21384151
Aligning the CMS muon endcap detector with a system of optical sensors
The positions and orientations of one sixth of 468 large cathode strip chambers in the endcaps of the CMS muon detector are directly monitored by several hundred sensors including 2-D optical sensors with linear CCDs illuminated by cross-hair lasers. Position measurements obtained by photo- grammetry and survey under field-off conditions show that chambers in the +Z endcap have been placed on the yoke disks with an average accuracy of about plusmn1 mm in all 3 dimensions. We reconstruct absolute Zciws-positions and orientations of chambers at B=0T and B=4T using data from the optical alignment system. The measured position resolution and sensitivity to relative motion is ~60 mum. The precision for measuring chamber positions taking into account mechanical tolerances is ~270 mum. Comparing reconstruction of optical alignment data and photogrammetry measurements at B=0T indicates an accuracy of ~ 680 mum currently achieved with the hardware alignment system. Optical position measurements at B=4T show significant chamber displacements of up to 13 mm due to yoke disk deformation.
118088627
Resonance production in two-photon collisions at LEP with the L3 detector
The ee→eeKS0K±π∓, ee→eeηπ+π− and e+e−→e+e−π+π−π+π− final states are studied with the L3 detector at LEP using data collected at center-of-mass energies from 160 GeV up to 202 GeV. The mass spectrum of the KS0K±π∓ final state shows an enhancement around 1470 MeV, which is identified with the pseudoscalar meson η(1440). This state is observed in γγ collisions for the first time and its two-photon width is measured. Clear evidence is also obtained for the formation of the axial vector mesons f1(1420) and f1(1285). In the ηπ+π− channel the f1(1285) is observed, and upper limits for the formation of η(1440) and η(1295) are obtained. The process e+e−→e+e−π+π−π+π− is dominated by ρ0ρ0 production. A spin-parity analysis of the ρ0ρ0 system for Wγγ 3GeV the f2(1270) meson is observed.
124722292
Volume-based Representation of the Magnetic Field
The access to the magnetic field has a large impact on both CPU performance and accuracy of simulation, reconstruction and analysis software. An approach to the magnetic field access based on a volume geometry is described. The volumes are constructed in such a way that their boundaries correspond to field discontinuities, which are due to changes in magnetic permeability of the materials. The field in each volume is continuous. The value of the field at a given point of a volume is obtained by interpolation from a regular grid of values resulting from a TOSCA calculation or, when it is available, from a parameterization. To allow global access to the magnetic field, a volume finding algorithm that exploits explicitly the layout and the symmetries of the detector is used. The main clients of the magnetic field, which are the simulation (GEANT) and the propagation of track parameters and errors in the reconstruction, can be made aware of the magnetic field volumes by connecting the per-volume magnetic field providers to the corresponding volume in the respective geometries. In this way the global volume search is by-passed and the access to the field is sped up significantly.
197518814
Heavy flavor production in gamma gamma collisions
122913826
On flavour production in CMS
The LHC provides new opportunities to improve our understanding of the b quark using high statistics data samples and the 14 TeV center-of-mass energy. The prospects to measure the cross section for inclusive b production in events containing jets and at least one muon are presented. Studies of detector systematic effects and theoretical uncertainties are included. QCD aspects of the beauty production are discussed. An outline of the basic vertex reconstruction algorithms used in CMS is given.
120010165
RESULTS FROM TWO-PHOTON COLLISIONS AT LEP
122971502
Design principles of the end cap drift chambers in the L3 experiment
Abstract The end cap detector based on multimodule construction has been designed and produced for the L3 experiment. The purpose of this article is to present a fruitful approach for solving the complex problem of selecting a set of strongly interrelated design parameters to satisfy performance criteria in the face of severe environmental and space constraints. The design principle of the end cap drift chamber affected by a complex of external problems caused by the layout is reviewed. It is shown that in the framework of detailed consideration of each parameter, a good space–time linearity, spatial and angular resolution is obtainable. The results of experimental tests are presented.
118636693
Polarization effects in the quasielastic (p, 2p) reaction with the nuclear S-Shell Protons at 1 GeV
The polarization of the secondary protons in the (p, 2p) reaction with the S-shell protons of nuclei 4He, 6Li, 12C, 28Si, 40Ca was measured at 1 GeV unpolarized proton beam. The spin correlation parameters Cij for the 4He and 12C targets also were for the first time obtained as well. The polarization measurements were performed by means of a two-arm magnetic spectrometer, each arm of which was equipped with the multiwire-proportional chamber polarimeter. This experiment was aimed to study a modification of the proton-proton scattering matrix in the nuclear medium.
121193004
Study of nuclear medium effects on polarization in (p, 2p) scattering at 1 GeV
We report on experimental investigation of the (p, 2p) reactions on nuclei 6Li, 7Li, 12C and 40Ca. In this experiment, polarizations of the secondary protons from the (p, 2p) reactions are measured using 1 GeV proton beam of the PNPI synchrocyclotron. Two final protons from the reaction are detected in coincidence by means of a two-arm magnetic spectrometer at non-symmetric scattering angles. The resolution of the spectrometer on separation energy of 4.5 MeV (FWHM) is enough to distinguish reliably the shell structure of the investigated nuclei. In order to measure polarization of the two secondary protons, both spectrometer arms are equipped with multiwire proportional chamber polarimeters.Strong reduction of polarizations (large depolarization factor) relatively to free pp scattering is observed in the experiment. The 6Li, 7Li P-shell data are interpreted in terms of this reduction being combined with classical phenomenon of the effective polarization calculated with the help of DWIA.For the S-shell protons the depolarization factors are apparently seen not being obscured by the spin-orbit coupling. In case of the 7Li S-shell data the depolarization factors calculated by deviation from IA are found to be ΔP/P=0.31±0.07 and 0.39±0.04 for the scattered and recoil proton polarization, respectively. As estimations show, significant and roughly equal polarization reduction of the two secondary protons with essentially different energies (≈-200 and 800 MeV) can hardly be explained by a trivial nuclear distortion effect like depolarization due to rescatterings in nuclear matter. Measurements with heavier nucleus targets (12C, 40Ca) show that magnitude of the depolarization is a decreasing function of the nuclear density in the part of the nucleus volume which effectively contributes to the pp scattering in a nucleus. An explanation of the observed depolarization might be done in terms of modification of the pp-scattering amplitude in the nuclear meidum.
55963955
Study of aging properties of a wire chamber operating with high-pressure hydrogen
The project for a precision measurement of the mp-capture rate (mCAP experiment) is based on an application of a multi-wire proportional chamber (MWPC) operating in ultra-pure hydrogen at 10 bar pressure. A special test setup was constructed at PNPI to investigate the MWPC performance under the expected experimental conditions. The aging studies of the MWPCs were performed with intense irradiation from an a-source ð 241 AmÞ and a b-source ð 90 SrÞ: After 45 days of continuous irradiation by a-particles no changes in the currents, in the signal shapes, and in the counting rates were observed. It was demonstrated that the MWPCs can operate without degradation at least up to accumulated charges of 0: 1C =cm wire. These irradiation conditions are much more severe than in the real experiment. During the study of the MWPC we have observed an appearance of short duration signals with amplitudes an order of magnitude larger than those of normal signals from the a-particles. The number of such signals (‘‘streamers’’) strongly depend on HV. We shall continue these tests in the future with the goal of obtaining more detailed information about aging properties of MWPCs operating with high-pressure hydrogen.