Search results for "nuclear physics"
showing 10 items of 5307 documents
Model discriminating power ofμ→econversion in nuclei
2009
13 pages, 12 figures, 1 table.-- PACS nrs.: 13.35.Bv; 11.30.Hv.-- ArXiv pre-print available at: http://arxiv.org/abs/0904.0957
QCD JETS AT HERA I.: O(αs) RADIATIVE CORRECTIONS TO ELECTROWEAK CROSS SECTIONS AND JET RATES
1989
We present the complete O(αs) corrections to the electroweak cross sections of both neutral current and charged current deep inelastic e±p scattering including lepton polarization effects. Changes in the cross section due to the inclusion of next-to-leading-log (NLL) effects are parametrized by K factors, which are defined as the ratio of the NLL O(αs) cross sections and the Born cross section. Using the standard redefinition scheme of the parton densities, we find that the K factors deviate substantially from unity for small values of the Bjorken-Scaling variable x. We also elaborate on problems that arise when defining jet cross sections in ep scattering and present numerical results for…
Charged-pion cross sections and double-helicity asymmetries in polarizedp+pcollisions ats=200 GeV
2015
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 root s = p + 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. The char…
Direct photon production in Pb–Pb collisions atsNN=2.76 TeV
2016
Direct photon production at mid-rapidity in Pb–Pb collisions at √sNN = 2.76 TeV was studied in the transverse momentum range 0.9<pT<14 GeV/c. Photons were detected with the highly segmented electromagnetic calorimeter PHOS and via conversions in the ALICE detector material with the e+e− pair reconstructed in the central tracking system. The results of the two methods were combined and direct photon spectra were measured for the 0–20%, 20–40%, and 40–80% centrality classes. For all three classes, agreement was found with perturbative QCD calculations for pT≳5 GeV/c. Direct photon spectra down to pT≈1 GeV/c could be extracted for the 20–40% and 0–20% centrality classes. The significance of th…
The Institute for Nuclear Physics at the University of Mainz
2008
MAMI, the MAinz MIcrotron, has become a synonym for a cw electron scattering facility in the 1.5 14;GeV range with an outstanding beam quality and reliability. The Institute for Nuclear Physics (IKP) at the Johannes Gutenberg-University of Mainz, the home of MAMI, has developed and built this cascade of four recirculating machines for precision scattering experiments mostly with polarized electrons and photons for research in the field of hadron and nuclear physics. The central physics topic is the investigation of strongly interacting systems with the electroweak probe. This field, nowadays called strong QCD, which means QCD in the strongly coupled, non perturbative regime, still poses a n…
Measurement of the production cross section of an isolated photon associated with jets in proton-proton collisions ats=7 TeVwith the ATLAS detector
2012
A measurement of the cross section for the production of an isolated photon in association with jets in proton-proton collisions at a center-of-mass energy root s = 7 TeV is presented. Photons are ...
High-ET isolated-photon plus jets production in pp collisions at s=8 TeV with the ATLAS detector
2017
The dynamics of isolated-photon plus one-, two- and three-jet production in pp collisions at a centre-of-mass energy of 8 TeV are studied with the ATLAS detector at the LHC using a data set with an ...
Bottomonium spectroscopy and radiative transitions involving theχbJ(1P,2P)states atBaBar
2014
We use (121±1) million Υ(3S) and (98±1) million Υ(2S) mesons recorded by the BABAR detector at the PEP-II e^+e^− collider at SLAC to perform a study of radiative transitions involving the χ_(bJ)(1P,2P) states in exclusive decays with μ^+μ^−γγ final states. We reconstruct twelve channels in four cascades using two complementary methods. In the first we identify both signal photon candidates in the electromagnetic calorimeter (EMC), employ a calorimeter timing-based technique to reduce backgrounds, and determine branching-ratio products and fine mass splittings. These results include the best observational significance yet for the χ_(b0)(2P)→γΥ(2S) and χ_(b0)(1P)→γΥ(1S) transitions. In the se…
Prospects of medium tomography using back-to-back hadron correlations
2006
We discuss the prospects of extracting information about the bulk QCD matter distribution and evolution on the basis of hard hadronic back-to-back correlations in ultrarelativistic heavy-ion collisions. Using both hydrodynamical and parametrized evolution models for the spacetime evolution of the produced matter, which have been tested against RHIC data, we study six different setups for the spacetime dependence of hard-parton energy losses. Assuming that the energy loss of hard partons traversing the medium is radiative and calculable in the BDMPS formalism, we adjust one parameter, the quenching power scale, to the measured R_AA in each of the setups and study the systematic variations of…
In-medium jet shape from energy collimation in parton showers: Comparison with CMS PbPb data at 2.76 TeV
2014
We present the medium-modified energy collimation in the leading-logarithmic approximation (LLA) and next-to-leading-logarithmic approximation (NLLA) of QCD. As a consequence of more accurate kinematic considerations in the argument of the Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (DGLAP) fragmentation functions (FFs) we find a new NLLA correction ${\cal O}(\alpha_s)$ which accounts for the scaling violation of DGLAP FFs at small $x$. The jet shape is derived from the energy collimation within the same approximations and we also compare our calculations for the energy collimation with the event generators Pythia 6 and YaJEM for the first time in this paper. The modification of jets by the …