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Register a new userConstraints on Delta G through Longitudinal Double Spin Asymmetry Measurements of Inclusive Jet Production in Polarized p+p Collisions at 200 GeV
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M. Sarsour
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We report measurements of the longitudinal double spin asymmetry for inclusive jet production using polarized p+p collisions at sqrt{s} = 200 GeV at RHIC. Results from the 2005 and 2006 runs are presented. These results set substantial new constraints on the polarized gluon distribution in the proton over the kinematic range 0.02 < x< 0.3, when compared to next-to-leading order global analyses of DIS data. The first measurement of the transverse single-spin asymmetry for inclusive jets at mid-rapidity is also presented.
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We present preliminary results for the first measurements of the double longitudinal spin asymmetry A_LL in inclusive jet production at mid-rapidity in polarized proton-proton collisions at sqrt(s) = 200 GeV. The data amount to ~ 0.5 pb-1 collected at RHIC in 2003 and 2004 with beam polarizations up to 45%. The jet transverse energies are in the range of 5 < pT < 17 GeV/c. The data are consistent with theoretical evaluations using deep-inelastic scattering parametrizations for gluon polarization in the nucleon, and tend to disfavor large positive values of gluon polarization.
We report high-precision measurements of the longitudinal double-spin asymmetry, $A_{LL}$, for midrapidity inclusive jet and dijet production in polarized $pp$ collisions at a center-of-mass energy of $sqrt{s}=200,mathrm{GeV}$. The new inclusive jet data are sensitive to the gluon helicity distribution, $Delta g(x,Q^2)$, for gluon momentum fractions in the range from $x simeq 0.05$ to $x simeq 0.5$, while the new dijet data provide further constraints on the $x$ dependence of $Delta g(x,Q^2)$. The results are in good agreement with previous measurements at $sqrt{s}=200,mathrm{GeV}$ and with recent theoretical evaluations of prior world data. Our new results have better precision and thus strengthen the evidence that $Delta g(x,Q^2)$ is positive for $x > 0.05$.
We report a measurement of the longitudinal double-spin asymmetry A_LL and the differential cross section for inclusive midrapidity jet production in polarized proton collisions at sqrt(s)=200 GeV. The cross section data cover transverse momenta 5 < pT < 50 GeV/c and agree with next-to-leading order perturbative QCD evaluations. The A_LL data cover 5 < pT < 17 GeV/c and disfavor at 98% C.L. maximal positive gluon polarization in the polarized nucleon.
We report on event structure and double helicity asymmetry ($A_LL$) of jet production in longitudinally polarized p+p collisions at $sqrt{s}$=200 GeV. Photons and charged particles were measured at midrapidity $|eta| < 0.35$ with the requirement of a high-momentum ($>2$ GeV/$c$) photon in each event. Measured event structure is compared with {sc pythia} and {sc geant} simulations. The shape of jets and the underlying event were well reproduced at this collision energy. For the measurement of jet $A_{LL}$, photons and charged particles were clustered with a seed-cone algorithm to obtain the cluster $p_T$ sum ($p_T^{rm reco}$). The effect of detector response and the underlying events on $p_T^{rm reco}$ was evaluated with the simulation. The production rate of reconstructed jets is satisfactorily reproduced with the NLO pQCD jet production cross section. For $4 < p_T^{rm reco} < 12$ GeV/$c$ with an average beam polarization of $< P > = 49%$ we measured $A_{LL} = -0.0014 pm 0.0037^{rm stat}$ at the lowest $p_T^{rm reco}$ bin (4-5 GeV/$c$) and $-0.0181 pm 0.0282^{rm stat}$ at the highest $p_T^{rm reco}$ bin (10-12 GeV/$c$) with a beam polarization scale error of 9.4% and a $pT$ scale error of 10%. Jets in the measured $p_T^{rm reco}$ range arise primarily from hard-scattered gluons with momentum fraction $0.02 < x < 0.3$ according to {sc pythia}. The measured $A_{LL}$ is compared with predictions that assume various $Delta G(x)$ distributions based on the GRSV parameterization. The present result imposes the limit $-1.1 < int_{0.02}^{0.3}dx Delta G(x, mu^2 = 1 {rm GeV}^2) < 0.4$ at 95% confidence level or $int_{0.02}^{0.3}dx Delta G(x, mu^2 = 1 {rm GeV}^2) < 0.5$ at 99% confidence level.
We report a new high-precision measurement of the mid-rapidity inclusive jet longitudinal double-spin asymmetry, $A_{LL}$, in polarized $pp$ collisions at center-of-mass energy $sqrt{s}=200$ GeV. The STAR data place stringent constraints on polarized parton distribution functions extracted at next-to-leading order from global analyses of inclusive deep inelastic scattering (DIS), semi-inclusive DIS, and RHIC $pp$ data. The measured asymmetries provide evidence for positive gluon polarization in the Bjorken-$x$ region $x>0.05$.
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