A measurement is presented of inelastic photo- and electroproduction of
J
/
ψ
mesons in
ep
scattering at HERA. The data were recorded with the H1 detector in the period from 2004 to 2007. Single and ...double differential cross sections are determined and the helicity distributions of the
J
/
ψ
mesons are analysed. The results are compared to theoretical predictions in the colour singlet model and in the framework of non-relativistic QCD. Calculations in the colour singlet model using a
k
T
factorisation ansatz are able to give a good description of the data, while colour singlet model calculations to next-to-leading order in collinear factorisation underestimate the data.
A model-independent search for deviations from the Standard Model prediction is performed using the full e±p data sample collected by the H1 experiment at HERA. All event topologies involving ...isolated electrons, photons, muons, neutrinos and jets with transverse momenta above 20 GeV are investigated in a single analysis. Events are assigned to exclusive classes according to their final state. A dedicated algorithm is used to search for deviations from the Standard Model in the distributions of the scalar sum of transverse momenta or the invariant mass of final state particles and to quantify their significance. Variables related to angular distributions and energy sharing between final state particles are also introduced to study the final state topologies. No significant deviation from the Standard Model expectation is observed in the phase space covered by this analysis.
A Monte Carlo event generator is implemented for a two-Higgs-doublet model with maximal CP symmetry, the MCPM. The model contains five physical Higgs bosons; the ρ', behaving similarly to the ...standard-model Higgs boson, two extra neutral bosons h and h", and a charged pair H.sup.±. The special feature of the MCPM is that, concerning the Yukawa couplings, the bosons h', h" and H.sup.+ or - couple directly only to the second-generation fermions but with strengths given by the third-generation-fermion masses. Our event generator allows the simulation of the Drell-Yan-type production processes of hh, h" and H.sup.± in proton-proton collisions at LHC energies. Also the subsequent leptonic decays of these bosons into the μ.sup.+μ.sup.-, μ.sup.+v.sub.μ and μ.sup.- bar.v.sub.μ channels are studied as well as the dominant background processes. We estimate the integrated luminosities needed in pp collisions at center-of-mass energies of 8 and 14 TeV for significant observations of the Higgs bosons hh, h" and H.sup.± in these muonic channels.
A measurement of the integrated luminosity at the
ep
collider HERA is presented, exploiting the elastic QED Compton process
ep
→
eγp
. The electron and the photon are detected in the backward ...calorimeter of the H1 experiment. The integrated luminosity of the data recorded in 2003 to 2007 is determined with a precision of 2.3 %. The measurement is found to be compatible with the corresponding result obtained using the Bethe–Heitler process.
Measurements are presented of single and double-differential dijet cross sections in diffractive photoproduction based on a data sample with an integrated luminosity of 47 pb
−1
. The events are of ...the type
ep
→
eXY
, where the hadronic system
X
contains at least two jets and is separated by a large rapidity gap from the system
Y
, which consists of a leading proton or low-mass proton excitation. The dijet cross sections are compared with QCD calculations at next-to-leading order and with a Monte Carlo model based on leading order matrix elements with parton showers. The measured cross sections are smaller than those obtained from the next-to-leading order calculations by a factor of about 0.6. This suppression factor has no significant dependence on the fraction
x
γ
of the photon four-momentum entering the hard subprocess. Ratios of the diffractive to the inclusive dijet cross sections are measured for the first time and are compared with Monte Carlo models.
A narrow resonance in D∗−p and D∗+p̄ invariant mass combinations is observed in inelastic electron–proton collisions at centre-of-mass energies of 300 GeV and 320 GeV at HERA. The resonance has a ...mass of 3099±3(stat.)±5(syst.) MeV and a measured Gaussian width of 12±3(stat.) MeV, compatible with the experimental resolution. The resonance is interpreted as an anti-charmed baryon with a minimal constituent quark composition of uuddc̄, together with the charge conjugate.
A search for single top quark production is performed in the full e±p data sample collected by the H1 experiment at HERA, corresponding to an integrated luminosity of 474 pb−1. Decays of top quarks ...into a b quark and a W boson with subsequent leptonic or hadronic decay of the W are investigated. A multivariate analysis is performed to discriminate top quark production from Standard Model background processes. An upper limit on the top quark production cross section via flavour changing neutral current processes σ(ep→etX)<0.25 pb is established at 95% CL. Limits on the anomalous coupling κtuγ are derived.
Measurements are presented of differential dijet cross sections in diffractive photoproduction (Q2<0.01 GeV2) and deep-inelastic scattering processes (DIS, 4<Q2<80 GeV2). The event topology is given ...by ep→eXY, in which the system X, containing at least two jets, is separated from a leading low-mass baryonic system Y by a large rapidity gap. The dijet cross sections are compared with NLO QCD predictions based on diffractive parton densities previously obtained from a QCD analysis of inclusive diffractive DIS cross sections by H1. In DIS, the dijet data are well described, supporting the validity of QCD factorisation. The diffractive DIS dijet data are more sensitive to the diffractive gluon density at high fractional parton momentum than the measurements of inclusive diffractive DIS. In photoproduction, the predicted dijet cross section has to be multiplied by a factor of approximately 0.5 for both direct and resolved photon interactions to describe the measurements. The ratio of measured dijet cross section to NLO prediction in photoproduction is a factor 0.5±0.1 smaller than the same ratio in DIS. This suppression is the first clear observation of QCD hard scattering factorisation breaking at HERA. The measurements are also compared to the two soft colour neutralisation models SCI and GAL. The SCI model describes diffractive dijet production in DIS but not in photoproduction. The GAL model fails in both kinematic regions.
The ATLAS Level-1 Calorimeter Trigger is one of the main elements of the first stage of event selection for the ATLAS experiment at the LHC. The input stage consists of a mixed analogue/digital ...component taking trigger sums from the ATLAS calorimeters. The trigger logic is performed in a digital, pipelined system with several stages of processing, largely based on FPGAs, which perform programmable algorithms in parallel with a fixed latency to process about 300 Gbyte/s of input data. The real-time output consists of counts of different types of physics objects and energy sums. The production of final modules started in 2006, and installation of these modules and the necessary infrastructure at ATLAS has been underway for some time, with the intention of having a full system in situ during 2007, before first collisions at the LHC. The first experiences of commissioning and running the full scale system will be presented, along with results from integration tests performed with the upstream calorimeters, and the downstream trigger and data flow systems.
PDF
