Sparticle Masses Research Articles

Seesaw-deflected Anomaly Mediation and the 125 GeV Higgs Boson

We investigate the phenomenology of a class of model that at the same time solves the tachyonic slepton problem of the pure anomaly mediated supersymmetry breaking (AMSB) model and generates neutrino masses. We introduce heavy fields in the seesaw mechanism that are the messengers in the deflected AMSB scenario. Various theoretical and phenomenological constraints have been taken into account, especially the Higgs mass limits. The viable parameter regions have been specified, and the properties of dark matter candidate have been studied. We point out that the type III seesaw with three generations of 24-messenger is excluded, while the type II seesaw and type III seesaw with two generations of 24-messenger are still allowed. The sparticle masses are heavy as in usual SUSY models. The spin-independent crosssection of the scattering between the lightest neutralino and proton show the possibility to see evidences of new physics from future dark matter search experiments. We find that the lepton flavor violation effects caused by the Yukawa mediation are suppressed due to the electroweak symmetry breaking condition.

The Higgs mass and natural supersymmetric spectrum from the landscape

In supersymmetric models where the superpotential mu term is generated with mu<< m_{soft} (e.g. from radiative Peccei-Quinn symmetry breaking or compactified string models with sequestration and stabilized moduli), and where the string landscape 1. favors soft supersymmetry (SUSY) breaking terms as large as possible and 2. where the anthropic condition that electroweak symmetry is properly broken with a weak scale m_{W,Z,h}~100 GeV ({\it i.e.} not too weak of weak interactions), then these combined landscape/anthropic requirements act as an attractor pulling the soft SUSY breaking terms towards values required by models with radiatively-driven naturalness: near the line of criticality where electroweak symmetry is barely broken and the Higgs mass is ~125 GeV. The pull on the soft terms serves to ameliorate the SUSY flavor and CP problems. The resulting sparticle mass spectrum may barely be accessible at high-luminosity LHC while the required light higgsinos should be visible at a linear e^+e^- collider with \sqrt{s}>2m(higgsino).

Light stop mass limits from Higgs rate measurements in the MSSM: is MSSM electroweak baryogenesis still alive after all?

We investigate the implications of the Higgs rate measurements from Run 1 of the LHC for the mass of the light scalar top partner (stop) in the Minimal Supersymmetric Standard Model (MSSM). We focus on light stop masses, and we decouple the second, heavy stop and the gluino to the multi-TeV range in order to obtain a Higgs mass of around 125 GeV. We derive lower mass limits for the light stop within various scenarios, taking into account the effects of a possibly light scalar tau partner (stau) or chargino on the Higgs rates, of additional Higgs decays to undetectable new physics, as well as of non-decoupling of the heavy Higgs sector. Under conservative assumptions, the stop can be as light as 123 GeV. Relaxing certain theoretical and experimental constraints, such as vacuum stability and model-dependent bounds on sparticle masses from LEP, we find that the light stop mass can be as light as 116 GeV. Our indirect limits are complementary to direct limits on the light stop mass from collider searches and have important implications for electroweak baryogenesis in the MSSM as a possible explanation for the observed matter-antimatter asymmetry of the Universe.

Search for Strongly-Produced Supersymmetric Particles in Decays with Two Leptons at [formula omitted

This contribution presents a search for squarks and gluinos in final states containing two isolated electrons or muons using the 20.3 fb-1 of s=8 TeV proton-proton collisions recorded by the ATLAS detector at the LHC during 2012. The search uses a set of variables carrying information on the event kinematics both transverse and parallel to the beam line. No excess above the Standard Model expectation is observed, therefore exclusion limits are set on sparticle masses for various simplified model scenarios and a minimal universal extra dimensions model.

Constraining natural SUSY via the Higgs coupling and the muon anomalous magnetic moment measurements

We use the Higgs coupling and the muon anomalous magnetic moment measurements to constrain the parameter space of the natural supersymmetry (SUSY) in the Generalized Minimal Supergravity (GmSUGRA) model. We scan the parameter space of the GmSUGRA model with small electroweak fine-tuning measure ($\Delta_{\rm EW} \leq 100$). The parameter space after applying various sparticle mass bounds, Higgs mass bounds, B-physics bounds, the muon magnetic moment constraint, and the Higgs coupling constraint from measurements at HL-LHC, ILC, and CEPC, is shown in the planes of various interesting model parameters and sparticle masses. Our study indicates that the Higgs coupling and muon anomalous magnetic moment measurements can constrain the parameter space effectively. It is shown that $\Delta_{\rm EW}\sim$ 30, consistence with all constraints, and having supersymmetric contributions to the muon anomalous magnetic moment within 1$\sigma$ can be achieved. The precision of $k_b$ and $k_{\tau}$ measurements at CEPC can bound $m_A$ to be above 1.2 TeV and 1.1 TeV respectively. The combination of the Higgs coupling measurement and muon anomalous magnetic moment measurement constrain $\tilde{e}_R$ mass to be in the range from 0.6 TeV to 2 TeV. The range of both $\tilde{e}_L$ and $\tilde{\nu}_e$ masses is 0.4 TeV $\sim$ 1.2 TeV. In all cases, the $\tilde{\chi}_1^0$ mass needs to be small (mostly $\leq$ 400 GeV). The comparison of bounds in the $\tan\beta - m_A$ plane shows that the Higgs coupling measurement is complementary to the direct collider searches for heavy Higgs when constraining the natural SUSY. A few mass spectra in the typical region of parameter space after applying all constraints are shown as well.

Analysis of the h, H, A → τμ decays induced from SUSY loops within the Mass Insertion Approximation

In this paper we study the lepton favor violating decay channels of the neutral Higgs bosons of the Minimal Supersymmetric Standard Model into a lepton and an anti-lepton of different flavor. We work in the context of the most general flavor mixing scenario in the slepton sector, in contrast to the minimal flavor violation assumption more frequently used. Our analytic computation is a one-loop diagrammatic one, but in contrast to the full one-loop computation which is usually referred to the physical slepton mass basis, we use here instead the Mass Insertion Approximation (MIA) which uses the electroweak interaction slepton basis and treats perturbatively the mass insertions changing slepton flavor. By performing an expansion in powers of the external momenta in the relevant form factors, we will be able to separate explicitly in the analytic results the leading non-decoupling (constant at asymptotically large sparticle masses) and the next to leading decoupling contributions (decreasing with the sparticle masses). Our final aim is to provide a set of simple analytic formulas for the form factors and the associated effective vertices, that we think may be very useful for future phenomenological studies of the lepton flavor violating Higgs boson decays, and for their comparison with data. The accuracy of the numerical results obtained with the MIA are also analyzed and discussed here in comparison with the full one-loop results. Our most optimistic numerical estimates for the three neutral Higgs boson decays channels into $\tau$ and $\mu$ leptons, searching for their maximum rates that are allowed by present constraints from $\tau \to \mu \gamma$ data and beyond Standard Model Higgs boson searches at the LHC, are also included.

Upper bounds on sparticle masses from naturalness or how to disprove weak scale supersymmetry

While it is often stated that the notion of electroweak (EW) naturalness in supersymmetric models is subjective, fuzzy and model-dependent, here we argue the contrary: electroweak naturalness can be elevated to a {\it principle} which is both objective and predictive. We demonstrate visually when too much fine-tuning sets in at the electroweak scale which corresponds numerically to the measure \Delta_{BG}~\Delta_{EW}> 30. While many constrained SUSY models are already excluded by this value, we derive updated upper bounds on sparticle masses within the two-extra parameter non-universal Higgs model (NUHM2). We confirm the classic Barbieri-Giudice (BG) result that \Delta_{BG}<30 implies mu <350 GeV. However, by combining dependent soft terms which appear as multiples of m_{3/2} in supergravity models, then we obtain m(gluino)< 4 TeV as opposed to the BG result that m(gluino)<350 GeV. We compare the NUHM2 results to a similar scan in the pMSSM with 19 weak scale parameters. In the pMSSM with complete one-loop scalar potential plus dominant two-loop terms, then a m(gluino)<7 TeV bound is found. Our tabulation of upper bounds provides a target for experimenters seeking to discover or else falsify the existence of weak scale supersymmetry. In an Appendix, we show contributions to the naturalness measure from one-loop contributions to the weak scale scalar potential.

Beyond the CMSSM without an accelerator: proton decay and direct dark matter detection.

We consider two potential non-accelerator signatures of generalizations of the well-studied constrained minimal supersymmetric standard model (CMSSM). In one generalization, the universality constraints on soft supersymmetry-breaking parameters are applied at some input scale M_{mathrm{in}}below the grand unification (GUT) scale M_{mathrm{GUT}}, a scenario referred to as ‘sub-GUT’. The other generalization we consider is to retain GUT-scale universality for the squark and slepton masses, but to relax universality for the soft supersymmetry-breaking contributions to the masses of the Higgs doublets. As with other CMSSM-like models, the measured Higgs mass requires supersymmetric particle masses near or beyond the TeV scale. Because of these rather heavy sparticle masses, the embedding of these CMSSM-like models in a minimal SU(5) model of grand unification can yield a proton lifetime consistent with current experimental limits, and may be accessible in existing and future proton decay experiments. Another possible signature of these CMSSM-like models is direct detection of supersymmetric dark matter. The direct dark matter scattering rate is typically below the reach of the LUX-ZEPLIN (LZ) experiment if M_{mathrm{in}} is close to M_{mathrm{GUT}}, but it may lie within its reach if M_{mathrm{in}} lesssim 10^{11} GeV. Likewise, generalizing the CMSSM to allow non-universal supersymmetry-breaking contributions to the Higgs offers extensive possibilities for models within reach of the LZ experiment that have long proton lifetimes.

Recent results from Beyond Standard Model (BSM) searches at LHC

We present the results and prospects for searches beyond the Standard Model (SM) at the LHC by the ATLAS and CMS collaborations. The minimal supersymmetric extension of the SM has been investigated in various configurations at 8TeV center of mass energy at LHC and lower limits are set on the s-particle masses. The searches for other scenarios of physics beyond the SM are also presented. The data are found to be consistent with the Standard Model. The non-observation of a signal is converted to limits at the 95% confidence level(C.L) on the production cross section times branching ratio and on the masses of the hypothesized new particles for appropriate benchmark models (new heavy gauge bosons, extra-dimensions, compositeness or dark matter).

Collider Interplay for Supersymmetry, Higgs and Dark Matter.

We discuss the potential impacts on the CMSSM of future LHC runs and possible e^+ e^- and higher-energy proton–proton colliders, considering searches for supersymmetry via / E_T 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 / E_T 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 e^+ e^- 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, it 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.

The pMSSM10 after LHC run 1.

We present a frequentist analysis of the parameter space of the pMSSM10, in which the following ten soft SUSY-breaking parameters are specified independently at the mean scalar top mass scale M_mathrm{SUSY}equiv sqrt{m_{tilde{t}_{1}} m_{tilde{t}_{2}}}: the gaugino masses M_{1,2,3}, the first-and second-generation squark masses m_{tilde{q}_1}= m_{tilde{q}_2}, the third-generation squark mass m_{tilde{q}_3}, a common slepton mass m_{tilde{ell }} and a common trilinear mixing parameter A, as well as the Higgs mixing parameter mu , the pseudoscalar Higgs mass M_A and tan beta , the ratio of the two Higgs vacuum expectation values. We use the MultiNest sampling algorithm with sim 1.2 times 10^9 points to sample the pMSSM10 parameter space. A dedicated study shows that the sensitivities to strongly interacting sparticle masses of ATLAS and CMS searches for jets, leptons + 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 electroweakly 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 of mathrm{BR}(B_s rightarrow mu ^+mu ^-) by LHCb and CMS, other B-physics observables, electroweak precision observables, the cold dark matter density and the XENON100 and LUX searches for spin-independent dark matter scattering, assuming that the cold dark matter is mainly provided by the lightest neutralino tilde{chi }^0_{1}. We show that the pMSSM10 is able to provide a supersymmetric interpretation of (g-2)_mu , unlike the CMSSM, NUHM1 and NUHM2. As a result, we find (omitting Higgs rates) that the minimum chi ^2 = 20.5 with 18 degrees of freedom (d.o.f.) in the pMSSM10, corresponding to a chi ^2 probability of 30.8 %, to be compared with chi ^2/mathrm{d.o.f.} = 32.8/24 (31.1/23) (30.3/22) in the CMSSM (NUHM1) (NUHM2). We display the one-dimensional likelihood functions for sparticle masses, and we show that they may be significantly lighter in the pMSSM10 than in the other models, e.g., the gluino may be as light as sim 1250 ,, mathrm {GeV} at the 68 % CL, and squarks, stops, electroweak gauginos and sleptons may be much lighter than in the CMSSM, NUHM1 and NUHM2. We discuss the discovery potential of future LHC runs, e^+e^- colliders and direct detection experiments.

Supernatural MSSM

We point out that the electroweak fine-tuning problem in the supersymmetric Standard Models (SSMs) is mainly due to the high energy definition of the fine-tuning measure. We propose super-natural supersymmetry which has an order one high energy fine-tuning measure automatically. The key point is that all the mass parameters in the SSMs arise from a single supersymmetry breaking parameter. In this paper, we show that there is no supersymmetry electroweak fine-tuning problem explicitly in the Minimal SSM (MSSM) with no-scale supergravity and Giudice-Masiero (GM) mechanism. We demonstrate that the $Z$-boson mass, the supersymmteric Higgs mixing parameter $\mu$ at the unification scale, and the sparticle spectrum can be given as functions of the universal gaugino mass $M_{1/2}$. Because the light stau is the lightest supersymmetric particle (LSP) in the no-scale MSSM, to preserve $R$ parity, we introduce a non-thermally generated axino as the LSP dark matter candidate. We estimate the lifetime of the light stau by calculating its 2-body and 3-body decays to the LSP axino for several values of axion decay constant $f_a$, and find that the light stau has a lifetime $\tau_{\tilde \tau_1}$ in $[10^{-4},100]$ s for an $f_a$ range $[10^{9},10^{12}]$ GeV. We show that our next to the LSP stau solutions are consistent with all the current experimental constraints, including the sparticle mass bounds, B-physics bounds, Higgs mass, cosmological bounds, and the bounds on long-lived charge particles at the LHC.

The minimal SUSY B − L model: from the unification scale to the LHC

This paper introduces a random statistical scan over the high-energy initial parameter space of the minimal SUSY B − L model — denoted as the B − L MSSM. Each initial set of points is renormalization group evolved to the electroweak scale — being subjected, sequentially, to the requirement of radiative B − L and electroweak symmetry breaking, the present experimental lower bounds on the B − L vector boson and sparticle masses, as well as the lightest neutral Higgs mass of ∼125 GeV. The subspace of initial parameters that satisfies all such constraints is presented, shown to be robust and to contain a wide range of different configurations of soft supersymmetry breaking masses. The low-energy predictions of each such “valid” point — such as the sparticle mass spectrum and, in particular, the LSP — are computed and then statistically analyzed over the full subspace of valid points. Finally, the amount of fine-tuning required is quantified and compared to the MSSM computed using an identical random scan. The B − L MSSM is shown to generically require less fine-tuninng.

GUT-inspired SUSY and the muon g − 2 anomaly: prospects for LHC 14 TeV

We consider the possibility that the muon g-2 anomaly, $\delta(g-2)$, finds its origins in low energy supersymmetry (SUSY). In the general MSSM the parameter space consistent with $\delta(g-2)$ and correct dark matter relic density of the lightest neutralino easily evades the present direct LHC limits on sparticle masses and also lies to a large extent beyond future LHC sensitivity. The situation is quite different in GUT-defined scenarios where input SUSY parameters are no longer independent. We analyze to what extent the LHC can probe a broad class of GUT-inspired SUSY models with gaugino non-universality that are currently in agreement with the bounds from $\delta(g-2)$, as well as with the relic density and the Higgs mass measurement. To this end we perform a detailed numerical simulation of several searches for electroweakino and slepton production at the LHC and derive projections for the LHC 14 TeV run. We show that, within GUT-scale SUSY there is still plenty of room for the explanation of the muon anomaly, although the current LHC data already imply strong limits on the parameter space consistent with $\delta(g-2)$. On the other hand, we demonstrate that the parameter space will be basically fully explored within the sensitivity of the 14 TeV run with 300 fb$^{-1}$. This opens up the interesting possibility that, if the g-2 anomaly is real then some positive signals must be detected at the LHC, or else these models will be essentially ruled out. Finally, we identify the few surviving spectra that will provide a challenge for detection at the LHC 14 TeV run and we characterize their properties.

The hierarchy solution to the LHC inverse problem

Supersymmetric (SUSY) models, even those described by relatively few parameters, generically allow many possible SUSY particle (sparticle) mass hierarchies. As the sparticle mass hierarchy determines, to a great extent, the collider phenomenology of a model, the enumeration of these hierarchies is of the utmost importance. We therefore provide a readily generalizable procedure for determining the number of sparticle mass hierarchies in a given SUSY model. As an application, we analyze the gravity-mediated SUSY breaking scenario with various combinations of GUT-scale boundary conditions involving different levels of universality among the gaugino and scalar masses. For each of the eight considered models, we provide the complete list of forbidden hierarchies in a compact form. Our main result is that the complete (typically rather large) set of forbidden hierarchies among the eight sparticles considered in this analysis can be fully specified by just a few forbidden relations involving much smaller subsets of sparticles.

A new tool for the study of the CP-violating NMSSM

Supersymmetric extensions of the Standard Model open up the possibility for new types of CP-violation. We consider the case of the Next-to-Minimal Supersymmet- ric Standard Model where, beyond the phases from the soft lagrangian, CP-violation could enter the Higgs sector directly at tree-level through complex parameters in the superpoten- tial. We develop a series of Fortran subroutines, cast within the public tool NMSSMTools and allowing for a phenomenological analysis of the CP-violating NMSSM. This new tool performs the computation of the masses and couplings of the various new physics states in this model: leading corrections to the sparticle masses are included; the precision for the Higgs masses and couplings reaches the full one-loop and leading two-loop order. The two-body Higgs and top decays are also attended. We use the public tools HiggsBounds and HiggsSignals to test the Higgs sector. Additional subroutines check the viability of the sparticle spectrum in view of LEP-limits and constrain the phases of the model via a confrontation to the experimentally measured Electric Dipole Moments. These tools will be made publicly available in the near future. In this paper, we detail the workings of our code and illustrate its use via a comparison with existing results. We also consider some consequences of CP-violation for the NMSSM Higgs sector.

The fate of long-lived superparticles with hadronic decays after LHC Run 1

Supersymmetry searches at the LHC are both highly varied and highly constraining, but the vast majority are focused on cases where the final-stage visible decays are prompt. Scenarios featuring superparticles with detector-scale lifetimes have therefore remained a tantalizing possibility for sub-TeV SUSY, since explicit limits are relatively sparse. Nonetheless, the extremely low backgrounds of the few existing searches for collider-stable and displaced new particles facilitates recastings into powerful long-lived superparticle searches, even for models for which those searches are highly non-optimized. In this paper, we assess the status of such models in the context of baryonic R-parity violation, gauge mediation, and mini-split SUSY. We explore a number of common simplified spectra where hadronic decays can be important, employing recasts of LHC searches that utilize different detector systems and final-state objects. The LSP/NLSP possibilities considered here include generic colored superparticles such as the gluino and light-flavor squarks, as well as the lighter stop and the quasi-degenerate Higgsino multiplet motivated by naturalness. We find that complementary coverage over large swaths of mass and lifetime is achievable by superimposing limits, particularly from CMS's tracker-based displaced dijet search and heavy stable charged particle searches. Adding in prompt searches, we find many cases where a range of sparticle masses is now excluded from zero lifetime to infinite lifetime with no gaps. In other cases, the displaced searches furnish the only extant limits at any lifetime.

Yukawa unification and sparticle spectroscopy in gauge mediation models

We explore the implications of t-b-tau (and b-tau) Yukawa coupling unification condition on the fundamental parameter space and sparticle spectroscopy in the minimal gauge mediated supersymmetry breaking (mGMSB) model. We find that this scenario prefers values of the CP-odd Higgs mass m_A > 1 TeV, with all colored sparticle masses above 3 TeV. These predictions will be hard to test at LHC13 but they may be testable at HE-LHC 33 TeV or a 100 TeV collider. Both t-b-tau and b-tau Yukawa coupling unifications prefer a relatively light gravitino with mass < 30 eV, which makes it a candidate hot dark matter particle. However, it cannot account for more than 15 % of the observed dark matter density.

Peccei-Quinn invariant singlet extended SUSY with anomalous U(1) gauge symmetry

Recent discovery of the SM-like Higgs boson with m h ≃ 125 GeV motivates an extension of the minimal supersymmetric standard model (MSSM), which involves a singlet Higgs superfield with a sizable Yukawa coupling to the doublet Higgs superfields. We examine such singlet-extended SUSY models with a Peccei-Quinn (PQ) symmetry that originates from an anomalous U(1) A gauge symmetry. We focus on the specific scheme that the PQ symmetry is spontaneously broken at an intermediate scale v PQ ∼ m SUSY M Pl by an interplay between Planck scale suppressed operators and tachyonic soft scalar mass $$ {m}_{\mathrm{SUSY}}\sim \sqrt{D_A} $$ induced dominantly by the U(1) A D-term D A . This scheme also results in spontaneous SUSY breaking in the PQ sector, generating the gaugino masses $$ {m}_{1/2}\sim \sqrt{D_A} $$ when it is transmitted to the MSSM sector by the conventional gauge mediation mechanism. As a result, the MSSM soft parameters in this scheme are induced mostly by the U(1) A D-term and the gauge mediated SUSY breaking from the PQ sector, so that the sparticle masses can be near the present experimental bounds without causing the SUSY flavor problem. The scheme is severely constrained by the condition that a phenomenologically viable form of the low energy operators of the singlet and doublet Higgs superfields is generated by the PQ breaking sector in a way similar to the Kim-Nilles solution of the μ problem, and the resulting Higgs mass parameters allow the electroweak symmetry breaking with small tan β. We find two minimal models with two singlet Higgs superfields, satisfying this condition with a relatively simple form of the PQ breaking sector, and briefly discuss some phenomenological aspects of the model.

Improving the sensitivity of stop searches with on-shell constrained invariant mass variables

The search for light stops is of paramount importance, both in general as a promising path to the discovery of beyond the standard model physics and more specifically as a way of evaluating the success of the naturalness paradigm. While the LHC experiments have ruled out much of the relevant parameter space, there are "stop gaps", i.e., values of sparticle masses for which existing LHC analyses have relatively little sensitivity to light stops. We point out that techniques involving on-shell constrained M_2 variables can do much to enhance sensitivity in this region and hence help close the stop gaps. We demonstrate the use of these variables for several benchmark points and describe the effect of realistic complications, such as detector effects and combinatorial backgrounds, in order to provide a useful toolkit for light stop searches in particular, and new physics searches at the LHC in general.