118371809
The Laser Beacon: A survey system for the torsion-free alignment and monitoring of the L3 Muon Spectrometer octants
Given the small sagitta of a few millimeters of high energetic muons in the L3 Muon Spectrometer at LEP (CERN) and the enormous dimensions (75 m2 × 14 m) of this instrument, it is evident that alignment is the most critical task for its proper evaluation. In the chambers of each of the sixteen modules (“octants”), which form the spectrometer, wire planes are precisely positioned with respect to the front side and the rear side centerlines. A novel system - the Laser Beacon System - allows to make these centerlines coplanar within 25 μ rad by the aid of a reference plane defined by a sweeping laser beam. This restricts a possible torsion induced systematic momentum error for a 50 GeV/c muon to 0.25%. The main design and production features of the Laser Beacon System are described. Results of measurements in test assemblies and in the octants are given.
15336878
Hot subdwarfs from the stable Roche lobe overflow channel
Context. Hot subdwarfs are core-helium-burning stars with extremely thin envelopes. We discuss the formation and evolution of hot subdwarfs formed through the stable Roche lobe overflow (RLOF) channel of intermediate-mass binaries, although their formation channels are various. Aims. In this study, we concentrate on the formation and evolution of hot subdwarfs binaries through the stable RLOF channel of intermediate-mass binaries. We aim at setting out the properties of hot subdwarfs and their progenitors, so that we can understand the formation and evolution of hot subdwarfs. Methods. Employing Eggleton's stellar evolution code, we have computed conservative and nonconservative population I binary evolution sequences. The initial mass of the primary ranges from 2.2 to 6.3 M(circle dot), spaced by approximately 0.1 in log M, the initial mass ratio q(i) = M(1)/M(2) is between 1.1 and 4.5, and the Roche lobe overflow begins at the main sequence, the Hertzsprung gap and the first giant branch. In nonconservative binary evolution, we assume that 50 percent of the mass lost from the primary leaves the system, carrying away the specific angular momentum of the primary, and the remaining mass is accreted on to the secondary during the RLOF. Also, we have studied the distributions of the mass and orbital periods of hot subdwarfs using the population synthesis approach. Results. We have obtained the ranges of the initial parameters of progenitor binaries and the properties of hot subdwarfs through the stable RLOF channel of intermediate-mass binaries, e. g. mass, envelope mass and age of hot subdwarfs. We have found that hot subdwarfs could be formed through stable Roche lobe overflow at the main sequence and Hertzsprung gap. We have also found that some subdwarf B or OB stars have anomalously high mass (similar to 1 M(circle dot)) with a thick envelope (similar to 0.07 M(circle dot)-similar to 0.16) in our models. By comparing our theoretical results with observations on the hot subdwarfs in open clusters, we suggest that more hot subdwarfs in binary systems might be found in open clusters in the future.
122970197
Multijet production in neutral current deep inelastic scattering at HERA and determination of alpha(s)
Multijet production rates in neutral current deep inelastic scattering (DIS) have been measured in the range of exchanged boson virtualities 10<Q2<5000 GeV2. The data were taken at the ep collider HERA with centre-of-mass energy using the ZEUS detector and correspond to an integrated luminosity of 82.2 pb-1. Jets were identified in the Breit frame using the kT cluster algorithm in the longitudinally invariant inclusive mode. Measurements of differential multijet cross sections are presented as functions of jet transverse energy , pseudorapidity and Q2 with and . Next-to-leading-order QCD calculations describe the data well. The value of the strong coupling constant αs(MZ), determined from the ratio of the trijet to dijet cross sections, is .
15702909
The continuum limit of perturbative coefficients calculated with a large field cutoff
Abstract We report MC calculations of perturbative coefficients for lattice scalar field theory in dimensions l, 2 and 3, where the large field contributions are cutoff. This produces converging (instead of asymptotic) perturbative series. We discuss the statistical errors and the lattice effects and sho-kv that accurate calculations are possible even in a crossover region where no approximation works. We show that the field cutoff is also a UV regulator. We point out the relevance for QCD questions discussed by Tomboulis ad Trottier at this conference.
36263241
New optimization methods for converging perturbative series with a field cutoff
We take advantage of the fact that in lambda phi ^4 problems a large field cutoff phi_max makes perturbative series converge toward values exponentially close to the exact values, to make optimal choices of phi_max. For perturbative series terminated at even order, it is in principle possible to adjust phi_max in order to obtain the exact result. For perturbative series terminated at odd order, the error can only be minimized. It is however possible to introduce a mass shift in order to obtain the exact result. We discuss weak and strong coupling methods to determine the unknown parameters. The numerical calculations in this article have been performed with a simple integral with one variable. We give arguments indicating that the qualitative features observed should extend to quantum mechanics and quantum field theory. We found that optimization at even order is more efficient that at odd order. We compare our methods with the linear delta-expansion (LDE) (combined with the principle of minimal sensitivity) which provides an upper envelope of for the accuracy curves of various Pade and Pade-Borel approximants. Our optimization method performs better than the LDE at strong and intermediate coupling, but not at weak coupling where it appears less robust and subject to further improvements. We also show that it is possible to fix the arbitrary parameter appearing in the LDE using the strong coupling expansion, in order to get accuracies comparable to ours.
121764664
The DIRC prototype for the WASA experiment at COSY
The implementation of a DIRC (Detector or Internally Reflected Cherenkov light) was planned for the WASA-at-COSY experiment, located at the Forschungszentrum Julich and is a major project for the future PANDA experiment at FAIR. In order to study the components and the behavior of the detector under experimental conditions, a large scale demonstrator made of acrylic glass was built and tested at the external proton beam of the COSY accelerator. The main properties of the components, especially of the newly developed front end electronics and the results of the first tests are presented.
16928527
The GRB‐Supernova Connection
Long‐duration gamma‐ray bursts (GRBs) are believed to be produced by the core collapse of massive stars and hence to be connected with supernovae (SNe). Indeed, for four pairs of GRBs and SNe, spectroscopically confirmed connection has been firmly established. For more than a dozen of GRBs the SN signature (the ‘red bump’) has been detected in the afterglow lightcurves. Based on the four pairs of GRBs and SNe with spectroscopically confirmed connection a tight correlation was found between the peak spectral energy of GRBs and the peak bolometric luminosity of the underlying SNe. The recent discovery of X‐ray flash 080109 associated with a normal core‐collapse SN 2008D confirmed this relation and extended the GRB‐SN connection. Progress on the GRB‐SN connection is briefly reviewed.
123070841
Open Charm Physics at BESIII
An integrated luminosity of 2.9 fb − 1 data had been collected at s = 3.773 GeV by May of 2011 with the BESIII detector at the BEPCII collider, which makes it possible to systematically study the properties of the semileptonic, leptonic and hadronic decays of the charmed mesons. With the data, many high precise measurements including the CKM matrix elements and the form factors, the decay constants, as well as the topics related to hadronic decays such as absolute branching fractions, searches for CP violations and Dalitz plot analyses are being studied at the BESIII. All these analyses are expected to be accomplished in the near future.
2141453
Probing the Cosmic Metallicity Evolution with Gamma-Ray Bursts
The current Swift sample of gamma-ray bursts (GRBs) with measured redshifts allows to test the assumption that GRBs trace the star formation in the Universe. Some authors have claimed that the rate of GRBs increases with cosmic redshift faster than the star formation rate, whose cause is not known yet. In this paper, I investigate the possibility for interpreting the observed discrepancy between the GRB rate history and the star formation rate history by the cosmic metallicity evolution, motivated by the observation that the cosmic metallicity evolves strongly with redshift and GRBs prefer to occur in low metallicity galaxies. Adopting a simple model for the relation between the GRB production and the cosmic metallicity history as proposed by Langer & Norman, and a star formation rate determined by Hopkins & Beacom from current observations, I show that the observed redshift distribution of the Swift GRBs can be reproduced with a fairly good accuracy. Although the results are limited by the small size of the GRB sample and the poorly understood selection biases in detection and localization of GRBs and in redshift determination, the results suggest that GRBs trace both the star formation and the metallicity evolution. If the star formation history can be accurately measured with other approaches, which is presumably achievable in the near future, it will be possible to determine the cosmic metallicity evolution with the study on the redshift distribution of GRBs.
18205314
Shock breakout in Type Ibc supernovae and application to GRB 060218/SN 2006aj
Recently, a soft blackbody component was observed in the early X-ray afterglow of GRB 060218, which was interpreted as shock breakout from the thick wind of the progenitor Wolf-Rayet (WR) star of the underlying Type Ic supernova 2006aj. In this paper, we present a simple model for computing the characteristic quantities (including energy, temperature and time duration) for the transient event from the shock breakout in Type Ibc supernovae produced by the core-collapse of WR stars surrounded by dense winds. In contrast to the case of a star without a strong wind, the shock breakout occurs in the wind region rather than inside the star, caused by the large optical depth in the wind. We find that, for the case of a WR star with a dense wind, the total energy of the radiation generated by the supernova shock breakout is larger than that in the case of the same star without a wind by a factor of > 10. The temperature can be either hotter or colder, depending on the wind parameters. The time duration is larger caused by the increase in the effective radius of the star due to the presence of a thick wind. Then, we apply the model to GRB 060218/SN 2006aj. We show that, to explain both the temperature and the total energy of the blackbody component observed in GRB 060218 by the shock breakout, the progenitor WR star has to have an unrealistically large core radius (the radius at optical depth of 20), larger than 100R ⊙ . In spite of this disappointing result, our model is expected to have important applications to the observations on Type Ibc supernovae in which the detection of shock breakout will provide important clues to the progenitors of Type Ibc supernovae.
15791171
Energy transfer and its effects on the secondaries in W Ursae Majoris type contact binaries
Based on the physical parameters of 133 W Ursae Majoris (W UMa) type contact binaries, energy transfer and its effects on the secondaries in W UMa contact binaries are investigated. Relations are given between the mass ratio (q) for W UMa contact binaries and the relative energy transfer rates, i.e. U(1), the ratio of the transferred luminosity to the surface luminosity of the primary, and U(2), the ratio of the transferred luminosity to the nuclear luminosity of the secondary. The theoretical curves(U(1) versus q and U(2) versus q) are derived based on various assumptions: that the two components in each W UMa system are nearly identical in effective temperature and just fill their inner Roche lobes, and the primaries are zero-age main-sequence stars. Although these curves can reflect the distribution of U(1) and U(2) versus q, some observational systems deviate significantly from these curves. This results mainly from the difference in effective temperatures of the components of W UMa systems. The radius and the density of the secondary are related to the relative energy transfer rate U(2): the higher U(2), the greater the expansion and the lower the density of the secondary in a W UMa system. In addition, it is found that the temperature difference of W UMa binary components is correlated with the relative energy transfer rate U(1) and decreases with increasing U(1). This might suggest that there is a thermal coupling between the two components in W UMa contact binaries, and that the classification of W UMa contact binaries into A or W types depends on the energy transfer from the primary to the secondary. The temperature difference of W UMa binary components is poorly correlated with the mass of the primary. This suggests that the properties of the common envelope of a W UMa contact binary might not have a significant effect on the energy transfer between the two components.