118340898
Measurement of the charm and beauty structure functions using the H1 vertex detector at HERA
Inclusive charm and beauty cross sections are measured in e−p and e+p neutral current collisions at HERA in the kinematic region of photon virtuality 5≤Q2≤2000 GeV2 and Bjorken scaling variable 0.0002≤x≤0.05. The data were collected with the H1 detector in the years 2006 and 2007 corresponding to an integrated luminosity of 189 pb−1. The numbers of charm and beauty events are determined using variables reconstructed by the H1 vertex detector including the impact parameter of tracks to the primary vertex and the position of the secondary vertex. The measurements are combined with previous data and compared to QCD predictions.
54180669
DARK MATTER AND MASSIVE NEUTRINOS
117033883
Measurement of the single-top-quark t-channel cross section in pp collisions at $ \sqrt{s}=7 $ TeV
A bstractA measurement of the single-top-quark t-channel production cross section in pp collisions at $ \sqrt{s}=7 $ TeV with the CMS detector at the LHC is presented. Two different and complementary approaches have been followed. The first approach exploits the distributions of the pseudorapidity of the recoil jet and reconstructed top-quark mass using background estimates determined from control samples in data. The second approach is based on multivariate analysis techniques that probe the compatibility of the candidate events with the signal. Data have been collected for the muon and electron final states, corresponding to integrated luminosities of 1.17 and 1.56 fb−1, respectively. The single-top-quark production cross section in the t-channel is measured to be 67.2±6.1 pb, in agreement with the approximate next-to-next-to-leading-order standard model prediction. Using the standard model electroweak couplings, the CKM matrix element |Vtb| is measured to be 1.020 ± 0.046 (meas.) ± 0.017 (theor.).
18536190
Search for Excited Electrons in ep Collisions at HERA
A search for excited electrons is performed using the full e±p data sample collected by the H1 experiment at HERA, corresponding to a total luminosity of 475 pb−1. The electroweak decays of excited electrons e*→eγ, e*→eZ and e*→νW with subsequent hadronic or leptonic decays of the W and Z bosons are considered. No evidence for excited electron production is found. Mass dependent exclusion limits on e* production cross sections and on the ratio f/Λ of the coupling to the compositeness scale are derived within gauge mediated models. These limits extend the excluded region compared to previous excited electron searches. The e* production via contact interactions is also addressed for the first time in ep collisions.
119204233
Search for new physics in events with same-sign dileptons and b-tagged jets in pp collisions at $ \sqrt {s} = 7 $ TeV
A bstractA search for new physics is performed using isolated same-sign dileptons with at least two b-quark jets in the final state. Results are based on a 4.98 fb−1 sample of proton-proton collisions at a centre-of-mass energy of 7 TeV collected by the CMS detector. No excess above the standard model background is observed. Upper limits at 95% confidence level are set on the number of events from non-standard-model sources. These limits are used to set constraints on a number of new physics models. Information on acceptance and efficiencies are also provided so that the results can be used to confront additional models in an approximate way.
36326465
Search for third-generation leptoquarks and scalar bottom quarks in pp collisions at $ \sqrt{s}=7\;TeV $
A bstractResults are presented from a search for third-generation leptoquarks and scalar bottom quarks in a sample of proton-proton collisions at $ \sqrt{s}=7\;TeV $ collected by the CMS experiment at the LHC, corresponding to an integrated luminosity of 4.7 fb−1. A scenario where the new particles are pair produced and each decays to a b quark plus a tau neutrino or neutralino is considered. The number of observed events is found to be in agreement with the standard model prediction. Upper limits are set at 95% confidence level on the production cross sections. Leptoquarks with masses below ~450 GeV are excluded. Upper limits in the mass plane of the scalar quark and neutralino are set such that scalar bottom quark masses up to 410 GeV are excluded for neutralino masses of 50 GeV.
122697839
A Combined Three-Phase Signal Extraction of the Sudbury Neutrino Observatory Data Using Markov Chain Monte Carlo Technique
Neutrino physics has entered an era of precision, after proving that the Standard Solar Model is a viable theory and going beyond the current Standard Model of particle physics by proving that neutrinos possess nonzero masses. The Sudbury Neutrino Observatory (SNO) experiment, along with other experiments, has restricted neutrino mixing angle (θ12) and the mass square difference (∆m21) to lie within the large mixing solution area. SNO, located 2 km underground in Sudbury, Canada, was an ultraclean heavy-water (D2O) imaging detector for observing neutrinos produced by fusion reactions in the Sun. Neutrino interactions with heavy water resulted in flashes of light called C̆erenkov radiation which was detected by an array of photomultiplier tubes. SNO took data from November 1999 to November 2006, totalling 1082 days of data taking. This work describes an improved measurement of the mixing parameters from a combined fit of all the data. For the signal extraction fit on the data consisting of 4 observable of an event – radial position, recoil electron energy, direction relative to the Sun and event isotropy – Markov Chain Monte Carlo (MCMC) method based on Metropolis algorithm was employed. The nuisance parameters (systematics), weighted by external constraints, were allowed to vary in the fit. The goal of the thesis was to extract the survival probabilities of electron neutrinos and determine the total flux of active-flavour neutrinos from B decay in the Sun measured through the neutral current interactions of neutrinos on deuterium. The B flux from the fit is (5.24 ± 0.02) × 10 cm−2 s−1; uncertainty from statistics and systematics is 3.56%. Along with B flux, the fit extracted energy spectra of charged current interactions of neutrinos on deuterium and elastic scattering interactions of neutrinos on electrons. The fit described the energy-dependent day survival probability of solar neutrinos as a quadratic equation and asymmetry on the day survival probability as a linear equation. Four polynomial coefficients of the survival probability were extracted from the fit: constant coefficient as 0.3206± 0.0197, linear coefficient as 0.005± 0.008 and quadratic coefficient as −0.0014± 0.0033. There are two coefficients on the day-night asymmetry: constant coefficient as 0.0496 ± 0.0347 and the linear coefficient as −0.018 ± 0.028. The day-night asymmetry (0.0496) observed is 1.4σ away from zero. Using these findings, the oscillation space in terms of ∆m21 and θ12 will be further constrained. Compared to the previous published SNO results, the uncertainty on B went down from 3.83% to 3.56% and average B νe survival probability (p0) went down from 6.57% to 6.14%. If the data were analysed with the same assumptions, the decrease in uncertainties would have been approximately twice as big; however, more conservative systematic uncertainties were assigned in some cases.
17207524
Independent measurement of the total active 8B solar neutrino flux using an array of 3He proportional counters at the Sudbury Neutrino Observatory.
The Sudbury Neutrino Observatory (SNO) used an array of 3He proportional counters to measure the rate of neutral-current interactions in heavy water and precisely determined the total active (nu_x) 8B solar neutrino flux. This technique is independent of previous methods employed by SNO. The total flux is found to be 5.54_-0.31;+0.33(stat)-0.34+0.36(syst)x10(6) cm(-2) s(-1), in agreement with previous measurements and standard solar models. A global analysis of solar and reactor neutrino results yields Deltam2=7.59_-0.21;+0.19x10(-5) eV2 and theta=34.4_-1.2;+1.3 degrees. The uncertainty on the mixing angle has been reduced from SNO's previous results.
209842301
SEARCHES FOR HIGH-FREQUENCY VARIATIONS IN THE 8B SOLAR NEUTRINO FLUX AT THE SUDBURY NEUTRINO OBSERVATORY
We have performed three searches for high-frequency signals in the solar neutrino flux measured by the Sudbury Neutrino Observatory, motivated by the possibility that solar g-mode oscillations could affect the production or propagation of solar 8B neutrinos. The first search looked for any significant peak in the frequency range 1-144 day–1, with a sensitivity to sinusoidal signals with amplitudes of 12% or greater. The second search focused on regions in which g-mode signals have been claimed by experiments aboard the Solar and Heliospheric Observatory satellite, and was sensitive to signals with amplitudes of 10% or greater. The third search looked for extra power across the entire frequency band. No statistically significant signal was detected in any of the three searches.
118692214
Symplectic computation of Lyapunov exponents
A recently developed method for the calculation of Lyapunov exponents of dynamical systems is described. The method is applicable whenever the linearized dynamics is Hamiltonian. By utilizing the exponential representation of symplectic matrices, this approach avoids the renormalization and reorthogonalization procedures necessary in usual techniques. It is also easily extendible to damped systems. The method is illustrated by considering two examples of physical interest: a model system that describes the beam halo in charged particle beams and the driven van der Pol oscillator.
119159912
The cosmic code comparison project
Current and upcoming cosmological observations allow us to probe structures on smaller and smaller scales, entering highly nonlinear regimes. In order to obtain theoretical predictions in these regimes, large cosmological simulations have to be carried out. The promised high accuracy from observations makes the simulation task very demanding: the simulations have to be at least as accurate as the observations. This requirement can only be fulfilled by carrying out an extensive code verification program. The first step of such a program is the comparison of different cosmology codes including gravitational interactions only. In this paper, we extend a recently carried out code comparison project to include five more simulation codes. We restrict our analysis to a small cosmological volume which allows us to investigate properties of halos. For the matter power spectrum and the mass function, the previous results hold, with the codes agreeing at the 10% level over wide dynamic ranges. We extend our analysis to the comparison of halo profiles and investigate the halo count as a function of local density. We introduce and discuss ParaView as a flexible analysis tool for cosmological simulations, the use of which immensely simplifies the code comparison task.