Morozov

Spin Effects in Forward π0-Production in Polarized Proton-Proton Collisions at STAR : 

Spin Effects in Forward π0-Production in Polarized Proton-Proton Collisions at STAR Dmitry Morozov, IHEP (Protvino) for the STAR Collaboration

Outlook: 

Outlook Motivation STAR/FPD overview Single Spin Asymmetry at FPD Differential cross sections for forward π0-Production Separated xF and pT dependence of cross section Conclusions

Motivation: 

Motivation Sivers effect: Flavor dependent correlation between the proton spin (Sp), momentum (Pp) and transverse momentum (kT) of the unpolarized partons inside. The unpolarized parton distribution function fq(x,kT) is modified to: Collins effect: Correlation between the quark spin (sq), momentum (pq) and transverse momentum (kT) of the pion. The fragmentation function of transversely polarized quark q takes the form: p +p→p0+Х ∆qNfq – Sivers and ∆NDp/q- Collins Functions may produce azimuthal anisotropy

The STAR Collaboration: 

The STAR Collaboration 522 collaborators 51 institutions 12 countries Solenoid Tracker At RHIC

STAR detector layout: 

STAR detector layout TPC: -1.0 <  < 1.0 FTPC: 2.8 <  < 3.8 BBC : 2.2 <  < 5.0 EEMC:1 <  < 2 BEMC:0 <  < 1 FPD: || ~ 4.0 & ~3.7

Forward Pion Detector: 

Forward Pion Detector FPD module (7×7 matrix of Pb-Glass: 3.8 × 3.8 × 45 cm3) 7 Pb-Glass active preshower detectors Two 48-strip scintillator SMD Pb plate in front ~2.5 radiation lengths

Single Spin Asymmetry: 

Single Spin Asymmetry Definition: PBeam – beam polarization dσ↑(↓) – differential cross section of π0 then incoming proton has spin up(down) Two measurements: Single arm calorimeter: R – relative luminosity (by BBC) Two arms (left-right) calorimeter: No relative luminosity needed π0, xF<0 π0, xF>0 Left Right p  p positive AN: more p0 going left to polarized beam

First AN Measurement at STAR: 

First AN Measurement at STAR STAR collaboration Phys. Rev. Lett. 92 (2004) 171801 Sivers: spin and k correlation in parton distribution functions (initial state) Collins: spin and k correlation in fragmentation function (final state) Qiu and Sterman (initial state) / Koike (final state): twist-3 pQCD calculations, multi-parton correlations Can be described by several models: Similar to result from E704 experiment (√s=20 GeV, 0.5 < pT < 2.0 GeV/c) √s=200 GeV, <η> = 3.8

AN for Forward π0 at STAR: 

AN for Forward π0 at STAR Shown at SPIN 2004, Trieste, Italy The asymmetry is found to be zero for negative -0.6 < xF < -0.2 AN for positive xF is consistent with zero up to xF ~ 0.35, then increases with increasing xF Run2 (2002): <PBeam>(online) = 20%, integrated luminosity ~ 0.15 pb-1 Run3 (2003): <PBeam>(online) = 30%, integrated luminosity ~ 0.5 pb-1  more precise measurements

ppp0X cross sections at 200 GeV: 

The error bars are point-to-point systematic and statistical errors added in quadrature The inclusive differential cross section for p0 production is consistent with NLO pQCD calculations at 3.3 < η < 4.0 As η increases, systematics regarding the comparison with NLO pQCD calculations begin to emerge. The data at low pT are more consistent with the Kretzer set of fragmentation functions. Similar to what was observed by PHENIX. ppp0X cross sections at 200 GeV

Separated xF and pT dependence: 

Separated xF and pT dependence The data is represented in the way similar to J. Singh, et al Nucl. Phys. B140 (1978) 189 - ISR experiment at √s=45 GeV Cross sections fall with pT at fixed xF with exponent (~ 6) independent of xF Data show exponential dependence on xF with fixed pT = 2 GeV/c. The value of the fitted exponent (~5) may be sensitive to the interplay between hard and soft scattering processes Data accumulated in different running years with different calorimeters with different readout electronics taken at different angles Although

Conclusions: 

Conclusions Large spin effects have been found at forward p0 production in p p reaction at highest energy √s = 200 GeV The single spin asymmetry for positive xF is consistent with zero up to xF~0.35, then increases with increasing xF The asymmetry is found to be zero for negative xF The inclusive differential cross section for forward p0 production at √s = 200 GeV is consistent with NLO pQCD calculations, in contrast to what was observed at lower √s Mapping of the cross section in xF pT plane has begun … coming soon with analyzing power!

BACK-UP SLIDES: 

BACK-UP SLIDES

Systematics: 

Systematics Measurements utilizing independent calorimeters consistent within uncertainties Systematics: Normalization uncertainty = 16%: position uncertainty (dominant) Energy dependent uncertainty = 13% - 27%: energy calibration to 1% (dominant) background/bin migration correction kinematical constraints

MC & Data comparison: 

MC & Data comparison

Di-Photon Mass Reconstruction: 

Di-Photon Mass Reconstruction Clustering analysis Fit to measured and parameterized shower shape Applying cuts: Number of photons ≥ 2 Etot > 20 GeV Fiducial volume cut = 1/2 cell from the calorimeter edge Energy sharing (<0.3 for cross sections) Gains are determined from π0 peak position for each tower Energy dependent gain correction Run/Luminosity dependent gain correction MC to data comparison Pb-Glass calorimeter analysis includes: Mass resolution ~ 20 MeV The calibration is known at 2% level Efficiencies is geometrically determined (dominated by the geometrical acceptance of the calorimeter)

Cluster categorization: 

Cluster categorization

Time/luminosity dependent gain shift corrections: 

Time/luminosity dependent gain shift corrections