# Presentation: 091233

## A Search for Neutral Higgs Bosons at High tanβ with the DØ Detector

- Axel Naumann
- University of Nijmegen / NIKHEF,
- The Netherlands
- for the DØ Collaboration

- DPF Meeting 2004

- 2004-08-30

## Outline

- Higgs in the Super-Symmetric World – an Introduction
- The bbh Signature
- Selecting bbh events
- Backgrounds
- Results

- DPF Meeting 2004

- 2004-08-30

## Higgs and MSSM

- MSSM introduces a second scalar doublet
- Three neutral eigenstates h, H (CP even) and A (CP odd); two charged H**+**, H**−**
- : neutral Higgs eigenstates’ mixing angle
- tan: ratio of neutral Higgs vacuum expectation values
- Modified SM Yukawa couplings:
- 	bbh: 	sin(-) − tan cos(-)
- 	bbH:	cos(-) + tan sin(-)
- 	bbA:	tan

- DPF Meeting 2004

- 2004-08-30

## MSSM Higgs At Large tanβ

- tan is free parameter; large values mt/mb favored
- At large tan
- A nearly degenerate with h or H, depending on mA
- A and one of h, H have enhanced b coupling
- branching ratio to bb ~90% in the mass range of our interest
- Production cross sections scale with tan2
- Here, h or H assumed to be degenerate with A, increasing the cross section of a visible neutral Higgs boson

- DPF Meeting 2004

- 2004-08-30

## h and bb

- For Tevatron, dominant Higgs signature is pp ( gb) ( bh)  bbb
- Three bottom quarks in final state increases signal rate over background rate; important signature for discovery

- DPF Meeting 2004

- 2004-08-30

## b(b)h Predictions

- H and b quark is field of active theoretical research, see e.g. NLO predictions for Tevatron and LHC in hep-ph/0405302 for bh and bbh production
- Cross section for at least two jets from b quarks (“b-jets”) in final state with ET>20 GeV

- DPF Meeting 2004

- 2004-08-30

## Selecting b(b)h

- Using 131pb-1 of DØ’s data from Sept 2002 to July 2003
- Look for peak in invariant mass spectrum of two highest ET jets in events with at least three b-tagged jets
- Signal selection, simulation:
- Event selection depends on mh, e.g. for mh=120GeV: 1 jet with ET>45GeV, one with ET>35GeV, 2 with ET>15GeV
- signal distributions predicted by Pythia, NLO re-weighting
- Background prediction, simulation:
- predict background from data, assuming negligible signal content
- distributions of bbj, bbjj, bbbb from ALPGEN
- tt from Pythia

- DPF Meeting 2004

- 2004-08-30

## Selecting bbh - Triggering

- Three levels of triggering (old and new trigger version)
- Efficiencies relative to offline selection of 68-80%, depending on mh

| Level | Old | New |
| --- | --- | --- |
| L1: tower ET | 4*5GeV | 3*5GeV |
| L2: jet ET(ET>5GeV) | 3*8GeV50GeV |  |
| L3: jet ET | 3*15GeV | 2*25GeV1*15GeV |

- DPF Meeting 2004

- 2004-08-30

## Selecting bbh – Tagging b-Jets

- Loose b-tag requirement: require secondary vertex, cut on 2D decay length significance
- Efficiency plateau for b-jets at 50%, light jet (“mis-tag”) efficiency ~2%, both derived from data

- p

- B

- 2D decaylength

- secondary vertex

- primary vertex

- DPF Meeting 2004

- 2004-08-30

## Backgrounds

- Main background contributions (j: light jet, b: b-jet)
- jjjj, 3 mis-tagged
- bbjj, mis-tagged jets
- bbbb small, Zbb and tt even smaller
- Estimate mis-tags: givena 2 b-tag mjj spectrum, calculate each bin’s contribution to 3 b-tag mjj spectrum

*≥ **4 jets**≥ 2 b-tags*

- DPF Meeting 2004

- 2004-08-30

## Results – Invariant Mass

- Invariant mass distribution of two leading jets in a 3 jet sample with 3 b-tagged jets
- Using Monte Carlo for prediction of b(b)h signal only

- DPF Meeting 2004

- 2004-08-30

## Results - Uncertainties

- Systematic uncertainties for backgrounds 8-10% (depending on njmin, mh); mostly b-tagging related

- Systematic uncertainties of acceptance in %

- DPF Meeting 2004

- 2004-08-30

## Results – Exclusion Limit

- Exclusion limits are calculated usingbackground / (signal + background)likelihood ratio using ROOT’s TLimit
- Based on mclimit (CLs method), see NIM A434, p. 435-443, 1999
- Sweep through tan, given mA

- DPF Meeting 2004

- 2004-08-30

## Results - Exclusion

- 131 pb-1 of data

- MSSM excluded for (mA, tan) parameter space
- Complementary to LEP results!

- DPF Meeting 2004

- 2004-08-30

## Summary & Outlook

- Limit compatible with old limits – this will change!
- Expect improvements soon due to

- larger dataset
- better b-tagging
- better JES
- better triggers
- better cuts

- DPF Meeting 2004

- 2004-08-30

## Summary & Outlook

- Limit compatible with old limits – this will change!
- Expect improvements soon due to

- larger dataset
- better b-tagging
- better JES
- better triggers
- better cuts (4b giving additional leverage)

*** 2**

- DPF Meeting 2004

- 2004-08-30