C. Jones

ππ Phase‐Shift Analysis from 600 to 1900 MeV

Wa have performed an energy‐dependent and an energy‐independent analysis of elastic ππ scattering, using data for the reaction π−pu2009⇒u2009π−π+n at 17.2 GeV/c. The ππ energy covers the range from 600 MeV to 1900 MeV. Apart from the well‐known resonances ρ, f and g, we find a strong S‐wave in the ρ and also in the f‐meson region. A P‐wave resonance occurs in both analyses at ∼ 1600 MeV with a total width of 180 MeV and an elasticity of 0.25, which can be identified with the ρ′ meson in its ππ decay mode. The zeros in the complex cos Θ plane of the scattering amplitude are studied as a function of the energy. The position of the real parts of the zeros are in qualitative agreement with the prediction of the Veneziano model. Furthermore, we show that an analogous relation holds also for the imaginary parts of the zero trajectories.

High statistics study of the reaction π−p→π−π+n: Apparatus, method of analysis, and general features of results at 17 GeV/c

Abstract A detailed account is given of a high statistics experiment measuring the reaction π−p→π−π+n at 17.2 GeV/c. The spark chamber and counter triggering system are desribed. The methods of data analysis are described, in particular the determination of angular distributions from apparatus with limited acceptance. Experimental data and their interpretation are presented.

Handling of the generation of primary events in Gauss, the LHCb simulation framework

The LHCb simulation application. Gauss, consists or two independent phases, the generation of the primary event and the tracking of particles produced in the experimental setup. For the LHCh experimental program it is particularly important to model IS meson decays: the KvtGcn code developed in CLEO and BaBah has been chosen and customized for non-coherent B production as necuring in pp collisions at the LHC, The initial proton-proto n collision is provided by a different generator engine, currently PYTHIA 6 for massive prwluclion of signal and generic pp collisions events. Beam gas events, background events originating from proton halo, cosmics and calibration events for different detectors can be generated in addition to pp collisions. Different generator packages as available in the physics community or specifically developed in LHCb are used for the different purposes. Running conditions affecting the events generated such as the size of the luminous region, the number of collisions occuring in a bunch crossing and the number of spill-over events from neighbouring bunches are modeled via dedicated algorithms appropriately configured. The design of the generator phase of Gauss will be described: a modular structure with well defined interfaces specific to the various tasks, e.g. pp collisions, particles decays, selections, etc. has been chosen. Different implementations are available for the various tasks allowing selecting and combining them as most appropriate at run time as in the case of Pythia 6 im pp collisions or HIJING for beam gas. The advantages of such structure, allowing for example to adopt transparently new generators packages will be discussed.

A study of the ππ phase-shift solutions in the mass region 1.0 to 1.8 GeV from π−p → π−π+n at 17.2 GeV

Abstract The ππ phase shifts from 1 to 1.8 GeV are presented. The method used was an essentially energy-independent parametrization of the amplitudes fitted simultaneously to the M ππ and t -dependence of the moments of the dipion angular distribution from the reaction π − p → π − π + n at 17.2 GeV. The various ambiguous solutions are discussed.

The extended OPAL silicon strip microvertex detector

Abstract The OPAL experiment at the CERN LEP collider recently increased the geometrical acceptance of its silicon microvertex detector. The azimuthal coverage is improved by adding one pair of detector modules to each of the two layers, while the polar angle coverage is extended by adding new detector modules in line with the existing ones. This improves the efficiency for high quality tracking in OPAL and in particular for b quark tagging in Higgs boson searches. A description of the detector is given, with emphasis on new or modified elements with respect to the earlier version. Results on the performance of the new detector are presented.

Isospin-two ππ phase shifts from an experiment π+p→π+n at 12.5 GeV/c

The Iu2009=u20092 s‐ and d‐wave ππ phase shifts δs2 and δd2 have been determined in the ππ mass region from 500–1500 MeV, using a sample of 17,500 events π+pu2009⇒u2009π+π+ from a spark chamber experiment. For this purpose the moments of the ππ angular distribution in the s‐channel helicity frame have veen written as bilinear expressions of OPE amplitudes modified by absorption and have been fitted to the measured values of the moments in four mass bins of width 0.25 GeV/c2. The value of δs2 in the ρ‐mass region (δs2u2009≃u2009−15.5°) corresponds to an elastic cross‐section of ≃u20097.5mb.The values of δd2 are about a factor of 10 smaller than the corresponding values of δs2 for the whole mass region considered.

ρ-Polarization in the reaction π−p → π+π−n AT 17 GeV

Abstract The data from a spark chamber experiment are analysed for dipion masses below 1 GeV in terms of the s- and p-wave density matrix. The measured elements are given as functions of the dipion mass and of the momentum transfer. Bounds for the unmeasured matrix elements ρ 11 , Im ρ 10 , Im ρ 0S , Im ρ 1s are calculated using the positivity constraint. The intervals are very small and suggest that the production process has the property of equal phases of the amplitudes referring to the same ππ angular momentum. Next, the eigenvalues of the density matrix are determined within the positivity domain, and presented as functions of the dipion mass and the momentum transfer, showing that the rank is never greater than 3, and equal to 2 at the peak of the ρ meson, but could also be generally 2.

t-Dependence and production mechanisms of the ϱ, f and g resonances from π−p → π−π+n at 17.2 GeV

Abstract The t-dependence of ϱ, f and g resonance production is compared using data from the CERN-Munich spectrometer. An amplitude analysis is performed, and the significance for various proposed models of the production mechanism discussed. The OPE term becomes increasingly adequate to describe the data as the resonant mass increases.

Measurement of the A−2 meson mass spectrum

Abstract We measure the reaction π−p→K−K0Sp at 17.2 GeV/c and observe some 1400 A−2→K−K0S decays, with no evidence for a double mass peak. The mass resolution is ±5.7 MeV. The A2 is produced in a nearly pure z.sfnc;j, m > = z.sfnc;2,1 > = z.sfnc;2,−1 > state in the Gottfried-Jackson system.

Measurement of the reaction π−p→(pp)n at 18.8 GeV/c

Abstract A sample of 10 350 π − p → p p n events with peripherally produced p p pairs has been observed in a spark chamber experiment. The differential cross-section dσ dt and the p p decay angular distribution suggest that one-pion exchange dominates the production process. The cross-section σ(π − π + → p p ) , obtained by a pole extrapolation, is compared with σ( p p →π + π − ) using detailed balance.