NLO SUSY-QCD contributions to associated production of gluinos and gauginos
are shown to enhance the cross sections by about 10% at the Tevatron and by as
much as a factor of two at the LHC. They shift the mass determinations or
discovery limits, soften the $p_T$ spectra, and stabilize the predictions
against variations of the renormalization and factorization scales.Comment: 4 pages, Latex (uses Moriond style file), 8 eps-figures. Talk
  presented at the XXXVth Rencontres de Moriond, QCD and High Energy Hadronic
  Interactions, Les Arcs, France, March 18-25, 200

Berger, Edmond L.

Klasen, Michael

Tait, Tim M. P.

English

arXiv

NLO SUSY-QCD contributions to associated production of gluinos and gauginos
are shown to enhance the cross sections by about 10% at the Tevatron and by as
much as a factor of two at the LHC. They shift the mass determinations or
discovery limits, soften the $p_T$ spectra, and stabilize the predictions
against variations of the renormalization and factorization scales

Berger, Edmond L

Tait, Tim MP

eScholarship - University of California

Predictions for associated production of gauginos and gluinos at NLO in SUSY-QCD

NLO SUSY-QCD contribution to associated production of gluinos and gauginos are shown to enhance the cross sections by about 10% at the Tevatron and by as much as a factor of two at the LHC. They shift the mass determinations or discovery limits, soften the p{sub T} spectra, and stabilize the predictions against variations of the renormalization and factorization scales

Berger, E. L.

Klasen, M.

Tait, T.

UNT Digital Library

Submittedto the Proceedings of the XXXV Rencontres de Moriond, Les Arcs,France, ~8-25 ~arch 2W... .–. *hepph/0005199ANL-HEP-CP-OO-057DESY 00-076The submitted manuscript has been createdby the University O! Chicago as Operator OfArgonne National Laboratory (“Argonne”)under Contraa No. W-31 -109-ENG-38 withthe U.S. Department of Energy. The U.S.Government retains for itself, and others act-ing on its behalf, a paid-up, nonexclusive,irrevocable worldwide license jn said afiicleto reproduce, prepare derivative works, dis:tribute copies to the public, and perform pub.Iicly and display publicly, by or on behalf ofthe Government,Q4?&~~ ~ ,PREDICTIONS FOR ASSOCIATED PRODUCTION OF@ ~ & GAUGINOS AND GLUINOS AT NLO IN SUSY-QCDQ-e4/42=+$0 E.L. BERGER”, M. KLASENb, AND T. TAIT=-w-a Argonne National Laboratory, Argonne, IL 60439, USAb II. Institzd fur Theoretische Physik, Universittit Hamburg, LuTuper Chaussee 149,D-22609 Hamburg, GermanyNLO SUSY-QCD contribution to associated production of gluinos and gauginos are shown toenhance the cross sections by about 10~0 at the Tevatron and by as much as a factor of two atthe LHC. They shift the mass determinations or discovery limits, eoften the p~ spectra, andetabilize the predictions against variations of the renormalization and factorization scales.1 IntroductionThe search for supersymmetry (SUSY) is a major goal of the Tevatron Run 11 and LHC physicsprograms. If SUSY exists at the electroweak scale, SUSY partners of the Standard Model (SM)particles will either be discovered at these hadron colliders, or a very large region of SUSYparameter space will be excluded, provided reliable theoretical predictions in next-to-leading12314. We calculate the NLO contributions for associatedorder (NLO) SUSY-QCD are available ‘ ‘56 This production channel is enhancedproduction of gauginos and gluinos at hadron colliders ~ .by the strong coupling of the gluino and by the mass of the gaugino which is small in manypopular models of SUSY breaking. The leptonic decay of the gaugino makes this process a goodcandidate for a mass determination of the gluino or the discovery or exclusion of a light gluino.2 NLO SUSY-QCD FormalismThe associated production of a gluino and a gaugino proceeds in leading order (LO) througha quark-antiquark initial state and the exchange of an intermediate squark in the t-channel oru-channel. At NLO, virtual loop corrections must be considered which involve the exchange ofintermediate SM or SUSY particles in self-energy, vertex correction, or box diagrams. UltravioletDJSCLAIMEI?This report was prepared as an account of work sponsoredby an agency of the United States Government. Neitherthe United States Government nor any agency thereof, norany of their employees, make any warranty, express orimplied, or assumes any legal liability or responsibility forthe accuracy, completeness, or usefulness of anyinformation, apparatus, product, or process disclosed, orrepresents that its use would not infringe privateiy ownedrights. Reference herein to any specific commercialproduct, process, or service by trade name, trademark,manufacturer, or otherwise does not necessarily constituteor impfy its endorsement, recommendation, or favoring bythe United States Government or any agency thereof. Theviews and opinions of authors expressed herein do notnecessarily state or reflect those of the United StatesGovernment or any agency thereof.DISCLAIMERPortions of this document may be illegiblein electronic image products. Images areproduced from the best available originaldocument.pp+ ~ nt~S=2.0 TeV.110-210z~-30 10104-510300 420 5420 6C0 700 mm;[ON]10pp+ ~~tit ~S = 14TeVl“(’I’’’’ 1’’’’ 1, ’’1 ’1’ ‘1’’”1zao -210-3101041,, ,! 1, !, !l, !!!11!!!1! !>!l?!!! 1!!,,-300 WI 500 1500 71XI 800 ‘XM ICOOm; [(kVlFigure 1: Total hadronic cross sectionsat Run IIofthe Tevatron and at the LHC in atypical SUGRAmodeIasfunctions of thegluino mass.and infrared divergences appear at the upper and lower boundaries of integration over unobservedloop momenta. They are regulated dimensionally and removed through renormalization orcancellation wit h corresponding divergences in 2 to 3 parton (real emission) diagrams that havean additional gluon radiated into the final state. At NLO there is a second 2 to 3 parton process,one with a qg initial state and a light quark emitted into the final state. In addition to softdivergences, real emission contributions have collinear divergences that are factored into theNLO parton densities.3 Tevatron and LHC Cross SectionsTo obtain quantitative predictions for the associated production of gauginos and giuinos at RunII of the Tevatron and at the LHC, we convolve LO and NLO partonic cross sections withCTEQ5 parton densities in LO and NLO (~) along with 1- and 2-loop expressions for as,the corresponding values of A, and five active quark flavors. To constrain the SUSY parameterspace, we choose an illustrative SUGRA model with m. = 100 GeV, AO=300 GeV, tan @ = 4,sgn p = +, and we vary mllz between 100 and 400 GeV. The resulting masses for ~~...4 varybetween 31...162, 63...317, 211...665, and 241...679 GeV, and j@2 are almost mass degeneratewith ~~,4. The mass mx: <0 inside a polarization sum. Our method is not restricted to theSUGRA case and can be applied to any SUSY breaking model.We present the total hadronic cross sections in Figure 1 as functions of the gluino mass.The light gaugino channels should be observable at both colliders, while the heavier Higgsinochannels are suppressed by about one order of magnitude and might be observable only at theLHC.The impact of the NLO corrections can be seen more readily in the ratio of NLO to LOcross sections computed at a renormalization scale set equal to the average mass of the finalstate particles. Figure 2 shows that the NLO effects are moderate (of O (1OYO))at the Tevat ron,while at the LHC the NLO contributions can incre~e the cross sections by as much as a factorof two. Enhancements of this size can shift mass determinations or discovery limits for SUSYparticles by tens of GeV and must therefore always be taken into account..,m,1.11.0751,051.025Ml0.9750.950.9250.9L ,.. . .. . .. ..$ ~..!:, .%... ..,, . . . . . .. . ..- &i: ‘..,, ‘ .. .. --0 ‘.Sz3‘...‘.‘... ‘... . . . . “..&* ‘.. ‘.,‘..,------ * . .at %..,‘....,+,- ‘“-”-”-Z ..1 1 I300 400 500 600 7(MI 8CXI21.8z 1.61.41.2m; Kiev] m; [GeV]Figure 2: A’ factors at Run II of the Tevatron and at the LHC in the SUGRA model as functions of the gluinomass.An important measure of the theoretical uncertainty is the variation of the hadronic crosssection with the renormalization and factorization scales. At LO, these scales enter only in thestrong coupling constant and the parton densities, while at NLO they appear also explicitly inthe hard cross section. As a result, the scale dependence is reduced considerably, as can be seenin Figure 3. The Tevatron (LHC) cross sections vary by +23( 12)Y0 at LO, but only by +8(4.5) Toin NLO when the scale is varied by a factor of two around the central scale.For experimental searches, distributions in transverse momentum are important since cutson pT help to enhance the signal. In Figure 4 we demonstrate that NLO contributions can havea large impact on pT spectra, especially at the LHC, where contributions from the gq initialstate become important. At the Tevatron the NLO pT-distribution is shifted to lower pT withrespect to the LO expectation.4 ConclusionsThe directsearchfor SUSY particles is a major goal at hadron colliders. For associated produc-tion of gauginos and gluinos, we demonstrate that NLO SUSY-QCD corrections stabilize the LOestimates against variations of the renormalization and factorization scale.are increased by as much as a factor of two at the LHC, and the pl’ spectraAcknowledgmentsThe cross sectionsare softened.M.K. thanks the organizers of the XXXVth Rencontres de Moriond for the kind invitationand financial support. Work at ANL is supported by the U.S. Department of Energy, Divi-sion of High Energy Physics, under Contract W-31 -109-ENG-38. M.K. is supported by the13undesministerium fiir Blldung und Forschung under Contract 05 HT9GIJA 3, by DeutscheForschungsgemeinschaft under Contract KL 1266/1-1, and by the European Commission underContract ERBFMRXCT980194.,.0.05 ,,pp + a: m 4s = 2.0 ‘revI‘, ~0.045 1-“ — NLO 4.s‘s j0.04. . . . .‘> LO‘.‘,‘.0.035 ‘.‘.~ ‘.‘,js 0.03 ‘.\o0.025‘w :&:0.015 . . . . . . . . . ------0.01 I 1...10-’ 102 It&+q1.31.21.10.80.70.6~ ““’...\jL-xFigure 3: Dependence of the total j~~ cross section in the SUGRA model on the common renormalization andfactorization scale p. The LO dependence is reduced considerably in NLO.References1. S. Abel et IZL [SUGRA Working Group Collaboration], hep-ph/OO03154.2. E. L. Berger, B. Harris, M. Klasen and T. Tait, hep-ph/9903237.3. E. L. Berger, M. Klasen and T. Tait, Phys. Rev. D59 (1999) 074024 [hepph/9807230].4. W. Beenakker, M. Klasen, M. Kramer, T. Plehn, M. Spira and P. M. Zerwa.s, Phys. Rev.Lett. 83 (1999) 3780 [hepph/9906298].5. E. L. Berger, M. Kla.sen and T. Tait, Phys. Lett. B459 (1999) 165 [hep-ph/9902350].6. E. L. Berger, M. Klasen and T. Tait, ANL-HEP-PR-OO-045, DESY 00-069 [hep-ph/0005196].~m :m0.10.040.020 I I I I I Io 50 100 150 2(UI 250 303 350 4CQFigure 4:chargino.0.C0200310,-------- ..,/, ....,’ . .,’ . .. .. .. .. .. .. .. .. . . .I I I I I0501001502C025030G 350 4C0PT.; [Gevl P~,~ [GevlDependence of the cross section for cjjj~ in the SUGRA model on the transverse momentum of the lightThe NLO distributions are shifted to lower pT with respect to LO. At the LHC, the NLO enhancementis more prominent.

Predictions for associated production of gauginos and gluinos at NLO in SUSY-QCD

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