2,655 research outputs found
Measurement of Heavy Quark cross-sections at CDF
The measurement of heavy quark cross-sections provides important tests of the
QCD theory. This paper reviews recent measurements of single b-quark and
correlated b-quark cross-sections at CDF. Two new measurements of the single
b-quark production at CDF agree with the first result from CDF Run II. This
clarifies the experimental situation and confirms the recent agreement of
theoretical prediction with data. A new measurement of the correlated
cross-section with dimuon events at CDF is presented. It agrees with
theory and it does not confirm the anomalously large cross-section
seen in Run I by CDF and D in dimuon events.Comment: EPS HEP2007 conference held in Mancheste
Collinear Subtractions in Hadroproduction of Heavy Quarks
We present a detailed discussion of the collinear subtraction terms needed to
establish a massive variable-flavour-number scheme for the one-particle
inclusive production of heavy quarks in hadronic collisions. The subtraction
terms are computed by convoluting appropriate partonic cross sections with
perturbative parton distribution and fragmentation functions relying on the
method of mass factorization. We find (with one minor exception) complete
agreement with the subtraction terms obtained in a previous publication by
comparing the zero-mass limit of a fixed-order calculation with the genuine
massles results in the MSbar scheme. This presentation will be useful for
extending the massive variable-flavour-number scheme to other processes.Comment: 29 pages, 17 figures include
The RR Lyrae Period - K Luminosity relation for Globular Clusters: an observational approach
The Period - metallicity - K band luminosity (PLK) relation for RR Lyrae
stars in 15 Galactic globular clusters and in the LMC globular cluster
Reticulum has been derived. It is based on accurate near infrared (K)
photometry combined with 2MASS and other literature data. The PLK relation has
been calibrated and compared with the previous empirical and theoretical
determinations in literature. The zero point of the absolute calibration has
been obtained from the K magnitude of RR Lyr whose distance modulus has been
measured via trigonometric parallax with HST. Using this relation we obtain a
distance modulus to the LMC of (m-M)_0 = 18.54 \pm 0.15 mag, in good agreement
with recent determinations based on the analysis of Cepheid variable stars.Comment: 6 pages, 4 figures, accepted for publication by MNRA
Heavy-to-light ratios as a test of medium-induced energy loss at RHIC and the LHC
The ratio of nuclear modification factors of high- heavy-flavored mesons
tolight-flavored hadrons (heavy-to-light ratio) is shown to be a sensitive tool
to test medium-induced energy loss at RHIC and LHC energies. Heavy-to-light
ratios of mesons at RHIC in the region GeV, and of and
mesons at the LHC in the region GeV, are proposed for such a test.
Finally, the different contributions to the nuclear modification factor for
electrons at RHIC are analyzed. Preliminary PHENIX and STAR data are compatible
with radiative energy loss provided the contribution of electrons from beauty
decays is small compared to that from charm.Comment: 5 pages, latex, 4 eps figs included using graphicx; to appear in the
proceedings of 18th International Conference on Ultrarelativistic
Nucleus-Nucleus Collisions: Quark Matter 2005 (QM 2005), Budapest, Hungary,
4-9 Aug 200
How sensitive are high-pt electron spectra at RHIC to heavy quark energy loss?
In nucleus-nucleus collisions, high-pt electron spectra depend on the medium
modified fragmentation of their massive quark parents, thus giving novel access
to the predicted mass hierarchy of parton energy loss. Here we calculate these
spectra in a model, which supplements the perturbative QCD factorization
formalism with parton energy loss. In general, we find - within large errors -
rough agreement between theory and data on the single inclusive electron
spectrum in pp, its nuclear modification factor, and its azimuthal anisotropy.
However, the nuclear modification factor depends on the relative contribution
of charm and bottom production, which we find to be affected by large
perturbative uncertainties. In order for electron measurements to provide a
significantly more stringent test of the expected mass hierarchy, one must then
disentangle the b- and c-decay contributions, for instance by reconstructing
the displaced decay vertices.Comment: 9 pages RevTex, 4 eps-figures, asci-file containing numerical tables
of results include
Optimal jet radius in kinematic dijet reconstruction
Obtaining a good momentum reconstruction of a jet is a compromise between
taking it large enough to catch the perturbative final-state radiation and
small enough to avoid too much contamination from the underlying event and
initial-state radiation. In this paper, we compute analytically the optimal jet
radius for dijet reconstructions and study its scale dependence. We also
compare our results with previous Monte-Carlo studies.Comment: 30 pages, 11 figures; minor corrections; published in JHE
J/psi Production: Tevatron and Fixed-Target Collisions
In this talk I show the results of a fit of the NRQCD matrix elements to the
CDF data for direct production, by including the radiative corrections
to the colour-singlet channel and the effect of the -smearing. Furthermore
I perform the NLO NRQCD analysis of production in fixed-target
proton-nucleon collisions and I fit the colour-octet matrix elements to the
available experimental data. The results are compared to the Tevatron ones.Comment: 6 pages, 3 figures. Talk given at the QCD99 Euroconference,
Montpellier, France, July 199
FastJet user manual
FastJet is a C++ package that provides a broad range of jet finding and
analysis tools. It includes efficient native implementations of all widely used
2-to-1 sequential recombination jet algorithms for pp and e+e- collisions, as
well as access to 3rd party jet algorithms through a plugin mechanism,
including all currently used cone algorithms. FastJet also provides means to
facilitate the manipulation of jet substructure, including some common boosted
heavy-object taggers, as well as tools for estimation of pileup and
underlying-event noise levels, determination of jet areas and subtraction or
suppression of noise in jets.Comment: 69 pages. FastJet 3 is available from http://fastjet.fr
Extraction of the x-dependence of the non-perturbative QCD b-quark fragmentation distribution component
Using recent measurements of the b-quark fragmentation distribution obtained
in events registered at the Z pole, the non-perturbative
QCD component of the distribution has been extracted independently of any
hadronic physics modelling. This distribution depends only on the way the
perturbative QCD component has been defined. When the perturbative QCD
component is taken from a parton shower Monte-Carlo, the non-perturbative QCD
component is rather similar with those obtained from the Lund or Bowler models.
When the perturbative QCD component is the result of an analytic NLL
computation, the non-perturbative QCD component has to be extended in a
non-physical region and thus cannot be described by any hadronic modelling. In
the two examples used to characterize these two situations, which are studied
at present, it happens that the extracted non-perturbative QCD distribution has
the same shape, being simply translated to higher-x values in the second
approach, illustrating the ability of the analytic perturbative QCD approach to
account for softer gluon radiation than with a parton shower generator.Comment: 13 page
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