Transverse Single Spin Asymmetries in p+p Collisons at RHIC L.C. Bland Brookhaven National Laboratory Transverse Partonic Structure Workshop Yerevan, 21 June 2009

Transverse Partonic Structure, Yerevan 2 Relativistic Heavy Ion Collider Outline Review 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

Transverse Partonic Structure, Yerevan 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 jet quark Proton has rich structure of quarks anti-quarks, gluons

Transverse Partonic Structure, Yerevan 4   A N measurements initially motivated by search for local polarimeter

Transverse Partonic Structure, Yerevan 5 Transverse Single-Spin Asymmetries (A N ) Probing for (1) orbital motion within transversely polarized protons; (2) Evidence of transversely polarized quarks in polarized protons.

Transverse Partonic Structure, Yerevan 6 STAR Large acceptance near midrapidity Windows to large rapidity

Transverse Partonic Structure, Yerevan 7 PHENIX Detector BBC ZDC EMCal    detection Electromagnetic Calorimeter (PbSc/PbGl): High p T photon trigger to collect  0 's,  ’s,  ’s Acceptance: |  |  x  High granularity (~10*10mrad 2 )     Drift Chamber (DC) for Charged Tracks Ring Imaging Cherenkov Detector (RICH) High p T charged pions (p T >4.7 GeV). Relative Luminosity Beam Beam Counter (BBC) Acceptance: 3.0<  3.9 Zero Degree Calorimeter (ZDC) Acceptance: ±2 mrad Local Polarimetry ZDC Shower Maximum Detector (SMD)

Transverse Partonic Structure, Yerevan 8 BRAHMS

Transverse Partonic Structure, Yerevan 9 Brahms Transvers beam pol Particle ID BRAHMS measured A N  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

Transverse Partonic Structure, Yerevan 10 Medieval Times First polarized p+p collisions at RHIC

Transverse Partonic Structure, Yerevan 11 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) J. Adams et al. (STAR), PRL 92 (2004) ; and PRL 97 (2006) Cross sections agree with NLO pQCD down to p T ~2 GeV/c over a wide range, 0 <  < 3.8, of pseudorapidity (  = -ln tan  /2) at  s = 200 GeV. STAR

Transverse Partonic Structure, Yerevan 12 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)

Transverse Partonic Structure, Yerevan 13 Measuring A N : Inclusive  0 Production PRL 92, ( 2004 ) PRL 97, (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, = 3.8 RHIC Runs 2-3 with Forward Pion Detector (FPD) STAR

Transverse Partonic Structure, Yerevan 14 STAR-Forward Cross Sections Similar to ISR analysis J. Singh, et al Nucl. Phys. B140 (1978) 189. Expect QCD scaling of form:  Require  s dependence (e.g., measure   cross sections at  s = 500 GeV) to disentangle p T and x T dependence

Transverse Partonic Structure, Yerevan 15 The Renaissance

Transverse Partonic Structure, Yerevan 16 Idea: directly measure k T by observing momentum imbalance of a pair of jets produced in p+p collision and attempt to measure if k T is correlated with incoming proton spin Boer & Vogelsang, PRD 69 (2004) jet A N  p beam  ( k T  S T ) p beam into page STAR Results vs. Di-Jet Pseudorapidity Sum Run-6 Result STAR PRL 99 (2007) Emphasizes (50%+ ) quark Sivers A N 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)

Transverse Partonic Structure, Yerevan 17 x F Dependence of Inclusive  0 A N RHIC Run 6 with FPD++ Fits to SIDIS (HERMES) is consistent with data A N at positive x F grows with increasing x F PRL 101, ( 2008 ) arXiv: v1 [hep-ex] U. D’Alesio, F. Murgia Phys. Rev. D 70, (2004) arXiv:hep-ph/ C. Kouvaris, J. Qiu, W. Vogelsang, F. Yuan, Phys. Rev. D 74, (2006). STAR

Transverse Partonic Structure, Yerevan 18 x F dependence is consistent with Sivers model Rising p T dependence is not explained 6/1/200918Chris Perkins STAR, PRL 101 (2008) RHIC Runs 3,5,6 with FPD p T Dependence of Inclusive  0 A N B.I. Abelev et al. (STAR) PRL 101 (2008) STAR

Transverse Partonic Structure, Yerevan 19 x F and p T dependence of A N for p  +p  ± +X,  s=62 GeV A N (  +) ~ -A N (  - ), consistent with results at lower  s and u,d valence differences At fixed x F, evidence that A N grows with p T I. Arsene, et al. PRL101 (2008)

Transverse Partonic Structure, Yerevan 20 Transverse Spin Effects for Kaons I. Arsene, et al. PRL101 (2008) p  +p  K ± +X,  s=62 GeV Large transverse single spin asymmetries are observed for kaons

Transverse Partonic Structure, Yerevan 21 PHENIX Muon Piston Calorimeter SOUTH 192 PbWO4 crystals with APD readout Better than 80% of the acceptance is okay 2.2  2.2  18 cm 3

Transverse Partonic Structure, Yerevan 22 PHENIX Goes Forward First 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)

Transverse Partonic Structure, Yerevan 23 STAR 2006 PRELIMINARY Heavier mesons also accessible at high X F 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: ( S. Heppelmann, PANIC 2008)

Transverse Partonic Structure, Yerevan 24 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.

Transverse Partonic Structure, Yerevan 25 Guzey, Strikman and Vogelsang Phys. Lett. B603 (2004) 173 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 x gluon provide sensitivity to higher p T for forward    reduce 2  3 (inelastic) parton process contributions thereby reducing uncorrelated background in  correlation.

Transverse Partonic Structure, Yerevan 26 1 Brookhaven National Laboratory 2 University of California- Berkeley 3 Pennsylvania State University 4 IHEP, Protvino 5 Stony Brook University 6 Texas A&M University 7 Utrecht, the Netherlands 8 Zagreb University STAR Forward Calorimeter Projects F.Bieser 2, L.Bland 1, E. Braidot 7, R.Brown 1, H.Crawford 2, A.Derevshchikov 4, J.Drachenberg 6, J.Engelage 2, L.Eun 3, M.Evans 3, D.Fein 3, C.Gagliardi 6, A. Gordon 1, S.Hepplemann 3, E.Judd 2, V.Kravtsov 4, J. Langdon 5, Yu.Matulenko 4, A.Meschanin 4, C.Miller 5, N. Mineav 4, D.Morozov 4, M.Ng 2, L.Nogach 4, S.Nurushev 4, A.Ogawa 1, H. Okada 1, J. Palmatier 3, T.Peitzmann 7, S. Perez 5, C.Perkins 2, M.Planinic 8, N.Poljak 8, G.Rakness 1,3, A.Vasiliev 4, N.Zachariou 5 These people built the Forward Meson Spectrometer (FMS) and/or its components

Transverse Partonic Structure, Yerevan 27 STAR Forward Meson Spectrometer PRL 101 (2008)  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 Run 8 FMS North half of FMS before closing

Transverse Partonic Structure, Yerevan 28 Run-8 Results from STAR Forward Meson Spectrometer (FMS) Full azimuth spanned with nearly contiguous electromagnetic calorimetry from -1<  <4  approaching full acceptance detector

Transverse Partonic Structure, Yerevan 29 Run 8 FMS Inclusive  0 Results Octant subdivision of FMS for inclusive   spin sorting. arXiv: Nikola Poljak – SPIN08 Azimuthal dependence as expected A N comparable to prior measurements x y P

Transverse Partonic Structure, Yerevan 30 Negative x F arXiv: (J. Drachenberg– SPIN08) Akio Ogawa – CIPANP 09 Positive x F RHIC Run 8 with East FPD/FMS p T Dependence Indication of Positive A N persists up to p T ~5 GeV Needs more transverse spin running Negative x F consistent with zero

Transverse Partonic Structure, Yerevan 31 First Look at “Jet-like” Events in the FMS Event 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” p T > 1 GeV/c ; x F > 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: (Nikola Poljak – SPIN08)

Transverse Partonic Structure, Yerevan 32 Comparison to dAu Spin-1 meson A N High x F Vector Mesons RHIC Run 8 with FMS Background only MC Run8 FMS data Fit is gaussian + P3 μ=0.784±0.008 GeV σ=0.087±0.009 GeV Scale=1339±135 Events 3 photon events to look for  0   BR  P T (triplet)>2.5 GeV/c E(triplet)>30 GeV P T (photon cluster)>1.5 GeV/c P T (π 0 )>1 GeV/c Significant (10  )  0  signal seen in the data. arXiv: A Gordon– Moriond09 Triple Photons :  0  Next :

Transverse Partonic Structure, Yerevan 33 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)

Transverse Partonic Structure, Yerevan 34 Azimuthal Correlations with Large  E. Braidot (for STAR), Quark Matter 2009 Uncorrected Coincidence Probability (radian -1 ) p+p   +h ± +X,  s=200 GeV   requirements: p T,  >2.5 GeV/c 2.8<   <3.8 h ± requirements: 1.5<p T,h <p T,   h  <0.9 clear back-to-back peak observed, as expected for partonic 2  2 processes fixed and large  trigger, with variable  h  map out Bjorken- x dependence of greatest interest for forward direct-  trigger

Transverse Partonic Structure, Yerevan 35 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 x Bj gluon Akio Ogawa- CIPANP 09

Transverse Partonic Structure, Yerevan 36 Proposals for the Future

Transverse Partonic Structure, Yerevan 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  +p  jet + X at  s = 200 GeV. Real jet physics at RHIC by combined action of FHC + FMS

Transverse Partonic Structure, Yerevan 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.

Transverse Partonic Structure, Yerevan 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

Transverse Partonic Structure, Yerevan 40 Future Opportunities Transverse spin for forward  +jet Test of predictive power of theory 10 4 useable forward photon + jet coincidences are expected in a 30 pb -1 data sample with 60% beam polarization

Transverse Partonic Structure, Yerevan 41 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.

Transverse Partonic Structure, Yerevan 42 Future Opportunities Transverse spin for forward  +jet Test of predictive power of theory (A. Bacchetta et al. PRL 99 (2007) ) Restricting the measurement of the forward photon to E  >35 GeV at =3.2 produces a signal:background ratio of 2.1.

Transverse Partonic Structure, Yerevan 43 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