41 research outputs found
Charged Higgs Observability Through Associated Production With W at a Muon Collider
The observability of a charged Higgs boson produced in association with a W
boson at future muon colliders is studied. The analysis is performed within the
MSSM framework. The charged Higgs is assumed to decay to tb and a fully
hadronic final state is analyzed, i.e., mu+mu- \rightarrow H\pmW\mp \rightarrow
tbW \rightarrow WbbW \rightarrow jjjjbb. The main background is tt production
in fully hadronic final state which is an irreducible background with very
similar kinematic features. It is shown that although the discovery potential
is almost the same for a charged Higgs mass in the range 200 GeV < mH\pm < 400
GeV, the signal significance is about 1sigma for tanbeta = 50 at integrated
luminosity of 50 fb-1. The signal rate is well above that at e+e- linear
colliders with the same center of mass energy and enough data (O(1 ab-1)) will
provide the same discovery potential for all heavy charged Higgs masses up to
mH\pm \sim 400 GeV, however, the muon collider cannot add anything to the LHC
findings.Comment: 18 pages, 11 figure
A systematic study of J/psi suppression in cold nuclear matter
Based on a Glauber model, a statistical analysis of all mid-rapidity J/psi
hadroproduction and leptoproduction data on nuclear targets is carried out.
This allows us to determine the J/psi-nucleon inelastic cross section, whose
knowledge is crucial to interpret the J/psi suppression observed in heavy-ion
collisions, at SPS and at RHIC. The values of sigma are extracted from each
experiment. A clear tension between the different data sets is reported. The
global fit of all data gives sigma=3.4+/-0.2 mb, which is significantly smaller
than previous estimates. A similar value, sigma=3.5+/-0.2 mb, is obtained when
the nDS nuclear parton densities are included in the analysis, although we
emphasize that the present uncertainties on gluon (anti)shadowing do not allow
for a precise determination of sigma. Finally, no significant energy dependence
of the J/psi-N interaction is observed, unless strong nuclear modifications of
the parton densities are assumed.Comment: 25 pages, 5 figure
Associated Production of a Z Boson and a Single Heavy-Quark Jet
The leading-order process for the production of a Z boson and a heavy-quark
jet at hadron colliders is gQ -> ZQ (Q=c,b). We calculate this cross section at
next-to-leading order at the Tevatron and the LHC, and compare it with other
sources of ZQ events. This process is a background to new physics, and can be
used to measure the heavy-quark distribution function.Comment: 15 pages, 9 figures. Version to appear in Phys. Rev.
Backward pion-nucleon scattering
A global analysis of the world data on differential cross sections and
polarization asymmetries of backward pion-nucleon scattering for invariant
collision energies above 3 GeV is performed in a Regge model. Including the
, , and trajectories, we
reproduce both angular distributions and polarization data for small values of
the Mandelstam variable , in contrast to previous analyses. The model
amplitude is used to obtain evidence for baryon resonances with mass below 3
GeV. Our analysis suggests a resonance with a mass of 2.83 GeV as
member of the trajectory from the corresponding Chew-Frautschi
plot.Comment: 12 pages, 16 figure
Top A_FB at the Tevatron vs. charge asymmetry at the LHC in chiral U(1) flavor models with flavored Higgs doublets
We consider the top forward-backward (FB) asymmetry at the Tevatron and top
charge asymmetry at the LHC within chiral U(1)^\prime models with
flavor-dependent U(1)^\prime charges and flavored Higgs fields, which were
introduced in the ref. [65]. The models could enhance not only the top
forward-backward asymmetry at Tevatron, but also the top charge asymmetry at
LHC, without too large same-sign top pair production rates. We identify
parameter spaces for the U(1)^\prime gauge boson and (pseudo)scalar Higgs
bosons where all the experimental data could be accommodated, including the
case with about 125 GeV Higgs boson, as suggested recently by ATLAS and CMS.Comment: 11 pages, 6 figures, figures and discussion adde
Signatures of Relativistic Neutrinos in CMB Anisotropy and Matter Clustering
We present a detailed analytical study of ultra-relativistic neutrinos in
cosmological perturbation theory and of the observable signatures of
inhomogeneities in the cosmic neutrino background. We note that a modification
of perturbation variables that removes all the time derivatives of scalar
gravitational potentials from the dynamical equations simplifies their solution
notably. The used perturbations of particle number per coordinate, not proper,
volume are generally constant on superhorizon scales. In real space an
analytical analysis can be extended beyond fluids to neutrinos.
The faster cosmological expansion due to the neutrino background changes the
acoustic and damping angular scales of the cosmic microwave background (CMB).
But we find that equivalent changes can be produced by varying other standard
parameters, including the primordial helium abundance. The low-l integrated
Sachs-Wolfe effect is also not sensitive to neutrinos. However, the gravity of
neutrino perturbations suppresses the CMB acoustic peaks for the multipoles
with l>~200 while it enhances the amplitude of matter fluctuations on these
scales. In addition, the perturbations of relativistic neutrinos generate a
*unique phase shift* of the CMB acoustic oscillations that for adiabatic
initial conditions cannot be caused by any other standard physics. The origin
of the shift is traced to neutrino free-streaming velocity exceeding the sound
speed of the photon-baryon plasma. We find that from a high resolution, low
noise instrument such as CMBPOL the effective number of light neutrino species
can be determined with an accuracy of sigma(N_nu) = 0.05 to 0.09, depending on
the constraints on the helium abundance.Comment: 38 pages, 7 figures. Version accepted for publication in PR
A simple event weighting technique for optimizing the measurement of the forward-backward asymmetry of Drell-Yan dilepton pairs at hadron colliders
We describe a simple technique for optimizing the extraction of the
forward-backward asymmetry () of Drell-Yan lepton pairs (,) produced in and collisions at hadron colliders.
The method employs simple event weights which are functions of the rapidity and
decay angle of the lepton pair. It yields the best estimate of the
acceptance corrected parton level () forward backward asymmetry as a
function of final state dilepton mass (). Typically, when
compared to the simple count method, the technique reduces the statistical
errors by 20% for , and 40% for collisions, respectively. The
technique can be used to search for new high mass and large width Z' bosons
which may be best detected through the observation of deviations from the
Standard Model expectation for the forward-backward asymmetry. In addition, we
derive expressions for the QCD angular coefficients for Drell-Yan events.Comment: 13 pages, 1 figure, 4 tables. Accepted for publication in EPJ
Associated Production of Bottomonia and Higgs Bosons at Hadron Colliders
We study the associated production of bottomonia and Higgs bosons at hadron
colliders within the factorization formalism of nonrelativistic quantum
chromodynamics providing all contributing partonic cross sections in analytic
form. While such processes tend to be suppressed in the standard model, they
may have interesting cross sections in its minimal supersymmetric extension,
especially at large values of tan(beta), where the bottom Yukawa couplings are
enhanced. We present numerical results for the processes involving the lighter
CP-even h^0 boson and the CP-odd A^0 boson appropriate for the Fermilab
Tevatron and the CERN LHC.Comment: 33 pages, 7 figures, Latex, to appear in Phys. Rev.