ATLAS Monitored Drift Tube Chambers in E = 11 MeV Neutron Background

The influence of fast neutrons on the occupancy and the single tube resolution of ATLAS muon drift detectors was investigated by exposing a chamber built out of 3 layers of 3 short standard drift tubes to neutron flux-densities of up to 16 kHz/cm2 at a neutron energy of E=11 MeV. Pulse shape capable NE213 scintillaton detectors and a calibrated BF3 neutron detector provided monitoring of the neutron flux-density and energy. The sensitivity of the drift chamber to the neutrons was measured to be 4*10-4 by comparing data sets with and without neutron background. For the investigation of tracks of cosmic muons two silicon-strip detectors above and underneath the chamber allow to compare measured drift-radii with reference tracks. Alternatively, the single tube resolution was determined using the triple-sum method. The comparison between data with and without neutron irradiation shows only a marginal effect on the resolution and little influence on the muon track reconstruction.Comment: 4 pages, 11 figures, conferenc

A Cosmic Ray Measurement Facility for ATLAS Muon Chambers

Monitored Drift Tube (MDT) chambers will constitute the large majority of precision detectors in the Muon Spectrometer of the ATLAS experiment at the Large Hadron Collider at CERN. For commissioning and calibration of MDT chambers, a Cosmic Ray Measurement Facility is in operation at Munich University. The objectives of this facility are to test the chambers and on-chamber electronics, to map the positions of the anode wires within the chambers with the precision needed for standalone muon momentum measurement in ATLAS, and to gain experience in the operation of the chambers and on-line calibration procedures. Until the start of muon chamber installation in ATLAS, 88 chambers built at the Max Planck Institute for Physics in Munich have to be commissioned and calibrated. With a data taking period of one day individual wire positions can be measured with an accuracy of 8.3 micrometers in the chamber plane and 27 micrometers in the direction perpendicular to that plane.Comment: 14+1 pages, 11 figures, contributed paper to the EPS2003 conference, Aache

The Fourth Standard Model Family and the Competition in Standart Model Higgs Boson Search at Tevatron and LHC

The impact of the fourth Standard Model family on Higgs boson search at Tevatron and LHC is reviewed.Comment: 7 pages, 13 figure

Dirac Neutrino Dark Matter

We investigate the possibility that dark matter is made of heavy Dirac neutrinos with mass in the range [O(1) GeV- a few TeV] and with suppressed but non-zero coupling to the Standard Model Z as well as a coupling to an additional Z' gauge boson. The first part of this paper provides a model-independent analysis for the relic density and direct detection in terms of four main parameters: the mass, the couplings to the Z, to the Z' and to the Higgs. These WIMP candidates arise naturally as Kaluza-Klein states in extra-dimensional models with extended electroweak gauge group SU(2)_L* SU(2)_R * U(1). They can be stable because of Kaluza-Klein parity or of other discrete symmetries related to baryon number for instance, or even, in the low mass and low coupling limits, just because of a phase-space-suppressed decay width. An interesting aspect of warped models is that the extra Z' typically couples only to the third generation, thus avoiding the usual experimental constraints. In the second part of the paper, we illustrate the situation in details in a warped GUT model.Comment: 35 pages, 25 figures; v2: JCAP version; presentation and plots improved, results unchange

Cosmic ray tests of the D0 preshower detector

The D0 preshower detector consists of scintillator strips with embedded wavelength-shifting fibers, and a readout using Visible Light Photon Counters. The response to minimum ionizing particles has been tested with cosmic ray muons. We report results on the gain calibration and light-yield distributions. The spatial resolution is investigated taking into account the light sharing between strips, the effects of multiple scattering and various systematic uncertainties. The detection efficiency and noise contamination are also investigated.Comment: 27 pages, 24 figures, submitted to NIM

Hunt for new phenomena using large jet multiplicities and missing transverse momentum with ATLAS in 4.7 fb−1 of s√=7TeV proton-proton collisions

Results are presented of a search for new particles decaying to large numbers of jets in association with missing transverse momentum, using 4.7 fb−1 of pp collision data at s√=7TeV collected by the ATLAS experiment at the Large Hadron Collider in 2011. The event selection requires missing transverse momentum, no isolated electrons or muons, and from ≥6 to ≥9 jets. No evidence is found for physics beyond the Standard Model. The results are interpreted in the context of a MSUGRA/CMSSM supersymmetric model, where, for large universal scalar mass m 0, gluino masses smaller than 840 GeV are excluded at the 95% confidence level, extending previously published limits. Within a simplified model containing only a gluino octet and a neutralino, gluino masses smaller than 870 GeV are similarly excluded for neutralino masses below 100 GeV

Differential (2+1) Jet Event Rates and Determination of alpha_s in Deep Inelastic Scattering at HERA

Events with a (2+1) jet topology in deep-inelastic scattering at HERA are studied in the kinematic range 200 < Q^2< 10,000 GeV^2. The rate of (2+1) jet events has been determined with the modified JADE jet algorithm as a function of the jet resolution parameter and is compared with the predictions of Monte Carlo models. In addition, the event rate is corrected for both hadronization and detector effects and is compared with next-to-leading order QCD calculations. A value of the strong coupling constant of alpha_s(M_Z^2)= 0.118+- 0.002 (stat.)^(+0.007)_(-0.008) (syst.)^(+0.007)_(-0.006) (theory) is extracted. The systematic error includes uncertainties in the calorimeter energy calibration, in the description of the data by current Monte Carlo models, and in the knowledge of the parton densities. The theoretical error is dominated by the renormalization scale ambiguity.Comment: 25 pages, 6 figures, 3 tables, submitted to Eur. Phys.

Search for the standard model Higgs boson in ℓν\bm{\ellν}+jets final states in 9.7~fb−1\bm{^{-1}} of ppˉ\bm{p\bar{p}} collisions with the D0 detector

We present, in detail, a search for the standard model Higgs boson, $H$, in final states with a charged lepton (electron or muon), missing energy, and two or more jets in data corresponding to 9.7 fb$^{-1}$ of integrated luminosity collected at a center of mass energy of $\sqrt{s}$ = 1.96 TeV with the D0 detector at the Fermilab Tevatron $p\bar{p}$ Collider. The search uses $b$-jet identification to categorize events for improved signal versus background separation and is sensitive to associated production of the $H$ with a $W$ boson, $WH\to\ell\nu b\bar{b}$; gluon fusion with the Higgs decaying to $W$ boson pairs, $H\to WW\to\ell\nu jj$; and associated production with a vector boson where the Higgs decays to $W$ boson pairs, $VH\to VWW \to \ell\nu jjjj$ production (where $V = W$ or $Z$). We observe good agreement between data and expected background. We test our method by measuring $WZ$ and $ZZ$ production with $Z\to b\bar{b}$ and find production rates consistent with the standard model prediction. For a Higgs boson mass of 125 GeV, we set a 95%\ C.L. upper limit on the production of a standard model Higgs boson of \obslimA$\times\sigma_{\rm SM}$, where $\sigma_{\rm SM}$ is the standard model Higgs boson production cross section, while the expected limit is \explimA$\times\sigma_{\rm SM}$. We also interpret the data considering models with fourth generation fermions, or a fermiophobic Higgs boson

A search for charged massive long-lived particles

We report on a search for charged massive long-lived particles (CMLLPs), based on 5.2 fb$^{-1}$ of integrated luminosity collected with the D0 detector at the Fermilab Tevatron $p\bar{p}$ collider. We search for events in which one or more particles are reconstructed as muons but have speed and ionization energy loss $(dE/dx)$ inconsistent with muons produced in beam collisions. CMLLPs are predicted in several theories of physics beyond the standard model. We exclude pair-produced long-lived gaugino-like charginos below 267 GeV and higgsino-like charginos below 217 GeV at 95% C.L., as well as long-lived scalar top quarks with mass below 285 GeV.Comment: submitted to Phys. Rev. Letter