118144507
Search for narrow pion-proton states in s-channel at EPECUR: experiment status
An experiment EPECUR, aimed at the search of the cryptoexotic non-strange member of the pentaquark antidecuplet, started its operation at a pion beam line of the ITEP 10 GeV proton synchrotron. The invariant mass range of the interest (1610-1770) MeV will be scanned for a narrow state in the pion-proton and kaon-lambda systems in the formation-type experiment. The scan in the s-channel is supposed to be done by the variation of the incident pi- momentum and its measurement with the accuracy of up to 0.1% with a set of 1 mm pitch proportional chambers located in the first focus of the beam line. The reactions under the study will be identified by a magnetless spectrometer based on wire drift chambers with a hexagonal structure. Because the background suppression in this experiment depends on the angular resolution, the amount of matter in the chambers and setup is minimized to reduce multiple scattering. The differential cross section of the elastic pi-p-scattering on a liquid hydrogen target in the region of the diffractive minimum will be measured with statistical accuracy 0.5% in 1 MeV steps in terms of the invariant mass. For KLambda-production the total cross section will be measured with 1% statistical accuracy in the same steps. An important byproduct of this experiment will be a very accurate study of Lambda polarization. The setup was assembled and tested in December 2008 and in April 2009 we had the very first physics run. About 0.5x10^9 triggers were written to disk covering pion beam momentum range 940-1135 MeV/c.
119049564
Focusing of a 1-GeV proton beam as it is brought into the channeling regime by a curved single crystal
The possibility of focusing high-energy particles by means of bulk capture of particles in the channeling regime is demonstrated experimentally. Protons with energies of 1 GeV, as they were bulk captured by the (111) plane of a curved silicon crystal from an angular interval with FWHM = 7.2 mrad at the exit from the crystal, had an angular divergence with FWHM = 1.6 mrad. The phase space of the beam of channeling particles in this case decreased slightly (by a factor of 1.8).
125946313
SPATIAL FOCUSING OF 1-GeV PROTONS BY A BENT MONOCRYSTAL
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.
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.
53583095
High Precision Measurements of the Pion Proton Differential Cross Section
Study of the elastic scattering can produce a rich information on the dynamics of the strong interaction. The EPECUR collaboration is aimed at the research of baryon resonances in the second resonance region via pion-proton elastic scattering and kaon-lambda production. The experiment features high statistics and better than 1 MeV resolution in the invariant mass thus allowing searches for narrow resonances with the coupling to the pi p channel as low as 5%. The experiment is of "formation" type, i.e. the resonances are produced in s-channel and the scan over the invariant mass is done by the variation of the incident pion momentum which is measured with the accuracy of 0.1% with a set of 1 mm pitch proportional chambers located in the first focus of the beam line. The reaction is identified by a magnetless spectrometer based on wire drift chambers with a hexagonal structure. Background suppression in this case depends on the angular resolution, so the amount of matter in the chambers and the setup was minimized to reduce multiple scattering. 
The measurements started in 2009 with the setup optimized for elastic pion-proton scattering. With 3 billions of triggers already recorded the differential cross section of the elastic pi p-scattering on a liquid hydrogen target in the region of the diffraction minimum is measured with statistical accuracy about 1% in 1 MeV steps in terms of the invariant mass. The paper covers the experimental setup, current status and some preliminary results.
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.
123930049
Heavy Quark Production at CMS and ATLAS
measured with the new data against the framework of quantum chromodynamics (QCD). Two general-purpose detectors, ATLAS [1] and CMS [2], designed to explore the physics at the TeV scale, have an extensive research program for heavy-flavour studies. The two experiments are very different in the layout chosen for the magnet system. In ATLAS, a solenoid provides the magnetic ﬁeld for the Inner Tracker, while a system of air-core toroids outside the calorimeters provides the ﬁeld for the Muon Spectrometer. The magnetic ﬁeld in CMS is provided by a single very large solenoid which contains both the Inner Tracker and the calorimeters. The muon chambers are embedded in the iron of the solenoid return yoke. The magnet layout determines the weight (ATLAS is larger but lighter) of the two detectors. The potential of ATLAS and CMS for heavy-flavour measurements is presented for the LHC start-up luminosities (10 pb
2455980
Design and Performance of the Alignment System for the CMS Muon Endcaps
The alignment system for the CMS muon endcap detector employs several hundred sensors such as optical 1-D CCD sensors illuminated by lasers and analog distance- and tilt-sensors to monitor the positions of one sixth of 468 large cathode strip chambers. The chambers mounted on the endcap yoke disks undergo substantial deformation on the order of centimeters when the 4 T field is switched on and off. The muon endcap alignment system is required to monitor chamber positions with 75-200 mum accuracy in the Rphi plane, ~400 mum in the radial direction, and ~1 mm in the z-direction along the beam axis. The complete alignment hardware for one of the two endcaps has been installed at CERN. A major system test was performed when the 4 T solenoid magnet was ramped up to full field for the first time in August 2006. We present the overall system design and first results on disk deformations, which indicate that the measurements agree with expectations.
31428202
An object-oriented simulation program for CMS
The CMS detector simulation package, OSCAR, is based on the Geant4 simulation toolkit and the CMS object-oriented framework for simulation and reconstruction. Geant4 provides a rich set of physics processes describing in detail electromagnetic and hadronic interactions. It also provides the tools for the implementation of the full CMS detector geometry and the interfaces required for recovering information from the particle tracking in the detectors. This functionality is interfaced to the CMS framework, which, via its "action on demand" mechanisms, allows the user to selectively load desired modules and to configure and tune the final application. The complete CMS detector is rather complex with more than 1 million geometrical volumes. OSCAR has been validated by comparing its results with test beam data and with results from simulation with a GEANT3-based program. It has been successfully deployed in the 2004 data challenge for CMS, where more than 35 million events for various LHC physics channels were simulated and analysed.
122362196
Accelerator constraints on dark matter
Abstract The relic density of supersymmetric dark matter is calculable in terms of supersymmetric and Standard Model parameters. The discovery of supersymmetric particles and determination of their parameters could well happen at the next generation hadron collider LHC presently under construction at CERN. The accelerator constraints on the SUSY parameter space at the LHC are presented as well as the accuracy with which the density of supersymmetric cold dark matter could be predicted from collider measurements.