Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userThe gluon spin contribution to the proton spin from the double helicity asymmetry in inclusive pi^0 production in polarized p+p collisions at sqrt(s)=200 GeV
137
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
The double helicity asymmetry in neutral pion production for p_T = 1 to 12 GeV/c has been measured with the PHENIX experiment in order to access the gluon spin contribution, Delta-G, to the proton spin. Measured asymmetries are consistent with zero, and at a theory scale of mu^2 = 4 GeV^2 give Delta-G^[0.02,0.3] = 0.1 to 0.2, with a constraint of -0.7 < Delta-G^[0.02,0.3] < 0.5 at Delta-chi^2 = 9 (~3 sigma) for our sampled gluon momentum fraction (x) range, 0.02 to 0.3. The results are obtained using predictions for our measured asymmetries generated from four representative fits to polarized deep inelastic scattering data. We also consider the dependence of the Delta-G constraint on the choice of theoretical scale, a dominant uncertainty in these predictions.
rate research
Read More
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.
The PHENIX experiment presents results from the RHIC 2006 run with polarized proton collisions at sqrt(s) = 62.4 GeV for inclusive pi^0 production at mid-rapidity. Unpolarized cross section results are measured for transverse momenta p_T = 0.5 to 7 GeV/c. Next-to-leading order perturbative quantum chromodynamics calculations are compared with the data, and while the calculations are consistent with the measurements, next-to-leading logarithmic corrections improve the agreement. Double helicity asymmetries A_LL are presented for p_T = 1 to 4 GeV/c and probe the higher range of Bjorken_x of the gluon (x_g) with better statistical precision than our previous measurements at sqrt(s)=200 GeV. These measurements are sensitive to the gluon polarization in the proton for 0.06 < x_g < 0.4.
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.
PHENIX measurements are presented for the cross section and double-helicity asymmetry ($A_{LL}$) in inclusive $pi^0$ production at midrapidity from $p$$+$$p$ collisions at $sqrt{s}=510$~GeV from data taken in 2012 and 2013 at the Relativistic Heavy Ion Collider. The next-to-leading-order perturbative-quantum-chromodynamics theory calculation is in excellent agreement with the presented cross section results. The calculation utilized parton-to-pion fragmentation functions from the recent DSS14 global analysis, which prefer a smaller gluon-to-pion fragmentation function. The $pi^{0}A_{LL}$ results follow an increasingly positive asymmetry trend with $p_T$ and $sqrt{s}$ with respect to the predictions and are in excellent agreement with the latest global analysis results. This analysis incorporated earlier results on $pi^0$ and jet $A_{LL}$, and suggested a positive contribution of gluon polarization to the spin of the proton $Delta G$ for the gluon momentum fraction range $x>0.05$. The data presented here extend to a currently unexplored region, down to $xsim0.01$, and thus provide additional constraints on the value of $Delta G$. The results confirm the evidence for nonzero $Delta G$ using a different production channel in a complementary kinematic region.
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 $x > 0.05$.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
