We have measured the response of an array of ATLAS muon spectrometer drift tubes to fast neutrons, produced by a t(d,n)/sup 4/He reaction at the 5.5-MV TANDEM Van de Graaff accelerator of the ...National Centre of Scientific Research "Demokritos." The setup consisted of 24 drift tubes in a 6/spl times/4 arrangement. The neutron energy was 18.3 MeV. The anode wire voltage varied from 2200 to 2800 V. For a neutron flux of about 2.75 kHz/cm/sup 2/, the drift tube sensitivity to 18.3-MeV neutrons ranged from 0.031% to 0.606% for anode voltages between 2200 and 2800 V, respectively.
The ATLAS detector at the Large Hadron Collider at CERN is designed to study the products of proton collisions at energies up to 14 TeV. One of its subdetectors is a high-resolution Muon ...Spectrometer, designed to exploit the physics potential of the collisions. It consists of 1206 monitored drift tube chambers, which have to pass very strict quality criteria. For this purpose dedicated setups have been developed and automated at the National Technical University of Athens. In the present report the results of testing about 10,000 drift tubes are presented. These criteria comprise the anode wire mechanical tension, the high voltage dark current, the anode wire displacement, and the gas leak rate of the endplugs and the cylindrical drift tube.
In this study, we apply the geometrical properties of the Legendre transform in order to implement a segment reconstruction algorithm for drift tube chambers used in High Energy Physics experiments. ...The output signal of a drift tube chamber consists of a collection of circles, each of which corresponds to a drift tube and defines the trajectory of the charged particle. The particle track candidate is reconstructed as the common tangent line to the drift circles. We tested the method both on an ideal case and on a case of high noise conditions using Monte Carlo generated tracks.
Could it be that walking toward (vs. away) someone else changes your self-evaluation in the direction of what this person is? We answer positively and argue that approach movements lead to ...self-evaluative assimilation (a higher self-evaluation with a high vs. a low standard), while avoidance movements lead to self-evaluative contrast (a lower self-evaluation with a high vs. a low standard). Hence, we predict that approach/avoidance moderates the impact of comparison information on self-evaluation. To test this idea, participants were either primed with approach or avoidance before processing comparison information (Study 1) or physically had to walk toward or away from this information (Studies 2 and 3). Results on self-evaluated adjustment (Studies 1 and 2) and self-evaluated attractiveness measures (Study 3) confirmed our predictions. These studies suggest ways to behave to self-evaluate positively when hearing about others.
ATLAS (a toroidal LHC apparatus) is a general purpose experiment that will start its operation at the large hadron collider (LHC) at CERN in 2007. The ATLAS detector is designed to explore numerous ...physics processes by recording, measuring, and investigating the products emerging from proton-proton collisions at energies up to 14 TeV. High-precision muon momentum measurement (dp/p/spl sim/10% at p/sub T/=1 TeV/c) over large areas using monitored drift tube (MDT) chambers is crucial for the ATLAS experiment. More than 1200 MDT chambers, consisting of approximately 370 000 drift tubes, will provide a total coverage of 5500 m/sup 2/. Three Greek universities have taken the responsibility to construct 130 barrel inner small (BIS)-MDT chambers using 30 000 drift tubes of /spl sim/1.7 m length that have been quality tested before assembly. The design of the muon drift tubes aims at high detection efficiency (>95%) and a spatial single tube resolution of <80 /spl mu/m. This paper describes the cosmic ray test setup, which has been instrumented in order to verify that the BIS-MDT chamber Module-0 fulfills its design requirements. The analysis of its data shows that the chamber meets these requirements; it has low noise levels, uniform drift properties, good spatial resolution, and high particle detection efficiency.
A direct search for the standard model Higgs boson decaying to a pair of charm quarks is presented. Associated production of the Higgs and Z bosons, in the decay mode ZH→ + -cc is studied. A data set ...with an integrated luminosity of 36.1 fb-1 of pp collisions at s=13TeV recorded by the ATLAS experiment at the LHC is used. The H→cc signature is identified using charm-tagging algorithms. The observed (expected) upper limit on σ(pp→ZH)×B(H→cc) is 2.7 (3.9-1.1+2.1) pb at the 95% confidence level for a Higgs boson mass of 125 GeV, while the standard model value is 26 fb.
A search for the narrow structure, X(5568), reported by the D0 Collaboration in the decay sequence X→Bs0π±, Bs0→J/ψφ, is presented. The analysis is based on a data sample recorded with the ATLAS ...detector at the LHC corresponding to 4.9 fb-1 of pp collisions at 7 TeV and 19.5 fb-1 at 8 TeV. No significant signal was found. Upper limits on the number of signal events, with properties corresponding to those reported by D0, and on the X production rate relative to Bs0 mesons, ρX, were determined at 95% confidence level. The results are N(X)<382 and ρX<0.015 for Bs0 mesons with transverse momenta above 10 GeV, and N(X)<356 and ρX<0.016 for transverse momenta above 15 GeV. Limits are also set for potential Bs0π± resonances in the mass range 5550 to 5700 MeV.
We use K(L)'s in the 100-200 GeV energy range to produce 147 candidate events of the axial vector pair K1(1270)-K1(1400) in the nuclear Coulomb field of a Pb target and determine the radiative widths ...Gamma(K1(1400)-->K0+gamma)=280.8+/-23.2(stat)+/-40.4(syst) keV and Gamma(K1(1270)-->K0+gamma)=73.2+/-6.1(stat)+/-28.3(syst) keV. These first measurements appear to be lower than the quark-model predictions. We also place upper limits on the radiative widths for K(*)(1410) and K(*)(2)(1430) and find that the latter is vanishingly small in accord with SU(3) invariance in the naive quark model.
The production of a top quark in association with a Z boson is investigated. The proton–proton collision data collected by the ATLAS experiment at the LHC in 2015 and 2016 at a centre-of-mass energy ...of s=13TeV are used, corresponding to an integrated luminosity of 36.1fb-1. Events containing three identified leptons (electrons and/or muons) and two jets, one of which is identified as a b-quark jet are selected. The major backgrounds are diboson, tt¯ and Z+jets production. A neural network is used to improve the background rejection and extract the signal. The resulting significance is 4.2σ in the data and the expected significance is 5.4σ. The measured cross-section for tZq production is 600±170(stat.)±140(syst.)fb.
A search for the standard model Higgs boson produced in association with a top-quark pair, ttH, is presented. The analysis uses 36.1 fb-1 of pp collision data at s=13 TeV collected with the ATLAS ...detector at the Large Hadron Collider in 2015 and 2016. The search targets the H→bb decay mode. The selected events contain either one or two electrons or muons from the top-quark decays, and are then categorized according to the number of jets and how likely these are to contain b-hadrons. Multivariate techniques are used to discriminate between signal and background events, the latter being dominated by tt+jets production. For a Higgs boson mass of 125 GeV, the ratio of the measured ttH signal cross-section to the standard model expectation is found to be μ=0.84-0.61+0.64. A value of μ greater than 2.0 is excluded at 95% confidence level (C.L.) while the expected upper limit is μ<1.2 in the absence of a ttH signal.
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