We investigate the potential for discovery of super-symmetry during the next Tevatron Collider run in the light of new results fro LEP and CDF

Amos, N.

De, K.

White, A

Yamin, P.

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• ' BNL-48223_" Proc. DPF Summer Study on Research Directions for the Decade, Snowmaaa, COJuly 1990. Ed. E.L. Berger, 516-518 World Scientific (1992).Status and Future prospects for Supersymmetry at the Tevatron.._N. AmosFermilab, Batavia, Illinois 60510K. DeUniversity of Michigan, Anu Arbor, Michigan B1_...-48223 :_A. White DE93 006390 :;_University of Florida, Gainesville, Florida 32611 !!P. YaminBrookhaven National Laboratory, Long Island, New YorkABSTRACT number of parameters that can be varied during model :;.calculations. These parameters are the gluino mass, a '-:supersymmetric Higgs mass (mu) and the ratio (called ':We investigate the potential for discovery of super- tan(beta)) of the vacuum expectation values of the two . ,_symmetry during the next Tevatron Collider run in the Higgs fields. A plot of the current and future LEP ex- ),._!_light of new rcsults from LEP and CDF. clusion regions in a gluino mass vs. supersymmetric :..:!__ig_s mass (mu) shows that almost the enti..re l_sitive :_:. ....I. INTRODUCTION mu sector can already be excluded for gluino masses .._.less than 200 GeV. Since, as this paper will show, the _This work was carried out for subgroups 2.4.4 and next collider run can probably only search up to 200 )!_7_1.4 (Beyond the Standard Model). Important new re- GeV, we have chosen s value of mu for our calculations ....suits from LEP and CDF were discussed in subgroup which is negative. (It should be noted that previous ;_1.4 and will be summarized here since they define the calculations (at Snowmass '88 and the Breckenridge "=_conditions under which the present studies were per- workshop '89 (Refs. 3,4) used positive values for mu). . i_¢i::formed. The purposeof the presentpaper isto ex- For theworkpresentedhere,a valueof-300,was used '.:.plorethe potentialgluinomass searchregionforthe formu. Additionally,our previouscalculationsu ed .,:.next Tevatron collider run in the light of the new re- a value for tan(beta) of 1.5. New Higgs sector results '::_v ,,1'.suits from CDF and LEP which already significantly from LEP have shown that 1.5 is excluded and we have :_;_,_• :{constrain the parameters of the minimal SUSY model, chosen to use a value of 2.0. !/:.II. NEW RESULTS III. OUR STUDIESThe latest (preliminary) CDF results (tel.l) pre- We have chosen to use two gluino masses, 150 and• ./i!.sented at this workshop show limits on the gluino and 200 GeV. The 150 GeV case corresponds approxi- .l.__squark masses of approximately 150 and 170 GeV re- mately to the latest preliminary CDF limit, while forspectively. These results were obtained without the the 200 GeV case we expect (Ref.1) O(50) gluino pairpossiblity of cascade decays of these particles which events before cuts for 25 inverse picobarns of accumu-are expected to weaken the limits by 10-20% (ref.6). lated data - a conservative expectation for the nextNevertheless, these new results represent a significant Tevatron collider run. We therefore used 200 GeV inextension of the limits over the earlier CDF results the hope that a useful number of events would remain(ref.2) and put important new constraints on the pa- after cuts were applied.ran_eters of the minimal supersymmetric extension of In this range of masses many new decay branchingthe Standard Model. rati_ start to attain significant values and the directThe other major source of new results reievant to the gluino decay to p pbar and photino drops accordingly.search for supersymmetry are the LEP experiments, lt is therefore important to account correctly for these ' ':_A summary of the latest LEP results is presented in new decays in our simulation. To this end we took full, ,._'these Proceeding_ (see section on Beyond the Stan- advantage of the work carried out by a number of pea-$'!_dard Model). T_ minimal SUSY model has a small pie (Ref.3,4) at recent workshops to produce a com- ::_'This work has been _suavpor_ed by- the U.S, Department of Energyttplete set of branching ratios for ghinos and squarks V. RESULTSof any mass in a form that is directly readable byour standard physics generator ISAJET . During the The results for a gluino mass of 150 GeV, beforepresent workshop further improvements were made, cuts, of the ISA3ET and simple detector simulationand detailed checking of the entire decay calculation runs are shown in Fig. 1.procedure was carried out. "_,'IV. SIMULATION DETAILS 1o-5 ' " l ' " " " l ' '"' _ l " ' _ ' l " ".' ' l ....In order to generate specific predictions we have used 10"e L QCD Mgluino = 150 GeV -ISAJET witha simpledetectorsimulationwhich con- _ 1o._ "I,L/ NO CUTS _o _GLUINOtainsthe basiccharacteristicsof the DO detectoratFermilab: _ t°'e10-0Ir_[< 4.5_. 10"I0,&7 x 6_b= 0.Ix 0.i j 10-11e.m. resolution- 20% / sqrt(E) 10-12hadronicresolution= 50% / sqrt(E) 1°"130 _0 too _o 200 n0 _oo ,PT ml,stnq (GEV)In addition we have used a cone jet algorithm with a _ .-cone radius of 0.7, and a minimum accepted jet Et of5 GeV. Fig. 1. The missing Et spectrum before cuts fromOur signal consisted of gluino pairs produced as ghino pairs of mass 150 GeV, and QCD and Z-bosonbackgrounds at the Tevatronp _ --- gluino gluino + X at 2 TeVwith subsequent decay of the gluinos via cascade de- We use the missing Et distribution as our primary:: cays.Most theoreticalargumentspreferm(squark)> parameter. Charcteristicallythe QCD heavy quarkm(gluino)and we havesetm(squark)= 2m(gluino). backgroundexceedsthe signalout to about 80 GeV,but the main featureis the dominance of the Z +-: Following experience from our earlier calculations jets background beyond the same point in missing Et.and CDF analysis results, we chose to study two back- There are various ways that have been used to reducei• groundprocesses: thesebackgroundsbased on the expectedsignaland- QCD heavy quark productionwith decayto high backgroundcharcteristics._'nenumber ofjetsinthePt chargedleptonsor neutrinos, signalisgenerallyhigherthan forthe backgrounds,and thePt ofthehardestjetintheeventishigheronAs reportedinearlierpapers(Refs.3,4)aspecialvet- averageforthe signalevents.In additionthe SUSYsionofISA3ET (calledISALEP) was developedwhich eventstend to have a more sphericaltopologythanproducesan enrichedsample of heavy quarks with thebackgroundevents.We have combined theseex-semi-hptonic decays, while correctly taking account of pected differences into a series of cuts the effects ofthe associated cross-section. We have used this pro- which are seen in Fig. 2. It may be seen that thecedure again in the present work and have generated QCD background is significantly lowered with respectevents in the Pt range 50 - 500 GeV/c. to the signal, and that the Z -6 jets background now- Z 4- jets, with Z --- neutrinos, also falls below the signal. However, the Z .6 jets eventsremain the dominant background after cuts. We haverecent work by CDF (Ref.2) has shown that this is attempted to estimate the eignal that would be ex-the dominant irreducible physics backgrvund remain- pected after background subtraction in the region ofing after cuts (to be described below) are applied, missing Et between 65 and 120 GeV. the result is 66Other related backgrounds such as W -- e nu from W events for a luminosity of 4.4 invert': picobarns (corre-+ jets are successfully removed using specific selection sponding to the luminosity for the CDF data reportedcriteria, in Ref.2). This is to be compared with an independent517CDF estimatewith somewhat differentcutsand de- ltisseenthatovera regionwhere the QCD back-tectorsimulationof37 eventsforthesame missingEt ground iswellsuppressed(approximately90 to 170interval.We takethisas reasonablygood agreement GeV) the Z + jetsbackground isat the same levelconsideringthe differencesinthe two procedures, asthesignal.The estimatedexcesscross-sectionafterbackgroundsubtractionislessthan ipb. whichwouldyieldonly25 eventsbeforeapplicationfefficiencyfac-10-s.... I.... I.... I.... I.... i' _'I tots.Thus 200 GeV probablyrepresentsthe practicalI limitofgluinomass reachwith cascadedecaysto be10"S SPHERICITY> 0.1 __ expected from the next collider run.Mgluino = 150 GeV fll0 "7 . QCD N_za>4 l10-e I _( pT_,x_>60 _ VI.CONCLUSIONSZ _ GLUINO'_ 10"Q _ Z +JETS -_ Guided by recentresultsfrom LEP and CDF wehavesimulatedthe expectedsignalfrom the minimal10-t0 - Supersymmetrymodel forgluinomassesof150and 200"g t°'zt i GeV producedin a simplerepresenetationfthe DOdetector. Also simulated were the QCD heavy quark10-12 and Z plusmultijetsbackgrounds.Our resultshow10-13. . . [_3. thatwe may expectto accessa regionup to 200 GeVo so too iso 200 2so 300 in gluino mass in the next Tevatron collider run.PT mtssmq(GEV) _..!-.._VII. REFERENCESFig.2.The missingEt spectrumaftercutsfromgluinopairsofmass 150 GeV, and QCD and Z-boson [I]H. Baer,A. White etal.intheseProceedings.backgroundsattheTevatron [2]seee.g.V.Barnes,Aspen Wintermeeting,1990.The calculationsabove w,,'erepeatedfora gluino [3]Proceedingsof the 1988Snowmass Workshop onmass ,.,f200 GeV and the results,aftercutsareshown High Energy Physicsinthe 1990's.inFig.3. [41Proceedingsof the 1989 BreckenridgeWorkshopon PhysicsatFermilabinthe1990's[5] H.Baer et el. Phys. Rer. D41,906 (1990)._0"5 "' ' ' I .... I .... I .... I ' ' ' ' I'' " '__ Mgluino= 200 GeVi0-0NO CUTS_¢_ 10"7 -k / GLUINO.810.910"10i I0.I1wI0-12- _ .f10"130 50 I00 150 200 250 300PT mlsslrq (GEV)Fig.3. The missingEt spectrumaftercutsfromgluinopairsofmass 200 GeV, and QCD and Z-bosonbackgroundsattheTevatron• 518DISCLAIMERThis report was prepared as an account of work sponsored by an agency of the United StatesGovernment. Neither the United States Government nor any agency thereof, nor any of theiremployees, makes any warranty, express or implied, or assumes any legal liability or responsi-bility for the accuracy, completeness, or usefulness of any information, apparatus, product, orprocess disclosed, or represents that its use would not infringe privately owned rights. Refer-ence herein to any specific commercial product, process, or service by trade name, trademark,manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recom- kmendation, or favoring by the United States Government or any agency thereof. The viewsand opinions of authors expressed herein do not necessarily state or reflect those of theUnited States Government or any agency thereof.

Status and Future Prospects for Supersymmetry at the Tevatron

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Status and Future Prospects for Supersymmetry at the Tevatron

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