The study of elastic bremsstrahlung and electron tagging in electron-proton or ion collisions is gaining importance with the planned construction of several experimental facilities focused on ...deep-inelastic scattering (DIS) measurements. This paper describes a program which generates bremsstrahlung photons in electron-proton and electron-ion interactions as well as scattered electrons in bremsstrahlung processes and in a quasi-real photon approximation to the general DIS process. The effects of electron beam divergence and the spread of the interaction vertex are implemented. The program can be used as an input to simulations of instrumentation for bremsstrahlung photon detection, luminosity measurements, electron tagging, and the determination of the cross sections of corresponding processes.
Program Title: GETaLM
CPC Library link to program files:https://doi.org/10.17632/pynthy4j43.1
Developer's repository link:https://github.com/adamjaro/GETaLM
Licensing provisions: GNU GPLv3
Programming language: Python
External routines: ROOT
Nature of problem: Photons due to relativistic bremsstrahlung processes are produced in collisions of electrons with protons and with ions. Detection of these bremsstrahlung photons is a promising method for luminosity measurements. The detection of electrons scattered at small angles will impact these measurements. The program generates the bremsstrahlung photons along with final state electrons in the bremsstrahlung process and in an approximation to general electron-proton scattering.
Solution method: Analytic formulas for the cross sections of the specific processes and the relativistic kinematics are used to generate the photons and scattered electrons. A set of effects imposed by the interacting beams can be applied to the generated particles. The output of the program is created using the ROOT program. Total cross sections are obtained by integrating the specific cross section formulas over a given kinematic region.
Additional comments including restrictions and unusual features: Currently the electron and proton (ion) beams are assumed to collide head-on, no crossing angle is considered.
The study of elastic bremsstrahlung and electron tagging in electron-proton or ion collisions is gaining importance with the planned construction of several experimental facilities focused on ...deep-inelastic scattering (DIS) measurements. This paper describes a program which generates bremsstrahlung photons in electron-proton and electron-ion interactions as well as scattered electrons in bremsstrahlung processes and in a quasi-real photon approximation to the general DIS process. Here, the effects of electron beam divergence and the spread of the interaction vertex are implemented. The program can be used as an input to simulations of instrumentation for bremsstrahlung photon detection, luminosity measurements, electron tagging, and the determination of the cross sections of corresponding processes.
We report systematic measurements of bulk properties of the system created in Au+Au collisions at √SNN = 14.5 GeV recorded by the STAR detector at the Relativistic Heavy Ion Collider (RHIC). The ...transverse momentum spectra of π±, K± and p(p¯) are studied at mid-rapidity (|y| < 0.1) for nine centrality intervals. The centrality, transverse momentum (pT), and pseudorapidity (η) 3 dependence of inclusive charged particle elliptic flow (v2), and rapidity-odd charged particles directed flow (v1) results near mid-rapidity are also presented. These measurements are compared with the published results from Au+Au collisions at other energies, and from Pb+Pb collisions at √SNN =2.76 TeV. The results at √SNN = 14.5 GeV show similar behavior as established at other energies and fit well in the energy dependence trend. Furthermore, these results are important as the 14.5 GeV energy fills the gap in μB, which is of the order of 100 MeV, between √SNN =11.5 and 19.6 GeV. Comparisons of the data with UrQMD and AMPT models show poor agreement in general.
We report the first measurement of rapidity-odd directed flow (v1) for D0 and D¯0 mesons at mid-rapidity (|y| < 0.8) in Au+Au collisions at √sNN = 200 GeV using the STAR detector at the Relativistic ...Heavy Ion Collider. In 10–80% Au+Au collisions, the slope of the v1 rapidity dependence (dv1/dy), averaged over D0 and D¯0 mesons, is -0.080 ± 0.017 (stat.) ± 0.016 (syst.) for transverse 3 momentum pT above 1.5 GeV/c. The absolute value of D0-meson dv1/dy is about 25 times larger than that for charged kaons, with 3.4σ significance. Here, these data give a unique insight into the initial tilt of the produced matter, and offer constraints on the geometric and transport parameters of the hot QCD medium created in relativistic heavy-ion collisions.
Ultra-relativistic heavy ions generate strong electromagnetic fields which offer the possibility to study gamma-gamma, gamma-nucleus and gamma-proton processes at the LHC in ultra-peripheral Pb-Pb ...and p-Pb collisions. Exclusive photoproduction of J/ψ vector mesons is sensitive to the gluon distribution of the target. Here we report on the ALICE measurement of J/ψ coherent photoproduction in Pb-Pb ultra-peripheral collisions at √sNN = 2.76 TeV for the rapidity ranges -3.6 < y < -2.6 and |y| < 0.9, and on preliminary results on the J/ψ photoproduction in p-Pb at √sNN = 5.02 TeV. The J/ψ mesons have been identified through their leptonic decays.
The longitudinal spin transfer DLL to Λ and $\bar{Λ}$ hyperons produced in high-energy polarized proton–proton collisions is expected to be sensitive to the helicity distribution functions of strange ...quarks and anti-quarks of the proton, and to longitudinally polarized fragmentation functions. We report an improved measurement of DLL from data obtained at a center-of-mass energy of $\sqrt{s}$= 200 GeV with the STAR detector at RHIC. The data have an approximately twelve times larger 3 figure-of-merit than prior results and cover |η| < 1.2 in pseudo-rapidity with transverse momenta pT up to 6GeV/c. The dependences on η and pT are presented and compared with model evaluations.
Understanding gluon density distributions and how they are modified in nuclei are among the most important goals in nuclear physics. In recent years, diffractive vector meson production measured in ...ultraperipheral collisions (UPCs) at heavy-ion colliders has provided a new tool for probing the gluon density. In this Letter, we report the first measurement of J / ψ photoproduction off the deuteron in UPCs at the center-of-mass energy $\sqrt{s_{NN}}$ = 200 GeV in d + Au collisions. The differential cross section as a function of momentum transfer - t is measured. In addition, data with a neutron tagged in the deuteron-going zero-degree calorimeter is investigated for the first time, which is found to be consistent with the expectation of incoherent diffractive scattering at low momentum transfer. Theoretical predictions based on the color glass condensate saturation model and the leading twist approximation nuclear shadowing model are compared with the data quantitatively. A better agreement with the saturation model has been observed. With the current measurement, the results are found to be directly sensitive to the gluon density distribution of the deuteron and the deuteron breakup process, which provides insights into the nuclear gluonic structure.
Global polarization of Ξ and Ω hyperons has been measured for the first time in Au+Au collisions at $\sqrt{s_{NN}}$=200 GeV. The measurements of the $Ξ^{-}$ and $\overline{Ξ}^{+}$ hyperon ...polarization have been performed by two independent methods, via analysis of the angular distribution of the daughter particles in the parity violating weak decay Ξ→Λ+π, as well as by measuring the polarization of the daughter Λ hyperon, polarized via polarization transfer from its parent. The polarization, obtained by combining the results from the two methods and averaged over $Ξ^{-}$ and $\overline{Ξ}^{+}$, is measured to be $\langle{P_{Ξ}}\rangle$=0.47±0.10(stat)±0.23(syst)% for the collision centrality 20%-80%. The $\langle{P_{Ξ}}\rangle$ is found to be slightly larger than the inclusive Λ polarization and in reasonable agreement with a multiphase transport model. The $\langle{P_{Ξ}}\rangle$ is found to follow the centrality dependence of the vorticity predicted in the model, increasing toward more peripheral collisions. Finally, the global polarization of Ω, $\langle{P_{Ω}}\rangle$=1.11±0.87(stat)±1.97(syst)% was obtained by measuring the polarization of daughter Λ in the decay Ω→Λ+K, assuming the polarization transfer factor $C_{ΩΛ}=1$.
Here, we report a new measurement of D0-meson production at mid-rapidity (|y|\,<\,1) in Au+Au collisions at √sNN = 200GeV utilizing the Heavy Flavor Tracker, a high resolution silicon detector at the ...STAR experiment. Invariant yields of D0-mesons with transverse momentum pT ≲9\,GeV/c are reported in various centrality bins (0-10%, 10-20%, 20-40%, 40-60% and 60-80%). Blast-Wave thermal models are used to fit the D0-meson pT spectra to study D0 hadron kinetic freeze-out properties. The average radial flow velocity extracted from the fit is considerably smaller than that of light hadrons (π,K and p), but comparable to that of hadrons containing multiple strange quarks (φ,Ξ¯), indicating that D0 mesons kinetically decouple from the system earlier than light hadrons. The calculated D0 nuclear modification factors re-affirm that charm quarks suffer large amount of energy loss in the medium, similar to those of light quarks for pT > 4 GeV/c in central 0-10% Au+Au collisions. At low pT, the nuclear modification factors show a characteristic structure qualitatively consistent with the expectation from model predictions that charm quarks gain sizable collective motion during the medium evolution. The improved measurements are expected to offer new constraints to model calculations and help gain further insights into the hot and dense medium created in these collisions.
In this erratum we report changes on the D0pT spectra and nuclear modification factor (RAA) in Au+Au collisions at √sNN = 200 GeV by fixing the errors in the efficiency and selection criteria that ...affected the Au+Au results. Here, the p+p reference spectrum has changed as well and is updated with new fragmentation parameters.
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