Search for New Phenomena at Colliders

Search for New Phenomena at CollidersE. Nagy (CPPM)for theCDF, D0 (Tevatron)andH1, ZEUS (HERA)Collaborations

E.Nagy: Searches for New Phenomena at Colliders

In spite of the great success of the SM we still miss an ultimate theory (TOE) which would provide unification of all the 4 known forces (gravity!) into a finite (renormalizable) theory.

Therefore, new, BSM physics is expected at some energy scale MX.

The questions are: what is the TOE and what is MX?

Today only elements of such a theory are proposed for experimental tests. In the present talk: some arbitrary choice of topics addressed by two active colliders: Tevatron and HERA.


Extra DimensionsSuper SymmetryZ, Lepto-Quarks, Beyond SM HiggsesSubstructure (Contact Interactions, Excited Leptons)AnomaliesFrequently, the same event topology (e.g. high mass di-leptons) allows to test several theoretical modelsFor MX the natural value is MPl to unify gravity.However this leads to unnatural fine tuning of scalar masses (problem of hierarchy).Some of the above topics present solution to this problem.


Tevatron~ 200 pb-1 and only most recent results from Run II reported here>3 times more luminosity than in Run I;soon L is 1032cm-2s-1 and counted in fb-1


HERAResults mainly from HERA IHERA I LuminosityHERA II will deliver ~10 times more luminosity (at present ~70 pb-1) + longitudinal polarisation of e-beam


Extra Dimensions (ED) EDs provide framework for unification with gravity (Th. Klauza, 1919) EDs are compact since not seen (O. Klein, 1926) Compact EDs generate replica of particles (KK-tower) propagating in them In string theories, EDs restore QM probabilities in the range [0,1]. EDs can be large (LED: R>>TeV-1) if only gravity can propagate in them LED can explain why gravity is weak: 1/G~M2Pl~Msn+2 Rn and can solve the hierarchy problem: Ms~MW LED can be tested by gravity experiments (n2). Smaller EDs (R~ TeV-1) can also be tested at colliders (interference of KK states) Randall-Sundrum model (1 small ED of size R~1/MGUT with a metric damped by e-kR ) predicts graviton resonances (S=2) of k~1.


Determination of Ms of LED Look for effects of virtual gravitons in high mass lepton (photon) pairs


Select: 2 (and only 2) high pT em objects: pT>25 GeVPrecisely determined vertexCompare:SM and instrumental (mis-ID) backgroundExtract limit:

(TeV-4)MS(TeV) = +10.2921.22 = -1-0.4321.10


CDF ee limitLimit on MS from HERA=/MS4

(TeV-4)MS(TeV) = +11.170.961 = -11.050.987

H1ZEUS= +10.820.78 = -10.780.79


Determination of Md from KK graviton emissonSignature is Monojet + METSelection:Leading jet pT>150 GeV2nd jet pT < 50 GeVMET>150 GeVLepton (e,) vetoMain Background:Z(->)+njW(->l)+njMain uncertainty:Jet energy scale


Determination of MC of TeV-1-size (Longitudinal) EDFermions are confined in the ordinary 3d world.Gauge bosons can propagate in 3+ brane of compact ED.Look for effects of KK replica of gauge bosons in high mass lepton pairs and determine the scale MC of ED. Same selection as above + trackmatch of at least 1 em object Data is compatible with SM Mc > 1.12 TeV @ 95%Interference of KK states


Search for Randall-Sundrum resonancesin high mass di-lepton states


SUper SYmmetrySymmetry of Nature for BosonFermion interchange Basic ingredient for unification with gravity (SuperString/M-theory) The only nontrivial extension of the Lorentz-Poincar group Provides elegant solution for the hierarchy problem

Minimal extension of the SM: MSSM every SM particle has S = 1/2 partner R = (-1)3B+2L+S = +1 (SM); = -1 (SUSY) 2nd Higgs doublet is neededIf SUSY were exact: only 1 additional parameter () needed


SUSY is a broken symmetry since nobody has seen the partners many more parameters describe breaking with additional hypotheses they are reduced in the 2 models treated here gravitation mediated (mSUGRA) model to 5 (m0, m1/2, tan, sgn, A0) gauge mediated (GMSB) model to 6 (, Mm, N5, tan, sgn, Cgrav) parameters.

R-parity is approximately conserved: severe limits on B- and L-violating processes SUSY partners are pair produced LSP is stable (neutral and weakly interacting)

Basic signature is MET (LSP), + multiple jets and leptons from cascade decays

Main bg is t tb and gauge boson pair production

Small violation of R-parity is not excluded: allows single resonant formation of SUSY particles many more jets/leptons in final state additional couplings (48)

At Tevatron both RPC and RPV can be studiedHERA is competitive only for RPV processes


The golden signature: chargino (1) and neutralino (20) pair productionThe signatures exploited by D0:MET from 10 and +3 leptons (e,,l/e,e,l) or2 leptons (, ) of same signD0 has searched beyond the stringent mSUGRA LEP limitand has chosen the following parameter region:


e+ +l High quality, isolatedelectron: pT>12 GeVmuon: pT>8 GeVcharged trackJet vetomTe >15 GeVmee 250 GeV21 data 0.270.42 bge+e+l High quality, isolatedelectrons: pT>8,12 GeVJet vetomTmin >15 GeV15 3 GeV0 data 0.540.25 bg


High quality, isolatedlike-sign muons: pT1>11 GeV, pT2>5 GeVMET>15 GeVm

mSUGRAAt least 2 jets: pT1>60 GeVlepton vetoMETjmin>30oMETjmax175 GeVHT=pTj>275 GeV4 data 2.670.95 bgBg mainly Z->vv+nj


GMSB Select 2 photons pT > 20 GeVExpected signalvs M=2 messenger mass scaleBest limit on: > 78.8 TeVm0 > 105 GeV, m > 192 GeVSignal is at high MET:MET > 40 GeVData: 1 Bg: 2.50.5


R-parity violationIntroduces 48 new L and B violating Yukawa couplings: with more leptons, jets in the final stateSingle sparticle production and decaydepends on coupling Decay of the LSP (10) if fast,does not depend on coupling


Look for signal in multiple event topology (H1). Below an exemple of the lepton-jet(s) inv mass spectrum No deviation from the SM -> Limits on 1j1 and m0, msq, tan


R-parity violation in GMSB (H1)Signature: MET>25 GeV, and an isolated (pT>25 GeV)1 event found, 2.551.30 expectedLimits on 1j1, mNLSP, msel


CDF: agreement of the high mass di-lepton spectra with the SM is transformed into limits on and msnu


Z is predicted in several extensions of the SME6 and little Higgs models are considered hereZ

0o90o37.76o-37.76o ZZZ Z ZI


SM Couplings CDF : 750 D: 780

E6 ZI Z Z Z CDF: 570 610 625 650 D: 575 640 650 680

Limits for e+e- (in GeV)Similar, somewhat smaller limits for +-


Little Higgs Proposes new fermions and bosons to solve the hierarchy problem.Contrary to SUSY, here the quadratically divergent diagrams are cancelled by the same type of particle (fermion-loops by fermion-loops, etc.)ZH is one of the new bosons to cancel divergent boson loop.Its coupling is parametrized by .CDF establishes limits on the mass of ZH and in both of ee and final states.


Lepto-QuarksHypothetical bosons (scalars or vectors) carrying both L and B.Proposed in several extension of SM based on Q-L symmetry.HERA is an ideal machine to produce 1st generation LQs.No deviation is found wrt SM -> Limits on MLQ and coupling


ZEUS has also searched for taus in the final state: Lepton Flavour Violation No events have been found:limits on eq1 = qj vs MLQ


1st generation Lepto-Quarks at TevatronDominantly produced in pairs of the same generation (avoid topology of FCNC or LFV)Production is ~independent of Final state is characterized by 2j+2llepton can be charged or neutral with BR -> possible final states: 2j+2l, 2j+l+MET, 2j+MET2j+2e channel:2j ET>20 GeV2e ET>25 GeVZ-vetoST=ETj+Ete>450GeV0 data, 0.40.1 bg2j+ev channel:2j ET>25 GeV1e ET>25 GeVMET>30 GeVW-veto: mT>130 GeVST>330GeV2 data, 4.70.9 bgD0 MLQ1 limits in GeV

0.10.51.0Run I110204225Run II155213238


Similar analyses of CDF - also in the jjMET channelMET+Jets channel:>2j (j1,2 central w/4 tracks)Jets and MET shouldnt be alignede/-vetoMET>60 GeV80

2nd generation Lepto-Quarks at Tevatronjj+ channel:2 pT>25 GeV2j ET1,2>30, 15 GeVZ-vetoTopological cuts (see Fig.)2 data, 3.21.2 bgMLQ

Beyond SM HiggsesH->H->WW Neutral SUSY/2-Doublets: h,H,A H++/--

On the way to discover HSM one may find BSM Higgses


In some extensions of the SM BR(H->) can be ~ 1(e.g. Fermiophobic or Topcolor Higgs)Select 2 isolated photons:pT1,2>25 GeVpT>35 GeVEstimate background:Instrumental, DY, Determine limit on BR:sliding window technique


H->WW->2l+METee (OS) channel:pT1,2>12,8 GeVMET>20 GeVMETsig>15 GeV1/2:pT+MET>100 GeV12< Mee < 80 GeVJet-vetoee12,8 GeVMET>20 GeVMETsig>15 GeV1/2:pT+MET>90 GeVMTmin < 20 GeVJet-vetoe20,10 GeVMET>30 GeVMET>10+0.75pT1 GeVJet-vetoZ-veto

H,h,A ()

Select:>2j ET1>20 GeV, ET2,3> 15 GeV with well defined vertex (>3 tracks)Apply b-tag with SVT algorithmtag=0.75, btag=0.51, ctag= 1/4btag, fake=0.02Background:Multijet fakes (estimated from data)HF + fakes (estimated from data and MC)Bg is normalized to data outside the signalLimits for mA=mh(135GeV)and for tan are calculated~tan2


H++/--

TEVATRONPredicted in L-R symmetric, Triple Higgs, Little Higgs, etc. modelsSignature is multilepton (SS) eventsAt HERA one searched for multi-e events (in general): H1 finds 6 multi-e events with M12>100 GeV (0.540.6 expected)No excess for ZEUS: 2 found (1.20.1 expected)However only 1 event of H1 agrees with H++/-- topolgyLimit on coupling hee vs MH


D0 selected events in the 2 channel:At least 2 isolated muons, pT>15 GeV of same charge with

Substructure of quarks and leptonsA possible substructure manifests itself by: Excited states of quarks and leptons Finite size of quarks and leptons Contact interaction of qs / ls of scale >>sqrt(s)


Excited Leptons at the Tevatron (CDF)Contact interactionGauge mediated interactionSelect ee events: ETe1,ETe2,ET>25 GeVZ-veto3 events observedExpected background events:


Excited Leptons at the Tevatron (CDF) - compositness scalef relative coupling strength to SU2L gauge boson


Contact InteractionsDeviation from the SM of inclusive ep->eX is parametrized as:No deviation (ZEUS, H1) is transformed to limits on :and also to limits on q-radius:Rq

General search for deviations from the SMpioneered by D0, here carried out by H1HERA IHERA IISelect events with at least 2 isolated objects: e, , j , , with PT > 20 GeV to look for large deviation from SM in Mall and pTLargest deviationin -j-


Excess of isolated leptons at HERA

5 H1 events are compatible with FCNC single top production:(ep->etX) = 0.290.15 pbAlternatively, upper limit on: ktu

ConclusionsThe performances of both Tevatron and HERA improve steadilyallowing to test experimentally many new ideas in the search for an ultimate theory Although some anomalies observed already,no conclusive sign of new, BSM physics yetMore results are expected soon


Acknowledgments for help in preparing this material

to colleagues of the D0, CDF, H1 and ZEUS collaborationsand especially to Elisabetta Gallo (ZEUS) andJianming Qian (D0) Apologies for subjects I havent had time to present here


Backup slides


The CDF upgraded detector


The D0 upgraded detector


The H1 detector


The ZEUS detector


Extra Dimensions


Highest DiEm MassesMee = 475 GeVcos*=0.01M = 435 GeVcos*=0.02


Analogous study for stop (H1) assuming mst>msbDoesnt explain isolated lepton events -> Limits on 131 and mst


Z->


Excited Leptons


Excited Leptons at the Tevatron (CDF)


Multi-e events at HERA II


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Search for New Phenomena at Colliders