OAM in p T dependent pp - Overview L.C. Bland Brookhaven National Lab INT Workshop on OAM in QCD 10 February 2012 STAR A N DY PHENIX

Outline Brief (and incomplete) Summary of Hadron Production Measurements in p  +p at RHIC Towards a Measurement of Drell Yan Production for p  +p at RHIC Summary

Where is the spin of the proton?

RHIC Polarized Collider BRAHMS & PP2PP STAR PHENIX AGS LINAC BOOSTER Pol. H - Source Spin Rotators (longitudinal polarization) Siberian Snakes 200 MeV Polarimeter RHIC pC Polarimeters Absolute Polarimeter (H  jet) AGS pC Polarimeter Strong AGS Snake Helical Partial Siberian Snake PHOBOS Spin Rotators (longitudinal polarization) Siberian Snakes 2006: 1 MHz collision rate; Polarization=0.6

…capable of colliding essentially all positive ions over a broad range of  s …with large L/  s, where L is free space at interaction region  large x F possible …with a broad and diverse physics program aimed at important questions oWhat is quark-gluon plasma?  heavy-ion collisions oHow does the proton get its spin?  polarized proton collisions oDoes the gluon density saturate in a heavy nucleus?  d+Au/p+Au collisions RHIC is a Unique Collider… Source:

arXiv: RHIC Spin (2006) Highlights New insights from RHIC after 30 years of polarized deep inelastic scattering Where is the spin of the proton? Gluon polarization is not large… If not from gluons, then is the spin from orbital motion? STAR

Kinematics large- p T physics in p+p collisions p beam -p beam large p T  or jet or  or … Largest p T reached by detecting produced particles at ~ 90  (midrapidity,  ~0)

Kinematics large- x F (with sufficient p T ) physics in p+p collisions p beam -p beam large p L  or jet or  or … Large p L (produced particle at large  ) is required to reach large Feynman- x, x F = p L / p beam = 2 p L /  s

gluon quark pion or jet quark RHIC Spin/Low-x Probes Polarized proton collisions / d+Au collisions 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

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-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 hep-ex/

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  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

Forward  0 – Forward  0 Azimuthal Correlations Jet-like patterns observed for two-particle correlations Significant pedestal persists even with increasing p T Azimuthal correlation pedestal complicates extraction of spin observables from particle correlations. Akio Ogawa- CIPANP 09 L.C.Bland – Exclusive Reactions, JLab 2010

x F Dependence of Inclusive  0 A N RHIC Runs 3,5,6 with FPD 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).

p T Dependence of Inclusive  0 A N Rising p T dependence is not explained STAR, PRL 101 (2008) RHIC Runs 3,5,6 with FPD B.I. Abelev et al. (STAR) PRL 101 (2008) STAR

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)

 s=20 GeV, p T = GeV/c   0 – E704, PLB261 (1991) 201.   +/- - E704, PLB264 (1991) 462. QCD theory expects very small (A N ~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). Similar A N (x F ) observed at lower  s

Expectations from Theory What would we see from this gedanken experiment? F  0 as m q  0 in vector gauge theories, so A N ~ m q / p T or, A N ~ for p T ~ 2 GeV/c Kane, Pumplin and Repko PRL 41 (1978) 1689

Two of the Explanations for Large Transverse SSA Require experimental separation of Collins and Sivers contributions Collins mechanism requires transverse quark polarization and spin- dependent fragmentation Sivers mechanism requires spin-correlated transverse momentum in the proton (orbital motion). SSA is present for jet or 

Issues Transverse single spin asymmetries for inclusive particle production in p  +p collisions cannot establish whether the k T from transverse-momentum dependence is in the initial state (distribution function or Sivers effect) or the final state (fragmentation function or Collins effect). There are many theoretical subtleties in calculating p  +p  +X and essentially all attempts to relate it to semi-inclusive deep inelastic transverse single spin asymmetry results  color-charge interactions. Experiment instrumentation focuses on mid-rapidity at RHIC. STAR,PHENIX have severe space constraints. The remainder of this talk will address these issues

FPD++ Physics for Run6 Run-5 FPD We staged a large version of the FPD as an engineering test of the STAR FMS and to measure jet-like events (see next page), The center annulus of the run-6 FPD++ is similar to arrays used to measure forward   SSA. The FPD++ annulus is surrounded by additional calorimetry to increase the acceptance for jet-like events

Strategy of Measurement Trigger event readout on energy sum in small cells of FPD++ Apply cone jet finder with radius R=[            to reconstruct jet-like object Reconstruct neutral pion in small cells Impose event requirements… weighted tower multiplicity ≥ 10 [w(small)=1, w(large =1.52)] ; “jet-like” p T ≥ 1.5 GeV/c, “jet-like” E ≥ 20 GeV ; 2-perimeter fiducial volume cut Reconstruct azimuthal angle of neutral pion relative to jet-like object Measure cross-ratio spin asymmetry as a function of cos(  ) Cross-ratio asymmetry definition For the bin near γ=  : stands for spin-up left-scattered jet and right fragmented pion stands for spin-down right scattered jet and left fragmented pion (related to by a rotation around the beam axis) arXiv:

“Jet-like” events selection and results ≥4 towers with E ≥ 0.4GeV, weighted sum of towers ≥ 10 (w(small)=1, w(large =1.52), “jet-like” pT ≥ 1.5 GeV/c, “jet-like” E ≥ 20 GeV, max. cone radius of 0.5 in the eta-phi space, 2 perimeter fiducial volume cut arXiv: Following calibration, mass is computed by attributing  E tower to a photon  “Jet-like” mass distributions are found to agree for different detector configurations. “Jet-like” objects are not jets, since the clustering is only from EM calorimeter “Jet-like” objects are found in PYTHIA to have on average 2.5 meson fragments/event arXiv:

Association analysis and event jettiness Simulations show good agreement with data. The neutral pion is well reconstructed and carries most of the energy of the event. "jet-like" events reconstructed from simulation are found to be associated with a hard-scattered or a radiated parton. The “jet-event” axis agrees well with the direction of the parton. arXiv: N.Poljak, PhD dissertation

Jet-like Collins angle – definition and results The jet-like Collins angle distributions show agreement in data/simulations. The magnitude of k T is in the domain of TMD fragmentation. Well reconstructed as confirmed by association analysis arXiv: arXiv:

Results - asymmetry The pion asymmetry for the events was calculated in bins in the cosine of the jet-like angle,  The negative x F asymmetry is consistent with zero The x F >0 asymmetry is greater than zero in all bins (av ±0.014), but doesn’t show a dependence on cos(γ) The “jet-like” events x F >0 asymmetry is positive, but doesn’t show any Collins effect contributions. arXiv:

The A N DY Project A new effort at RHIC to make the first measurement of the analyzing power (A N ) for Drell Yan (DY) production at  s=500 GeV

E.C.Aschenauer, A. Bazilevsky, L.C. Bland, K. Drees, K.O. Eyser, C. Folz, Y. Makdisi, A. Ogawa, P. Pile, T.G. Throwe Brookhaven National Laboratory H.J. Crawford, J.M. Engelage, E.G. Judd University of. California, Berkeley/Space Sciences Laboratory C.W. Perkins University of. California, Berkeley/Space Sciences Laboratory /Stony Brook University A. Derevshchikov, N. Minaev, D. Morozov, L.V. Nogach Institute for High Energy Physics, Protvino G. Igo University of California, Los Angeles M.X. Liu Los Alamos National Laboratory H. Avakian Thomas Jefferson National Accelerator Facility E.J.Brash Christopher Newport University and TJNAF C.F.Perdrisat College of William and Mary V. Punjabi Norfolk State University Li, Xuan Shandong University, China Mirko Planinic, Goran Simatovic University of Zagreb, Croatia A. Vossen Indiana University G. Schnell University of the Basque Country and IKERBASQUE,Spain A. Shahinyan, S. Abrahamyan Yerevan Physics Institute K. Gnovo, N. K. Liyanage University of Virginia E. Cisbani INFN Roma, Italy A N DY “Large Rapidity Drell Yan Production at RHIC” Letter of Intent submitted 24 May 2010: ford_LoI v1.pdf PAC presentation: enauer_DY-collider_june10.pdfe10.pdf Proposal to 2011 PAC: pro_110516_final.2.pdf Construction Proposal Nearing Completion JLab-SBS GEM experts

Simple QED example: DIS: attractive Drell-Yan: repulsive Same in QCD: As a result: Attractive vs Repulsive Sivers Effects Unique Prediction of Gauge Theory ! Transverse Spin Drell-Yan Physics at RHIC (2007)

Goal of A N DY Project Measure the analyzing power for forward Drell-Yan production to test the predicted change in sign from semi-inclusive deep inelastic scattering to DY associated with the Sivers function Projected precision for proposed A N DY apparatus GEANT model of proposed A N DY apparatus (run-13)

Why A N DY? Largest spin effects are found at RHIC when Feynman-x > 0.1 Predicted change of sign for Sivers function between transverse single spin measurements for semi-inclusive deep inelastic scattering and the analyzing power for Drell Yan is likely best done in this range, but limited to x F < 0.3 to match HERMES/COMPASS (SIDIS) kinematics as closely as possible Forward upgrades of STAR and PHENIX are major undertakings and would benefit from a feasibility demonstration of forward DY production (i.e., A N DY). Forward DY production is of interest for more than just the analyzing power, e.g. most robust observable to low-x parton distributions for intercomparison to a future electron-ion collider. A N DY can run in parallel with RHIC W program.

Previous Work on Low-Mass DY at a Collider p+p DY at ISR,  s=53,63 GeV Phys. Lett. B91 (1980) 475 Comments (note: large x F at collider breaks new ground)… e+e- low-mass DY done at ISR and by UA2 [see review J.Phys. G19 (1993) D1] UA2 [PLB275 (1992) 202] did not use magnet / CCOR did [PLB79 (1979) 398] most fixed target experiments do  +  - DY

Comments… RHIC pp luminosity largest at  s=500 GeV partonic luminosities increase with  s net result is that DY grows with  s in any case, largest  s probes lowest x  Consider large-x F DY at  s=500 GeV Collision Energy Dependence of Drell Yan Production Transverse Spin Drell-Yan Physics at RHIC (2007)  Forward DY production probes valence region for “beam” and x 2    for “target” for  s=500 GeV (M>4 GeV/c 2 )

Pair mass from bare EMcal arXiv: arXiv: pair mass backgrounds well modeled J/  e+e- observation at ~0.67 emboldens DY consideration p+p  J/  +X  e + e ¯ +X,  s=200 GeV ~0.67

Backgrounds h ± /e ± discrimination – requires estimates of p+p collisions and EMcal response charged/neutral discrimination photon conversion background – requires estimates of p+p collisions and materials hep-ex/ PYTHIA 5.7 compared well to  s=200 GeV data [PRL 97 (2006) ] Little change until “underlying event” tunings for LHC created forward havoc  Stick to PYTHIA for estimates

Strategy for estimates ~10 12 p+p interactions in 50 / pb at  s=500 GeV  full PYTHIA/GEANT not practical Parameterize GEANT response of EMcal and use parameterized response in fast simulator applied to full PYTHIA events Estimate rejection factors from GEANT for hadron calorimeter and preshower detector (both critical to h ± /e ± discrimination) Explicit treatment in fast simulator to estimate pathlengths through key elements (beam pipe and preshower), to simulate photon conversion to e+e- pair Estimate effects from cluster merging in EMcal (d <  d cell / use  =1 for estimates) Estimate/simulate EMcal cluster energy and position resolutions.  E =15%/  E and  x(y) =0.1d cell, used to date for    rejection. GEANT simulation of EMcal response to E>15 GeV  ± from PYTHIA incident on (3.8cm) 2 x45cm lead glass calorimeter. GEANT response not so different from 57-GeV pion test beam data from CDF [hep-ex/ ]

Background Estimate Comments: Conversion photons significantly reduced by    veto Preshower thickness tuned, although perhaps is not so critical given photon veto Linearly decreasing dN/df (fast-simulation model for hadronic response of ECal) estimates smaller hadronic background  increased sophistication needed for reliable estimates, although other model uncertainties could easily dominate. Open heavy flavor backgrounds also estimated and found small due to large rapidity

Dileptons from open beauty at large x F Comments… open beauty dileptons are a background 2x larger than DY for PHENIX  direct production of open beauty results in ~15% background at large xF large forward acceptance for the future would require discrimination (isolation)

What did we learn from run-11 A N DY? Left/right symmetric HCal Left/right symmetric ECal Left/right symmetric preshower Trigger/DAQ electronics Blue-facing BBC Beryllium vacuum pipe

Schematic of detector for Run-11 Polarized proton collisions at  s=500 GeV from February to April 2011 Beam-beam counter (BBC) for minimum-bias trigger and luminosity measurement from PHOBOS [NIM A474 (2001) 38] Zero-degree calorimeter and shower maximum detector for luminosity measurement and local polarimetry (ZDC/ZDC-SMD, not shown) Hadron calorimeter modules (HCal) are 9x12 modules from AGS-E864 (NIM406,227) Small (~120 cells) ECal loaned from BigCal at JLab Pre-shower detector

Jet Trigger Jet trigger sums HCal response excluding outer two perimeters (rather than just two columns closest to beam) Definition is consistent with objective of having jet thrust axis centered in hadron calorimeter modules HCal energy scale is now determined >750M jet-triggered events acquired during RHIC run 11 Hadron calorimeter is quiet ~107ns before jet event Hadron calorimeter is quiet again ~107ns after jet event

Select from jet-trigger events for HCal “high-tower” to be centered in module Display for each detector of each module the ADC count as color scale (black=greatest count  yellow=lowest count) Events look “jetty”, as expected Cosmic ray trigger is essentially the same as jet trigger, except that the threshold on the summed calorimeter response is set at 5 pC (20 counts) This is a trigger that will work without beam. We have other cosmic-ray triggers that will work with beam, when commissioned, for continuous monitoring. The tracks test noise, patterns, etc. HCal Events

Calibration of Hadron Calorimeter Based on    reconstruction require: (1) 1-tower clusters; (2) E>1.8 GeV; (3) |x|>50 cm to avoid ECal shadow; (4) >1 clusters to form pairs; (5) E pair >5 GeV; (6) M pair <0.5 GeV; and (7) z pair <0.5. Apply to 20M minimum-bias events from run-11 data Apply to 20M PYTHIA events subjected to BBC charge sum trigger emulation (no vertex cut) Data and simulations are both absolutely normalized, so PYTHIA is expected to provide a good basis for QCD backgrounds to DY. Hadronic corrections expected to be small. Mass reconstructions to demonstrate this are underway.

Towards Forward Jets Good agreement between data and PYTHIA/GEANT simulation for summed HCal response excluding outer two perimeters of cells  QCD backgrounds can be modeled Good agreement between data and simulation for jet shape Next up: forward jet analyzing power

Forward Jet Energy Scale Jet energy scale determined by association analysis of simulation Required to add ECal energy deposition to masked summed HCal response Small rescaling (<10%) of HCal energy scale is applied, likely to account for hadronic corrections

Dileptons from Run 11 Data A N DY profiling methods were applied to a limited data sample (L int =0.5 / pb) of run-11 ECal triggered data. Dominant backgrounds are now from , and are suppressed by using MIP response of beam-beam counters to tag clusters. Individual detector    calibration for HCal was an essential step to reconstruct J/  Limited granularity of BBC and poor position resolution of HCal-EM cluster results in less photon suppression than expected for final A N DY apparatus (project ~100x better suppression) Hadron suppression is not yet required, but will be in going from dileptons to DY J/  e+e- peak has ~120 events with 5.4  statistical significance. PYTHIA with NRQCD expects 420 events in the run-11 acceptance, approximately consistent with observation after crude efficiency correction. From PYTHIA 6.425, DY with M>4 GeV/c 2 is 170x smaller in this acceptance. J/  is a window to heavy flavor via B  J/  K and  b  J/  p  that would help quantify intrinsic b from proton backgrounds to DY

Dileptons from Run 11 Data versus Simulation Compare run-11 mass distribution to model used to make background estimates for DY Large-mass background found to be well-represented by fast-simulator model in both magnitude and shape

A N DY Staging Assumptions: 1) ~4 week polarized proton test run at  s=500 GeV in RHIC run 11 2) 12 week polarized proton W production run at  s=500 GeV in RHIC run 13 3) 12 week polarized proton W production run at  s=500 GeV in RHIC run 14 Planned Staging: 1)Hcal + newly constructed BBC at IP2 for RHIC run 11 with goals of establishing impact of 3IR operation and demonstrate calibration of Hcal to get first data constraints on charged hadron backgrounds 2)Hcal + EMcal + neutral/charged veto + BBC for RHIC run 13 with goals of zero-field data sample with L int ~ 100 / pb and P beam =50% to observe dileptons from J/ ,  and intervening continuum. Split-dipole tests envisioned. 3)Hcal + EMcal + neutral/charged veto + BBC + split-dipole for RHIC run 14 with goals data sample with L int ~ 100 / pb and P beam =50% to observe dileptons from J/ ,  and intervening continuum to address whether charge sign discrimination is required

Summary and Conclusions Pion production cross sections and azimuthal corrlations agree with hard scattering, unlike at lower  s Analyzing powers for pion production persist for large x F at RHIC energies First attempt at Collins/Sivers separation for forward neutral pions is consistent with no contribution from the Collins effect Polarized Drell Yan production at large rapidity looks feasible for RHIC