16790063
An algorithm for Landau gauge fixing in Lattice QCD
An algorithm for gauge fixing to the minimal Landau gauge in lattice QCD is described. The method, a combination of an evolutionary algorithm with a steepest descent method, is able to solve the problem of the nonperturbative gauge fixing. The performance of the combined algorithm is investigated on 8, β = 5.7, and 16, β = 6.0, lattice SU(3) gauge configurations.
16286511
Infrared exponents of gluon and ghost propagators from Lattice QCD
The compatibility of the pure power law infrared solution of QCD Dyson-Schwinger equations (DSE) and lattice data for the gluon and ghost propagators in Landau gauge is discussed. For the gluon propagator, the lattice data is compatible with the DSE infrared solution with an exponent $\kappa\sim0.53$, measured using a technique that suppresses finite volume effects and allows to model these corrections to the lattice data. For the ghost propagator, the lattice data does not seem to follow the infrared DSE power law solution.
118792625
Some properties of two Nambu-Jona-Lasinio -type models with inputs from lattice QCD
IPNL, Universit´e de Lyon/Universit´e Lyon 1, CNRS/IN2P3, 4 rue E.Fermi,F-69622 Villeurbanne Cedex, FranceWe investigate the phase diagram of the so-called Polyakov–Nambu–Jona-Lasinio (PNJL) model at ﬁnite temperature and nonzero chemicalpotential. The calculations are performed in the light and strange quarksectors (u, d, s), which includes the ’t Hooft instanton induced interactionterm that breaks the axial symmetry, and the quarks are coupled to the(spatially constant) temporal background gauge ﬁeld. On one hand, a spe-cial attention is payed to the critical end point (CEP). The strength of theﬂavor-mixing interaction alters the CEP location, since when it becomesweaker the CEP moves to low temperatures and can even disappear. Onthe other hand, we also explore the connection between QCD, a nonlocalNambu–Jona-Lasinio type model and the Landau gauge gluon propaga-tor. Possible links between the quenched gluon propagator and low energyhadronic phenomenology are investigated.PACS numbers: 11.10.Wx, 11.30.Rd, 12.40.-y
118493159
Gluon screening mass at finite temperature from the Landau gauge gluon propagator in lattice QCD
We address the interpretation of the Landau gauge gluon propagator at finite temperature as a massive-type bosonic propagator. Using pure gauge SU(3) lattice simulations at a fixed lattice volume $\ensuremath{\sim}(6.5\text{ }\text{ }\mathrm{fm}{)}^{3}$, we compute the electric and magnetic form factors, extract a gluon mass from Yukawa-like fits, and study its temperature dependence. This is relevant both for the Debye screening at high temperature $T$ and for confinement at low $T$.
7542535
Exploring the infrared Landau gauge propagators using large asymmetric lattices
We report on the infrared limit of the quenched lattice Landau gauge gluon and ghost propagators computed from large asymmetric lattices. In particular, the compatibility of the pure power law infrared solutions of the Dyson-Schwinger equations with the lattice data is investigated and the exponent $\kappa$ is measured. The gluon lattice data favour $\kappa \sim 0.52$, which would imply a vanishing zero momentum gluon propagator. For the subset of lattices where the ghost propagator was computed, the data is not compatible with a pure power law. Our data also show a decreasing running coupling in the infrared region. Furthermore, positivity violation for the gluon propagator is also verified.
117914077
Force Gradient Integrators
We present initial results of the use of Force Gradient integ rators for lattice field theories. These promise to give significant performance improvements, espe cially for light fermions and large lattices. Our results show that this is indeed the case, indi cating a speed-up of more than a factor of two, which is expected to increase as the integration step size becomes smaller for larger lattices and smaller fermion masses.
118843154
Performance and operation of the CMS electromagnetic calorimeter
The operation and general performance of the CMS electromagnetic calorimeter using cosmic-ray muons are described. These muons were recorded after the closure of the CMS detector in late 2008. The calorimeter is made of lead tungstate crystals and the overall status of the 75 848 channels corresponding to the barrel and endcap detectors is reported. The stability of crucial operational parameters, such as high voltage, temperature and electronic noise, is summarised and the performance of the light monitoring system is presented.
1419821
Search for a standard-model-like Higgs boson with a mass in the range 145 to 1000 GeV at the LHC
A search for a standard-model-like Higgs boson in the H→WW and H→ZZ decay channels is reported, for Higgs boson masses in the range 145<mH<1000 GeV. The search is based upon proton–proton collision data samples corresponding to an integrated luminosity of up to 5.1 fb−1 at $\sqrt{s} = 7~\mbox{TeV}$ and up to 5.3 fb−1 at $\sqrt{s} = 8~\mbox{TeV}$, recorded by the CMS experiment at the LHC. The combined upper limits at 95 % confidence level on products of the cross section and branching fractions exclude a standard-model-like Higgs boson in the range 145<mH<710 GeV, thus extending the mass region excluded by CMS from 127–600 GeV up to 710 GeV.
15081043
Fixed points and vacuum energy of dynamically broken gauge theories
We show that if a gauge theory with dynamical symmetry breaking has nontrivial fixed points, they will correspond to extrema of the vacuum energy. This relationship provides a different method to determine fixed points.
19615803
Probing the eV-Mass range for solar axions with CAST
The CERN Axion Solar Telescope (CAST) is searching for solar axions which could be produced in the core of the Sun via the so-called Primakoff effect. Not only would these hypothetical particles solve the strong CP problem, but they are also one of the favored candidates for dark matter. In order to look for axions originating from the Sun, CAST uses a decommissioned LHC prototype magnet. In its 10 m long magnetic field region of 9 Tesla, axions could be reconverted into X-ray photons. Different X-ray detectors are installed on both ends of the magnet, which is mounted on a structure built to follow the Sun during sunrise and sunset for a total of about 3 hours per day. The analysis of the data acquired during the first phase of the experiment with vacuum in the magnetic field region yielded the most restrictive experimental upper limit on the axion-to-photon coupling constant for axion masses up to about 0.02 eV. In order to extend the sensitivity of the experiment to a wider mass range, the CAST experiment continues its search for axions with helium in the magnet bores. In this way it is possible to restore coherence of conversion for larger masses. Changing the pressure of the helium gas enables the experiment to scan different axion masses in the range of up to about 1.2 eV. Especially at high pressures, a precise knowledge of the gas density distribution is crucial to obtain accurate results. In the first part of this second phase of CAST, 4He was used and the axion mass region was extended up to 0.39 eV, a part of phase space favored by axion models. In CAST's ongoing 3He phase the studied mass range is now being extended further. In this contribution the final results of CAST's 4He phase will be presented and the current status of the 3He run will be given. This includes latest results as well as prospects of future axion experiments.
119095331
A study on analytic parametrizations for proton–proton cross-sections and asymptotia
A comparative study on some representative parametrizations for the total and elastic cross-sections as a function of energy is presented. The dataset comprises pp and scattering in the c.m. energy interval 5 GeV–8 TeV. The parametrization for the total cross-section at low and intermediate energies follows the usual reggeonic structure (non-degenerate trajectories). For the leading high-energy pomeron contribution, we consider three distinct analytic parametrizations: either a power (P) law, or a log-squared (L2) law or a log-raised-to-γ (Lγ) law, where the exponent γ is treated as a real free fit parameter. The parametrizations are also extended to fit the elastic (integrated) cross-section data in the same energy interval. Our main conclusions are the following: (1) the data reductions with the logarithmic laws show strong dependence on the unknown energy scale involved, which is treated here either as a free parameter or fixed at the energy threshold; (2) the fit results with the P law, the L2 law (free scale) and the Lγ law (fixed scale and exponent γ above 2) are all consistent within their uncertainties and with the experimental data up to 7 TeV, but they partially underestimate the high-precision TOTEM measurement at 8 TeV; (3) once compared with these results, the L2 law with fixed scale is less consistent with the data and, in the case of a free scale, this pomeron contribution decreases as the energy increases below the scale factor (which lies above the energy cutoff); (4) in all cases investigated, the predictions for the asymptotic ratio between the elastic and total cross-sections, within the uncertainties, do not exceed the value 0.430 (therefore, below the black-disc limit) and the results favor rational limits between 1/3 and 2/5. We are led to conclude that the rise of the hadronic cross-sections at the highest energies still constitutes an open problem, demanding further and detailed investigation.