Giles Barr

Abstract:

The particle identification (PID) methods used for the calculation of secondary pion yields with the HARP forward spectrometer are presented. Information from time of flight and Cherenkov detectors is combined using likelihood techniques. The efficiencies and purities associated with the different PID selection criteria are obtained from the data. For the proton-aluminium interactions at 12.9 GeV/c incident momentum, the PID efficiencies for positive pions are 86 % in the momentum range below 2 GeV/c, 92 % between 2 and 3 GeV/c and 98 % in the momentum range above 3 GeV/c. The purity of the selection is better than 92 % for all momenta. Special emphasis has been put on understanding the main error sources. The final PID uncertainty on the pion yield is 3.3 %. © 2007 Elsevier B.V. All rights reserved.

Abstract:

The new data on pion production in p+C interactions from the NA49 experiment at the CERN SPS are used for a detailed study of hadronization in the collision of protons with light nuclei. The comparison to the extensive set of data from p+p collisions obtained with the same detector allows for the separation and extraction of the projectile and target contributions to the pion yield both in longitudinal and in transverse momentum. © 2007 Springer-Verlag.

Abstract:

The production of charged pions in minimum bias p+C interactions is studied using a sample of 377000 inelastic events obtained with the NA49 detector at the CERN SPS at 158 GeV/c beam momentum. The data cover a phase space area ranging from 0 to 1.8 GeV/c in transverse momentum and from -0.1 to 0.5 in Feynman xF. Inclusive invariant cross sections are given on a grid of 270 bins per charge, thus offering for the first time a dense coverage of the projectile hemisphere and of the cross-over region into the target fragmentation zone. © 2007 Springer-Verlag.

Abstract:

HARP is a high-statistics, large solid angle experiment to measure hadron production using proton and pion beams with momenta between 1.5 and 15 GeV/c impinging on many different solid and liquid targets from low to high Z. The experiment, located in the T9 beam of the CERN PS, took data in 2001 and 2002. For the measurement of momenta of produced particles and for the identification of particle types, the experiment includes a large-angle spectrometer, based on a Time Projection Chamber and a system of Resistive Plate Chambers, and a forward spectrometer equipped with a set of large drift chambers, a threshold Cherenkov detector, a time-of-flight wall and an electromagnetic calorimeter. The large angle system uses a solenoidal magnet, while the forward spectrometer is based on a dipole magnet. Redundancy in particle identification has been sought, to enable the cross-calibration of efficiencies and to obtain a few percent overall accuracy in the cross-section measurements. Detector construction, operation and initial physics performances are reported. In addition, the full chain for data recording and analysis, from trigger to the software framework, is described. © 2006 Elsevier B.V. All rights reserved.

Abstract:

We present a measurement of the ratio of the decay rates Γ (KL → π⁺ π^-) / Γ (KL → π^± e^∓ ν), denoted as ΓK 2 π / ΓK e 3. The analysis is based on data taken during a dedicated run in 1999 by the NA48 experiment at the CERN SPS. Using a sample of 47 000 K2 π and five million Ke 3 decays, we find ΓK 2 π / ΓK e 3 = (4.835 ± 0.022stat . ± 0.016syst .) × 10^-3. From this we derive the branching ratio of the CP violating decay KL → π⁺ π^- and the CP violation parameter | η+ - |. Excluding the CP conserving direct photon emission component KL → π⁺ π^- γ, we obtain the results BR (KL → π⁺ π^-) = (1.941 ± 0.019) × 10^-3 and | η+ - | = (2.223 ± 0.012) × 10^-3. © 2006 Elsevier B.V. All rights reserved.