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Register a new userLongitudinal Double-Spin Asymmetries for Dijet Production at Intermediate Pseudorapidity in Polarized $pp$ Collisions at $sqrt{s}$ = 200 GeV
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We present the first measurements of the longitudinal double-spin asymmetry $A_{LL}$ for dijets with at least one jet reconstructed within the pseudorapidity range $0.8 < eta < 1.8$. The dijets were measured in polarized $pp$ collisions at a center-of-mass energy $sqrt{s}$ = 200 GeV. Values for $A_{LL}$ are determined for several distinct event topologies, defined by the jet pseudorapidities, and span a range of parton momentum fraction $x$ down to $x sim$ 0.01. The measured asymmetries are found to be consistent with the predictions of global analyses that incorporate the results of previous RHIC measurements. They will provide new constraints on $Delta g(x)$ in this poorly constrained region when included in future global analyses.
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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 the first measurement of the inclusive jet and the dijet longitudinal double-spin asymmetries, $A_{LL}$, at midrapidity in polarized $pp$ collisions at a center-of-mass energy $sqrt{s} = 510$ GeV. The inclusive jet $A_{LL}$ measurement is sensitive to the gluon helicity distribution down to a gluon momentum fraction of $xapprox 0.015$, while the dijet measurements, separated into four jet-pair topologies, provide constraints on the $x$ dependence of the gluon polarization. Both results are consistent with previous measurements made at $sqrt{s}= 200$ GeV in the overlapping kinematic region, $x > 0.05$, and show good agreement with predictions from recent next-to-leading order global analyses.
We report the first measurement of the longitudinal double-spin asymmetry $A_{LL}$ for mid-rapidity di-jet production in polarized $pp$ collisions at a center-of-mass energy of $sqrt{s} = 200$ GeV. The di-jet cross section was measured and is shown to be consistent with next-to-leading order (NLO) perturbative QCD predictions. $A_{LL}$ results are presented for two distinct topologies, defined by the jet pseudorapidities, and are compared to predictions from several recent NLO global analyses. The measured asymmetries, the first such correlation measurements, support those analyses that find positive gluon polarization at the level of roughly 0.2 over the region of Bjorken-$x > 0.05$.
The differential cross section and spin asymmetries for neutral pions produced within the intermediate pseudorapidity range 0.8 < {eta} < 2.0 in polarized proton-proton collisions at sqrt{s} = 200 GeV are presented. Neutral pions were detected using the endcap electromagnetic calorimeter in the STAR detector at RHIC. The cross section was measured over a transverse momentum range of 5 < p_T < 16 GeV/c and is found to be within the scale uncertainty of a next-to-leading order perturbative QCD calculation. The longitudinal double-spin asymmetry, A_LL, is measured in the same pseudorapidity range. This quantity is sensitive to the gluonic contribution to the proton spin, {Delta}g(x), at low Bjorken-x (down to x approx 0.01), where it is less constrained by measurements at central pseudorapidity. The measured A_LL is consistent with model predictions. The parity-violating asymmetry, A_L, is also measured and found to be consistent with zero. The transverse single-spin asymmetry, A_N, is measured within a previously unexplored kinematic range in Feynman-x and p_T. Such measurements may aid our understanding of the on-set and kinematic dependence of the large asymmetries observed at more forward pseudorapidity ({eta} approx 3) and their underlying mechanisms. The A_N results presented are consistent with a twist-3 model prediction of a small asymmetry within the present kinematic range.
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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