119402979
Antimatter and matter production in heavy ion collisions at CERN (The NEWMASS experiment NA52)
Besides the dedicated search for strangelets NA52 measures light (anti)particle and (anti)nuclei production over a wide range of rapidity. Compared to previous runs the statistics has been increased in the 1998 run by more than one order of magnitude for negatively charged objects at different spectrometer rigidities. Together with previous data taking at a rigidity of -20 GeV/c we obtained 10^6 antiprotons 10^3 antideuterons and two antihelium3 without centrality requirements. We measured nuclei and antinuclei (p,d,antiprotons, antideuterons) near midrapidity covering an impact parameter range of b=2-12 fm. Our results strongly indicate that nuclei and antinuclei are mainly produced via the coalescence mechanism. However the centrality dependence of the antibaryon to baryon ratios show that antibaryons are diminished due to annihilation and breakup reactions in the hadron dense environment. The volume of the particle source extracted from coalescence models agrees with results from pion interferometry for an expanding source. The chemical and thermal freeze-out of nuclei and antinuclei appear to coincide with each other and with the thermal freeze-out of hadrons.
118548096
Measurement of the two-photon absorption cross-section of liquid argon with a time projection chamber
This paper reports on laser-induced multiphoton ionization at 266?nm of liquid argon in a time projection chamber (LAr TPC) detector. The electron signal produced by the laser beam is a formidable tool for the calibration and monitoring of next-generation large-mass LAr TPCs. The detector that we designed and tested allowed us to measure the two-photon absorption cross-section of LAr with unprecedented accuracy and precision: ?ex=(1.24?0.10stat?0.30syst)?10? 56?cm4?s? 1.
14164208
A prototype liquid Argon Time Projection Chamber for the study of UV laser multi-photonic ionization
This paper describes the design, realization and operation of a prototype liquid Argon Time Projection Chamber (LAr TPC) detector dedicated to the development of a novel online monitoring and calibration system exploiting UV laser beams. In particular, the system is intended to measure the lifetime of the primary ionization in LAr, in turn related to the LAr purity level. This technique could be exploited by present and next generation large mass LAr TPCs for which monitoring of the performance and calibration play an important role. Results from the first measurements are presented together with some considerations and outlook.
119238918
A beam monitor detector based on doped silica and optical fibres
A beam monitor detector prototype based on doped silica fibres coupled to optical fibres has been designed, constructed and tested, mainly for accelerators used in medical applications. Scintillation light produced by Ce and Sb doped silica fibres moving across the beam has been measured, giving information on beam position, shape and intensity. Mostly based on commercial components, the detector is easy to install, to operate and no electronic components are located near the beam. Tests have been performed with a 2 MeV proton pulsed beam at an average current of 0.8 μA. The response characteristics of Sb doped silica fibres have been studied for the first time.
16665734
Top Quark Production and Decay Properties at the Tevatron
The latest results from the CDF and D0 collaborations on the top-quark pair-production cross section and limits on electroweak production are presented. Included are measurements of properties of the top quark such as charge, lifetime, and the decay branching ratio t->Wb. In addition to measurements about the top quark, the selected event samples are used to study the helicity of the W boson and to search for additional exotic quarks (t') and resonances in the ttbar invariant mass spectrum.
109891378
The DØ silicon micro-strip tracker
The D0 silicon micro-strip tracker (SMT) is part of the D0 upgrade for the Tevatron RunII at Fermilab. The detector has been running successfully since the start of the RunII physics data taking. The tracking and vertexing performance match the expectation from Monte-Carlo studies. An additional inner layer (Layer0) of silicon sensors at R = 1.6cm will be installed in 2005.
110779087
The SVX4 integrated circuit
Abstract A first prototype of the SVX4 readout IC with enclosed transistor layout for radiation tolerance has been fabricated in a commercial 0.25 μm bulk CMOS process. The SVX4 is intended to instrument the CDF and D0 Run IIB silicon strip detector upgrades at Fermilab. The design and test results are discussed.
15629487
Precise predictions for the Higgs-boson decay H ---> WW/ZZ ---> 4 leptons
The decay of the standard model Higgs boson into four leptons via a virtual $W$- or $Z$-boson pair is one of the most important decay modes in the Higgs-boson search at the Large Hadron Collider. We present the complete electroweak radiative corrections of $\mathcal{O}(\ensuremath{\alpha})$ to these processes, including improvements beyond $\mathcal{O}(\ensuremath{\alpha})$ originating from heavy-Higgs effects and final-state radiation. The intermediate $W$- and $Z$-boson resonances are described (without any expansion or on-shell approximation) by consistently employing complex mass parameters for the gauge bosons (complex-mass scheme). The corrections to partial decay widths typically amount to some percent and increase with growing Higgs mass ${M}_{H}$, reaching about 8% at ${M}_{H}\ensuremath{\sim}500\text{ }\text{ }\mathrm{GeV}$. For not too large Higgs masses (${M}_{H}\ensuremath{\lesssim}400\text{ }\text{ }\mathrm{GeV}$) the corrections to the partial decay widths can be reproduced within $\ensuremath{\lesssim}2%$ by simple approximations. For angular distributions the corrections are somewhat larger and distort the shapes. For invariant-mass distributions of fermion pairs they can reach several tens of percent depending on the treatment of photon radiation. The discussed corrections have been implemented in a Monte Carlo event generator called Prophecy4f.
118621343
Validation of Kalman Filter alignment algorithm with cosmic-ray data using a CMS silicon strip tracker endcap
A Kalman Filter alignment algorithm has been applied to cosmic-ray data. We discuss the alignment algorithm and an experiment-independent implementation including outlier rejection and treatment of weakly determined parameters. Using this implementation, the algorithm has been applied to data recorded with one CMS silicon tracker endcap. Results are compared to both photogrammetry measurements and data obtained from a dedicated hardware alignment system, and good agreement is observed.
122383524
DIELECTRON SPECTROSCOPY IN COLD NUCLEAR MATTER
We report recent data on e+e- pair emission in proton nucleus collisions at energies slightly above the light vector meson production threshold. Invariant mass distributions for the p+Nb system at Ekin = 3.5 GeV/c2 show a clear ρ/ω signal and are compared to data from elementary p+p reactions. We observe a constant π0/ω yield ratio for both systems.
122289502
Development of SiTCP based DAQ system of double-sided silicon strip super-module
Abstract The super-module integration concept based on double-sided silicon strip modules has been developed for the future upgrade of the ATLAS detector. A super-module consists of 12 double-sided modules with 122 880 readout strips in total. Since the number of readout strips becomes very large to keep the hit occupancy at an acceptable level, the data readout is one of the key issues. A SiTCP based DAQ system has been developed by using the Soi EvAluation BoArd with Sitcp (SEABAS). The SEABAS processes the data by means of an FPGA (User-FPGA) and transfers data to a computer via Ether-net with the SiTCP protocol, which is a hardware implementation of TCP/IP on a FPGA device, enabling it to achieve high speed data transfers. The firmware and software have been developed for the SEABAS together with the readout hardware chain, and the basic functionality for reading out the super-module has been established.