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Top as a Window to New Physics. Robin D. Erbacher University of California, Davis. Aspen Winter Conference -- January 9, 2007. Mark Kruse gave us the big picture…. New Physics?!?. Just beginning to study top. Top can reveal new physics….
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Top as a Window to New Physics Robin D. Erbacher University of California, Davis Aspen Winter Conference -- January 9, 2007
New Physics?!? Just beginning to study top
Top can reveal new physics… Top can be our window beyond the Standard Model in various ways: • 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 mimicks top signatures.
Top as Indicator of Where New Physics Lies Measured top parameters could point to something new.
Top mass points to a new paradigm? • Rainer Wallny’s Talk: Precise top mass (and W) places constraints on Higgs boson mass. • Further, top important constraint to models of any new BSM paradigm. • Top mass in the coming decade(s) precise enough to provide important consistency checks?: if SM top, what is the interplay with the new physics we are seeing?
What can we expect for Mtop? • Tevatron: Expect 1% combined by end… progress makes us optimistic… pushing lower. (talk by Wallny)
What can we expect for Mtop? • Tevatron: Expect 1% combined by end… progress makes us optimistic… pushing lower. • LHC:Pushing for Mtop~1 GeV. • Assume MW~15 MeV, 2004 central • values. SM constraint on Higgs: MH = 63 ± 20 GeV (mH/mH 32%) Winter 07 constraint: MH = 80 ± 31 GeV (mH/mH 39%)
What can we expect for Mtop? • Tevatron: Expect 1% combined by end… progress makes us optimistic… pushing lower. • LHC:Pushing for Mtop~1 GeV. • Assume MW~15 MeV, 2004 central • values. • ILC:Will benefit from a scan in • √s, allowing a threshold scan for • top production. Expect to • Improve uncertainty such that • Mtop~100 MeV!
Top mass for different decay channels Rainer’s talk yesterday: • Are the channels consistent? • We compare them taking into account their correlated systematic uncertainties => Determination of Mtop from the 3 different channels is consistent with one another Mtop(All Jets) = 173.4 ± 4.3 GeV/c2 Mtop(Dilepton) = 167.0 ± 4.3 GeV/c2 Mtop(Lepton+Jets) = 171.3 ± 2.2 GeV/c2
Is Top Produced as Expected? • Measure ratio of qq/gg top pair production. (M. Kruse) • Tevatron: 85% qq annihilation, 15% gg fusion. • LHC: 13% qq annihilation, 87% gg fusion. • Signs of new, heavy particles decaying to t-tbar: • Heavy Z’ boson decaying to ttbar (TopColor) • MSSM Higgs, strong EWSB, technicolor • RS gravitons or other resonances decaying to ttbar • Some theories with heavy top t’ decay to top(talk by L. Wang)
Resonances decaying to top pairs • Invariant mass of t-tbar system: • Compare with Standard Model expectations. • Add signal of new physics, such as a narrow leptophobic Z’ resonance.
Resonances decaying to top pairs Excludea narrow leptophobic Z’ resonance. 680 pb-1 MX < 725 GeV 370 pb-1 MX< 680 GeV • 955 pb-1 • MX <~725 GeV!
Resonances decaying to top pairs 1.6 TeV resonance xBR required for a discovery σxBR [fb] 30 fb-1 830 fb Mtt 300 fb-1 mtt [GeV/c2] 1 TeV • LHC: Atlas studied resonance X once x, x and BR(Xtt) is known. • Reconstruction efficiency for semileptonic (L+J): • 20% mtt = 400 GeV • 15% mtt = 2 TeV
Expected EWK top production s-channel t-channel (Wg fusion) W-associated Tevatron: 0.9 pb 2 pb 0 pb LHC: 10 pb 62 pb 245 pb • Small signals (~1/2 ttbar production) at Tevatron together with large W+2jets background make it difficult to find. • Similar signatures as Higgs, demonstrational challenge: increase acceptance, multivariate methods, modeling, resolutions, sophisticated techniques get us there… Tevatron: See Single Top talks by Sullivan & Coaddou tomorrow
Expected EWK top production • Single top: primary access to top CC interaction. Already test the W-t-b weak interaction (W helicity), and measure |Vtb| indirectly through branching ratios. • We know |Vtb| to four decimal places: CKM unitarity. New physics (eg: 4th gen) would modify this. Other new physics (charged Higgs, FCNC) modifies channels differently. (Tait, Yuan ‘01) LHC can get t-channel to / ~9% with 10 fb-1. s, Wt channels more difficult.
Does top decay as expected? • Top decay branching ratios (Tevatron) shown by Kruse, gives us |Vtb|. Precision poor, improves at LHC. • Light charged Higgs? • CDF looked for tH+b • affecting four channels • in a correlated way, • excluding when • data inconsistent: • Topdilepton (ee, , e)+jets • Topdilepton (e, )+jets • Toplepton(e)+jets+1 b-tag • Toplepton(e)+jets+2 b-tags Varying model parameters changes: BR(tH+b) BR(H+) BR(H+cs) BR(H+t*b) BR(H+W+h0) BR(H+W+A0) Shown here: Variations as a function of tan particular set of MSSM parameters
Does top decay as expected? • Calculate BR(tH+b) and H+ BR’s as function of MA and tan • 6 MSSM benchmarks used, #1 is shown below. No evidence yet! Collab with M. Carena, thanks!
Anomalies in Top Properties Is it simply Standard Model top?
Many properties could show anomalies… Dil+LJ 200 pb-1 750 pb-1 Dilepton only 200 pb-1 • Top charge(Kruse: D0 results, CDF soon!): -4/3e close to ruled out. LHC gets 5 separation with 24 pb-1, easy. • W helicityKruse: D0/CDF consistent with V-A within statistics, still poor. LHC gets F+ (FR) to 0.02 with 10 fb-1. However… • Separate channel fits still look funny!
Forward-backward asymmetry in top pair production • Afb typically associated with parity-violating weak processes • Not expected in top, but for BSM. • Diagram interference at NLO predicts 3.8% effect.(Kuhn, Rodrigo 99) • Massive neutral gauge boson Z’ could produce an asymmetry. • Look for Moriond results from the Tevatron. mc@NLO 500 GeV Z’
Flavor-changing Neutral Currents Tree level FCNC No FCNCs in SM at tree level • Allowed in higher order penguins Light quark penguins observed • e.g. b→sγ observed by CLEO in 1995, BR O(10-4) Not yet observed for top • SM BR: O(10-12) New Physics models predict BRs up to O(10-2) • SUSY, Higgs doublet, Warped extra dimensions(J. A. Aguilar-Saavedra, Acta Phys. Polon. B35 (2004) 2695) Penguin
FCNC limits so far… Search in tt sample, tZ, CDF Run I: • ttWb qZ, Wjj, Zl+l- • Limit: BR(tqZ)< 33% @95% CL • ttWb q • Limit: BR(tq)< 3.2% @95% CL Search for single top, LEP: • e+e- γ*/Z* t q • Limit: BR(tqZ)< 13.7% @ 95% CL • Best limit so far for tZ
FCNC from Tevatron, LHC CMS sensitivity: Expected sensitivity (5): • BR ~ 1.5 x 10-3 (L=10 fb-1) • BR ~ 4 x 10-4 (L=100 fb-1) New CDF search, ~1fb-1: example exclusion (not final) Expected limit at 95% C.L. (no signal): • Anti-tagged sample: 23-30% • Tagged sample: 18-24% • Combined: 10-15% • Previous limits: 13.7% (LEP), 33% (CDF Run I)
More top properties to look for anomalies… • Properties that we are measuring (and LHC/ILC are studying that I didn’t have time to discuss): • Top anti-top spin correlations: top decays as a bare quark, transfers properties to decay products. • EWK Top couplings (ttZ, tt): (LHC/ILC) form factors: vector, axial vector, anom mag moment, electric (weak) dipole mom. • Anomalous top couplings: W helicity: right-handed PR New coupling: no righ-handed, Interference effects (tough!)
New Physics in Top Quark Samples Are top-like events really unknown physics?
Measuring top pair production Nevents - Nbackground (tt) = Luminosity * Production Cross Section • Why is measuring the rate of top production important? • Higher cross section than predicted could be a sign of non-standard model production mechanisms • Resonant state X tt OR Anomalous couplings in QCD? • It could also mean new physics in the top sample! One of the first things to measure is the top pair production rate.
Run 1: Excess in the b-tagged 2-jet bin sample • Observed excess of b-tags in the 2 jet bin • Too many SVX double tags (more than one b-tagged jet/event) • Too many multiple tags (more than one b-tag/jet) A lot of speculation, but nothing solid.
Lepton+Jets: How’re the double tags? Signal: lepton+ ≥3 jets, MET, ≥2 b-tags! Signal: lepton+ ≥3 jets, MET, ≥1 b-tag L=695pb-1 7-input neural Network, no tag required L=695pb-1 CDF CDF signal signal (tt)=8.2±0.6(stat)±1.0(sys) pb (tt)=8.8±1.2(stat)±1.7(sys)pb
Lepton+Jets channel cross sections Signal: lepton+ ≥3 jets, MET Signal: lepton+ ≥3 jets, MET, ≥1 b-tag L=695pb-1 7-input neural Network, no tag required L=760pb-1 CDF signal CDF Consistency 7% (tt)=8.2±0.6(stat)±1.0(sys) pb (tt)=6.0±0.6(stat)±1.1(sys)pb
Idea: use kinematics again to separate t’ from t New physics in top samples • 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 4th chiral generation is consistent with EWK data; can accommodate a heavy Higgs (500 GeV) without any other new physics • Several SUSY models provide for a 4th generation t’ or mimic top-like signatures(Beautiful Mirrors: Choudhury, Tait, Wagner) • Little Higgs models predict a heavy t’ -like particle
Variables are ~model- independent, to maintain sensitivity to many BSM scenarios • We use the top mass fitter, and fit observed 2D data distribution of HT vs Mrecon Search for massive top
Exclude with 95%CL region of t´ masses below258 GeV Limits on t'
1-d Projection: Fit results for M(t) = 350 GeV 2-d Scatter: Expected (MC) for M(t) = 400 GeV v. data (black), number points for ~7.5 fb-1 Data v. Projections
Top plus missing ET ET mTW • Search for anomalous events that look like top+MET. • SUSY cascades, TAht (L. Wang), … • Similar (based on) t’ search but optimize for extra MET. • Search underway at CDF.
Physics with top is rich • 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, and studies are vibrant at the LHC and ILC. • Beginning to have sensitivity to the unexpected in particle properties and the data samples!
Forward to the Femtobarn Era! • More data makes us smarter ! • It is not just the luminosity factor. We become more daring and more creative. • New techniques and ideas are making our results more sensitive than expected. • Let’s hope nature is kind and top physics indeed becomes our window beyond the Standard Model! Physics with top quarks is just starting !
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