Searches for New Physics in the Top Quark Sector Prof. Robin Erbacher University of California, Davis December 2008 Prof. Robin Erbacher University of California, Davis December 2008 t First UC Davis-Taiwan Workshop National Taiwan University, Taipei, Taiwan

R. Erbacher-Taiwan2 top history Top Discovery! Tevatron Run Top Discovery! Tevatron Run

R. Erbacher-Taiwan3 Top Rediscovered in Run 2 Top Rediscovered in Run 2!

R. Erbacher-Taiwan4 Periodic Table of the Particles 5 orders of magnitude!

R. Erbacher-Taiwan5 Many top properties measurements are beginning to have sensitivity: lots about top still to understand! New Physics?!?

6 Top as a Window to New Physics… Top results point to new physics: Properties lead to expectations of partners or other new particles. Top is Not what we expect: Measured top properties are anomalous, contrary to SM. Top is Not all that we find: New physics mimics top signatures. Top can reveal physics beyond the Standard Model in various ways:

R. Erbacher-Taiwan 7 New Physics Mimics Top t’ -- Massive top, T A h t SUSY stop production Heavy W’ boson to tb New Physics Mimics Top t’ -- Massive top, T A h t SUSY stop production Heavy W’ boson to tb Top Properties non SM-like Top Pair Cross Section Forward-Backward Asymmetry W helicity (V-A) FCNC Top Properties non SM-like Top Pair Cross Section Forward-Backward Asymmetry W helicity (V-A) FCNC Top points to new particles Top Mass EWK Production: single top Produced by new Resonances? Branching Ratios Top  charged higgs Top points to new particles Top Mass EWK Production: single top Produced by new Resonances? Branching Ratios Top  charged higgs UC Davis Analyses

8 Events Characterized by W Decays t  Wb ~ 100% R. Erbacher-Taiwan

9 Dilepton Decay Mode

R. Erbacher-Taiwan10 Lepton+Jets Decays

R. Erbacher-Taiwan11 All-Hadronic Decays

12 -- MIP signal In calorimeter Jet 2 secondary vertex interaction point Jet 1 secondary vertex interaction point Muon + jets event with 2 tagged b-quark jets Muon + jets event with 2 tagged b-quark jets R. Erbacher-Taiwan

13 One top pair each inelastic collisions at  s = 1.96 TeV Strong Pair Production at the Tevatron Rarely!! How is top produced? ~85% ~15%

R. Erbacher-Taiwan14 Electroweak Single Top Production Electroweak Single Top Production New Resonance Production? New Resonance Production? s-channel ~1 pb t-channel ~2 pb

R. Erbacher-Taiwan15 Fermilab, Chicago, IL U.S.A. Tevatron DØCDF Chicago Booster Wrigley Field  p source Main Injector Fermilab Tevatron

R. Erbacher-Taiwan16 Tevatron luminosity profile and status Record luminosities (>>3x ) lately, in spite of slow 2007 shutdown recovery Record luminosities (>>3x ) lately, in spite of slow 2007 shutdown recovery CDF: Up to 2.9 fb -1 of data with all subdetectors used.

R. Erbacher-Taiwan17

18 Top as a Window to New Physics… Top results point to new physics: Properties lead to expectations of partners or other new particles. Top is Not what we expect: Measured top properties are anomalous, contrary to SM. Top is Not all that we find: New physics mimics top signatures. Top can reveal physics beyond the Standard Model in various ways:

19 Top as Indicator of Where New Physics Lies Measured top parameters can open a window to something new.

R. Erbacher-Taiwan20 Top Points to New Particles Top Mass EWK Production: single top Produced by new Resonances? Top decaying to charged higgs Top Points to New Particles Top Mass EWK Production: single top Produced by new Resonances? Top decaying to charged higgs

R. Erbacher-Taiwan21 Top Quark Mass: Important EWK Parameter Top Quark Mass Important EWK parameter Key role in BSM physics models Constrains the Higgs mass Heavy: Unexpected role in EWSB? Top Quark Mass Important EWK parameter Key role in BSM physics models Constrains the Higgs mass Heavy: Unexpected role in EWSB? What a theorist sees…What an experimentalist sees Challenges: combinatorics, b-tagging efficiencies, jet energy scale. Solutions: sophisticated analyses, in-situ W  jj calibration

R. Erbacher-Taiwan22 New for summer 2007! Top mass: Exciting Program of measurements at the Tevatron Top mass: Exciting Program of measurements at the Tevatron Most precise single measurement M t =172.2 ± 1.0 (stat+JES) ± 1.3 (sys) GeV/c 2

R. Erbacher-Taiwan23 New Top Mass World Average July 2008: New Top Mass World Average July 2008: M top =172.4 ± 1.2 GeV/c 2 D0-CDF Joint Systematics Effort Underway! New publications are coming this fall…

R. Erbacher-Taiwan24 Top mass summary and combination Implications for New Physics Implications for New Physics M H ~87 GeV, or 114 GeV)

R. Erbacher-Taiwan25 Resonances decaying to ttbar Electroweak Single Top Production Points to New Physics? Electroweak Single Top Production Points to New Physics? T. Tait and C. P. Yuan, Phys.Rev.D63: (2001) t-channel ~2 pb s-channel ~1 pb

R. Erbacher-Taiwan26 Wbb Wcc Wc non-W Mistags tt Z/Dib Backgrounds! Best channels S/B~1/20 Signal smaller than background uncertainty! Single Top Production: Rate  |V tb | 2 in SM Sensitive to H +, 4 th gen, W ’, FCNC, … Signature ~ SM Higgs SM cross section ~3 pb Single Top Production: Rate  |V tb | 2 in SM Sensitive to H +, 4 th gen, W ’, FCNC, … Signature ~ SM Higgs SM cross section ~3 pb S<<B!

27 Results for Single Top from CDF Single Top Status Summary of Measurements of  s +  t Best Sensitivity: NN analysis 3.7  observed 5.0  expected R. Erbacher-Taiwan

28 Resonances decaying to ttbar New Resonance Production? New Resonance Production? Bump-hunting for X  ttbar! (Narrow resonance  X = 0.012M X )

R. Erbacher-Taiwan29 Resonances decaying to ttbar Technicolor leptophobic Z´ New D0: Observed Limit M Z´ > 760 GeV D0: Expected Limit M Z´ > 800 GeV M tt and Z

R. Erbacher-Taiwan30 Resonances decaying to ttbar M tt and Z Earlier CDF Searches Observed Limits for 700pb -1 and 1 fb -1 both: M Z´ > 725 GeV

R. Erbacher-Taiwan31 Resonances decaying to ttbar M tt and Massive Gluon M tt and Massive Gluon New Color Octet Particle G: Limits on coupling = q G : Fitted coupling strength consistent with SM within 1.7  in the (width/mass) range from 0.05 to 0.5 Dynamic Likelihood (ME-style) Reconstruction

32 Top as a Window to New Physics… Top results point to new physics: Properties lead to expectations of partners or other new particles. Top is Not what we expect: Measured top properties are anomalous, contrary to SM. Top is Not all that we find: New physics mimics top signatures. Top can reveal physics beyond the Standard Model in various ways:

33 Anomalies in Top Properties Is it simply Standard Model top?

R. Erbacher-Taiwan34 Top Properties non SM-like Top Pair Cross Section Forward-Backward Asymmetry Top Quark Charge W helicity (V-A) FCNC Top Properties non SM-like Top Pair Cross Section Forward-Backward Asymmetry Top Quark Charge W helicity (V-A) FCNC

R. Erbacher-Taiwan35 N events - N background  (tt)  L uminosity *  Top Pair Production Cross Section: As QCD predicts? Only SM top? By heavy particles? Top Pair Production Cross Section: As QCD predicts? Only SM top? By heavy particles?

R. Erbacher-Taiwan36 Top pair Event topology Discriminant: No b-jet tagging Event topology Discriminant: No b-jet tagging Requiring two identified b-jets: Ultra pure top pair sample Requiring two identified b-jets: Ultra pure top pair sample Top pair  tt =7.2 ± 0.4 (stat) ± 0.6 (sys) pb  tt =6.8 ± 0.4 (stat) ± 0.7 (sys) pb UC Davis Analyses Previous results with 760 pb -1 using the 2 methods were only 7% compatible, now quite consistent!

R. Erbacher-Taiwan37 Forward-Backward Production Asymmetry Forward-Backward Production Asymmetry A fb Diagram interferences for qq No asymmetry expected at LO, but 4-6% expected at NLO in parton frame J. Kuhn, et al. Reduced Asymmetry in tt+jet -- Uwer, et al. Smaller asymmetry in lab frame

R. Erbacher-Taiwan38 Afb CDF A fb Result from CDF NLO: (4 ±1%) in cos  * (lab frame) A fb =(17 ± 7 (stat) ± 4 (syst) ) % (Fully corrected) A fb =(17 ± 7 (stat) ± 4 (syst) ) % (Fully corrected) Background distributions UC Davis Analysis

39 < 0 Afb How would new physics look? For M Z' = 750 GeV: F < 0.44 (expected) F < 0.81 (observed) >0 >0 A fb = 12 ± 8 (stat) ± 1 (syst) % (Uncorrected for reconstruction) A fb = 12 ± 8 (stat) ± 1 (syst) % (Uncorrected for reconstruction) A fb Result from D0 F: fraction of top pair events produced via Z' resonance

R. Erbacher-Taiwan40 Afb CDF 2 nd A fb Results from CDF Compare with D0 result: A fb (bkg sub) =(14.4 ± 6.7 (stat) ) % NLO: (4-7%) in  y*Q l A fb =(24 ± 13 (stat) ± 4 (syst) ) % (Fully corrected) A fb =(24 ± 13 (stat) ± 4 (syst) ) % (Fully corrected) A(parton rest frame) = 1.3A(lab frame)

Top results point to new physics: Properties lead to expectations of partners or other new particles. Top is Not what we expect: Measured top properties are anomalous, contrary to SM. Top is Not all that we find: New physics mimics top signatures. 41 Top as a Window to New Physics… Top can reveal physics beyond the Standard Model in various ways:

42 New Physics in Top Quark Samples Are top-like events really unknown physics?

43 New Physics Mimics Top SUSY stop production t’ -- Massive top, T A h t Heavy W’ boson to tb New Physics Mimics Top SUSY stop production t’ -- Massive top, T A h t Heavy W’ boson to tb R. Erbacher-Taiwan

44 New for summer 2007! Top mass Measurements at the Tevatron 2007 Tevatron Combination: 7% chance that LJ and DIL results more discrepant than observed Fermilab-TM-2380-E, TEVEWWG/top 2007/01

R. Erbacher-Taiwan45 New for summer 2007! Top mass Measurements at the Tevatron Stop mass below the mass of the top quark? Can the top data have an admixture of stop quarks?

R. Erbacher-Taiwan 46 Stop Search

Reconstruction difficult due to many invisible particles. What’s Special about Stop? M(stop)<M(top) in SUSY electroweak baryogenesis models C. Balazs, M. Carena, C. Wagner PRD 70 (2004) m(t 1 ) ≤ m t  1 0 is the LSP Supported by Cosmological observations: dark matter relic density (WMAP) Light stop mimics top quark events ~ q q Top DileptonTop Lepton+Jets

R. Erbacher-Taiwan 48 Stop Search In the lepton + jets channel stop signal is hidden in backgrounds: SUSY stop could hide alongside top dileptons? SUSY stop could hide alongside top dileptons? Would bias top dilepton mass towards a value lower by a few GeV. UC Davis Analysis

R. Erbacher-Taiwan 49 Stop Search CDF: No evidence for stop (Limits in M(   ) - M(stop) plane) CDF: No evidence for stop (Limits in M(   ) - M(stop) plane) Meanwhile, box opened for top mass with 1.8 fb -1, and dilepton mass consistent with L+J avg: SUSY stop could hide alongside top dileptons? SUSY stop could hide alongside top dileptons?

50 Tprime search Massive or 4 th Generation Top: t While on the energy frontier, we look for interesting events on the tails of the top quark distributions Can a t’ exist? Can it mimic top? Generic 4 th chiral generation is consistent with EWK data; can accommodate a heavy Higgs (500 GeV) without any other new physics (He/Polonsky/Su hep-ph/ ) Interesting seesaw model (LSND/4 th gen) (Hou/Soddu hep- ph/ ) Several SUSY models provide for a 4 th generation t ’ or mimic top-like signatures (Beautiful Mirrors: Choudhury, Tait, Wagner) Little Higgs models predict a heavy t’ -like particle UC Davis Analysis

51 Tprime search 4 th Generation Top? G. Kribs, T. Plehn, M. Spannowsky, T. Tait hep-ph/ Possible 4 th generation quark with mass of few hundreds GeV can be consistent with EWK data Oblique corrections drive Higgs Mass to ~ 500 GeV Almost degenerate b ´ and t ´ masses: M(t ´ ) - M(b ´ ) < M(W) Decays as top! t´ -> Wq (q=d,s,b)

52 Tprime search Other New Particles Mimic Top? Discrepancy with the SM?!  FB - b-quark forward-backward asymmetry ~ 2.6  away (LEP) As a result: sin  w,lep is ~ 3.3  away from sin  w,had Assumptions on mistakes in the LEP measurements  Underestimated systematic uncertainty  Systematical shift in the measured value are not satisfactory

53 Tprime search Other New Particles Mimic Top? Fits to leptonic data +A b FB +A c FB M. Chanowitz, PRL 97 (2001)  C.L.

Example model: Beautiful Mirror Quarks Standard Mirrors Top-less Mirrors Perfect for Tevatron searchesMight have to wait for LHC New physics in Z->bb? Different coupling of the b-quark to Z? D. Choudhury, T. Tait C. Wagner, PRD 65 (2002) Mirror quarks of b-quarks improve the fit Two scenarios: with and without top mirror quarks

55 Variables to Discriminate Variables to Discriminate 2-d fit with systematics as nuisance parameters in the likelihood. Quasi model-independent: variables retain sensitivity to many beyond the SM scenarios R. Erbacher-Taiwan HTHT M reco

R. Erbacher-Taiwan 56 Massive or 4 th Generation Top: t Exclude with 95% CL region of t ´ masses below 311 GeV PRL 100 (2008) excluding 256 GeV

57 Tprime search Massive Top 2-d Scatter: Expected (MC) for M(t) = 175 GeV v. data (black), number points for ~2.8 fb -1 R. Erbacher-Taiwan 1-d Projections: Fit results for M(t) = 450 GeV

R. Erbacher-Taiwan58 Couple of Strange Ones…

R. Erbacher-Taiwan59 Couple of Strange Ones…

R. Erbacher-Taiwan60 Couple of Strange Ones…

R. Erbacher-Taiwan61 Summary The top quark is the least known quark, and the most interesting for new physics. The top physics program is very active at the Tevatron, with both precision measurements and first results appearing all the time. Beginning to have sensitivity to the unexpected in particle properties and in the data samples!

R. Erbacher-Taiwan 62 Conclusions

R. Erbacher-Taiwan63 Backups

R. Erbacher-Taiwan64 Afb and higher orders

R. Erbacher-Taiwan65 Method inherited from CDF Run I (G. Unal et. al.) Measure fraction of W+jets events with heavy flavor (b,c) in Monte Carlo Normalize fractions to W+jets events found in data New improvement: get normalization from W + 1 jet bin (instead of generic dijet sample) Correct data for non W+jets events W + Heavy Flavor Estimate Heavy flavor fractions and b-tagging efficiencies from LO ALPGEN Monte Carlo Calibrate ALPGEN heavy flavor Fractions from W + 1 jet bin Note: Similar for W+charm background Large uncertainties from Monte Carlo estimate and heavy flavor calibration (~25-30%) CDF Run II Reference for standard method: PhysRevD.71,052003

R. Erbacher-Taiwan66 Heavy Flavor Normalization Improve heavy flavor estimate by calibrating it in W+1 jet side band Take advantage of NN based flavor separator Compare Loose Secondary Vertex mass and NN flavor separator output: –consistent results within errors K-factor for heavy flavor: 1.4 ± 0.4 Applied to predict W + Heavy Flavor content of W + 2 jets bin mistags / charm ………. beauty

R. Erbacher-Taiwan67 Jet1 Jet2 Lepton Central Electron Candidate Charge: -1, Eta=-0.72 MET=41.6 GeV Jet1: Et=46.7 GeV Eta=-0.6 b-tag=1 Jet2: Et=16.6 GeV Eta=-2.9 b-tag=0 QxEta = 2.9 (t-channel signature) EPD=0.95 Single Top Candidate Event t-channel single top production has a kinematic peculiarity: - Distinct asymmetry in Q x  distribution: lepton charge (Q) x pseudo-rapidity  =-log (tan  /2) of untagged jet Run: , Event: EPD > 0.9

R. Erbacher-Taiwan68 New Ideas Top mass with cross section constraint: trades stat uncertainty for theory Top mass extracted from cross sections: Compare to theory and across channels! Consistent with kinematic measurement? dilepton New Ideas! Cacciari, Mangano, et al hep-ph/ Cacciari, Mangano, et al hep-ph/ LEPTON+JETS DILEPTON

Top mass Best per channel R. Erbacher-Taiwan69 Snapshot: most precise per channel Snapshot: most precise per channel M top =172.2 ± 1.6 GeV/c 2 M t =171.2 ± 2.7 (stat) ± 2.9 (sys) GeV/c 2 all-hadronic from winter 2008, 2.1 fb -1 : M t =176.9 ± 3.8 (stat+JES) ± 1.7 (sys) GeV/c 2 Most precise!

70 Results for Single Top from CDF New CDF Results: Search for Single Top in 2.7 fb -1  s+t = 2.7 ± 0.8 pb Expected sensitivity: 3.4  Observed significance: 2.0  Expected sensitivity: 4.5  Observed Significance: 3.4   s+t = 2.1 ± 0.7 pb Neural Network Discriminant Matrix Element Discriminant R. Erbacher-Taiwan

71 Using the Matrix Element cross section measurement, CDF determines |V tb | assuming |V tb | >> |V ts |, |V td | |V tb |= 0.88 ± 0.14 (expt) ± 0.07 (theory) Z. Sullivan, Phys.Rev. D70 (2004) t-channel s-channel D0 |V tb |>0.68, |V tb | = 1.3 ±0.2

R. Erbacher-Taiwan 72 Limits on charged higgs New CDF Results on Charged Higgs New CDF Results on Charged Higgs Explore the possibility that t  H + b with H +  c s Limits on BR(t  H + b)

73 Resonances decaying to ttbar d  /dM ttbar Test SM Consistency Possible BSM Contributions: Z’, MSSM Higgs, colorons, axigluons… Sensitive to interference effects No evidence for BSM effects: P-value of 0.45 R. Erbacher-Taiwan

74 Reconstruction difficult due to many invisible particles. What’s Special about Stop? UC Davis Analysis M(stop)<M(top) in SUSY electroweak baryogenesis models: C. Balazs, M. Carena, C. Wagner PRD 70 (2004) >  m(t 1 ) ≤ m t  1 0 is the LSP: Supported by Cosmological observations: dark matter relic density (WMAP) Light stop mimics top dileptons: ~ p p t1t1 t1t1 b b W-W- e+e+ e ~ ++ 00 -- 00 ~ W+W+ e-e- e m( l       ) = m    m( l       ) = m    b