17193732
JET PRODUCTION AT HERA : PROGRESS AND PROBLEMS
This contribution reviews the measurements related to jet production at HERA which are available in`98. The reasons for the considerable progress achieved in the last years are summarized. The major diiculties and the limitations of these measurements as seen today are discussed. 1. What has been measured ? One of the many fascinating topics of research at the electron{proton collider HERA is the study of multi{jet events. The application of jet algorithms to characterize the properties of multi{particle hadronic nal states turned out to be a powerful and natural approach. Jet algorithms have been used intensively in the analysis of deeply inelastic scattering (DIS) and photoproduction processes. In leading{order QCD, the cross section of multi{jet events in DIS is proportional to the strong coupling constant s and the parton density functions of the proton. Several determinations of s based on jets have been performed at HERA 1, 2, 3, 4]. There are (preliminary) extractions of the proton's gluon content in NLO 5]. This approach is more direct than determinations of the gluon density from inclusive structure function measurements, and it probes the gluon density at larger momentum fractions. Events with a jet in the very forward (proton) direction of the detectors have been studied in attempts to search for signatures expected when the BFKL parton density evolution equations are valid at HERA 6]. In photoproduction, evidence for the partonic structure of the photon has been shown in studies of jet distributions 7]. In events with two reconstructed jets x , the share of the photon's momentum entering the hard scattering process, can be calculated. From the measurement of dijet cross sections diierential in x and transverse jet energy, photon parton densities could be constrained, and the p t dependence of the anomalous component of the real photon predicted by QCD could be connrmed 8]. Jet polar angle distributions for direct and resolved photons where measured to be sensitive to the spin of the corresponding gluon or quark propagators 9]. Also, LO eeective parton densities were extracted 8].
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.
54868784
Series tests of fine mesh photomultiplier tubes in magnetic fields of up to 1.2 Tesla
Abstract The new lead/scintillating-fibre calorimeter (“SpaCal”) for the backward region of the H1 experiment at HERA (DESY) is equipped with fine mesh phototubes which operate in a magnetic field close to 1 T. A large sample of these tubes of the types Hamamatsu R5505 and R5506, and Hamamatsu R2490-05, have been tested in fields of up to 1.2T. We have investigated the cathode homogeneity with and without magnetic field, the gain loss under the influence of the magnetic field, and stability with time. For a subsample of tubes, we have performed additional studies on stability with respect to temperature changes, variation of gain as a function of the magnetic field, high voltage discharges, single photo-electron response, and linearity. We finally summarize the experience with these tubes after one year of operation in the experiment.
55139157
SLHC tracker upgrade: challenges and strategies in ATLAS
The Large Hadron Collider (LHC) will be upgraded to the Super-LHC in ≈2016 to provide a ten-fold increased luminosity and data rate. The inner silicon tracking detectors of the ATLAS and CMS experiments will be replaced by even more powerful devices. The new detectors will face unprecedented particle densities and radiation levels. Limiting the power consumption of the front-end electronics, distributing power efficiently and minimizing detector mass, while keeping the costs of the detector affordable, are key challenges. Possible design solutions and the status of R&D for ATLAS are described.
119863129
Performance of the H1 lead/scintillating-fibre calorimeter
Abstract In the winter-shutdown 1994/95 the backward region of the H1 detector has been equipped with a new lead/scintillating-fibre calorimeter. The purpose of the calorimeter is to perform precise measurements of the energy and the position of scattered electrons in ep collisions at HERA. In addition, the calorimeter determines the hadronic energy flow in the backward region and provides detailed trigger information and efficient background rejection exploiting the difference of impact times for physics events and beam related background events. The first data-taking experience with the new device is described.
7496605
Serial Powering for Silicon Strip Detectors at SLUC
Serial powering of silicon sensors is a novel powering scheme that would reduce the total power, the number of cables, the passive detector material, and the costs of future silicon trackers by large factors. Modules are chained in series and are served by a single current source. Serial powering is of great interest for future large-scale silicon tracking detectors for particle physics with many thousands of densely packed detector modules. Tests with six ATLAS semiconductor tracker (SCT) modules using both serial powering and the conventional independent powering have been carried out. The electrical performance of SCT modules powered in series is excellent. We present selected results and discuss the system aspects of a serial powering.
120842226
GALACTIC MODEL UNCERTAINTIES IN INDIRECT DARK MATTER SEARCH
If Dark Matter (DM) particles are a thermal relic from the early universe, they are expected to annihilate into quarks and leptons in order to reduce the number density with respect to the number of photons. The annihilation into quarks is expected to be dominant which may lead to a significant excess in gamma rays, antiprotons and positrons, as discussed in recent reviews. An excess in gamma rays above the background from interactions between cosmic rays (CR) and the interstellar medium has indeed been observed by the EGRET gamma ray spectrometer on board of the NASA Compton Gamma Ray Observatory, which has been taken data in space between the years 1991 and 2000. This excess shows all the properties of the annihilation of a 60 GeV Weakly Interacting Massive Particle (WIMP), as discussed by de Boer et al. . Especially the distribution of the excess could be used to predict the shape of the rotation curve of the Galaxy, thus proving that the excess is a tracer of Dark Matter. The main assumption in this analysis was that the shape of the CR background is the same everywhere in the Galaxy, as is expected from the fact that the energy loss time for protons is large compared with the diffusion time. The interaction of CR protons with the interstellar gas is the major source of background for gamma ray energies in the few GeV range. The CR electrons have large energy losses by inverse Compton scattering and Bremsstrahlung, which are additional sources of gamma rays. It is the main purpose of the present note to study the uncertainties in the shape of the CR background and the corresponding uncertainties in the gamma ray spectra. This was done with the publicly available GALPROP propagation model after modifying it to include DMA. In addition the effects of the inhomogeneous local solar neighborhood were studied. Furthermore anisotropic diffusion, expected in spiral galaxies with strong anisotropic magnetic fields, was studied which increases the uncertainties of charged secondary particles by a wide margin. The latter is relevant, since in a recent paper Bergstrom et al. claimed that the flux of antiprotons excludes the DMA interpretation of the EGRET excess. This conclusion was based on their isotropic propagation model in the DarkSusy program.
125650653
Study of hadronic event shapes with the CMS detector at LHC
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.
117392007
Recent results from experiment NA52 at the CERN SPS
We present recent results of the NA52 experiment on the strangelet search and on particle, antiparticle, light nuclei and antinuclei production in minimum bias Pb + Pb collisions at 158 A GeV and zero production angle. Upper limits for the production of strangelets are given and one candidate found using less stringent lifetime cuts is discussed. The rapidity dependence of K+(K−), p(), d(), t and as well as first results on 4He, 6Li and 7Be at forward rapidities are presented. First results on the centrality dependence of the /p ratio are reported. Within the framework of a thermodynamical and a coalescence model, the temperature, the baryon- and strangeness-chemical potentials and the radius of the particle source at midrapidity have been estimated.
122217457
The low energy effective Higgs potential of the minimal nonlinear supersymmetric SU(5)-model and its phenomenology
Abstract. The low energy effective Higgs potential of the minimal nonlinear supersymmetric SU(5)-Model is derived. The physical Higgs particle spectra are the same as those of the linear supersymmetric model MSSM: two scalar bosons, a pseudo-scalar and a charged scalar. Mass relations are derived and compared to those of the MSSM. Production cross sections are calculated for LEP1, LEP2, LC-500, LC-1000 and LC-2000 and discussed how far this model might be tested at these colliders.
