Resonant production of the first generation vector diquarks at the CERN Large
Hadron Collider (LHC) is investigated. It is shown that the LHC will be able to
discover vector diquarks with masses up to 9 TeV for quark-diquark-quark
coupling alpha_(D)=0.1 and 4 TeV for alpha_(D)=5x10^(-4).Comment: 9 pages, 4 tables, 4 figure

ATLAS collaboration

D. Schaile

Engin Arik

I.A. D'Souza

Orhan Çakir

S. Ata?

S. Sultansoy

Saleh Sultansoy

Serkant A Çetin

T.G. Rizzo

English

arXiv

Crossref

A Search for Vector Diquarks at the CERN LHC

Resonant production of the first generation vector diquarks at the CERN Large Hadron Collider (LHC) have been investigated. It is shown that the LHC will be able to discover vector diquarks with masses up to 9 (8) TeV if coupling alpha_(D)~alpha_(s) (alpha_(em))

Arik, E

Cakir, O

Cetin, S A

Sultansoy, S F

CERN Document Server

A Search for Vector Diquarks at the CERN LHCE. Arika, O. Cakrb, S. A. Cetina and S. Sultansoyc,da Bogazici University, Faculty of Sciences, Department of Physics,80815, Bebek, Istanbul, Turkeyb Ankara University, Faculty of Sciences, Department of Physics,06100 Tandogan, Ankara, Turkeyc Gazi University, Faculty of Arts and Sciences, Department of Physics,06500, Teknikokullar, Ankara, Turkeyd Azerbaijan Academy of Sciences, Institute of Physics,H. Cavid av., 33, Baku, AzerbaijanResonant production of the rst generation vector diquarks at theCERN Large Hadron Collider (LHC) have been investigated. It is shownthat the LHC will be able to discover vector diquarks with masses upto 9 (8) TeV if coupling αD ’ αs(αem).I. INTRODUCTIONThe existence of at least three fermion families naturally leads to the hypothesis thatthey are made up of more fundamental constituents frequently called preons [1]. Today, thecompositeness should be considered as a candidate for beyond the standard model (BSM)physics on the same footing as SUSY. Moreover, some assumptions made in order to getrid of huge number of free parameters in three family MSSM have natural explanation (see[2] and references therein) in the framework of preonic models. These models predict arich spectrum of new particles with unusual quantum numbers at high energies such asexcited quarks and leptons, diquarks, dileptons, leptoquarks, leptogluons, sextet quarks,octet bosons etc. In preonic models, diquarks are as natural as leptoquarks [3]. Theyare colored objects having integer-spin and baryon number jBj = 2=3. Diquarks are alsopredicted in the framework of superstring-inspired E6 models [4].Recent collider limits on the diquark masses come from Tevatron data which exclude theregion 290 < M <420 GeV (for E6 diquarks) [5]. Diquark production at e+e− colliders, epcolliders and pp colliders have been analyzed in [6], [7] and [8], respectively. Recently, theresonance production of scalar diquarks at CERN LHC has been studied in [9].In this work, the sensitivity of LHC to composite vector diquark production is estimated.In section II, interaction lagrangian and quantum numbers of diquarks are discussed. Decaywidth and production cross section of a vector diquark at the CERN LHC are considered insection III. Then, in section IV, vector diquark signal and corresponding backgrounds areanalyzed. Finally, in section V we give some conclusions and remarks.II. INTERACTION LAGRANGIAN AND CLASSIFICATIONA model independent, most general, eective SU(3)C  SU(2)W  U(1)Y invariant la-grangian for diquarks has the form [9]:L= g1LqcLi2qLDc1 + g1RucRdRDc1 + ~g1R dcRdR~Dc1 + ~g01RucRuR~D0c1 + g3LqcLi2~qL:~Dc3+g2DcT2µ dcRi2γµqL + ~g2 ~DcT2µ ucRi2γµqL + h:c: (1)where qL = (uL; dL) and qc = CqT (qc = −qT C−1). For the sake of simplicity, color andgeneration indices are ommitted. Scalar diquarks D1, ~D1, ~D01 are SU(2)W singlets and ~D3 isSU(2)W triplet. Vector diquarks D2 and ~D2 are SU(2)W doublets. Diquarks may transformas anti-triplet or sextet under SU(3)C . At this stage, we assume each SM generation hasits own diquarks and couplings in order to avoid restrictions imposed by mK etc.Lagrangian (1) can be rewritten in the following more transparent form:1L = LS + LV (2)LS =g1L(ucPLd− dcPLu+ g1RucPRdD1 + ~g1R dcPRd ~D1 + ~g01RucPRu ~D01+p2g3LucPLuD+3 −p2g3L dcPLdD−3 − g3L(ucPLd + dcPLuD03 + h:c: (3)LV = g2 dcγµPLdD12µ − g2 dcγµPLuD22µ + ~g2ucγµPLd ~D12µ − ~g2ucγµPLu ~D22µ + h:c: (4)where PL = (1− γ5)=2 and PR = (1 + γ5)=2. A general classication of the rst generation,color 3¯ diquarks is shown in Table I.III. DECAY WIDTH AND PRODUCTION CROSS SECTIONFor the present analysis, we will take into account the color 3¯ vector diquark D2 whichcouples to ud-pair as described by the eective lagrangian (4). The decay width ΓD, derivedfrom the same lagrangian, isΓD = CFg22MD24(5)where CF is the color factor for triplet representation and MD is the mass of vector diquark.We will use the denition g22 = 4D for numerical calculations:ΓD = CFDMD6’ 17 GeV (CF MD1 TeV) for D = 0:1 ’ s (6)’ 1:3 GeV (CF MD1 TeV) for D ’ em : (7)In the narrow width approximation (Γ=M < 0:1), the cross section of the s-channeldiquark resonance production can be obtained as(pp ! D2X) =XabC2F D2sZ 1M2D/sdxxfa(x; s^)fb(M2Dsx; s^) (8)where s^ = xaxbs, fa and fb are quark distribution functions of each proton. In Fig. 1,using the CTEQ5L quark distribution functions [10], the cross section versus diquark massis plotted for coupling D = s and D = em at the LHC energy (ps = 14 TeV).IV. SIGNAL AND BACKGROUNDD2-type diquark resonance in s-channel will be formed via the subprocess u + d ! D2 !u + d. Therefore, the signal will contain two hard jets in the nal state. Considering onlythe interference with the t-channel gluon exchange, the following dierential cross section isobtained:d^dt^(qiqj ! qiqj) = C2F [2D(s^ + t^)2s^2[(s^−M2D)2 + M2DΓ2D]+22ss^2(2s^2 + t^2 + 2s^t^)t^2− 2Dst^(s^ + t^)2(s^−M2D)s^2[(s^−M2D)2 + M2DΓ2D]] : (9)At the LHC, QCD processes contributing to two jet nal states and their integrated crosssections are given in Table II. The values in Table II have been generated by PYTHIA 6.1[11] at parton level with various pT cuts.The cross section as a function of the dijet invariant mass Mjj with the rapidity cutjy1,2j  Y , where y1 and y2 are rapidities of the massless nal quarks, is given by2ddMjj=M3jj2sZ Y−Ydy2Z ymax1ymin1dy11cosh2 y?(10)[fu/A(xu; Q2)fd/B(xd; Q2)d^dt^(s^; t^; u^)+fd/A(xd; Q2)fu/B(xu; Q2)d^dt^(s^; u^; t^)]withy? = (y1 − y2)=2; yb = (y1 + y2)=2xu =peyb; xd =pe−ybs^ = xuxds; t^ = −xupTpse−y1 ; u^ = −xdpTpsey1ymin1 = max(−Y; log  − y2); ymax1 = min(Y;− log  − y2);  = M2jj=s :Fig. 2 shows jet-jet invariant mass distribution for the process pp ! D2 ! jjX togetherwith the estimation of the QCD background at the LHC. For comparison, signal peaksfor vector diquark masses MD = 2; 4; 6; 8 TeV and D = 0:1 are superimposed on thebackground distribution.We have estimated signal and background events for an integrated LHC luminosity of105 pb−1 taking into account, as an example, the energy resolution of ATLAS hadroniccalorimeter [12]:EE=50%pE+ 3% (11)for jets with jyj < 3. The mass resolution can be expressed as [9]MjjMjj Ep2E: (12)We have chosen 2Mjj as the mass window centered at Mjj for signal and backgroundestimations.Number of signal (S), background (B) events and the corresponding signicances forD = 0:1 are tabulated in Table III. Evidently, tighter cut on the rapidity y improves thesignicance considerably. In Table IV, we present the achievable mass limits for dierentvalues of D. As discovery criteria, we adopt S=pB  5 and S  25.V. CONCLUSIONSThe example of D2 shows that the resonance production of vector diquarks at the LHChas large cross section. With reasonable cuts, it may be possible to cover the region up to9 TeV. The LHC potential for the discovery of D2 is clearly demonstrated in Fig. 3 whereminimum integrated luminosities, needed to satisfy the adopted criteria, are plotted as afunction of MD for various D values.3VI. REFERENCES[1] H. Terazawa, Phys. Rev. 22 (1980) 184; H. Harari, Phys. Rep. 104 (1984) 159; D’Souza andKalman, Preons, World Scientic Publishing, (1992).[2] S. Sultansoy, hep-ph/0003269 (2000).[3] J. Wudka, Phys. Lett. B167 (1986) 337.[4] J.L. Hewett and T.G. Rizzo, Phys. Rep. 183 (1989) 193.[5] F. Abe et al., CDF Collaboration, Phys. Rev. Lett. 77 (1996) 5336; B. Abbott et al., D0Collaboration, Phys. Rev.. Lett. 80 (1998) 666.[6] D. Schaile and P.M. Zerwas: Proceedings of the Workshop on Physics at Future Accelerators,CERN Yellow Report 87-07, Vol. II, p.251 (1987).[7] T.G. Rizzo, Z. Phys. C43 (1989) 223.[8] V.D. Angelopoulos et al., Nucl. Phys. B292, 59 (1987).[9] S. Atag, O. Cakr, and S. Sultansoy, Phys. Rev. D59, 015008 (1998).[10] CTEQ Collaboration, H.L. Lai et al., Eur. Phys. J. C12 (2000) 375.[11] Torbjo¨rn Sjo¨strand et al., hep-ph/0010017 (2000).[12] ATLAS Collaboration, ATLAS TDR 14, CERN/LHCC 99-14 (1999).4TABLE I. Quantum numbers of the rst generation, color 3 diquarks described by the eectivelagrangian given in the text according to SU(3)C  SU(2)W U(1)Y invariance. Qem = I3 + Y/2Scalar Diquarks SU(3)C SU(2)W U(1)Y Q CouplingsD1 3? 1 2/3 1/3 uLdL(g1L), uRdR(g1R)~D1 3? 1 -4/3 4/3 dRdR(~g1R)~D01 3? 1 8/3 -2/3 uRuR(~g01R)D3 3? 3 2/3 4/31/3−2/3! 0@ uLuL(p2g3L)uLdL(−g3L)dLdL(−p2g3L)1AVector DiquarksD2µ 3? 2 -1/34/31/3 dRdL(g2)dRuL(−g2)~D2µ 3? 2 5/34/31/3 uRdL(~g2)uRuL(−~g2)TABLE II. Cross sections (pb) for QCD backgrounds contributing to j-j nal states at partonlevel generated by PYTHIA 6.1 with various cuts.Process pT > 100 GeV pT > 500 GeV pT > 1000 GeV pT > 1500 GeV pT > 2000 GeVgg ! gg 6.3105 2.0102 2.3100 8.610−2 5.710−3qig ! qig 6.4105 4.8102 1.0101 6.410−1 5.710−2qiqj ! qiqj 1.0105 1.8102 6.7100 6.310−1 8.810−2gg ! qk qk 2.4104 9.8100 1.010−1 4.910−3 2.910−4qiqi ! qk qk 1.6103 2.8100 1.310−1 9.010−3 1.110−3qiqi ! gg 1.5103 2.5100 6.710−2 8.110−3 8.510−4Total 1.4106 8.8102 1.9101 1.4100 1.510−1TABLE III. Observability of the vector diquark D2 with αD = 0.1 at LHC for Lint = 105pb−1.MD (TeV) 1 2 3 4 5 6 7 8 9jyj < 2S 7.7107 6.6106 1.1106 2.4105 5.0104 9.9103 1.7103 2.5102 2.7101B 2.8108 5.6106 4.2105 5.4104 8.4103 1.4103 2.2102 3.0101 3.1100S/pB 4585 2787 1768 1027 545 266 118 46 16jyj < 1S 2.6107 2.8106 5.8105 1.3105 2.9104 6.1103 1.1103 1.6102 1.8101B 2.5107 5.2105 4.0104 5.0103 7.9102 1.3102 2.1101 2.8100 3.010−1S/pB 5213 3946 2889 1842 1044 534 245 99 34TABLE IV. Achievable diquark mass limits for dierent diquark-quark-quark couplings in theframework of discovery criteria given in the text. The rapidity cut jyj < 2 is applied.αD MD(TeV) S B S/pB0.1 9 27 3.1 16.00.01 8 25 30 4.60.001 5 500 8400 5.40.0005 4 1200 540006 5.1510-510-410-310-210-11001011021031000 2000 3000 4000 5000 6000 7000 8000 9000 10000σ(pb)MV(GeV)√s=14 TeVαD=αsαD=αemFIG. 1. Integrated cross section versus diquark mass for coupling strength αD = αs andαD = αem.10-810-710-510-410-310-210-11001011000 2000 3000 4000 5000 6000 7000 8000 9000dσ/dMjj(pb/GeV)Mjj(GeV)√s=14 TeVαD=0.1|y|<2QCD B2 TeV4 TeV6 TeV8 TeVFIG. 2. Dijet invariant mass distribution for MD = 2, 4, 6, 8 TeV superimposed over the QCDbackground.6FIG. 3. The minimum integrated luminosities, needed to satisfy the adopted discovery criteria,as a function of MD for various αD values.7

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A Search for Vector Diquarks at the CERN LHC

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