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Measurement of Angular Distributions of Drell-Yan Dimuons in $p + p$ Interactions at 800 GeV/c

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 Added by Jen-Chieh Peng
 Publication date 2009
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and research's language is English




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We report a measurement of the angular distributions of Drell-Yan dimuons produced using an 800 GeV/c proton beam on a hydrogen target. The polar and azimuthal angular distribution parameters have been extracted over the kinematic range $4.5 < m_{mu mu} < 15$ GeV/c$^2$ (excluding the $Upsilon$ resonance region), $0 < p_T < 4 $ GeV/c, and $0 < x_F < 0.8$. The $p+p$ angular distributions are similar to those of $p+d$, and both data sets are compared with models which attribute the $cos 2 phi$ distribution either to the presence of the transverse-momentum-dependent Boer-Mulders structure function $h_1^perp$ or to QCD effects. The data indicate the presence of both mechanisms. The validity of the Lam-Tung relation in $p+p$ Drell-Yan is also tested.



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Results on $phi$ meson production in inelastic p+p collisions at CERN SPS energies are presented. They are derived from data collected by the NA61/SHINE fixed target experiment, by means of invariant mass spectra fits in the $phi to K^+K^-$ decay channel. They include the first ever measured double differential spectra of $phi$ mesons as a function of rapidity $y$ and transverse momentum $p_T$ for proton beam momenta of 80 GeV/c and 158 GeV/c, as well as single differential spectra of $y$ or $p_T$ for beam momentum of 40 GeV/c. The corresponding total $phi$ yields per inelastic p+p event are obtained. These results are compared with existing data on $phi$ meson production in p+p collisions. The comparison shows consistency but superior accuracy of the present measurements. The emission of $phi$ mesons in p+p reactions is confronted with that occurring in Pb+Pb collisions, and the experimental results are compared with model predictions. It appears that none of the considered models can properly describe all the experimental observables.
47 - Salvatore Fazio 2016
Accessing the Sivers TMD function in proton+proton collisions through the measurement of transverse single spin asymmetries (TSSAs) in Drell-Yan and weak boson production is an effective path to test the fundamental QCD prediction of the non-universality of the Sivers function. Furthermore, it provides data to study the spin-flavor structure of valence and sea quarks inside the proton and to test the evolution of parton distributions. The TSSA amplitude, $A_{N}$, has been measured at STAR in proton+proton collisions at $sqrt{s} = 500$ GeV, with a recorded integrated luminosity of 25 pb$^{-1}$. Within relatively large statistical uncertainties, the current data favor theoretical models that include a change of sign for the Sivers function relative to observations in SIDIS measurements, if TMD evolution effects are small. RHIC plans to run proton+proton collisions of transversely polarized beams at $sqrt{s} = 510$ GeV in 2017, delivering an integrated luminosity of 400 pb$^{-1}$. This will allow STAR to perform a precise measurement of TSSAs in both Drell-Yan and weak boson production. The present status and future plans for the Sivers function program at STAR will be discussed as well as other observables sensitive to the non-universality of the Sivers function in the Twist-3 framework, e.g. the TSSA of direct photons.
Inclusive production of $Lambda$-hyperons was measured with the large acceptance NA61/SHINE spectrometer at the CERN SPS in inelastic p+p interactions at beam momentum of 158~GeVc. Spectra of transverse momentum and transverse mass as well as distributions of rapidity and x$_{_F}$ are presented. The mean multiplicity was estimated to be $0.120,pm0.006;(stat.),pm 0.010;(sys.)$. The results are compared with previous measurements and predictions of the EPOS, UrQMD and FRITIOF models.
The Fermilab E866/NuSea Collaboration has measured the Drell-Yan dimuon cross sections in 800 GeV/$c$ $pp$ and $pd$ collisions. This represents the first measurement of the Drell-Yan cross section in $pp$ collisions over a broad kinematic region and the most extensive study to date of the Drell-Yan cross section in $pd$ collisions. The results indicate that recent global parton distribution fits provide a good description of the light antiquark sea in the nucleon over the Bjorken-$x$ range $0.03 lesssim x < 0.15$, but overestimate the valence quark distributions as $x to 1$.
We present measurements of the polarization of the $ J/psi $ produced in 800-GeV proton interactions with a copper target. Polarization of the $ J/psi $ is sensitive to the $ c bar{c} $ production and hadronization processes. A longitudinal polarization is observed at large $ x_{F} $, while at small $ x_{F} $ the state is produced essentially unpolarized or slightly transversely polarized. No significant variation of the polarization is observed versus $ p_{T} $.
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