19 research outputs found
WW Production Cross Section and W Branching Fractions in e+e- Collisions at 189 GeV
From a data sample of 183 pb^-1 recorded at a center-of-mass energy of roots
= 189 GeV with the OPAL detector at LEP, 3068 W-pair candidate events are
selected. Assuming Standard Model W boson decay branching fractions, the W-pair
production cross section is measured to be sigmaWW = 16.30 +- 0.34(stat.) +-
0.18(syst.) pb. When combined with previous OPAL measurements, the W boson
branching fraction to hadrons is determined to be 68.32 +- 0.61(stat.) +-
0.28(syst.) % assuming lepton universality. These results are consistent with
Standard Model expectations.Comment: 22 pages, 5 figures, submitted to Phys. Lett.
Measurement of and charged current inclusive cross sections and their ratio with the T2K off-axis near detector
We report a measurement of cross section and the first measurements of the cross section
and their ratio
at (anti-)neutrino energies below 1.5
GeV. We determine the single momentum bin cross section measurements, averaged
over the T2K -flux, for the detector target material (mainly
Carbon, Oxygen, Hydrogen and Copper) with phase space restricted laboratory
frame kinematics of 500 MeV/c. The
results are and $\sigma(\nu)=\left( 2.41\
\pm0.022{\rm{(stat.)}}\pm0.231{\rm (syst.)}\ \right)\times10^{-39}^{2}R\left(\frac{\sigma(\bar{\nu})}{\sigma(\nu)}\right)=
0.373\pm0.012{\rm (stat.)}\pm0.015{\rm (syst.)}$.Comment: 18 pages, 8 figure
Search for Lorentz and CPT violation using sidereal time dependence of neutrino flavor transitions over a short baseline
A class of extensions of the Standard Model allows Lorentz and CPT violations, which can be identified
by the observation of sidereal modulations in the neutrino interaction rate. A search for such modulations
was performed using the T2K on-axis near detector. Two complementary methods were used in this study,
both of which resulted in no evidence of a signal. Limits on associated Lorentz and CPT-violating terms
from the Standard Model extension have been derived by taking into account their correlations in this
model for the first time. These results imply such symmetry violations are suppressed by a factor of more
than 10 20 at the GeV scale
Search for Hâγγ produced in association with top quarks and constraints on the Yukawa coupling between the top quark and the Higgs boson using data taken at 7 TeV and 8 TeV with the ATLAS detector
A search is performed for Higgs bosons produced in association with top quarks using the diphoton decay mode of the Higgs boson. Selection requirements are optimized separately for leptonic and fully hadronic final states from the top quark decays. The dataset used corresponds to an integrated luminosity of 4.5 fbâ14.5 fbâ1 of protonâproton collisions at a center-of-mass energy of 7 TeV and 20.3 fbâ1 at 8 TeV recorded by the ATLAS detector at the CERN Large Hadron Collider. No significant excess over the background prediction is observed and upper limits are set on the ttÂŻH production cross section. The observed exclusion upper limit at 95% confidence level is 6.7 times the predicted Standard Model cross section value. In addition, limits are set on the strength of the Yukawa coupling between the top quark and the Higgs boson, taking into account the dependence of the ttÂŻH and tH cross sections as well as the Hâγγ branching fraction on the Yukawa coupling. Lower and upper limits at 95% confidence level are set at â1.3 and +8.0 times the Yukawa coupling strength in the Standard Model
Power corrections in the dispersive model for a determination of the strong coupling constant from the thrust distribution
In the context of the dispersive model for non-perturbative corrections, we extend the leading renormalon subtraction to NNLO for the thrust distribution in e + e - annihilation. Within this framework, using a NNLL+NNLO perturbative description and including bottom-quark mass effects to NLO, we analyse data in the centre-of-mass energy range sqrt{s}=14{-}206 {GeV} in view of a simultaneous determination of the strong coupling constant and the non-perturbative parameter α 0. The fits are performed by matching the resummed and fixed-order predictions both in the R and the log-R matching schemes. The final values in the R scheme are αs(MZ) = 0.1131^{+0.0028}_{-0.0022}, α0(2 GeV) = 0.538^{+0.102}_{-0.047}
Measurements of <i>ÎœÌ </i><sub><i>ÎŒ </i></sub>and<i>ÎœÌ </i><sub><i>ÎŒ</i></sub> + Îœ<sub>ÎŒ</sub> charged-current cross-sections without detected pions or protons on water and hydrocarbon at a mean anti-neutrino energy of 0.86 GeV
We report measurements of the flux-integrated || and || charged-current cross-sections on water and hydrocarbon targets using the T2K anti-neutrino beam with a mean beam energy of 0.86 GeV. The signal is defined as the (anti-)neutrino charged-current interaction with one induced || and no detected charged pion or proton. These measurements are performed using a new WAGASCI module recently added to the T2K setup in combination with the INGRID Proton Module. The phase space of muons is restricted to the high-detection efficiency region, |p_{\mu}>400~{\rm MeV}/c| and |\theta_{\mu}<30^{\circ}|â , in the laboratory frame. An absence of pions and protons in the detectable phase spaces of |p_{\pi}>200~{\rm MeV}/c|â , |\theta_{\pi}<70^{\circ}| and |p_{\rm p}>600~{\rm MeV}/c|â , |\theta_{\rm p}<70^{\circ}| is required. In this paper, both the || cross-sections and || cross-sections on water and hydrocarbon targets and their ratios are provided by using the DâAgostini unfolding method. The results of the integrated || cross-section measurements over this phase space are ||â , ||â , and ||â . The || cross-section is ||â , ||â , and ||â
A study of W+W-gamma events at LEP
A study of W+W- events accompanied by hard photon radiation, Egamma > 2.5 GeV, produced in e(+)e(-) collisions at LEP is presented. Events consistent with being two on-shell W-bosons and an isolated photon are selected from 681 pb(-1) of data recorded at 180 GeV < roots < 209 GeV. From the sample of 187 selected W(+)W(-)gamma candidates with photon energies greater than 2.5 GeV, the W(+)W(-)gamma cross-section is determined at five values of roots. The results are consistent with the Standard Model expectation. Averaging over all energies, the ratio of the observed cross-section to the Standard Model expectation is R(data/SM) = 0.99 +/- 0.09 +/- 0.04, where the errors represent the statistical and systematic uncertainties respectively. These data provide constraints on the related O(alpha) systematic uncertainties on the measurement of the W-boson mass at LEP. Finally, the data are used to derive 95% confidence level upper limits on possible anomalous contributions to the W(+)W(-)gammagamma and W(+)W(-)Z(0)y vertices: -0.020 GeV-2 < a(0)/Lambda(2) < 0.020 GeV-2, -0.053 GeV-2 < a(c)/Lambda(2) < 0.037 GeV-2, -0.16 GeV-2 < a(n)/Lambda(2) < 0.15 GeV-2, where Lambda represents the energy scale for new physics and a(0), a(c) and a(n) are dimensionless coupling constants. (C) 2003 Elsevier B.V. All rights reserved
Measurement of the e+ e- W+ W- cross section and W decay branching fractions at LEP
From a total data sample of 701.1 pb(-1) recorded with e(+)e(-) centre-of- mass energies of root s = 161 - 209 GeV with the OPAL detector at LEP, 11693 W-pair candidate events are selected. These data are used to obtain measurements of the W-pair production cross sections at 10 different centre-of-mass energies. The ratio of the measured cross sections to the standard model expectation is found to be: data/SM = 1.002 +/- 0.011(stat.) +/- 0.007 (syst.) +/- 0.005(theory), where the uncertainties are statistical, experimental systematics and theory systematics respectively. The data are used to determine the W boson branching fractions, which are found to be consistent with lepton universality of the charged current interaction. Assuming lepton universality, the branching ratio to hadrons is determined to be 67.41 +/- 0.37(stat.) +/- 0.23(syst.)%, from which the CKM matrix element |V-cs| is determined to be 0.969 +/- 0.017(stat.) +/- 0.012(syst.). The differential cross section as a function of the W- production angle is measured for the qqev and qq mu v final states. The results described in this paper are consistent with the expectations from the standard model
Event Generators for High-Energy Physics Experiments
We provide an overview of the status of Monte-Carlo event generators for
high-energy particle physics. Guided by the experimental needs and
requirements, we highlight areas of active development, and opportunities for
future improvements. Particular emphasis is given to physics models and
algorithms that are employed across a variety of experiments. These common
themes in event generator development lead to a more comprehensive
understanding of physics at the highest energies and intensities, and allow
models to be tested against a wealth of data that have been accumulated over
the past decades. A cohesive approach to event generator development will allow
these models to be further improved and systematic uncertainties to be reduced,
directly contributing to future experimental success. Event generators are part
of a much larger ecosystem of computational tools. They typically involve a
number of unknown model parameters that must be tuned to experimental data,
while maintaining the integrity of the underlying physics models. Making both
these data, and the analyses with which they have been obtained accessible to
future users is an essential aspect of open science and data preservation. It
ensures the consistency of physics models across a variety of experiments.Comment: 153 pages, 10 figures, contribution to Snowmass 202