# Presentation: 698188

## DØ Higgs Physics Results

***Jyothsna Rani***
***Tata Institute of Fundamental Research***
***Mumbai, India***
***on behalf of the D******Ø Collaboration***
***Lake Louise Winter Institute***
***20******th****** – 26******th******  February 2005***
***Alberta, Canada***

## Outline

**Standard Model Higgs searches**
**Associated production of *****H***** with *****W***
***H ************ W W****** for m****H**** > 135 GeV**
**Non Standard Model Higgs searches**
**MSSM Neutral Higgs in (*****b)bh************(b)bbb***** **
**   ****final state  **

***    ******Results presented here are based on 174 – 260 pb******-1***

***NEW***

- Jyothsna Rani - Tata Institute

- LLWI, 24th Feb 2005

## Missing Piece in Standard Model

- The mass of elementary particles in the Standard Model is explained by the presence of Higgs boson.
- The mass of the Higgs boson is not predicted in SM.
- Precision measurements constrain:
-          114 GeV < mH < 260 GeV
- Tevatron provides:
- Indirect search
- Precision mt and mw measurements
- Direct searches
- SM Higgs
- non-SM Higgs

**LEP**

- Jyothsna Rani - Tata Institute

- LLWI, 24th Feb 2005

## SM Higgs Decays

**Search strategies are a function of **
**Decay modes and **
**Production channels**
**Two search strategies at Tevatron:**
**Low mass Higgs searches m****H**** < 135 GeV **
**    *****H ************ b************b ***
**High mass Higgs searches m****H**** > 135 GeV **
**	*****H ************ W W****

**Excluded at LEP**

**Higgs Mass (GeV/c****2****)**

- Jyothsna Rani - Tata Institute

- LLWI, 24th Feb 2005

## SM Higgs  Production at Tevatron

**Gluon Fusion: **
**	*****gg ************ H*****    ******** ~ 1pb**
**	****At low mass (*****H ************ b************b***** ****),  **
**           ****high QCD background.**
**	****At High mass usable with**
**	*****H************ W W****** decay mode.**
**Associated Production:**
**	*****WH or ZH*****  **** ******** ~ 0.1pb**
**	****Used at low mass with**
**	*****H ************ b************b***** decay mode.**

**Excluded at LEP**

- Jyothsna Rani - Tata Institute

- LLWI, 24th Feb 2005

## Identifying b-jets

**  ****Secondary Vertex.**
**  ****Large Impact Parameter **
**     ****of the tracks.**

**Tagging the b-jets is important for *****H ************ b************b***** decay modes.**

***Performance of Secondary Vertex Tagging algorithm***

- Jyothsna Rani - Tata Institute

- LLWI, 24th Feb 2005

## SM Higgs Search: WH  lbb

_***SM Higgs Search: WH ***__******__*** l***__******__***bb***_

- Search Strategy:
- Use sample of W(e)+2 b-tagged jets.
- Require exactly 2 jets  to suppress top background.
- 4.4  1.2 events expected and 6 events observed.
- (*WH*)*BR(*H**** b****b* ) < 9.0 pb @ 95% C.L. for mH =115 GeV
- Also (*W* *b****b* ) < 6.6 pb @ 95% C.L. for pT(b) > 20 GeV

**115 GeV**

- Jyothsna Rani - Tata Institute

- LLWI, 24th Feb 2005

## SM Higgs Search: H  WW  ll

-  Search strategy:
-  2 high pT leptons and MET
-  WW comes from spin 0 Higgs:
-          leptons prefer to point in the
-          same direction

**    ******** ***** BR(*****H→WW*****) < 5.7pb **
**@ 95% C.L. for m****H****=160 GeV **

- Jyothsna Rani - Tata Institute

- LLWI, 24th Feb 2005

## Higgs in Minimal Supersymmetry

**MSSM has *****pairs***** of Higgs doublet fields**
*** ******H******u***** couples to up-type quarks and leptons and *****H******d***** ****to down-type**
** *****tan ************ = <H******u******>/<H******d******>***
** ****5 Higgs particles after  EWSB:  *****h******0******, H******0******, A******0******, H******+******, H******-***
** ****h****0**** is predicted to be light: **
***     ******m *****h0***** < ~ 130 GeV***** (MSSM)**

***   ******h******0******, H******0******, A******0***** production**

**      ****@ ****Tevatron**

***    ******Z+b***  **Probe of b-quark PDF ******** *****bh***** and *****single top***** production**
**         ********(*****Z+b*****) / ********(*****Z+j*****) = 0.023 ******** 0.005 (****DØ – hep-ex/0410078)**
**	****	****         ****= 0.018 ******** 0.004** **(CTEQ6 prediction)**

**~ tan ******

- Jyothsna Rani - Tata Institute

- LLWI, 24th Feb 2005

## Higgs Production and Large tan 

** ****Large *****tan************ *****→*****  *****enhanced***** ******bbh/H/A***
** ****At tree level , cross section rises like *****tan******2************ ***
** ****A and h/H are produced simultaneously.**

- CP odd
- Higgs

- CP even
- Higgs

**h**

**H**

**A**

**Total cross section**

- Jyothsna Rani - Tata Institute

- LLWI, 24th Feb 2005

## Analysis Overview

** ****Signal:**
** ****at least 3 b-tagged jets **
** ****Invariant  mass of two leading**
**  ****p****T** **jets**
** ****Backgrounds:**
** “****QCD heavy flavor” : ****  *****bbjj, ccjj, cccc, bbcc, bbbb***
** “****QCD fakes” : *****jjjj***
*** “******Other” : ******Z(bb,cc),***** *****tt***
** ****Kinematic cuts**
** ****Cut on p****T**** of leading jets**
** ****(Optimized for each Higgs mass)**
** ****Search for an excess of events**
**  ****in di-jet invariant mass distribution **
**  ****consistent with a Higgs signal **
**  ****shape.**

** ****Di-jet invariant mass in**
**     ******** ****3b-tagged events**

***260 pb******-1***

- Jyothsna Rani - Tata Institute

- LLWI, 24th Feb 2005

## (b)bh Limits on  and tan 

_***(b)bh Limits on ***__******__*** and tan***__******__*** ***_

**Two benchmark scenarios******** ****Max Mixing: X****t**** = A****t**** - ********cot******** = ********6;**** ****No Mixing: X****t**** = 0**
**For m****A**** = 120 GeV **
**	****** **< 31 pb-1 @ 95% C.L.****      and          ****tan****** **< 55 @ 95% C.L.**** **(**Max Mixing)**

***260 pb******-1***

***260 pb******-1***

***NEW***

- Jyothsna Rani - Tata Institute

- LLWI, 24th Feb 2005

## Summary

**Higgs hunting at Tevatron is ongoing.**
**SM Higgs searches:**
**D****Ø placed l****imits on cross section on *****WH(************ bb).***
******(*****Z+b*****) / ********(*****Z+j*****) ratio has been measured.**
**Understanding of backgrounds is improving.**
***H ************ W W****** searches placed limits on cross section.**
**Non SM Higgs searches:**
**Enhanced Higgs production at high *****tan*********** is used to exclude (*****m******A******, tan***********) plane.**
**Expect substantial improvements in Higgs hunting with ~0.6 fb****-1**** already on tapes.**

- Jyothsna Rani - Tata Institute

- LLWI, 24th Feb 2005