Single transversespin asymmetry measurement in neutral pion and

Single transverse-spin asymmetry measurement in neutral pion and charged hadron production at PHENIX JPS autumn meeting at Kochi Univ. September 28, 2004 Yuji Goto (RIKEN/RBRC) for the PHENIX collaboration September 28, 2004 Yuji Goto (RIKEN/RBRC)

Outline • Introduction – single transverse-spin asymmetry (AN) measurements – possible effects • Measurement at PHENIX mid-rapidity – 0 and charged hadrons – asymmetry calculation and systematic error • Results and summary – cross section and AN September 28, 2004 Yuji Goto (RIKEN/RBRC) 2

Single transverse-spin asymmetry (AN) • Left-right asymmetry left right • Forward-rapidity – Fermilab-E 704 • fixed-target experiment at s = 19. 4 Ge. V – RHIC-STAR • s = 200 Ge. V • large asymmetry at x. F > 0. 3 – and more fixed-target data at lower energies September 28, 2004 Yuji Goto (RIKEN/RBRC) 3

Single transverse-spin asymmetry (AN) • Forward-rapidity – ~ 20% asymmetry – many QCD-based theories developed s = 19. 4 Ge. V s = 200 Ge. V Fermilab-E 704 Phys. Rev. Lett. 92 (2004) 171801 September 28, 2004 Yuji Goto (RIKEN/RBRC) 4

Disentangle possible effects • Sivers effect • left-right asymmetry in transverse momentum distribution of partons (“k. T”) inside the transversely polarized nucleon • Transversity & Collins effect – transversity • transverse polarization of partons inside the transversely polarized nucleon – last unmeasured leading-twist distribution – Collins fragmentation function • left-right asymmetry (analyzing power) in the fragmentation process of transversely polarized final partons • Higher-twist effect September 28, 2004 Yuji Goto (RIKEN/RBRC) 5

Disentangle possible effects • Soft physics at fixed-target energy ? 0 at mid-rapidity – important to show cross section measurement PRL 92 (2004) 171801 • Advantage of RHIC September 28, 2004 Yuji Goto (RIKEN/RBRC) PHENIX s = 200 Ge. V Fermilab s = 19. 4 Ge. V Bourrely and Soffer hep-ph/0311110 6

Mid-rapidity at PHENIX • Different kinematic region – forward-rapidity at STAR (x. F > 0. 3) • quark-gluon reaction dominant • large contribution from x ~ 0. 6 quark polarization/transversity – mid-rapidity at PHENIX (x. F ~ 0) • contribution from both gluon-gluon and quark-gluon reactions • x = 0. 03 – 0. 1 • small quark polarization/transversity • no gluon transversity in leading twist • negligible transversity & Collins effect contribution September 28, 2004 Yuji Goto (RIKEN/RBRC) fraction of 0 s produced gq gg qq p. T (Ge. V/c) 7

Polarized-proton runs at RHIC • 2001 – 2002 – transverse polarization ~ 15% – integrated luminosity 0. 15 pb-1 this presentation • 2003 – longitudinal polarization ~ 27% – integrated luminosity 0. 35 pb-1 • 2004 – 5 weeks machine development – longitudinal polarization ~ 40% – integrated luminosity ~ 0. 1 pb-1 September 28, 2004 Yuji Goto (RIKEN/RBRC) 8

PHENIX detector • Central arms – | | < 0. 35, = 90° × 2 – 0 measurement • EMCal: EM calorimeter – Pb. Sc: lead-scintillator – Pb. Gl: lead glass – charged hadron measurement • DC: drift chamber • PC: pad chamber • RICH: ring-image Cherenkov counter • EMCal September 28, 2004 Yuji Goto (RIKEN/RBRC) 9

Trigger system • Minimum-bias – BBC (beam-beam countrer) • High-p. T trigger – EMCal-RICH trigger – 0. 8 Ge. V EMCal threshold h ( 0) September 28, 2004 Yuji Goto (RIKEN/RBRC) 10

Asymmetry calculation • Square-root formula – detector / luminosity asymmetry cancelled in O 3(asym) order • Luminosity formula – for left and right detectors independently – R: relative luminosity • measured by BBC and ZDC (Zero-Degree Calorimeter) – P: RHIC polarization • next two talks (O. Jinnouchi and H. Okada) September 28, 2004 Yuji Goto (RIKEN/RBRC) 11

Systematic error evaluation – comparison of independent measurement for two polarized beams • both beams (“blue” and “yellow”) polarized – comparison of independent measurement for left and right detectors – comparison of minimum-bias and high-p. T triggered data samples – store-by-store consistency of asymmetry values – “bunch shuffling” • randomly reassign the polarization direction for each bunch crossing • recalculate the asymmetry • repeat many times to produce a shuffled asymmetry distribution centered around zero • compare width of “shuffled” distribution to statistical error on the physics asymmetry September 28, 2004 Yuji Goto (RIKEN/RBRC) 12

Results • Neutral pion • data covers over 8 orders of magnitude • NLO p. QCD calculation is consistent with our data • no significant soft physics component polarization scaling error 32% not included 0 5 10 p. T (Ge. V/c) PHENIX preliminary 0 Phys. Rev. Lett. 91 (2003) 241803 September 28, 2004 Yuji Goto (RIKEN/RBRC) 13

Results • Charged hadrons NLO p. QCD W. Vogelsang et al. CTEQ 6 M PDF KKP FF =2 p. T, 1/2 p. T polarization scaling error 32% not included PHENIX preliminary h- h+ PHENIX preliminary September 28, 2004 Yuji Goto (RIKEN/RBRC) 14

Results – AN for both 0 and charged hadrons consistent with zero at mid-rapidity – 5 -10 times smaller asymmetry than STAR forwardrapidity data (~ 20%) – comparable data with Fermilab-E 704 for 0 and charged hadrons PHENIX preliminary Fermilab-E 704 polarization scaling error 32% not included Phys. Rev. D 53 (1996) 4747 September 28, 2004 Yuji Goto (RIKEN/RBRC) 15

Summary – cross section and AN of 0 and charged hadrons measured at mid-rapidity, s = 200 Ge. V – AN of both 0 and charged hadrons consistent with zero – 5 -10 times smaller asymmetry than STAR forwardrapidity data (~ 20%) – expected to be compared with QCD-based theory calculations – expected to be used to disentangle many possible effects by combining other data September 28, 2004 Yuji Goto (RIKEN/RBRC) 16

Backup slides September 28, 2004 Yuji Goto (RIKEN/RBRC) 17

Summary – cross section and AN of 0 and charged hadrons measured at mid-rapidity, s = 200 Ge. V – AN of both 0 and charged hadrons consistent with zero – 5 -10 times smaller asymmetry than STAR forwardrapidity data (~ 20%) – expected to be compared with p. QCD calculations – expected to be used to disentangle many effects by combining other data • other information source – polarized semi-inclusive DIS at Hermes, SMC, Compass – fragmentation function at Belle September 28, 2004 Yuji Goto (RIKEN/RBRC) 18

HERMES • Polarized semi-inclusive DIS longitudinal polarized target A +~A 0>0 A -<0 and smaller September 28, 2004 transverse polarized target A +>0 A 0~A -<0 and larger Yuji Goto (RIKEN/RBRC) 19

Fragmentation function at BELLE • Collins fragmentation function – e+e- ® +jet 1 -jet 2 X – reaction plane defined with beam (z-axis) and jet axis – product ( ) plane defined with and jet axis – : angle between the planes A µ H 1^(z 1)H 1^(z 2)cos(f 1+f 2) – can analyze with/without using jet axis A µ H 1^(z 1)H 1^(z 2)cos(2 f) September 28, 2004 Yuji Goto (RIKEN/RBRC) 20

Advantage of RHIC • High s and high Q 2 – s = 200 Ge. V and 500 Ge. V in the future – perturbative QCD applicable • scale dependence of the NLO p. QCD calculation in the cross section measurement • scale dependence is expected to largely cancel in the asymmetry measurement M. Stratmann and W. Vogelsang September 28, 2004 Yuji Goto (RIKEN/RBRC) 21

Advantage of RHIC • Cancellation of systematic uncertainty – flexible combination of spin direction every crossing IP 4 and IP 10 STAR and IP 12 PHENIX and PP 2 PP September 28, 2004 Yuji Goto (RIKEN/RBRC) 22

Store-by-store consistency • Charged hadrons – fitting 0. 5 Ge. V/c < p. T < 1 Ge. V/c < p. T < 2 Ge. V/c < p. T < 5 Ge. V/c September 28, 2004 Yuji Goto (RIKEN/RBRC) 23

Bunch shuffling • Charged hadrons – compare 2 distribution from shuffling – compare width of shuffled distribution September 28, 2004 Yuji Goto (RIKEN/RBRC) 24