7,341 research outputs found
Differential cross section measurements for the production of a W boson in association with jets in proton–proton collisions at s√=7  TeV
Measurements are reported of differential cross sections for the production of a W boson, which decays into a muon and a neutrino, in association with jets, as a function of several variables, including the transverse momenta (pTpT) and pseudorapidities of the four leading jets, the scalar sum of jet transverse momenta (HTHT), and the difference in azimuthal angle between the directions of each jet and the muon. The data sample of pp collisions at a centre-of-mass energy of 7 TeV was collected with the CMS detector at the LHC and corresponds to an integrated luminosity of 5.0 fb−1. The measured cross sections are compared to predictions from Monte Carlo generators, MadGraph + pythia and sherpa, and to next-to-leading-order calculations from BlackHat + sherpa. The differential cross sections are found to be in agreement with the predictions, apart from the pTpT distributions of the leading jets at high pTpT values, the distributions of the HTHT at high-HTHT and low jet multiplicity, and the distribution of the difference in azimuthal angle between the leading jet and the muon at low values.Funded by SCOAP
Multi-lepton signals from the top-prime quark at the LHC
We analyze the collider signatures of models with a vector-like top-prime
quark and a massive color-octet boson. The top-prime quark mixes with the top
quark in the Standard Model, leading to richer final states than ones that are
investigated by experimental collaborations. We discuss the multi-lepton final
states, and show that they can provide increased sensitivity to models with a
top-prime quark and gluon-prime. Searches for new physics in high multiplicity
events are an important component of the LHC program and complementary to
analyses that have been performed.Comment: 7 pages, 4 figures, 2 table
Experimental limits on massive neutrinos from e(+)e(-) annihilations at 29 GeV
This is the publisher's version, also available electronically from http://journals.aps.org/prd/abstract/10.1103/PhysRevD.37.577.A search was made in 29-GeV e(+)e(-) annihilations for massive neutrinos decaying to e(±)X(∓)(ν) where X is a muon or meson. A 300-pb(-1) data sample yielded just one candidate event with a mass m(e)X>1.8 GeV. Significant limits are found for new neutrinos with masses from 1.8 to 6.7 GeV and with mixing parameters in the range 3×10(-6)<‖U‖(2)<1. .A
Measurement of the hadronic activity in events with a Z and two jets and extraction of the cross section for the electroweak production of a Z with two jets in pp collisions at s√=7 TeV
This is the publisher's version, also available electronically from http://link.springer.com/article/10.1007%2FJHEP10%282013%29062.The first measurement of the electroweak production cross section of a Z boson with two jets (Zjj) in pp collisions at s√=7 TeV is presented, based on a data sample recorded by the CMS experiment at the LHC with an integrated luminosity of 5 fb(−1). The cross section is measured for the ℓℓjj (ℓ = e, μ) final state in the kinematic region m(ℓℓ) > 50 GeV, m(jj) > 120 GeV, transverse momenta p(j)(T)>25 GeV and pseudorapidity |η(j)| < 4.0. The measurement, combining the muon and electron channels, yields σ = 154 ± 24 (stat.) ± 46 (exp. syst.) ± 27 (th. syst.) ± 3 (lum.) fb, in agreement with the theoretical cross section. The hadronic activity, in the rapidity interval between the jets, is also measured. These results establish an important foundation for the more general study of vector boson fusion processes, of relevance for Higgs boson searches and for measurements of electroweak gauge couplings and vector boson scattering
An SU(3) model for octet baryon and meson fragmentation
The production of the octet of baryons and mesons in e^+ e^- collisions is
analysed, based on considerations of SU(3) symmetry and a simple model for
SU(3) symmetry breaking in fragmentation functions. All fragmentation
functions, D_q^h(x, Q^2), describing the fragmentation of quarks into a member
of the baryon octet (and similarly for fragmentation into members of the meson
octet) are expressed in terms of three SU(3) symmetric functions, \alpha(x,
Q^2), \beta(x, Q^2), and \gamma(x, Q^2). With the introduction of an SU(3)
breaking parameter, \lambda, the model is successful in describing
hadroproduction data at the Z pole. The fragmentation functions are then
evolved using leading order evolution equations and good fits to currently
available data at 34 GeV and at 161 GeV are obtained.Comment: 24 pages LaTeX file including 11 postscript figure file
Charm production in nonresonant e(+)e(-) annihilations at √s =10.55 GeV
This is the publisher's version also available electronically from http://journals.aps.org/prd/abstract/10.1103/PhysRevD.37.1719We report results on the differential and total cross sections for inclusive production of the charmed particles D*+, D*(0), D(0), D(+), D(s), and Λc in e(+)e(-) annihilations at √s=10.55 GeV. Widely used quark fragmentation models are discussed and compared with the measured charmed-particle momentum distributions. This comparison, as well as that with measurements at other center-of-mass energies, shows the need to take QCD corrections into account and their importance for a correct interpretation of the model parameters. The observed rate of D(0) and D(+) production is compared to the expected total charm production cross section. We measure the probability of a charmed meson being produced as a vector meson and the D*(+) decay branching fraction into D(0)π+
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
Statistical approach for unpolarized fragmentation functions for the octet baryons
A statistical model for the parton distributions in the nucleon has proven
its efficiency in the analysis of deep inelastic scattering data, so we propose
to extend this approach to the description of unpolarized fragmentation
functions for the octet baryons. The characteristics of the model are
determined by using some data on the inclusive production of proton and
in unpolarized deep inelastic scattering and a next-to-leading
analysis of the available experimental data on the production of unpolarized
octet baryons in annihilation. Our results show that both parton
distributions and fragmentation functions are compatible with the statistical
approach, in terms of a few free parameters, whose interpretation will be
discussed.Comment: 14 pages, 7 eps figures, to appear in Phys. Rev.
Search for associated Higgs boson production using like charge dilepton events in p(p)over-bar collisions at root s=1.96 TeV
We present a search for associated Higgs boson production in the process p (p) over bar -> W/ZH -> l(+/-)l'(+/-) + X in ee, e mu, and mu mu final states. The search is based on data collected by the D0 experiment at the Fermilab Tevatron Collider at root s = 1.96 TeV corresponding to 5.3 fb(-1) of integrated luminosity. We require two isolated leptons (electrons or muons) with the same electric charge and additional kinematic requirements. No significant excess above background is observed, and we set 95% C. L. observed (expected) upper limits on ratio of the production cross section to the standard model prediction of 6.4 (7.3) for a Higgs boson mass of 165 GeV and 13.5 (19.8) for a mass of 115 GeV
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