2,706 research outputs found
Does the `Higgs' have Spin Zero?
The Higgs boson is predicted to have spin zero. The ATLAS and CMS experiments
have recently reported of an excess of events with mass ~ 125 GeV that has some
of the characteristics expected for a Higgs boson. We address the questions
whether there is already any evidence that this excess has spin zero, and how
this possibility could be confirmed in the near future. The excess observed in
the gamma gamma final state could not have spin one, leaving zero and two as
open possibilities. We calculate the angular distribution of gamma gamma pairs
from the decays of a spin-two boson produced in gluon-gluon collisions, showing
that is unique and distinct from the spin-zero case. We also calculate the
distributions for lepton pairs that would be produced in the W W* decays of a
spin-two boson, which are very different from those in Higgs decays, and note
that the kinematics of the event selection used to produce the excess observed
in the W W* final state have reduced efficiency for spin two.Comment: 22 pages, 22 figures, Version accepted for publication in JHEP,
includes additional plots of dilepton mass distribution
Recent studies of top quark properties and decays at hadron colliders
The top quark is the heaviest known elementary particle. Observed for the
first time in 1995 at the Tevatron by the CDF and D0 experiments, it has become
object of several studies aimed at fully characterize its properties and
decays. Precise determinations of top quark characteristics verify the internal
consistency of the standard model and are sensitive to new physics phenomena.
With the advent of the large top quark production rates generated at the LHC,
top quark studies have reached unprecedented statistical precision. This review
summarizes the recent measurements of top quark properties and studies of its
decays performed at the LHC and Tevatron.Comment: 13 pages, 4 figures, 5 tables, Presented at Flavor Physics and CP
Violation (FPCP 2012), Hefei, China, May 21-25, 201
Cross Section Ratios between different CM energies at the LHC: opportunities for precision measurements and BSM sensitivity
The staged increase of the LHC beam energy provides a new class of
interesting observables, namely ratios and double ratios of cross sections of
various hard processes. The large degree of correlation of theoretical
systematics in the cross section calculations at different energies leads to
highly precise predictions for such ratios. We present in this letter few
examples of such ratios, and discuss their possible implications, both in terms
of opportunities for precision measurements and in terms of sensitivity to
Beyond the Standard Model dynamics.Comment: 19 pages, 9 figure
Where is SUSY?
The direct searches for Superymmetry at colliders can be complemented by
direct searches for dark matter (DM) in underground experiments, if one assumes
the Lightest Supersymmetric Particle (LSP) provides the dark matter of the
universe. It will be shown that within the Constrained minimal Supersymmetric
Model (CMSSM) the direct searches for DM are complementary to direct LHC
searches for SUSY and Higgs particles using analytical formulae. A combined
excluded region from LHC, WMAP and XENON100 will be provided, showing that
within the CMSSM gluinos below 1 TeV and LSP masses below 160 GeV are excluded
(m_{1/2} > 400 GeV) independent of the squark masses.Comment: 16 pages, 10 figure
Bound-state/elementary-particle duality in the Higgs sector and the case for an excited 'Higgs' within the standard model
Though being weakly interacting, QED can support bound states. In principle,
this can be expected for the weak interactions in the Higgs sector as well. In
fact, it has been argued long ago that there should be a duality between bound
states and the elementary particles in this sector, at least in leading order
in an expansion in the Higgs condensate. Whether this remains true beyond the
leading order is investigated using lattice simulations, and support is found.
This provides a natural interpretation of peaks in cross sections as bound
states. Unambiguously, this would imply the existence of (possibly very broad)
resonances of Higgs and W and Z bound states within the standard model.Comment: 15 pages, 3 figures v2: added appendix with technical details, some
minor improvement
Coherent and Non-Coherent Double Diffractive Production of - pairs in Collisions of Heavy Ions at High Energies
The double coherent and non-coherent diffractive production of heavy quark -
antiquark pairs () in heavy ion scattering at high energies (LHC) is
considered. The total and differential cross sections of these processes with
the formation of and pairs in , and
collisions are evaluated. The contribution of the considered mechanisms is a
few per cent of the number of heavy quark - antiquark pairs obtained in the
processes of hard (QCD) scattering, and it will be taken into account in the
registration of , quarks or, for instance, in the study of the heavy
quarkonia suppression effects in Quark - Gluon Plasma, in the search for
intermediate mass Higgs bosons and so on. It is shown that the cross section of
the coherent scattering process is great enough. This makes it suitable for
studying collective effects in nuclear interactions at high energies. An
example of such effects is given: large values of the invariant mass of a pair, M_{Q \bar{Q}} \gsim 100 GeV, in association with a large
rapidity gap between diffractive jets .Comment: 22 pages, 5(.eps) figures, 3 tables, LaTe
Top Quark Physics at the LHC: A Review of the First Two Years
This review summarizes the highlights in the area of top quark physics
obtained with the two general purpose detectors ATLAS and CMS during the first
two years of operation of the Large Hadron Collider LHC. It covers the 2010 and
2011 data taking periods, where the LHC provided pp collisions at a
center-of-mass energy of sqrt(s)=7 TeV. Measurements are presented of the total
and differential top quark pair production cross section in many different
channels, the top quark mass and various other properties of the top quark and
its interactions, for instance the charge asymmetry. Measurements of single top
quark production and various searches for new physics involving top quarks are
also discussed. The already very precise experimental data are in good
agreement with the standard model.Comment: 107 pages, invited review for Int. J. Mod. Phys. A, v2 is identical
to v1 except for the addition of the table of content
Extracting Muon Momentum Scale Corrections for Hadron Collider Experiments
We present a simple method for the extraction of corrections for bias in the
measurement of the momentum of muons in hadron collider experiments. Such bias
can originate from a variety of sources such as detector misalignment, software
reconstruction bias, and uncertainties in the magnetic field. The two step
method uses the mean for muons from $Z\to \mu\mu$ decays to
determine the momentum scale corrections in bins of charge, $\eta$ and $\phi$.
In the second step, the corrections are tuned by using the average invariant
mass of events in the same bins of charge
and . The forward-backward asymmetry of pairs
as a function of mass, and the distribution of bosons
in the Collins-Soper frame are used to ascertain that the corrections remove
the bias in the momentum measurements for positive versus negatively charged
muons. By taking the sum and difference of the momentum scale corrections for
positive and negative muons, we isolate additive corrections to
that may originate from misalignments and multiplicative corrections that may
originate from mis-modeling of the magnetic field . This method has recently been used in the CDF experiment at
Fermilab and in the CMS experiment at the Large Hadron Collider at CERNComment: 6 pages, 3 figures, to be published in EPJC 201
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