Christine Aidala Columbia University Transversity 2004, Trento June 14, 2004

Transcription

1 Single Transverse Spin Asymmetries at RHIC Christine Aidala Columbia University Transversity 2004, Trento June 14, 2004

2 RHIC Physics Broadest possible study of QCD in A-A, p-a, p-p collisions Heavy ion physics Investigate nuclear matter under extreme conditions Examine systematic variations with species and energy Explore the spin of the proton In particular, contributions from Gluon polarization ( G) Sea-quark polarization u, d Transversity distributions (δq) Nucleon structure in a nuclear environment Nuclear dependence of pdf s Saturation physics ( ) Continue to explore in erhic C. Aidala, Transversity 2004, June 14,

3 Hard Scattering Processes in p+p: Factorization and Universality ( ) ( z) ˆ ( ) ˆ σ qg qγ γ σ ( pp γx ) f ( x ) f ( x ) σ qg qγ ˆ ( sˆ ) Hard probes have predictable rates given: q 1 Parton distribution functions (need experimental input) pqcd hard scattering rates (calculable in pqcd) Fragmentation functions (need experimental input) g 2 C. Aidala, Transversity 2004, June 14, Universality

4 c 3 ) -2 (mb GeV 3 σ/dp 3 E*d π 0 Cross Section from Run PHENIX, η < 0.35 STAR, 3.4 < η < 4.0 PRL 91, (2003) PHENIX Data KKP FF Kretzer FF a) PRL 92, (2004) 10-7 σ/σ (%) (Data-QCD)/QCD b) c) % normalization error not shown (GeV/c) p T d) Good agreement between NLO pqcd calculations and experiment Can use NLO pqcd analysis to extract spin-dependent pdf s C. Aidala, Transversity 2004, June 14,

5 Nucleon Transversity and Factorization s p 1 P 2 δq i ( x 1 ) Proton Structure q i ( x 2 ) x P 2 2 x 1 P 1 σ ij ( pp π π X ) + Jet + π π 7 d σ π π, 3 +, d σ ( q1q2 q δq( x1) q( x2) 2 dx dx dtdzdm d cosθdϕ dx dx dt 1 2 Hard Scattering Process at RHIC Interference Fragmentation ρ,σ measured parton dis. 1 Jet Experiment: pqcd 2 3 Jian Tang, Thesis MIT, June 1999 R. Jaffe, X.Jin, J. Tang Phys. Rev. D57 (1999)5920 X. Ji, Phys. Rev. D49 (1994)114 J. Collins, S. Heppelmann, G. Ladinsky, Nucl.Phys. B420 (1994)565 A. Bianconi, S. Boffi, R. Jakob, M. Radici, Phys. Rev. D62 (2000) A = 1 P beam N N + N N Currently unknown: b-factories,lep 2 q4) d M 2 dzdm d cosθdϕ Model Calculations C. Aidala, Transversity 2004, June 14,

6 3.83 km circumference Two independent rings Up to 120 bunches/ring 106 ns crossing time Energy: Up to 500 GeV for p-p Up to 200 GeV for Au-Au (per N-N collision) Luminosity Au-Au: 2 x cm -2 s -1 p-p : 2 x cm -2 s -1 (polarized) RHIC Specifications C. Aidala, Transversity 2004, June 14,

7 RHIC as a Polarized p-p Collider source: Thomas Roser, BNL! "# " #!. AGS $$$ % 3 $%& ' s = 200GeV( L peak ~ 6 10 cm s )$*+ (**%, %. * ' / 0 ' 11!"#( 11! #.2. C. Aidala, Transversity 2004, June 14,

8 Absolute Polarimetry for RHIC: Polarized Hydrogen Gas Jet Target thickness of > p/cm 2 polarization = 93% (+1 2)%! no depolarization from beam wake fields Silicon recoil spectrometer to measure The left-right asymmetry A N in pp elastic scattering in the CNI region to A N < 10-3 accuracy. Calibrate the p-carbon polarimeters Two large data samples at 24 and 100 GeV Expect results on P Beam to 10% in the near future Polarized H Jet Target Courtesy Sandro Bravar, STAR and Yousef Makdisi, CAD C. Aidala, Transversity 2004, June 14,

9 Spin Running at RHIC So Far Transversely polarized p+p collisions Average polarization of ~15% Integrated luminosity 0.15 pb Longitudinally polarized p+p collisions achieved Average polarization of ~27% Integrated luminosity 0.35 pb weeks polarized p+p commissioning Specifically to work on spin tune and AGS polarization Commission hydrogen jet polarimeter 1 week data-taking Average polarization ~45% Flipping spin of bunches every ~100 or 200 ns aids in eliminating systematic errors C. Aidala, Transversity 2004, June 14,

10 Possible Schedule for Future Runs example: STAR 32 week scenario all schedules subject to further advances in RHIC operations! L= 6x10 30 cm -2 s -1 8x10 31 cm -2 s -1 P= s= GeV pp pb -1 Inclusive hadrons + Jets Transverse Physics Charm Physics A LL (hadrons, Jets) A LL (charm) direct photons Bottom physics W-physics A LL ( ) A L (W) C. Aidala, Transversity 2004, June 14,

11 RHIC s Experiments Transverse spin only. Precision A N! STAR C. Aidala, Transversity 2004, June 14,

12 The PHENIX Detector 2 central spectrometers - Track charged particles and detect electromagnetic processes 2 forward spectrometers - Identify and track muons 3 global detectors - Determine when there s a collision C. Aidala, Transversity 2004, June 14,

13 PHENIX Detector Overview Central arms Photons, electrons, identified charged hadrons η < 0.35 φ = 180 degrees Forward muon arms Track and identify muons 1.2 < η < 2.4 φ = 2π Detector fully operational for intermediate luminosities. Upgrades planned for highluminosity running. C. Aidala, Transversity 2004, June 14,

14 Measurement of Proton Spin Structure Gluon polarization G( x) G( x) at RHIC Inclusive jets, hadrons, photons, and heavy flavor in STAR and PHENIX Flavor separation of quark polarizations q( x), q( x) q( x) q( x) Transverse spin structure of the nucleon δq( x) q( x) Single lepton asymmetries A L (e,µ) in W-production in STAR and PHENIX A T in Collins- and Interferencefragmentation and A N in STAR, PHENIX, and BRAHMS, A TT in jets and Drell-Yan C. Aidala, Transversity 2004, June 14,

15 Avenues to Transversity at RHIC Present and Near Future 1 Ldt = 320pb, s = 200GeV Precision measurement of A N CollinsEffectin Jets: + π, π InterferenceFragmentation : + ( p p ( π, π ) X ) A T + Inclusive jet production ATT A T ( pp π + Jet + X ) J.C. Collins, Nucl. Phys. B396, 161(1993) J. Collins, S. Heppelmann, G. Ladinsky, Nucl.Phys. B420 (1994)565 R. Jaffe, X.Jin, J. Tang Phys. Rev. D57 (1999)5920 A. Bianconi, S. Boffi, R. Jakob, M. Radici, Phys. Rev. D62 (2000) W. Vogelsang and M. Stratmann, RBRC Wrkshp on Transversity (2000) BRAHMS, PHENIX, STAR Drell Yan: Ldt = 8fb A TT Upgrades 1 at RHIC, erhic Direct Photon : Collins in Jets, Interference Fragmentation ( p p ll) δq δq J.Ralston and D.E. Soper, Nucl. Phys. B152, 109(1979) Collins Effect in Jets Interference Fragmentation PHENIX, STAR erhic A N C. Aidala, Transversity 2004, June 14,

16 Transverse Spin at RHIC: Present Measure AN : A N ( pp h + X ) Ldt = 1 10 pb Precision measurement at BRAHMS, also PHENIX, STAR (I) STAR Phys. Rev. Lett. 92:171801, , s = 200 GeV STAR and PHENIX (II) Boer and Vogelsang (hep-ph/ ): azimuthal back to back correlation between hadrons in opposite hemisphere jets: Separation of transversity and Sivers with high-precision and large p T range? Clean channel for Sivers effect! C. Aidala, Transversity 2004, June 14,

17 AT Interference Fragmentation: Near-Term E Ldt = 32 pb π, π 1 p 2 2 1T > + 4 GeV p 2 2T > 800 MeV < m A Tang and Long-Term Projections 1 4 GeV π, π 1 2 PH < 950 MeV 0 ENIX cosφ sinδ sinδ sin( δ δ p T of pair [GeV/c] Small aymmetry below 5% but good rate! ) Interference FF in jet-direct photon production AT RHIC Luminosity Upgrade: Ldt C. Aidala, Transversity 2004, June 14, = 8 fb 1 Large aymmetry, but lots of luminosity required! [GeV] E jet

18 J.Ralston and D.E. Soper, Nucl. Phys. B152, 109(1979) Drell-Yan Physics at RHIC 1 Ldt = 320 pb, at PHENIX Drell- Yan: A TT ( p p ll) Observable δq δq δq δq A TT A TT Ldt = 1 8 fb, RHIC upgrade O.Martin, A. Schaefer, M. Stratmann, W. Vogelsang Phys.Rev. D60, (1999) lepton pair mass C. Aidala, Transversity 2004, June 14, [GeV]

19 Components of the Transversity Program at RHIC δqˆ H in e+e- using b-factory data (2005) I, 1 RBRC active in Belle Precision measurement of A N at BRAHMS (2005) Tensor charge lattice calculation at RBRC (2005?) 10 Tflops! T. Blum, S. Sasaki, S. Ohta δq δqˆ I at STAR, PHENIX δq H1 at STAR δq δq at PHENIX (after luminosity upgrade) (2006-8) C. Aidala, Transversity 2004, June 14,

20 A N of Neutral Pions and Non-Identified Charged Hadrons at Midrapidity η < 0.35 A N for both charged hadrons and neutral pions consistent with zero. PH ENIX Fraction π 0 's produced qq qg gg C. Aidala, Transversity 2004, June 14,

21 A N of Neutral Pions at Forward Rapidity Large asymmetry seen For <η> = 3.7 possible contributions to A N are: Sivers Effect Spin dependent initial partonic transverse momentum Collins Effect Spin dependent transverse momentum kick in fragmentation Sterman and Qiu Initialstate twist 3 Koike Final-state twist 3 PRL 92 (2004) C. Aidala, Transversity 2004, June 14, 2004 = 21

22 Neutron A N at IP12 A N measurement at IP12 large neutron A N was discovered Y. Fukao A N = preliminary preliminary A N = Local polarimeter at PHENIX ZDC + position sensitive counters to measure the neutron A N C. Aidala, Transversity 2004, June 14,

23 Single-Spin Asymmetries for Local Polarimetry: Confirmation of Longitudinal Polarization Spin Rotators OFF Vertical polarization Blue Yellow Spin Rotators ON Current Reversed! Radial polarization Blue Yellow Spin Rotators ON Correct Current Longitudinal polarization! Blue Yellow C. Aidala, Transversity 2004, June 14,

24 A N of Charged Hadrons at BRAHMS (2005) Dedicated transverse spin measurements (no spin rotators) p ±, K ±,π ± identified from 0 < y < 4, 0.2 < p T < 3 GeV/c at forward rapidity High-precision measurement of A N C. Aidala, Transversity 2004, June 14,

25 Single-spin asymmetries seen at RHIC so far P T X F π 0, ~0% h +/- ~0% PHENIX CENTRAL STAR TPC PHENIX MUON STAR FPD 0 o CAL π ~ +20% Neutron -10% γ ~0 % π 0 ~0% Pseudorapidity C. Aidala, Transversity 2004, June 14,

26 Summary RHIC has been successful as the world s first polarized proton collider, opening up new kinematic regions for investigating the spin of the proton The first transverse spin results are out, and non-zero asymmetries have been observed at RHIC energies A N of forward neutral pions (~+10-20%) A N of forward neutrons (~-10%) A N of neutral pions and non-identified charged hadrons at midrapidity (~0%) An extensive program planned for the near- and long-term future Many more years of exciting data and results to look forward to! C. Aidala, Transversity 2004, June 14,

27 Extra Slides C. Aidala, Transversity 2004, June 14,

28 pqcd Scale Dependence at RHIC Theoretical uncertainty of pqcd calculations in channels relevant for gluon polarization measurements: π 0 data vs pqcd with different factorization scales: σ ( µ 0 / 2) σ ( µ ) 0 HERMES (hadron pairs) COMPASS (hadron pairs) PHENIX (inclusive hadrons) RHIC PHENIX (direct (direct photon) photon) CDF (direct photon) 2 (factorization scale) Statistical errors only C. Aidala, Transversity 2004, June 14, /2

29 RHIC vs. DIS Kinematic Coverage prompt photon bb e ± µ X RHIC : s = 200GeV cc e ± X C. Aidala, Transversity 2004, June 14,

30 Siberian Snakes Effect of depolarizing resonances averaged out by rotating spin by 180 degrees on each turn PHENIX RHIC STAR 4 helical dipoles S. snake 2 snakes in each ring - axes orthogonal to each other LINAC AGS C. Aidala, Transversity 2004, June 14,

31 Carbon filament target (5µg/cm 2 ) in the RHIC beam Measure recoil carbon ions at θ~90 º 100 kev < E carbon < 1 MeV E950 Experiment at AGS (1999) RHIC polarimetry now RHIC Polarimetry C. Aidala, Transversity 2004, June 14,

32 $&'( The PHENIX Detector &)$'# *$' +, $*&$ & 2 central spectrometers - Track charged particles and detect electromagnetic processes 2 forward spectrometers - Identify and track muons 3 global detectors - Determine when there s a collision C. Aidala, Transversity 2004, June 14,

33 The STAR Detector!%%& η "#$#$! C. Aidala, Transversity 2004, June 14,

34 Access to Sivers Functions in STAR High-rapidity π 0 Production p p π 0 + X Mid-rapidity Leading Charged Particle Analysis p p h +/- + X φ Di-jet production p p jet + jet + X C. Aidala, Transversity 2004, June 14,

35 Forward Pion Detector at STAR!"'( ( )! ( *! )'+ *,!-' ( "*"'+-. /( * 0+' &.4 C. Aidala, Transversity 2004, June 14,

36 An Example: High Energy Proton Polarimeters for p= 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: , 2003 o Spin asymmetries in forward multiplicity production as seen by beam-beam counters in STAR J. Kiryluk, AIP Conf. Proc. 675, 424 (2003) C. Aidala, Transversity 2004, June 14,

37 Number of elastic pp events Jet profile FWHM ~ 6 mm As designed Hor. pos. of Jet cts. = 2.5 mm Data collected so far in this run: TDC: 1 ct = 1.2 ns CNI peak A N 1 < E REC < 2 MeV ADC: 1 ct = 40 kev prompt events and beam gas Recoil protons elastic pp pp scattering α source calibration 100 GeV ~ 700,000 events at the peak of the analyzing power (~ 3 x 10 6 total useful pp elastic events) 24 GeV ~ 120,000 events at the peak of the analyzing power (~ 5 x 10 5 total useful pp elastic events) C. Aidala, Transversity 2004, June 14,

38 First Results: A LL PHENIX A LL ( 0 ) at <0.35, hep-ex/ plot from Vogelsang hep-ph/ Run 03, Ldt ~ 0.2pb -1, P~0.27 Standard GRSV G(x) Input: G(x)=G(x) G(x)=0 G(x)= -G(x) First results on longitudinal double spin asymmetries from RHIC consistent with DIS sample result disfavors large G egldt = 3pb -1 and P-0.4 (2005) errors will reduce by factor 8 Experiments are ready for spin measurements at low to moderate luminosities! 65% scale uncertainty from polarization relative luminosity ~5x10-4 trigger polarization analysis data analysis C. Aidala, Transversity 2004, June 14,

39 (I) Transverse Spin at RHIC STAR, PHENIX and BRAHMS Measure AN : A N ( pp h + X ) STAR Phys. Rev. Lett. 92:171801, 2004 (A) Physics Channels for Low Luminosity Ldt = 1 10 pb 1, s = 200 GeV STAR and PHENIX (II) Boer and Vogelsang (hep-ph/ ): azimuthal back to back correlation between hadrons in opposite hemisphere jets: Separation of intrinsic transverse Clean channel for Sivers effect! quark spin (transversity) from transverse momentum effects (Sivers)? C. Aidala, Transversity 2004, June 14,