Neutron Detection in the A2 Collaboration Experiment on Neutral Pion Photo-production on Neutron

Neutron detection is of crucial importance for the neutral pion photo-production study on a neutron target that now is in progress at MAMI. Two electro-magnetic calorimeters, based on NaI and BaF2 crystals, are used in the A2 experiment. While these calorimeters are optimized for pion decay photon detection, they have a reason able efficiency for neutron detection also. The paper describes the method, which has been used to measure this efficiency using the same data taken for pion photo-production study on deuterium target with tagged photon been of 800 MeV maximal energy. The detection efficiency is a rising function of neutron momentum that reaches 40% near 1 GeV/c.

Direct photon production in pp, p–Pb and Pb–Pb collisions measured with the ALICE experiment

We review recent ALICE results on direct photon production in pp, p–Pb and Pb–Pb collisions at LHC energies. In light systems, pp and p–Pb, no signal of direct photons at low pT < 3-5 GeV/c is observed within uncertainties, while at high pT our measurements are consistent with NLO pQCD calculations. In central and mid-central Pb–Pb collisions a thermal photon contribution is observed at low pT < 3 - 4 GeV/c with slopes Teff = (304 ± 11stat ± 40syst) MeV and (407 ± 61stat ± 96syst) MeV respectively. A collective elliptic flow of direct photons is measured and appeared to be close to the decay photon flow.

AZIMUTHAL ANISOTROPY MEASUREMENT OF DIRECT PHOTON IN $\sqrt{^SNN} = 200\ {\rm GeV}$Au + Au COLLISIONS AT RHIC-PHENIX

Azimuthal anisotropy of direct photons is measured in [Formula: see text] Au + Au collisions by the PHENIX experiment at RHIC. Direct photons are one of the most effective probes to study properties of hot dense medium at initial state (also QGP state) of heavy ion collisions because photons do not interact strongly with medium once produced. They keep their conditions when they are created. Within statistical and systematic errors, the elliptic flow parameter (v2) of direct photons is consistent with zero. Direct photons v2 is measured by the hadron decay photon background v2 from inclusive photon v2 in intermediate to high transverse momentum (pT) region (0 to 10 GeV/c) for 3 centrality selections (20% steps) and minimum bias.

PHOTON-HADRON CORRELATIONS IN $\sqrt{^SNN} = 200\ {\rm GeV/c}$ COLLISIONS WITH THE PHENIX DETECTOR

The yield of charged hadrons at intermediate pT (2-5 GeV/c) on the away-side of a high pT hadron trigger is known to be suppressed in central relativistic heavy-ion collisions. The mechanism by which the jet opposite the trigger has its redistributed is not yet fully understood. Although rarer than dijets, direct photon-jet pairs may provide additional constraints on parton energy loss models. The benefits of direct photon triggers are two-fold. In contrast to dijet systems where the jet energy is known only after full jet reconstruction, the direct photon carries approximately the full energy of the jet. Also, the trigger photons do not suffer from the same geometrical bias that causes high pT hadrons from jets to be produced predominately near the surface of the collision region. This poster discusses the method by which the direct photon correlation signal can be separated from the decay photon correlation signal. We present the results of two particle correlation studies of charged hadrons associated with high pT photon triggers in p − p collisions. The results are compared to data from Au−Au collisions and expectations from the PYTHIA event generator.

DARK MATTER DECAY AND THE IONISATION OF NITROGEN IN THE INTERSTELLAR MEDIUM

The recent COBE data on diffuse [NII] emission in the Galaxy show that if my neutrino decay hypothesis is correct then the decay photons must be able to ionise nitrogen as well as hydrogen. The hypothesis then requires that the decay photon energy Eγ, the mass mντ of the decaying neutrino, and the Hubble constant H0 are given by Eγ=14.65 ± 0.15 eV , mντ = 29.3 ± 0.3 eV and H0=57±0.2 km sec −1 Mpc −1. This represents a threefold increase of precision over my previous estimates.