2,370 research outputs found
Triggering and W-Polarisation Studies with CMS at the LHC
Results from studies on the commissioning of the Global Calorimeter Trigger (GCT)
of the CMS experiment are presented. Event-by-event comparisons of the hardware
with a bit-level software emulation are used to achieve 100% agreement for all trigger
quantities. In addition, a missing energy trigger based on jets is motivated using a
simulation study, and consequently implemented and commissioned in the GCT.
Furthermore, a templated-fit method for measuring the polarisation of W bosons
at the LHC in the âHelicity Frameâ is developed, and validated in simulation. An
analysis of the first 3.2 pbâ1 of
â
s = 7 TeV LHC data in the muon channel yields
values of (fL â fR)+ = 0.347 ± 0.070, f+
0 = 0.240 ± 0.176, and (fL â fR)â =
0.097 ± 0.088, fâ
0 = 0.262 ± 0.196 for positive and negative charges respectively.
The errors quoted are statistical. A preliminary systematic study is also presented
Closing in on the Tip of the CMSSM Stau Coannihilation Strip
Near the tip of the stau coannihilation strip in the CMSSM with a neutralino
LSP, the astrophysical cold dark matter density constraint forces the
stau-neutralino mass difference to be small. If this mass difference is smaller
than the tau mass, the stau may decay either in the outer part of an LHC
detector - the `disappearing track' signature - or be sufficiently long-lived
to leave the detector before decaying - the long-lived massive charged-particle
signature. We combine searches for these signatures with conventional missing
transverse energy searches during LHC Run 1, identifying the small remaining
parts of the CMSSM stau coannihilation strip region that have not yet been
excluded, and discussing how they may be explored during Run 2 of the LHC.Comment: 19 pages, 6 figures. Fig. 1 and the corresponding text are changed
due to the updated ATLAS result (ref.[16]). More details of our simulation
are provided in Section 3.1. The caption of Fig. 6 and the corresponding text
are changed. Matches the published versio
LHC Missing-Transverse-Energy Constraints on Models with Universal Extra Dimensions
We consider the performance of the ATLAS and CMS searches for events with
missing transverse energy, which were originally motivated by supersymmetry, in
constraining extensions of the Standard Model based on extra dimensions, in
which the mass differences between recurrences at the same level are
generically smaller than the mass hierarchies in typical supersymmetric models.
We consider first a toy model with pair-production of a single vector-like
quark U1 decaying into a spin-zero stable particle A1 and jet, exploring the
sensitivity of the CMS alphaT and ATLAS meff analysis to U1 mass and the U1-A1
mass difference. For this purpose we use versions of the Delphes generic
detector simulation with CMS and ATLAS cards, which have been shown to
reproduce the published results of CMS and ATLAS searches for supersymmetry. We
then explore the sensitivity of these searches to a specific model with two
universal extra dimensions, whose signal is dominated by the pair production of
quark recurrences, including searches with leptons. We find that the LHC
searches have greater sensitivity to this more realistic model, due partly to
the contributions of signatures with leptons, and partly to events with large
missing transverse energy generated by the decays of higher-level Kaluza-Klein
recurrences. We find that the CMS alphaT analysis with ~5/fb of data at 7 TeV
excludes a recurrence scale of 600 GeV at a confidence level above 99%,
increasing to 99.9% when combined with the CMS single-lepton search, whereas a
recurrence scale of 700 GeV is disfavoured at the 72% confidence level.Comment: 29 pages, 11 figures, 5 tables, references adde
XQCAT: eXtra Quark Combined Analysis Tool
XQCAT (eXtra Quark Combined Analysis Tool) is a tool aimed at determining
exclusion confidence levels for scenarios of new physics characterised by the
presence of one or multiple heavy extra quarks which interact through Yukawa
couplings with any of the Standard Model quarks. The code uses a database of
efficiencies for pre-simulated processes of QCD-induced pair production of
extra quarks and their subsequent on-shell decays. In the version 1.2 of XQCAT
the efficiencies have been computed for a set of seven publicly available
search results by the CMS experiment. The input for the code is a text file in
which masses, branching ratios and dominant chirality of the couplings of the
new quarks are provided. The output of the code is the exclusion confidence
levels of the test point for each implemented experimental analysis considered
individually and, when possible, in statistical combination.Comment: 18 pages, 2 figures, version accepted for publication in Comp. Phys.
Comm., fixed formatting problems caused by the arXiv's autotex syste
Collider Interplay for Supersymmetry, Higgs and Dark Matter
We discuss the potential impacts on the CMSSM of future LHC runs and possible
electron-positron and higher-energy proton-proton colliders, considering
searches for supersymmetry via MET events, precision electroweak physics, Higgs
measurements and dark matter searches. We validate and present estimates of the
physics reach for exclusion or discovery of supersymmetry via MET searches at
the LHC, which should cover the low-mass regions of the CMSSM parameter space
favoured in a recent global analysis. As we illustrate with a low-mass
benchmark point, a discovery would make possible accurate LHC measurements of
sparticle masses using the MT2 variable, which could be combined with
cross-section and other measurements to constrain the gluino, squark and stop
masses and hence the soft supersymmetry-breaking parameters m_0, m_{1/2} and
A_0 of the CMSSM. Slepton measurements at CLIC would enable m_0 and m_{1/2} to
be determined with high precision. If supersymmetry is indeed discovered in the
low-mass region, precision electroweak and Higgs measurements with a future
circular electron-positron collider (FCC-ee, also known as TLEP) combined with
LHC measurements would provide tests of the CMSSM at the loop level. If
supersymmetry is not discovered at the LHC, is likely to lie somewhere along a
focus-point, stop coannihilation strip or direct-channel A/H resonance funnel.
We discuss the prospects for discovering supersymmetry along these strips at a
future circular proton-proton collider such as FCC-hh. Illustrative benchmark
points on these strips indicate that also in this case FCC-ee could provide
tests of the CMSSM at the loop level.Comment: 47 pages, 26 figure
Framework for Model Independent Analyses of Multiple Extra Quark Scenarios
In this paper we present an analysis strategy and a dedicated tool to
determine the exclusion confidence level for any scenario involving multiple
heavy extra quarks with generic decay channels, as predicted in several
extensions of the Standard Model. We have created, validated and used a
software package, called XQCAT (eXtra Quark Combined Analysis Tool), which is
based on publicly available experimental data from direct searches for top
partners and from Supersymmetry inspired searches. By means of this code, we
recast the limits from CMS on new heavy extra quarks considering a complete set
of decay channels. The resulting exclusion confidence levels are presented for
some simple scenarios with multiple states and general coupling assumptions.
Highlighting the importance of combining multiple topology searches to obtain
accurate re-interpretations of the existing searches, we discuss the reach of
the SUSY analyses so as to set bounds on new quark resonances. In particular,
we report on the re-interpretation of the existing limits on benchmark
scenarios with one and multiple pair-produced top partners having non-exclusive
couplings to the third Standard Model generation of quarks.Comment: 31 pages, 6 figures, 3 tables, version accepted for publication in
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