Longitudinal Double-spin Asymmetry and Cross Section for Inclusive Neutral Pion Production in Polarized Proton Collisions at [the Square Root of Sigma]

Longitudinal Double-spin Asymmetry and Cross Section for Inclusive Neutral Pion Production in Polarized Proton Collisions at [the Square Root of Sigma]
Author: Alan Michael Hoffman
Publisher:
Total Pages: 126
Release: 2009
Genre:
ISBN:

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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].

Neutral Pion Double Helicity Asymmetry in Polarized Proton-Proton Collisions at [the Square Root of Sigma]

Neutral Pion Double Helicity Asymmetry in Polarized Proton-Proton Collisions at [the Square Root of Sigma]
Author: William Axel Leight
Publisher:
Total Pages: 112
Release: 2012
Genre:
ISBN:

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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].

High Energy Physics

High Energy Physics
Author: Hesheng Chen
Publisher: World Scientific
Total Pages: 1424
Release: 2005-05-03
Genre: Science
ISBN: 9814481270

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The 32nd International Conference on High Energy Physics belongs to the Rochester Conference Series, and is the most important international conference in 2004 on high energy physics. The proceedings provide a comprehensive review on the recent developments in experimental and theoretical particle physics. The latest results on Top, Higgs search, CP violation, neutrino mixing, pentaquarks, heavy quark mesons and baryons, search for new particles and new phenomena, String theory, Extra dimension, Black hole and Lattice calculation are discussed extensively. The topics covered include not only those of main interest to the high energy physics community, but also recent research and future plans. Contents: Neutrino Masses and MixingsQuark Matter and Heavy Ion CollisionsParticle Astrophysics and CosmologyElectroweak PhysicsQCD Hard InteractionsQCD Soft InteractionsComputational Quantum Field TheoryCP Violation, Rare Kaon Decay and CKMR&D for Future Accelerator and DetectorHadron Spectroscopy and ExoticsHeavy Quark Mesons and BaryonsBeyond the Standard ModelString Theory Readership: Experimental and theoretical physicists and graduate students in the fields of particle physics, nuclear physics, astrophysics and cosmology.Keywords:High Energy Physics;Particle Physics;Electroweak;QCD;Heavy Quark;Neutrino;Particle Astrophysics;Hadron Spectroscopy;CP Violation;Quark Matter;Future Accelerator

VII Latin American Symposium on Nuclear Physics and Applications

VII Latin American Symposium on Nuclear Physics and Applications
Author: Ricardo Alarcon
Publisher: American Inst. of Physics
Total Pages: 538
Release: 2007-11-09
Genre: Science
ISBN: 9780735404618

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These proceedings aim to show the vitality and significance of nuclear science. The focus is the promotion of Nuclear Physics and its applications among Latin American laboratories and the international community. This Volume covers six main topics: Applications of Nuclear Physics, QCD in Nuclear Physics, Fundamental Symmetries and Neutrinos, Nuclear Structure and Reactions, Nuclear and Particle Astrophysics, and Facilities and Instrumentation.

Charge Multiplicity Asymmetry Correlation Study Searching for Local Parity Violation at RHIC for STAR Collaboration

Charge Multiplicity Asymmetry Correlation Study Searching for Local Parity Violation at RHIC for STAR Collaboration
Author: Quan Wang
Publisher: Springer Science & Business Media
Total Pages: 153
Release: 2013-08-13
Genre: Science
ISBN: 3319007564

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It has been suggested that local parity violation (LPV) in Quantum Chromodynamics (QCD) would lead to charge separation of quarks by the Chiral Magnetic Effect (CME) in heavy ion collisions. Charge Multiplicity Asymmetry Correlation Study Searching for Local Parity Violation at RHIC for STAR Collaboration presents the detailed study of charge separation with respect to the event plane. Results on charge multiplicity asymmetry in Au+Au and d+Au collisions at 200 GeV by the STAR experiment are reported. It was found that the correlation results could not be explained by CME alone. Additionally, the charge separation signal as a function of the measured azimuthal angle range as well as the event-by-event anisotropy parameter are studied. These results indicate that the charge separation effect appears to be in-plane rather than out-of-plane. It is discovered that the charge separation effect is proportional to the event-by-event azimuthal anisotropy and consistent with zero in events with zero azimuthal anisotropy. These studies suggest that the charge separation effect, within the statistical error, may be a net effect of event anisotropy and correlated particle production. A potential upper limit on the CME is also presented through this data.

Neutral Pion Production in Nucleus-nucleus Collisions at 158 and 200 GeV/nucleon

Neutral Pion Production in Nucleus-nucleus Collisions at 158 and 200 GeV/nucleon
Author:
Publisher:
Total Pages: 11
Release: 1998
Genre:
ISBN:

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Two years ago, at the 12th Winter Workshop on Nuclear Dynamics held here in Snowbird, the authors presented WA80 limits on direct photon production in 200-GeV 32S + Au collisions. It was found that the results were consistent (within 1[sigma]) with the absence of an excess of photons over those that can be accounted for by the two-photon decay branches of [pi]° and [eta] mesons and by the small photon contributions from other radiative decays. They are in the process of finalizing the direct-photon production results from collisions of lead nuclei at 158 GeV/nucleon. The author briefly discusses the status of the analysis and gives some preliminary results at the end of this talk. However, most of this presentation is concerned with a very different aspect of the photon measurements: distributions of neutral pions. In contrast to direct photons which probe initial collision conditions, hadrons, such as neutral pions, interact strongly and decouple late in the reaction evolution and, thus, provide information concerning the system at freeze out. Transverse momentum spectra at low and intermediate p{sub T} relate to thermodynamic and hydrodynamic descriptions of the hot, dense systems. In addition, the high-p{sub T} region reflects the hard-scattering regime and may help one understand initial-state particle production by forming a bridge to proton-proton and proton-nucleus results. It follows that it is essential that the [pi]° measurements cover a large p{sub T} range.

Proceedings of the 17th International Spin Physics Symposium

Proceedings of the 17th International Spin Physics Symposium
Author: Kenichi Imai
Publisher: American Inst. of Physics
Total Pages: 1196
Release: 2007-07-02
Genre: Science
ISBN:

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Getting down to the bottom line is what this proceedings digest is all about, as any physicist will tell you: spin is the fundamental concept in physics. The applications are pretty universal due to the fact that, using spin-related phenomena, physicists are trying to reveal the fundamental principles of nature – and things don’t come much more bottom-line than that. This volume is the proceedings of the 17th International Spin Physics Symposium which is a forum to discuss spin physics and related topics.

Measurement of Inclusive Production of Neutral Pions at High Transverse Momentum. [100 to 300 GeV/c, Scaling]

Measurement of Inclusive Production of Neutral Pions at High Transverse Momentum. [100 to 300 GeV/c, Scaling]
Author:
Publisher:
Total Pages:
Release: 1978
Genre:
ISBN:

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These are the results of a measurement of inclusive production at high transverse momentum (P perpendicular to) of neutral pions (.pi./sup 0/) from protons by beams of proton (p), kaon (K), pion (.pi.), and antiproton (antiproton) particles. The experiment used the Fermilab M2 beam line at momenta of 100, 200 and 300 GeV/c striking a liquid hydrogen target. The data include center of mass (cm) production angles of the .pi./sup 0/ between 2/sup 0/ and 115/sup 0/ for P perpendicular to greater than 1 GeV/c. A pair of differential Cherenkov counters distinguished the types of beam particles. The photon (.gamma.) detector of a lead and scintillator sandwich measured both photons from the .pi./sup 0/ .-->. 2.gamma. decay and enabled a reconstruction of the .pi./sup 0/ kinematics. The measurements show several remarkable features distinguishing the production rates for these different beams, including a forward peak in the cm for .pi.p collisions and much less .pi./sup 0/ production at high P perpendicular to in pp than in .pi.p or Kp collisions. A simple parametrization accurately represents the data over most of its range, showing approximate scaling in the radial variable x/sub R/ = 2P/.sqrt.s (in the cm). Several parton models are compared with the data. A heuristic picture in terms of the quark constituents of the interacting hadrons accounts for many features of the data in an intuitive way. 62 references.