Spin Physics with PHENIX (an overview, but mainly D G)

Spin Physics with PHENIX (an overview, but mainly

DG)

Abhay DeshpandeStony Brook University

RIKEN BNL Research Center

PANIC’11 at MITJuly 28, 2011

Abhay L. Deshpande, Nucleon spin studies with PHENIX at RHIC 2

Outline Introduction

Relativistic Heavy Ion Collide 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 PHENIX spin measurements leading to DG in near

future The question of anti-quark polarization

Summary & outlook7/28/11


Complementary techniques

Polarized DIS discovered and established the nucleon spin crisis: quarks carry a small fraction of nucleon’s spin. Do gluon 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!

7/28/11

pDIS p+p


RHIC as a polarized Collider

7/28/11

BRAHMS & now ANDY

STARPHENIX

AGS

LINAC BOOSTER

Pol. H- Source

Spin Rotators(longitudinal polarization)

Siberian Snakes

200 MeV PolarimeterInternal Polarimeter

pC PolarimetersAbsolute Polarimeter (H jet)

pC Polarimeter10-25% 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


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) 7/28/11


Probes available at RHIC

7/28/11

LuminosityLow

High

500 GeVCM

7/28/11Abhay L. Deshpande, Nucleon spin studies with PHENIX at RHIC 7

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

Exquisite control over false asymmetries due to ultra fast rotations of the target and probe spin.


DG program at PHENIX7/28/11


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 ChambersEM Calorimetry: Df x Dh ~ 0.01 x 0.01Particle ID: RHIC, TOFSi VTX tracker (|h| < 1)

Forward arms:Mu trackers and identifier (1.2 < h < 2.4)Global detectors: Beam-Beam collisions counters, Zero Degree CalorimetersMuon Piston Calorimeter (3.1 < h < 3.9)

Online monitoring, calibration & fast production the data

7/28/11


Access to DG in p+p collisions:

Df = Dq, input from polarized DIS

DG to be measured!

7/28/11

From ep (& pp)(HERA mostly)

NLO pQCD From e+e-(& SIDIS,pp)

pp hX

Spin dependence

PDF


p0s in PHENIX Large cross section, predominantly g-g interactions 2-g photon invariant mass reconstructed using high

pT photon triggers

7/28/11

Partonic contribution to p0

s=200GeV, |h|<0.35

p0 pT wBG

2 20%5 8%10 5%

pT (GeV/c) vs.

% background under signal

PRD 76, 051106 (2007)


p0 cross section & ALL ( CM: 200 GeV)

7/28/11

PRL 103, 012003 (2009)PRD 76, 051106 (2007)


Impact: Early studies by PHENIX

7/28/11

PRL 103, 012003 (2009)

at m2 = 4 GeV2


p0 cross section & ALL ( CM: 62.4 GeV)

Lower CM Energy: accesses higher x

No evidence of significant asymmetry,

Consistent within uncertainties with asymmetry measurements at 200 GeV

7/28/11

p0

PRD 79, 012003 (2009)


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)

7/28/11

DSSV: PRL 101, 072001 (2008)

RHIC


PHENIX p0 (2009, preliminary)

7/28/11

Dataset <PB> (%) <PY> (%) Lanalyzed (pb-1) FOM (P4L)

Run5 50 49 2.5 0.15Run6 56 57 6.5 0.66

Run9 57 57 14 1.5

Run5Run6Run9


Other measurements related to DG

Most of these measurements “luminosity starved”.

Current impact is limited, but are important complimentary measurements, anticipated to be

impactful in the next few years

7/28/11

Abhay L. Deshpande, Nucleon spin studies with PHENIX at RHIC 187/28/11

PRD83,032001(2011)

PHENIX Direct PhotonPHENIX p+p h +X

Un-polarized NLO cross-section calculations compare well with the measured cross sections, in all cases.


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

7/28/11


Asymmetric x1 & x2: The Muon Piston Calorimeter (MPC)

3.1 < h < 3.9, both m arms

EM showers: For pT < 2 GeV (p02g) For pT > 2 GeV merged cluster

algorithm developed

PYTHIA indicates 80% events from p0

7/28/11

x1 x2

pT=0.5 GeV/c…pT=4

(ref.) |h|<0.35


PHENIX MPC p0: X-section & ALL

7/28/11


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


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

7/28/11

DSSV: PRL 101, 072001 (2008)


PHENIX W physicsPHENIX accesses Q and Qbar via W production & its PV decay

Needs identification of charge of the final state lepton PHENIX measures electrons/positrons in the central arm

& muons in forward arm Measurement of cross section & comparison with

Standard Model Calculation an essential first step 7/28/11


PHENIX p+pW cross section

7/28/11

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)


Summary (mainly DG) PHENIX has measured double longitudinal spin asymmetries

for various final in polarized p+p collisions at 62.4, 200 & 500 GeV in CM

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 upgrade of RHIC including possible construction

of eRHIC at BNL are aimed with such measurement (See M. Stratmann’s talk later today)

Other components to the nucleon’s spin budget (anti-quark’s spin contribution & orbital motion: transverse spin results) being discussed in this and other sessions. (Talks by R. Fatemi, D. Kleinjan, T. Horn)

7/28/11


Thanks

7/28/11


The nucleon spin puzzle

Polarized DIS explored DS: Attempts of measurement at low x, resulting in the discovery of the nucleon spin puzzle

DG: the gluon’s contribution to the nucleon spin (the principle focus of this talk)

LQ+G: connected to the transverse motion and transverse momentum dependence of the partons

7/28/11


Impact: Global Analysis at NLO (II)

7/28/11

DSSV: PRL 101, 072001 (2008)

Documents

Spin Physics with PHENIX (an overview, but mainly D G)