# Presentation: 169616

## Search for Neutral Supersymmetric Higgs Bosons with the DØ Detector at the Tevatron in Run II

- Andy HaasUniversity of Washington*on behalf of the D**Ø** Collaboration*
- APS MeetingSession P14 – Higgs PhysicsPhiladelphia, PAApril 7, 2003

## Supersymmetry and Higgs

- A *highly motivated* new symmetry of nature
- Stabilizes the mass of a scalar particle, such as the Higgs
- Allows for the unification of gauge couplings at a high energy
- Provides a Cold Dark Matter candidate
- Demands ***pairs*** of Higgs doublet fields (to cancel anomalies)
*H**u* couples to up-type quarks and leptons and *H**d* to down-type
- The ratio of their VEV’s is defined as:
***tan ************ = <H******u******>/<H******d******>***
**5** Higgs particles after EWSB: h0, H0, A0, H+, H-
- h0 is ‘guaranteed’ to be light:
***m******h******0****** ******< ~130 GeV***** **(MSSM) 	      ***<*** ***~210 GeV***** **(General SUSY)
- Other ‘two-doublet’ models are possible as well...

- Q

- Bosons

- Fermions

- Andy Haas - UW Physics

- April 7, 2003

**Notes:**
Mass of higgs < mZ at first order... higher order corrections can raise mass, but not too far.

## Higgs Production and Large tan 

- _Higgs Production and Large __*tan *__**_

- Low *tan ****, *→ Standard Model Higgs
- High *tan ****, *→* *enhanced* **bbH*
- Cross section rises like*** tan******2*********
- Recent work indicates that the LO cross-sections are an underestimate by a factor ~3
- Some theoretical bias towards expecting *tan **** > ~30*
*b-t-**τ* Yukawa unification at the GUT scale → mt/mb ~ *tan **** ?*

***CP-odd Higgs******Production***

***CP-even Higgs******Production***

*~tan ***

- Andy Haas - UW Physics

- April 7, 2003

## The Tevatron

- _The Tevatron_

- World’s largest, highest-energy, running accelerator!
- Started Run II about 2 years ago...
- Luminosity performance is still improving...
- Producing about *1 pb**-1* /day  (~*10 h**0**bb* events /day at high *tan *** )
- Hope for *300 pb**-1* this year

- Andy Haas - UW Physics

- April 7, 2003

## The DØ Detector

- Same fine-grained, high-resolution compensating Calorimeter as Run I
- 3-level high-bandwidth trigger system with full event reconstruction at ~1 kHz
- Forward muon system, with greatly improved halo shielding
- New inner tracking, with 2T solenoid and silicon vertex strip detector
*b*-tagging possible at high pseudorapidity (< ~2.5)

- Andy Haas - UW Physics

- April 7, 2003

## Signal

- Higgs decays 90% to a *b*-quark pair at high *tan **** *
**4 *****b*****-jet final state**

- Two hard, central *b*-jets
- roughly mh/2
- Another hard *b*-jet balancing the pT of the Higgs
- One softer, forward b-jet

*CompHEP+Pythia MC*

- _M__h__=120 GeV_

- _p__T __> 20 GeV_

***QCD***

***Signal***

- Andy Haas - UW Physics

- April 7, 2003

## Triggering

- Make full use of the 3-level trigger system
- Use the primary vertex to:
- correct jet ET
- veto interactions beyond the fiducial silicon volume
- Demand 3 jets with *E**T** > (25,25,15)* GeV***or****E**T** > (15,15,15)* GeV *and *a muon
**Efficiency is >70% ***(relative to loose offline cuts)*
- Run I : ~8% efficient using:
- 4 jets > 15 GeV
- HT > 125 GeV
*> 50 pb**-1* already on tape

**Jet Trigger (2,25)(3,15)**

**Using L3 Vertex**

**RUN I**

- Andy Haas - UW Physics

- April 7, 2003

## b - Tagging

- Jets are tagged as coming from *b*-quarks:
- High-resolution tracking-based tag
- Muon tag
- Soft-electron tag (being studied)
- In Monte Carlo : *~60% efficient and ~1.5% fake*
- Currently working on understanding and improving efficiency and rejection in data

- Jet η

- Jet pT

*b*-tagging Efficiency (DØ Run II MC)

- 1.5% fake

- c

- b

- Andy Haas - UW Physics

- April 7, 2003

## Di-b-jet Mass Resolution

- Need good *b*-jet ET resolution to see a Higgs peak
- Jet-energy corrections are used
- Various cone-sizes and jet algorithms were studied
- Jet reconstruction and energy-scale corrections do well in MC
- 12% mass resolution
- Need to study and improve resolution in data

- Reconstructed Higgs mass in Monte CarloNo backgrounds included!

- CompHEP +Pythia MC**NO JES Corr.**mh = 120 GeV

- Andy Haas - UW Physics

- April 7, 2003

## The bbH Analysis

- Backgrounds
- QCD ‘heavy flavor’ : *bbjj, ccjj, cccc, bbcc, bbbb*
- QCD ‘fakes’ : *jjjj*
- Top-quark production : *tt*
- Electroweak : *Z(bb,cc), W(bb,cc)*
- Kinematic cuts
- Optimize for each Higgs mass individually
- Demand no more than 4 jets?
- May be necessary to reduce the top quark background
*b*–tagging
- Tag 3 or more jets in the event
- Use a combination of tracking-based, muon, and soft-electron tags
- Look at di-jet invariant masses of the leading *b*-jet combinations...
- Search for an excess of events inside a ‘mass-window’ optimized for each Higgs mass

**CompHEP + Pythia MC****m****h**** = 120 GeV**

- Andy Haas - UW Physics

- April 7, 2003

## Summary / Outlook

- Lots of progress in the last year
- Theoretical signal cross-sections are now on firmer ground
- The Tevatron is producing decent, stable luminosity
- DØ recording data with > ~85% efficiency
- All pieces of DØ needed for this analysis are functional
- A specialized trigger for this signal has been commissioned and measured
- Basic analysis methods have been established and applied to the data

- Now need to understand the *data* in detail
- Measure *b*-tag efficiencies and fake rates in complicated multi-jet events
- Understand the di-*b*-jet mass resolution and optimize the Higgs mass peak reconstruction
- Hope for *100 pb**-1* of luminosity, and the first results of this analysis by summer 2003!

- 4 *b*-tag event with mh=113 GeV

- Andy Haas - UW Physics

- April 7, 2003