application/xmlSearch for R-parity violating decays of supersymmetric particles in e+e− collisions at LEPL3 CollaborationP. AchardO. AdrianiM. Aguilar-BenitezJ. AlcarazG. AlemanniJ. AllabyA. AloisioM.G. AlviggiH. AnderhubV.P. AndreevF. AnselmoA. ArefievT. AzemoonT. AzizP. BagnaiaA. BajoG. BaksayL. BaksayS.V. BaldewS. BanerjeeSw. BanerjeeA. BarczykR. BarillèreP. BartaliniM. BasileN. BatalovaR. BattistonA. BayF. BecattiniU. BeckerF. BehnerL. BellucciR. BerbecoJ. BerdugoP. BergesB. BertucciB.L. BetevM. BiasiniM. BigliettiA. BilandJ.J. BlaisingS.C. BlythG.J. BobbinkA. BöhmL. BoldizsarB. BorgiaS. BottaiD. BourilkovM. BourquinS. BracciniJ.G. BransonF. BrochuA. BuijsJ.D. BurgerW.J. BurgerX.D. CaiM. CapellG. Cara RomeoG. CarlinoA. CartacciJ. CasausF. CavallariN. CavalloC. CecchiM. CerradaM. ChamizoY.H. ChangM. ChemarinA. ChenG. ChenG.M. ChenH.F. ChenH.S. ChenG. ChiefariL. CifarelliF. CindoloI. ClareR. ClareG. CoignetN. ColinoS. CostantiniB. de la CruzS. CucciarelliJ.A. van DalenR. de AsmundisP. DéglonJ. DebreczeniA. DegréK. DeitersD. della VolpeE. DelmeireP. DenesF. DeNotaristefaniA. De SalvoM. DiemozM. DierckxsensD. van DierendonckC. DionisiM. DittmarA. DoriaM.T. DovaD. DuchesneauP. DuinkerB. EchenardA. ElineH. El MamouniA. EnglerF.J. EpplingA. EwersP. ExtermannM.A. FalaganS. FalcianoA. FavaraJ. FayO. FedinM. FelciniT. FergusonH. FesefeldtE. FiandriniJ.H. FieldF. FilthautP.H. FisherW. FisherI. FiskG. ForconiK. FreudenreichC. FurettaYu. GalaktionovS.N. GanguliP. Garcia-AbiaM. GataullinS. GentileS. GiaguZ.F. GongG. GrenierO. GrimmM.W. GruenewaldM. GuidaR. van GulikV.K. GuptaA. GurtuL.J. GutayD. HaasD. HatzifotiadouT. HebbekerA. HervéJ. HirschfelderH. HoferM. HohlmannG. HolznerS.R. HouY. HuB.N. JinL.W. JonesP. de JongI. Josa-Mutuberrı́aD. KäferM. KaurM.N. Kienzle-FocacciJ.K. KimJ. KirkbyW. KittelA. KlimentovA.C. KönigM. KopalV. KoutsenkoM. KräberR.W. KraemerW. KrenzA. KrügerA. KuninP. Ladron de GuevaraI. LaktinehG. LandiM. LebeauA. LebedevP. LebrunP. LecomteP. LecoqP. Le CoultreJ.M. Le GoffR. LeisteP. LevtchenkoC. LiS. LikhodedC.H. LinW.T. LinF.L. LindeL. ListaZ.A. LiuW. LohmannE. LongoY.S. LuK. LübelsmeyerC. LuciL. LuminariW. LustermannW.G. MaL. MalgeriA. MalininC. MañaD. MangeolJ. MansJ.P. MartinF. MarzanoK. MazumdarR.R. McNeilS. MeleL. MerolaM. MeschiniW.J. MetzgerA. MihulH. MilcentG. MirabelliJ. MnichG.B. MohantyG.S. MuanzaA.J.M. MuijsB. MusicarM. MusyS. NagyS. NataleM. NapolitanoF. Nessi-TedaldiH. NewmanT. NiessenA. NisatiH. NowakR. OfierzynskiG. OrgantiniC. PalomaresD. PandoulasP. PaolucciR. ParamattiG. PassalevaS. PatricelliT. PaulM. PauluzziC. PausF. PaussM. PedaceS. PensottiD. Perret-GallixB. PetersenD. PiccoloF. PierellaM. PioppiP.A. PirouéE. PistolesiV. PlyaskinM. PohlV. PojidaevJ. PothierD.O. ProkofievD. ProkofievJ. QuartieriG. Rahal-CallotM.A. RahamanP. RaicsN. RajaR. RamelliP.G. RancoitaR. RanieriA. RasperezaP. RazisD. RenM. RescignoS. ReucroftS. RiemannK. RilesB.P. RoeL. RomeroA. RoscaS. Rosier-LeesS. RothC. RosenbleckB. RouxJ.A. RubioG. RuggieroH. RykaczewskiA. SakharovS. SaremiS. SarkarJ. SalicioE. SanchezM.P. SandersC. SchäferV. SchegelskyS. Schmidt-KaerstD. SchmitzH. SchopperD.J. SchotanusG. SchweringC. SciaccaL. ServoliS. ShevchenkoN. ShivarovV. ShoutkoE. ShumilovA. ShvorobT. SiedenburgD. SonP. SpillantiniM. SteuerD.P. SticklandB. StoyanovA. StraessnerK. SudhakarG. SultanovL.Z. SunS. SushkovH. SuterJ.D. SwainZ. SzillasiX.W. TangP. TarjanL. TauscherL. TaylorB. TelliliD. TeyssierC. TimmermansSamuel C.C. TingS.M. TingS.C. TonwarJ. TóthC. TullyK.L. TungJ. UlbrichtE. ValenteR.T. Van de WalleV. VeszpremiG. VesztergombiI. VetlitskyD. VicinanzaG. ViertelS. VillaM. VivargentS. VlachosI. VodopianovH. VogelH. VogtI. VorobievA.A. VorobyovM. WadhwaW. WallraffX.L. WangZ.M. WangM. WeberP. WienemannH. WilkensS. WynhoffL. XiaZ.Z. XuJ. YamamotoB.Z. YangC.G. YangH.J. YangM. YangS.C. YehAn. ZaliteYu. ZaliteZ.P. ZhangJ. ZhaoG.Y. ZhuR.Y. ZhuH.L. ZhuangA. ZichichiG. ZiliziB. ZimmermannM. ZöllerPhysics Letters B 524 (2002) 65-80. doi:10.1016/S0370-2693(01)01367-3journalPhysics Letters BCopyright © 2002 Elsevier Science B.V. All rights reserved.Elsevier B.V.0370-26935241-23 January 20022002-01-0365-80658010.1016/S0370-2693(01)01367-3http://dx.doi.org/10.1016/S0370-2693(01)01367-3doi:10.1016/S0370-2693(01)01367-3http://vtw.elsevier.com/data/voc/oa/OpenAccessStatus#Full2014-01-01T00:14:32ZSCOAP3 - Sponsoring Consortium for Open Access Publishing in Particle Physicshttp://vtw.elsevier.com/data/voc/oa/SponsorType#FundingBodyhttp://creativecommons.org/licenses/by/3.0/

Journals

S300.3

PLB18179S0370-2693(01)01367-310.1016/S0370-2693(01)01367-3Elsevier Science B.V.Experiments

Fig. 1

Data and Monte Carlo distributions of (a) the number of leptons, (b) thrust, (c) the normalised visible energy and (d) ln(y34) after the λijk preselection. The solid histograms show the expectations for Standard Model processes. The dotted and dashed histograms show two examples of signal, with dominant coupling λ133. The dotted histograms represent the process e+e−→χ̃01χ̃01, for Mχ̃01=42 GeV, corresponding to two hundred times the luminosity of the data. The dashed ones represent e+e−→χ̃+1χ̃−1, with Mχ̃±1=92 GeV and ΔM=Mχ̃±1−Mχ̃01=50 GeV, corresponding to twenty times this luminosity.

Fig. 2

Data and Monte Carlo distributions of (a) thrust, (b) ln(y34), (c) ln(y45) and (d) width of the most energetic jet after the λ″ijk preselection. The solid histograms show the expectations for Standard Model processes. The dashed and dotted histograms show two examples of signal, with dominant coupling λ″212, corresponding to decays into c, d and s quarks. The dotted histograms represent the process e+e−→χ̃01χ̃01, with Mχ̃01=40 GeV, corresponding to one hundred times the luminosity of the data. The dashed ones represent e+e−→χ̃+1χ̃−1, with Mχ̃±1=90 GeV and ΔM=Mχ̃±1−Mχ̃01=60 GeV, corresponding to fifteen times this luminosity.

Fig. 3

MSSM exclusion contours, at 95% C.L., for the masses of (a) ẽR, (b) μ̃R, (c) τ̃R and (d) ν̃μ,τ as a function of the neutralino mass. The solid and dashed lines, show the λ and λ″ exclusion contours, respectively. The dotted line corresponds to ΔM=0. For ΔM<0, above this line, the exclusion contours from direct decays are shown.

Fig. 4

MSSM exclusion contours, at 95% C.L., for the masses of (a) up-type (b) down-type scalar quarks (c) b̃1 and (d) t̃1 as a function of the neutralino mass, for λ″ coupling. The solid and dashed lines show the exclusion contours for (a) ũL, ũR and (b) d̃L, d̃R, respectively. For ΔM<0, above the dotted line, the exclusion contours from direct decays are shown.

Fig. 5

MSSM mass limits from combined analyses. The solid and dashed lines, labelled with the corresponding coupling, show the 95% C.L. lower limits on the masses of (a) χ̃01, (b) χ̃02 and (c) ℓ̃R, as a function of tanβ, for 0⩽M2⩽1000 GeV and −500 GeV⩽μ⩽500 GeV. m0=500 GeV in (a) and (b) and m0=0 in (c). For those values of m0 the global minima on the mass limit are obtained.

Table 1

R-parity violating decays of the supersymmetric particles considered in this analysis. Charged conjugate states are implied. Indirect decays via scalar leptons are relevant only for neutralinos when the scalar lepton is the LSP. Only supersymmetric partners of the right-handed charged leptons are taken into account. Decays to more than three fermions are not listed. Z∗ and W∗ indicate virtual Z and W bosons

ParticleDirect decaysIndirect decaysλijkλ″ijkvia χ̃10via ℓ̃χ̃01ℓi−νjℓk+, νiℓ+jℓ−kūid̄jd̄k−ℓℓ̃χ̃0n (n⩾2)ℓi−νjℓk+, νiℓ+jℓ−kūid̄jd̄kZ∗χ̃0m (m<n),ℓℓ̃W∗χ̃±1χ̃+1νiνjℓ+k, ℓ+iℓ+jℓ−kd̄id̄jd̄k, uiujdk,W∗χ̃01, W∗χ̃02uidjukℓ̃−kRνiℓ−j, νjℓ−i−ℓ−kχ̃01−ν̃i, ν̃jℓ−jℓ+k, ℓ−iℓ+k−νiχ̃01, νjχ̃01ũiR−d̄jd̄kuiχ̃01−d̃jR,d̃kR−ūid̄k, ūid̄jdjχ̃01,dkχ̃01−Table 2

Processes considered in the λijk analysis and corresponding selections [11]. χ̃0mχ̃0n indicates neutralino pair-production with m=1,2 and n=1,…,4. “Cascades” refers to all possible final state combinations of Table 1

Direct decaysSelectionse+e−→χ̃0mχ̃0n→ℓℓℓℓνν4ℓ+E/e+e−→χ̃+1χ̃−1→ℓℓℓℓℓℓ6ℓℓℓℓℓνν4ℓ+E/ℓℓνννν2ℓ+E/e+e−→ℓ̃+Rℓ̃−R→ℓνℓν2ℓ+E/e+e−→ν̃ν̃→ℓℓℓℓ4ℓ+E/Indirect decaysSelectionse+e−→χ̃0mχ̃0n(n⩾2)→ cascades⩾4ℓ+(jets)+E/e+e−→χ̃+1χ̃−1→χ̃1(2)0χ̃1(2)0W∗W∗⩾4ℓ+(jets)+E/e+e−→ℓ̃+Rℓ̃−R→ℓℓℓℓℓℓνν⩾4ℓ+(jets)+E/e+e−→ν̃ν̃→ℓℓℓℓνννν4ℓ+E/Table 3

Efficiency values (ϵ, in %) and 95% C.L. cross section upper limits (σ, in pb) for direct decays of the supersymmetric particles, as a function of their mass (M, in GeV). As an example the efficiencies at s=206 GeV are shown, for the most conservative choice of the couplings. At the other centre-of-mass energies they are compatible within the uncertainties. Typical relative errors on the signal efficiencies, due to Monte Carlo statistics, are between 2% and 5%. χ̃0mχ̃0n indicates neutralino pair-production with m=1,2 and n=1,…,4. For direct neutralino decays we quote the χ̃01χ̃01 efficiencies. The upper limits on the pair-production cross sections are calculated using the full data sample, with a total luminosity of 627 pb−1, except for the last mass point, where only the data collected at s⩾204 GeV are used, corresponding to a luminosity of 216 pb−1. Chargino and scalar lepton pair-production via λijk couplings are not investigated for mass values excluded in Ref. [11]. For the processes marked with ∗ we refer to four-body decays, as described in Section 4

CouplingProcessM30405060708090102Direct decaysλ133χ̃0mχ̃0nϵ1524323740424546σ0.070.050.040.030.030.030.020.07λ133χ̃+1χ̃−1ϵ––––38404343σ––––0.070.060.060.17λ12kℓ̃+Rℓ̃−Rϵ––––6686σ––––0.390.360.271.16λ121ν̃ν̃ϵ––––6875σ––––0.200.150.170.68λ″212χ̃0mχ̃0n, χ̃+1χ̃−1ϵ3949404442434656σ0.110.100.080.120.120.110.100.18λ″212ẽ+Rẽ−R ∗, μ̃+Rμ̃−R ∗ϵ3949404442434656σ0.110.100.080.120.120.110.100.18λ″212τ̃+Rτ̃−R ∗ϵ3949384442191413σ0.110.100.150.120.110.180.220.28λ″212ν̃ν̃ ∗ϵ714292121222556σ0.660.160.130.180.180.170.150.18λ″212q̃q̃ϵ2726223231343434σ0.100.130.070.050.280.270.160.13Table 4

Efficiency values (ϵ, in %) and 95% C.L. cross section upper limits (σ, in pb) for indirect decays of the supersymmetric particles, as a function of ΔM (in GeV). As an example the efficiencies at s=206 GeV are shown, for the most conservative choice of the couplings. At the other centre-of-mass energies they are compatible within the uncertainties. Typical relative errors on the signal efficiencies, due to Monte Carlo statistics, are between 2% and 5%. χ̃0mχ̃0n indicates neutralino pair-production with m=1,2 and n=2,…,4. The efficiencies correspond to Mχ̃0m+Mχ̃0n=206 GeV. For indirect decays of charginos, scalar leptons and scalar quarks, the selection efficiencies correspond to a mass of 102 GeV. The upper limits on the pair-production cross sections are calculated using the data at s⩾204 GeV, with an integrated luminosity of 216 pb−1

CouplingProcessΔM102030405060708090100Indirect decaysλ133χ̃0mχ̃0n(n⩾2)ϵ49484847454341383635σ0.090.090.090.090.100.100.110.120.120.13λ133χ̃+1χ̃−1ϵ47433934312520–––σ0.080.090.100.110.120.150.18–––λ133ẽ+Rẽ−Rϵ61626354463524–––σ0.060.060.060.070.080.110.15–––λ133μ̃+Rμ̃−Rϵ71768077757065–––σ0.050.050.050.050.050.050.06–––λ133τ̃+Rτ̃−Rϵ52596665646056–––σ0.070.060.060.060.060.060.07–––λ133ν̃ν̃ϵ50494943413936–––σ0.070.070.070.080.080.090.10–––λ″212χ̃0mχ̃0n(n⩾2)ϵ57606368666462585446σ0.180.170.160.150.150.160.170.180.200.23λ″212χ̃+1χ̃−1ϵ65706973727071–––σ0.160.150.150.140.150.150.15–––λ″212ẽ+Rẽ−Rϵ295156636669564636–σ0.180.090.050.050.050.050.050.060.08–λ″212μ̃+Rμ̃−Rϵ202841495255524227–σ0.100.050.050.050.050.050.050.060.09–λ″212τ̃+Rτ̃−Rϵ535763564640291713–σ0.150.130.130.130.150.160.220.230.24–λ″212ν̃ν̃ϵ414344393732405035–σ0.130.120.120.120.140.150.080.110.12–λ″212q̃q̃ϵ555964656358474543–σ0.180.160.150.150.160.170.220.220.23–Table 5

Processes considered in the λ″ijk analysis and corresponding selections [11]. For masses below 50 GeV or small ΔM values not all jets in the event can be resolved. χ̃0mχ̃0n indicates neutralino pair-production with m=1,2 and n=1,…,4. For final states with neutrinos we use selections with no explicit missing energy requirement, because for those topologies E/ is small, except for the scalar neutrino decays

Direct decaysSelectionse+e−→χ̃0mχ̃0n→qqqqqqmultijetse+e−→χ̃+1χ̃−1→qqqqqqmultijetsIndirect decaysSelectionse+e−→χ̃0mχ̃0n(n⩾2)→qqqqqq qqmultijetsqqqqqq ℓℓmultijets+lepton(s)qqqqqq ννmultijetse+e−→χ̃+1χ̃−1→qqqqqq qqqqmultijetsqqqqqq qq ℓνmultijets+lepton(s)qqqqqq ℓℓννmultijets+lepton(s)e+e−→ℓ̃+Rℓ̃−R→qqqqqq ℓℓ6 jets+2ℓe+e−→ν̃ν̃→qqqqqq νν6 jets+E/e+e−→q̃q̃→qqqqqq qqmultijetsTable 6

Number of observed data (Ndata) and expected background (Nback) events for the different selections in the sample at s=192–208 GeV. A process can give rise to several topologies, or the same topology may occur for more than a final state. The uncertainty on the expected background is due to Monte Carlo statistics. The deficit in the number of observed data in the multijet and scalar lepton λ″ijk selections is correlated among the channels

CouplingSelectionNbackNdataλijk4ℓ+E/4.9±0.56(⩾4)ℓ+ (jets) +E/10.1±0.3102ℓ+E/31±2346ℓ0.85±0.091λ″ijkMultijets (Mχ̃01=30–40 GeV)146±2147Multijets (Mχ̃01=40–50 GeV)100±2109Multijets446±3404Multijets+lepton(s) (semileptonic)11.8±0.79Multijets+lepton(s) (leptonic)6.1±0.756 jets+2 leptons413±23616 jets+E/671±66694 jets3387±133411Table 7

Number of observed data (Ndata) and expected background (Nback) events for the different processes in the sample at s=192–208 GeV. Details on the selection of each topology are given in Table 6. The uncertainty on the expected background is due to Monte Carlo statistics. The deficit in the number of observed data in the neutralino, chargino and slepton λ″ijk analyses is correlated among the channels

CouplingProcessNbackNdataλijkχ̃01χ̃014.9±0.56χ̃0mχ̃0n14.7±0.615χ̃+1χ̃−1 (indirect)10.1±0.310χ̃+1χ̃−1 (direct)37±340ℓ̃+Rℓ̃−R (indirect)10.1±0.310ℓ̃+Rℓ̃−R (direct)31±234ν̃ν̃4.9±0.56λ″ijkχ̃01χ̃01661±4605χ̃+1χ̃−1446±3404ℓ̃+Rℓ̃−R413±2361ν̃ν̃671±6669q̃q̃3387±133411Table 8

Lower limits at 95% C.L. on the masses of the scalar leptons and scalar quarks. The limits result from direct comparison of the 95% C.L. cross section upper limits with the scalar particle pair-production cross sections. ũR, ũL, d̃R and d̃L refer to any type of up and down supersymmetric partners of the right-handed and left-handed quarks. t̃1 and b̃1 limits are quoted in the case of minimal production cross section. For λ″ijk direct decays of scalar leptons we refer to four-body processes

CouplingMass limit (GeV)MẽRMμ̃RMτ̃RMν̃μ,τMν̃eMũRMũLMd̃RMd̃LMt̃1Mb̃1λijk (direct)6961616595––––––λijk (indirect)7987867899––––––λ″ijk (direct)9686757099808756867755λ″ijk (indirect)9686757099798755867748Table 9

Lower limits at 95% C.L. on the masses of the supersymmetric particles considered in this analysis. The limits result from combined analysis at each MSSM point and from a global scan in the parameter space, as detailed in Section 6. The limits on Mℓ̃R hold for ẽR, μ̃R and τ̃R

CouplingMass limit (GeV)Mχ̃01Mχ̃02Mχ̃03Mχ̃±1Mℓ̃RMν̃λijk40.284.0107.2103.082.7152.7λ″ijk39.980.0107.2102.788.7149.0Search for R-parity violating decays of supersymmetric particles in e+e− collisions at LEP

L3 Collaboration

Achard

Adriani

Aguilar-Benitez

Alcaraz

Alemanni

Allaby

Aloisio

M.G.

Alviggi

Anderhub

V.P.

Andreev

Anselmo

Arefiev

Azemoon

Aziz

Bagnaia

Bajo

Baksay

S.V.

Baldew

Banerjee

Sw.

Banerjee

Barczyk

Barillère

Bartalini

Basile

Batalova

Battiston

Bay

Becattini

Becker

Behner

Bellucci

Berbeco

Berdugo

Berges

Bertucci

B.L.

Betev

Biasini

Biglietti

Biland

J.J.

Blaising

S.C.

Blyth

G.J.

Bobbink

Böhm

Boldizsar

Borgia

Bottai

Bourilkov

Bourquin

Braccini

J.G.

Branson

Brochu

Buijs

J.D.

Burger

W.J.

Burger

X.D.

Cai

Capell

Cara Romeo

Carlino

Cartacci

Casaus

Cavallari

Cavallo

Cecchi

Cerrada

Chamizo

Y.H.

Chang

Chemarin

Chen

G.M.

Chen

H.F.

Chen

H.S.

Chen

Chiefari

Cifarelli

Cindolo

Clare

Coignet

Colino

Costantini

de la Cruz

Cucciarelli

J.A.

van Dalen

de Asmundis

Déglon

Debreczeni

Degré

Deiters

della Volpe

Delmeire

Denes

DeNotaristefani

De Salvo

Diemoz

Dierckxsens

van Dierendonck

Dionisi

Dittmar

Doria

M.T.

Dova

Duchesneau

Duinker

Echenard

Eline

El Mamouni

Engler

F.J.

Eppling

Ewers

Extermann

M.A.

Falagan

Falciano

Favara

Fay

Fedin

Felcini

Ferguson

Fesefeldt

Fiandrini

J.H.

Field

Filthaut

P.H.

Fisher

Fisk

Forconi

Freudenreich

Furetta

Yu.

Galaktionov

S.N.

Ganguli

Garcia-Abia

Gataullin

Gentile

Giagu

Z.F.

Gong

Grenier

Grimm

M.W.

Gruenewald

Guida

van Gulik

V.K.

Gupta

Gurtu

L.J.

Gutay

Haas

Hatzifotiadou

Hebbeker

Hervé

Hirschfelder

Hofer

Hohlmann

Holzner

S.R.

Hou

B.N.

Jin

L.W.

Jones

de Jong

Josa-Mutuberrı́a

Käfer

Kaur

M.N.

Kienzle-Focacci

J.K.

Kim

Kirkby

Kittel

Klimentov

A.C.

König

Kopal

Koutsenko

Kräber

R.W.

Kraemer

Krenz

Krüger

Kunin

Ladron de Guevara

Laktineh

Landi

Lebeau

Lebedev

Lebrun

Lecomte

Lecoq

Le Coultre

J.M.

Le Goff

Leiste

Levtchenko

Likhoded

C.H.

Lin

W.T.

Lin

F.L.

Linde

Lista

Z.A.

Liu

Lohmann

Longo

Y.S.

Lübelsmeyer

Luci

Luminari

Lustermann

W.G.

Malgeri

Malinin

Maña

Mangeol

Mans

J.P.

Martin

Marzano

Mazumdar

R.R.

McNeil

Mele

Merola

Meschini

W.J.

Metzger

Mihul

Milcent

Mirabelli

Mnich

G.B.

Mohanty

G.S.

Muanza

A.J.M.

Muijs

Musicar

Musy

Nagy

Natale

Napolitano

Nessi-Tedaldi

Newman

Niessen

Nisati

Nowak

Ofierzynski

Organtini

Palomares

Pandoulas

Paolucci

Paramatti

Passaleva

Patricelli

Paul

Pauluzzi

Paus

Pauss

Pedace

Pensotti

Perret-Gallix

Petersen

Piccolo

Pierella

Pioppi

P.A.

Piroué

Pistolesi

Plyaskin

Pohl

Pojidaev

Pothier

D.O.

Prokofiev

Quartieri

Rahal-Callot

M.A.

Rahaman

Raics

Raja

Ramelli

P.G.

Rancoita

Ranieri

Raspereza

Razis

Ren

Rescigno

Reucroft

Riemann

Riles

B.P.

Roe

Romero

Rosca

Rosier-Lees

Roth

Rosenbleck

Roux

J.A.

Rubio

Ruggiero

Rykaczewski

Sakharov

Saremi

Sarkar

Salicio

Sanchez

M.P.

Sanders

Schäfer

Schegelsky

Schmidt-Kaerst

Schmitz

Schopper

D.J.

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aI. Physikalisches Institut, RWTH, D-52056 Aachen, Germany11

Supported by the German Bundesministerium für Bildung, Wissenschaft, Forschung und Technologie.

, III. Physikalisches Institut, RWTH, D-52056 Aachen, Germany1bNational Institute for High Energy Physics, NIKHEF, and University of Amsterdam, NL-1009 DB Amsterdam, The NetherlandscUniversity of Michigan, Ann Arbor, MI 48109, USAdLaboratoire d'Annecy-le-Vieux de Physique des Particules, LAPP, IN2P3-CNRS, BP 110, F-74941 Annecy-le-Vieux Cedex, FranceeInstitute of Physics, University of Basel, CH-4056 Basel, SwitzerlandfLouisiana State University, Baton Rouge, LA 70803, USAgInstitute of High Energy Physics, IHEP, 100039 Beijing, PR China66

Supported by the National Natural Science Foundation of China.

hHumboldt University, D-10099 Berlin, Germany1iUniversity of Bologna, and INFN, Sezione di Bologna, I-40126 Bologna, ItalyjTata Institute of Fundamental Research, Mumbai (Bombay) 400 005, IndiakNortheastern University, Boston, MA 02115, USAlInstitute of Atomic Physics and University of Bucharest, R-76900 Bucharest, RomaniamCentral Research Institute for Physics of the Hungarian Academy of Sciences, H-1525 Budapest 114, Hungary22

Supported by the Hungarian OTKA fund under contract numbers T019181, F023259 and T024011.

nMassachusetts Institute of Technology, Cambridge, MA 02139, USAoPanjab University, Chandigarh 160 014, IndiapKLTE-ATOMKI, H-4010 Debrecen, Hungary33

Also supported by the Hungarian OTKA fund under contract number T026178.

qINFN, Sezione di Firenze, and University of Florence, I-50125 Florence, ItalyrEuropean Laboratory for Particle Physics, CERN, CH-1211 Geneva 23, SwitzerlandsWorld Laboratory, FBLJA Project, CH-1211 Geneva 23, SwitzerlandtUniversity of Geneva, CH-1211 Geneva 4, SwitzerlanduChinese University of Science and Technology, USTC, Hefei, Anhui 230 029, PR China6vUniversity of Lausanne, CH-1015 Lausanne, SwitzerlandwInstitut de Physique Nucléaire de Lyon, IN2P3-CNRS, Université Claude Bernard, F-69622 Villeurbanne, FrancexCentro de Investigaciones Energéticas, Medioambientales y Tecnologı́cas, CIEMAT, E-28040 Madrid, Spain44

Supported also by the Comisión Interministerial de Ciencia y Tecnologı́a.

yFlorida Institute of Technology, Melbourne, FL 32901, USAzINFN, Sezione di Milano, I-20133 Milan, ItalyaaInstitute of Theoretical and Experimental Physics, ITEP, Moscow, RussiaabINFN, Sezione di Napoli, and University of Naples, I-80125 Naples, ItalyacDepartment of Physics, University of Cyprus, Nicosia, CyprusadUniversity of Nijmegen and NIKHEF, NL-6525 ED Nijmegen, The NetherlandsaeCalifornia Institute of Technology, Pasadena, CA 91125, USAafINFN, Sezione di Perugia, and Università Degli Studi di Perugia, I-06100 Perugia, ItalyagNuclear Physics Institute, St. Petersburg, RussiaahCarnegie Mellon University, Pittsburgh, PA 15213, USAaiINFN, Sezione di Napoli, and University of Potenza, I-85100 Potenza, ItalyajPrinceton University, Princeton, NJ 08544, USAakUniversity of California, Riverside, CA 92521, USAalINFN, Sezione di Roma, and University of Rome “La Sapienza”, I-00185 Rome, ItalyamUniversity and INFN, Salerno, I-84100 Salerno, ItalyanUniversity of California, San Diego, CA 92093, USAaoBulgarian Academy of Sciences, Central Laboratory of Mechatronics and Instrumentation, BU-1113 Sofia, BulgariaapThe Center for High Energy Physics, Kyungpook National University, 702-701 Taegu, South KoreaaqUtrecht University and NIKHEF, NL-3584 CB Utrecht, The NetherlandsarPurdue University, West Lafayette, IN 47907, USAasPaul Scherrer Institut, PSI, CH-5232 Villigen, SwitzerlandatDESY, D-15738 Zeuthen, GermanyauEidgenössische Technische Hochschule, ETH Zürich, CH-8093 Zürich, SwitzerlandavUniversity of Hamburg, D-22761 Hamburg, GermanyawNational Central University, Chung-Li, Taiwan, ROCaxDepartment of Physics, National Tsing Hua University, Taiwan, ROC5

Also supported by CONICET and Universidad Nacional de La Plata, CC 67, 1900 La Plata, Argentina.

Editor: L. Rolandi

Abstract

A search, in e+e− collisions, for chargino, neutralino, scalar lepton and scalar quark pair-production is performed, without assuming R-parity conservation in decays, in the case that only one of the coupling constants λ or λ″ is non-negligible. No signal is found in data up to a centre-of-mass energy of 208 GeV. Limits on the production cross sections and on the masses of supersymmetric particles are derived.

Introduction

The most general superpotential of the Minimal Supersymmetric Standard Model (MSSM) [1], which describes a supersymmetric, renormalizable and gauge-invariant theory, with minimal particle content, includes the term WR [2,3]: (1)WR=λijkLiLjĒk+λ′ijkLiQjD̄k+λ″ijkŪiD̄jD̄k, where λijk, λ′ijk and λ″ijk denote the Yukawa couplings and i,j and k the generation indices; Li and Qi are the left-handed lepton- and quark-doublet superfields, Ēi, D̄i and Ūi are the right-handed singlet superfields for charged leptons, down- and up-type quarks, respectively. The LiLjĒk and LiQjD̄k terms violate the leptonic quantum number L, while the ŪiD̄jD̄k terms violate the baryonic quantum number B.R-parity is a multiplicative quantum number defined as: (2)R=(−1)3B+L+2S, where S is the spin. For ordinary particles R is +1, while it is −1 for their supersymmetric partners. R-parity conservation implies that supersymmetric particles can only be produced in pairs and then decay in cascade to the lightest supersymmetric particle (LSP), which is stable [4]. This hypothesis is formulated in order to prevent a fast proton decay [5], disfavoured by present limits [6]. However, the absence of either the B- or the L-violating terms is enough to prevent such a decay, and the hypothesis of R-parity conservation can be relaxed. As a consequence, two new kinds of processes are allowed: single production of supersymmetric particles [7,8], or LSP decays into Standard Model particles via scalar lepton or scalar quark exchange. For these decays, the MSSM production mechanisms are unaltered by the operators in Eq. (1). In this Letter the cases in which either a neutralino or a scalar lepton is the LSP are considered.In this Letter we describe the search for pair-produced neutralinos (e+e−→χ̃0mχ̃0n, with m=1,2 and n=1,…,4), charginos (e+e−→χ̃+1χ̃−1), scalar leptons (e+e−→ℓ̃+Rℓ̃−R, where ℓ̃±R represents scalar electrons, muons or tau and e+e−→ν̃ν̃) and scalar quarks (e+e−→q̃q̃) with subsequent R-parity violating decays, assuming that only one of the coupling constants λijk or λ″ijk is non-negligible. Only the supersymmetric partners of the right-handed charged leptons, ℓ̃R, are considered, as they are expected to be lighter than the corresponding left-handed ones.Supersymmetric particles can either decay directly into two or three fermions according to the dominant interaction term, or indirectly via the LSP. The different decay modes are detailed in Table 1

. Four-body decays of the lightest scalar lepton are also taken into account in the case of λ″ijk. In the present analysis, the dominant coupling is assumed to be greater than 10−5 [9], which corresponds to decay lengths below 1 cm.

Previous L3 results at centre-of-mass energies (s) up to 189 GeV are reported in Refs. [10] and [11], where also λ′ijk couplings are discussed. Two new analyses are presented in this letter: e+e−→ν̃ν̃ and e+e−→q̃q̃ in the case of λ″ijk couplings. New interpretations for scalar leptons and scalar quarks in the MSSM framework are also performed.Searches for R-parity violating decays of supersymmetric particles were also reported by other LEP experiments [8,12].2

Data and Monte Carlo samples

The data used correspond to an integrated luminosity of 450.6 pb−1 collected with the L3 detector [13] at s=192–208 GeV. For the search for scalar quarks and scalar neutrinos decaying via λ″ijk couplings, also the data sample collected at s=189 GeV is used. This corresponds to an additional integrated luminosity of 176.4 pb−1.The signal events are generated with the program SUSYGEN [14] for different mass values and for all possible choices of the generation indices.The following Monte Carlo generators are used to simulate Standard Model background processes: PYTHIA [15] for e+e−→Ze+e− and e+e−→ ZZ, BHWIDE [16] for e+e−→e+e−, KK2F [17] for e+e−→μ+μ−, e+e−→τ+τ− and e+e−→qq̄, PHOJET [18] and PYTHIA for e+e−→e+e− hadrons, DIAG36 [19] for e+e−→e+e−ℓ+ℓ− (ℓ=e,μ,τ), KORALW [20] for e+e−→W+W− and EXCALIBUR [21] for e+e−→qq̄′ℓν and e+e−→ℓνℓ′ν. The number of simulated events corresponds to at least 50 times the luminosity of the data, except for Bhabha and two-photon processes, where the Monte Carlo samples correspond to 2 to 10 times the luminosity.The detector response is simulated using the GEANT package [22]. It takes into account effects of energy loss, multiple scattering and showering in the detector materials. Hadronic interactions are simulated with the GHEISHA program [23]. Time-dependent detector inefficiencies are also taken into account in the simulation procedure.Data and Monte Carlo samples are reconstructed with the same program. Isolated leptons (ℓ= e, μ,τ) are identified as described in Ref. [11]. Remaining clusters and tracks are classified as hadrons. Jets are reconstructed with the DURHAM algorithm [24]. The jet resolution parameter ymn is defined as the ycut value at which the event configuration changes from n to m jets. At least one time of flight measurement has to be consistent with the beam crossing to reject cosmic rays.3

λijk analysis

The different topologies arising when λijk couplings dominate are shown in Table 2

and can be classified into four categories: 2ℓ+E/, 4ℓ+E/, 6ℓ, ⩾4ℓ plus possible jets and E/. The missing energy E/ indicates final state neutrinos escaping detection. After a common preselection [11], based on the visible energy, the event multiplicity and the number of identified leptons, a dedicated selection is developed for each group, taking into account lepton flavours, particle boosts and virtual W and Z decay products.

After the preselection is applied, 2567 events are selected in the data sample and 2593±12 events are expected from Standard Model processes. The main contributions are: 44.5% from W+W−, 21.5% from qq̄, 14.7% from qq̄′eν, 6.6% from two-photon processes (3.9% from e+e−ℓ+ℓ− and 2.7% from e+e− hadrons), and 5.6% from τ+τ− events.

Fig. 1

shows the distributions of the number of leptons, thrust, normalised visible energy and ln(y34) after the preselection. The data are in good agreement with the Monte Carlo expectations.

The final selection criteria are discussed in Ref. [11] and yield the efficiencies for direct and indirect decays of the supersymmetric particles summarized in Tables 3 and 4

, respectively. Here and in the following sections we discuss only the results obtained for those choices of the generation indices which give the lowest selection efficiencies. The quoted results will thus be conservatively valid for any ijk combination. In the case of direct R-parity violating decays, the efficiencies are estimated for different mass values of the pair-produced supersymmetric particles. In the case of indirect decays, the efficiencies are estimated for different masses and ΔM ranges. ΔM is defined as the mass difference Msusy−Mχ̃01, where Msusy is the mass of the supersymmetric particle under investigation.

For direct neutralino or chargino decays, as well as for all indirect decays studied, the lowest efficiencies are found for λijk=λ133, due to the presence in the final state of taus, whose detection is more difficult.In the case of pair-production of scalar charged leptons, followed by direct decays via λijk, the final state contains two leptons plus missing energy. The lepton flavours are given by the indices i and j, independently of the value of k. The lowest selection efficiency is found for λijk=λ12k, i.e., for events with electrons and muons in the final state, since these low multiplicity events require a tight selection to suppress the large background from lepton pair-production.Direct decays of scalar neutrinos yield four leptons in the final state. The 4ℓ+E/ selections are used as they provide a good analysis sensitivity comparable to that of the dedicated selections for scalar electrons, muons and taus. Scalar neutrino decays into electrons and muons are selected with lower efficiency than decays into taus, due to the missing energy requirements. In particular, the lowest efficiency is obtained for λ121, which can give rise to the decays ν̃e→μ−e+ and ν̃μ→e−e+.4

λ″ijk analysis

When the λ″ijk couplings dominate, the flavour composition depends on the generation indices. In the case of neutralino and chargino pair-production, the different topologies can be classified into two groups: multijets and multijets with leptons and/or missing energy, as shown in Table 5

. After a common preselection [11], dedicated selections are developed for each group, depending on the particle boosts, the ΔM values and the virtual W decay products.

In the case of neutralino, chargino, scalar charged lepton and scalar quark pair-production, the preselection aims at selecting well balanced hadronic events and yields 11770 events in the data sample to be compared with 11719±31 expected from Standard Model processes, of which 62.0% are from qq̄ and 32.8% W+W−. Fig. 2

shows the distributions of thrust, ln(y34), ln(y45) and width of the most energetic jet after the preselection. The width of a jet is defined as pTjet/Ejet, where the event is clustered into exactly two jets, and pTjet is the sum of the projections of the particle momenta on to a plane perpendicular to the jet axis, and Ejet is the jet energy. There is good agreement between data and Monte Carlo expectations. The efficiencies for direct and indirect decays of the supersymmetric particles after the selections discussed in Ref. [11] are summarized in Tables 3 and 4, respectively.

Scalar quarks and scalar neutrinos, not studied in our previous papers, are searched for as follows. Scalar quark pairs can decay directly into 4 or indirectly into 8 quarks, as shown in Table 1. In the first case, the main background sources are qq̄ events and W+W− decays. For low masses of the primary scalar quarks, the signal configuration is more similar to two back-to-back jets, due to the large jet boost. In this case we use the least energetic jet width to reject the qq̄ background, which is the dominant one at low masses. For larger scalar quark masses (Mq̃>50 GeV), the signal events are better described by a 4-jet configuration and selection criteria are applied on y34 and the χ2 of a kinematical fit, which imposes four-momentum conservation and equal mass constraints. In the case of indirect decays into 8 quarks, the same selections as for χ̃01χ̃01 decays into 6 quarks are used [11].For scalar neutrino pair-production, a different preselection is performed, to take into account the missing momentum in the final state. Low multiplicity events, such as leptonic Z and W decays, are rejected by requiring at least 13 calorimetric clusters. At least one charged track has to be present. The visible energy has to be greater than 0.2s. In order to remove background contributions from two-photon interactions, the energy in a cone of 12° half-opening angle around the beam axis has to be below 20% of the total visible energy. Furthermore, the thrust axis is required to be well contained in the detector. Unbalanced events with an initial state radiation photon in the beam pipe are removed. Semileptonic W+W− decays are rejected by the requirement that neither the dijet invariant mass nor that of any identified lepton and the missing four-momentum should be in a 5 GeV interval around the W mass. This preselection yields 13950 events in the data at s=189–208 GeV where 13662±45 are expected from Standard Model processes and the main contributions are 50.6% from qq̄, 32.8% from W+W−, 9.2% from e+e−qq̄ and 4.0% from qq̄′eν. The difference in the number of found and expected data appears in the region where the visible energy is below 0.5s, where an important contribution from two-photon interactions and ℓνℓ′ν events is expected. Such events are afterwards rejected by the optimization procedure, which requires a high visible energy.In the case of indirect decays of scalar neutrinos, the only visible decay products are the jets coming from neutralino decays. Therefore, we have derived five selections according to the neutralino mass value, reflecting the different boost and jet broadening configurations. The final selection criteria are optimized [11] by taking into account the following variables: jet widths, ln(y34) and ln(y45), visible energy and polar angles of the missing momentum vector and of the thrust axis.Supersymmetric partners of the right-handed leptons have no direct two-body decays via λ″ijk couplings. However, when scalar leptons are lighter than χ̃01, the four-body decay ℓ̃R→ℓqqq can occur [3] providing the same final state as that resulting from indirect decays, but with virtual χ̃01 production. The non-resonant four-body decay is not implemented in the generator. For this reason, we use the results of the indirect decay analysis, performing a scan over all neutralino mass values up to Mℓ̃R. The resulting lowest efficiency is conservatively quoted in the following for four-body decays. It is found in most cases for Mχ̃01≃Mℓ̃R, as the resulting low energy lepton can not be resolved from the nearby jet. For scalar taus with masses above 70 GeV, the lowest efficiency is found for high ΔM values, as in the case of indirect decays.5

Model-independent results

Table 6

and Table 7

show the overall numbers of candidates and expected background events for the different selections and processes, respectively. The same process may give rise to different final states (such as chargino direct decays via λijk) or the same final state (like “multijets”) can be present as a decay product of more than one process. No significant excess of events is observed. Therefore, upper limits are set on the neutralino, chargino and scalar lepton pair-production cross sections assuming direct or indirect R-parity violating decays.

In the case of λijk couplings, upper limits are set for each process, independently of the mass value of the supersymmetric particle considered. For λ″ijk couplings, upper limits are derived for each process depending on the mass range of the supersymmetric particles, since this procedure improves the sensitivity of analyses with high background level.These limits take into account the estimated background contamination. Systematic uncertainties on the signal efficiency are dominated by Monte Carlo statistics. The typical relative error is between 2% and 5% and it is included in the calculations of the signal upper limits [26].Tables 3 and 4 show the 95% confidence level (C.L.) upper limits on supersymmetric particle pair-production cross sections. For each mass point, all data collected at centre-of-mass energies above the production threshold are combined. For low mass values, the data at s=189 GeV are also used. Therefore, these upper limits should be interpreted as a limit on the luminosity-weighted average cross section.6

Interpretation in the MSSM

In the MSSM framework, neutralino and chargino masses, couplings and cross sections depend on the gaugino mass parameter, M2, the higgsino mass mixing parameter, μ, the ratio of the vacuum expectation values of the two Higgs doublets, tanβ, and the common mass of the scalar particles at the GUT scale, m0. The results presented in this section are obtained by performing a scan in the ranges: 0⩽M2⩽1000 GeV, −500 GeV⩽μ⩽500 GeV, 0⩽m0⩽500 GeV and 0.7⩽ tanβ⩽40. They do not depend on the value of the trilinear coupling in the Higgs sector, A.6.1

Mass limits from scalar lepton and scalar quark searches

For scalar lepton and scalar quark pair-production, mass limits are derived by direct comparison of the 95% C.L. cross section upper limits with the scalar particle pair-production cross sections, which depend on the scalar particle mass.We assume no mixing in the scalar lepton sector. Scalar electron and scalar electron neutrino pair-production have an additional contribution from the t-channel exchange of a neutralino or chargino, whose mass spectrum depends on the MSSM parameters. In this case the mass limits are derived at a given value of tanβ and μ, here chosen to be tanβ=2 and μ=−200 GeV. For scalar quarks, mixing is taken into account for the third generation. The cross section depends on the scalar quark mass and on the mixing angle θLR. For s=189–208 GeV the production cross section for scalar top pairs is minimal for cosθLR∼0.51 and for scalar bottom pairs for cosθLR∼0.36. These values are conservatively used in this analysis.

Figs. 3 and 4

show the excluded 95% C.L. contour for different scalar lepton and scalar quark masses, as a function of the neutralino mass. Indirect decays of the scalar leptons dominate over direct ones in the region with ΔM>2GeV. For 0⩽ΔM<2 GeV 100% branching ratio either into direct or indirect decays is assumed and the worst result is shown. In the negative ΔM region only direct decays contribute. For λ″ijk direct decays of the scalar leptons we quote the results from four-body processes. The 95% C.L. lower mass limits are shown in Table 8

, for both direct and indirect decays.

6.2

Mass limits from combined analyses

A point in the MSSM parameter space is excluded if the total number of expected events is greater than the combined upper limit at 95% C.L. on the number of signal events. Neutralino, chargino, scalar lepton and scalar quark analyses are combined since several processes can occur at a given point. Gaugino and scalar mass unification at the GUT scale is assumed. The constraints from the L3 lineshape measurements at the Z pole [25] are also taken into account [11]. We derive lower limits at 95% C.L. on the neutralino, chargino and scalar lepton masses, as detailed in Table 9

Fig. 5

shows the 95% C.L. lower limits on neutralino and scalar lepton masses as a function of tanβ. The χ̃01 and χ̃02 mass limits are shown for m0=500 GeV and the ℓ̃R ones for m0=0. These values of m0 correspond to the absolute minima from the complete scan on M2, μ, m0 and tanβ. The chargino mass limit is almost independent of tanβ, and is close to the kinematic limit for any value of tanβ and m0. For high m0 values, neutralino and scalar lepton pair-production contributions are suppressed and the mass limits are given mainly by the chargino exclusion. For low m0, the possible production of intermediate real scalar particles does not affect our limits.

For 0 ⩽m0<50 GeV and 1⩽ tanβ<2, the lightest scalar lepton, the supersymmetric partner of the right-handed electron, can be the LSP. Therefore, in this region only the scalar lepton analysis contributes to the limit on the scalar lepton mass. For higher values of tanβ, χ̃01 is the LSP and the lower limit on the scalar lepton mass is mainly given by the χ̃01χ̃01 exclusion contours. The absolute limit on Mℓ̃R is found at tanβ=0.8 in the case of λijk and at tanβ=0.7 for λ″ijk. The difference in the limits is due to the lower cross section upper limit of λ″ijk for scalar lepton direct decays, since the limit on Mℓ̃R is found when the ℓ̃R is the LSP. The same limits are obtained without the assumption of a common scalar mass at the GUT scale. For λijk the bounds on the scalar lepton masses are found in the case in which the ℓ̃R is the LSP. For λ″ijk the limits are found when the ℓ̃R and χ̃01 are nearly degenerate in mass. In both cases, the neutralino analyses give the main contribution to the exclusion in the regions of the parameter space around the limit. The remaining sensitivity is due to searches for direct slepton decays via λijk. As these searches are equally sensitive to scalar electron, muon or tau signals, as shown in Table 3, the limits are unchanged. The scalar neutrino mass limit is also mainly due to neutralino exclusions, resulting in a 95% C.L. lower limit on the scalar neutrino mass above the kinematic limit.The search for R-parity violating decays of supersymmetric particles reaches at least the same sensitivity as in the R-parity conserving case [27]. Therefore, the supersymmetry limits obtained at LEP are independent of R-parity conservation assumptions.

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