Longitudinal double-spin asymmetry and cross section for inclusive jet production in polarized proton collisions at sqrt(s) = 200 GeV

Abstract

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.

Figures (3)

• Figure 1: Jet profile $\Psi(\Delta r,r_{\rm{cone}},p_\mathrm{T})$ versus inner cone size $\Delta r$ at $r_{\rm{cone}}= 0.4$ for MB (open squares) and HT (filled circles) data compared with STAR Monte Carlo simulation in two jet $p_\mathrm{T}$ bins (a) $5.0 < p_\mathrm{T} < 6.2$ and (b) $14.1 < p_\mathrm{T} < 17.3\,\mathrm{GeV/c}$. In (b) the MB jet yield was too small to measure.
• Figure 2: (a) Inclusive differential cross section for $p+p \rightarrow {\rm{jet}} +X$ at $\sqrt{s} = 200\,\mathrm{GeV}$ versus jet $p_\mathrm{T}$ for a jet cone radius of $0.4$. The symbols show MB (open squares) and HT (filled circles) data from the years 2003 and 2004 combined. The horizontal bars indicate the ranges of the $p_\mathrm{T}$ intervals. The curve shows a NLO calculationJager:2004. (b) Comparison of theory and data. The band indicates the experimental systematic uncertainty. The upper (lower) dashed line indicates the relative change of the NLO calculation when it is evaluated at $\mu = p_\mathrm{T}/2$ ($\mu = 2p_\mathrm{T}$).
• Figure 3: The longitudinal double-spin asymmetry $A_{LL}$ in $\vec{p}+\vec{p} \rightarrow {\rm{jet}} +X$ at $\sqrt{s} = 200\,\mathrm{GeV}$ versus jet $p_\mathrm{T}$. The uncertainties on the data points are statistical. The gray band indicates the systematic uncertainty from the beam polarization measurement, and the hatched band the total systematic uncertainty. The curves show predictions based on deep-inelastic scattering parametrizations of gluon polarization Jager:2004CTEQ6:2004.