2,356 research outputs found
Multiplicity Structure of the Hadronic Final State in Diffractive Deep-Inelastic Scattering at HERA
The multiplicity structure of the hadronic system X produced in
deep-inelastic processes at HERA of the type ep -> eXY, where Y is a hadronic
system with mass M_Y< 1.6 GeV and where the squared momentum transfer at the pY
vertex, t, is limited to |t|<1 GeV^2, is studied as a function of the invariant
mass M_X of the system X. Results are presented on multiplicity distributions
and multiplicity moments, rapidity spectra and forward-backward correlations in
the centre-of-mass system of X. The data are compared to results in e+e-
annihilation, fixed-target lepton-nucleon collisions, hadro-produced
diffractive final states and to non-diffractive hadron-hadron collisions. The
comparison suggests a production mechanism of virtual photon dissociation which
involves a mixture of partonic states and a significant gluon content. The data
are well described by a model, based on a QCD-Regge analysis of the diffractive
structure function, which assumes a large hard gluonic component of the
colourless exchange at low Q^2. A model with soft colour interactions is also
successful.Comment: 22 pages, 4 figures, submitted to Eur. Phys. J., error in first
submission - omitted bibliograph
Differential (2+1) Jet Event Rates and Determination of alpha_s in Deep Inelastic Scattering at HERA
Events with a (2+1) jet topology in deep-inelastic scattering at HERA are
studied in the kinematic range 200 < Q^2< 10,000 GeV^2. The rate of (2+1) jet
events has been determined with the modified JADE jet algorithm as a function
of the jet resolution parameter and is compared with the predictions of Monte
Carlo models. In addition, the event rate is corrected for both hadronization
and detector effects and is compared with next-to-leading order QCD
calculations. A value of the strong coupling constant of alpha_s(M_Z^2)=
0.118+- 0.002 (stat.)^(+0.007)_(-0.008) (syst.)^(+0.007)_(-0.006) (theory) is
extracted. The systematic error includes uncertainties in the calorimeter
energy calibration, in the description of the data by current Monte Carlo
models, and in the knowledge of the parton densities. The theoretical error is
dominated by the renormalization scale ambiguity.Comment: 25 pages, 6 figures, 3 tables, submitted to Eur. Phys.
Searches at HERA for Squarks in R-Parity Violating Supersymmetry
A search for squarks in R-parity violating supersymmetry is performed in e^+p
collisions at HERA at a centre of mass energy of 300 GeV, using H1 data
corresponding to an integrated luminosity of 37 pb^(-1). The direct production
of single squarks of any generation in positron-quark fusion via a Yukawa
coupling lambda' is considered, taking into account R-parity violating and
conserving decays of the squarks. No significant deviation from the Standard
Model expectation is found. The results are interpreted in terms of constraints
within the Minimal Supersymmetric Standard Model (MSSM), the constrained MSSM
and the minimal Supergravity model, and their sensitivity to the model
parameters is studied in detail. For a Yukawa coupling of electromagnetic
strength, squark masses below 260 GeV are excluded at 95% confidence level in a
large part of the parameter space. For a 100 times smaller coupling strength
masses up to 182 GeV are excluded.Comment: 32 pages, 14 figures, 3 table
Multi-Jet Event Rates in Deep Inelastic Scattering and Determination of the Strong Coupling Constant
Jet event rates in deep inelastic ep scattering at HERA are investigated
applying the modified JADE jet algorithm. The analysis uses data taken with the
H1 detector in 1994 and 1995. The data are corrected for detector and
hadronization effects and then compared with perturbative QCD predictions using
next-to-leading order calculations. The strong coupling constant alpha_S(M_Z^2)
is determined evaluating the jet event rates. Values of alpha_S(Q^2) are
extracted in four different bins of the negative squared momentum
transfer~\qq in the range from 40 GeV2 to 4000 GeV2. A combined fit of the
renormalization group equation to these several alpha_S(Q^2) values results in
alpha_S(M_Z^2) = 0.117+-0.003(stat)+0.009-0.013(syst)+0.006(jet algorithm).Comment: 17 pages, 4 figures, 3 tables, this version to appear in Eur. Phys.
J.; it replaces first posted hep-ex/9807019 which had incorrect figure 4
Measurements of Transverse Energy Flow in Deep-Inelastic Scattering at HERA
Measurements of transverse energy flow are presented for neutral current
deep-inelastic scattering events produced in positron-proton collisions at
HERA. The kinematic range covers squared momentum transfers Q^2 from 3.2 to
2,200 GeV^2, the Bjorken scaling variable x from 8.10^{-5} to 0.11 and the
hadronic mass W from 66 to 233 GeV. The transverse energy flow is measured in
the hadronic centre of mass frame and is studied as a function of Q^2, x, W and
pseudorapidity. A comparison is made with QCD based models. The behaviour of
the mean transverse energy in the central pseudorapidity region and an interval
corresponding to the photon fragmentation region are analysed as a function of
Q^2 and W.Comment: 26 pages, 8 figures, submitted to Eur. Phys.
Deep-Inelastic Inclusive ep Scattering at Low x and a Determination of alpha_s
A precise measurement of the inclusive deep-inelastic e^+p scattering cross
section is reported in the kinematic range 1.5<= Q^2 <=150 GeV^2 and
3*10^(-5)<= x <=0.2. The data were recorded with the H1 detector at HERA in
1996 and 1997, and correspond to an integrated luminosity of 20 pb^(-1). The
double differential cross section, from which the proton structure function
F_2(x,Q^2) and the longitudinal structure function F_L(x,Q^2) are extracted, is
measured with typically 1% statistical and 3% systematic uncertainties. The
measured partial derivative (dF_2(x,Q^2)/dln Q^2)_x is observed to rise
continuously towards small x for fixed Q^2. The cross section data are combined
with published H1 measurements at high Q^2 for a next-to-leading order DGLAP
QCD analysis.The H1 data determine the gluon momentum distribution in the range
3*10^(-4)<= x <=0.1 to within an experimental accuracy of about 3% for Q^2 =20
GeV^2. A fit of the H1 measurements and the mu p data of the BCDMS
collaboration allows the strong coupling constant alpha_s and the gluon
distribution to be simultaneously determined. A value of alpha
_s(M_Z^2)=0.1150+-0.0017 (exp) +0.0009-0.0005 (model) is obtained in NLO, with
an additional theoretical uncertainty of about +-0.005, mainly due to the
uncertainty of the renormalisation scale.Comment: 68 pages, 24 figures and 18 table
Journal Staff
We present the first measurements of the differential cross section d sigma/dp(T)(gamma) for the production of an isolated photon in association with at least two b-quark jets. The measurements consider photons with rapidities vertical bar y(gamma)vertical bar < 1.0 and transverse momenta 30 < p(T)(gamma) < 200 GeV. The b-quark jets are required to have p(T)(jet) > 15 GeVand vertical bar y(jet)vertical bar < 1.5. The ratio of differential production cross sections for gamma + 2 b-jets to gamma + b-jet as a function of p(T)(gamma) is also presented. The results are based on the proton-antiproton collision data at root s = 1.96 TeV collected with the D0 detector at the Fermilab Tevatron Collider. The measured cross sections and their ratios are compared to the next- to- leading order perturbative QCD calculations as well as predictions based on the k(T)- factorization approach and those from the sherpa and pythia Monte Carlo event generators
Measurement of the W boson mass
We present a measurement of the W boson mass in W -> ev decays using 1 fb^-1
of data collected with the D0 detector during Run II of the Fermilab Tevatron
collider. With a sample of 499830 W -> ev candidate events, we measure M_W =
80.401 +- 0.043 GeV. This is the most precise measurement from a single
experiment.Comment: As published in PR
Double parton interactions in photon+3 jet events in ppbar collisions sqrt{s}=1.96 TeV
We have used a sample of photon+3 jets events collected by the D0 experiment
with an integrated luminosity of about 1 fb^-1 to determine the fraction of
events with double parton scattering (f_DP) in a single ppbar collision at
sqrt{s}=1.96 TeV. The DP fraction and effective cross section (sigma_eff), a
process-independent scale parameter related to the parton density inside the
nucleon, are measured in three intervals of the second (ordered in pT) jet
transverse momentum pT_jet2 within the range 15 < pT_jet2 < 30 GeV. In this
range, f_DP varies between 0.23 < f_DP < 0.47, while sigma_eff has the average
value sigma_eff_ave = 16.4 +- 0.3(stat) +- 2.3(syst) mb.Comment: 15 pages, 13 figure
Dependence of the production cross section on the transverse momentum of the top quark
We present a measurement of the differential cross section for
events produced in collisions at TeV as a function
of the transverse momentum () of the top quark. The selected events
contain a high- lepton (), four or more jets, and a large imbalance
in , and correspond to 1 fb of integrated luminosity recorded
with the D0 detector. Each event must have at least one candidate for a
jet. Objects in the event are associated through a constrained kinematic fit to
the process. Results
from next-to-leading-order perturbative QCD calculations agree with the
measured differential cross section. Comparisons are also provided to
predictions from Monte Carlo event generators using QCD calculations at
different levels of precision.Comment: 8 pages, 6 figures, 4 tables, updated to reflect the published
versio
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