+p), pDIS (inclusive & semi-inclusive)
RHIC (p+p): Included PHENIX p0 at 200 & 62.4 GeV CM and STAR inclusive jets 200 GeV (Run-6)
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DSSV: PRL 101, 072001 (2008)
RHIC
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PHENIX p0 (2009, preliminary)
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Dataset <PB> (%) <PY> (%) Lanalyzed (pb-1) FOM (P4L)
Run5 50 49 2.5 0.15
Run6 56 57 6.5 0.66
Run9 57 57 14 1.5
Run5Run6Run9
Abhay L. Deshpande, Nucleon spin studies with PHENIX at RHIC 17
Other measurements related to DG
Most of these measurements “luminosity starved”.
Current impact is limited, but anticipated to be impactful in the next few years
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Other measurements (I)
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PRD83,032001(2011)
PHENIX p+p h +X
Un-polarized NLO cross-section
calculations compare well with the
measured cross sections, in all cases.
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Other measurements (II)
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Direct Photon Jets arXiv:1009.4921
Abhay L. Deshpande, Nucleon spin studies with PHENIX at RHIC 20
What’s next for DG investigations @
PHENIX?Substantial uncertainties in DG at low x, accessible by:• Accessing a different
event geometry • Collisions at higher
center of mass energy
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Abhay L. Deshpande, Nucleon spin studies with PHENIX at RHIC 21
Asymmetric x1 & x2: The Muon Piston Calorimeter (MPC)
3.1 < h < 3.9, both m arms
EM showers:
For pT < 2 GeV (p02 ) g
For pT > 2 GeV help from simulation
PYTHIA indicates 80% events from p0
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x1 x2
pT=0.5 GeV/c…pT=4
(ref.) ||<0.35
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High h p0: X-section & ALL
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Low x using p+p at 500 GeV CM
Cross section measured
ALL(p0) analysis in progress 7/28/11
xmin dependance on CM Energy
xmin
xmin
xmin
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Quark/Anti-Quark Spin: W Physics at RHIC
: DS From DIS experiments, using g* as the probe Can not distinguish between quark and anti-quark’s contributions
Determined in semi-inclusive DIS (SIDIS) which employ fragmentation functions to tag quark & anti-quark flavors: resulting in large uncertainties
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DSSV: PRL 101, 072001 (2008)
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An alternate method: p+p W +/-
Q and Qbar via parity violating production & decay of W+/-
Needs identification of charge of the final state lepton
PHENIX: e+/- in the central arm & m+/- in forward arm
Crucial: Measurement of x-section & comparison with the SM
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p + p W e + n cross section
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Details of W measurements & its decay in to electrons (and progress on doing the same with) muons: in the following talk
by E. Kistenev
PHENIX PRL 106, 062001 (2011)
Abhay L. Deshpande, Nucleon spin studies with PHENIX at RHIC 27
Summary PHENIX has measured double longitudinal spin
asymmetries in polarized p+p collisions at 62.4, 200 & 500 GeV
Results indicate small contribution from DG to the nucleon’s spin in the currently measured regions. Low x access to DG being explored with forward detectors in
PHENIX and by raising the collision energy
Future possible Electron Ion Collider would address this naturally & exquisitely (Talk by M. Stratmann)
Other components to the nucleon’s spin budget (anti-quark’s spin contribution & orbital motion: transverse spin results) in this and other sessions. (Talks by R. Fatemi, D. Kleinjan & on EIC T. Horn)
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Thanks
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Impact: Global Analysis at NLO (II)
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DSSV: PRL 101, 072001 (2008)