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RHIC SPIN: Experimental Issues

RHIC SPIN: Experimental Issues. Matthias Grosse Perdekamp, UIUC and RBRC. Physics Goals PDFs from hadron collisions? A new experimental technique: Polarized proton-proton collisions at high energies! First Results from RHIC Upgrades Summary. Nucleon Structure.

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RHIC SPIN: Experimental Issues

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  1. RHIC SPIN: Experimental Issues Matthias Grosse Perdekamp, UIUC and RBRC • Physics Goals • PDFs from hadron collisions? • A new experimental technique: Polarized • proton-proton collisions at high energies! • First Results from RHIC • Upgrades • Summary

  2. Nucleon Structure Quark and Gluon (parton) Distribution Functions (well known) (moderately well known) (unknown) (moderately well known) What is the origin of the Proton Spin? (unknown)

  3. Proton Spin Structure at Hard Scales Physics Channels Inclusive jets, hadrons, heavy flavor, direct photons, in STAR and PHENIX Single lepton asymmetries AL(e,μ) in W-production in STAR and PHENIX AN in STAR, PHENIX and BRAHMS back to back correlations, AT in Collins- and interference fragmentation and ATT in Drell Yan in STAR and PHENIX. What is unique at RHIC? o Robust extraction of spin dep. pdfs from pQCD analysis o Broad x-range: 0.001<x<0.3 o Multiple channels: good control of of sys. and theor. uncertainties  determine G(x) and ∫∆G(x)dx ! o direct and theoretically clean flavor separation of spin dependent pdfs o sufficient statistical resolution  sea quark spin vs gluon spin o high precision measurements of multiple single and double spin asymmetries at hard scales aim at a separation of Sivers and Transversity contributions Gluon polarization Flavor separation of quark polarizations Transverse spin struc- ture of the Nucleon

  4. Can Gluon Distributions be Extractedfrom Hadron Collisions? • Let’s take a look at G(x,Q2) • NLO pQCD vs RHIC data

  5. Global QCD Analysis for G(x,Q2)and q(x,Q2): J. Pumplin et.al JEHP 0207:012 (2002) CTEQ6: use DGLAP Q2-evolution of quark and gluon distributions to extract q(x,Q2) and G(x,Q2) from global fit to data sets at different scales Q2. 2.0 error on G(x,Q2) +/- 10% Quark and Gluon Distributions 1.0 Ratio to CTEQ6 H1 + Zeus F2 CTEQ6M up-quarks CDF + D0 Jets gluon 0.5 CTEQ5M1 10-410-3 10-2 10-1 0.5 x 2.0 2.0 error for d(x,Q2) error for u(x,Q2) down 1.0 1.0 Ratio to CTEQ6 anti-down Ratio to CTEQ6 +/- 5% +/- 5% 10-410-3 10-2 10-1 0.5 x 0.5 0.5

  6. G(x,Q2) and q(x,Q2) + pQCD beautifully agree with HERA + Tevatron! J. Pumplin et.al JEHP 0207:012 (2002) ZEUS F2 D0 Jet Cross Section

  7. and RHIC ? q(x,Q2), G(x,Q2) and D(z,Q2) + pQCD nicely consistent with experiment! PHENIX π0 cross section a |η|<0.35 Phys.Rev.Lett.91:241803,2003 STAR π0 cross section a 3.4<η<4.0 Phys.Rev.Lett.92:171801,2004 gluon fragmentation !? o Good agreement between NLO pQCD calculations and experiment  can use a NLO pQCD analysis to extract spin dependent quark and gluon distributions from RHIC data!

  8. Direct Photons: NLO pQCD vs RHIC data • NLO-pQCD calculation • Private communication with W.Vogelsang • CTEQ6M PDF. • direct photon + fragmentation photon • Set Renormalization scale and factorization scale pT/2,pT,2pT The theory calculation shows good agreement with our result. Kensuke Okada’s SPIN 2004 talk

  9. 30 years of spin dependent DIS Field started with polarized electron sources and targets Yale/SLAC mid 70s SLAC, CERN, DESY • J. Ashman et al., Phys.Lett.B206:364,1988 • “Proton Spin Crisis” > 1200 citations on SPIRES Current Experiments on Nucleon Structure (as reported at DIS 2004) Helicity difference distribution quarks ∆q(x) : moderately well known gluons ∆G(x) : unknown Helicity flip (transversity) distribution quarks δq(x) : unknown

  10. A New Experimental Tool for Proton Spin StructureHigh Energy Polarized Proton Beams and Collisions RHIC pC Polarimeters Absolute Polarimeter (H jet) Siberian Snakes BRAHMS & PP2PP PHOBOS Spin 2004: M. Bai, H. Huang, V. Ptitsyn, T. Roser A. Bravar, P. Cameron, D. Sviridia, A. Zelenski, T. Wise, W. McKay Siberian Snakes Spin Flipper PHENIX STAR Run 04 achieved: Spin Rotators Partial Snake Helical Partial Snake Strong Snake Polarized Source Pb~45% , 55 bunches New working point with long beam and polarization lifetimes LINAC AGS BOOSTER Run 05 planned: 200 MeV Polarimeter Time to tune accelerator complex Measure:ALL(jets), ALL(π0) Commission strong supercon-ducting AGS snake Rf Dipole AGS Internal Polarimeter AGS pC Polarimeter

  11. An Example: High Energy Proton Polarimeters for p=20-250 GeV/c High Energy Polarimeter Requirement for RHIC Spin • Absolute RHIC polarimeter • Fast relative RHIC and AGS polarimeters for monitoring and tuning • Local Polarimeters to confirm spin orientation at collision point RHIC polarimetery relies on newly observed spin asymmetries: o Sizeable elastic proton-Carbon spin asymmetries at high energies  J. Tojo et al. Phys. Rev. Lett. 89:052302, 2002 o Very forward neutron asymmetries  A. Bazilevsky et al. AIP Conf. Proc. 675: 584-588, 2003 o Spin asymmetries in forward multiplicity production as seen by beam-beam counters in STAR  J. Kiryluk, AIP Conf. Proc. 675, 424 (2003)

  12. Run 04: The Polarized Jet Target for RHIC Courtesy Sandro Bravar, STAR and Yousef Makdisi, CAD • Polarized Hydrogen Gas Jet Target • thickness of > 1012p/cm2 • polarization > 93% (+1 −2)%! • no depolarization from beam wake fields • Silicon recoil spectrometer to measure • The left-right asymmetry AN in pp elastic scattering in the CNI region to AN < 10-3 accuracy. • Transfer this to the beam polarization • Calibrate the p-Carbon polarimeters • For 2004 we expect to measure PB to 10%

  13. Recoil protons elastic pp pp scattering Jet profile FWHM ~ 6 mm As designed Number of elastic pp events TDC: 1 ct = 1.2 ns ADC: 1 ct = 40 keV Hor. pos. of Jet 10000 cts. = 2.5 mm CNI peak AN 1 < E REC < 2 MeV  source calibration prompt events and beam gas • Data collected in this run: • 100 GeV ~ 700,000 events at the peak of the analyzing power (~ 3 x 106 total useful pp elastic events) • 24 GeV ~ 120,000 events at the peak of the analyzing power (~ 5 x 105 total useful pp elastic events)

  14. Local Polarimetry in PHENIX: Transverse Neutron Asymmetry in ZDC Rotators on--> radial polarization Rotators on --> vertical polarization Yellow Blue

  15. First Results: AN Run 02, ∫Ldt ~ 0.2pb-1, P~0.15 STAR AN(π0) at 3.4<η<4.0 Phys.Rev.Lett.92:171801,2004 PHENIX AN(π0) and AN(π0)at |η|<0.35 C. Aidala, DIS 2004, to be published o Experiments are ready for spin measurements at low luminosity  relative luminosity ~ 5x10-4  trigger  polarization analysis  data analysis o First spin results from RHIC  AN sizeable in forward XF  AN compatible with 0 at η~0 (as expected from pQCD)

  16. First Results: ALL Run 3 and 4 combined B.Jager et al., PRD67, 054005 (2003) ∆G(x)=G(x) First results on longitudinal double spin asymmetries from RHIC consistent with DIS sample result disfavors large ∆G if ∫Ldt = 3pb-1 and P-0.4 (2005) errors will reduce by factor 8 Experiments are ready for spin measurements at low to moderate luminosities!  relative luminosity ~5x10-4  trigger  polarization analysis  data analysis Run3+4 GRSV ∆G(x)

  17. Schedule for RHIC Spin example: STAR 32 week scenario  all schedules subject to further advances in RHIC operations and/or funding! L= 6x1030cm-2s-1 8x1031cm-2s-1 P= 0.45 0.5 0.7 …………………………………………. √s= ……………………….. 200 GeV ………………….........| 2004 2005 2006 2007 2008 2009 …. pp 5+1 5+10 5+11 0 5+9 156pb-1 Inclusive hadrons + Jets Transverse Physics Charm Physics direct photons Bottom physics W-physics ALL(hadrons, Jets) ALL(charm) AL(W) ALL(γ)

  18. ALL in inclusive jet production (STAR) Jager, Stratmann, Vogelsang hep-ph/0404057 ALL(Jets) ∫Ldt=3pb-1 P=0.4 Input: ∆G(x)=G(x) GRSV: standard ∆G(x) ∆G(x)=0 ∆G(x)= -G(x) pT [GeV/c] Gluon Polarization at Low Luminosity:Inclusive Jets and Hadrons: (1pb-1< ∫Ldt < 30pb-1, 0.4<P<0.6) ALL in inclusive π0 production (PHENIX) Vogelsang hep-ph/0405069 ALL(π0) ∫Ldt=3pb-1 P=0.4 Input: ∆G(x)=G(x) GRSV: standard ∆G(x) ∆G(x)= -G(x) ∆G(x)=0 pT [GeV/c] • GRSV standard ∆G(x) • Gluon distribution from NLO pQCD fit to DIS data on A1, Gluck Reya, Stratmann, Vogelsang Phys. Rev. D63:094005, 2001 Expected in run 05: ∫Ldt =5pb-1 P =0.5 All required instrumentation in STAR and PHENIX is in place!

  19. Gluon Polarization at Moderate Luminosity:Charm Production: ( ∫Ldt > 30pb-1, P>0.6) from Wei Xie, PHENIX ALL for single electrons in PHENIX Silicon Vertex Detector Upgrade! --- ∫Ldt=32pb-1 --- ∫Ldt=320pb-1 GS-A/B/C: ∆G(xg) parametrization from Gehrmann and Stirling Phys.Rev. D53 6100-6109,1996 ∫GA(x)dx =1.8 ∫GB(x)dx =1.6 ∫GC(x)dx =0.2

  20. Sensitivity to Gluon Polarization at RHIC from Les Bland, STAR GS-A/B/C: ∆G(xg) parametrization from Gehrmann and Stirling Phys.Rev. D53 6100-6109,1996 ∫GA(x)dx =1.8 ∫GB(x)dx =1.6 ∫GC(x)dx =0.2 xgluon PHENIX and STAR are sensitive to ∆G through several independent channels: Inclusive photons, inclusive jets, jet-photon, J/ψ production, heavy flavor production Good control of experimental and theoretical uncertainties!

  21. Sensitivity to Gluon Polarization at RHIC from F.-H. Heinsius, DIS 2004 RHIC data at hard scale  pQCD applicable for the extraction of polarized pdfs. (I) HERMES Phys. Rev.Lett.84:2584- 2588,2000 (II) RHIC spans a broad range of xgluon  Determine first moment ∫∆G(x)dx = gluon contribution to the proton spin! (III) Assumes data sample of 320pb-1 at √s=200 GeV and 800pb-1 at √s=500 GeV; P=0.7.(This is baseline spin!) (IV) Upgrades extending kinematic coverage to low x decrease error on ∫∆G(x)dx (low x behavior has been critical in proton spin structure in the past: SLAC E80/E130 vs EMC  spin crisis) SMC, B. Adeva et al. hep-ex/0402010

  22. W Production in Polarized pp Collisions Single Spin Asymmetry in the naive Quark Parton Model Parity violation of the weak interaction in combination with control over the proton spin orientation gives access to the flavor spin structure in the proton! Experimental Requirements:  tracking at high pT event selection for muons difficult due to hadron decays and beam backgrounds. W Z

  23. Access to quark polarizations through measurements of inclusive longitudinal single spin asymmetry? • Yes! Complete theoretical treatment from first principles by Nadolsky and Yuan at NLO pQCD (Nucl. Phys.B 666(2003) 31). Can We Connect Observables: inclusive AL(lepton) with quark polarizations? • Machine and detector requirements: • ∫Ldt=800pb-1, P=0.7 at √s=500 GeV • Upgrades: o Muon trigger in PHENIX o Forward tracking in STAR pTm[GeV]

  24. Quark Polarization: RHIC vs HERMES from Naohito Saito, PHENIX • W-production at RHIC • No fragmentation ambiguity • x-range limited • Semi-inclusive DIS • Wide x-range • Limited sensitivity to sea flavors • Fragmentation functions poorly known at low scales (HERMES)

  25. Transverse Spin at RHIC (A) Physics Channels for Low Luminosity STAR and PHENIX STAR, PHENIX and BRAHMS (I) (II) Boer and Vogelsang (hep-ph/0312320): azimuthal back to back correlation between hadrons in opposite hemisphere jets: STAR Phys. Rev. Lett. 92:171801, 2004 Clean channel for Sivers effect! Separation of intrinsic transverse quark spin (transversity) from trans- verse momentum effects (Sivers)?

  26. Transverse Spin Physics Elsewhere Transverse Spin at RHIC HERMES, COMPASS and Jefferson Lab (B) Physics Channels for high L STAR and PHENIX Separate transverse quark spin (transversity) and transverse momentum contributions (Sivers) in semi- inclusive deep Inelastic scattering: o low scale leads to significant theoretical ambiguities o Final data set from HERMES available in mid 2005 J.C. Collins, Nucl. Phys. B396, 161(1993) J. Collins, S. Heppelmann, G. Ladinsky, Nucl.Phys. B420 (1994)565 Brahms AN measurements from 2004 and 2005 polarized proton runs! Brief PHENIX and STAR runs on AN and back-to-back correlations as ∫ Ldt/week>1pb-1/week (2006?) Brief PHENIX and STAR runs on AT as ∫ Ldt/week>10pb-1/week R. Jaffe, X.Jin, J. Tang Phys. Rev. D57 (1999)5920 Statistical sensitivity for AT with 32pb-1 Spin Rotators: Give flexibility!

  27. Upgrades and RHIC Spin • Upgrades required for core spin program • flavor separation of spin dependent quark distribution • in W-production • STAR: integrated forward tracking • PHENIX: muon trigger • Upgrades aimed at a precision measurement of • the first moment ∫∆G(x)dx  constrain orbital angular mometum? • STAR: micro vertex detector • PHENIX: Silicon Vertex Detector, nose cone calorimeter

  28. Measurement of the first moment ∫∆G(x)dx DG at low x  0.001 Upgrades extends the range of xG for the prompt-gmeasurement down to XG~0.001 atÖs =200 GeV Measurement of ∫∆G(x)dx over a wide x range will be essential in constraining spin sum 1/2∆Σ+ ∆G+Lz Sensitivity to shape of polarized gluon distribution over a large x range (important input in fixing the shape and extrapolation to low x in global QCD analysis aimed at extracting ∆G) GS95 prompt photon Silicon Tracker +NCC

  29. Summary: Polarized Proton Collisions o A new experimental method has been successfully developed and we are beginning to exploit a truly novel experimental tool on proton spin structure. o Fixed target DIS experiments are carried out at comparably soft scales and are subject to various theoretical uncertainties. Leader- ship in the field will shift from DIS experiments to RHIC spin. o First physics results are available from exploratory runs. 2005 promises to be the first spin physics run at RHIC. o Integrated forward tracking (STAR) and muon trigger upgrades (PHENIX) are necessary for W-physics. o Measurement of gluon spin (first moment) contribution to the proton spin requires larger kinematic range  eg. nose-cone calorimeter in PHENIX

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