3d parton structure, int1 overview of transverse single spin asymmetry measurements at rhic l.c....

3D parton structure, INT 1

Overview of Transverse Single Spin Asymmetry Measurements at RHIC

L.C. Bland

Brookhaven National Laboratory

INT Workshop on 3D parton structure of the nucleon

Seattle, September 2009

OutlineReview of Findings on Transverse SSA at RHIC

• Motivations/goals and methods

• Findings from the first polarized proton collisions at RHIC (medieval times)

• Findings from the renaissance

• First findings from the modern age

• Possible paths forward (more on Friday)


In QCD: proton is not just 3 quarks !

Rich structure of quarksanti-quarks, gluons

Recall: simple quark model

RHIC Spin Goals - IHow is the proton built from its known quark and gluon constituents?

As with atomic and nuclear structure, this is an evolving understanding


RHIC Spin Goals - IIUnderstanding the Origin of Proton Spin

Spin Sum Rules

Longitudinal Spin

Transverse Spin PRD 70 (2004) 114001

Understanding the origin of proton spin helps to understand its structure


RHIC Spin Goals - III Objectives

• Determination of polarized gluon distribution (G) using multiple probes

• Determination of flavor identified anti-quark polarization using parity violating production of W

• Transverse spin: connections to partonic orbital angular momentum (Ly) and transversity ()

gluon

quark pion or jet

quark

RHIC Spin Probes - IPolarized proton collisions / hard scattering probes of G

Describe p+p particle production at RHIC energies (s 62 GeV) using perturbative QCD at Next to Leading Order,

relying on universal parton distribution functions and fragmentation functions

cabccbb

cbaaacba dzDxfxfdzdxdxd

ˆ)()()( ,,


p + p, s = 200 GeV

jets direct

PRL 97 (2006) 252001

PRL 98 (2007) 012002

p + p + X, s = 200 GeV PRD 76 (2007) 051106 PRL 92 (2004) 171801

Large rapidity ,K,p cross sections for p+p, s=200 GeV

PRL 98 (2007) 252001

Good agreement between experiment and theory calibrated hard scattering probes of proton spin

RHIC Spin Probes - IIUnpolarized cross sections as benchmarks and heavy-ion references


Longitudinal Two-Spin (ALL)

Status of probing for gluon polarization viameasurements of ALLfor midrapidity jet,production


ALL: 0

PRL 103 (2009) 012003

0.1(scale)(shape)0.1(sys)(stat)1.02.0 0.00.4-

]3.0,02.0[ GRSVG


Inclusive ALLjets Results

STARSTARB. Jager et.al, Phys.Rev.D70, 034010

The inclusive measurements give sensitivity to gluon polarization over a broad momentum range

Data are compared to predictions within the GRSV framework with several input values of G.

GRSV-std

arXiv:0805.3004


Global AnalysisDetermining g from Existing World Data

PRL 101 (2008) 072001

g(x,Q2) is small in the accessible range of momentum fraction [presently measured]


RHIC as a Polarized Proton Collider

BRAHMS & PP2PP

STAR

PHENIX

AGS

LINACBOOSTER

Pol. H- Source

Spin Rotators(longitudinal polarization)

Siberian Snakes

200 MeV Polarimeter

RHIC pC PolarimetersAbsolute Polarimeter (H jet)

AGS pC PolarimeterStrong AGS Snake

Helical Partial Siberian Snake

PHOBOS

Spin Rotators(longitudinal polarization)

Siberian Snakes

3D parton structure, INT 12 AN measurements initially motivated by search for local polarimeter


Transverse Single-Spin Asymmetries (AN)

Probing for (1) orbital motion within transversely polarized protons;

(2) Evidence of transversely polarized quarks in polarized protons.

Analyzing power is a tool to measure polarization and is one example of transverse single spin asymmetries (SSA) with origins yet to be fully understood


Expectations from Theory

What would we see from this gedanken experiment?

F0 as mq0 in vector gauge theories, so AN ~ mq/pT

or,AN ~ 0.001 for pT ~ 2 GeV/cKane, Pumplin and Repko PRL 41 (1978) 1689


s=20 GeV, pT=0.5-2.0 GeV/c

�0 – E704, PLB261 (1991) 201.�+/- - E704, PLB264 (1991) 462.

Xpp

• QCD theory expects very small (AN~10-3) transverse SSA for particles produced by hard scattering.

A Brief History…

• The FermiLab E-704 experiment found strikingly large transverse single-spin effects in p+p fixed-target collisions with 200 GeV polarized proton beam (s = 20 GeV).


STAR

• Large acceptance near midrapidity

• Windows to large rapidity


PHENIX Detector

BBC

ZDCZDC

EMCal detection• Electromagnetic Calorimeter (PbSc/PbGl):

• High pT photon trigger to collect 0's, ’s, ’s

• Acceptance: ||x • High granularity (~10*10mrad2)

• Drift Chamber (DC) for Charged Tracks• Ring Imaging Cherenkov Detector (RICH)

• High pT charged pions (pT>4.7 GeV).Relative Luminosity• Beam Beam Counter (BBC)

• Acceptance: 3.0< 3.9• Zero Degree Calorimeter (ZDC)

• Acceptance: ±2 mradLocal Polarimetry• ZDC• Shower Maximum Detector (SMD)


BRAHMS


Brahms

•Transvers beam pol•Particle ID

BRAHMS measured AN s=62.4 GeV and 200 GeV•Large xF dependent SSAs seen for pions and kaons•Collinear factorization and (NLO) pQCD describe unpolarized

cross-section at RHIC in wide kinematic region


Medieval TimesFirst polarized p+p collisions at RHIC


Transverse Spin Asymmetries at Midrapidity

p+p /h± + X, s = 200 GeV

Transverse single spin asymmetries are consistent with zero at midrapidity

PRL 95 (2005) 202001


Measuring AN: Inclusive 0 Production

PRL 92, 171801 (2004)PRL 97, 152302 (2006)

Cross-section is consistent with NLO pQCD calculations

Transverse spin asymmetries found at lower √s persist to √s=200 GeV

p+p+X, √s=200 GeV, <η> = 3.8

RHIC Runs 2-3 with Forward Pion Detector (FPD)

STARSTAR


STAR-Forward STAR-Forward Cross SectionsCross Sections

Similar to ISR analysisJ. Singh, et al Nucl. Phys. B140 (1978) 189.

6

5

13

3

B

C

pxdp

dE B

TC

F

Expect QCD scaling of form:

anBpxspxxdp

dE an

TC

F

anT

CF

aT 12/1

3

3

Require s dependence (e.g., measure cross sections at s = 500 GeV) to disentangle pT and xT dependence


The Renaissance


Idea: directly measure kT by observing momentum imbalance of a pair of jets produced in p+p collision and attempt to measure if kT is correlated with incoming proton spin

Boer & Vogelsang, PRD 69 (2004) 094025

jet

jet

AN pbeam (kT ST)

pbeam into page

STAR Results vs. Di-Jet Pseudorapidity SumSTAR Results vs. Di-Jet Pseudorapidity SumRun-6 ResultRun-6 Result

STARSTAR PRL 99 (2007) 142003

Emphasizes (50%+ ) quark Sivers

AN consistent with zero

~order of magnitude smaller in pp di-jets than in semi-inclusive DIS quark Sivers asymmetry!

VY 1, VY 2 are calculations by Vogelsang & Yuan, PRD 72 (2005) 054028


xF Dependence of Inclusive 0 ANRHIC Run 6 with FPD++

Fits to SIDIS (HERMES) is consistent with data

AN at positive xF

grows with increasing xF

PRL 101, 222001 (2008)arXiv:0801.2990v1 [hep-ex]

U. D’Alesio, F. MurgiaPhys. Rev. D 70, 074009 (2004)arXiv:hep-ph/0712.4240

C. Kouvaris, J. Qiu, W. Vogelsang, F. Yuan, Phys. Rev. D 74, 114013 (2006).

STARSTAR

http://arxiv.org/abs/0801.2990v1


• xF dependence is consistent with Sivers model

• Rising pT dependence is not explained

6/1/2009 27Chris Perkins

STAR, PRL 101 (2008) 222001

RHIC Runs 3,5,6 with FPDpT Dependence of Inclusive 0 AN

B.I. Abelev et al. (STAR) PRL 101 (2008) 222001

STARSTAR


xF and pT dependence of AN for p+p±+X, s=62 GeV

• AN(+) ~ -AN(-), consistent with results at lower s and u,d valence differences

• At fixed xF, evidence that AN grows with pT

I. Arsene, et al. PRL101 (2008) 042001


Transverse Spin Effects for Kaons

I. Arsene, et al. PRL101 (2008) 042001

p+pK±+X, s=62 GeV

• Large transverse single spin asymmetries are observed for kaons


PHENIX Muon Piston Calorimeter

SOUTH

• 192 PbWO4 crystals with APD readout

• Better than 80% of the acceptance is okay

2.22.2 18 cm3


PHENIX Goes ForwardFirst results with muon piston calorimeter from run 6

p+p+X, s = 62 GeV

Transverse SSA persists with similar characteristics over a broad range of collision energy (20 < s < 200 GeV)


p p M X M 200s GeV

STAR 2006 PRELIMINARY

Heavier mesons also accessible at high XF

Di-photons in FPD with E(pair)>40 GeV

No “center cut” (requirement that two-photon system point at middle of an FPD module)

With center cut and Z<0.85

Average Yellow Beam Polarization=56%

arXiv:0905.2840 (S. Heppelmann, PANIC 2008)


Towards Modern Times

• To separate Sivers and Collins effects need to move beyond inclusive production

• To isolate Sivers effect, need to either avoid fragmentation or integrate azimuthally• Full Jets, Di-Jets (away side), Direct photons, Drell-Yan

• To isolate Collins effect, need to look azimuthally within a jet.


Guzey, Strikman and Vogelsang Guzey, Strikman and Vogelsang Phys. Lett. B603 (2004) 173Phys. Lett. B603 (2004) 173

PYTHIA Simulation PYTHIA Simulation

• constrain x value of gluon probed by high-x quark by detection of second hadron serving as jet surrogate.

• span broad pseudorapidity range (-1<<+4) for second hadron span broad range of xgluon

• provide sensitivity to higher pT for forward reduce 23 (inelastic) parton process contributions thereby reducing uncorrelated background in correlation.

1Brookhaven National Laboratory2University of California- Berkeley3Pennsylvania State University4IHEP, Protvino5Stony Brook University6Texas A&M University7Utrecht, the Netherlands

8Zagreb University

STAR Forward Calorimeter ProjectsF.Bieser2, L.Bland1, E. Braidot7, R.Brown1, H.Crawford2, A.Derevshchikov4, J.Drachenberg6, J.Engelage2, L.Eun3, M.Evans3, D.Fein3, C.Gagliardi6, A. Gordon1, S.Hepplemann3, E.Judd2, V.Kravtsov4, J. Langdon5, Yu.Matulenko4, A.Meschanin4, C.Miller5, N. Mineav4, A. Mischke7, D.Morozov4, M.Ng2, L.Nogach4, S.Nurushev4, A.Ogawa1, H. Okada1, J. Palmatier3, T.Peitzmann7, S. Perez5, C.Perkins2, M.Planinic8, N.Poljak8, G.Rakness1,3, J. Tatarowicz3, A.Vasiliev4, N.Zachariou5

These people built the Forward Meson Spectrometer (FMS) and/or its components


STAR Forward Meson Spectrometer

PRL 101 (2008) 222001

• 50 larger acceptance than the run-3 forward pion detector (FPD).

• azimuth for 2.5<<4.0

• Discriminate single from up to ~60 GeV

Runs 3-6

FPD

Run8

FMSNorth half of FMS

before closing


Run-8 Results from STAR Forward Meson Spectrometer

(FMS)

Full azimuth spanned with nearly contiguous electromagnetic calorimetry from -1<<4

approaching full acceptance detector


Run 8 FMS Inclusive 0 Results

Octant subdivision of FMS for inclusive spin sorting. arXiv:0901.2828

Nikola Poljak – SPIN08

• Azimuthal dependence as expected• AN comparable to prior

measurements

x

y

P


Negative xF

arXiv:0901.2763 (J. Drachenberg– SPIN08)Akio Ogawa – CIPANP 09

Positive xF

RHIC Run 8 with East FPD/FMSpT Dependence

Indication of Positive AN persists up to pT ~5 GeVNeeds more transverse spin running

Negative xF consistent with zero


First Look at “Jet-like” Events in the FMSEvent selection:

• “Jet shape” in data matches simulation well• Reconstructed Mass doesn’t match as well• High-Tower Trigger used in Run 8 biases Jets

• >15 detectors with energy > 0.4GeV in the event (no single pions in the event)• cone radius = 0.5 (eta-phi space)• “Jet-like” pT > 1 GeV/c ; xF > 0.2• 2 perimeter fiducial volume cut (small/large cells)

“Jet-shape” distribution of energy within jet-like objects in the FMS as a function of distance from the jet axis.

arXiv:0901.2828 (Nikola Poljak – SPIN08)


•Comparison to dAu •Spin-1 meson AN

High xF Vector MesonsRHIC Run 8 with FMS

Background only MCRun8 FMS dataFit is gaussian + P3

μ=0.784±0.008 GeV σ=0.087±0.009 GeV Scale=1339±135 Events

3 photon events to look for0BR

•PT(triplet)>2.5 GeV/c •E(triplet)>30 GeV•PT(photon cluster)>1.5 GeV/c •PT(π0)>1 GeV/c

Significant (10) 0 signal seen in the data.

arXiv:0906.2332

A Gordon– Moriond09

Triple Photons : 0

Next :


STAR Detector• Large rapidity coverage for electromagnetic calorimetry (-

1<<+4) spanning full azimuth azimuthal correlations

• Run-8 was the first run for the Forward Meson Spectrometer (FMS)


Azimuthal Correlations with Large E. Braidot (for STAR), Quark Matter 2009

Unc

orre

cted

Coi

ncid

ence

P

roba

bilit

y (r

adia

n-1)

p+p+h±+X, s=200 GeV

requirements:

pT,>2.5 GeV/c

2.8<<3.8

h± requirements:

1.5<pT,h<pT,

h<0.9

• clear back-to-back peak observed, as expected for partonic 22 processes

• fixed and large trigger, with variable h map out Bjorken-x dependence

• of greatest interest for forward direct- trigger


Forward 0 – Forward 0 Azimuthal Correlations

• Possible back-to-back di-jet/di-hadron Sivers measurement• Possible near-side hadron correlation for Collins fragmentation function/Interference fragmentation function + Transversity • Low-x / gluon saturation study – accessing lowest xBj

gluon

Akio Ogawa- CIPANP 09


Proposals for the FutureSSA beyond inclusive meson production

• Forward jets

• Forward photons

• Forward virtual photons

(Just mentioned here… much more about future prospects on Friday)


Conclusions and Summary• Transverse spin asymmetries are present at RHIC

energies

• Transverse spin asymmetries are present at large

• Particle production cross sections and correlations are consistent with pQCD expectations at large where transverse spin effects are observed

• Essential to go beyond inclusive production to disentangle dynamical origins

3d parton structure, int1 overview of transverse single spin asymmetry measurements at rhic l.c....

Documents

structure slide

d parton structure

nuclear structure

production slide

jet quark rhic spin

int4 rhic spin goals

int3 rhic spin goals

transversity slide