International audienceA search for squarks and gluinos performed by the CDF and DØ collaborations is presented. The sample taken during the RunII of the Fermilab TeVatron collider at ps = 1.96 TeV is used. Supersymmetry (SUSY) is one of the most promising ways to solve crucial problems of the Standard Model (SM). This spacetime symmetry links bosons to fermions by introducing supersymmetric partners (sparticles) to all SM particles: squarks and gluinos are SUSY partners of quarks and gluons. The mass difference between the squark mass eigenstates depend on the mass of the corresponding quark. Hence squarks are (to a good approximation) mass degenerate for the two first generations whereas a (potentially) large mixing may appear for the third family, leading to a light stop. The former case corresponds to squarks and gluinos searches whereas dedicated searches for stop are performed for the latter

Gris, P.

HAL Clermont Université

Squarks and gluino searches at the TevatronP. GrisTo cite this version:P. Gris. Squarks and gluino searches at the Tevatron. XVI International Workshop on Deep-Inelastic Scattering and Related Subjects, DIS 2008, Apr 2008, Londres, United Kingdom.2008. <in2p3-00478490>HAL Id: in2p3-00478490http://hal.in2p3.fr/in2p3-00478490Submitted on 30 Apr 2010HAL is a multi-disciplinary open accessarchive for the deposit and dissemination of sci-entific research documents, whether they are pub-lished or not. The documents may come fromteaching and research institutions in France orabroad, or from public or private research centers.L’archive ouverte pluridisciplinaire HAL, estdestine´e au de´poˆt et a` la diffusion de documentsscientifiques de niveau recherche, publie´s ou non,e´manant des e´tablissements d’enseignement et derecherche franc¸ais ou e´trangers, des laboratoirespublics ou prive´s.Squarks and gluinos searches at the TeVatronPhilippe Gris1on behalf on the CDF and D0 collaborations1- Laboratoire de Physique Corpusculaire - IN2P3/CNRS24 avenue des Landais - 63177 Aubie`re cedex - FranceA search for squarks and gluinos performed by the CDF and DØ collaborations ispresented. The sample taken during the RunII of the Fermilab TeVatron collider at√s = 1.96 TeV is used.Supersymmetry (SUSY) is one of the most promising ways to solve crucial problems ofthe Standard Model (SM). This spacetime symmetry links bosons to fermions by introduc-ing supersymmetric partners (sparticles) to all SM particles: squarks and gluinos are SUSYpartners of quarks and gluons. The mass difference between the squark mass eigenstatesdepend on the mass of the corresponding quark. Hence squarks are (to a good approxima-tion) mass degenerate for the two first generations whereas a (potentially) large mixing mayappear for the third family, leading to a light stop. The former case corresponds to squarksand gluinos searches whereas dedicated searches for stop are performed for the latter.1 Squarks and gluinos searchesAt the TeVatron, the production cross section of squarks and gluinos is of the order of few pb.Searches have been performed in the mSUGRA model with the lightest neutralino χ˜01 asthe lightest supersymmetric particle (LSP). Three regimes may be distinguished leading tothree different analyses (Tab. 1). All squark species were considered except the stop (CDFand DØ) and the sbottom (CDF). The triggers retained were dijet+E/T and multijet+E/T .Regime main decay signatureproductionmq˜ << mg˜ q˜q˜ q˜ → qχ˜01 2 jets+E/T“dijet” analysismq˜ ∼ mg˜ q˜g˜ q˜ → qχ˜01 at least 3 jets+E/Tg˜ → qq¯χ˜01 “3 jets” analysismg˜ << mq˜ g˜g˜ g˜ → qq¯χ˜01 n(≥ 4) jets+E/T“gluino” analysisTable 1: Final states considered in the squark and gluino searchesby CDF and DØ.The main backgroundwas composed of twoparts: SM processes (W/Z+jets, dibosons, tt¯), esti-mated from Monte-Carlosimulations, and the in-strumental background (mis-measured jets), evaluatedfrom data. Selectionson E/T , jets requirementsand lepton vetos weremade at the first stagesof the analyses, followed by specific cuts for each final state. The ultimate se-lection was performed on E/T and HT (defined as the pT sum of the jets).The cut values were rather different for CDF and DØ. A good agreement wasobserved between data and MC expectation (Table 2) in a sample of 2 fb−1.The main systematics uncertainties considered were: the Jet Energy scale (JES)(6-15% DØ,15-30% CDF), the background normalization (15% DØ, 2-10% CDF), the luminosity (6%)and the ISR/FSR (6% DØ, 3-8% CDF). These uncertainties were combined to the statisticalDIS 2008ones to draw limits in the plane (mq˜,mg˜) (Fig. 1). For tanβ= 3, A0 = 0, and µ < 0,squark masses lower than 392 GeV/c2 and gluino mass lower than 327 GeV/c2 have beenexcluded at 95% C.L. by DØ [2]. These values decrease to 379 GeV/c2 and 308 GeV/c2 forsquarks and gluino respectively if theoretical uncertainties related to the Parton DistributionFunction (PDF’s) choice and to the renormalisation and factorisation scales are included.CDF has obtained similar results: for tanβ= 5, A0 = 0, and µ < 0, squark masses lowerthan 378 GeV/c2 and gluino mass lower than 280 GeV/c2 have been excluded at 95%C.L. These limits include the theoretical uncertainties. CDF and DØ results are the bestconstraints to date on the squarks and gluino masses.Gluino Mass (GeV)0 100 200 300 400 500 600Squark Mass (GeV)0100200300400500600 -1DØ, L=2.1 fb<0µ=0, 0=3, AβtanUA1UA2LEPCDF IBDØ IADØ IBDØ IIno mSUGRAsolution±χ∼LEP2  ±l~LEP2  )2 (GeV/cg~M0 100 200 300 400 500 600)2 (GeV/cq~M0100200300400500600CDF Run II Preliminary -1L=2.0 fbno mSUGRAsolutionLEP 1 + 2UA1UA2FNAL Run Ig~ = Mq~M)2 (GeV/cq~Mobserved limit 95% C.L.expected limit <0µ=5, β=0, tan0ATheoretical uncertainties includedin the calculation of the limitFigure 1: Limits on squark and gluinomasses for DØ (top) and CDF (bottom).In some region of the SUSY parame-ter space, squarks may decay to the light-est chargino χ˜±1 or the second neutralinoχ˜02, leading to final states with leptons. Forhigh tanβ values, the stau τ˜1 may bethe lightest slepton, and squark productiondominates. Final states wit τ ’s are thenfavoured. A search for squarks (stop ex-cepted) with τ ’s in the final state has beenperformed by DØ, in a 0.96 pb−1 data sam-ple. Acoplanar dijets and multijets trig-gers were used by two analyses which werethen ored after optimisation. Events wereselected on the basis of their E/T val-ues, and two jets were to be present.Suitable angular cuts were applied to re-move part of the instrumental background.At least one hadronic τ (in one of themode: pi±ντ , pi±pi0ντ , pi±pi±pi±(pi0)ντ ) wasrequested. The final optimisation was per-formed with two variables: sum of thetransverse energy of the leading τ and thejets, and on the E/T . A good agree-ment between data and SM expectations hasbeen interpreted as a limit in the plane(m0, m1/2) [3].For high tanβ values, the sbottom b˜1 maybe light. The g˜g˜ pair production cross sectionis quite high ( σg˜g˜ ≃ 10 σb˜1 b˜1) if b˜1 and g˜ aremass degenerate. In this configuration, the finalstate resulting from the gluino pair productiong˜g˜ → b˜1b˜1¯˜b1¯˜b1 → bb¯bb¯ χ˜01χ˜01χ˜01χ˜01 is comprisedof 4 bjets+E/T (χ˜01 LSP). CDF has searched thissignature in a data sample of 156 pb−1. Afterselecting the events with a jets+E/T trigger, standard cuts have been applied to removethe background(W/Z+jets, tt¯ , multijets): E/T > 80 GeV, ∆φ(E/T , jets) > 2pi/9.DIS 2008Events with at least three jets were selected and at least two b-identified. 4 events remainedin data whereas 2.6±0.7 were expected. A limit in the plane (mg˜,mb˜1) has thus beenestimated (Fig. 2). Systematic uncertainties (JES, luminosity, b-tagging efficiency and rate,cross sections) were taken into account. A gluino mass lower than 280 GeV/c2 has beenexcluded for a sbottom mass of 230 GeV/c2 [4].2 Stop searchesdijet 3 jets gluinoHT > 330 E/T >225 HT >375 E/T >175 HT > 400 E/T >100DØ 11 11.1±1.2 9 10.7±0.9 20 17.7±1.1HT > 330 E/T >180 HT >330 E/T >120 HT > 280 E/T >90CDF 18 16±5 38 37±12 45 47±17Table 2: Final selections for the squarks and gluino searches.At the TeVatron, scalartops are pair producedthrough gluon-gluon fu-sion or qq¯ annihilation.For a stop mass of100 (160) GeV/c2, 9000(1000) events are ex-pected at√s = 1.96 TeV.The number of possible stop decays may be numerous, depending on the model under con-sideration. Two channels were considered at the TeVatron: t˜1 → cχ˜01 and t˜1 → blν˜l.Figure 2: CDF limit in the gluino decaying tosbottom search.The t˜1 → cχ˜01 decay leads toa final state with two acoplanar jetsand E/T coming mainly from undetectedχ˜01-LSP. DØ and CDF studied this sig-nature in data sample of a luminosity of995 pb−1 and 295 pb−1 respectively. Thejets+E/T trigger was used. The searchstrategy involved three steps which in-clude the application of the selection cri-teria on kinematical variables, heavy fla-vor (HF) tagging and optimization of thefinal selection depending on the t˜1 andχ˜01 masses. Fifteen selection criteria are ap-plied to remove the multijet and the W+jetsbackgrounds. At the final stage of theanalysis, additional criteria on three kine-matic variables: E/T , S=∆φmin + ∆φmax(∆φmin(∆φmax) is the smallest(largest) az-imuthal separation between a jet and E/T ),and HT (scalar sum of the pT of all jets), are optimized by maximizing the expected lowerlimit on the neutralino mass for a given mt˜1 . Systematic uncertainties, evaluated for eacht˜1 and χ˜01 mass combination, included jet energy scale (1.7-2%), jet energy resolution (1%),trigger (6%), scale factor(5%), HF tagging (3-4%) and the normalization of the background(10%). A good agreement has been observed between data and SM expectation. A limithas been drawn in the plane (mt˜1 ,mχ˜01) assuming that t˜1 decays into a charm quark and aneutralino with a 100% branching ratio. The largest stop mass excluded is 155 GeV/c2, fora neutralino mass of 70 GeV/c2 (Fig. 3)[5].In the t˜1 → blν˜l case, ν˜l is considered to be the LSP. The most promising final state isDIS 2008t˜1¯˜t1→ bb¯e±µ±ν˜eν˜µ: the cross section times the branching ratio is twice the one of the sameflavor case, and the SM background is also lower. The signal characteristics (lepton or b-jetpT ’s, E/T spectrum) depend both on the stop mass and on the difference between the stopmass and the sneutrino mass ∆m = mt˜1 −mν˜ : the pT ’s decrease with ∆m . For a given∆m , E/T values increase with the stop mass. For a stop mass, E/T values increase with∆m . A search for t˜1¯˜t1→ bb¯e±µ±ν˜eν˜µ has been performed by DØ in a 1 fb−1data sample.A leptonic trigger (electron+muon) has been used. The SM background was composed ofZ/γ∗ → τ+τ−, multijets, WW and tt¯. Events were selected with the following criteria: oneelectron and one muon with pT bigger than 15 GeV/c, E/T bigger than 30 GeV. Additionalcuts were applied to remove Drell-Yan and instrumental background events. After the last se-lection, 61 events survived in data whereas 64±4 were expected (mostly WW and tt¯ events).Limits were drawn in the plane (mt˜1 ,mν˜) assuming that the stop decays to blν˜l with a 100%branching ratio. A stop mass of 175 GeV/c2 has been excluded if mν˜= 45 GeV/c2(Fig. 3). (GeV)t~m40 60 80 100 120 140 (GeV)0 1χ∼m020406080100 c + m1oχ∼ = mt~moχ∼ + mb + mW = Mt~mo = 56θLEP o = 0θLEP -1CDF Run II 295 pb -1D0 Run II 360 pbObserved Expected -1 DØ, L = 995 pb)2 (GeV/c1t~ M60 80 100 120 140 160 180 200)2 (GeV/cν∼M405060708090100110120)2 (GeV/cν∼MKinematically excludedLEP ILEP II ALO-1) obs 428 pbµµ,µD0 Run II (e-1) exp 428 pbµµ,µD0 Run II (e-1) obs 1fbµD0 Run II (e-1) exp 1fbµD0 Run II (eD0 RunII PreliminaryL=1 fb-1Figure 3: Stop limits for the cχ˜01 case(top) and the blν˜l analysis (bottom).3 ConclusionThe most constraining direct limits on squarkand gluino masses to date have been ob-tained at the TeVatron: squark masses lowerthan 392 GeV/c2 and gluino mass lower than327 GeV/c2 have been excluded at 95% C.L. fortanβ= 3, A0 = 0, and µ < 0. Stop pair produc-tion has been searched in the cχ˜01 and blν˜l chan-nels. No excess with respect to the StandardModel expectations has been observed and massregions have been excluded. CDF and DØ haveperformed an impressive set of SUSY researchand further information may be found on thepublic web pages of the two experiments [6].AcknowledgementSpecial thanks to my colleagues from CDF andDØ for providing the results. I also thank theorganizers of the conference for their hospitality.References[1] Slides:http://indico.cern.ch/getFile.py/access?contribId=73&sessionId=15&resId=0&materialId=slides&confId=24657[2] V.M. Abazov et al., Phys. Lett. B 660 449 (2008).[3] http://www-d0.fnal.gov/Run2Physics/WWW/results/prelim/NP/N58/[4] A. Ambulencia et al., Phys. Rev. Lett. 96 171802 (2006).[5] V.M. Abazov et al., FERMILAB-PUB-08-063E, submitted to Phys. Lett. B.[6] http://www-d0.fnal.gov/Run2Physics/WWW/results/np.htmhttp://www-cdf.fnal.gov/physics/exotic/exotic.htmlDIS 2008

Squarks and gluino searches at the Tevatron

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