Digging deeper into SUSY parameter space with the CMS experiment
DDigging deeper into SUSY parameter space with the CMSexperiment
Sezen Sekmen, for the CMS Collaboration π, β π Center for High Energy Physics, Kyungpook National UniversityDaegu, South Korea
E-mail: [email protected]
The classic searches for supersymmetry have not given any strong indication for new physics.Therefore CMS is designing dedicated searches to target the more diο¬cult and speciο¬c super-symmetry scenarios. This contribution present three such recent searches based on 13 TeVproton-proton collisions recorded with the CMS detector in 2016, 2017 and 2018: a search forheavy gluinos cascading via heavy next-to-lightest neutralino in ο¬nal states with boosted Z bosonsand missing transverse momentum; a search for compressed supersymmetry in ο¬nal states with softtaus; and a search for compressed, long-lived charginos in hadronic ο¬nal states with disappearingtracks. β Speaker Β© Copyright owned by the author(s) under the terms of the Creative CommonsAttribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0). https://pos.sissa.it/ a r X i v : . [ h e p - e x ] J a n igging deeper into SUSY parameter space with the CMS experiment Sezen Sekmen, for the CMSCollaborationThe Compact Muon Solenoid (CMS) Experiment [1] at the Large Hadron Collider (LHC) hascollected an unprecedented 137 fb β of data with proton-proton collisions at a center-of-mass energyof 13 TeV, which is continuously explored for traces of supersymmetry in a wide variety of searches.As of 2020, classical searches, such as those looking for gluinos and squarks in inclusive SUSYο¬nal states with a large number of search bins, looking for top squarks in hadronic, single lepton ordilepton ο¬nal states, or looking for charginos or neutralinos in single lepton, dilepton or trileptonο¬nal states have not yet observed a deviation from the standard model (SM), and excluded parts ofthe SUSY parameter space. However, SUSY can still be realized in many alternative well-motivatedways in hidden, remote corners of the vast, multi-dimensional SUSY parameter space, to which themore standard and inclusive searches may not be sensitive. Nowadays, CMS is enriching its physicsprogram by an increasing diversity of dedicated searches to probe such corners and enhance thechances of discovery.One example of a special scenario with a ο¬nal state diο¬cult to observe is that of a compressedmass spectrum where masses of two accessible SUSY partners are very close to each other. Here,decays of the heavier particle lead to ο¬nal states with low momentum (soft) objects and low missingtransverse momentum. Such ο¬nal states are explored by searches that use soft objects and a highmomentum initial state radiation jet. Another consequence of compressed spectra can be long-livedparticles, for which an increasing number of searches are being developed. On the opposite end,there are scenarios with high mass SUSY partners and high mass diο¬erences, for which severalsearches featuring objects with high Lorentz boost, leading to merged decay products, and thussubstructure, are being designed. Moreoever, there are dedicated searches for direct production ofsleptons or staus, which are hard to access due to low cross sections and challenges in triggering.Cascade decays with Higgs boson are also explored by explicitly reconstructing the Higgs bosonand incorporating it into multi-object SUSY ο¬nal states. Additionally, signatures with specialcombinations of objects predicted by certain SUSY scenarios, such as πΎ + π jets or πΎ + lepton areinvestigated. Besides all these searches, which are mainly targeting π -parity conserving models,a whole suite of analyses targeting variations of π -parity violating SUSY scenarios exist or are inprogress. This contribution presents 3 examples of recent non-classical SUSY searches based onCMS data collected in 2016, 2017 and 2018, aiming to dig deeper into the SUSY parameter space. Boosted
π π + π πππ π π search: The ο¬rst search is targeting a scenario motivated by naturalness,where pair-produced gluinos with βΌ π to a light Λ π and a π boson [2]. The large mass diο¬erence between Λ π and Λ π give the π bosons a large Lorentzboost. The signature for a boosted π boson candidate is a wide-cone jet having a measured masscompatible with the π boson mass. The analysis, performed on 137 fb β of 13 TeV data, selectsevents with 0 leptons, β₯ π bosons, β₯ π πππ π π >
300 GeVand hadronic transverse momentum π» π >
400 GeV. The π boson candidates are selected amonganti- π π jets with a size parameter of 0.8 (AK8 jets), and are required to have π π >
200 GeV and amass of 40 GeV < π π΄πΎ πππ‘ <
140 GeV. The 2nd highest π π π boson should be separated from any π -jet by an angular distance of Ξ π ( π , π ) > . π (β ππ )+ jets process. SM backgroundsare estimated directly from data, in control regions deο¬ned using the masses of the π candidate jetsas seen in Figure 1, top left. The mass sideband control regions are used to ο¬t the leading AK8jet mass distribution for estimating the background normalization integrated over π πππ π π , as seen2 igging deeper into SUSY parameter space with the CMS experiment Sezen Sekmen, for the CMSCollaborationin Figure 1, top right. The π πππ π π control region is used to derive the π πππ π π shape, based on theassumption that jet mass and π πππ π π have minimal correlation.The estimated background yields are shown as a function of π πππ π π and compared to data, asshown in Figure 1, bottom left. No excess over the SM expectation is observed. The results areinterpreted using a simpliο¬ed SUSY model of gluino pair production in which the gluino decays toa low momentum quark pair and Λ π , and Λ π decays to a boosted π + Λ π , where π Λ π β π Λ π =
50 GeVand π Λ π = Figure 1:
Deο¬nition of the search and control regions in the plane of subleading vs. leading jet mass(top left), leading AK8 jet mass shape ο¬t in the mass sidebands (top right), observed data and backgroundprediction as functions of π πππ π π (bottom left), and the 95% CL upper limit on the production cross section forthe gluino signal model as a function of the gluino mass (bottom right) in the boosted π π + π πππ π π search [2]. Compressed SUSY search with soft taus:
The second search targets directly or indirectlyproduced staus with low π Λ π β π Λ π ( <
50 GeV), a compressed case favored by dark matter coannihi-lation scenarios, where the coannihilation between the stau and the lightest neutralino can generatethe observed relic density. It is the ο¬rst LHC search for a signature of one soft, hadronically decaying π lepton ( π β ), one energetic jet from initial-state radiation (ISR), and large transverse momentumimbalance [3]. The search, using 77 fb β of 13 TeV data, selects events having exactly one π β with20 < π π ( π β ) <
40 GeV, an ISR jet with π π >
100 GeV, π πππ π π >
230 GeV, angular separation be-tween the ISR jet and π πππ π π Ξ π ( π πΌ ππ , π πππ π π ) > . π -jets. The analysis looks for an excessin the distribution of π transverse mass π π ( π β , π πππ π π ) = βοΈ π πππ π π π π ( π β ) ( β cos Ξ π ( (cid:174) π πππ π π , π β )) .3 igging deeper into SUSY parameter space with the CMS experiment Sezen Sekmen, for the CMSCollaborationThe dominant SM backgrounds are π‘π‘ + jets and π / π + jets. Their π π shapes are estimated fromcontrol regions and yields are extrapolated from simulation. Data-simulation agreement in controlregions is used to validate the modeling of the π β selections and to measure data-tosimulationscale factors to correct ISR jet and the π πππ π π modeling. For QCD multΔ³et backgrounds, both π π shape and yields are estimated from data control regions. The resulting π π distribution is shownin Figure 2, top, where data are seen to be consistent with the SM. Figure 2 (bottom left) showsthe interpretation of this result in a simpliο¬ed SUSY model of Λ π Λ π Β± / Λ π + Λ π β production. For 100%wino Λ π / π , π Λ π Β± β π Λ π =
50 GeV, π Λ π = ( π Λ π Β± + π Λ π ) and BR( Λ π Β± β Λ ππ π β π Λ π π π ) = π / Λ π Β± masses up to 290 GeV are excluded at 95% conο¬dence level. This sensitivity exceeds thatof all other searches to date, including the LEP exclusion of π π > . π production signal cross section to the theoretical cross section as a function of π Λ π and Ξ π ( Λ π, Λ π ) .No sensitivity is achieved to direct stau pair production yet. Figure 2:
The π π distribution of data, background prediction and signal benchmarks in the signal region(top); the 95% CL upper limits on the Λ π Λ π Β± / Λ π + Λ π β production cross sections as a function of π ( Λ π Β± ) (bottomleft); and ratio of the 95% CL upper limit on the direct Λ π pair production cross section to the theory predictionas function of π ( Λ π ) and Ξ π ( Λ π, Λ π ) (bottom right) in the compressed SUSY search with soft taus [3]. Disappearing track search using π π : For compressed SUSY with π Λ π Β± β π Λ π βΌ π ( πππ ) ,Λ π Β± is long lived. It would decay in the CMS tracker to a soft, undetectable pion and a Λ π . Thiswould lead to a disappearing track + πΈ πππ π π signature. The ο¬nal search presented here looks in 137fb β of 13 TeV data for such compressed charginos in gluino or squark decays by extending theclassical inclusive hadronic search based on the stransverse mass variable π π with ο¬nal statesconsisting of disappearing tracks (DTs) and at least 2 jets and π π >
200 GeV [5]. The search4 igging deeper into SUSY parameter space with the CMS experiment
Sezen Sekmen, for the CMSCollaborationexplores categories of short and medium/long DT selections, which consist of hits in the pixel orpixel + strip tracking detectors of CMS, respectively, in order to search for a wide range of lifetimes.Including DTs in the search gives a possibility to loosen kinematic requirements without accumu-lating large amounts of backgrounds. For instance, the π π requirement is reduced from 400 to200 GeV. The analysis categorizes events in 68 search bins deο¬ned in jet multiplicity, hadronictransverse momentum π» π , DT length and DT π π . Main sources of backgrounds are hadrons andleptons poorly reconstructed in the tracker and tracks built out of incorrect combinations of hits.They are estimated by calculating fake rates in data control regions and applying these fake rates toDT candidates. Figure 3:
Exclusion limits at 95% CL for direct gluino pair production where the gluinos decay to light-ο¬avorquarks (top left), light squark pair production (top center), and top squark pair production (top right) with ππ ( Λ π Β± ) =
50 cm. Exclusion limits on π Λ π with π Λ π Β± = π Λ π + π ( πππ ) as a function of Λ π Β± properdecay length for gluino pair production with π Λ π = π Λ π = π Λ π‘ = π π [5]. The search found no deviation in data from the SM expectation. Figure 3 shows the interpreta-tion of the search results in various simpliο¬ed SUSY models. The top row shows exclusion limits at95% CL for direct gluino pair production where the gluinos decay to light-ο¬avor (u, d, s, c) quarks(top left), light squark pair production (top center), and top squark pair production (top right) for ππ ( Λ π Β± ) =
50 cm. Extending the inclusive π π search with disappearing tracks increased π Λ π reachfrom βΌ .
46 TeV and π Λ π reach from βΌ βΌ π Λ π reach from βΌ βΌ π Λ π reach from βΌ βΌ π Λ π‘ reachfrom βΌ π Λ π reach from βΌ βΌ igging deeper into SUSY parameter space with the CMS experiment Sezen Sekmen, for the CMSCollaborationcases, sensitivity in the compressed region was signiο¬cantly improved. The bottom row in Figure 3shows exclusion limits versus chargino decay length for selected gluino, squark and stop masses.In summary, 3 recent examples of dedicated CMS SUSY searches targeting speciο¬c scenariosand exclusive signatures were presented, namely, a boosted
π π + π πππ π π search, which extended thegluino mass reach to 1.9 TeV for π Λ π β π Λ π =
50 GeV; a soft hadronic π + π πππ π π + ISR jet searchfor compressed staus motivated by dark matter coannihilation models, which obtained a sensitivityfor charginos extending the LEP limits; and a search that added regions with disappearing tracksto the inclusive hadronic π π search, which increased gluino and squark mass limits by 400-600GeV and signiο¬cantly improved sensitivity in the compressed region. Other searches dedicated tospeciο¬c ο¬nal states have been performed earlier, such as the search for π» β ππ using razor and π π variables [6]; searches for hadronic and semileptonic staus [7, 8]; πΈ πππ π π and boosted Higgs to ππ [9]; SUSY in vector boson fusion channels [10]; RPV smuons [11]; selectrons and smuons [12];the searches in diphoton and πΈ πππ π π ο¬nal states [13], π jets and photons ο¬nal states [14], and photon,lepton and πΈ πππ π π ο¬nal states [15]. More searches are ongoing for soft opposite-sign 2 leptonsignatures and steath and RPV stops. Acknowledgements:
I would like to thank my colleagues in the CMS Collaboration for theirhard work in producing the results in this contribution, and to the organizers of ICHEP 2020 fortheir eο¬orts in realizing this important conference virtually during the diο¬cult Covid-19 period.
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