3,354 research outputs found
Tagging Two-Photon Production at the LHC
Tagging two-photon production offers a significant extension of the LHC
physics programme. Effective luminosity of high-energy gamma-gamma collisions
reaches 1% of the proton-proton luminosity and the standard detector techniques
used for measuring very forward proton scattering should allow for a reliable
extraction of interesting two-photon interactions. Particularly exciting is a
possibility of detecting two-photon exclusive Higgs boson production at the
LHC.Comment: 9 pages and 4 figure
High energy photon interactions at the LHC
Experimental prospects for studying high-energy photon-photon and
photon-proton interactions at the CERN Large Hadron Collider (LHC) are
discussed. Cross sections are calculated for many electroweak and beyond the
Standard Model processes. Selection strategies based on photon interaction
tagging techniques are studied. Assuming a typical LHC multipurpose detector,
various signals and their irreducible backgrounds are presented after applying
acceptance cuts. Prospects are discussed for the Higgs boson search, detection
of supersymmetric particles and of anomalous quartic gauge couplings, as well
as for the top quark physics.Comment: 17 pages, 16 tables and 14 figure
Hot Topics in Ultra-Peripheral Collisions
Ultra-peripheral collisions of relativistic heavy ions involve long-ranged
electromagnetic interactions at impact parameters too large for hadronic
interactions to occur. The nuclear charges are large; with the coherent
enhancement, the cross sections are also large. Many types of photonuclear and
purely electromagnetic interactions are possible. We present here an
introduction to ultra-peripheral collisions, and present four of the most
compelling physics topics. This note developed from a discussion at a workshop
on ``Electromagnetic Probes of Fundamental Physics,'' in Erice, Italy, Oct.
16-21, 2001.Comment: 7 pages, with 3 figures. This developed from a discussion at the
workshop on "Electromagnetic Probes of Fundamental Physics," Oct. 16-21,
Erice, Ital
Deviation from standard QED at large distances: influence of transverse dimensions of colliding beams on bremsstrahlung
The radiation at collision of high-energy particles is formed over a rather
long distances and therefore is sensitive to an environment. In particular the
smallness of the transverse dimensions of the colliding beams leads to
suppression of bremsstrahlung cross section for soft photons. This beam-size
effect was discovered and investigated at INP, Novosibirsk around 1980. At that
time an incomplete expression for the bremsstrahlung spectrum was calculated
and used because a subtraction associated with the extraction of pure
fluctuation process was not performed. Here this procedure is done. The
complete expression for the spectral-angular distribution of incoherent
bremsstrahlung probability is obtained. The case of Gaussian colliding beams is
investigated in details. In the case of flat beams the expressions for the
bremsstrahlung spectrum are simplified essentially. Comparison of theory with
VEPP4 and HERA data is performed. Possible application of the effect to linear
collider tuning is discussed.Comment: 23 pagers,5 figure
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Search for MSSM Higgs bosons decaying to ÎŒ+ÎŒ-in proton-proton collisions at âs=13TeV
A search is performed for neutral non-standard-model Higgs bosons decaying to two muons in the context of the minimal supersymmetric standard model (MSSM). Proton-proton collision data recorded by the CMS experiment at the CERN Large Hadron Collider at a center-of-mass energy of 13TeVwere used, corresponding to an integrated luminosity of 35.9fb-1. The search is sensitive to neutral Higgs bosons produced via the gluon fusion process or in association with a bbquark pair. No significant deviations from the standard model expectation are observed. Upper limits at 95% confidence level are set in the context of the mmod+hand phenomenological MSSM scenarios on the parameter tanÎČas a function of the mass of the pseudoscalar Aboson, in the range from 130 to 600GeV. The results are also used to set a model-independent limit on the product of the branching fraction for the decay into a muon pair and the cross section for the production of a scalar neutral boson, either via gluon fusion, or in association with bquarks, in the mass range from 130 to 1000GeV
Heavy Quark Photoproduction in Ultra-peripheral Heavy Ion Collisions
Heavy quarks are copiously produced in ultra-peripheral heavy ion collisions.
In the strong electromagnetic fields, c c-bar and b b-bar are produced by
photonuclear and two-photon interactions; hadroproduction can occur in grazing
interactions. We present the total cross sections, quark transverse momentum
and rapidity distributions, as well as the Q Q-bar invariant mass spectra from
the three production channels. We consider AA and pA collisions at the
Relativistic Heavy Ion Collider and Large Hadron Collider. We discuss
techniques for separating the three processes and describe how the AA to pA
production ratios might be measured accurately enough to study nuclear
shadowing.Comment: Minor changes to satisfy referees and typo fixes; 52 pages including
17 figure
Measurement of inclusive D*+- and associated dijet cross sections in photoproduction at HERA
Inclusive photoproduction of D*+- mesons has been measured for photon-proton
centre-of-mass energies in the range 130 < W < 280 GeV and a photon virtuality
Q^2 < 1 GeV^2. The data sample used corresponds to an integrated luminosity of
37 pb^-1. Total and differential cross sections as functions of the D*
transverse momentum and pseudorapidity are presented in restricted kinematical
regions and the data are compared with next-to-leading order (NLO) perturbative
QCD calculations using the "massive charm" and "massless charm" schemes. The
measured cross sections are generally above the NLO calculations, in particular
in the forward (proton) direction. The large data sample also allows the study
of dijet production associated with charm. A significant resolved as well as a
direct photon component contribute to the cross section. Leading order QCD
Monte Carlo calculations indicate that the resolved contribution arises from a
significant charm component in the photon. A massive charm NLO parton level
calculation yields lower cross sections compared to the measured results in a
kinematic region where the resolved photon contribution is significant.Comment: 32 pages including 6 figure
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