Radiation from a charged particle-in-flight from a laminated medium to vacuum

The radiation from a charged particle-in-flight from a semi-infinite laminated medium to vacuum and back,- from vacuum to the laminated medium, has been investigated. Expressions for the spectral-angular distribution of radiation energy in vacuum (at large distances from the boundary of laminated medium) were obtained for both the cases with no limitations on the amplitude and variation profile of the laminated medium permittivity. The results of appropriate numerical calculations are presented and possible applications of the obtained results are discussed.Comment: 8 pages, 6 figures, contribution to Proceedings of International Symposium RREPS-2009, 07-11 September, 2009, Zvenigorod, Russi

Search for long-lived particles that decay into final states containing two electrons or two muons in proton-proton collisions at s√=8 TeV

A search is performed for long-lived particles that decay into final states that include a pair of electrons or a pair of muons. The experimental signature is a distinctive topology consisting of a pair of charged leptons originating from a displaced secondary vertex. Events corresponding to an integrated luminosity of 19.6 (20.5)  fb−1 in the electron (muon) channel were collected with the CMS detector at the CERN LHC in proton-proton collisions at s√=8  TeV. No significant excess is observed above standard model expectations. Upper limits on the product of the cross section and branching fraction of such a signal are presented as a function of the long-lived particle’s mean proper decay length. The limits are presented in an approximately model-independent way, allowing them to be applied to a wide class of models yielding the above topology. Over much of the investigated parameter space, the limits obtained are the most stringent to date. In the specific case of a model in which a Higgs boson in the mass range 125–1000  GeV/c2 decays into a pair of long-lived neutral bosons in the mass range 20–350  GeV/c2, each of which can then decay to dileptons, the upper limits obtained are typically in the range 0.2–10 fb for mean proper decay lengths of the long-lived particles in the range 0.01–100 cm. In the case of the lowest Higgs mass considered (125  GeV/c2), the limits are in the range 2–50 fb. These limits are sensitive to Higgs boson branching fractions as low as 10−4

Detection of X-ray galaxy clusters based on the Kolmogorov method

The detection of clusters of galaxies in large surveys plays an important part in extragalactic astronomy, and particularly in cosmology, since cluster counts can give strong constraints on cosmological parameters. X-ray imaging is in particular a reliable means to discover new clusters, and large X-ray surveys are now available. Considering XMM-Newton data for a sample of 40 Abell clusters, we show that their analysis with a Kolmogorov distribution can provide a distinctive signature for galaxy clusters. The Kolmogorov method is sensitive to the correlations in the cluster X-ray properties and can therefore be used for their identification, thus allowing to search reliably for clusters in a simple way

Measurements of the γv p → p\u27π+π− Cross Section with the CLAS Detector for 0.4 GeV\u3csup\u3e2\u3c/sup\u3e \u3c Q\u3csup\u3e2\u3c/sup\u3e \u3c 1.0 GeV\u3csup\u3e2\u3c/sup\u3e and 1.3 GeV \u3c W \u3c 1.825 GeV

New results on the single-differential and fully integrated cross sections for the process γvp → p\u27π+π− are presented. The experimental data were collected with the CLAS detector at Jefferson Laboratory. Measurements were carried out in the kinematic region of the reaction invariant mass W from 1.3 to 1.825 GeV and the photon virtuality Q2 from 0.4 to 1.0 GeV2. The cross sections were obtained in narrow Q2 bins (0.05 GeV2) with the smallest statistical uncertainties achieved in double-pion electroproduction experiments to date. The results were found to be in agreement with previously available data where they overlap. A preliminary interpretation of the extracted cross sections, which was based on a phenomenological meson-baryon reaction model, revealed substantial relative contributions from nucleon resonances. The data offer promising prospects to improve knowledge on the Q2 evolution of the electrocouplings of most resonances with masses up to ∼1.8 GeV

Using gamma+jets Production to Calibrate the Standard Model Z(nunu)+jets Background to New Physics Processes at the LHC

The irreducible background from Z(nunu)+jets, to beyond the Standard Model searches at the LHC, can be calibrated using gamma+jets data. The method utilises the fact that at high vector boson pT, the event kinematics are the same for the two processes and the cross sections differ mainly due to the boson-quark couplings. The method relies on a precise prediction from theory of the Z/gamma cross section ratio at high pT, which should be insensitive to effects from full event simulation. We study the Z/gamma ratio for final states involving 1, 2 and 3 hadronic jets, using both the leading-order parton shower Monte Carlo program Pythia8 and a leading-order matrix element program Gambos. This enables us both to understand the underlying parton dynamics in both processes, and to quantify the theoretical systematic uncertainties in the ratio predictions. Using a typical set of experimental cuts, we estimate the net theoretical uncertainty in the ratio to be of order 7%, when obtained from a Monte Carlo program using multiparton matrix-elements for the hard process. Uncertainties associated with full event simulation are found to be small. The results indicate that an overall accuracy of the method, excluding statistical errors, of order 10% should be possible.Comment: 22 pages, 14 figures; Accepted for publication by JHE

Modified Signals for Supersymmetry in the NMSSM with a Singlino-like LSP

In the framework of the NMSSM with a singlino-like LSP, we study quantitatively the impact of the additional bino -> singlino cascade on the efficiencies in several search channels for supersymmetry of the ATLAS and CMS collaborations. Compared to the MSSM, the additional cascade reduces the missing transverse energy, but leads to additional jets or leptons. For the NMSSM benchmark lines which generalize cMSSM benchmark points, the efficiencies in the most relevant 2/3 jet + missing energy search channels can drop by factors ~1/3 to ~1/7, and can reduce the present lower bounds on M_{1/2} by as much as ~0.9 - 0.75 in the NMSSM for large bino-singlino mass differences. The larger efficiencies in multijet or multilepton search channels are not strong enough to affect this conclusion. In the fully constrained cNMSSM, sparticle decay cascades via the lightest stau can lead to signal cross sections in multilepton and 2tau search channels which are potentially visible at the LHC with 7 TeV center of mass energy.Comment: 24 pages, 9 Figures, misprint in Table 1 correcre

Stau Kinks at the LHC

The kink signature of charged tracks is predicted in some SUSY models, and it is very characteristic signal at collider experiments. We study the kink signature at LHC using two models, SUSY models with a gravitino LSP and a stau NLSP, and R-parity violating SUSY models with a stau (N)LSP. We find that a large number of kink events can be discovered in a wide range of the SUSY parameters, when the decay length is O(10-10^5)mm. Model discrimination by identifying the daughter particles of the kink tracks is also discussed.Comment: 19 pages, 4 figures; Version published in JHEP; abstract refined, reference added and several minor corrections in tex

Some Open Points in Nonextensive Statistical Mechanics

We present and discuss a list of some interesting points that are currently open in nonextensive statistical mechanics. Their analytical, numerical, experimental or observational advancement would naturally be very welcome.Comment: 30 pages including 6 figures. Invited paper to appear in the International Journal of Bifurcation and Chao

Theoretical predictions for charm and bottom production at the LHC

We present predictions for a variety of single-inclusive observables that stem from the production of charm and bottom quark pairs at the 7 TeV LHC. They are obtained within the FONLL semi-analytical framework, and with two "Monte Carlo + NLO" approaches, MC@NLO and POWHEG. Results are given for final states and acceptance cuts that are as close as possible to those used by experimental collaborations and, where feasible, are compared to LHC data.Comment: 22 pages, 10 figure

Overview of experimental results in PbPb collisions at sqrt{s_NN} = 2.76 TeV by the CMS Collaboration

The CMS experiment at the LHC is a general-purpose apparatus with a set of large acceptance and high granularity detectors for hadrons, electrons, photons and muons, providing unique capabilities for both proton-proton and ion-ion collisions. The data collected during the November 2010 PbPb run at sqrt{s_NN} = 2.76 TeV was analyzed and multiple measurements of the properties of the hot and dense matter were obtained. Global event properties, detailed study of jet production and jet properties, isolated photons, quarkonia and weak bosons were measured and compared to pp data and Monte Carlo simulations.Comment: 8 pages, 10 figures, proceedings for Quark Matter 2011, Annecy, France, May 23-28, 201