7,191 research outputs found
Report of the GDR working group on the R-parity violation
This report summarizes the work of the "R-parity violation group" of the
French Research Network (GDR) in Supersymmetry, concerning the physics of
supersymmetric models without conservation of R-parity at HERA, LEP, Tevatron
and LHC and limits on R-parity violating couplings from various processes. The
report includes a discussion of the recent searches at the HERA experiment,
prospects for new experiments, a review of the existing limits, and also
theoretically motivated alternatives to R-parity and a brief discussion on the
implications of R-parity violation on the neutrino masses.Comment: 60 pages, LaTeX, 22 figures, 2 table
String theory predictions for future accelerators
We consider, in a string theory framework, physical processes of
phenomenological interest in models with a low string scale. The amplitudes we
study involve tree-level virtual gravitational exchange, divergent in a
field-theoretical treatment, and massive gravitons emission, which are the main
signatures of this class of models. First, we discuss the regularization of
summations appearing in virtual gravitational (closed string) Kaluza-Klein
exchanges in Type I strings. We argue that a convenient manifestly ultraviolet
convergent low energy limit of type I string theory is given by an effective
field theory with an arbitrary cutoff in the closed (gravitational)
channel and a related cutoff in the open (Yang-Mills) channel.
We find the leading string corrections to the field theory results. Second, we
calculate exactly string tree-level three and four-point amplitudes with gauge
bosons and one massive graviton and examine string deviations from the
field-theory result.Comment: 39 pages, 8 figures, references adde
Scalar kinks and fermion localisation in warped spacetimes
Scalar kinks propagating along the bulk in warped spacetimes provide a thick
brane realisation of the braneworld. We consider here, a class of such exact
solutions of the full Einstein-scalar system with a sine-Gordon potential and a
negative cosmological constant. In the background of the kink and the
corresponding warped geometry, we discuss the issue of localisation of spin
half fermions (with emphasis on massive ones) on the brane in the presence of
different types of kink-fermion Yukawa couplings. We analyse the possibility of
quasi-bound states for large values of the Yukawa coupling parameter
(with , the warp factor parameter kept fixed) using appropriate, recently
developed, approximation methods. In particular, the spectrum of the low--lying
states and their lifetimes are obtained, with the latter being exponentially
enhanced for large . Our results indicate quantitatively, within
this model, that it is possible to tune the nature of warping and the strength
and form of the Yukawa interaction to obtain trapped massive fermion states on
the brane, which, however, do have a finite (but very small) probability of
escaping into the bulk.Comment: 22 pages, 4 figures, RevTex
Looking For TeV-Scale Strings and Extra-Dimensions
In contrast to the old heterotic string case, the (weakly coupled) type I
brane framework allows to have all, part or none of the standard model gauge
group factors propagating in large extra--dimensions of TeV size. We
investigate the main experimental signatures of these possibilities, related to
the production of Kaluza-Klein excitations of gluons and electroweak gauge
bosons. A discovery through direct observation of resonances is possible only
for compactification scales below 6 TeV. However effects due to exchange of
virtual Kaluza-Klein excitations could be observed for higher scales. We find
that LHC can probe compactification scales as high as 20 TeV for excitations of
gluons and 8-15 TeV for excitations of electroweak gauge bosons. Finally, in
the case where no gauge boson feels the extra-dimension, we find that effective
contact interactions due to massive string mode oscillations dominate those due
to the exchange of Kaluza-Klein excitations of gravitons and could be used to
obtain bounds on the string scale.Comment: 13 pages, latex, 6 eps figure
Search for associated Higgs boson production using like charge dilepton events in p(p)over-bar collisions at root s=1.96 TeV
We present a search for associated Higgs boson production in the process p (p) over bar -> W/ZH -> l(+/-)l'(+/-) + X in ee, e mu, and mu mu final states. The search is based on data collected by the D0 experiment at the Fermilab Tevatron Collider at root s = 1.96 TeV corresponding to 5.3 fb(-1) of integrated luminosity. We require two isolated leptons (electrons or muons) with the same electric charge and additional kinematic requirements. No significant excess above background is observed, and we set 95% C. L. observed (expected) upper limits on ratio of the production cross section to the standard model prediction of 6.4 (7.3) for a Higgs boson mass of 165 GeV and 13.5 (19.8) for a mass of 115 GeV
Domain wall generation by fermion self-interaction and light particles
A possible explanation for the appearance of light fermions and Higgs bosons
on the four-dimensional domain wall is proposed. The mechanism of light
particle trapping is accounted for by a strong self-interaction of
five-dimensional pre-quarks. We obtain the low-energy effective action which
exhibits the invariance under the so called \tau-symmetry. Then we find a set
of vacuum solutions which break that symmetry and the five-dimensional
translational invariance. One type of those vacuum solutions gives rise to the
domain wall formation with consequent trapping of light massive fermions and
Higgs-like bosons as well as massless sterile scalars, the so-called branons.
The induced relations between low-energy couplings for Yukawa and scalar field
interactions allow to make certain predictions for light particle masses and
couplings themselves, which might provide a signature of the higher dimensional
origin of particle physics at future experiments. The manifest translational
symmetry breaking, eventually due to some gravitational and/or matter fields in
five dimensions, is effectively realized with the help of background scalar
defects. As a result the branons acquire masses, whereas the ratio of Higgs and
fermion (presumably top-quark) masses can be reduced towards the values
compatible with the present-day phenomenology. Since the branons do not couple
to fermions and the Higgs bosons do not decay into branons, the latter ones are
essentially sterile and stable, what makes them the natural candidates for the
dark matter in the Universe.Comment: 34 pages, 2 figures, JHEP style,few important refs. adde
Journal Staff
We present the first measurements of the differential cross section d sigma/dp(T)(gamma) for the production of an isolated photon in association with at least two b-quark jets. The measurements consider photons with rapidities vertical bar y(gamma)vertical bar < 1.0 and transverse momenta 30 < p(T)(gamma) < 200 GeV. The b-quark jets are required to have p(T)(jet) > 15 GeVand vertical bar y(jet)vertical bar < 1.5. The ratio of differential production cross sections for gamma + 2 b-jets to gamma + b-jet as a function of p(T)(gamma) is also presented. The results are based on the proton-antiproton collision data at root s = 1.96 TeV collected with the D0 detector at the Fermilab Tevatron Collider. The measured cross sections and their ratios are compared to the next- to- leading order perturbative QCD calculations as well as predictions based on the k(T)- factorization approach and those from the sherpa and pythia Monte Carlo event generators
Measurement of the W boson mass
We present a measurement of the W boson mass in W -> ev decays using 1 fb^-1
of data collected with the D0 detector during Run II of the Fermilab Tevatron
collider. With a sample of 499830 W -> ev candidate events, we measure M_W =
80.401 +- 0.043 GeV. This is the most precise measurement from a single
experiment.Comment: As published in PR
Radiation hardness qualification of PbWO4 scintillation crystals for the CMS Electromagnetic Calorimeter
This is the Pre-print version of the Article. The official published version can be accessed from the link below - Copyright @ 2010 IOPEnsuring the radiation hardness of PbWO4 crystals was one of the main priorities during the construction of the electromagnetic calorimeter of the CMS experiment at CERN. The production on an industrial scale of radiation hard crystals and their certification over a period of several years represented a difficult challenge both for CMS and for the crystal suppliers. The present article reviews the related scientific and technological problems encountered
- …