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

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

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

MSM Higgs production cross-sections

Gluon fusion

Associated production WH or ZH

Gluon fusion dominates but WH/ZH production more accessible ...

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

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

MSM Higgs searches in Run I

CDF MSM Higgs searches (1998) ...

… similar results from DØ for lbb

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

Run I MSSM: production limits

Convert .BR limits intotan vs. Higgs mass exclusion region ...

bb

LEP vs. Tevatron MSSM limitsFor the most optimistic LEP performance scenario (Priorities for LEP in 2000 - P.Janot) …… the Tevatron beautifully complements LEP!

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 !

Run II : Coming March 2001

2-30fb-1Ldt

21032Luminosity

2.0 TeVs

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

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

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!

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

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

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

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

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)

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

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!

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

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

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

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

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!!)