31,885 research outputs found
Observables in the Decays of B to Two Vector Mesons
In general there are nine observables in the decay of a B meson to two vector
mesons defined in terms of polarization correlations of these mesons. Only six
of these can be detected via the subsequent decay angular distributions because
of parity conservation in those decays. The remaining three require the
measurement of the spin polarization of one of the decay products.Comment: 12 pages, no figur
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.
Survival probability in diffractive dijet photoproduction
We confront the latest H1 and ZEUS data on diffractive dijet photoproduction
with next-to-leading order QCD predictions in order to determine whether a
rapidity gap survival probability of less than one is supported by the data. We
find evidence for this hypothesis when assuming global factorization breaking
for both the direct and resolved photon contributions, in which case the
survival probability would have to be E_T^jet-dependent, and for the resolved
or in addition the related direct initial-state singular contribution only,
where it would be independent of E_T^jet.Comment: 8 pages, 7 figures, to appear in the proceedings of the 2008
CERN-DESY workshop on "HERA and the LHC
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
Inclusive D* Production in Photon-Photon Collisions at Next-to-Leading Order QCD
The next-to-leading order cross section for the inclusive production of charm
quarks in gamma-gamma collisions is calculated as a function of the transverse
momentum pT and the rapidity y in approaches using massive or massless charm
quarks. For the direct cross section we derive the massless limit from the
massive theory with the result that this limit differs from the massless
version with MSbar factorization by finite corrections. Subtracting or adding
these corrections allows us to compare the two approaches on equal footing. We
establish massless and massive versions with 3 and 4 initial flavours which are
shown to approach the massless approximations very fast with increasing pT.
With these results we calculate the inclusive D* cross section in gamma-gamma
collisions using realistic evolved fragmentation functions with appropriate
factorization scales and compare with recent data for dsigma/dpT from three LEP
collaborations after single- and double-resolved contributions have been added.Comment: 27 pages, 8 figures, LaTe
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
Factorization Breaking in Diffractive Photoproduction of Dijets
We have calculated the diffractive dijet cross section in low-Q^2 ep
scattering in the HERA regime. The results of the calculation in LO and NLO are
compared to recent experimental data of the H1 collaboration. We find that in
LO the calculated cross sections are in reasonable agreement with the
experimental results. In NLO, however, some of the cross sections disagree,
showing that factorization breaking occurs in that order. By suppressing the
resolved contribution by a factor of approximately three, good agreement with
all the data is found. The size of the factorization breaking effects in
diffractive dijet photoproduction agrees well with absorptive model
predictions.Comment: 13 pages, 9 figures. Talk presented at the 12th International
Workshop on Deep Inelastic Scattering (DIS 2004), Strbske Pleso, Slovakia,
14-18 April 2004. To appear in the proceeding
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
- âŠ