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Full-Text Articles in Physics

Cross Sections And Double-Helicity Asymmetries Of Midrapidity Inclusive Charged Hadrons In P Plus P Collisions At Root S = 62.4 Gev, Andrew Adare, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, Alexey Yu. Semenov, Carla Vale, Feng Wei, Et Al., Phenix Collaboration Nov 2012

Cross Sections And Double-Helicity Asymmetries Of Midrapidity Inclusive Charged Hadrons In P Plus P Collisions At Root S = 62.4 Gev, Andrew Adare, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, Alexey Yu. Semenov, Carla Vale, Feng Wei, Et Al., Phenix Collaboration

Physics and Astronomy Publications

Unpolarized cross sections and double-helicity asymmetries of single-inclusive positive and negative charged hadrons at midrapidity from p + p collisions at root s = 62.4 GeV are presented. The PHENIX measurement of the cross sections for 1.0 < p(T) < 4.5 GeV/c are consistent with perturbative QCD calculations at next-to-leading order in the strong-coupling constant, alpha(s). Resummed pQCD calculations including terms with next-to-leading-log accuracy, yielding reduced theoretical uncertainties, also agree with the data. The double-helicity asymmetry, sensitive at leading order to the gluon polarization in a momentum-fraction range of 0.05 less than or similar to x(gluon) less than or similar to 0.2, is consistent with recent global parametrizations disfavoring large gluon polarization.


Direct Photon Production In P Plus P Collisions At Root S=200 Gev At Midrapidity, Andrew Adare, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, Alexey Yu. Semenov, Carla Vale, Feng Wei, Et Al., Phenix Collaboration Oct 2012

Direct Photon Production In P Plus P Collisions At Root S=200 Gev At Midrapidity, Andrew Adare, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, Alexey Yu. Semenov, Carla Vale, Feng Wei, Et Al., Phenix Collaboration

Physics and Astronomy Publications

The differential cross section for the production of direct photons in p + p collisions at root s = 200 GeV at midrapidity was measured in the PHENIX detector at the Relativistic Heavy Ion Collider. Inclusive direct photons were measured in the transverse momentum range from 5: 5-25 GeV/c, extending the range beyond previous measurements. Event structure was studied with an isolation criterion. Next-to-leading-order perturbative-quantum-chromodynamics calculations give a good description of the spectrum. When the cross section is expressed versus x(T), the PHENIX data are seen to be in agreement with measurements from other experiments at different center-of-mass energies.


Evolution Of Pi(0) Suppression In Au Plus Au Collisions From Root S(Nn)=39 To 200 Gev, Andrew Adare, Lei Ding, Alan Dion, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, C. L. Silva, Feng Wei, Et Al., Phenix Collaboration Oct 2012

Evolution Of Pi(0) Suppression In Au Plus Au Collisions From Root S(Nn)=39 To 200 Gev, Andrew Adare, Lei Ding, Alan Dion, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, C. L. Silva, Feng Wei, Et Al., Phenix Collaboration

Physics and Astronomy Publications

Neutral-pion pi(0) spectra were measured at midrapidity (vertical bar y vertical bar < 0.35) in Au + Au collisions at root s(NN) = 39 and 62.4 GeV and compared with earlier measurements at 200 GeV in a transverse-momentum range of 1 < p(T) < 10 GeV/c. The high-p(T) tail is well described by a power law in all cases, and the powers decrease significantly with decreasing center-of-mass energy. The change of powers is very similar to that observed in the corresponding spectra for p + p collisions. The nuclear modification factors (RAA) show significant suppression, with a distinct energy, centrality, and p(T) dependence. Above p(T) = 7 GeV/c, R-AA is similar for root sNN = 62.4 and 200 GeV at all centralities. Perturbative-quantum-chromodynamics calculations that describe R-AA well at 200 GeV fail to describe the 39 GeV data, raising the possibility that, for the same p(T) region, the relative importance of initial-state effects and soft processes increases at lower energies. The p(T) range where pi(0) spectra in central Au + Au collisions have the same power as in p + p collisions is approximate to 5 and 7 GeV/c for root sNN = 200 and 62.4 GeV, respectively. For the root sNN = 39 GeV data, it is not clear whether such a region is reached, and the x(T) dependence of the x(T)-scaling power-law exponent is very different from that observed in the root sNN = 62 and 200 GeV data, providing further evidence that initial-state effects and soft processes mask the in-medium suppression of hardscattered partons to higher p(T) as the collision energy decreases.


Measurement Of Direct Photons In Au Plus Au Collisions At Root S(Nn)=200 Gev, S. Afanasiev, Sergey Belikov, Paul Constantin, Nathan Conrad Grau, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Jan Rak, Marzia Rosati, S. Skutnik, Carla Vale, Et Al., Phenix Collaboration Oct 2012

Measurement Of Direct Photons In Au Plus Au Collisions At Root S(Nn)=200 Gev, S. Afanasiev, Sergey Belikov, Paul Constantin, Nathan Conrad Grau, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Jan Rak, Marzia Rosati, S. Skutnik, Carla Vale, Et Al., Phenix Collaboration

Physics and Astronomy Publications

We report the measurement of direct photons at midrapidity in Au + Au collisions at root s(NN) = 200 GeV. The direct photon signal was extracted for the transverse momentum range of 4 GeV/c < pT < 22 GeV/c, using a statistical method to subtract decay photons from the inclusive photon sample. The direct photon nuclear modification factor R-AA was calculated as a function of p(T) for different Au + Au collision centralities using the measured p + p direct photon spectrum and compared to theoretical predictions. R-AA was found to be consistent with unity for all centralities over the entire measured pT range. Theoretical models that account for modifications of initial direct photon production due to modified parton distribution functions in Au and the different isospin composition of the nuclei predict a modest change of R-AA from unity. They are consistent with the data. Models with compensating effects of the quark-gluon plasma on high-energy photons, such as suppression of jet-fragmentation photons and induced-photon bremsstrahlung from partons traversing the medium, are also consistent with this measurement.


Observation Of Direct-Photon Collective Flow In Au Plus Au Collisions At Root S(Nn)=200 Gev, Andrew Adare, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, Alexey Yu. Semenov, Carla Vale, Feng Wei, Et Al., Phenix Collaboration Sep 2012

Observation Of Direct-Photon Collective Flow In Au Plus Au Collisions At Root S(Nn)=200 Gev, Andrew Adare, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, Alexey Yu. Semenov, Carla Vale, Feng Wei, Et Al., Phenix Collaboration

Physics and Astronomy Publications

The second Fourier component v(2) of the azimuthal anisotropy with respect to the reaction plane is measured for direct photons at midrapidity and transverse momentum (p(T)) of 1-12 GeV/c in Au + Au collisions at root s(NN) = 200 GeV. Previous measurements of this quantity for hadrons with p(T) < 6 GeV/c indicate that the medium behaves like a nearly perfect fluid, while for p(T) > 6 GeV/c a reduced anisotropy is interpreted in terms of a path-length dependence for parton energy loss. In this measurement with the PHENIX detector at the Relativistic Heavy Ion Collider we find that for p(T) > 4 GeV/c the anisotropy for direct photons is consistent with ...


Ground And Excited State Charmonium Production In P Plus P Collisions At Root S=200 Gev, Andrew Adare, Alan Dion, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, Alexey Yu. Semenov, C. L. Silva, Carla Vale, Feng Wei, Et Al., Phenix Collaboration May 2012

Ground And Excited State Charmonium Production In P Plus P Collisions At Root S=200 Gev, Andrew Adare, Alan Dion, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, Alexey Yu. Semenov, C. L. Silva, Carla Vale, Feng Wei, Et Al., Phenix Collaboration

Physics and Astronomy Publications

We report on charmonium measurements [J/psi (1S), psi' (2S), and chi(c) (1P)] in p + p collisions at root s = 200 GeV. We find that the fraction of J/psi coming from the feed-down decay of psi' and chi(c) in the midrapidity region (vertical bar y vertical bar < 0: 35) is 9.6 +/- 2.4% and 32 +/- 9%, respectively. We also present the p(T) and rapidity dependencies of the J/psi yield measured via dielectron decay at midrapidity (vertical bar y vertical bar < 0.35) and via dimuon decay at forward rapidity (1.2 < vertical bar y vertical bar < 2.2). The statistical precision greatly exceeds that reported in our previous publication [Phys. Rev. Lett. 98, 232002 (2007)]. The new results are compared with other experiments and discussed in the context of current charmonium production models.


Search For A Heavy Charged Gauge Boson Decaying To A Muon And A Neutrino In 1 Fb-1 Of Proton-Proton Collisions At Sqrt(S) = 7 Tev Using The Atlas Detector, Alaettin Serhan Mete Jan 2012

Search For A Heavy Charged Gauge Boson Decaying To A Muon And A Neutrino In 1 Fb-1 Of Proton-Proton Collisions At Sqrt(S) = 7 Tev Using The Atlas Detector, Alaettin Serhan Mete

Graduate Theses and Dissertations

The ATLAS detector is used to search for high-mass states, such as heavy charged gauge bosons (W'), decaying to a muon and a neutrino. Results are presented based on the analysis of pp collisions at a center-of-mass energy of 7 TeV corresponding to an integrated luminosity of 1.04 fb-1. No excess beyond standard model expectations is observed. A W' with sequential standard model couplings is excluded at 95% confidence level for masses below 1.98 TeV. Results from the muon channel are also combined with the electron channel to further extend the mass limit up to 2.15 TeV ...


Measurement Of The Drell-Yan Differential Cross-Section D(Sigma)/D(Pt) At High Dilepton Mass In Proton-Proton Collisions At Sqrt(S) = 7 Tev With The Atlas Detector, Kyoko Yamamoto Jan 2012

Measurement Of The Drell-Yan Differential Cross-Section D(Sigma)/D(Pt) At High Dilepton Mass In Proton-Proton Collisions At Sqrt(S) = 7 Tev With The Atlas Detector, Kyoko Yamamoto

Graduate Theses and Dissertations

A measurement of the Drell-Yan transverse momentum (pTμμ) distribution above the Z-boson mass region (116 GeV < Mμμ) in proton-proton collisions at a center-of-mass energy of 7 TeV is presented. Results are obtained using Z/γ* → μ+μ- decays in a data sample collected with the ATLAS detector at the LHC, corresponding to an integrated luminosity of 36 pb-1. The normalized differential cross-section is measured up to pTμμ of 180 GeV. We measure the ratio of the pTμμ distribution in the high mass region to that in the Z-boson mass region and multiply it with ...