Transverse Single Spin Asymmetries in p+p Collisons at RHIC L.C. Bland Brookhaven National Laboratory Transverse Partonic Structure Workshop Yerevan, 21

Transverse Single Spin Asymmetries in p+p Collisons at RHIC

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

L.C. BlandBrookhaven National LaboratoryTransverse Partonic Structure WorkshopYerevan, 21 June 2009

Transverse Partonic Structure, Yerevan

2

Relativistic Heavy Ion Collider

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


3

Motivations• How does a composite object (e.g, the proton) get its spin from its constituents?

• Can the transverse spin effects observed in semi-inclusive deep inelastic scattering be related to transverse spin effects observed in p+p collisions? Or, more broadly, what is the underlying dynamics in kinematics where transverse spin effects are observed?

gluon

quark pion or jetquark

Proton has rich structure of quarksanti-quarks, gluons


4 AN measurements initially motivated by search for local polarimeter


5

Transverse Single-Spin Asymmetries (AN)

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

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


6

STAR

• Large acceptance near midrapidity

• Windows to large rapidity


7

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)


8

BRAHMS


9

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


10

Medieval TimesFirst polarized p+p collisions at RHIC


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Does pQCD describe particle production at RHIC?Compare cross sections measured for p+p +X at s=200 GeV

to next-to-leading order pQCD calculations

S.S. Adler et al. (PHENIX), PRL 91 (2003) 241803

J. Adams et al. (STAR), PRL 92 (2004) 171801; and PRL 97 (2006) 152302

Cross sections agree with NLO pQCD down to pT~2 GeV/c over a wide

range, 0 < < 3.8, of pseudorapidity ( = -ln tan /2) at s = 200 GeV.

STARSTAR


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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


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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


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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


15

The Renaissance


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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


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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




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• xF dependence is consistent with Sivers model

• Rising pT dependence is not explained

6/1/2009 18Chris 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


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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


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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


21

PHENIX Muon Piston Calorimeter

SOUTH

• 192 PbWO4 crystals with APD readout

• Better than 80% of the acceptance is okay

2.22.2 18 cm3


22

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)


23

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)


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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.


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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.


26

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, 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, A.Vasiliev4, N.Zachariou5

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


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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


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Run-8 Results from STAR Forward Meson Spectrometer

(FMS)

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

approaching full acceptance detector


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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


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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


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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)


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•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 :


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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)


34

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


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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


36

Proposals for the Future


37

Forward Jets

Jet energy profile from Forward Hadron Calorimeter (FHC)+Forward Meson Spectrometer (FMS) combination, with trigger on calibrated sum of hadronic and electromagnetic energy

Estimated statistical precision for uncertainty in analyzing power for p+pjet + X at s = 200 GeV.

Real jet physics at RHIC by combined action of FHC + FMS


38

What is the FHC?• Two identical 9x12 enclosures of E864 hadron calorimeter detectors (T.A. Armstrong et al., Nucl. Instr. and Meth. A 406 (1998) 227 )

• Refurbished and used by PHOBOS collaboration as forward hadron multiplicity detectors for run-3 d+Au

• A third 5x10 enclosure of E864 detectors, that can fill in the remaining ~21 empty slots in the existing enclosures.


39

Where is the FHC proposed to be staged?

At a minimal z from the FMS, positioned symmetrically left (South) and right (North) of west DX

magnet


40

Future OpportunitiesTransverse spin for forward +jetTest of predictive power of theory

104 useable forward photon + jet coincidences are expected in a 30 pb-1 data sample with 60% beam polarization


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Large FMS acceptance allows rejection of 0 background

Search for photons in yellow band and reject events with nearby photon to reduce background from 0 and decays. Large acceptance of FMS makes this possible.

Large acceptance also allows calorimeter isolation criterion to help reduce background from photons that result from fragmentation.

For E>25, 95% of second photon from 0 decays occur within radius of ~4 large cells (~23 cm).

Example 0 rejection region.


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Future OpportunitiesTransverse spin for forward +jet

Test of predictive power of theory (A. Bacchetta et al. PRL 99 (2007) 212002)

Restricting the measurement of the forward photon to E>35 GeV at <>=3.2 produces a signal:background ratio of 2.1.


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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

Documents

Transverse Single Spin Asymmetries in p+p Collisons at RHIC L.C. Bland Brookhaven National Laboratory Transverse Partonic Structure Workshop Yerevan, 21