This paper describes measurements of the sum of the transverse energy of particles as a function of particle pseudorapidity, η, in proton-proton collisions at a centreof-mass energy, √ s = 7 TeV using the ATLAS detector at the Large Hadron Collider. The measurements are performed in the region |η| < 4.8 for two event classes: those requiring the presence of particles with a low transverse momentum and those requiring particles with a significant transverse momentum. In the second dataset measurements are made in the region transverse to the hard scatter. The distributions are compared to the predictions of various Monte Carlo event generators, which generally tend to underestimate the amount of transverse energy at high |η|. The ATLAS collaboration 33
Keywords: Hadron-Hadron Scattering
IntroductionThe main aim of the Large Hadron Collider (LHC) general-purpose detectors is to explore physics in collisions around and above the electroweak symmetry-breaking scale. Such processes typically involve high momentum transfer, which distinguishes them from the dominant processes, namely low momentum transfer strong force interactions described by non-perturbative Quantum Chromodynamics (QCD). In order to collect enough data -1 -
JHEP11(2012)033to be sensitive to rare processes it is necessary to run the LHC at high instantaneous luminosities, meaning that multiple proton-proton interactions are very likely to occur each time the proton bunches collide. It is essential that the Monte Carlo event generators used to simulate these processes have an accurate description of the soft particle kinematics in inclusive proton-proton interactions over the entire acceptance of the LHC experiments, such that reliable comparisons can be made between theoretical predictions and the data for any process of interest.Protons are composite objects made up of partons, the longitudinal momentum distributions of which are described by parton distribution functions (PDFs). When protons interact at the LHC the dominant parton-parton interaction is t-channel gluon exchange. Due to the composite nature of the protons it is possible that multiple parton-parton interactions (MPI) occur in the same proton-proton interaction. Therefore, if a hard partonparton interaction occurs it will likely be accompanied by additional QCD interactions, again predominately low momentum t-channel gluon exchange. Any part of the interaction not attributed to the hard parton-parton scatter is collectively termed the underlying event, which includes MPI as well as soft particle production from the beam-beam remnants. Monte Carlo event generators that simulate any hard process at the LHC must also include an accurate description of the underlying event.At low momentum transfer, perturbative calculations in QCD are not meaningful and cross-sections cannot currently be computed from first principles. Phenomenological models are therefore used to describe the kinematics of particle production in inclusive protonproton interactions and in the underlying event in ...
We measure the branching fraction for the charmless semi-inclusive process B --> eta'Xs, where the eta' meson has a momentum in the range 2.0 to 2.7 GeV/c in the upsilon4S center-of-mass frame and Xs represents a system comprising a kaon and zero to four pions. We find B(B --> eta'Xs) = [3.9 +/- 0.8(stat) +/- 0.5(syst) +/- 0.8(model)] x 10(-4). We also obtain the Xs mass spectrum and find that it fits models predicting high masses.
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