5,638 research outputs found
Heavy Flavours in Collider Experiments
Current issues in the studies of Heavy Flavours in colliders are described
with particular emphasis on experiments in which the UK is involved. Results on
charm production at HERA are examined and compared to those at the Tevatron. B
production rates at the Tevatron as well as the status of B lifetimes and
mixing in the LEP collaborations and at the Tevatron are highlighted. The
measurement of sin2beta from CDF is described as well as the most recent
results on top physics at the Tevatron
Jets in deep-inelastic scattering at HERA
Jet cross sections in deep-inelastic scattering over a wide region of phase
space have been measured at HERA. These cross section measurements provide a
thorough test of the implementation of Quantum Chromodynamics in
next-to-leading order (NLO) calculations. They also provide the opportunity to
test the consistency of the gluon distribution in the proton as extracted from
(mainly) inclusive DIS measurements. Comparison of the cross sections with NLO
enables accurate extractions of the strong coupling constant, , to be
made, several of which are reported here.Comment: Talk presented at "New Trends in HERA Physics", Ringberg Workshop,
June 2001. 13pages, 12figure
Prompt photon and associated heavy quark production at hadron colliders with kt-factorization
In the framework of the kt-factorization approach, the production of prompt
photons in association with a heavy (charm or beauty) quarks at high energies
is studied. The consideration is based on the O(\alpha \alpha_s^2) off-shell
amplitudes of gluon-gluon fusion and quark-(anti)quark interaction
subprocesses. The unintegrated parton densities in a proton are determined
using the Kimber-Martin-Ryskin prescription. The analysis covers the total and
differential cross sections and extends to specific angular correlations
between the produced prompt photons and muons originating from the semileptonic
decays of associated heavy quarks. Theoretical uncertainties of our evaluations
are studied and comparison with the results of standard NLO pQCD calculations
is performed. Our numerical predictions are compared with the recent
experimental data taken by the D0 and CDF collaborations at the Tevatron.
Finally, we extend our results to LHC energies.Comment: 14 pages, 10 figure
Physics Beyond the Standard Model
I briefly summarize the prospects for extending our understanding of physics
beyond the standard model within the next five years.Comment: 9 pages, 2 figures, LaTeX. Presented at the 1999 UK Phenomenology
Workshop, Durham, September 1999. To be published in Journal of Physics
Soft Color Interactions and Diffractive Hard Scattering at the Fermilab Tevatron
An improved understanding of nonperturbative QCD can be obtained by the
recently developed soft color interaction models. Their essence is the
variation of color string-field topologies, giving a unified description of
final states in high energy interactions, e.g., diffractive and nondiffractive
events in ep and ppbar. Here we present a detailed study of such models (the
soft color interaction model and the generalized area law model) applied to
ppbar, considering also the general problem of the underlying event including
beam particle remnants. With models tuned to HERA ep data, we find a good
description also of Tevatron data on production of W, beauty and jets in
diffractive events defined either by leading antiprotons or by one or two
rapidity gaps in the forward or backward regions. We also give predictions for
diffractive J/psi production where the soft exchange mechanism produces both a
gap and a color singlet ccbar state in the same event. This soft color
interaction approach is also compared with Pomeron-based models for
diffraction, and some possibilities to experimentally discriminate between
these different approaches are discussed.Comment: 35 pages, 15 figures, uses REVTeX. Minor changes, version to appear
in Phys. Rev.
Three Numerical Puzzles and the Top Quark's Chiral Weak-Moment
Versus the standard model's t --> W b decay helicity amplitudes, three
numerical puzzles occur at the 0.1 % level when one considers the amplitudes in
the case of an additional (f_M + f_E) coupling of relative strength 53 GeV. The
puzzles are theoretical ones which involve the t --> W b decay helicity
amplitudes in the two cases, the relative strength of this additional coupling,
and the observed masses of these three particles. A deeper analytic realization
is obtained for two of them. Equivalent realizations are given for the
remaining one. An empirical consequence of these analytic realizations is that
it is important to search for effects of a large chiral weak-moment of the
top-quark, the effective mass-scale is about 53 GeV. A full theoretical
resolution would include relating the origin of such a chiral weak-moment and
the mass generation of the top-quark, the W-boson, and probably the b-quark.Comment: 18 pages, 1 postscript table (revised to better explain notation,
model #1, add a little material...
On the possibility of a very light A^0 at low \tan\beta
The searches at LEP II for the processes e^+e^-\to h^0Z and e^+e^-\to h^0A^0
in the Minimal Supersymmetric Standard Model (MSSM) fail to exclude regions of
the m_h,m_A plane where \tan\beta <1, thus allowing a very light A^0 (m_A< 20
GeV). Such a parameter choice would predict a light H^\pm with m_{H^\pm}< m_W.
Although the potentially large branching ratio for H^\pm \to A^0 W^* would
ensure that H^\pm also escaped detection in direct searches at LEP II and the
Tevatron Run I, we show that this elusive parameter space is overwhelmingly
disfavoured by electroweak precision measurements.Comment: 11 pages, 2 figures, Revtex, references added, minor additions to
tex
Diffractive production of dijets by double Pomeron exchange processes
A phenomenological description of diffractive dijet hadroproduction via
double Pomeron exchange is presented. This description is based on a modified
version of the Ingelman-Schlein model which includes the evolution of the
Pomeron structure function and corrections regarding rapidity gap suppression
effects. The same quark-dominant Pomeron structure function employed in a
previous report to describe diffractive dijet and W production via single
Pomeron processes is shown here to yield results consistent with the available
data for double Pomeron processes as well.Comment: 4 pages, REVTEX4.
Asymptotically Free Non-Abelian Gauge Theories With Fermions and Scalars As Alternatives to QCD
In this paper we construct non-Abelian gauge theories with fermions and
scalars that nevertheless possess asymptotic freedom.The scalars are taken to
be in a chiral multiplet transforming as under
and transforming as singlets under the colour SU(3) group. We consider two
distinct scenarios, one in which the additional scalars are light and another
in which they are heavier than half the Z-boson mass. It is shown that
asymptotic freedom is obtained without requiring that all additional couplings
keep fixed ratios with each other. It is also shown that both scenarios can not
be ruled out by what are considered standard tests of QCD like R- parameter,
g-2 for muons or deep inelastic phenomena. The light mass scenario is however
ruled out by high precision Z-width data (and only by that one data).The heavy
mass scenario is still viable and is shown to naturally pass the test of
flavour changing neutral currents. It also is not ruled out by precision
electroweak oblique parameters. Many distinctive experimental signatures of
these models are also discussed.Comment: 37 pages in LATEX with 10 fig
The exclusive B_s -> phi mu+ mu- process in a constituent quark model
We consider the exclusive B_s -> phi mu+ mu- process in the standard model
using a constituent quark loop model approach together with a simple
parameterization of the quark dynamics. The model allows to compute the decay
form factors and therefore can give predictions for the decay rates, the
invariant mass spectra and the asymmetries. This process is suppressed in the
standard model but can be enhanced if new physics beyond the standard model is
present, such as flavor-violating supersymmetric models. It constitutes
therefore an interesting precision test of the standard model at forthcoming
experiments.Comment: 17 pages, 6 figures, 5 tables, LaTeX; minor changes to the
introduction, table III and figure 3. Few references adde
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