Searches for New Physics at the Tevatron

B. Heinemann Searches for New Physics at the Tevatron1

Searches for New Physics at the Tevatron

B. HeinemannUniversity of Liverpool

“From Tevatron to the LHC”Cosenor’s House, 24-25.04.2004


OutlineIntroductionHiggsSUSYHigh mass dileptons: Z’ and LED’sConclusions and OutlookOther results on: Leptoquarks, Magnetic Monopoles, ADD LED’s, Excited electrons, …

Difficulties:• XXX• YYY


The Tevatron: Run 2

Expect 2 /fb by 2006 and 4.4-8.6 /fb by 2009 sensitivity to New Physics improved by>5 compared to Run 1

Run 2 started in June 01:

CMS energy 1.96 TeV

Delivered Lumi: 480/pb

Promising slope in 2004!

Data taking efficiencies about 90%

Physics Analyses:

Use about 200/pb (2x run 1)

But it’s still early days in Run 2!


The Challenge

Higgs

?WW, Wγ, Zγ,

Cross Sections (fb)

QCD and EWK cross sections 10-5 orders of magnitude larger than new physics!Finding the needle in the heystack…

Good understanding of SM backgroundsUse data and MC to estimate themUseful: new enhanced LO MC’s (Alpgen, Madgraph)

NN and Likelihood methods require excellent modelling of BG


HiggsStandard ModelSUSY:

Enhanced production at high tan

Bosophilic Higgs:h→γγ

Doubly Charged HiggsBackup slides


Standard Model HiggsCross sections small: 0.1 - 1 pb MH 135 GeV: decay into bb

gg H: QCD BG too largeHW and HZ associated production have lower (but still large!) BGBest channels:

Wh→lνbbZh→ννbb

MH >135 GeV: decay into WW

gg H WW(*)l+l- final states can be explored BR only 1%

In this talk (both done by CDF and D0):Wh→lνbb (CDF)h→WW (D0)

H bb

H WW(*)

Dominant decay modes

Production Cross section


Prospects for SM HiggsOriginal study in 1998 confirmed in 2003Study still based on some extrapolationsNo sensitivity expected with current Luminosity of 200/pb (not even on plot!)But search now anyway:

Get ready for high LuminosityPossibly new bright students develop smarter ideas than anticipated in studies Understand systematic errors realistically (and start working on them!)

2009

2006

• E.g. SM Higgs at 115 GeV •exclude at 95% C.L. in 2006•3 evidence in 2009


Event selectionCentral isolated e/ pT > 20 GeVMissing ET > 20 GeV

Two jets: ET > 15 GeV, || < 2Veto

Di-lepton, extra jet, etc.

Observe 2072 events in data

• Simulations performed with Alpgen plus Herwig passed through detailed detector response

CDF: WH→lvbb (I)

Data in good agreement with Background expectationMain Background:

W+light jets now require b-tag


Require at least one b-tagged jet

Observe 62 events in data Expect 61 ± 5 events

• Main contributions to background

• Mass Resolution: 17%• Expect 0.3 evts from Higgs

– Signal acceptance ~ 1.8% for MH = 110 – 130 GeV

Mistags

Wc(c) Wbb QCD top

14 13 12 10 9

CDF: Higgs: WH→lvbb (II)


Set limits on the Higgs production cross section times branching ratio:

WH×BR(W→lv, h→bb) < 5 pb

(D0: <12.4 pb at mh=115 GeV)

Systematics studies

• Exceeds CDF’s Run I limit ×BR < 14 – 19 pbfor MH = 70 – 120 GeV PRL 79, 3819 (1997)

• Expect improvements due to•Di-jet mass resolution (17%→12-10%)•More sophisticated analysis techniques•Cut and b-tag optimisation

Source Error (%)

ISR / FSR 19

Secondary vertex

8.6

Lepton ID 5

Jet energy scale 3

PDF 1

Trigger 0.7

Total 22

CDF: Higgs: WH→lvbb (III)

Difficulties:• 3rd jet veto introduces large syst. Error due to ISR/FSR• jet energy resolution: optimise in Z→bb• long term: need to use NN or so how reliable is MC?


D0: H WW(*) l+l- Event selection include

Isolated e/pT(e1) > 12 GeV, pT(e2) > 8 GeVpT(e/1) > 12 GeV, pT(e/2) > 8 GeVpT(1) > 20 GeV, pT(2) > 10 GeV

Reduce Drell-Yan background:ET>20 GeV (ee, e); 30 GeV ()

Veto on Z resonance

Reduce top backgroundVeto energetic jets

Data correspond to integrated lumi. of

~ 180 (ee), 160 (e) and 150 () pb-1

Higgs Signal


Higgs mass reconstruction not possible due to two neutrionsEmploy spin correlations to suppress the bkgd. (ll) variable is particularly

useful

Leptons from H WW(*) l+l- tend to be collinear

DØ: H WW(*) l+l-

W+ e+

W- e-

(ll) between e and (after preselection cuts)

Higgs of 160 GeV


Number of events after selections

Dominant bkgd. in e sample

DØ: H WW(*) l+l-• Expect 0.11 events for 160

GeV SM Higgs now

WW W+jets WZ tt

2.51±0.05

0.34±0.02

0.11±0.01

0.13±0.01

ee e

Observed 2 2 5

Expected2.7±0.4

3.1±0.3

5.3±0.6

Excluded cross section timesBranching Ratio at 95% C.L.

DØ Run II Preliminary

Higgs of 160 GeV


Higgs in SUSY at high tanStandard Model:

σ(bbH) =1-10 fb: 100 x smaller than WH

SUSY: Cross section enhanced at high tanβ: σ(bb) ~ tanβ! (Willenbrook et al.)

E.g. for M(A)=120 GeV:5 discovery for tan>30 3 evidence for tan>20

Experimentally:1 b-jet typically soft:Require 3 jets with b-tags

CDF Run I 95% C.L.

bbbbbbqqgg , (=h,H,A)BR( ) ~ 90%bb


D0: Neutral Higgs at High TanEvent Selection:

At least 3 jets:ET cuts on jets optimized for different Higgs mass values 3 b-tagged jets

Look for signal in the invariant mass spectrum from the two leading b-jetsMain Background:

QCD multi b-productionDifficult for LO MC: determined from data and/or ALPGEN 1.2

Signal acceptance about 0.2-1.5% depending on Mass

∫Ldt=131 pb-1

AND FINAL STATE??????????

Difficulties:• triggering: 3 b-jets, 4th jet soft: e.g.=2 % in CDF• background: 3 b-jets beyond LO MC abilities and generating enough MC challenging CPU wise• mass resolution: optimise and check in Z→bb


D0: Non-SM Light HSome extensions of SM contain Higgs w/ large B(H)

Fermiophobic Higgs : does not couple to fermionsTopcolor Higgs : couples to only to top (i.e. no other fermions)

Important discovery channel at LHC

Event selection 2 Isolated ’s with

pT > 25 GeV||<1.05 (CC) or 1.5<||<2.4 (EC)

pT () > 35 GeV (optimised)BG: mostly jets faking photons

Syst. error about 30% per photon!Estimated from Data

∫Ldt=191 pb-1

Central-Central Central-Forward


Photon Fake RateRate of jets with leading meson (pi0, eta) which cannot be distinguished from prompt photons: Depends on

detector capabilities, e.g. granularity of calorimeterCuts!

Systematic error about 30-80% depending on EtData higher than Pythia and HerwigPythia describes data better than Herwig

CDF (preliminary result)


Perform counting experiments on optimized sliding mass window to set limit on B(H) as function of M(H)

Non-SM Light Higgs H

Difficulties:• jets faking photons: leading pi0’s• NLO MC of SM necessary: Pt() cut


Supersymmetry ReminderSM Fermions Boson SuperpartnersSM Bosons Fermion Superpartners

Physical SUSY sparticles: neutralinos (Higgs, Photon, Z partners), charginos (Higgs, W partners), squarks (quark partners), sleptons (lepton partners)

Different SUSY models:Supergravity: SUSY broken near GUT scale

GUT scale parameters: scalar mass m0 , gaugino mass m1/2 , ratio of Higgs v.e.v’s tanβ, Higgs mixing parameter μ

LSP is neutralino or sneutrino ν

Gauge-mediated models (GMSB): SUSY broken at lower energies – breaking scale important parameter.

Gravitino G is the LSP (NLSP χ0 →Gγ )

01

~ ~

~

~


“Trilepton” SearchChargino+neutralino production: three leptons and missing energy signature

Main challenge - weak production low cross sections

LEP limits are very restrictive

select two identified leptons, so far:

eeeμμ± μ±

Add Et cut and topological cutsRequire an additonal isolated track

Sensitive to tau’s tooAt high tan>10 stau may be light

Chargino and neutralino decay into stau’s which then decay into tau’s3-tau final state: dedicated analysis required (not covered here)

/


D0: Trileptons: ee+lepton (I)2 Electrons: EM cluster+track match

• PT>12 (8) GeV• ||<1.1 (3.0)

1. Anti-Z15<Mee<60 GeV(ee)<2.8

2. Anti Conversion electrons3. Anti top

Veto jets with ET>80GeV4. Anti-Drell Yan

Missing ET>20GeV

(e,ET)>23 degrees

5. Isolated Track: Pt>3 GeV

6. ET x Pt > 250 GeV2

Potential signal

175pb-1

/

Cuts reduce BG by 4 orders of magnitude!ε(signal)=2-3%


D0: Combined tri-leptons

3(2) events compared to 2.9(0.9) expectedRun 1 cross section limit much improvedSoon will reach MSugra prediction (in the best scenario with low slepton masses)

Channel

Data Background Signal

e e l 1 0.30.4 0.8-1.6

e 1 2.50.5 0.7-1.0

e l 0 0.50.2 0.6-0.9

1 0.130.04 0-0.4

Results:

Difficulties:• trigger: leptons are soft: 3rd lepton 3 GeV!• background: jets faking lepton, e.g. conversions• background: difficult to make enough b MC • understanding Missing Et: e.g. jet mismeasurements


Squarks and GluinosStop quark:

Maybe best discovery potential in Run 2Theorists say “it should be light”Searches so far only for stable stopUnfortunately no result yet in promising decay modes in Run 2 but triggers in place and analyses ongoing!

Sbottom quarkpp→gg→bbbb→bbbbpp→bb→bbSearch for b-jets + ET

Generic squarksSearch for jets + ET

Large QCD backgrounds must be suppressed

~~~~~~~~ ~~

LEP2 limit


D0: Squarks and GluinosSquarks and gluions: Strong production

large cross section, but really large instrumental backgrounds (2 orders of magnitude over SM processes)

4 events left 2.67±0.95 expected from SM sources:

50% from Zjj -> vvjjOther BG from Wjj

QCD background negligible (exponential fit to the data)17.1 event expected for M0=25,M1/2=100GeV

2 jets ET>60 (50) GeV30<(jet,MET)<165o

Final cuts:Missing ET>175 GeV

HT>275 GeV

85 pb-1


D0: Squarks and GluinosM0=25GeV; A0=0; tan=3; <0

M(gluino)>333GeVRun 1 – 310 GeV

M(squark)>292GeV

Difficulties:• understanding Missing Et: e.g. jet mismeasurements• jet energy scale and resolution uncertainty• generating enough MC to estimate QCD BG!• handling large jet datasets


Jet Energy Scale @ CDFUse test beam to set charged pion scaleUse in situ Z ee to set pi0 scaleAccount for MI and UECorrect for jet to hadron levelCorrect for hadron to parton level (e.g. top mass)Cross checks:

gamma-jet: 5% difference between Pythia and Herwig after full simulationZ-jet: statistically limitedZ bb and W jj in top at Et of 50 GeV or socalibration at high Et relies on MC tuning of

Response to single particlesFragmenation/radiation in MC

Difficulties:• understand large difference between Pythia and Herwig• no calibration process in interesting region: Et>400 GeV!• will be dominant error on e.g. top mass


Sbottom: B-jets and ET

High tan() scenario under study: sbottom is lighter than other squarks and gluino

•4b-jets+missing energy

•>=3jets (ET>10 GeV)•Missing ET>35 GeV

•1 b-tag– 5.6+-1.4 events SM predicted - 4 observed

•2 b-tags –0.5+-0.1 events SM predicted - 1 observed

01

~~;

~~~~ bbbbbbgg

Difficulties:• understanding Missing Et: e.g. jet mismeasurements• b-tagging efficiency and purity• QCD background: LO MC unreliable for multi-b production


Long Lived Particles!LSP – charged particle, orNLSP – charged particle (e.g. stop) with long decay timeSignature – isolated track of a rather slow particleUse TOF system: NEW

in Run 2 for CDFEnsure efficient tracking:

βγ>0.4 (Pt>40 for M=100 GeV) Efficiency about 1-3%BG: 2.9±3.2Data: 7 observed Use dE/dx and COT timing

in future

Difficulties:• cosmic background• track efficiency for massive/slow particles (v≠c)


GMSB ModelMetGauge mediated SUSY breaking scale Gravitino – LSPNLSP (neutralino) LSPDominant SUSY mode:

Signature – 2 photons, missing energyPT(photon)>20 GeV in ||<1.1

1 event survived 2.5±0.5 expected from SM

Missing ET>40 GeV

185 pb-1

New D0 event taken recently:2 γ, 1e, large Et:Et(γ)=69 GeV, Et(γ)=27 GeVEt(e)=24 GeVEt=63 GeV/


GMSB ModelMetData consistent with SM backgroundDerive upper limit on cross sectionCompare to NLO cross sectionResult:

GeVm

GeVm

TeV

180)(

105)(

8.78

1

01

Difficulties:• understanding QCD BG due to Et mismeasurement• instrumental (cosmic/beam-halo) BG


CDF: Bs->μ+μ-

New Physics can enhance branching ratios of B-mesons:

Measure BR in decay modes suppressed in SM

E.g. Bs→μμ:Bs = bound state of b and s quarkSM: BR(Bs→μμ)~10-9

SUSY: BR may be A LOT higher at high tan

Blind analysis with a priori optimisation:

1 event observed, ~1+-0.3 expected

90% CL limits: BR(Bs→μμ)<5.8 X 10-7

BR(Bd→μμ)<1.5 X 10-7

SM vs e.g. SUSY


SUSY Sensitivity: Bs->μμ

SO(10) GUT model (R. Dermisek et al.: hep/ph-0304101) :

accounts for dark matter and massive neutrinos largely ruled out by new result

mSugra at high tanβ (A. Dedes et al.: hep/ph-0108037):

Just about scratching the corner of parameter spaceIn direct competition with

Higgs (g-2)μ

Expect <1x10-7 by end of year start exceeding limits set by higgs

90% CL limit: BR(Bs→μμ)<5.8 x 10-7


Physics Potential of Tau’sLight higgs decays to tau’s 8% of the time:

E.g. for 120 GeV higgs have already 20 H→ττ events on tapeDecay to tau’s enhanced in MSSM at high tan

At high tan the stau is light:Charginos and Neutralinos can decay into stau’s

Stau may be LSPTau’s are difficult at pp machines…No search result yet though but building foundations measure:

Z-> tau tauW-> tau nu


W→τν and Z→τ+τ− Signals

nb)(16.0)(21.0)(07.062.2)(BR lumsyststatWpp

Look for hadronic tau decaysNarrow isolated jetLow track multiplicityIdentify π0 candidate in ShowerMax detectorinvariant mass of tracks and π0 < m(τ)

Efficiency about 50%

Z→τ+τ− signal:• 1 hadronic tau decay (jet) • 1 τ→eν or τ→μν decayBackgrounds from Z→l+l−, QCD

Difficulties:• triggering: CDF has new trigger “lepton + track”• jets faking hadronic taus: about 0.3% right now• tau ID efficiency: no clean way to get from data

2345 W→τν candidates in 72/pb

NNLO prediction: 2.73 nb


Di-lepton Production @ High Mass

Select 2 opposite sign leptons: ee or μμ (ττ soon)Here ee channel:

2 central e (CC) 1 central and 1 forward e (CP)NEW: 2 forward e’s (PP)

Good agreement with SM prediction


Model Independent Limits: spin-0, spin-1 and spin-2 particles

spin-0

spin-2

spin-1

• model-independent limits on σxBR for particles with spins 0, 1 and 2

• applicable to any new possible future theory

•Observed limit consistent with expectation

•New Plug-Plug result not yet included

•Muon analysis also ongoing


Limits on Several Models

Z’ occurs naturally in extensions of SM towards GUT scale, e.g. “E6” models

M(Z’)>570 GeV for E6 models (depends on exact model: couplings to quarks and leptons)M(Z’)>750 GeV for SM coupling

Sneutrino in R-Parity violating SUSY may decay to 2 leptons:

M>600 GeV for couplingxBR=0.01

Randall-Sundrum gravitonsMass> 600 GeV for k/MPl >0.01

Techni- pion’s, -omega’s

G

ν

Z’

~

Difficulties:• Mass dependent k-factor (NNLO) for Z’ signal recently provided by J. Stirling• No mass dependent k-factor for DY background versus di-lepton mass yet: will use MC@NLO

G


Summary of Black BoxesBackground Monte Carlo:

Enhanced LO MC’s (Alpgen, Madgraph etc.) being used more and more Much better description of data than e.g. Pythia/Herwig:Starting to use MC@NLOCPU intense: often impractical to generate enough in remote corners of phase space

Jet energy scale and resolution crucial for many measurements:

Tuning of Pythia and Herwig required to describe jets better

Jets faking leptons, photons, tau’s:Fake rate measurements big industry at CDF and D0: it is an art to correctly measure a fake rate!

Biggest experimental problems arise when data NOT modelled by MC

Generator detector simulation

Input and suggestions from theorists (or anybody) to maximise physics are very very welcome!


Conclusions and OutlookHave done many searches and not found anything, butThis is just the beginning:

expect a factor of 10 more data by 2006/7Analyses can be optimisedUnderstanding of detector and techniques improvingNew/better MC tools becoming availableIdentify and solve experimental and phenomenological challenges

Invaluable experience for the LHC onBackground estimationJet energy and Missing Et measurementsReliability and understanding of MC and it’s limitationsCommissioning the largest scale detectors to dateOptimising triggers and handling large data samples

Publishing papers now whenever result is competitive


WH: compare to HSWG

CDF 2 CDF 1 HSWG Case 0

HSWG default

(M) 17% 15% 15% 10%

S 0.27 0.31 0.13 0.13

B 24.5 50.7 3.2 2.1

S/sqrt(B) 0.054 0.04 0.075 0.090

Mh=115 GeV


It’s early days for searches…Analyses not yet fully optimised for maximal sensitivity:

Extrapolation of current result to 2 fb-1 not validLegacy of Run 1: “going back to Run 1” required BEFORE making improvements upon Run 1

Largest scale detectors world-wideE.g. 720k RO channels for CDF Silicon detectorCommissioning and maintenance take a lot of resources

Optimisation of triggers still ongoingConstantly increasing Luminosity requires frequent changes to optimise physics potential

Offline software and Data Handling permanent struggleMonte Carlo statistics often limited, e.g. no full survey of SUSY parameter space

Development of offline tools e.g. b-tagging, jet calibration, tracking algorithms vital for long term successRequires people focussing on this rather than analyses

Many (good) people focused on EWK and top measurements instead to gain understanding of detectors (quite rightly!)


Doubly Charged Higgs: H++/H--

H++/H-- predicted in some extensions of SM:

Left-Right (LR) symmetric modelsSUSY LR models : low mass (~100 GeV – 1 TeV)Single and Pair production

Striking signature: decay into 2 like-sign leptons

ee channel: M(ee)>100 GeV to suppress large BG from Z’s (conversions: e±→e±γ→e±e+e- )

eμ and μμ channels

Sensitive to single and pair production of H++/H—

CDF


Doubly Charged Higgs: H++/H--

Blind analysissearch region: M>100 GeV0 events observed4.3±1.3 events expected

Result: 95% C.L. upper limit on cross section x BR for pair production (pp→H++ H--→l+ l+ l- l-)

Mass Limit

CDF 240 pb-1

D 106 pb-1

HL++ HR

++ HL++ HR

++

ee 135 ~102-113

135 113 116 95

e 115


Perspectives: Stops and Sbottoms

Stops may be light due to mixing between partners of left, right-handed topSimilar for sbottomsLook for direct pair production of stops or sbottoms

•Stop mass reach up to ~175GeV/c2

•Sbottom sensitivity up to 250GeV/c2


Apparent symmetry between the lepton & quark sectors: common origin ?

e e

Lepton + Quark Resonances : Leptoquarks

• LQs appear in many extensions of SM (compositeness, technicolor…)

• Connect lepton & quark sectors • Scalar or Vector color triplet bosons• Carry both lepton and baryon number • fractional em. Charge: +-1/3, +-4/3, etc.• Braching ratio β unknown, convention:

•β=1 means 100% BR LQ→l±q•β=0 means 100% BR LQ→νq

•Also sensitive to e.g. squarks in RPV (exactly the same!)

Nice competition between world’s accelerators:

•HERA, LEP and Tevatron

•At Tevatron: independent of coupling λ


Leptoquarks: 1st generation

New analysis in run 2:Search for LQ’s decaying LQ→νq (β=1)

2 jets (Et>) and Et>60 GeV:Experimentally challenging

Result:124 events observed118.3±14.5 events expected exclude LQ masses with 78<M<118 GeV

eejj channel: M(LQ)>230 GeV for β=1 (72 pb-1 )

Difficulties:• understanding Missing Et: e.g. jet mismeasurements• ISR and FSR uncertainties???


Summary of 1st Generation Leptoquark Results

Beta 1st 2nd 1 225 2001/2 2040 98 98

1 220 2021/2 182 1640 1231

Beta 1st 2nd 1 225 2001/2 2040 98 98

1 220 2021/2 182 1640 1231

1 c c3rd generation not shown

Run 1 Run 2

Beta 1st 2nd 1.0 238 2000.5 213 in progress

0.0 in progress in progress

1.0 230 2400.5 197 in progress

0.0 117 117

Beta 1st 2nd 1.0 238 2000.5 213 in progress

0.0 in progress in progress

1.0 230 2400.5 197 in progress

0.0 117 117


eenalysisCDF has done a search for excited electron, predicted in many compositeness modelsProduce via contact or gauge mediated interactions

The cross section depends on e* mass and

L = 200 pb-1L = 200 pb-12 electron /2 electron /At least one Central electronAt least one Central electronExpected 2.98 Expected 2.98 +0.4+0.4

-0.3 -0.3 ; observed: 3; observed: 3

first time searchContact interaction: At 95% C.L. Me*>889GeV (Me* = )

Gauge mediated: At 95% C.L. Me*>208GeV (Me*= )


Jets Analysis

jj channel (=1)Two muons 2 jets MJYRemove events in the Z peak(Et(j1)+ Et(j2) ) > 85 GeV

(Pt(1)+ Pt(2)) > 85 GeV

√ j(Et )2+ (Pt)2>200 GeV

CDF observe 2 events w/~200 pb-1

CDF expects 3.15±0.17Upper limit at 95%C.LMLQ> 240 GeV (=1)

Second generation LeptoQuarksSecond generation LeptoQuarks


e AnalysisDØ has done model independent search in e channelSearch for an excess over the SM prediction in the kinematic spaceLook at the Missing ET ,

sensitive to new PhysicsSet upper limits at 95 % C.L.

L L = 98 pb= 98 pb-1-1

1 electron E1 electron Ett>25 GeV>25 GeV

1 muon Pt>25 GeV1 muon Pt>25 GeVGood fiducial volumeGood fiducial volume0/1 jet0/1 jet


Dilepton High Mass AnalysesSearch for resonances in high invariant mass

Results can be interpreted under many different models: Z’ (E6, sequential, little higgs)

Large Extra Dimensions

Randall Sundrum

Technicolor

SUSY

Etc

CDF and DØ has slightly different approach:

CDF : Calculate the acceptances Calculate the acceptances and resonances for 3 different and resonances for 3 different spin assumption( 0,1,2) and spin assumption( 0,1,2) and applied to many models. applied to many models. DØ: Calculate the acceptances Calculate the acceptances and resonances for eachand resonances for each specific specific modelmodel

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Searches for New Physics at the Tevatron