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OAM in p T dependent pp - Overview

A N DY. OAM in p T dependent pp - Overview. PHENIX. STAR. L.C. Bland Brookhaven National Lab INT Workshop on OAM in QCD 10 February 2012. Outline. Brief (and incomplete) Summary of Hadron Production Measurements in p  +p at RHIC

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OAM in p T dependent pp - Overview

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  1. ANDY OAM in pT dependent pp - Overview PHENIX STAR L.C. Bland Brookhaven National Lab INT Workshop on OAM in QCD 10 February 2012

  2. 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

  3. Where is the spin of the proton?

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

  5. RHIC is a Unique Collider… Source: http://www.agsrhichome.bnl.gov/RHIC/Runs/ • …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 xF possible • …with a broad and diverse physics program aimed at important questions • What is quark-gluon plasma?  heavy-ion collisions • How does the proton get its spin?  polarized proton collisions • Does the gluon density saturate in a heavy nucleus?  d+Au/p+Au collisions

  6. arXiv:0901.2828 STAR RHIC Spin (2006) HighlightsNew insights from RHIC after 30 years of polarized deep inelastic scatteringWhere is the spin of the proton? If not from gluons, then is the spin from orbital motion? Gluon polarization is not large…

  7. pbeam -pbeam large pT por jet or g or … Largest pT reached by detecting produced particles at  ~ 90 (midrapidity, h~0) Kinematicslarge-pT physics in p+p collisions

  8. pbeam -pbeam large pL por jet or g or … Large pL (produced particle at large h) is required to reach large Feynman-x, xF = pL/ pbeam= 2 pL/ s Kinematicslarge-xF (with sufficient pT) physics in p+p collisions

  9. Does pQCD describe particle production at RHIC?Compare cross sections measured for p+pp0 +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 < h< 3.8, of pseudorapidity (h = -ln tan /2) at s = 200 GeV.

  10. STAR-Forward Cross Sections Similar to ISR analysis J. Singh, et al Nucl. Phys. B140 (1978) 189. hep-ex/0505024 Expect QCD scaling of form:  Require s dependence (e.g., measure p0 cross sections at s = 500 GeV) to disentangle pT and xT dependence

  11. STAR Detector • Large rapidity coverage for electromagnetic calorimetry (-1<h<+4) spanning full azimuth  azimuthal correlations • Run-8 was the first run for the Forward Meson Spectrometer (FMS)

  12. Uncorrected Coincidence Probability (radian-1) Azimuthal Correlations with Dh~3E. Braidot (for STAR), Quark Matter 2009 p+pp0+h±+X, s=200 GeV • p0 requirements: • pT,p>2.5 GeV/c • 2.8<hp<3.8 • h± requirements: • 1.5<pT,h<pT,p • |hh|<0.9 • clear back-to-back peak observed, as expected for partonic 22 processes • fixed and large h trigger, with variable hh  map out Bjorken-x dependence

  13. Forward p0 – Forward p0 Azimuthal Correlations Akio Ogawa- CIPANP 09 L.C.Bland – Exclusive Reactions, JLab 2010 • Jet-like patterns observed for two-particle correlations • Significant pedestal persists even with increasing pT • Azimuthal correlation pedestal complicates extraction of spin observables from particle correlations.

  14. xF Dependence of Inclusive p0 AN RHIC Runs 3,5,6 with FPD PRL 101, 222001 (2008) arXiv:0801.2990v1 [hep-ex] C. Kouvaris, J. Qiu, W. Vogelsang, F. Yuan, Phys. Rev. D 74, 114013 (2006). U. D’Alesio, F. Murgia Phys. Rev. D 70, 074009 (2004) arXiv:hep-ph/0712.4240

  15. pT Dependence of Inclusive p0 AN STAR Rising pT dependence is not explained RHIC Runs 3,5,6 with FPD B.I. Abelev et al. (STAR) PRL 101 (2008) 222001 STAR, PRL 101 (2008) 222001

  16. xF and pT dependence of AN for p+pp±+X, s=62 GeV I. Arsene, et al. PRL101 (2008) 042001 • AN(p+) ~ -AN(p-), consistent with results at lower s and u,d valence differences • At fixed xF, evidence that AN grows with pT

  17. A Brief History… s=20 GeV, pT=0.5-2.0 GeV/c • QCD theory expects very small (AN~10-3) transverse SSA for particles produced by hard scattering. • 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 AN(xF) observed at lower s • 0 – E704, PLB261 (1991) 201. • +/- - E704, PLB264 (1991) 462.

  18. Expectations from Theory What would we see from this gedanken experiment? F0 as mq0 in vector gauge theories, so AN ~ mq/pT or,AN ~ 0.001 for pT ~ 2 GeV/c Kane, Pumplin and Repko PRL 41 (1978) 1689

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

  20. Issues • Transverse single spin asymmetries for inclusive particle production in p+p collisions cannot establish whether the kT 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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

  21. Run-5 FPD FPD++ Physics for Run6 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 p0 SSA. The FPD++ annulus is surrounded by additional calorimetry to increase the acceptance for jet-like events

  22. Strategy of Measurement arXiv:1109.0360 • Trigger event readout on energy sum in small cells of FPD++ • Apply cone jet finder with radius R=[(0-)2+(f0-f)2]1/2=0.5 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” pT≥ 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(g) 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 1800 rotation around the beam axis)

  23. “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 • Following calibration, mass is computed by attributing DEtower 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:1012.0221 arXiv:1109.0360

  24. 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. N.Poljak, PhD dissertation arXiv:1109.0360 "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.

  25. Jet-like Collins angle – definition and results The jet-like Collins angle distributions show agreement in data/simulations. The magnitude of kT is in the domain of TMD fragmentation. =γ • Well reconstructed as confirmed by association analysis arXiv:1109.0360 arXiv:1012.0221

  26. Results - asymmetry • The pion asymmetry for the events was calculated in bins in the cosine of the jet-like angle, g • The negative xF asymmetry is consistent with zero • The xF>0 asymmetry is greater than zero in all bins (av. 0.031±0.014), but doesn’t show a dependence on cos(γ) arXiv:1012.0221 The “jet-like” events xF>0 asymmetry is positive, but doesn’t show any Collins effect contributions.

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

  28. ANDY JLab-SBS GEM experts 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 “Large Rapidity Drell Yan Production at RHIC” Letter of Intent submitted 24 May 2010: http://www.bnl.gov/npp/docs/pac0610/Crawford_LoI.100524.v1.pdf PAC presentation:http://www.bnl.gov/npp/docs/pac0610/aschenauer_DY-collider_june10.pdf Proposal to 2011 PAC: http://www.bnl.gov/npp/docs/pac0611/DY_pro_110516_final.2.pdf Construction Proposal Nearing Completion

  29. Attractive vs Repulsive Sivers Effects Unique Prediction of Gauge Theory ! Simple QED example: Drell-Yan: repulsive DIS: attractive Same inQCD: As a result: Transverse Spin Drell-Yan Physics at RHIC (2007) http://spin.riken.bnl.gov/rsc/write-up/dy_final.pdf

  30. Goal of ANDY Project GEANT model of proposed ANDY apparatus (run-13) Projected precision for proposed ANDY apparatus 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

  31. Why ANDY? • 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 xF < 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., ANDY). 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. ANDY can run in parallel with RHIC W program.

  32. 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 xF 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 m+m- DY

  33. Collision Energy Dependence of Drell Yan Production • 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-xF DY at s=500 GeV  Forward DY production probes valence region for “beam” and x210-4for “target” for s=500 GeV (M>4 GeV/c2) Transverse Spin Drell-Yan Physics at RHIC (2007) http://spin.riken.bnl.gov/rsc/write-up/dy_final.pdf

  34. Pair mass from bare EMcal p+p  J/+X e+e¯+X, s=200 GeV <xF>~0.67 arXiv:0906.2332 arXiv:0907.4396 • pair mass backgrounds well modeled • J/ye+e- observation at <xF>~0.67 emboldens DY consideration

  35. 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 • PYTHIA 5.7 compared well to s=200 GeV data [PRL 97 (2006) 152302] • Little change until “underlying event” tunings for LHC created forward havoc •  Stick to PYTHIA 6.222 for estimates hep-ex/0403012

  36. Strategy for estimates • ~1012 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 < edcell / use e=1 for estimates) • Estimate/simulate EMcal cluster energy and position resolutions. sE=15%/E and sx(y)=0.1dcell, used to date for p0gg rejection. GEANT simulation of EMcal response to E>15 GeV p± from PYTHIA 6.222 incident on (3.8cm)2x45cm lead glass calorimeter. GEANT response not so different from 57-GeV pion test beam data from CDF [hep-ex/0608081]

  37. Background Estimate • Comments: • Conversion photons significantly reduced by p0gg 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

  38. Dileptons from open beauty at large xF • Comments… • open beauty dileptons are a background 2x larger than DY for PHENIX m+m- • direct production of open beauty results in ~15% background at large xF • large forward acceptance for the future would require discrimination (isolation)

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

  40. Schematic of detector for Run-11Polarized 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 41

  41. Jet Trigger Hadron calorimeter is quiet ~107ns before jet event • 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 again ~107ns after jet event

  42. HCal Events • 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. • 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

  43. Calibration of Hadron CalorimeterBased on p0gg 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) Epair>5 GeV; (6) Mpair<0.5 GeV; and (7) zpair<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.

  44. 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

  45. 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

  46. Dileptons from Run 11 Data • ANDY profiling methods were applied to a limited data sample (Lint=0.5 / pb) of run-11 ECal triggered data. • Dominant backgrounds are now from g, and are suppressed by using MIP response of beam-beam counters to tag clusters. • Individual detector p0ggcalibration 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 ANDY 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 5.4s statistical significance. PYTHIA 6.425 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/c2 is 170x smaller in this acceptance. • J/ is a window to heavy flavor via BJ/ K and LbJ/ p p- that would help quantify intrinsic b from proton backgrounds to DY

  47. 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

  48. ANDY 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: • 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 • Hcal + EMcal + neutral/charged veto + BBC for RHIC run 13 with goals of zero-field data sample with Lint ~ 100 / pb and Pbeam=50% to observe dileptons from J/y, U and intervening continuum. Split-dipole tests envisioned. • Hcal + EMcal + neutral/charged veto + BBC + split-dipole for RHIC run 14 with goals data sample with Lint ~ 100 / pb and Pbeam=50% to observe dileptons from J/y, U and intervening continuum to address whether charge sign discrimination is required

  49. 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 xF 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

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