17991299
Strangelets, strangeness and antimatter: results from the experiment NA52 at CERN
We present results of the CERN experiment NA52 which measures Pb+Pb collisions at 158 A GeV. The topics we address are: 1. strangelet search, 2. nuclei and antinuclei production and 3. strangeness production. No strangelets have been found. We set upper limits which stretch down to the minimal values of ∼ 2 10−10 for negatively and 3 10−9 for positively charged strangelets. We observed 5 3He near midrapidity. Nuclei and antinuclei cross sections suggest production mainly through coalescence, out of a thermalised particle source, at the time of the thermal freeze-out as witnessed by their temperature of 100-120 MeV. Charged kaons per participant nucleon (Np) show an onset of enhancement followed by saturation at Np ∼ 80, corresponding approximately to an initial energy density of i ∼ 1.3 GeV/fm. This onset may be connected to the onset of the QCD phase transition.
124310260
Baryon and antibaryon production in lead-lead collisions at 158 A GeV/c
Abstract We report on baryon and antibaryon as well as K + and K − production cross sections measured in lead-lead collisions at 158 GeV /c per nucleon. The presented data were taken at zero degree production angle with a minimum bias trigger. The measurements covered a wide range of rapidity 1.4 y
122225376
An investigation of the antinuclei and nuclei production mechanism in Pb + Pb collisions at 158 A GeV
We investigate the production mechanisms of p, d, t, 3He, 4He, 6Li, , and in Pb+Pb collisions at 158 A GeV measured near zero transverse momentum with the NA52 experiment at the CERN SPS. We find evidence that nuclei and antinuclei in Pb+Pb collisions are mainly produced via the coalescence mechanism out of a thermalized source of hadrons, at a time close to the thermal freeze-out of hadrons corresponding to a temperature of ~120 MeV.
123035541
The NA52 strangelet search
The NA52 experiment searches for long-lived charged strangelets in 158 A GeV c-1 Pb + Pb collisions at CERN SPS. The experiment is able to identify single particles coming from the collisions at pt = 0. We collected 1013 Pb + Pb interactions looking for negatively charged strangelets and 3 × 1011 Pb + Pb interactions for positively charged ones. No evidence for the production of strangelets has been observed. We present here resulting experimental differential and total upper production limits.
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.
124388402
Strangelet search and particle production studies in Pb + Pb collisions at 158-A-GeV/c at CERN SPS
We searched for long-lived strange quark matter particles, so-calledstrangelets, and studied particle and antiparticle production in Pb+Pb collisions at 158 GeV/c per nucleon at zero degree production angle. We give upper limits for the production of strangelets covering a mass to charge ratio up to 120 GeV/c 2 and lifetimest lab>1.2 μs and plot invariant differential production cross sections as a function of rapidity for a variety of particles.
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.
120399805
Gluon Initiated Vector Boson Fusion
The gluon-gluon induced terms for Higgs production through vector-boson fusion are calculated. They are a finite and gauge-invariant subset of the NNLO corrections in the strong coupling constant. This is also the lowest order with t-channel colour exchange between the scattering quarks, leading to additional hadronic activity between the outgoing jets.
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.
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.

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.