178 research outputs found
Parton Density Uncertainties and the Determination of Electroweak Parameters at Hadron Colliders
We discuss the determination of electroweak parameters from hadron collider
observables, focusing on the boson mass measurement. We revise the
procedures adopted in the literature to include in the experimental analysis
the uncertainty due to our imperfect knowledge of the proton structure. We show
how the treatment of the proton parton density functions (PDFs) uncertainty as
a source of systematic error, leads to the automatic inclusion in the fit of
the bin-bin correlation of the kinematic distributions with respect to PDF
variations. In the case of the determination of from the charged lepton
transverse momentum distribution, we observe that the inclusion of this
correlation factor yields a strong reduction of the PDF uncertainty, given a
sufficiently good control over all the other error sources. This improvement
depends on a systematic accounting of the features of the QCD-based PDF model,
and it is achieved relying only on the information available in current PDF
sets. While a realistic quantitative estimate requires to take into account the
details of the experimental systematics, we argue that, in perspective, the
proton PDF uncertainty will not be a bottleneck for precision measurements.Comment: 5 pages, 6 figures; v2: title changed, minor textual changes, version
published on PR
Towards precise predictions for Higgs-boson production in the MSSM
We study the production of scalar and pseudoscalar Higgs bosons via gluon
fusion and bottom-quark annihilation in the MSSM. Relying on the NNLO-QCD
calculation implemented in the public code SusHi, we provide precise
predictions for the Higgs-production cross section in six benchmark scenarios
compatible with the LHC searches. We also provide a detailed discussion of the
sources of theoretical uncertainty in our calculation. We examine the
dependence of the cross section on the renormalization and factorization
scales, on the precise definition of the Higgs-bottom coupling and on the
choice of PDFs, as well as the uncertainties associated to our incomplete
knowledge of the SUSY contributions through NNLO. In particular, a potentially
large uncertainty originates from uncomputed higher-order QCD corrections to
the bottom-quark contributions to gluon fusion.Comment: 62 pages, 24 pdf figures; v2: minor clarifications, improved plot
quality, matches published versio
Low-energy SUSY facing LHC constraints
Supersymmetry (SUSY) represents one of the most theoretically interesting extensions of the Standard Model (SM) and probably one of the most widely studied. In its low-energy incarnation it provides a simple solution to the hierarchy problem and it offers the perspective of being accessible to the LHC. However, up to now, no signs of the superpartners have been detected. In this talk we review the current status of low-energy SUSY in light of the current LHC constraints, using the results from the global fits of the MasterCode Collaboration as our main tool
Supersymmetric Dark Matter after LHC Run 1
Different mechanisms operate in various regions of the MSSM parameter space
to bring the relic density of the lightest neutralino, neutralino_1, assumed
here to be the LSP and thus the Dark Matter (DM) particle, into the range
allowed by astrophysics and cosmology. These mechanisms include coannihilation
with some nearly-degenerate next-to-lightest supersymmetric particle (NLSP)
such as the lighter stau (stau_1), stop (stop_1) or chargino (chargino_1),
resonant annihilation via direct-channel heavy Higgs bosons H/A, the light
Higgs boson h or the Z boson, and enhanced annihilation via a larger Higgsino
component of the LSP in the focus-point region. These mechanisms typically
select lower-dimensional subspaces in MSSM scenarios such as the CMSSM, NUHM1,
NUHM2 and pMSSM10. We analyze how future LHC and direct DM searches can
complement each other in the exploration of the different DM mechanisms within
these scenarios. We find that the stau_1 coannihilation regions of the CMSSM,
NUHM1, NUHM2 can largely be explored at the LHC via searches for missing E_T
events and long-lived charged particles, whereas their H/A funnel, focus-point
and chargino_1 coannihilation regions can largely be explored by the LZ and
Darwin DM direct detection experiments. We find that the dominant DM mechanism
in our pMSSM10 analysis is chargino_1 coannihilation: {parts of its parameter
space can be explored by the LHC, and a larger portion by future direct DM
searches.Comment: 21 pages, 8 figure
The pMSSM10 after LHC Run 1
We present a frequentist analysis of the parameter space of the pMSSM10, in
which the following 10 soft SUSY-breaking parameters are specified
independently at the mean scalar top mass scale Msusy = Sqrt[M_stop1 M_stop2]:
the gaugino masses M_{1,2,3}, the 1st-and 2nd-generation squark masses M_squ1 =
M_squ2, the third-generation squark mass M_squ3, a common slepton mass M_slep
and a common trilinear mixing parameter A, the Higgs mixing parameter mu, the
pseudoscalar Higgs mass M_A and tan beta. We use the MultiNest sampling
algorithm with 1.2 x 10^9 points to sample the pMSSM10 parameter space. A
dedicated study shows that the sensitivities to strongly-interacting SUSY
masses of ATLAS and CMS searches for jets, leptons + MET signals depend only
weakly on many of the other pMSSM10 parameters. With the aid of the Atom and
Scorpion codes, we also implement the LHC searches for EW-interacting
sparticles and light stops, so as to confront the pMSSM10 parameter space with
all relevant SUSY searches. In addition, our analysis includes Higgs mass and
rate measurements using the HiggsSignals code, SUSY Higgs exclusion bounds, the
measurements B-physics observables, EW precision observables, the CDM density
and searches for spin-independent DM scattering. We show that the pMSSM10 is
able to provide a SUSY interpretation of (g-2)_mu, unlike the CMSSM, NUHM1 and
NUHM2. As a result, we find (omitting Higgs rates) that the minimum chi^2/dof =
20.5/18 in the pMSSM10, corresponding to a chi^2 probability of 30.8 %, to be
compared with chi^2/dof = 32.8/24 (31.1/23) (30.3/22) in the CMSSM (NUHM1)
(NUHM2). We display 1-dimensional likelihood functions for SUSY masses, and
show that they may be significantly lighter in the pMSSM10 than in the CMSSM,
NUHM1 and NUHM2. We discuss the discovery potential of future LHC runs, e+e-
colliders and direct detection experiments.Comment: 47 pages, 29 figure
Direct detection of Higgs-portal dark matter at the LHC
We consider the process in which a Higgs particle is produced in association
with jets and show that monojet searches at the LHC already provide interesting
constraints on the invisible decays of a 125 GeV Higgs boson. Using the
existing monojet searches performed by CMS and ATLAS, we show the 95%
confidence level limit on the invisible Higgs decay rate is of the order of the
total Higgs production rate in the Standard Model. This limit could be
significantly improved when more data at higher center of mass energies are
collected, provided systematic errors on the Standard Model contribution to the
monojet background can be reduced. We also compare these direct constraints on
the invisible rate with indirect ones based on measuring the Higgs rates in
visible channels. In the context of Higgs portal models of dark matter, we then
discuss how the LHC limits on the invisible Higgs branching fraction impose
strong constraints on the dark matter scattering cross section on nucleons
probed in direct detection experiments.Comment: 6 pages, 3 figures; v2: references added; v3: monojet and Higgs data
updated, version published in EPJ
Quark masses in Higgs production with a jet veto
We study the impact of finite mass effects due to top and bottom loops in the jet-veto distribution for Higgs production. We discuss the appearance of non-factorizing logarithms in the region p t,veto ≳ m b . We study their numerical impact and argue that these terms can be treated as a finite remainder. We therefore detail our prescription for resumming the jet-vetoed cross section and for assessing its uncertainty in the presence of finite mass effects. Resummation for the jet-veto, including mass effects, has been implemented in the public code JetVHeto
Slepton pair production in the POWHEG BOX
We present an implementation for slepton pair production at hadron colliders
in the POWHEG BOX, a framework for combining next-to-leading order QCD
calculations with parton-shower Monte-Carlo programs. Our code provides a SUSY
Les Houches Accord interface for setting the supersymmetric input parameters.
Decays of the sleptons and parton-shower effects are simulated with PYTHIA.
Focussing on a representative point in the supersymmetric parameter space we
show results for kinematic distributions that can be observed experimentally.
While next-to-leading order QCD corrections are sizable for all distributions,
the parton shower affects the color-neutral particles only marginally.
Pronounced parton-shower effects are found for jet distributions.Comment: 10 pages, 4 figure
Likelihood analysis of the pMSSM11 in light of LHC 13-TeV data
We use MasterCode to perform a frequentist analysis of the constraints on a phenomenological MSSM model with 11 parameters, the pMSSM11, including constraints from ∼36 /fb of LHC data at 13 TeV and PICO, XENON1T and PandaX-II searches for dark matter scattering, as well as previous accelerator and astrophysical measurements, presenting fits both with and without the (g−2)μ constraint. The pMSSM11 is specified by the following parameters: 3 gaugino masses M1,2,3 , a common mass for the first-and second-generation squarks mq~ and a distinct third-generation squark mass mq~3 , a common mass for the first-and second-generation sleptons mℓ~ and a distinct third-generation slepton mass mτ~ , a common trilinear mixing parameter A, the Higgs mixing parameter μ , the pseudoscalar Higgs mass MA and tanβ . In the fit including (g−2)μ , a Bino-like χ~01 is preferred, whereas a Higgsino-like χ~01 is mildly favoured when the (g−2)μ constraint is dropped. We identify the mechanisms that operate in different regions of the pMSSM11 parameter space to bring the relic density of the lightest neutralino, χ~01 , into the range indicated by cosmological data. In the fit including (g−2)μ , coannihilations with χ~02 and the Wino-like χ~±1 or with nearly-degenerate first- and second-generation sleptons are active, whereas coannihilations with the χ~02 and the Higgsino-like χ~±1 or with first- and second-generation squarks may be important when the (g−2)μ constraint is dropped. In the two cases, we present χ2 functions in two-dimensional mass planes as well as their one-dimensional profile projections and best-fit spectra. Prospects remain for discovering strongly-interacting sparticles at the LHC, in both the scenarios with and without the (g−2)μ constraint, as well as for discovering electroweakly-interacting sparticles at a future linear e+e− collider such as the ILC or CLIC
Heavy-quark mass effects in Higgs boson production at the LHC
We study the impact of heavy-quark masses in Higgs boson production through
gluon fusion at the LHC. We extend previous computations of the fully
differential cross section and of the transverse momentum spectrum of the Higgs
boson by taking into account the finite top- and bottom-quark masses up to
O(alpha_S^3). We also discuss the issues arising when the heavy-quark mass is
much smaller than the Higgs mass. Our results are implemented in updated
versions of the HNNLO and HRes numerical programs.Comment: Minor modifications, results unchanged. Discussion on uncertainties
added. Version published on JHE
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