SearcharxivSearch

arXiv subjects

J. Wessels

Publications and source records attributed to J. Wessels.

5 recordsLinked to original sources

NLO Monte Carlo predictions for heavy-quark production at the LHC: pp collisions in ALICE

Next-to-leading order (NLO) QCD predictions for the production of heavy quarks in proton-proton collisions are presented within three different approaches to quark mass, resummation and fragmentation effects. In particular, new NLO and parton shower simulations with POWHEG are performed in the ALICE kinematic regime at three different centre-of-mass energies, including scale and parton density variations, in order to establish a reliable baseline for future detailed studies of heavy-quark suppression in heavy-ion collisions. Very good agreement of POWHEG is found with FONLL, in particular for centrally produced D^0, D^+ and D^*+ mesons and electrons from charm and bottom quark decays, but also with the generally somewhat higher GM-VFNS predictions within the theoretical uncertainties. The latter are dominated by scale rather than quark mass variations. Parton density uncertainties for charm and bottom quark production are computed here with POWHEG for the first time and shown to be dominant in the forward regime, e.g. for muons coming from heavy-flavour decays. The fragmentation into D_s^+ mesons seems to require further tuning within the NLO Monte Carlo approach.

hep-ph

A method to disentangle single- and multi-meson production in missing mass spectra from quasi-free pn --> pn X reactions

The separation of contributions from multi- and single-meson production in the missing mass spectrum of the quasi-free pn --> pnX reaction constitutes a~challenging task when the reaction is studied close to threshold. This is especially true if the resolution of the mass determination is comparable with the excess energy and if the investigated signal appears close to the kinematical limit. In this article we outline a method which permits the extraction of the signal originating from the creation of a single meson without the necessity of conducting model-dependent simulations. For the pd --> pnXp(spectator) reactions, the method allows one to combine events corresponding to multi-meson production at various excess energies with respect to the pn --> pn meson process, and hence leads to an increase of the statistics needed for the determination of the shape of the multi-meson background. As an example of the application of the method, we demonstrate that the evaluation of the data from the pd --> pnXp(sp) process according to the described technique enables one to extract a signal of the pn --> pn eta reaction whose shape is consistent with expectations, supporting the correctness and usefulness of the method introduced.

nucl-ex

COSY-11: an experimental facility for studying meson production in free and quasi-free nucleon-nucleon collisions

The COSY-11 experimental setup is an internal facility installed at the COoler SYnchrotron COSY in Juelich. It allows to investigate meson production in free and quasi-free nucleon-nucleon collisions, eg. pp --> pp meson and pd --> p_sp np meson reactions. Drift chambers and scintillators permit to measure outgoing protons, separated in magnetic field of COSY-11 dipole. Neutrons are registered in the neutron modular detector installed downstream the beam. Recently, the experimental setup has been extended with spectator detector, deuteron drift chamber and polarization monitoring system, and since then meson production can be investigated also as a function of spin and isospin of colliding nucleons.

hep-ex

Isospin dependence of the eta' meson production in nucleon--nucleon collisions

According to the quark model, the masses of eta and eta' mesons should be almost equal. However, the empirical values of these masses differ by more than the factor of two. Similarly, though the almost the same quark-antiquark content, the total cross section for the creation of these mesons close to the kinematical thresholds in the pp --> ppX reaction differs significantly. Using the COSY-11 detection setup we intend to determine whether this difference will also be so significant in the case of the production of these mesons in the proton-neutron scattering. Additionally, the comparison of the pp --> pp eta' and pn --> pn eta' total cross sections will allow to learn about the production of the eta' meson in the channels of isospin I = 0 and I = 1 and to investigate aspects of the gluonium component of the eta' meson.

hep-ex

Prototype tests for the ALICE TRD

A Transition Radiation Detector (TRD) has been designed to improve the electron identification and trigger capability of the ALICE experiment at the Large Hadron Collider (LHC) at CERN. We present results from tests of a prototype of the TRD concerning pion rejection for different methods of analysis over a momentum range from 0.7 to 2 GeV/c. We investigate the performance of different radiator types, composed of foils, fibres and foams.

nucl-ex