An inclusive analysis strategy for SUSY searches in pp collisions at sqrt(s)=14 TeV with the CMS detector is discussed. The missing transverse energy plus multijets canonical signature is used. Emphasis is put in methods to normalize the backgrounds using the data and in understanding the experimental systematic uncertainties. A 5 sigma excess can be observed with O(pb^-1) at a particular low mass SUSY point. The 5 sigma discovery reach contours in the mSUGRA parameter space for 1 and 10 fb^-1 are obtained

Spiropulu, M

Yetkin, T

Acta Physica Polonica B

CERN Document Server

Inclusive SUSY searches using missing energy plus multijets in p p collisions at s**(1/2) = 14-TeV with CMS

3rd Physics at LHC Conference -- JUL 03-08, 2006 -- Cracow, POLANDWOS: 000244783800043We discuss an inclusive analysis strategy for SUSY searches in pp collisions at root s = 14 TeV with the CMS detector, where the missing transverse energy plus multijets canonical signature is used. Emphasis is put on methods to normalize the backgrounds using the data and on understanding the experimental systematic uncertainties. A 5 sigma excess can be observed with O(pb(-1)) at a particular low mass SUSY point. The 5 sigma, discovery reach contours in the mSUGRA parameter space for 1 and 10 fb(-1) are obtained.Inst Nucl Phys Polish Acad Sci, AGH Univ Sci & Technol, Polish Acad Arts Sci, Univ Florida, CERN, DAPHNIA CEA, Polish Minist Educ & Sci, Charles Univ, Czech Tech Uni

Yetkin, T.

Spiropulu, M.

Çukurova University Institutional Repository

Inclusive SUSY searches using missing energy plus multijets in pp collisions at root s=14 TeV with CMS

Institute of Nuclear Physics PAN;AGH University of Science and Technology;University of Florida;CERN;DAPHNIA CEA Saclay3rd Physics at the LHC Conference --3 July 2006 through 8 July 2006 -- Krakow --We discuss an inclusive analysis strategy for SUSY searches in pp collisions at ?s = 14 TeV with the CMS detector, where the missing transverse energy plus multijcts canonical signature is used. Emphasis is put on methods to normalize the backgrounds using the data and on understanding the experimental systematic uncertainties. A 5? excess can be observed with O(pb-1) at a particular low mass SUSY point. The 5? discovery reach contours in the mSUGRA parameter space for 1 and 10 fb-1 are obtained

Yetkin T.

Spiropulu M.

Inclusive susy searches using missing energy plus multijets in pp collisions at ?s = 14 TeV with CMS

Available on CMS information server CMS CR 2006/070CMS Conference Report02 October 2006Inclusive SUSY Searches using Missing Energyplus multijets in pp collisions at√s = 14 TeV withCMST. Yetkin1)Department of Physics, C¸ukurova University, Adana, 01330, Turkey.M. SpiropuluEuropean Laboratory for Nuclear Search CERN, Geneva, Switzerland.On Behalf of the CMS collaborationAbstractAn inclusive analysis strategy for SUSY searches in pp collisions at√s = 14 TeV with the CMS de-tector is discussed. The missing transverse energy plus multijets canonical signature is used. Emphasisis put in methods to normalize the backgrounds using the data and in understanding the experimen-tal systematic uncertainties. A 5σ excess can be observed with O(pb−1) at a particular low massSUSY point. The 5σ discovery reach contours in the mSUGRA parameter space for 1 and 10 fb−1are obtained.Presented at Physics at LHC Conference, 3-8 July 2006, Krakow, Poland.1) Present Address: Department of Physics, Mersin University, Mersin, 33343, Turkey1 IntroductionOne of the most compelling and robust extensions of the Standard Model [1] is supersymmetry (SUSY) [2]. Forsimplicity the minimal construction (MSSM) is often used to link SUSY with the Standard Model [3]. The mostgeneral MSSM would induce proton decay with a weak-interaction lifetime; to avoid this, baryon and leptonconservation are enforced in the MSSM by postulating a new conserved quantity, R-parity, R = (−1)3(B−L)+2s,where for each particle s is the spin, and B and L are the respective baryon and lepton assignments. R-parityconservation leads to characteristic SUSY signatures with missing transverse energy in the final state due to thestable lightest supersymmetric particle (LSP).We consider gluino (the fermionic partners of gluons) and squark (the bosonic partners of quarks) production in ppcollisions at√s = 14 TeV within the minimal supergravity model (mSUGRA)[3]. In this model the entire SUSYmass spectrum is essentially determined by only five unknown parameters: the common scalar mass at the GUTscale, M0; the common gaugino mass at the GUT scale, M1/2; the common trilinear coupling at the GUT scale,A0; the sign of the Higgsino mixing parameter, sign(µ); and the ratio of the Higgs vacuum expectation values,tanβ. The search for the production and decay of gluinos and squarks is using the large missing transverse energyplus multijet signature. The large missing energy originates from the two LSPs in the final states of the squark andgluino decays. The three or more hadronic jets result from the hadronic decays of the q˜ and/or g˜.2 Data SamplesFor the SUSY signal event generation the Monte Carlo program ISAJET (v7.69) [4] interfaced with PYTHIA(v6.225) [5] (which provides the parton shower and underlying event model) is used. The analysis is performedat the CMS test point “LM1” ([6], [7]) with parameters M0 = 60GeV/c2, M1/2 = 250GeV/c2, A0 = 0, µ > 0and tanβ = 10. For this set of parameters m(g˜) > m(q˜) the production of g˜q˜ is 53%, q˜q˜ 28% and g˜g˜ 12%. Thedecay g˜ → ˜qL,R + q is dominant. Some of the resulting masses are m(g˜) ∼ 600GeV/c2, m(q˜) ∼ 550GeV/c2,and χ01 ∼ 120 GeV/c2.The total leading order production cross section for squarks and gluinos with the givenmSUGRA parameters is ∼50 pb.The major Standard Model background processes include production of Z+jets with the Z decaying invisibly,W+jets, top-antitop pairs, dibosons, single top and QCD jets. The single top sample (containing only the mostsignificant t-channel production) is generated with TopReX 4.11 [8]. The remaining Standard Model backgroundsare produced inclusively using PYTHIA.Unless otherwise stated, the data samples used in this analysis were simulated with the CMS GEANT4-basedsimulation OSCAR [9] and reconstructed using the detailed CMS reconstruction ORCA [10].2.1 Jet and Missing Transverse Energy ReconstructionThe CMS detector is described in detail in [11]. The momenta of charged particles are measured in the siliconand pixel tracking devices which are positioned inside a 4 T superconducting solenoidal magnet. The centraland end-cap electromagnetic and hadronic calorimeters (also within the magnet) are arranged in a semi-projectivetower geometry, cover the pseudorapidity region |η| < 3 [11] and are used to identify jets. Jets are defined aslocalized energy depositions in the calorimeters and are reconstructed using an iterative clustering algorithm witha fixed cone of radius ∆R ≡√∆η2 +∆φ2 = 0.5 in η − φ space [11]. Jets are ordered in transverse energy,ET = E sin θ, where E is the scalar sum of energy deposited in the calorimeter towers within the cone, and θ isthe angle formed by the beam-line, the event vertex, and the cone center. Jets with ET > 30 GeV and with |η| < 3are used throughout this analysis. The jet corrections described in section 3.3 are not applied at this stage.The offline missing transverse energy is defined as the negative vector sum of the transverse energy in the electro-magnetic and hadronic calorimeter towers,−−−→EmissT = −∑i(Ei sin θi)nˆi, where Ei is the energy of the i-th tower,nˆi is a transverse unit vector pointing to the center of each tower, and θi is the polar angle of the tower; the sum ex-tends to |η| < 5. The data sample is selected with a hardware trigger which requires Emiss,L1T > 46 GeV (|η| <5coverage) and a central jet of ET > 88 GeV. A parametrization of the L1 trigger efficiency as measured in a dijetsample is applied to all data analyzed. For the confirmation of the High Level Trigger (HLT) the EmissT is requiredto be above 200 GeV where the HLT trigger is fully efficient. The details of L1 and HLT triggers and application tothis analysis can be found at [11, 12]. In the following sections we detail the methodology and analysis strategiestoward a search for SUSY using a dataset of events collected according to the missing transverse energy plus jetL1 and HLT trigger path.2Table 1: Cleanup pre-selection efficiency.Sample/Requirement Fem > 0.1 Fch > 0.175 Both(%)LM1 99.88% 91.32% 91.24%3 Data Clean-up and Analysis Path3.1 Event Electromagnetic and Event Charged FractionIn anticipation of real data, a pre-selection clean-up filter is used to reject accelerator- and detector-related back-grounds (such as beam halo and noise), and cosmic ray events. At least one primary vertex is required in the event.The event electromagnetic fraction, Fem (defined as the ET –weighted jet electromagnetic fraction sum over theelectromagnetic calorimeter acceptance, |ηd| ≤ 3.0) and the event charged fraction, Fch (defined as the sum of thePT of the associated to the jet tracks for jets within |η| < 1.7, over the calorimetric jet transverse energy) are usedin the pre-selection to distinguish real jet events from the fake jet events. The pre-selection requirements and theirefficiency on the signal are shown in Table 1. The values of the requirements are chosen based on the Tevatrondata clean-up [13].3.2 Indirect Lepton VetoIn this analysis there is no explicit lepton identification. Leptons in the signal SUSY events result from cascadedecays of squarks and gluinos through charginos and neutralinos. To reduce the large Standard Model backgroundcontribution mainly from W (→ `ν) + jets, Z(→ ``) + jets and tt¯ production and decays an indirect lepton veto(ILV) scheme is designed. The aim of the ILV is twofold: a) to retain large signal efficiency b) to achieve largerejection of the W,Z, tt¯ backgrounds.The ILV scheme uses two parts of the detector: tracker and calorimeter. In the calorimeter events are selected ifthe first and second highest ET jets are not purely electromagnetic, i.e. fem,j(1) < 0.9 and fem,j(2) < 0.9. In thetracker a tracking isolation strategy is employed as follows: If the leading track in the event has PT ≥ 15GeV/cand the ratio of the sum of the PT of all tracks around it in a cone of ∆R=0.35 over the PT of the track is less than10% the event is dropped. In the analysis path table below this requirement is noted as Isolead trk=0The cumulative W/Z+jets rejection efficiency when both requirements of the ILV are applied is between 50% and90% depending on the lepton flavour, with lower rejection as expected when the boson decay product includes a τlepton. When applied in the full analysis path the ILV rejects 40% of tt¯ inclusive events. The cumulative SUSYsignal efficiency is ∼80%.3.3 Missing Transverse Energy in QCD ProductionDue the very high QCD production cross section the SM background to a large missing transverse energy plusjets data-sample is dominated by QCD events. The observed missing transverse energy in QCD jet production islargely a result of jet mis-measurements and detector resolution.In this study, topological requirements are designed to eliminate as much as possible the QCD contribution. Wellmeasured QCD dijet events with back-to-back in φ jet topology are used for obtaining jet corrections. Theseare well balanced events with low missing transverse energy. Large missing energy in QCD events originatesfrom jet mis-measurements. In such events the highest ET jet is typically the most accurately measured. Whenany jet in the event is mis-measured, usually the second or third jet, the EmissT direction is pulled close in φto the mis-measured jet direction. We eliminate such residual QCD component by using the correlation in theδφ1 = |φj(1) − φ(EmissT )| versus δφ2 = |φj(2) − φ(EmissT )| plane. Events with R1 > 0.5 rad and R2 > 0.5 rad,where R1 =√δφ22 + (pi − δφ1)2and R2 =√δφ21 + (pi − δφ2)2, are accepted. In addition we require that no jetin the event be closer than 0.3 rad to the missing energy direction and that the second jet be further than 20◦ fromit.After a baseline selection of Nj ≥ 2 and EmissT > 93GeV the cumulative efficiency of the angular requirementsis ∼90% for the SUSY signal. They reject ∼85 % of all QCD events.33.4 The Standard Z Boson Candle CalibrationEvents with large missing transverse energy and ≥3 jets in the final state are expected from Z(→ νν¯)+ ≥3jets and W (→ τν)+ ≥2 jets (the third jet originating from the hadronic τ decay) processes. Additional residualcontribution is expected also fromW (→ µν, eν)+ ≥3 jets. A comprehensive normalization program is developedthat relies on the Z+multijet data to accurately estimate the W and Z+multijet background contribution in a largeEmissT plus multijet search.The Monte Carlo predictions for events with ≥ 3 jets and Z boson PT > 200 GeV/c will be normalized to theobserved Z(→ µµ)+ 2 jets data sample ( where Z boson PT > 200 GeV/c) via the measured R = dNeventsdNjets ratio,where dNevents is the number of events accumulated with ∼1 fb−1 of data.The ratio ρ ≡ σ(pp→W (→µν)+jets)σ(pp→Z(→µ+µ−)+jets) will be used to normalize the W+jets Monte Carlo predictions. By normal-izing the MC predictions to data large systematic effects are avoided that are due to the renormalization scale, thechoice of parton density functions, initial- and final-state radiation, and the jet energy scale. The total uncertainty(∼5%) is then dominated by the uncertainty on the luminosity measurement, the uncertainty on the measured ratioR = dNeventsdNjets (to be measured with the data), and the uncertainty on the ratio ρ as a function of the jet multiplicity,Njet. The details of the normalization can be found in reference [7].4 Analysis Path and ResultsThe signal to background ratio is further enhanced after clean-up pre-selection requirements in the final steps ofthe analysis by following the path shown in Table 2. The global signal efficiency for the analysis is ∼13% whilethe signal to background ratio is ∼26. The results after the analysis path applied are shown in Table 3.Table 2: The EmissT + multijet SUSY search analysis path.Requirement RemarkLevel 1 Level-1 trigger param.HLT, EmissT > 200 GeV trigger/signal signatureprimary vertex ≥ 1 primary cleanupFem ≥ 0.175, Fch ≥ 0.1 primary cleanupNj ≥ 3,|η1jd | < 1.7 signal signatureδφmin(EmissT − jet) ≥ 0.3 rad, R1, R2 > 0.5 rad,δφ(EmissT − j(2)) > 20◦ QCD rejectionIsolead trk = 0 ILV (I) W/Z/tt¯ rejectionfem(j(1)), fem(j(2)) < 0.9 ILV (II), W/Z/tt¯ rejectionET,j(1) > 180 GeV,ET,j(2) > 110 GeV S/B optimizationHT ≡ ET (2) + ET (3) + ET (4) + EmissT > 500GeV S/B optimizationTable 3: Selected SUSY and SM background events for 1 fb−1 at LM1 .Signal tt¯ single t Z(→ νν¯)+ jets (W/Z,WW/ZZ/ZW ) + jets QCD6319 53.9 2.6 48 33 1074.1 Systematic UncertaintiesFor the major background components the systematic uncertainties are found as follows:• tt¯ uncertainties: 7% EmissT shape, 22% JES, 13% statistical,• Z −→ νν¯+jets, W/Z+jets: 5% Luminosity (direct candle normalization to the data),• QCD: EmissT 7% shape, 22% JES, 10% statistical.Details on the systematic uncertainty estimates can be found in [7]. The number of backgrounds events per back-ground component and their uncertainties are tabulated in Table 4.4Table 4: SM background components and uncertainties for 1 fb−1.Sample Number of Eventstt¯,single top 56 ± 11(sys) ± 7.5(stat)Z(→ νν¯)+ jets 48 ± 3.5 (all)(W/Z,WW/ZZ/ZW ) + jets 33 ± 2.5 (all)QCD 107 ± 25(sys) ±10(stat)5 SUSY Discovery Potential with EmissT + JetsTo perform the 5σ discovery scan in the mSUGRA parameter space CMS fast simulation FAMOS [14] is used. Ahigh mass (“HM1”) CMS test point with the five mSUGRA parameters M0 = 180GeV/c2, M1/2 = 850GeV/c2A0 = 0, µ > 0 and tanβ = 10 (m(g˜) ∼ 1890GeV/c2, m(q˜) ∼ 1700GeV/c2) is used as optimization referenceand the EmissT and HT requirements are raised to 600 GeV and 1500 GeV correspondingly. The result is shown inFigure 1.Figure 1: 5σ reach for 1 fb−1 and 10 fb−1 using multijets and missing transverse energy final state.6 Discussion and ConclusionsBased on the SM background estimates and their uncertainties, a 5σ observation of low mass SUSY (m(g˜) ∼600GeV/c2) is in principle achievable with ∼6 pb−1 in events with large missing energy plus multijets. Withadequate data-based strategies of controlling and estimating the SM backgrounds and their uncertainties, low massSUSY can be discovered with 0.1-1 fb−1.The comparison of the signal, total background and its components for the EmissT and Meff ≡ ET (1) + ET (2) +ET (3) + ET (4) + EmissT are shown in Figure 2 for the low mass SUSY test point LM1. The EmissT and HTdistributions comparison between the HM1 SUSY signal and SM backgrounds are shown in Figure 3 for the highmass test point HM1.We would like to thank to the organizers of the Physics at LHC Conference for the possibility to present our workand for their hospitality. We are grateful to Gu¨lsen O¨nengu¨t, Shuichi Kunori and Jim Freeman for supporting thisanalysis.References[1] S. L. Glashow, Nucl. Phys. 22 588 (1961); S. Weinberg, Phys. Rev. Lett. 19, 1264 (1967); A. Salam, Proc. 8thNobel Symposium, Stockholm (1979).5Figure 2: LM1 signal and SM background distributions for EmissT (left) and Meff (right).Figure 3: HM1 signal and SM background distributions (1 fb−1) for EmissT (left) and HT (right).[2] S. Coleman and J. Mandula, Phys. Rev. 159, 1251 (1967); P. Ramond, Phys. Rev. D3, 2415 (1971);A. H. Chamseddine, R. Arnowitt, and P. Nath, Phys. Rev. Lett. 49, 970 (1982); Phys. Rev. Lett. 50, 232 (1983);R. Barbieri, S. Ferrara, and C. A. Savoy, Phys. Lett. B119, 343 (1982); L. Hall, J. Lykken and S. Weinberg,Phys. Rev. D27, 2359 (1983); H.P. Nilles, Phys. Rept. 110, 1 (1984).[3] For a review see S.P. Martin, “A Supersymmetry Primer”, hep-ph/9709356 (1997), in Perspectives onsupersymmetry, 1-98, Kane, G.L. (ed.) (1997).[4] H. Baer et al., ISAJET 7.69: A Monte Carlo Event Generator for pp, p¯p, and e+ + e− Interactions”,hep-ph/0312045 (2003).[5] T. Sjostrand, S. Mrenna and P. Skands, J. High Energy Phys., 0605 (2006) 026.[6] M.Battaglia et al. Eur. Phys. J. C 33 (2004) 273, hep-ph/0306219.[7] CMS Collaboration, “The CMS Physics Technical Design Report, Volume 2: Physics Performance”,CERN/LHCC 2006-021 (2006).[8] S. R. Slabospitsky, L. Sonnenschein, Comput. Phys. Commun. , 148 (2002) 87, hep-ph/0201292,http://sirius.ihep.su/∼spitsky/toprex/toprex.html[9] “Object oriented Simulation for CMS Analysis and Reconstruction”,http://cmsdoc.cern.ch/oscar/.[10] “Object oriented Reconstruction for CMS Analysis”, http://cmsdoc.cern.ch/orca/.[11] CMS Collaboration, “The CMS Physics Technical Design Report, Volume 1: Detector Performance andSoftware”, CERN/LHCC 2006-001 (2006).[12] T. Yetkin, Ph.D. Thesis (C¸ukurova U.), CMS TS-2006/005, March 2006, 169pp.[13] M. Spiropulu, Ph.D. Thesis (Harvard U.), FERMILAB-THESIS-2000-16, UMI-99-88600, Nov 2000. 338pp.6[14] http://cmsdoc.cern.ch/famos/.[15] M. L. Mangano et al., J. High Energy Phys., 0307 (2003) 001.7

Inclusive SUSY Searches using Missing Energy plus Multijets in pp collisions at $\sqrt{s}$ =14 TeV with CMS

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Çukurova University Institutional Repository

Çukurova University Institutional Repository

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Inclusive SUSY Searches using Missing Energy plus Multijets in pp collisions at s\sqrt{s}s​=14 TeV with CMS

Abstract

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Available Versions

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Inclusive SUSY Searches using Missing Energy plus Multijets in pp collisions at $\sqrt{s}$ =14 TeV with CMS