Gregorio Bernardi / LPNHE-Paris Gregorio Bernardi, LPNHE-Paris VI & VII Status of Higgs Searches @ DØ Publications Publications to come, p17 prel. SM Higgs

Gregorio Bernardi / LPNHE-Paris

Gregorio Bernardi, LPNHE-Paris VI & VII

Status of Higgs Searches @ DØ

Publications

Publications to come, p17 prel.

SM Higgs Searches at High mass

Combined D0 and CDF+D0 results.

Susy Higgs status

Future plans

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Publications

‘03 : 1 H++

‘04 : 2 WH, Zb/Zj (and WW x-section)

‘05 : 2 bbh , H WW*

‘06: 4 so far (based on 260-350 pb-1 of data)

h (includes combination with hbb)

WH WWW*

ZH b b

Z + n jets x-section

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P14 Publications coming

SM: WH (e, ) (moriond)

ZH l+ l- b b (ee, ) (ICHEP)

SM combination (ICHEP)

Z bb (x-section) (ICHEP)

SUSY: bbh with h - (ICHEP)

Technicolor: e and channels (ICHEP)

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P17 Preliminary ResultsSM: Z+jets Sherpa study (moriond)

H WW* (ee, e(moriond)

(ICHEP)

Updated SM combination (+ CDF)

SUSY bbh with hbb (ICHEP)

In the works (cf Higgs p17 meeting tue/fri.)

ZH b b, ZH l+ l- b b (ee, )

WH (e, )

h

H+ (direct, indirect)

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SM “Heavy” Higgs: H WW* ll

Search strategy: 2 high Pt leptons and missing Et

WW comes from spin 0 Higgs:leptons prefer to point in the same

direction.

But Higgs mass peak cannot be reconstructed due to the presence of 2

look for an excessCDF and DØ already published on 0.3-0.4

fb-1

H

4th generation?

W+ e+

W- e-

Updated DØ analysis: L ~ 950 pb-1 in H WW* ee and e L ~ 930 pb-1 in H

WW* Selection :• Presection: lepton ID, trigger, opposite charge leptons• Remove QCD and Zl+l-: ET > 20 GeV

• Higgs Mass Dependent Cuts: Invariant Mass (Ml+l-); Min. Transverse Mass Sum of lepton pT

l and ET (pT

l + ET)

• Anti tt(bar) cut: HT = PTjet < 100 GeV

• Spin correlation in WW pair: (l,l) < 2.0

Major backgrounds: WW production , W + jet/ production

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HWW* : final selection

MH=160GeV (x10)

selections

e ee

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SM only a factor 4 away

We exclude 4th generation models, for which

mH=150-185 GeV

Results for HWW*

Expected/Observed # of events for mH = 160 GeV (L ~ 950 pb-1):

If mH= 160 GeV, ~ 2 higgs in our sample!

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Low BR, but channel important in the “intermediate region” 125-145 GeV

Search for WHWWW* (2 like-sign leptons)

Event preselection: Same charge di-lepton from W’s (one from HWW, the other from prompt W)

Suppress SM backgrounds pT (lepton)> 15 GeV, || < 1.1/2.0

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Final Selection for WWW*Topological Likelihood discriminant, built on 3 variables per channel

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Exclusion limit for WWW*

Events after Topological Likelihood discriminant

Effect on global combination significant in the intermediate region (125-145 GeV)

Being improved in p17 with ZHZWW and also with HZZ*

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With low statistics (0.3 fb-1), the cross-section factorsData/SM = ~ 15 at 115 GeV ~ 9 at 160 GeVWith higs statistics (1 fb-1)Data/SM = ~ 5 at 160 GeV

Based on our first experiences with Data, can cdf+dØ reach exclusion for a 115 GeV Higgs with 2 fb-1 of data, as early simulation studies were expecting ?

Combined Higgs boson Search @ DØ

New channel

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Expected Improvements @ DØ

New b-tagging tool at DØ (bh)– Combines various variables

from the track based b-tagging tools in a Neural Network, trained on Monte Carlo

– Performance measured on data

– Substantial improvement in performance over constituent input b-taggers

– Increase of 33% in efficiency for a fixed fake rate of 0.5 %

• Jet energy resolution (recalibration + track-jet algorithm)

Subtract expected energy deposition in cal

Add the track momentumAdd the energy of out-of-cone tracks

Improve the jet energy resolution by ~20%

• Use improved calorimeter calibration Z bb to calibrate b-jet response

• L1-cal Trigger (DØ Upgrade)– Important for difficult channels

efficiency improvement (ZHbb, hbb)

• Addition of SMT Layer 0 (DØ Upgrade)– r@L1 = 2.7 cm r@L0 = 1.6 cm

better impact parameter resolution

- redundancy in pattern recongnition for higher luminosity reduce fake track

– Keep performance if degradation of Layer 1 due to radiation damage

further b-tag improvement (~15%) improvement on Higgs sensitivity


On the Horizon✗ Will 6 times more lumi take our x-section factors at 115/160 GeV of ~15/9 down to 1?? Maybe.. with analyses improvements under work in CDF and DØ Close !

Ingredients (DØ)Equiv Lumigain (@115)

Today with ~330 pb-1 - 15 96.0 6.1 3.7

Combine DØ and CDF 2.0

NN b-Tagger/L0 3.0 3.5NN analysis selections 1.7 2.7 2.8

Dijet-mass resolution 1.5 2.2Increased Acceptance 1.2 2.0 2.5New channels 1.2 1.9 2.1

1.7Reduced Systematics 1.21.2 1.5

At 160 GeV needs ~5 fb-

1

At 115 GeV needs ~3 fb-1

Xsec Factor Xsec FactormH=115 GeV mH= 160 GeV

Sensitivity Prospects extrapolated from 0.3 fb-1 results

Lumi = 2.0 fb-1

95% CL exclusion for mH= 115-185 GeV with 8 fb-1

(assuming similar improvements at DØ and CDF)


Combination Procedure

Combining Higgs boson Searches

DØ uses the CLs (LEP) Method the CLS confidence interval is a normalization of CLS+B

CLS+B = signal + bkgd hypothesis, CLB = bkgd only hypothesis

CLS = CLS+B/CLB : CLS+B & CLB are defined using a “test statistic”

Test statistic used is the Log-Likelihood Ratio (LLR=-2 ln Q)

generated via Poisson statistics (Q=e-(s+b)(s+b)d/e-bbd) s,b,d=sig.,bkd,data)

Tevatron Higgs combination is done with both methods they give results compatible within 10%.

CDF uses a Bayesian approach

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Tevatron SM Higgs Combination

mH Limit/SM

(GeV) Exp. Obs.

115 7.6 10.4

130 10.1 10.6

160 5.0 3.9

180 7.5 5.8

Note: the combined result is essentially equivalent to one experiment with 1.3 fb-1, since both experiments have “complementary” statistics at low and high mass

we are indeed already close to the sensitivity required to exclude or “evidence” the higgs at the Tevatron

All CDF and DØ results now combined for the first time

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Low mass, use Z bb

MC:

83.3 GeV

13.0 GeV

4.4 sigma evidence based on about 300 pb-1 of data, shown at ICHEP. Rate consistent with SM production.

After double b-tag and “shift” correction

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SUSY HiggsNew channels released at ICHEP:

bh b tau tau

(3 evts vs 6.3 +- 0.6)

Need to combine with bbb and htautau

Note: p17 available or close for these channels btautau also getting preparedH+ started,

to be done with top group

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Manpower Issues

Team work to provide best combination, we are strengthening p17 teams and form p20 teams.

Enquiry sent around to the group, to find out about new students:

12 institutions have answered with new students there won’t be one topic per student, rather teams of 1-3 student+1-2 postdoc per channel, and use different timescale (2 milestones per years).

SM Channels: WH, ZH (nunu), ZH (l+l-), WW, WWW, tau-channels.

SUSY Channels: h tautau, bbb, btautau, H+ direct, H+ indirect.

BMSSM “higgs” H++, TC, ….


Conclusions✗ First time with essentially complete result All channels have been analyzed with ~0.3-1 fb-1 of

data✗ Full impact of systematics uncertainties is included✗ Analyses are steadily improving due to optimization,

already close to the Prospective reports

Combined limit looks very promising

Our outlook for the future looks very interesting✗ LHC experiments will have to work hard to get the

signal before Tevatron, if the Higgs is light (<130 GeV)

✗ But the Tevatron has insight also if it is close to 160 GeV and can exclude at 95%CL from 115 to 185 GeV.

✗ Barring accidents, the Tevatron could have evidence by 2009-2010, if it’s there…

But we need to be fast and clever in analyzing more efforts are needed, input of seniors is welcome !!

Besides all analyzers, I would like to thank Suyong and Kazu for excellent collaboration, and welcome Sasha Khanov

Summary

Documents

Gregorio Bernardi / LPNHE-Paris Gregorio Bernardi, LPNHE-Paris VI & VII Status of Higgs Searches @ DØ Publications Publications to come, p17 prel. SM Higgs