Search results for "partícules"
showing 10 items of 522 documents
Search for diphoton events with large missing transverse momentum in 7 TeV proton-proton collision data with the ATLAS detector
2012
A search for diphoton events with large missing transverse momentum has been performed using proton–proton collision data at √s = 7 TeV recorded with the ATLAS detector, corresponding to an integrated luminosity of 4.8 fb[superscript −1]. No excess of events was observed above the Standard Model prediction and model-dependent 95% confidence level exclusion limits are set. In the context of a generalised model of gauge-mediated supersymmetry breaking with a bino-like lightest neutralino of mass above 50 GeV, gluinos (squarks) below 1.07 TeV (0.87 TeV) are excluded, while a breaking scale Λ below 196 TeV is excluded for a minimal model of gauge-mediated supersymmetry breaking. For a specific …
First observation of the doubly charmed baryon decay Ξcc++→Ξc+π+
2018
The doubly charmed baryon decay Ξcc++→Ξc+π+ is observed for the first time, with a statistical significance of 5.9σ, confirming a recent observation of the baryon in the Λc+K−π+π+ final state. The data sample used corresponds to an integrated luminosity of 1.7 fb−1, collected by the LHCb experiment in pp collisions at a center-of-mass energy of 13 TeV. The Ξcc++ mass is measured to be 3620.6±1.5(stat)±0.4(syst)±0.3(Ξc+) MeV/c2 and is consistent with the previous result. The ratio of branching fractions between the decay modes is measured to be [B(Ξcc++→Ξc+π+)×B(Ξc+→pK−π+)]/[B(Ξcc++→Λc+K−π+π+)×B(Λc+→pK−π+)]=0.035±0.009(stat)±0.003(syst).
Measurement of the c0 Baryon Lifetime
2018
We report a measurement of the lifetime of the $��_c^0$ baryon using proton-proton collision data at center-of-mass energies of 7 and 8~TeV, corresponding to an integrated luminosity of 3.0 fb$^{-1}$ collected by the LHCb experiment. The sample consists of about 1000 $��_b^-\to��_c^0��^-\bar��_�� X$ signal decays, where the $��_c^0$ baryon is detected in the $pK^-K^-��^+$ final state and $X$ represents possible additional undetected particles in the decay. The $��_c^0$ lifetime is measured to be $��_{��_c^0} = 268\pm24\pm10\pm2$ fs, where the uncertainties are statistical, systematic, and from the uncertainty in the $D^+$ lifetime, respectively. This value is nearly four times larger than, …
Study of W Boson Production in Association with Beauty and Charm
2015
The associated production of a W boson with a jet originating from either a light parton or heavy-flavor quark is studied in the forward region using proton-proton collisions. The analysis uses data corresponding to integrated luminosities of 1.0 and 2.0 fb[superscript -1] collected with the LHCb detector at center-of-mass energies of 7 and 8 TeV, respectively. The W bosons are reconstructed using the W → μν decay and muons with a transverse momentum, p[subscript T], larger than 20 GeV in the pseudorapidity range 2.0 20 GeV and 2.2 20 GeV. The fraction of W + jet events that originate from beauty and charm quarks is measured, along with the charge asymmetries of the W + b and W + c produ…
An investigation of the very rare K+ → π+ vv¯ decay
2020
The NA62 experiment reports an investigation of the K+→π+ν ̄ν mode from a sample of K+ decays collected in 2017 at the CERN SPS. The experiment has achieved a single event sensitivity of (0.389±0.024)×10−10, corresponding to 2.2 events assuming the Standard Model branching ratio of (8.4±1.0)×10−11. Two signal candidates are observed with an expected background of 1.5 events. Combined with the result of a similar analysis conducted by NA62 on a smaller data set recorded in 2016, the collaboration now reports an upper limit of 1.78×10−10 for the K+→π+ν ̄ν branching ratio at 90% CL. This, together with the corresponding 68% CL measurement of (0.48+0.72−0.48)×10−10, are currently the most preci…
Oriented event shapes at (NLL)-L-3 + O(alpha(2)(S))
2013
We analyze oriented event-shapes in the context of Soft-Collinear Effective Theory (SCET) and in fixed-order perturbation theory. Oriented event-shapes are distributions of event-shape variables which are differential on the angle theta(T) that the thrust axis forms with the electron-positron beam. We show that at any order in perturbation theory and for any event shape, only two angular structures can appear: F-0 = 3/8 (1+cos(2) theta(T)) and F-1 = (1 ¿ 3 cos(2) theta(T)). When integrating over theta(T) to recover the more familiar event-shape distributions, only F-0 survives. The validity of our proof goes beyond perturbation theory, and hence only these two structures are present at the …
Width difference in the B-s(0)-(B)over-bar-(0)(s) system from lattice HQET
2001
We present recent results for the prediction of the B-s(0)-(B) over bar (0)(s) lifetime difference from lattice Heavy Quark Effective Theory simulations. In order to get a next-to-leading order result we have calculated the matching between QCD and HQET and the two loop anomalous dimension in the HQET for all the DeltaB = 2 operators, in particular for the operators which enter in the width difference. me obtain far the B-s(0)-(B) over bar (0)(s) lifetime difference, Delta GammaB(s)/GammaB(s) = (5.1 +/- 1.9 +/- 1.7) x 10(-2).
Feasibility studies of time-like proton electromagnetic form factors at PANDA at FAIR
2016
Simulation results for future measurements of electromagnetic proton form factors at P¯ANDA (FAIR) within the PandaRoot software framework are reported. The statistical precision with which the proton form factors can be determined is estimated. The signal channel p¯p→e+e−p¯p→e+e− is studied on the basis of two different but consistent procedures. The suppression of the main background channel, i.e. p¯p→π+π−p¯p→π+π− , is studied. Furthermore, the background versus signal efficiency, statistical and systematical uncertainties on the extracted proton form factors are evaluated using two different procedures. The results are consistent with those of a previous simulation study using an older, …
Feasibility study for the measurement of pi N transition distribution amplitudes at (P)over-barANDA in (P)over-barp -> J/psi pi(0)
2017
The exclusive charmonium production process in pp¯ annihilation with an associated π0 meson pp¯ → J=ψπ0 is studied in the framework of QCD collinear factorization. The feasibility of measuring this reaction through the J=ψ → eþe− decay channel with the AntiProton ANnihilation at DArmstadt (PANDA ¯ ) experiment is investigated. Simulations on signal reconstruction efficiency as well as the background rejection from various sources including the pp¯ → πþπ−π0 and pp¯ → J=ψπ0π0 reactions are performed with PANDAROOT, the simulation and analysis software framework of the PANDA ¯ experiment. It is shown that the measurement can be done at PANDA ¯ with significant constraining power under the assu…
A Study of radiactive muon-pair events at Z° energies and limits on an additional Z' gauge boson
1995
An analysis is reported on the channele + e −→μ+μ−(nγ), n=1,2..., using data taken with the DELPHI detector at LEP from 1990 to 1992. Differential cross sections of the radiative photons as a function of photon energy and of the angle between the photon and the muon are presented. No significant deviations from expectations are observed. The data are also used to extract the muon-pair cross section and asymmetry below the Z0 peak by using those events with relatively hard initial state radiative photon(s). The measured cross section and asymmetry show no significant deviation from the Standard Model expectations. These results together with the DELPHI cross section and asymmetry measurement…