317 research outputs found
Beyond the Standard Model at HERA
The prospects of physics beyond the standard model in deep inelastic
scattering are reviewed, emphasizing the search for contact interactions, for
leptoquarks and for supersymmetry with R-parity violation. R-parity violating
supersymmetry is explored as a speculative source of events with high energy
muons and missing transverse momentum, but no convincing explanation for events
of this type observed at H1 is found.Comment: 13 pages, 7 eps-figures included. Lecture notes to appear in the
proceedings of the Ringberg Workshop 'New Trends in HERA Physics 1999
Inclusive D-Meson Production at the LHC
I present predictions for the inclusive production of D mesons at the CERN
LHC in the general-mass variable-flavor-number scheme at next-to-leading order.
Numerical results are compared to data where available, and uncertainties due
to scale variations, parton distribution functions and charm mass are
discussed. I point out that measurements at large rapidity have the potential
to pin down models of intrinsic charm.Comment: Contribution to DIS 2012, Bon
b-Hadron production in the general-mass variable-flavour-number scheme and LHC data
We study inclusive b-hadron production in pp collisions at the LHC at
different center-of-mass energies and compare with experimental data from the
LHCb and CMS collaborations. Our predictions for cross sections differential in
the transverse momentum and (pseudo-)rapidity agree with data within
uncertainties due to renormalization scale variations. A small tension is found
if data and theory predictions are compared for cross section ratios at
different center-of-mass energies.Comment: 22 pages. Replaced LHCb data: now match with revised version (v9) of
arXiv:1612.0514
Inclusive D* production in gamma-gamma collisions: including the single-resolved contribution with massive quarks
We have calculated the next-to-leading order cross section for the inclusive
production of charm quarks as a function of the transverse momentum p_T and the
rapidity in two approaches using massive or massless charm quarks. For the
single-resolved cross section we have derived the massless limit from the
massive theory. We find that this limit differs from the genuine massless
version with MS-bar factorization by finite corrections. By adjusting
subtraction terms we establish a massive theory with MS-bar subtraction which
approaches the massless theory very fast with increasing transverse momentum.
With these results and including the equivalent results for the direct cross
section obtained previously as well as double-resolved contributions, we
calculate the inclusive D*+- cross section in gamma-gamma collisions using
realistic evolved non-perturbative fragmentation functions and compare with
recent data from the LEP collaborations ALEPH, L3 and OPAL. We find good
agreement.Comment: 34 pages including postscript figure
LARGE LOGARITHM BEHAVIOUR OF e^+e^- JET CROSS SECTIONS AND EVENT SHAPE DISTRIBUTIONS IN O(alpha_s^2)
We have calculated the leading and next-to-leading logarithm coefficients of
annihilation jet cross sections, thrust distribution
and energy-energy correlation in the two-jet limit when the jet resolution and
the event shape variables vanish. We have compared our results with
expectations based on leading logarithm approximations used to resum the
pertubative cross sections where this is possible. There is good agreement for
the leading and next-to-leading coefficients of jet cross sections in the
Durham scheme. Also for the thrust distribution and energy-energy correlation
we find results which are consistent with the leading logarithm predictions.Comment: 22 pages, uuencoded postscript, no figure
Inclusive photoproduction of bottom quarks for low and medium pT in the general-mass variable-flavour-number scheme
We present predictions for b-quark production in photoprodcution and compare
with experimental data from HERA. Our theoretical predictions are obtained at
next-to-leading-order in the general-mass variable-flavor-number scheme, an
approach which takes into account the finite mass of the b quarks. We use
realistic evolved nonperturbative fragmentation functions obtained from fits to
e+e- data. We find in general good agreement of data with both the GM-VFNS and
the FFNS calculations, while the more precise ZEUS data seem to prefer the
GM-VFNS predictions.Comment: 11 page
Study of heavy meson production in p-Pb collisions at =5.02 TeV in the general-mass variable-flavour-number scheme
We study inclusive charm and bottom production, for both D and B mesons, in
p-Pb collisions at the LHC. Numerical results for p_T-differential production
cross sections are obtained at next-to-leading-order in the general-mass
variable-flavor-number scheme. We compare our results with recent data from
ALICE, LHCb and CMS at a center-of-mass energy of 5 TeV and find good
agreement. A comparison with p-p cross sections does not reveal the presence of
nuclear initial-state interaction effects that could be expected to become
visible as deviations of the ratio of p-Pb and p-p cross sections from one.Comment: 20 pages, extended discussion, agrees with published version in
Nucl.Phys.
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