Search results for "Jet"
showing 10 items of 4711 documents
A systematic comparison of jet quenching in different fluid-dynamical models
2010
Comparing four different (ideal and viscous) hydrodynamic models for the evolution of the medium created in 200 AGeV Au-Au collisions, combined with two different models for the path length dependence of parton energy loss, we study the effects of jet quenching on the emission-angle dependence of the nuclear suppression factor R_AA(phi) and the away-side per trigger yield I_AA(phi). Each hydrodynamic model was tuned to provide a reasonable description of the single-particle transverse momentum spectra for all collision centralities, and the energy loss models were adjusted to yield the same pion nuclear suppression factor in central Au-Au collisions. We find that the experimentally measured…
Angular variation of hard back-to-back hadron suppression in heavy-ion collisions
2008
The basic idea of jet tomography is to infer information about the density evolution of the medium created in heavy-ion (A-A) collisions by studying the suppression of hard probes in an A-A environment as compared to the baseline process known from p-p collisions. The suppression of back-to-back correlations in heavy-ion collisions allows, due to a different geometrical bias, a view into the medium which is qualitatively different from the one offered by single hadron suppression. A control parameter for the suppression corresponding to a systematic variation of in-medium pathlengths and density can be obtained by studying collisions at finite impact parameter b. A systematic variation of p…
Top quark mass measurement in thett¯all hadronic channel using a matrix element technique inpp¯collisions ats=1.96 TeV
2009
We present a measurement of the top quark mass in the all hadronic channel ($t\overline{t}\ensuremath{\rightarrow}b\overline{b}{q}_{1}{\overline{q}}_{2}{q}_{3}{\overline{q}}_{4}$) using $943\text{ }\text{ }{\mathrm{pb}}^{\ensuremath{-}1}$ of $p\overline{p}$ collisions at $\sqrt{s}=1.96\text{ }\text{ }\mathrm{TeV}$ collected at the CDF II detector at Fermilab (CDF). We apply the standard model production and decay matrix element (ME) to $t\overline{t}$ candidate events. We calculate per-event probability densities according to the ME calculation and construct template models of signal and background. The scale of the jet energy is calibrated using additional templates formed with the invaria…
Measurement of the top quark mass in thelepton+jetsfinal state with the matrix element method
2006
We present a measurement of the top quark mass with the Matrix Element method in the lepton+jets final state. As the energy scale for calorimeter jets represents the dominant source of systematic uncertainty, the Matrix Element likelihood is extended by an additional parameter, which is defined as a global multiplicative factor applied to the standard energy scale. The top quark mass is obtained from a fit that yields the combined statistical and systematic jet energy scale uncertainty.
Sensitivity of jet quenching to enhancement of the medium opacity near TC
2014
One of the main goals of the study of high transverse momentum (P_T) observables in the context of ultrarelativisic heavy-ion collisions is the determination of properties of the produced QCD matter. In particular, the transport coefficients qhat and ehat, characterizing the interaction of the medium with a high p_T parton, are accessible via high P_T probes. However, a precision extraction of their temperature dependence from current data faces the problem that neither the spacetime geometry of the evolving matter droplet nor the link between thermodynamics and transport coefficients is unambiguously known, and various conjectured scenarios how thermodynamics and transport coefficients beh…
Zeroing in on the initial state — tomography using bulk, jets and photons
2014
One of the unsolved problems in the current 'standard model' of heavy ion physics is the apparent rapid thermalization of QCD matter in the pre-equilibrium stage. While it is challenging to probe this mechanism directly, there are now several observables available which allow tomographic imaging of the initial state geometry, which is expected to carry remnant information of the equilibration mechanism. On the fluid dynamics side, scaled fluctuations in the momentum space anisotropy parameters v_n image the initial eccentricity fluctuations epsilon_n almost directly with only a weak dependence on the details of the fluid dynamical evolution. From a different direction, due to the strong non…
Measurement of the top quark mass in final states with two leptons
2009
We present measurements of the top quark mass in ttbar candidate events with two final state leptons using 1 inverse fb of data collected by the D0 experiment. Our data sample is selected by requiring two fully identified leptons or by relaxing one lepton requirement to an isolated track if at least one jet is tagged as a b jet. The top quark mass is extracted after reconstructing the event kinematics under the ttbar hypothesis using two methods. In the first method, we integrate over expected neutrino rapidity distributions, and in the second we calculate a weight for the possible top quark masses based on the observed particle momenta and the known parton distribution functions. We analyz…
First simultaneous measurement of the top quark mass in thelepton+jetsand dilepton channels at CDF
2009
We present a measurement of the mass of the top quark using data corresponding to an integrated luminosity of 1.9 fb{sup -1} of pp collisions collected at {radical}(s)=1.96 TeV with the CDF II detector at Fermilab's Tevatron. This is the first measurement of the top quark mass using top-antitop pair candidate events in the lepton+jets and dilepton decay channels simultaneously. We reconstruct two observables in each channel and use a nonparametric kernel density estimation technique to derive two-dimensional probability density functions from simulated signal and background samples. The observables are the top quark mass and the invariant mass of two jets from the W decay in the lepton+jets…
Precision measurement of the top-quark mass inlepton+jetsfinal states
2015
We measure the mass of the top quark in lepton + jets final states using the full sample of p (p) over bar collision data collected by the D0 experiment in Run II of the Fermilab Tevatron Collider at root s = 1.96 TeV, corresponding to 9.7 fb(-1) of integrated luminosity. We use a matrix element technique that calculates the probabilities for each event to result from t (t) over bar production or background. The overall jet energy scale is constrained in situ by the mass of the W boson. We measure m(t) = 174.98 +/- 0.76 GeV. This constitutes the most precise single measurement of the top-quark mass.
The Matrix Element Method and its Application to Measurements of the Top Quark Mass
2010
The most precise measurements of the top quark mass are based on the Matrix Element method. We present a detailed description of this analysis method, taking the measurements of the top quark mass in final states with one and two charged leptons as concrete examples. In addition, we show how the Matrix Element method is suitable to reduce the dominant systematic uncertainties related to detector effects, by treating the absolute energy scales for b-quark and light-quark jets independently as free parameters in a simultaneous fit together with the top quark mass. While the determination of the light-quark jet energy scale has already been applied in several recent measurements, the separate …