arXiv subjects

Andre Lessa

Publications and source records attributed to Andre Lessa.

At least 37 records · Page 2Linked to original sources

arXiv2018

SModelS v1.2: long-lived particles, combination of signal regions, and other novelties

SModelS is an automatised tool enabling the fast interpretation of simplified model results from the LHC within any model of new physics respecting a $\mathbb{Z}_2$ symmetry. With the version 1.2 we announce several new features. First, previous versions were restricted to missing energy signatures and assumed prompt decays within each decay chain. SModelS v1.2 considers the lifetime of each $\mathbb{Z}_2$-odd particle and appropriately takes into account missing energy, heavy stable charge particle and R-hadron signatures. Second, the current version allows for a combination of signal regions in efficiency map results whenever a covariance matrix is available from the experiment. This is an important step towards fully exploiting the constraining power of efficiency map results. Several other improvements increase the user-friendliness, such as the use of wildcards in the selection of experimental results, and a faster database which can be given as a URL. Finally, smodelsTools provides an interactive plots maker to conveniently visualize the results of a model scan.

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arXiv2018

Constraining new physics with searches for long-lived particles: Implementation into SModelS

We present the implementation of heavy stable charge particle (HSCP) and R-hadron signatures into SModelS v1.2. We include simplified-model results from the 8 and 13 TeV LHC and demonstrate their impact on two new physics scenarios motivated by dark matter: the inert doublet model and a gravitino dark matter scenario. For the former, we find sensitivity up to dark matter masses of 580 GeV for small mass splittings within the inert doublet, while missing energy searches are not able to constrain any significant part of the cosmologically preferred parameter space. For the gravitino dark matter scenario, we show that both HSCP and R-hadron searches provide important limits, allowing to constrain the viable range of the reheating temperature.

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arXiv2018

SModelS extension with the CMS supersymmetry search results from Run 2

We present the update of the SModelS database with the simplified model results from CMS searches for supersymmetry at Run 2 with 36 fb$^{-1}$ of data. The constraining power of these new results is compared to that of the 8 TeV results within the context of a full model, the pMSSM. The new database, v1.1.2, is publicly available and can readily be employed for physics studies with SModelS.

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arXiv2018

On the coverage of the pMSSM by simplified model results

We investigate to which extent the SUSY search results published by ATLAS and CMS in the context of simplified models actually cover the more realistic scenarios of a full model. Concretely, we work within the phenomenological MSSM (pMSSM) with 19 free parameters and compare the constraints obtained from SModelSv1.1.1 with those from the ATLAS pMSSM study in arXiv:1508.06608. We find that about 40-45% of the points excluded by ATLAS escape the currently available simplified model constraints. For these points we identify the most relevant topologies which are not tested by the current simplified model results. In particular, we find that topologies with asymmetric branches, including 3-jet signatures from gluino-squark associated production, could be important for improving the current constraining power of simplified models results. Furthermore, for a better coverage of light stops and sbottoms, constraints for decays via heavier neutralinos and charginos, which subsequently decay visibly to the lightest neutralino are also needed.

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arXiv2018

SModelS v1.1 user manual

SModelS is an automatised tool for the interpretation of simplified model results from the LHC. It allows to decompose models of new physics obeying a Z2 symmetry into simplified model components, and to compare these against a large database of experimental results. The first release of SModelS, v1.0, used only cross section upper limit maps provided by the experimental collaborations. In this new release, v1.1, we extend the functionality of SModelS to efficiency maps. This increases the constraining power of the software, as efficiency maps allow to combine contributions to the same signal region from different simplified models. Other new features of version 1.1 include likelihood and chi-square calculations, extended information on the topology coverage, an extended database of experimental results as well as major speed upgrades for both the code and the database. We describe in detail the concepts and procedures used in SModelS, explaining in particular how upper limits and efficiency map results are dealt with in parallel. Detailed instructions for code usage are also provided.

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arXiv2016

Simplified Models for Exotic BSM Searches

Simplified models are a successful way of interpreting current LHC searches for models beyond the standard model (BSM). So far simplified models have focused on topologies featuring a missing transverse energy (MET) signature. However, in some BSM theories other, more exotic, signatures occur. If a charged particle becomes long-lived on collider time scales - as it is the case in parts of the SUSY parameter space - it leads to a very distinct signature. We present an extension of the computer package SModelS which includes simplified models for heavy stable charged particles (HSCP). As a physical application we investigate the CMSSM stau co-annihilation strip containing long-lived staus, which presents a potential solution to the Lithium problem. Applying both MET and HSCP constraints we show that, for low values of $\tanβ$, all this region of parameter space either violates Dark Matter constraints or is excluded by LHC searches.

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arXiv2015

Dark Matter Constraints on Composite Higgs Models

In composite Higgs models the pseudo-Nambu-Goldstone Boson (pNGB) nature of the Higgs field is an interesting alternative for explaning the smallness of the electroweak scale with respect to the beyond the Standard Model scale. In non-minimal models additional pNGB states are present and can be a Dark Matter (DM) candidate, if there is an approximate symmetry suppressing their decay. Here we assume that the low energy effective theory (for scales much below the compositeness scale) corresponds to the Standard Model with a pNGB Higgs doublet and a pNGB DM multiplet. We derive general effective DM Lagrangians for several possible DM representations (under the SM gauge group), including the singlet, doublet and triplet cases. Within this framework we discuss how the DM observables (relic abundance, direct and indirect detection) constrain the dimension-6 operators induced by the strong sector assuming that DM behaves as a Weakly Interacting Particle (WIMP) and that the relic abundance is settled through the freeze-out mechanism. We also apply our general results to two specific cosets: $SO(6)/SO(5)$ and $SO(6)/SO(4) \times SO(2)$, which contain a singlet and doublet DM candidate, respectively. In particular we show that if compositeness is a solution to the little hierarchy problem, representations larger than the triplet are strongly disfavored. Furthermore, we find that composite models can have viable DM candidates with much smaller direct detection cross-sections than their non-composite counterparts, making DM detection much more challenging.

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arXiv2015

Coupled Boltzmann computation of mixed axion neutralino dark matter in the SUSY DFSZ axion model

The supersymmetrized DFSZ axion model is highly motivated not only because it offers solutions to both the gauge hierarchy and strong CP problems, but also because it provides a solution to the SUSY mu problem which naturally allows for a Little Hierarchy. We compute the expected mixed axion-neutralino dark matter abundance for the SUSY DFSZ axion model in two benchmark cases-- a natural SUSY model with a standard neutralino underabundance (SUA) and an mSUGRA/CMSSM model with a standard overabundance (SOA). Our computation implements coupled Boltzmann equations which track the radiation density along with neutralino, axion (produced thermally (TH) and via coherent oscillations (CO)), saxion (TH- and CO-produced), axino and gravitino densities. In the SUSY DFSZ model, axions, axinos and saxions go through the process of freeze-in-- in contrast to freeze-out or out-of-equilibrium production as in the SUSY KSVZ model-- resulting in thermal yields which are largely independent of the re-heat temperature. We find the SUA case with suppressed saxion-axion couplings (ξ=0) only admits solutions for PQ breaking scale f_a~< 5\times 10^{12} GeV where the bulk of parameter space tends to be axion-dominated. For SUA with allowed saxion-axion couplings (ξ=1), then f_a values up to ~ 2\times 10^{14} GeV are allowed. For the SOA case, almost all of SUSY DFSZ parameter space is disallowed by a combination of overproduction of dark matter, overproduction of dark radiation or violation of BBN constraints. An exception occurs at very large f_a~ 10^{15}-10^{16} GeV where large entropy dilution from CO-produced saxions leads to allowed models.

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arXiv2015

Mixed axion-wino dark matter

A variety of supersymmetric models give rise to a split mass spectrum characterized by very heavy scalars but sub-TeV gauginos, usually with a wino-like LSP. Such models predict a thermally-produced underabundance of wino-like WIMP dark matter so that non-thermal DM production mechanisms are necessary. We examine the case where theories with a wino-like LSP are augmented by a Peccei-Quinn sector including an axion-axino-saxion supermultiplet in either the SUSY KSVZ or SUSY DFSZ models and with/without saxion decays to axions/axinos. We show allowed ranges of PQ breaking scale f_a for various cases which are generated by solving the necessary coupled Boltzmann equations. We also present results for a model with radiatively-driven naturalness but with a wino-like LSP.

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arXiv2014

SModelS v1.0: a short user guide

SModelS is a tool for the automatic interpretation of simplified-model results from the LHC. Version 1.0 of the code is now publicly available. This document provides a quick user guide for installing and running SModelS v1.0.

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arXiv2014

SModelS: a tool for interpreting simplified-model results from the LHC and its application to supersymmetry

We present a general procedure to decompose Beyond the Standard Model (BSM) collider signatures presenting a Z2 symmetry into Simplified Model Spectrum (SMS) topologies. Our method provides a way to cast BSM predictions for the LHC in a model independent framework, which can be directly confronted with the relevant experimental constraints. Our concrete implementation currently focusses on supersymmetry searches with missing energy, for which a large variety of SMS results from ATLAS and CMS are available. As show-case examples we apply our procedure to two scans of the minimal supersymmetric standard model. We discuss how the SMS limits constrain various particle masses and which regions of parameter space remain unchallenged by the current SMS interpretations of the LHC results.

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arXiv2013

SUSY discovery potential of LHC14 with 0.3-3~ab^{-1} : A Snowmass whitepaper

We examine the discovery reach of LHC14 for supersymmetry for integrated luminosity ranging from 0.3 to 3 ab^{-1}. In models with gaugino mass unification and M_1,\ M_2<< |μ| (as for mSUGRA/CMSSM), we find a reach of LHC14 with 3 ab^{-1} for gluino pair production extends to m_{\tg} 2.3 TeV while the reach via \tw_1\tz_2 \to W h +ETmiss extends to m_{\tg}\sim 2.6 TeV.

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arXiv2013

Implications of mixed axion/neutralino dark matter for the Cosmic Frontier: a Snowmass whitepaper

If one simultaneously invokes the SUSY solution to the gauge hierarchy problem and the PQ solution to the strong CP problem, then one might expect mixed axion/neutralino dark matter (DM), i.e. two dark matter particles. In this case, dark matter production involves oscillation production of axions, thermal and non-thermal neutralino production and thermal and non-thermal production of axinos and saxions. The latter particles may feed additional neutralinos into the cosmic soup, or dilute all relics via additional entropy production, or feed dark radiation into the cosmos. Depending on the SUSY and PQ model, the PQ scale can easily exist from 10^9-10^{16} GeV. Axions may lie well beyond the range currently being probed by experiment. In the case of relic WIMPs, theoretical predictions must be rescaled for the possibility that WIMPs only comprise a fraction of the local DM abundance.

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arXiv2013

Dark Radiation Constraints on Mixed Axion/Neutralino Dark Matter

Recent analyses of WMAP9 data show that dark radiation-- parametrized by the apparent number of additional neutrinos ΔN_{eff} contributing to the cosmic expansion-- is consistent with the Standard Model and bounded from above by about ΔN_{eff} ~< 0.5 at 95% CL. We consider the mixed axion/neutralino cold dark matter scenario which arises in R-parity conserving supersymmetric (SUSY) models wherein the strong CP problem is solved by hadronic axions with a concommitant axion(a)/saxion(s)/axino(\ta) supermultiplet. Our new results include improved calculations of thermal axion and saxion production and include effects of saxion decay to axinos and axions. We show that the above bound on ΔN_{eff} is easily satisfied if saxions are mainly thermally produced and m_{LSP} < m_{\ta} \lesssim m_s. However, if the dominant mechanism of saxion production is through coherent oscillations, the WMAP9 data provides a strong bound on saxion production followed by saxion decays to axions. Furthermore we show that scenarios with mixed neutralino/axion dark matter are highly constrained by combined WMAP9, BBN and Xe-100 constraints. In particular, supersymmetric models with a standard overabundance of neutralino dark matter are excluded for all values of the Peccei-Quinn breaking scale. Next generation WIMP direct detection experiments may be able to discover or exclude mixed axion-neutralino CDM scenarios where $s\to aa$ is the dominant saxion decay mode.

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arXiv2012

Discovery potential for SUSY at a high luminosity upgrade of LHC14

After completion of the LHC8 run in 2012, the plan is to upgrade the LHC for operation close to its design energy sqrt{s}=14 TeV, with a goal of collecting hundreds of fb^{-1} of integrated luminosity. The time is propitious to begin thinking of what is gained by even further LHC upgrades. In this report, we compute an LHC14 reach for SUSY in the mSUGRA/CMSSM model with an anticipated high luminosity upgrade. We find that LHC14 with 300 (3000) fb^{-1} has a reach for SUSY via gluino/squark searches of m(gluino)\sim3.2 TeV (3.6 TeV) for m(squark)\sim m)gluino), and a reach of m(gluino)\sim1.8 TeV (2.3 TeV) for m(squark)>> m(gluino). In the case where m(squark)>> m(gluino), then the LHC14 reach for chargino-neutralino production with decay into the Wh+MET final state reaches to m(gluino)\sim2.6 TeV for 3000 fb^{-1}.

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arXiv2012

LHC discovery potential for supersymmetry with \sqrt{s}=7 TeV and 5-30 fb^{-1}

We extend our earlier results delineating the supersymmetry (SUSY) reach of the CERN Large Hadron Collider operating at a centre-of-mass energy \sqrt{s}=7 TeV to integrated luminosities in the range 5 - 30 fb^{-1}. Our results are presented within the paradigm minimal supergravity model (mSUGRA or CMSSM). Using a 6-dimensional grid of cuts for the optimization of signal to background ratio -- including missing E_T-- we find for m(gluino) \sim m(squark) an LHC 5σSUSY discovery reach of m(gluino) \sim 1.3,\ 1.4,\ 1.5 and 1.6 TeV for 5, 10, 20 and 30 fb^{-1}, respectively. For m(squark)>> m(gluino), the corresponding reach is instead m(gluino)\sim 0.8,\ 0.9,\ 1.0 and 1.05 TeV, for the same integrated luminosities.

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arXiv2012

WZ plus missing-E_T signal from gaugino pair production at LHC7

LHC searches for supersymmetry currently focus on strongly produced sparticles, which are copiously produced if gluinos and squarks have masses of a few hundred GeV. However, in supersymmetric models with heavy scalars, as favored by the decoupling solution to the SUSY flavor and CP problems, and m_{\tg}> 500 GeV as indicated by recent LHC results, chargino--neutralino (\tw_1^\pm\tz_2) production is the dominant cross section for m_{\tw_1} \sim m_{\tz_2} < m_{\tg}/3 at LHC with \sqrt{s}=7 TeV (LHC7). Furthermore, if m_{\tz_1}+m_Z \lesssim m_{\tz_2}\lesssim m_{\tz_1}+m_h, then \tz_2 dominantly decays via \tz_2\to\tz_1 Z, while \tw_1 decays via \tw_1\to \tz_1 W. We investigate the LHC7 reach in the WZ + MET channel (for both leptonic and hadronic decays of the W boson) in models with and without the assumption of gaugino mass universality. In the case of the mSUGRA/CMSSM model with heavy squark masses, the LHC7 discovery reach in the WZ+MET channel becomes competetive with the reach in the canonical MET + jets channel for integrated luminosities \sim 30 fb^-1. We also present the LHC7 reach for a simplified model with arbitrary m_{\tz_1} and m_{\tw_1} \sim m_{\tz_2}. Here, we find a reach of up to m_{\tw_1}\sim 200 (250) GeV for 10 (30) fb^-1.

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arXiv2012

Wh plus missing-E_T signature from gaugino pair production at the LHC

In SUSY models with heavy squarks and gaugino mass unification, the gaugino pair production reaction pp-> \tw_1^\pm\tz_2 dominates gluino pair production for m_{\tg}\agt 1 TeV at LHC with \sqrt{s}=14 TeV (LHC14). For this mass range, the two-body decays \tw_1\to W\tz_1 and \tz_2\to h\tz_1 are expected to dominate the chargino and neutralino branching fractions. By searching for \ell b\bar{b}+MET events from \tw_1^\pm\tz_2 production, we show that LHC14 with 100 fb^{-1} of integrated luminosity becomes sensitive to chargino masses in the range m_{\tw_1}\sim 450-550 GeV corresponding to m_{\tg}\sim 1.5-2 TeV in models with gaugino mass unification. For 10^3 fb^{-1}, LHC14 is sensitive to the Wh channel for m_{\tw_1}\sim 300-800 GeV, corresponding to m_{\tg}\sim 1-2.8 TeV, which is comparable to the reach for gluino pair production followed by cascade decays. The Wh+MET search channel opens up a new complementary avenue for SUSY searches at LHC, and serves to point to SUSY as the origin of any new physics discovered via multijet and multilepton + MET channels.

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