54959647
Cross section for $b\bar{b}$ production via dielectrons in d$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV
We report a measurement of $e^+e^-$ pairs from semileptonic heavy-flavor decays in $d$$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV. Exploring the mass and transverse-momentum dependence of the yield, the bottom decay contribution can be isolated from charm, and quantified by comparison to {\sc pythia} and {\sc mc@nlo} simulations. The resulting $b\bar{b}$-production cross section is $\sigma^{d{\rm Au}}_{b\bar{b}}=1.37{\pm}0.28({\rm stat}){\pm}0.46({\rm syst})$~mb, which is equivalent to a nucleon-nucleon cross section of $\sigma^{NN}_{bb}=3.4\pm0.8({\rm stat}){\pm}1.1({\rm syst})\ \mu$b.
119184536
Direct photons in Au+Au collisions measured with the PHENIX detector at RHIC
A major goal of experiments in heavy-ion physics is the characterization of the quark gluon plasma (QGP) produced in the collision of heavy ions at high energy. Direct photons are a particularly good probe of the produced medium because they do not interact strongly and so can escape the medium unmodified, carrying information about when the photon was produced. It is expected that direct photon contributions from different sources (QGP radiation, hard scattering, hadron gas radiation) dominate at different transverse momentum ranges. Low momentum direct photons are dominated by thermal radiation (both from the QGP and hadron gas), while high momentum direct photons dominantly come from hard parton scatterings in the initial collision. We present a summary of techniques to measure direct photons with the PHENIX detector, with a focus on low momentum direct photons through their external conversion to dilepton pairs.
59439853
Centrality categorization for Rp(d)+A in high-energy collisions
High-energy proton- and deuteron-nucleus collisions provide an excellent tool for studying a wide array of physics effects, including modifications of parton distribution functions in nuclei, gluon saturation, and color neutralization and hadronization in a nuclear environment, among others. All of these effects are expected to have a significant dependence on the size of the nuclear target and the impact parameter of the collision, also known as the collision centrality. In this article, we detail a method for determining centrality classes in p(d) + A collisions via cuts on the multiplicity at backward rapidity (i.e., the nucleus-going direction) and for determining systematic uncertainties in this procedure. For d + Au collisions at root s(NN) = 200 GeV we find that the connection to geometry is confirmed by measuring the fraction of events in which a neutron from the deuteron does not interact with the nucleus. As an application, we consider the nuclear modification factors Rp(d)+A, for which there is a bias in the measured centrality-dependent yields owing to auto correlations between the process of interest and the backward-rapidity multiplicity. We determine the bias-correction factors within this framework. This method is further tested using the HIJING Monte Carlo generator. We find that for d + Au collisions at root s(NN) = 200 GeV, these bias corrections are small and vary by less than 5% (10%) up to p(T) = 10 (20) GeV/c. In contrast, for p + Pb collisions at v root s(NN) = 5.02 TeV we find that these bias factors are an order of magnitude larger and strongly pT dependent, likely attributable to the larger effect of multiparton interactions.
10854369
Global study of nuclear structure functions
We present the results of a phenomenological study of unpolarized nuclear structure functions for a wide kinematical region of x and Q2. As a basis of our phenomenology we develop a model which takes into account a number of different nuclear effects including nuclear shadowing, Fermi motion and binding, nuclear pion excess and off-shell correction to bound nucleon structure functions. Within this approach we perform a statistical analysis of available data on the ratio of the nuclear structure functions F2 for different nuclei in the range from the deuteron to the lead. We express the off-shell effect and the effective scattering amplitude describing nuclear shadowing in terms of few parameters which are common to all nuclei and have a clear physical interpretation. The parameters are then extracted from statistical analysis of data. As a result, we obtain an excellent overall agreement between our calculations and data in the entire kinematical region of x and Q2. We discuss a number of applications of our model which include the calculation of the deuteron structure functions, nuclear valence and sea quark distributions and nuclear structure functions for neutrino charged-current scattering.
1529836
Search for a new gauge boson in π0 decays
Abstract A search was made for a new light gauge boson X which might be produced in π 0 → γ + X decay from neutral pions generated by 450 GeV protons in the CERN SPS neutrino target. The X's would penetrate the downstream shielding and be observed in the NOMAD detector via the Primakoff effect, in the process of X → π 0 conversion in the external Coulomb field of a nucleus. With 1.45×10 18 protons on target, 20 candidate events with energy between 8 and 140 GeV were found from the analysis of neutrino data. This number is in agreement with the expectation of 18.1±2.8 background events from standard neutrino processes. A new 90 % C.L. upper limit on the branching ratio Br ( π 0 → γ + X ) −5 for X masses ranging from 0 to 120 MeV/ c 2 is obtained.
17734109
Neutrino production of opposite sign dimuons in the NOMAD experiment
Abstract The NOMAD Collaboration presents a study of opposite sign dimuon events in the framework of Leading Order QCD. A total of 2714 neutrino- and 115 antineutrino-induced opposite sign dimuon events with E μ 1 , E μ 2 >4.5 GeV, 15 E ν Q 2 >1 ( GeV / c ) 2 are observed in the Front-Calorimeter of NOMAD during the 1995 and 1996 runs. The analysis yields a value for the charm quark mass of m c =1.3 +0.3+0.3 −0.3−0.3 GeV / c 2 and for the average semileptonic branching ratio of B c =0.095 +0.007+0.014 −0.007−0.013 . The ratio of the strange to non-strange sea in the nucleon is measured to be κ =0.48 +0.09+0.17 −0.07−0.12 . The measured rate of charm-induced dimuon relative to single muon, as a function of neutrino energy, is consistent with the slow rescaling hypothesis of heavy quark production.
110065803
Status of design and construction of the Transition Radiation Tracker (TRT) for the ATLAS experiment at the LHC
The ATLAS Inner Detector consists of three sub-systems, the Pixel Detector at the innermost radius, the Semi-Conductor Tracker at intermediate radii, and the Transition Radiation Tracker (TRT) at the outermost radius in front of the electromagnetic calorimeter. The TRT provides a combination of continuous tracking with many projective measurements based on individual drift-tubes (or straws) and of electron identification based on radiator fibres or foils interleaved between the straws themselves. This paper describes the current status of design and construction of the various components of the TRT: the assembly of the barrel modules has recently been completed, that of the end-cap wheels is well underway, and the on-detector front-end electronics is in production. The detector modules and front-end electronics boards will be integrated together over the next year, the barrel and end-cap TRT parts will be assembled and tested with their SCT counterparts during 2005 and installation and commissioning in the ATLAS pit will take place at the end of 2005 and the beginning of 2006. (C) 2004 Elsevier B.V. All rights reserved. (Less)
111076382
Uniformity of channel leakage current increase in silicon detectors after neutron irradiation
Results of a high statistics study to search for anomolous leakage current behaviour of silicon detector channels after neutron irradiation up to 1.5× 10 14 n cm −2 are presented.