Spin Physics at RHIC. Particle Physics Phenomenology at KEK March 2, 2004 Yuji Goto (RIKEN/RBRC)

Transcription

1 Spin Physics at RHIC Particle Physics Phenomenology at KEK March 2, 2004 Yuji Goto (RIKEN/RBRC)

2 Spin physics at RHIC Longitudinal polarized proton collision helicity structure of the proton gluon polarization parity violating asymmetries Transverse polarized proton collision transverse structure/motion = orbital angular momentum transversity distribution last unmeasured leading-twist distribution single transverse-spin asymmetries transversity, higher twist, T-odd structure and fragmentation functions, Small-angle pp elastic scattering unpolarized & polarized measurements

3 Longitudinal polarized proton collision Origin of the proton spin 1/2? 1 2 = 2 1 Σ + g + L lepton beam or or nucleon target polarized DIS Σ = : quark contribution by polarized DIS experiments gluon contribution known poorly from scaling violations in pol. DIS experiments, spanning a small range of Q 2 γ * quark SMC : g ( Q = = 1GeV (stat) 2 ) (sys) (th)

4 Gluon polarization Polarized semi-inclusive DIS COMPASS/SMC/HERMES Polarized hadron collision Fermilab E704 π 0 /multi-photon RHIC polarized proton collision lepton beam or or nucleon target γ * heavy flavor gluon proton beam proton beam or or proton beam gluon photon or or proton beam gluon gluon heavy flavor

5 RHIC (Relativistic Heavy-Ion Collider)

6 RHIC polarized proton collision Absolute Polarimeter (H jet) RHIC pc CNI Polarimeters BRAHMS & PP2PP PHOBOS Spin Rotators PHENIX RHIC s = GeV STAR Siberian Snakes Pol. Proton Source 500 µa, 300 µs LINAC BOOSTER 200 MeV Polarimeter AGS Rf Dipoles Partial Solenoid Snake Partial Helical Snake AGS pc CNI Polarimeter AGS Quasi-Elastic Polarimeter s = 200 GeV transverse polarized proton collisions s = 200 GeV transverse+longitudinal polarized proton collisions 2004 s = 200 GeV longitudinal polarized proton collisions

7 RHIC polarized proton collision High s and high Q 2 s = 200 GeV and 500 GeV in the future perturbative QCD applicable scale dependence of the NLO pqcd calculation in the cross section measurement scale dependence is expected to largely cancel in the asymmetry measurement M. Stratmann and W. Vogelsang

8 RHIC polarized proton collision Cancellation of systematic uncertainty flexible combination of spin direction every crossing IP4 and IP10 STAR and IP12 PHENIX and PP2PP

9 RHIC polarized proton runs Run2: transverse polarized collision 150 nb -1 polarization ~15% Run3: 2003 transverse+longitudinal polarized collision 600 nb -1 polarization ~27% Run4: 2004 March-April (5 weeks) polarized proton commissioning run to develop more luminosity and more polarization longitudinal polarized collision data expected Run5: 2005 physics run again

10 Longitudinal polarized proton collision Double longitudinal-spin asymmetry A LL = = dσ dσ P P L+ R = L++ P: polarization 1 dσ + + dσ + N++ R N N + R N ++ AGS/RHIC proton-carbon CNI polarimeter polarized hydrogen gas-jet (absolute polarimeter) local polarimeters at experiments N: yield R: relative luminosity parallel anti-parallel

11 STAR

12 PHENIX

13 PHENIX

14 PHENIX π 0 cross section data covers over 8 orders of magnitude p T = 1 13 GeV/c NLO pqcd calculation is consistent with our data Run2 result hep-ex/ PRL 91, (2003) within the scale µ = p T /2-2p T confidence in understanding subprocesses input to the fragmentationfunction uncertainty 9.6% normalization error not shown

15 PHENIX A LL (π 0 ) A LL 0.1 π 0 A LL from pp at s=200 GeV PHENIX Preliminary GRSV-max GRSV-std GRSV-max: G = 1.84 GRSV-std: G = 0.42 (at Q 2 = 1 GeV 2 ) B. Jäger et al., PRD 67 (2003) NLO pqcd calculations Polarization scaling error ~30% is not included p T (GeV/c) Polarization scaling error δp/p ~30% is not included: - Analyzing power A N (100 GeV = A N (22 GeV) is assumed - δp/p ~ 30%: combined stat. and syst. error for A N (22 GeV [AGS-E950]

16 Gluon polarization SMC semi-inclusive hadron-pair measurement photon-gluon fusion lepton beam or or nucleon target γ * heavy flavor gluon COMPASS 2004: δ( G/G) stat ~ 0.15??

17 Gluon polarization B. Jäger et al., hep-ph/ NLO pqcd calculation cannot make sizable negative A LL (π 0 ) in this kinematic range Fraction of π 0 s produced gg gq qq

18 Transversity last unmeasured leading-twist distribution Near future π + π - interference fragmentation function J. Collins, S. Heppelmann, and G. Ladinsky, Nucl.Phys. B420 (1994)565 R. Jaffe, X.Jin, J. Tang Phys. Rev. D57 (1999)5920 A T ( pp π + Jet + X ) Collins effect in jets J.C. Collins, Nucl. Phys. B396, 161(1993) inclusive jet production + ( p p ( π, π X ) A T + ) W. Vogelsang and M. Stratmann, RBRC Workshop on Transversity (2000)

19 s v p 1 A Transversity at PHENIX Transversity throught π + π - interference FF P 2 non-vanishing support only in the ρ mass region δq i ( x 1 ) Proton Structure 1 P q i ( x 2 ) N N + x P 2 2 N N = beam x 1 P 1 = σ ij Hard Scattering Process Interference Fragmentation ρ,σ Jet + π π 6π sinδ 0 sinδ1 sin( δ 0 δ1) cos( φ) 4 Jet [ δq( x ˆ 1) G( x2) δqi ( z) ] qq 2 [ G( x ) G( x )] δσˆ +... sin δ δσˆ +... qg 2 { } [ qˆ ( z) + sin δ qˆ ( z) ] 1 2 gg Maximum Asymmetry η = 0, m δqˆ 2 I = 4qˆ qˆ, = 0.83 GeV, cosφ = 1 ρ σ 0 1 / 3, 0 0 2δq q + q qg 200 GeV 500 GeV p jet T [GeV ] 1 1

20 Transversity throught π + π - interference FF Projected asymmetry A ( p π + π + X ) T ATang(cos φ = 1, m = GeV) vs p pair T For 32pb -1 E Ldt = 32 pb π, π 1 p 2 2 1T > 4 GeV + p 2 2T (1 week of running) 1 > 4 GeV 800 MeV < m < 950 MeV 5.2 Million events in 32 pb -1 15% with pair after cuts A Tang cosφ sinδ sinδ sin( δ δ 1) Small aymmetry below 5% but good rate!

21 Fragmentation function at BELLE Collins fragmentation function e + e - π + jet1π - jet2x reaction plane defined with beam (z-axis) and jet axis product (π) plane defined with π and jet axis φ: angle between the planes A Η 1 (z 1 )Η 1 (z 2 )cos(φ 1 +φ 2 ) can analyze with/without using jet axis A Η 1 (z 1 )Η 1 (z 2 )cos(2φ) S. Lange, A.Ogawa (STAR) K. Hatsuko, M.G-Perdekamp (PHENIX)

22 Fragmentation function at BELLE π + π - interference fragmentation function e + e - (π + π - ) jet1 (π - π + ) jet2 X stay in the mass region around ρ mass find pion pairs in opposite hemispheres observe angles φ 1 +φ 2 between the event-plane (beam, jet-axis) and the two pion planes. A δq Ι (z 1, m 1 ) δq Ι (z 2, m 2 )cos(φ 1 +φ 2 )

23 HERMES Polarized semi-inclusive DIS ongitudinal olarized target A UL A π+ ~A π0 >0 A π- <0 and smaller transverse polarized target Collins A UT A π+ >0 A π0 ~A π- <0 and larger

24 Single transverse-spin asymmetries Left-right asymmetry Fermilab E704 s = 20 GeV unexpected large asymmetry at large-x F 0.2 < p T < 2.0 GeV/c left right Fermilab-E704 L R R L L R R L N N N N N N N N N P A + = 1 = + = L L R N R N N R N P A L L L L N 1 square-root formula luminosity formula

25 STAR forward π 0 FPD (Forward Pion Detector) EM calorimeters to cover largex F region BBC West BBC East FPD East

26 STAR forward π 0 Cross section consistent with NLO pqcd calculations A N large spin effects observed for s = 200 GeV pp collisions hep-ex/

27 Neutron asymmetry at IP12 PHENIX local polarimeter R&D Hadron Cal Base Neutron Veto Post-shower Scintillator Pb Charge Veto EM Cal Base W+Fiber Cal PbWO 4

28 Neutron asymmetry at IP12 Hadron Cal EM Cal A N = 0.116±0.018±0.020 A N = 0.126±0.008±0.041 preliminary preliminary very forward neutron A N ~ -12% x F > 0.2 p T < 0.3 GeV/c preliminary

29 PHENIX local polarimeter ZDC + SMD ZDC: Zero-Degree Calorimeter hadron calorimeters at the most forward location (~18m from IP) SMD: Shower-Maximum Detector plastic scintillator array X: 7 array, Y: 8 array SMD 1 ZDC

30 HENIX local polarimeter Spin Rotators OFF transversely-polarized proton collisions Blue Yellow Spin Rotators ON Current Reversed radially-polarized proton collisions Blue Yellow Spin Rotators ON Correct Current! longitudinally-polarized proton collisions Blue P B =35.5% P B =37% Yellow

31 PHENIX local polarimeter S L = ST, ST = ST vertical + ST radial S T is measured with PHENIX local polarimeter eft-right asymmetry up-down asymmetry S L ( blue) = S L ( yellow) =

32 STAR local polarimeter BBC (Beam-Beam Counter) η = 2 ~ 5 A N ~ +0.5% Measured asymmetry Yellow beam, BBC East 10 3 CNI drop ε CNI (ON-LINE) ε LR BBC = (2) ε TB BBC = (2) BBC Blue beam, BBC West 10 3 CNI drop ε CNI (ON-LINE) ε LR BBC = 0.13(2) ε TB BBC = -0.24(2) BBC OFF Rotators ON Run# OFF Rotators ON Run#

33 Summary We are giving first results of spin physics at RHIC gluon polarization in longitudinal polarized proton collisions (A LL ) single transverse-spin asymmetries (A N ) Many developments have been done and are ongoing polarimetry AGS/RHIC, polarized hydrogen gas-jet local polarimeter: application of the A N results more luminosity and polarization AGS snakes detector upgrades Many future topics more gluon polarization data transversity (with fragmentation functions) parity-violating asymmetries small-angle pp elastic scattering

34 Backup slides

35 Magnet Coils STAR Time Projection Chamber η < ~ 1.5 B=0.25T 0.5T Endcap EMC 1< η <2 φ = 2π Barrel EMC 0< η< 1 φ =2π/5 η < 1 φ = 2π Forward Pion Detector (FPD) 3.1 < η < upgrade Spin 2 m 4.2 m Run0 Run Run2 and beyond Silicon Vertex Tracker Forward TPCs 2.4 < η < 4.0 Central Trigger Barrel η < 1 + patch RICH: η <0.3, φ = π/6 Beam-Beam Counters 2.4< η < 5.0

36 Relative luminosity achieved relative luminosity precision δr = δa LL = 0.2% pessimistic estimation limited by ZDC statistics (30 times less than BBC statistics used in relative luminocity measurements) A LL of BBC relative to ZDC consistent with zero (<0.2%) strong indication that both A LL s are zero (very different kinematical regions, different physics signals) BBC ZDC

37 Zero-Degree Calorimeter (ZDC) tungsten + scintillating fiber hadron calorimeter 5.1 λ I, 149 X 0 (3 modules) beam beam

38 High-p T trigger s=200 GeV data collected with high-p T photon trigger Based on EMCal; Threshold ~1.4 GeV/c Rejection factor ~110 Analyzed data sample: 42.7M events (~0.215 pb -1 ) PbPy ~26% Minimum Bias data To obtain unbiased π 0 cross section at low p T For high-p T photon trigger efficiency study Trigger efficiency for π 0 Pi0 efficiency plateaus for p T >4 GeV/c Limited efficiency at p T <4 GeV/c: 1-2 GeV/c: 6% 2-3 GeV/c: 60% 3-4 GeV/c: 90% 4-5 GeV/c: 95% Monte Carlo reproduces Data well

39 π 0 reconstruction results obtained for four p T bins from 1 to 5 GeV/c π 0 peak width varies from 12 to 9.5 MeV/c 2 from lowest to highest p T bins background contribution under π 0 peak for ±25 MeV/c 2 mass cut varies from 45% to 5% from lowest to highest p T bins 1-2 GeV/c Bckgr=45% 3-4 GeV/c Bckgr=7% 2-3 GeV/c Bckgr=17% 4-5 GeV/c Bckgr=5%

40 π 0 counting for A LL N π0 : ±25 MeV/c 2 around π0 peak (and also ±15 and ±35 MeV/c 2 for cross checks) N bck1 : Two 50 MeV/c 2 wide areas adjacent to π0 peak N bck2 : 250 MeV/c 2 wide area between π0 and η peaks pt GeV/c N π0 and N bck accumulated statistics N π0 15 MeV/c 2 N π0 25 MeV/c 2 N π0 35 MeV/c 2 N bck1 N bck k 1777k 2129k 1470k 3478k k 1059k 1146k 335k 989k k 201k 208k 27k 83k k 38k 39k 3.9k 12k

41 A LL Calculations A LL averaged over fills 1-2 GeV/c 3-4 GeV/c 2-3 GeV/c 1-2 GeV/c A LL = -2.8% 1.2% χ 2 /ndf = 64/ GeV/c A LL = -2.2% 1.5% χ 2 /ndf = 34/ GeV/c 4-5 GeV/c A LL = -0.2% 3.3% χ 2 /ndf = 49/ GeV/c A LL = -2.3% 7.4% χ 2 /ndf = 39/48

42 Bunch shuffling Systematic error evaluation randomly shuffle the bunch combination to calculate false asymmetries hchi2_set0_pt0 Nent = 1000 Mean = RMS = GeV/c hchi2_set0_pt1 Nent = 1000 Mean = RMS = GeV/c hasym_set0_pt0 Nent = 1000 Mean = RMS = GeV/c hasym_set0_pt1 Nent = 1000 Mean = RMS = GeV/c hchi2_set0_pt2 Nent = 1000 Mean = RMS = hchi2_set0_pt3 Nent = 1000 Mean = RMS = GeV/c GeV/c hasym_set0_pt2 Nent = 1000 Mean = RMS = hasym_set0_pt3 Nent = 1000 Mean = RMS = GeV/c GeV/c χ 2 /ndf ~ 1 A LL : consistent with statistical error

43 A LL results pt GeV/c bck A π 0+ LL 15 MeV/c 2 bck A π 0+ LL 25 MeV/c 2 A π 0+ bck LL A bck1 LL 35 MeV/c 2 bck 2 A LL ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±0.14

44 A LL results: plots π0+bck MeV/c 2 0+bck MeV/c 2 0+bck MeV/c 2 Bck1 Bck2

45 Gluon polarization Fermilab E704 fixed target experiment s = 19.4 GeV LL(π 0 ) PLB 261 (1991) 197. A LL (multi-γ) PLB 336 (1994) 269. also shows negative A LL

46 Direct photon production Gluon polarization Gluon Compton process dominant factorization g( xg ) / g( xg A p ( x ) ) 1 q â LL A LL g( xg ) p ( pt ) = A ( xq ) aˆ 1 g( x ) : gluon polarization : measured in pol. DIS : calculable g LL GS95 NLO (A) s=500gev 800pb -1 s=200gev 320pb -1 photon + jet measurement inclusive photon measurement

47 PP2PP Spin physics at PP2PP single transverse-spin asymmetry measurement in CNI region Setup silicon microstrip detectors to measure (x,y) coordinates with 100 µm pitch Need special tune of accelerator and detectors to approach the proton beams m Roman Pot Station with Detectors ( used in 2002 ) to IR2 Roman Pot above beam Roman Pot below beam RHIC Intersection Region with PP2PP Basic CB Setup Accelerator magnets ensure that scattered protons have beam Inelastic Detectors momentum RP Stations D0 DX IR RP Station not used in m m 100. m D0 RP Stations

48 PP2PP 2002 engineering run collected ~300,000 elastic scattering events expected results of 2002 data analysis extraction of diffraction cone slope b calculation of single spin asymmetry A N preliminary t -distribution for elastically scattered protons with for all azimuthal angles and for a limited range of azimuth, resulting in full acceptance in t < φ < 135 Preliminary Arm A Full φ Acceptance t [ GeV 2 /c 2 ]

49 Quark polarization flavor decomposition W production parity-violating asymmetry A L + W u( xa ) d( xb ) d ( xa ) u( xb ) AL = u( x ) d( x ) + d( x ) u( x ) PHENIX Muon Arms a A L ~ u/u(x)~ at large-x no fragmentation ambiguity x-range limited complementary to HERMES semi-inclusive DIS wide x-range limited sensitivity to sea flavors b a b

50 Transversity throught π + π - interference FF Invariant mass resolution at PHENIX m > 2 GeV,into accep. E γ pythia m rec z > 0.3 p 1,p2 > 1 GeV,into accep. z > < m < 2.0 GeV p T > 4 GeV RMS=12 MeV m pythia m rec vs m

51 Parity violating asymmetries Jet production W/Z production J. -M. Virey, hep-ph/ A LL (jet) J. Murata