Charged Pion Cross Sections And Double Helicity Asymmetries In Polarized P P Collisions At S PDF Download
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| Release | : 2015 |
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Download Charged-pion Cross Sections and Double-helicity Asymmetries in Polarized P+p Collisions at S Book in PDF, ePub and Kindle
In this paper, we present midrapidity charged-pion invariant cross sections, the ratio of the ?- to ?+ cross sections and the charge-separated double-spin asymmetries in polarized p+p collisions at s=200 GeV. While the cross section measurements are consistent within the errors of next-to-leading-order (NLO) perturbative quantum chromodynamics predictions (pQCD), the same calculations overestimate the ratio of the charged-pion cross sections. This discrepancy arises from the cancellation of the substantial systematic errors associated with the NLO-pQCD predictions in the ratio and highlights the constraints these data will place on flavor-dependent pion fragmentation functions. Lastly, the charge-separated pion asymmetries presented here sample an x range of 0̃.03–0.16 and provide unique information on the sign of the gluon-helicity distribution.
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| Release | : 2015 |
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Download Charged-pion Cross Sections and Double-helicity Asymmetries in Polarized [math Display Book in PDF, ePub and Kindle
In this paper, we present midrapidity charged-pion invariant cross sections, the ratio of the [pi]- to [pi]+ cross sections and the charge-separated double-spin asymmetries in polarized p+p collisions at s=200 GeV. While the cross section measurements are consistent within the errors of next-to-leading-order (NLO) perturbative quantum chromodynamics predictions (pQCD), the same calculations overestimate the ratio of the charged-pion cross sections. This discrepancy arises from the cancellation of the substantial systematic errors associated with the NLO-pQCD predictions in the ratio and highlights the constraints these data will place on flavor-dependent pion fragmentation functions. Lastly, the charge-separated pion asymmetries presented here sample an x range of ~0.03-0.16 and provide unique information on the sign of the gluon-helicity distribution.
| Author | : James Prewitt Hays-Wehle |
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| Total Pages | : 83 |
| Release | : 2013 |
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Download Measurement of Double Longitudinal Spin Asymmetry of Jet-[pi] +/- Correlations in Polarized Proton-proton Collisions at [square Root Of] S Book in PDF, ePub and Kindle
Inclusive measurements from polarized proton-proton collisions at RHIC have constrained [Delta]g, the polarized gluon distribution function of the proton. Correlation observables, such as this pion+jet measurement, allow for reconstruction of initial parton kinematics and are thus sensitive to the x dependence of [Delta]g. By measuring charged pions opposite a jet, this particular measurement can be sensitive to the flavor of the struck parton. This measurement, which is dominated by the quark-gluon subprocess, can be divided into terms proportional to [Delta]u[Delta]g and [Delta]d[Delta]g. The relatively larger quark polarization amplifies the measured asymmetry thereby enhancing the statistical power. This thesis presents the result of the mid-rapidity pion+jet longitudinal double spin asymmetry analysis from 10.6 pb-1 of luminosity collected in the 2009 200 GeV p+p run.
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| Release | : 2005 |
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Download Beam-Helicity Asymmetries in Double-Charged-Pion Photoproduction on the Proton Book in PDF, ePub and Kindle
Beam-helicity asymmetries for the two-pion-photoproduction reaction gamma + p --> p pi+ pi- have been studied for the first time in the resonance region for center-of-mass energies between 1.35 GeV and 2.30 GeV. The experiment was performed at Jefferson Lab with the CEBAF Large Acceptance Spectrometer using circularly polarized tagged photons incident on an unpolarized hydrogen target. Beam-helicity-dependent angular distributions of the final-state particles were measured. The large cross-section asymmetries exhibit strong sensitivity to the kinematics and dynamics of the reaction. The data are compared with the results of various phenomenological model calculations, and show that these models currently do not provide an adequate description for the behavior of this new observable.
| Author | : William Axel Leight |
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| Total Pages | : 112 |
| Release | : 2012 |
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Download Neutral Pion Double Helicity Asymmetry in Polarized Proton-Proton Collisions at [the Square Root of Sigma] Book in PDF, ePub and Kindle
One of the primary goals of the spin physics program at the STAR experiment is to constrain the polarized gluon distribution function, [delta]g(X,Q2), by measuring the double longitudinal spin asymmetry, ALL, of various final-state channels. Neutral pions provide a potentially powerful final state because they are copiously produced in p+p collisions and have few backgrounds. In 2009, STAR took 14 pb-1 of integrated luminosity of 200 GeV p+p collisions, with average beam longitudinal polarization of 59%. Neutral pions produced in these collisions can be identified using STAR's large-acceptance electromagnetic calorimeter, with help from tracking from the STAR Time Projection Chamber. This work presents a measurement of the inclusive neutral pion ALL from this data, based on a new [pi]0 reconstruction algorithm. A comparison to theoretical predictions and other experimental results suggests that the current best-fit value of AG, the gluon contribution to the proton spin, is too small and that [delta]G is actually comparable in magnitude to the quark contribution to the proton spin [delta][sigma].
| Author | : Adam Philip Kocoloski |
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| Total Pages | : 105 |
| Release | : 2010 |
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Download Measurement of Longitudinal Double Spin Asymmetries of [pi]+/- Production in P[over-arrow] + P[over-arrow] Collisions at [sqrt]s Book in PDF, ePub and Kindle
Spin dependent measurements provide incisive tests for modern theories of particle physics. The discovery that the integral of the quark helicity distribution is much too small to account for the spin of the proton is an excellent case in point. It inspired an intense period of theoretical scrutiny and a new generation of experiments to study [Delta]g, the helicity distribution of gluons in the nucleon. In particular, the unique polarized proton collider at RHIC enables a class of asymmetry measurements that are directly sensitive to gluon polarization. The STAR experiment at RHIC measures the double spin asymmetry A[subscript LL] for a variety of final states in collisions of longitudinally polarized protons in order to constrain [Delta]g. Asymmetries for mid-rapidity charged pion production benefit from large cross sections and the excellent tracking and particle identification capabilities of the STAR Time Projection Chamber. This thesis presents the first measurements of charged pion A[subscript LL] at STAR. The measurements are compared to predictions based on perturbative QCD calculations and from this comparison model-dependent constraints are placed on the integral gluon polarization [Delta]G.
| Author | : Alan Michael Hoffman |
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| Total Pages | : 126 |
| Release | : 2009 |
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Download Longitudinal Double-spin Asymmetry and Cross Section for Inclusive Neutral Pion Production in Polarized Proton Collisions at [the Square Root of Sigma] Book in PDF, ePub and Kindle
Twenty years of polarized lepton-nucleon scattering experiments have found that the contribution from quark spins (1/2[delta] [sigma]) to the spin of the proton is only ~ 35%. This has lead researchers to look elsewhere, specifically to gluon spin ([delta sigma]) for a large contribution to proton spin. [delta sigma] has been only loosely constrained in polarized DIS and SIDIS experiments. Polarized proton-proton collisions at RHIC provide sensitivity to [delta sigma] through measurements of the longitudinal double-spin asymmetry, ALL. This work presents a measurement of ALL for inclusive 7ro production in polarized proton-proton collisions using the STAR detector and data from RHIC Run 6. 7r0s are abundantly produced at mid-rapidity in proton-proton collisions, making them natural candidates for studies of [delta] [sigma]. Novel techniques for reconstructing 7ros at STAR are discussed, and a measurement of the unpolarized cross section presented. Finally, the measured ALL is compared to perturbative QCD predictions and from this comparison constraints are placed on [delta] [sigma].
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| Release | : 2016 |
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Download Inclusive Cross Section and Double-helicity Asymmetry for [math Display Book in PDF, ePub and Kindle
We present PHENIX measurements for the cross section and double-helicity asymmetry (ALL) in inclusive [pi]0 production at midrapidity from p + p collisions at √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. Our [pi]0ALL results follow an increasingly positive asymmetry trend with pT and √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 ALL 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. Finally, the data presented here extend to a currently unexplored region, down to x similar to 0.01, and thus provide additional constraints on the value of [Delta]G.
| Author | : Albert M. Sirunyan |
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| Release | : 2020 |
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Download Measurements of the W Boson Rapidity, Helicity, Double-differential Cross Sections, and Charge Asymmetry in Pp Collisions at √s Book in PDF, ePub and Kindle
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| Release | : 2008 |
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Download Measurements of the Double Helicity Asymmetry in Pion Production in Proton Collisions at [square Root Of] Book in PDF, ePub and Kindle
