Neutralino Pair Production Research Articles

Combination and reinterpretation of LHC SUSY searches

To maximise the information obtained from various independent new physics searches conducted at the LHC, it is imperative to consider the combination of multiple analyses. To showcase the exclusion power gained by combining signal regions from different searches, we consider a simplified scenario inspired by supersymmetry, with all particles but one squark flavour and a bino-like neutralino decoupled. The corresponding signal therefore comprises strong squark pair production, associated squark-neutralino production, as well as weak neutralino pair production. We find that considering the associated and strong production mechanisms together significantly impacts mass limits, while contributions from the weak production are insignificant in the context of current exclusion limits. In addition, we demonstrate that the combination of uncorrelated signal regions as assessed from the recent TACO approach substantially pushes exclusion limits towards higher masses, relative to the bounds derived from the most sensitive individual analyses.

Searches for new phenomena in events with two leptons, jets, and missing transverse momentum in 139 fb^{-1} of varvec{sqrt{s}}=13 TeV varvec{pp} collisions with the ATLAS detector

Searches for new phenomena inspired by supersymmetry in final states containing an e^+e^- or mu ^+mu ^- pair, jets, and missing transverse momentum are presented. These searches make use of proton–proton collision data with an integrated luminosity of 139~text {fb}^{-1}, collected during 2015–2018 at a centre-of-mass energy sqrt{s}=13~TeV by the ATLAS detector at the Large Hadron Collider. Two searches target the pair production of charginos and neutralinos. One uses the recursive-jigsaw reconstruction technique to follow up on excesses observed in 36.1~text {fb}^{-1} of data, and the other uses conventional event variables. The third search targets pair production of coloured supersymmetric particles (squarks or gluinos) decaying through the next-to-lightest neutralino (tilde{chi }_2^0) via a slepton (tilde{ell }) or Z boson into ell ^+ell ^-tilde{chi }_1^0, resulting in a kinematic endpoint or peak in the dilepton invariant mass spectrum. The data are found to be consistent with the Standard Model expectations. Results are interpreted using simplified models and exclude masses up to 900 GeV for electroweakinos, 1550 GeV for squarks, and 2250 GeV for gluinos.

Search for long-lived particles decaying to jets with displaced vertices in proton-proton collisions at s=13 TeV

A search is presented for long-lived particles produced in pairs in proton-proton collisions at the LHC operating at a center-of-mass energy of 13 TeV. The data were collected with the CMS detector during the period from 2015 through 2018, and correspond to a total integrated luminosity of 140 fb$^{-1}$. This search targets pairs of long-lived particles with mean proper decay lengths between 0.1 and 100 mm, each of which decays into at least two quarks that hadronize to jets, resulting in a final state with two displaced vertices. No significant excess of events with two displaced vertices is observed. In the context of $R$-parity violating supersymmetry models, the pair production of long-lived neutralinos, gluinos, and top squarks is excluded at 95% confidence level for cross sections larger than 0.08 fb, masses between 800 and 3000 GeV, and mean proper decay lengths between 1 and 25 mm.

Search for trilepton resonances from chargino and neutralino pair production in s=13 TeV pp collisions with the ATLAS detector

A search is performed for the electroweak pair production of charginos and associated production of a chargino and neutralino, each of which decays through an $R$-parity-violating coupling into a lepton and a $W$, $Z$, or Higgs boson. The trilepton invariant-mass spectrum is constructed from events with three or more leptons, targeting chargino decays that include an electron or muon and a leptonically decaying $Z$ boson. The analyzed dataset corresponds to an integrated luminosity of 139 fb$^{-1}$ of proton-proton collision data produced by the Large Hadron Collider at a center-of-mass energy of $\sqrt{s}$ = 13 TeV and collected by the ATLAS experiment between 2015 and 2018. The data are found to be consistent with predictions from the Standard Model. The results are interpreted as limits at 95% confidence level on model-independent cross sections for processes beyond the Standard Model. Limits are also set on the production of charginos and neutralinos for a Minimal Supersymmetric Standard Model with an approximate $B$-$L$ symmetry. Charginos and neutralinos with masses between 100 GeV and 1100 GeV are excluded depending on the assumed decay branching fractions into a lepton (electron, muon, or $\tau$-lepton) plus a boson ($W$, $Z$, or Higgs).

Enhancing Long-Lived Particles Searches at the LHC with Precision Timing Information.

We explore the physics potential of using precision timing information at the LHC in searches for long-lived particles (LLPs). In comparison with the light standard model particles, the decay products of massive LLPs arrive at detectors with time delays around the nanosecond scale. We propose new strategies to take advantage of this time delay feature by using initial state radiation to time stamp the collision event and require at least one LLP to decay within the detector. This search strategy is effective for a broad range of models. In addition to outlining this general approach, we demonstrate its effectiveness with the projected reach for two benchmark scenarios: a Higgs boson decaying into a pair of LLPs, and pair production of long-lived neutralinos in the gauge mediated supersymmetry breaking models. Our strategy increases the sensitivity to the lifetime of the LLP by two orders of magnitude or more and particularly exhibits a better behavior with a linear dependence on the lifetime in the large lifetime region compared to traditional LLP searches. The timing information significantly reduces the standard model background and provides a powerful new dimension for LLP searches.

Precise predictions for electroweakino-pair production in association with a jet at the LHC

We present the full NLO SUSY-QCD corrections to the pair production of neutralinos and charginos at the LHC in association with a jet and their matching to partonshower programs in the framework of the POWHEG-BOX package. The code we have developed provides a SUSY Les Houches Accord interface for setting electroweak and supersymmetric input parameters. Decays of the neutralinos and charginos and parton-shower effects can be simulated with multi-purpose programs such as PYTHIA. The capabilities of the code are illustrated by phenomenological results for a parameter point in the framework of pMSSM10, compatible with present experimental limits on supersymmetry. We find that NLO-QCD corrections as well as parton-shower effects are of primary importance for the appropriate description of jet distributions.

Search for new physics in events with two soft oppositely charged leptons and missing transverse momentum in proton–proton collisions at [formula omitted

A search is presented for new physics in events with two low-momentum, oppositely charged leptons (electrons or muons) and missing transverse momentum in proton-proton collisions at a centre-of-mass energy of 13 TeV. The data collected using the CMS detector at the LHC correspond to an integrated luminosity of 35.9fb−1. The observed event yields are consistent with the expectations from the standard model. The results are interpreted in terms of pair production of charginos and neutralinos (χ˜1± and χ˜20) with nearly degenerate masses, as expected in natural supersymmetry models with light higgsinos, as well as in terms of the pair production of top squarks (t˜ ), when the lightest neutralino and the top squark have similar masses. At 95% confidence level, wino-like χ˜1±/χ˜20 masses are excluded up to 230 GeV for a mass difference of 20 GeV relative to the lightest neutralino. In the higgsino-like model, masses are excluded up to 168 GeV for the same mass difference. For t˜ pair production, top squark masses up to 450 GeV are excluded for a mass difference of 40 GeV relative to the lightest neutralino.

Combined search for electroweak production of charginos and neutralinos in proton-proton collisions at sqrt{s}=13 TeV

A statistical combination of several searches for the electroweak production of charginos and neutralinos is presented. All searches use proton-proton collision data at sqrt{s}=13 TeV, recorded with the CMS detector at the LHC in 2016 and corresponding to an integrated luminosity of 35.9 fb−1. In addition to the combination of previous searches, a targeted analysis requiring three or more charged leptons (electrons or muons) is presented, focusing on the challenging scenario in which the difference in mass between the two least massive neutralinos is approximately equal to the mass of the Z boson. The results are interpreted in simplified models of chargino-neutralino or neutralino pair production. For chargino-neutralino production, in the case when the lightest neutralino is massless, the combination yields an observed (expected) limit at the 95% confidence level on the chargino mass of up to 650 (570) GeV, improving upon the individual analysis limits by up to 40 GeV. If the mass difference between the two least massive neutralinos is approximately equal to the mass of the Z boson in the chargino-neutralino model, the targeted search requiring three or more leptons obtains observed and expected exclusion limits of around 225 GeV on the second neutralino mass and 125 GeV on the lightest neutralino mass, improving the observed limit by about 60 GeV in both masses compared to the previous CMS result. In the neutralino pair production model, the combined observed (expected) exclusion limit on the neutralino mass extends up to 650–750 (550–750) GeV, depending on the branching fraction assumed. This extends the observed exclusion achieved in the individual analyses by up to 200 GeV. The combined result additionally excludes some intermediate gaps in the mass coverage of the individual analyses.

Neutralino pair production via photon-photon collisions at the ILC

We provide complete one-loop predictions for the direct production of the neutralino pairs via photon-photon collisions which appears for the first time at one-loop level in the minimal supersymmetric standard model at the International Linear Collider. We present a comprehensive investigation of the dependence of total cross section on the center-of-mass energy and the tan$\beta$ for three different scenarios based on gaugino/Higgsino fractions of the neutralinos. Furthermore, by investigating the behavior with the most relevant parameters $\mu$ and $M_2$, we exhibit regions of the parameter space where the enhancement of the cross section is large enough to be detectable at linear colliders. Our analysis shows that the corresponding production cross section reaches its highest values when the lightest neutralino $\widetilde{\chi}_{1}^0$ has a dominant Higgsino component and/or the next-to-lightest neutralino $\widetilde{\chi}_{2}^0$ has a dominant gaugino component.

Multichannel assault on natural supersymmetry at the high luminosity LHC

Recent clarifications of naturalness in supersymmetry robustly require the presence of four light higgsinos with mass ~100-300 GeV while gluinos and (top)-squarks may lie in the multi-TeV range, possibly out of LHC reach. We project the high luminosity (300-3000 fb^{-1}) reach of LHC14 via gluino cascade decays and via same-sign diboson production. We compare these to the reach for neutralino pair production \tz_1\tz_2 followed by \tz_2\to\tz_1\ell^+\ell^- decay to soft dileptons which recoil against a hard jet. It appears that 3000 fb^{-1} is just about sufficient integrated luminosity to probe naturalness with up to 3\% fine-tuning at the 5-sigma level, thus either discovering natural supersymmetry or else ruling it out.

Electroweakino pair production at the LHC: NLO SUSY-QCD corrections and parton-shower effects

We present a set of NLO SUSY-QCD calculations for the pair production of neutralinos and charginos at the LHC, and their matching to parton-shower programs in the framework of the POWHEG-BOX program package. The code we have developed provides a SUSY Les Houches Accord interface for setting supersymmetric input parameters. Decays of the neutralinos and charginos and parton-shower effects can be simulated with PYTHIA. To illustrate the capabilities of our program, we present phenomenological results for a representative SUSY parameter point. We find that NLO-QCD corrections increase the production rates for neutralinos and charginos significantly. The impact of parton-shower effects on distributions of the weakinos is small, but non-negligible for jet distributions.

Electroweak SUSY Searches at CMS using LHC-data collected at [formula omitted

The searches presented in this summary correspond to the electroweak (EWK) pair production of neutralinos (χ˜i0) and charginos (χ˜1±) decaying to Higgs (h), Z, and W bosons, and the lightest supersymmetric particle (LSP). The searches were performed using 19.5 fb-1 of data from proton-proton collisions at the LHC, at a center of mass energy of 8 TeV collected in 2012 by the CMS detector. The main production modes correspond to pair production of χ˜i0, where each χ˜i0 decays to a h or a Z boson and a LSP, resulting in final states with hh, hZ and ZZ, with associated missing transverse energy (ETmiss). A second mechanism is the pair production χ˜1±χ˜i0, which leads to hW states in addition to ETmiss. The observed data is consistent with the estimation of the SM backgrounds. Therefore, no evidence of supersymmetric particles is found, and 95% confidence level upper limits are set on the pair production cross section of the respective process as a function of the χ˜i0 and χ˜1± masses.

NMSSM explanations of the Galactic center gamma ray excess and promising LHC searches

The Galactic Center Excess (GCE) is explained in the framework of the Next-to-Minimal Supersymmetric Standard Model (NMSSM) with a $Z_3$ discrete symmetry. We show that a resonant CP-odd Higgs boson with mass twice that of the Dark Matter (DM) candidate is favoured. Meanwhile, the DM candidate is required to have relatively large coupling with the $Z$ boson through its Higgsino component in order to obtain correct DM relic density. Its LHC discovery potential via four signatures is discussed in detail. We find that the most sensitive signals are provided by the Higgsino-like chargino and neutralino pair production with their subsequent decays into $W$ bosons, $Z$ bosons, and DM. The majority of the relevant parameter space can be probed at the Large Hadron Collider with a centre-of-mass energy of 14 TeV and an integrated luminosity 1000 fb$^{-1}$.

Investigation of neutralino pair production in photon-photon collider at the ILC

Neutralino pair production via photon-photon collision is analyzed in the context of the minimal supersymmetric standard model at a future linear collider. Since the photon does not have self- coupling, this process is only possible at next-to-leading order (NLO), and all the possible diagrams are calculated for the photon-photon interaction, including box, triangle, and quartic coupling diagrams. Numerical analysis of the production rates for ${\stackrel{\texttildelow{}}{\ensuremath{\chi}}}_{1}^{0}{\stackrel{\texttildelow{}}{\ensuremath{\chi}}}_{1}^{0}$, ${\stackrel{\texttildelow{}}{\ensuremath{\chi}}}_{1}^{0}{\stackrel{\texttildelow{}}{\ensuremath{\chi}}}_{2}^{0}$ and ${\stackrel{\texttildelow{}}{\ensuremath{\chi}}}_{2}^{0}{\stackrel{\texttildelow{}}{\ensuremath{\chi}}}_{2}^{0}$ are presented for four new distinct benchmark models which are presented in the light of LHC8. Angular dependence of each neutralino pair for the benchmark points is also analyzed. Total integrated photonic cross section goes up to 1.43 fb for the ${\stackrel{\texttildelow{}}{\ensuremath{\chi}}}_{2}^{0}{\stackrel{\texttildelow{}}{\ensuremath{\chi}}}_{2}^{0}$ pairs at $\sqrt{s}=1\text{ }\text{ }\mathrm{TeV}$ for the radiatively driven natural supersymmetric benchmark point.

Searches for electroweak neutralino and chargino production in channels with Higgs,Z, andWbosons inppcollisions at 8 TeV

Searches for supersymmetry (SUSY) are presented based on the electroweak pair production of neutralinos and charginos, leading to decay channels with Higgs, Z, and W bosons and undetected lightest SUSY particles (LSPs). The data sample corresponds to an integrated luminosity of about 19.5 inverse femtobarns of proton-proton collisions at a center-of-mass energy of 8 TeV collected in 2012 with the CMS detector at the LHC. The main emphasis is neutralino pair production in which each neutralino decays either to a Higgs boson (h) and an LSP or to a Z boson and an LSP, leading to hh, hZ, and ZZ states with missing transverse energy (ET(miss)). A second aspect is chargino-neutralino pair production, leading to hW states with ET(miss). The decays of a Higgs boson to a bottom-quark pair, to a photon pair, and to final states with leptons are considered in conjunction with hadronic and leptonic decay modes of the Z and W bosons. No evidence is found for supersymmetric particles, and 95% confidence level upper limits are evaluated for the respective pair production cross sections and for neutralino and chargino mass values.

Search for neutralino pair production at the CERN LHC

We provide the next-to-leading order (NLO) predictions for the neutralino pair production via quark-antiquark annihilation and gluon-gluon fusion at the CERN Large Hadron Collider, focusing on the lightest neutralino which is likely to be the lightest supersymmetric particle. The dependence of total LO, NLO cross sections, and $K$ factor on the center-of-mass energy, the ${M}_{2}\ensuremath{-}\ensuremath{\mu}$ mass plane, the squark mass, and the factorization and renormalization scales is comprehensively analyzed for three different scenarios in the minimal supersymmetric standard model and the constrained minimal supersymmetric standard model. We find that the LO cross section is considerably increased by the NLO correction, and the $K$ factor value is clearly related to the Higgsino/gaugino mass parameters, the squark mass, and the factorization and renormalization scales.

Bilinear $$R$$ R parity violation at the ILC: neutrino physics at colliders

Supersymmetry (SUSY) with bilinearly broken \(R\) parity (bRPV) offers an attractive possibility to explain the origin of neutrino masses and mixings. In such scenarios, the study of neutralino decays at colliders gives access to neutrino sector parameters. The ILC offers a very clean environment to study the neutralino properties as well as its subsequent decays, which typically involve a \(W\) or \(Z\) boson and a lepton. This study is based on ILC beam parameters according to the Technical Design Report for a center of mass energy of \(500~\hbox {GeV}\). A full detector simulation of the International Large Detector (ILD) has been performed for all Standard Model backgrounds and for neutralino pair production within a simplified model. The bRPV parameters are fixed according to current neutrino data. In this scenario, the \(\tilde{\chi }^0_1\) mass can be reconstructed with an uncertainty of \(\delta m^{{\mathrm {fit}}}_{\widetilde{\chi }^{0}_{1}}=(40\text {(stat.)} \oplus 50\text {(syst.)})~\hbox {MeV}\) for an integrated luminosity of \(500\,\hbox {fb}^{-1}\) from direct \(\tilde{\chi }^0_1\) pair production, thus, to a large extent independently of the rest of the SUSY spectrum. The achievable precision on the atmospheric neutrino mixing angle \(\sin ^2 \theta _{23}\) from measuring the neutralino branching fractions BR(\(\tilde{\chi }_1^0\rightarrow W\mu \)) and BR(\(\tilde{\chi }_1^0\rightarrow W \tau \)) at the ILC is in the same range than current uncertainties from neutrino experiments. Thus, the ILC could have the opportunity to unveil the mechanism of neutrino mass generation.

New ATLAS results in SUSY searches for 3rdgeneration squarks and electroweak production

Naturalness arguments for weak-scale supersymmetry favour supersymmet- ric partners of the third generation quarks with masses close to those of their Standard Model counterparts. Real and virtual production of third generation squarks via decay of a gluino can be significant if the mass of the gluino does not exceed the TeV scale. Top or bottom squarks with masses less than a few hundred GeV can also give rise to direct pair production rates at the LHC that can be observed in the 8 TeV data sample recorded by the ATLAS detector. Moreover, many supersymmetric models feature neu- tralinos, charginos and even sleptons with masses less than a few hundred GeV so that they can be observed in the available data sample. The talk presents recent ATLAS re- sults from searches for direct stop and sbottom pair production as well as pair production of charginos, neutralinos and sleptons.

Erratum to: SUSY Background to Neutral MSSM Higgs Boson Searches

Within the Minimal Supersymmetric Standard Model (MSSM) the production and decay of superpartners can give rise to backgrounds for Higgs boson searches. Here MSSM background processes to the vector boson fusion channel with the Higgs boson decaying into two tau leptons or two W-bosons are investigated, giving rise to dilepton plus missing transverse momentum signals of the Higgs boson. Starting from a scenario with relatively small masses of the supersymmetric (SUSY) particles, with concomitant large cross section of the background processes, one obtains a first conservative estimate of the background. Light chargino pair production plus two jets, lightest and next-to-lightest neutralino production plus two jets as well as slepton pair production plus two jets are identified as important contributions to the irreducible SUSY background. Light chargino and next-to-lightest neutralino production plus two jets and next-to-lightest neutralino pair production plus two jets give rise to reducible backgrounds, which can be larger than the irreducible ones in some scenarios. The relevant distributions are shown and additional cuts for MSSM background reduction are discussed. Extrapolation to larger squark masses is performed and shows that MSSM backgrounds are quite small for squark masses at the current exclusion limits.

ELECTROWEAK CORRECTIONS TO THE NEUTRALINO PAIR PRODUCTION AT CERN LHC

We apply the leading and subleading electroweak (EW) corrections to the Drell–Yan process of the neutralino pair production at proton–proton collision, in order to calculate the effects of these corrections on the neutralino pair production at the LHC. We provide an analysis of the dependence of the Born cross-sections for [Formula: see text] and the EW corrections to this process, on the center-of-mass energy [Formula: see text], on the M2–μ mass plane and on the squark mass for the three different scenarios. The numerical results show that the relative correction can be reached to the few tens of percent level as the increment of the center-of-mass energy, and the evaluation of EW corrections is a crucial task for all accurate measurements of the neutralino pair production processes.