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

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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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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

PDF

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

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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

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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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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)