Higgs hunting: the basics Run I Higgs searches MSM prospects for Run II Conclusions
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Higgses at the Tevatron: Status and ProspectsPeter Ratoff
Lancaster Universityrepresenting
the CDF and DØ Collaborations
Higgs hunting: the basics Run I Higgs searches MSM prospects for Run II Conclusions
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MSM Higgs mass constraint: experiment
Direct Searches -combined LEP data MH > 107.7 GeV
(95%CL)
Fits to precise EW data (LEP EWWG) MH = 76-38
+68 GeV
MH < 188 GeV (95%CL)
Moriond Electroweak 2000
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Higgs mass constraints: theory
MSSM requires MH 125 - 130 GeV
Any weakly coupled SUSY theory requires MH200 GeV
The MSM requires 130 MH 180 GeV
Vacuum stability lower bound
Landau pole upper bound
Probing the MSM Higgs up to ~ 180 GeV has profound implications for the scale of any new physics,
Riesselmann, hep-ph/9711456
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MSM Higgs production cross-sections
Gluon fusion
Associated production WH or ZH
Gluon fusion dominates but WH/ZH production more accessible ...
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MSM Higgs decay branching ratios
For MH 135 GeV H0 dominates …
but rate falling rapidly QCD background
precludes gg
For MH 135 GeV Gauge boson decays
dominate ( H0 WW )
bb
bb
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Tevatron: low mass Higgs searches
For MH 135 GeV: use the same basic strategy as LEP …… study associated production of ZH and WH
To the standard leptonic HZ channels add W l with H bb ... … the qqbb channel is very difficult as the
QCD backgrounds are severe
Low mass Higgs sensitivity depends on• the integrated luminosity collected • b-quark jet tagging performance• mass resolution of reconstructed bb jets
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MSM Higgs searches in Run I
CDF MSM Higgs searches (1998) ...
… similar results from DØ for lbb
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MSSM Higgs searches in Run ILarge bb cross-section at the Tevatron can be used to exploit enhanced Yukawa couplings ... e.g. Abb coupling tan cross-section tan2
search for bb production where = h, H, Ab
CDF searches for bbbb final states:
• Trigger: 4 level-2 jets (>15 GeV) + ET > 125 GeV• Offline: Mass-dependent jet ET selection
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Run I MSSM: production limits
Convert .BR limits intotan vs. Higgs mass exclusion region ...
bb
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LEP vs. Tevatron MSSM limitsFor the most optimistic LEP performance scenario (Priorities for LEP in 2000 - P.Janot) …… the Tevatron beautifully complements LEP!
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Fermilab SUSY/Higgs Run II Workshop Run II Physics Workshops throughout 1999 Draft report from Higgs Working Group (67 authors)
http://fnth37.fnal.gov/higgs.html
Workshop goals perform comprehensive survey of final states study effect of improved b-tagging and bb mass resolution determine integrated luminosity (as function of MH ) for
95% CL exclusion (1.96) 3 observation; Prob(bgnd) < 0.00135 5 discovery; Prob(bgnd) < 2.7 x 10-7
Workshop conclusions included a few surprises: effect of combining all search limits (like LEP) effect of new channels not previously considered
The Tevatron Higgs reach had been underestimated !
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Run II : Coming March 2001
2-30fb-1Ldt
21032Luminosity
2.0 TeVs
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Working Group Studies
Simulation and analysis methods: CDF fast detector simulation QFL’ Generic ‘Tevatron detector’ simulation
SHW with CDF Run I b-tag efficiencies Neural network analysis (NN) in some
cases
jet mass resolution
b-jet tagging
bb
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jet mass resolution
CDF (Run I) Z before/after b-quark specific jet corrections
• Higgs discovery critically dependent on bb di-jet mass resolution• jet corrections depend on missing ET, muon momentum, jet charged fraction ...• other important effects: jet algorithm, ISR/FSR, pileup due to multiple ints …• can use Zbb jets for calibration ...
bb
bb
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b-jet tagging
• Many algorithms possible …• illustrative example (DØ) :-
• jet pT > 15 GeV• 3 tracks with large I.P.’s• 3D constrained vertex fit • in x-y plane require L/ > 3• c-jet tags / b-jet tags 1/3• udsg jet tags <1% (pT<70 GeV)
• Much work still to do!
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Low mass MSM Higgs: 90-130 GeV
Working group studies concentrated on WH lbb 2 b-jets + isol l± + miss
ET
ZH bb 2 b-jets + large miss ET
ZH l+l-bb 2 b-jets + 2 isol l± + MZ
WH/ZH qqbb 2 b-jets + 2 non-b-jets pp ppH 2 b-jets + fwd pp
All channels combined for discovery potential
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WH l• the single most powerful channel for Higgs discovery• main backgrounds: W , tt, single top (W*tb, gWtb), WZ• efficiency x BR(H ) 2%
SHW, 10 fb-1, Significance = S/B
Effect of bb mass resolution
QFL’ , 1 fb-1, 30K PYTHIA WH / bin
MH = 110 GeV
bb
bbbb
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ZH / l+l-
• main backgrounds: Zbb, tt, single top, ZZ, (Wbb, WZ), bb-dijets, ...• more difficult to separate bb backgrounds from signal ...• … very conservative treatment of QCD background (bb-dijets)
SHW, Neural network
ZH / l+l- combined
SHW
bbbb
bb bb
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High mass MSM Higgs: 130-200 GeV Assoc. production with H runs out at 130 GeV
how can the Tevatron Higgs reach be extended ?
… make use of the rising H W W* branching ratio ! exploit the large gg H cross-section identify final state topologies with small SM contribution
focus on leptonic Gauge Boson decays ...
bb
Excellent trigger topologies
Less difficult QCDbackgrounds
Han, Turcot, Zhang
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MSM Higgs search: Tri-lepton channel
Cleanest signature ... Associated production
VHWWW(*) / ZWW(*)
Inclusive di-lepton trigger: pt1 > 10 GeV, pt2 > 5 GeV
OR inclusive high pt single lepton
Golden modes (like-sign, like-flavour leptons) OR
tight kinematic cuts to deal with WZ/ZZ
Small rate: limited sensitivity to MSM Higgs, but
… New Physics could observable
enhancements Baer + Wells (hep-ph/9710368)
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MSM Higgs search: Di-lepton + missing ET
inclusive production HX WW(*)X ll ’’ X
leading contribution from gluon fusion channel ... (ggH) x BR(HWW(*)) x BR(We,)2
7 - 14 fb in MH interval 140 - 190 GeV
SM backgrounds: WW ll ’’ 1090 fb +- l l ’’’ 23 pb tt bl bl ’’ 722 fb WZ, ZZ, tW ~220 fb
Background 25 pb S/B ~ 4 x 10-4
Han, Turcot, Zhang
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MSM Higgs search: Di-lepton + missing ET
Event selection:- step 1: basic cuts (maintain high efficiency
whilst reducing and tt backgrounds bgnd 165 fb (mainly WW)
step 2: apply 6-variable Likelihood discriminant step 3: background normalisation
bgnd 106 fb (dominated by WW and W + fake (je) )
step 4: final selection exploit different kinematics of WW productioncontinuum vs. at threshold via a spin 0 resonanceutilise angular correlations between leptons and
missing ET
… the best chance to discover high mass MSM Higgs in RunII!
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MSM Higgs search: Di-lepton + missing ET
Step 3: bgnd norml’n Step 4: final selection
10 fb-1 => 3.1% stat error on bgndHiggs contamination : S/B ~ (3-5)%
WW bgnd reduced by factor 40!... clear excess from Higgs prod’n
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MSM Higgs search: like-sign di-lepton + jets
Distinct signature: l l jet jet X standard New Physics search topology
Five contributions to consider WH WWW l l j j ZH ZWW l’ l’ l j j WH WZZ l l’ l’ j j WH WZZ l l l’ l’ j j ZH ZZZ l l l’ l’ j j
Large number of SM backgrounds … di-boson, tt, tri-boson, ttV, fakes, …
S/B larger than di-lepton + missing ET channel but smaller signal (x 3)
Bgnd systematic error larger ?
Marciano, Stange, Willenbrock (PRD49, 1354 (1994))
Schmitt + Turcot
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MSM Higgs: all channels Bayesian combination: all channels and both expts (CDF/DØ):
assume 10% mass resolution neural network analysis for H channels conservative treatment of QCD bgnd. for HZ systematic error: Min of 10% or 1/( L dt x B) bands represent 30% effect from varying Mbb resol, b, bgnds
bbbb
bb
95% CL exclusion to~ 185 GeV for 10 fb-1
3 observation to~ 185 GeV for ~ 20 fb-1
5 discovery up to ~ 125 GeV for ~ 30 fb-1
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Run II Luminosity Prospects
Annual expectations:- 2001-2 1 fb-1 per year (per expt) 2003-5 2-3 fb-1 per year 2005+ 5 fb-1 per year (until LHC
overtakes)
Integrated luminosity by ~ 2002 2 fb-1
2005 10 fb-1
2007 20 fb-1
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Conclusions Strong experimental and theoretical motivation that
the Higgs boson is within the reach of current accelerators
Run I Legacy: MSM Higgs searches were luminosity limited MSSM Higgs: interesting CDF limits for bb searches ... … probed parameter space inaccessible to LEP provided valuable experience for Run II
Run II Prospects: the potential to cover most of the mass range preferred by the
electroweak fits use of H WW(*) channels will significantly extend the Higgs
mass reach can test the validity of MSM up to Mplanck scale ! MSSM Higgs opportunities (no time to discuss today!!)