Compressed Mass Spectra Research Articles

Interplay of inert doublet and vector-like lepton triplet with displaced vertices at the LHC/FCC and MATHUSLA

We study the interaction between the inert Higgs doublet (IDM) dark matter and a vector-like SU(2) triplet lepton (VLL), both of which are Z2-odd. The vector current of the VLL with the Z-boson rules out a fermionic or two-component dark matter scenario. However, a compressed mass spectrum and a sufficiently small Yukawa coupling allows co-annihilation and late decay of the VLL into the IDM sector, affecting the relic density of the pseudoscalar dark matter. The same two factors enable displaced decay of the VLL states, providing novel signatures involving hadronically quiet displaced multi-lepton final states. Such signatures to probe the model are studied at the 14 and 27 TeV LHC, as well as the 100 TeV FCC-hh. In addition to being detectable at the CMS/ATLAS experiments, if the new particles have sub-100 GeV masses, signals can also be seen at the proposed MATHUSLA detector.

A fast and time-efficient machine learning approach to dark matter searches in compressed mass scenario

Various analyses for searching for the signature of SUSY or exotic particles have been carried out by the experiments at CERN. These analyses made use of traditional cut and count methods. While this method has yielded promising results, it has been challenging in the region where the mass difference between SUSY particles is small. Deep learning is currently widely employed in most data analysis tasks, including high energy physics, and has made significant advances in almost all fields for collecting and interpreting huge data samples. In this paper, a fast and time-efficient classification technique is proposed, utilizing machine learning algorithms to distinguish dark matter signal from SM background in compressed mass spectra scenarios at a center-of-mass energy of 14 TeV. A classification model was built in a short amount of time using 2D histograms produced with less amount of data, effectively reducing computational costs through the transfer learning of pre-trained deep models while maintaining a high level of classification accuracy.

Search for supersymmetric sleptons and charginos with the ATLAS detector

A new search for the electroweak production of supersymmetric particles decaying into two leptons with missing transverse momentum is presented. Two simplified models are considered: direct pair production of sleptons decaying into the lightest neutralinos through leptons of the Standard Model (SM) and direct pair production of the lightest charginos decaying into the lightest neutralinos through W bosons of the SM. The analysis targets phase space regions where the difference in mass between the slepton or the lightest chargino and the lightest neutralino is close to or below the mass of the W boson. Such regions with compressed mass spectra have not been covered by any searches conducted so far due to the low cross-section of the supersymmetric signal. Therefore, improved analysis strategies are crucial to separate the supersymmetric signal from the SM backgrounds. A search for an excess of same-flavour lepton pairs in opposite-sign lepton events is made in the direct slepton pair production analysis while a machine learning approach using boosted decision trees is exploited in the chargino pair production analysis and considering both the same-flavour and different-flavour channels. No significant excesses over the expected background are observed using proton-proton collisions data collected by the ATLAS experiment at √s = 13 TeV and exclusion limits at 95% confidence level are set for each considered model. Exclusion limits are also set for selectrons and smuons separately and portions of the region excluded by the search of smuons pair production are expected to be compatible with the g-2 anomaly for small tanβ values.

Probing compressed mass spectra in the type-II seesaw model at the LHC

Probing compressed mass spectra in the type-II seesaw model at the LHC

Probing Compressed Slepton Production at Future Large Hadron Collider

Various supersymmetry searches are carried out at the Large Hadron Collider (LHC) at CERN. While some searches have focused on the color sector, others focused on electroweak production of charginos-neutralinos and sleptons. Since no sign of supersymmetry has yet to be found, limits are set on the masses of the supersymmetric particles. In this phenomenological study, we probe direct slepton signal production in compressed mass spectra scenario at the potential future proton-proton collider operating at a center of mass energy of 33 TeV. We show that slepton signal with masses up to 270 GeV can be discovered at the future hadron collider with the data corresponding to 100 fb-1 integrated luminosity when ΔM =5 GeV.

Search for physics beyond the standard model in final states with two or three soft leptons and missing transverse momentum in proton-proton collisions at TeV

The most recent CMS results from a search for supersymmetry (SUSY) with a compressed mass spectrum in leptonic final states will be presented. The search is targeting signatures with missing transverse momentum and two or three low-momentum (soft) leptons. The dataset used is collected by the CMS experiment during the Run–2 proton-proton collisions at TeV at the LHC, and corresponds to an integrated luminosity of up to 137 fb−1. The observed data are found to be in agreement with the Standard Model prediction and exclusion upper limits are set on the SUSY particles production cross section. The results are interpreted in terms of electroweakino and top squark pair production. In both cases, a small mass difference between the produced SUSY particles and the lightest neutralino is considered. A wino-bino and a higgsino simplified models are used for the electroweakino interpretation. Exclusion limits at 95% confidence level are set on masses up to 280 GeV for a mass difference between the and the lightest neutralino of 10 GeV for the wino-bino production. In the higgsino interpretation masses are excluded up to 210 GeV for a mass difference of 7.5 GeV and up to 150 GeV for a mass difference of 3 GeV. The results for the higgsino production are additionally interpreted in terms of a phenomenological minimal SUSY extension of the standard model, excluding the higgsino mass parameter μ up to 180 GeV for bino mass parameter M1 = 800 GeV. Upper limits at 95% confidence level are set on the top squark pair production interpretation, excluding top squark masses up to 530 GeV in the four-body top squark decay model and up to 475 GeV in the chargino-mediated decay model for a mass difference between the top squark and the lightest neutralino of 30 GeV.

Search for top squarks in final states with two top quarks and several light-flavor jets in proton-proton collisions at s=13 TeV

Many new physics models, including versions of supersymmetry characterized by $R$-parity violation (RPV), compressed mass spectra, long decay chains, or additional hidden sectors, predict the production of events with top quarks, low missing transverse momentum, and many additional quarks or gluons. The results of a search for new physics in events with two top quarks and additional jets are reported. The search is performed using events with at least seven jets and exactly one electron or muon. No requirement on missing transverse momentum is imposed. The study is based on a sample of proton-proton collisions at $\sqrt{s} =$ 13 TeV corresponding to 137 fb$^{-1}$ of integrated luminosity collected with the CMS detector at the LHC in 2016-2018. The data are used to determine best fit values and upper limits on the cross section for pair production of top squarks in scenarios of RPV and stealth supersymmetry. Top squark masses up to 670 (870) GeV are excluded at 95% confidence level for the RPV (stealth) scenario, and the maximum observed local signal significance is 2.8 standard deviations for the RPV scenario with top squark mass of 400 GeV.

Confronting dark matter co-annihilation of Inert two Higgs Doublet Model with a compressed mass spectrum

We perform a comprehensive analysis for the light scalar dark matter (DM) in the Inert two Higgs doublet model (i2HDM) with compressed mass spectra, small mass splittings among three ℤ2 odd particles — scalar S, pseudo-scalar A, and charged Higgs H±. In such a case, the co-annihilation processes play a significant role to reduce DM relic density. As long as a co-annihilation governs the total interaction rate in the early universe, a small annihilation rate is expected to reach a correct DM relic density and its coupling λS between DM pair and Higgs boson shall be tiny. Consequently, a negligible DM-nucleon elastic scattering cross section is predicted at the tree-level. In this work, we include the one-loop quantum corrections of the DM-nucleon elastic scattering cross section. We found that the quartic self-coupling λ2 between ℤ2 odd particles indeed contributes the one-loop quantum correction and behaves non-trivially for the co-annihilation scenario. Interestingly, the parameter space, which is allowed by the current constraints considered in this study, can predict the DM mass and annihilation cross section at the present compatible with the AMS-02 antiproton excess. The parameter space can be further probed at the future high luminosity LHC.

Searches for electroweak production of supersymmetric particles with compressed mass spectra in s=13 TeV pp collisions with the ATLAS detector

This paper presents results of searches for electroweak production of supersymmetric particles in models with compressed mass spectra. The searches use 139 fb$^{-1}$ of $\sqrt{s}=13$ TeV proton-proton collision data collected by the ATLAS experiment at the Large Hadron Collider. Events with missing transverse momentum and two same-flavor, oppositely charged, low transverse momentum leptons are selected, and are further categorized by the presence of hadronic activity from initial-state radiation or a topology compatible with vector-boson fusion processes. The data are found to be consistent with predictions from the Standard Model. The results are interpreted using simplified models of $R$-parity-conserving supersymmetry in which the lightest supersymmetric partner is a neutralino with a mass similar to the lightest chargino, the second-to-lightest neutralino or the slepton. Lower limits on the masses of charginos in different simplified models range from 193 GeV to 240 GeV for moderate mass splittings, and extend down to mass splittings of 1.5 GeV to 2.4 GeV at the LEP chargino bounds (92.4 GeV). Similar lower limits on degenerate light-flavor sleptons extend up to masses of 251 GeV and down to mass splittings of 550 MeV. Constraints on vector-boson fusion production of electroweak SUSY states are also presented.

Connecting particle physics and cosmology: Measuring the dark matter relic density in compressed supersymmetry models at the LHC

Abstract The identity of Dark Matter (DM) is one of the relevant topics in particle physics today. The R-parity conserving Minimal Supersymmetric Standard Model (MSSM), which naturally provides a DM candidate in the form of the lightest neutralino ( χ 1 0 ), is used as a benchmark scenario to show that a measurement of the DM relic density, Ω χ 1 0 h 2 , can be achieved from measurements at the CERN Large Hadron Collider. Focus is placed on compressed mass spectra regions, where the mass difference Δ m between the χ 1 0 and the supersymmetric partner of the tau lepton ( τ 1 ) is small and where the τ 1 - χ 1 0 coannihilation (CA) mechanism of the early Universe plays an important role. The technique for measuring Ω χ 1 0 h 2 relies on two proposed searches for compressed Supersymmetry (SUSY): (1) production via Vector Boson Fusion (VBF) processes; and (2) production with associated energetic jets from initial state radiation (ISR). These approaches allow for the determination of the relic abundance at the LHC for any model where CA is an important DM reduction mechanism in the early Universe. Thus, it is possible to confirm that the DM we observe today corresponds to χ 1 0 ’s created in the early Universe. We show that from measurements in the VBF and ISR SUSY searches at the LHC, the mass gap Δ m and the dark matter relic density can be measured with an uncertainty of 4.5% and 25%, respectively, assuming 13 TeV proton–proton data from the high-luminosity LHC. The precise measurement of a small Δ m value would also confirm the existence of τ 1 - χ 1 0 CA.

Search for supersymmetry with a compressed mass spectrum in the vector boson fusion topology with 1-lepton and 0-lepton final states in proton-proton collisions at sqrt{s} = 13 TeV

A search for supersymmetric particles produced in the vector boson fusion topology in proton-proton collisions is presented. The search targets final states with one or zero leptons, large missing transverse momentum, and two jets with a large separation in rapidity. The data sample corresponds to an integrated luminosity of 35.9 fb−1 of proton-proton collisions at sqrt{s} = 13 TeV collected in 2016 with the CMS detector at the LHC. The observed dijet invariant mass and lepton-neutrino transverse mass spectra are found to be consistent with the standard model predictions. Upper limits are set on the cross sections for chargino left({tilde{upchi}}_1^{pm}right) and neutralino left({tilde{upchi}}_2^0right) production with two associated jets. For a compressed mass spectrum scenario in which the {tilde{upchi}}_1^{pm } and {tilde{upchi}}_2^0 decays proceed via a light slepton and the mass difference between the lightest neutralino {tilde{upchi}}_1^0 and the mass-degenerate particles {tilde{upchi}}_1^{pm } and {tilde{upchi}}_2^0 is 1 (30) GeV, the most stringent lower limit to date of 112 (215) GeV is set on the mass of these latter two particles.

HL/HE BÜYÜK HADRON ÇARPIŞTIRICISIN’DA EVRENSEL ÇOK BOYUTAR VE SÜPERSİMETRİ

Universal Extra Dimensional (UED) and Supersymmetric (SUSY) models show very similar signals at hadron colliders. In the minimal UED (mUED) where the mass spectrum is compressed, the production of level-1 KK quarks and/or gluons produce multi-jet and/or multi-lepton + missing transverse momenta final state as in the case of SUSY models with R-parity conservation and compressed mass spectrum. Moreover, this similarity can possibly be carried over to non-degenerate mass spectra in next-to-minimal UED (nmUED) model that is the extension of the mUED model with fermion bulk mass term μ and brane localized kinetic terms r, hence, completing the faking in both models. In this regard, we simulated the production of colored level-1 KK particles and their decays resulting in multi-jet + missing transverse momenta signals in both models at 14 TeV LHC and showed that the similarity of both models is indeed the case even with non-compressed mass spectra

Probing compressed mass spectra in electroweak supersymmetry with Recursive Jigsaw Reconstruction

The lack of evidence for the production of colored supersymmetric particles at the LHC has increased interest in searches for superpartners of the electroweak SM gauge bosons, namely the neutralinos and charginos. These are challenging due to the weak nature of the production process, and the existing discovery reach has significant gaps in due to the difficulty of separating the supersymmetric signal from SM diboson events that produce similar final states and kinematics. We apply the Recursive Jigsaw Reconstruction technique to study final states enriched in charged leptons and missing transverse momentum, focusing on compressed topologies with direct production of charginos and neutralinos decaying to the lightest neutral supersymmetric particle through the emission of W and Z bosons. After presenting prototype analysis designs for future LHC runs, we demonstrate that its detectors have the potential to probe a significant amount of unexplored parameter space for chargino-neutralino associated production within the next few years, and show that the very challenging successful search for chargino pair production with compressed spectra might be possible by the end of the LHC lifetime.

Constraining slepton and chargino through compressed top squark search

We examine the compressed mass spectrum with sub-TeV top squark left(tilde{t}right) as lightest colored (s)particle in natural supersymmetry (SUSY). Such spectra are searched along with an additional hard jet, not only to boost the soft decay particles, also to yield enough missing transverse momentum. Several interesting kinematic variables are proposed to improve the probe performance for this difficult region, where we concentrate on relatively clean dileptonic channel of the top squark decaying into lightest neutralino (χ10), which is also the lightest supersymmetric particle. In this work, we investigate the merit of these kinematic variables, sensitive to compressed mass region extending the search by introducing additional states, chargino and slepton (sneutrino) having masses in between the tilde{t} and χ10. Enhanced production and lack of branching suppression are capable of providing a strong limit on chargino and slepton/sneutrino mass along with top squark mass. We perform a detailed collider analysis using simplified SUSY spectrum and found that with the present LHC data {M}_{tilde{t}} can be excluded up to 710 GeV right away for {M}_{upchi_1^0} of 640 GeV for a particular mass gap between different states.

Search for electroweak production of supersymmetric states in scenarios with compressed mass spectra at s=13 TeV with the ATLAS detector

A search for electroweak production of supersymmetric particles in scenarios with compressed mass spectra in final states with two low-momentum leptons and missing transverse momentum is presented. This search uses proton-proton collision data recorded by the ATLAS detector at the Large Hadron Collider in 2015-2016, corresponding to 36.1 fb$^{-1}$ of integrated luminosity at $\sqrt{s}=13$ TeV. Events with same-flavor pairs of electrons or muons with opposite electric charge are selected. The data are found to be consistent with the Standard Model prediction. Results are interpreted using simplified models of R-parity-conserving supersymmetry in which there is a small mass difference between the masses of the produced supersymmetric particles and the lightest neutralino. Exclusion limits at 95% confidence level are set on next-to-lightest neutralino masses of up to 145 GeV for Higgsino production and 175 GeV for wino production, and slepton masses of up to 190 GeV for pair production of sleptons. In the compressed mass regime, the exclusion limits extend down to mass splittings of 2.5 GeV for Higgsino production, 2 GeV for wino production, and 1 GeV for slepton production. The results are also interpreted in the context of a radiatively-driven natural supersymmetry model with non-universal Higgs boson masses.

Clockwork graviton contributions to muon g−2

The clockwork mechanism for gravity introduces a tower of massive graviton modes, "clockwork gravitons," with a very compressed mass spectrum, whose interaction strengths are much stronger than that of massless gravitons. In this work, we compute the lowest order contributions of the clockwork gravitons to the anomalous magnetic moment, $g-2$, of muon in the context of extra dimensional model with a five dimensional Planck mass, $M_5$. We find that the total contributions are rather insensitive to the detailed model parameters, and determined mostly by the value of $M_5$. In order to account for the current muon $g-2$ anomaly, $M_5$ should be around $0.2~{\rm TeV}$, and the size of the extra dimension has to be quite large, $l_5 \gtrsim 10^{-7}\,$m. For $M_5\gtrsim1~{\rm TeV}$, the clockwork graviton contributions are too small to explain the current muon $g-2$ anomaly. We also compare the clockwork graviton contributions with other extra dimension models such as Randall-Sundrum models or large extra dimension models. We find that the leading contributions in the small curvature limit are universal, but the cutoff-independent subleading contributions vary for different background geometries and the clockwork geometry gives the smallest subleading contributions.

A search for new phenomena in pp collisions at sqrt{s} = 13,text {TeV} in final states with missing transverse momentum and at least one jet using the alpha _{mathrm {T}} variable

A search for new phenomena is performed in final states containing one or more jets and an imbalance in transverse momentum in pp collisions at a centre-of-mass energy of 13,text {TeV}. The analysed data sample, recorded with the CMS detector at the CERN LHC, corresponds to an integrated luminosity of 2.3,text {fb}^{-1}. Several kinematic variables are employed to suppress the dominant background, multijet production, as well as to discriminate between other standard model and new physics processes. The search provides sensitivity to a broad range of new-physics models that yield a stable weakly interacting massive particle. The number of observed candidate events is found to agree with the expected contributions from standard model processes, and the result is interpreted in the mass parameter space of fourteen simplified supersymmetric models that assume the pair production of gluinos or squarks and a range of decay modes. For models that assume gluino pair production, masses up to 1575 and 975,text {GeV} are excluded for gluinos and neutralinos, respectively. For models involving the pair production of top squarks and compressed mass spectra, top squark masses up to 400,text {GeV} are excluded.

Search for Dark Matter and Supersymmetry with a Compressed Mass Spectrum in the Vector Boson Fusion Topology in Proton-Proton Collisions at sqrt[s]=8 TeV.

A first search for pair production of dark matter candidates through vector boson fusion in proton-proton collisions at sqrt[s]=8 TeV is performed with the CMS detector. The vector boson fusion topology enhances missing transverse momentum, providing a way to probe supersymmetry, even in the case of a compressed mass spectrum. The data sample corresponds to an integrated luminosity of 18.5 fb^{-1}, recorded by the CMS experiment. The observed dijet mass spectrum is consistent with the standard model expectation. In an effective field theory, dark matter masses are explored as a function of contact interaction strength. The most stringent limit on bottom squark production with mass below 315GeV is also reported, assuming a 5GeV mass difference with respect to the lightest neutralino.

A search for new phenomena in pp collisions at $\sqrt {s} = 13$ TeV in final states with missing transverse momentum and at least one jet using the $α_{T}$ variable

A search for new phenomena is performed in final states containing one or more jets and an imbalance in transverse momentum in pp collisions at a centre-of-mass energy of 13TeV. The analysed data sample, recorded with the CMS detector at the CERN LHC, corresponds to an integrated luminosity of 2.3 $fb^{−1}$. Several kinematic variables are employed to suppress the dominant background, multijet production, as well as to discriminate between other standard model and new physics processes. The search provides sensitivity to a broad range of new-physics models that yield a stable weakly interacting massive particle. The number of observed candidate events is found to agree with the expected contributions from standard model processes, and the result is interpreted in the mass parameter space of fourteen simplified supersymmetric models that assume the pair production of gluinos or squarks and a range of decay modes. For models that assume gluino pair production, masses up to 1575 and 975GeV are excluded for gluinos and neutralinos, respectively. For models involving the pair production of top squarks and compressed mass spectra, top squark masses up to 400GeV are excluded.

New LUX result constrains exotic quark mediators with the vector dark matter

The scenario of the compressed mass spectrum between heavy quark and dark matter is a challenge for LHC searches. However, the elastic scattering cross-section between dark matter and nuclei in dark matter direct detection experiments can be enhanced with nearly degenerate masses between heavy quarks and dark matter. In this paper, we illustrate such scenario with a vector dark matter, using the latest result from LUX 2016. The mass constraints on heavy quarks can be more stringent than current limits from LHC, unless the coupling strength is very small. However, the compress mass spectrum with allowed tiny coupling strength makes the decay lifetime of heavy quarks longer than the timescale of QCD hadronization.