# Presentation: 865780

## Search for the Higgs Boson   in the h Channel

**Search for the Higgs Boson   in the** **h****** **Channel**

** ****APS-DPF 2003   ****	****Philadelphia**

- Alex Melnitchouk Brown University
-  **on behalf of the         D****Ø collaboration**

## Leading SM Higgs Production Processes at Tevatron

**	**

** ****80   100   120    140   160**

**0.01**

**0.1**

**1.0**

**10.0**

**Higgs Mass, GeV**

**Cross-Section, pb**

- gluon fusion

-  :   cross-section ~ m2                              the top-quark loop is dominant

- W/Z associated

- W/Z fusion

## h decay  in the Standard Model

-  no tree-level H coupling (Higgs is neutral)
-  diphoton decays happen via W or top-quark loop:                   						                     																																		           H branching fraction is small: ~ 10-3-10-4                   Higgs decays mostly to b-quark and W pairs
- however many extensions of the SM                                                          predict enhanced  decay rate of the Higgs

## h decays can be enhanced

- due to** suppressed couplings** to
- 	 **** all fermions    *(Fermiophobic Higgs)*                                                   	*H.E.Haber et al, Nucl. Phys. ****B161****, 493 (1979)  *
*       ****** *all fermions but top quark   *(Topcolor Higgs)*                                              	*B.Dobrescu, Phys. Rev****. D63, ****015004 (2001) *
**	**** ****** top and bottom quark*                                                          **	**J.D. Wells, Phys. Rev. ****D56****,  1504 (1997)*
**	**** ****** down-type fermions,                                            	                       	*H. Baer, J.D. Wells, Phys. Rev. ****D57****, 446 (1998)*
- Enhanced  rate is also predicted by some models that employ **Large Extra Dimensions**                                                  *L. Hall, C.Kolda, Phys. Lett. ****B459****, 213 (1999)*
- in addition   decay loop can be enhanced by a contribution from a **heavy charged particle** coming from new physics

## Examples of Enhancement            of h decays 

**h************ ****Branching Fraction **

**Higgs Mass, GeV**

**Standard Model**

**no couplings to fermions ***(Fermiophobic Higgs)*

- no couplings to                    down-type fermions

- in general we should be prepared for any h

- branching fraction ( up to 1.0 ) due to new physics

*S.Mrenna, J.Wells, Phys. Rev. ****D63****, 015006 (2001) *

- no couplings to                        top,bottom quarks

## h Search Strategy                              Focus on 2 Scenarios

***Fermiophobic Higgs ****(does not couple to fermions)*
- Production: W/Z associated + W/Z fusion
- Main signature with diphotons :  + 2jets
- Current Mass Limits** :                                                         ****D0/CDF RunI :       78.5 / 82.0 GeV **at 95% CL
-  **LEP :**  **108.3 GeV **at 95% CL *hep- ex/0212038 (2002)*
***Topcolor Higgs ****(of all fermions couples only to top)*
- Production: all three leading processes
- Main signature with diphotons :  
***Remaining models would give similar signal to                  one of the two scenarios:****                                                         e.g. no couplings to down-type fermions **** topcolor **	** no t,b couplings **** fermiophobic; *

*B.Abbot et al. Phys. Rev. Lett. ****82****, 2244 (1999 )                                                      F.Abe et al. Phys. Rev. ****D59****, 092002 (1999) LEP*** **

**Current   **setting limits on Cross-Section   B()                                                                **Focus :     **for the Topcolor Higgs assuming SM couplings

## Major Backgrounds :               Drell-Yan and QCD

**Z/************e****+****e****-**** **with                              e+e- misidentified                           as photons

** ****1. two photons **

- e.g.

**  ****3. two hadronic jets misidentified as photons                         **

** ****2. a photon**** **and** ****a hadronic jet   misidentified as photon**** **

**QCD processes**  **that in the final state  contain** :

- e.g.

## Selection                                              of Candidate Events

***Trigger:***                                                                           di-EM* high pT trigger
***Offline:*** *(on both objects)*
**    ****Kinematic cuts: **pT > 25GeV
**    ****Acceptance cuts: **Central or End Cap 			            Calorimeter up to ||=2.4
**     ****Photon ID:  **-** **shower shape consistent 		      with EM* shape (EMfraction, 		      Isolation, H-matrix 2)
-  		               - track veto
- 	 **EM = Electromagnetic Object (Photon or Electron) **	**	*

## Invariant Mass and               from Data and Signal MC

- Central Calorimeter

- End-Cap Calori- meter

**EM**

**Hadronic**

**Events / 3GeV**

- DØ RunII Preliminary

- DØ RunII Preliminary

**EM**

**Hadronic**

- look  separately at :                        – both ’s central                – both ’s in end-cap                     – central, end-cap

- Detectors differ slightly in  mass resolution and                      ID performance

## Mass Distributions                     and Event Counts (Ldt=52pb-1)

| Event Count (Central,Central) |
| --- |
|    QCD background : 411  48 |
| Drel-Yan background : 107  24 |
|    Total background : 519  53 |
|                        Data :  577 |

| Event Count (Central,End-Cap) |
| --- |
|    QCD background : 507  34 |
| Drel-Yan background : 182  24 |
|    Total background : 689  42 |
|                        Data :  707 |

| Event Count (End-Cap,End-Cap) |
| --- |
|    QCD background : 232  16 |
| Drel-Yan background : 42  14 |
|    Total background : 275  21 |
|                        Data :  322 |

## Higgs Cross-Section Limits (Assuming B(

-   Approaching B(h   region of interest
-   To increase sensitivity : need analysis optimization  and better understanding  of photon misidentification rate

-   Make a counting experiment in the optimized mass resolution dependent sliding mass window

- Experimental Upper Limit @ 95% CL

*Ldt*=52pb-1

- 

- DØ RunII Preliminary

*G.Landsberg , K.Matchev*  *Phys. Rev. ****D62****, 035004 (2000)*

## Conclusions

- A Search for the Topcolor Higgs was performed in the inclusive h  X   channel with 52pb-1 of DØ data collected between September 2002 and January 2003
- Measured  spectrum is in agreement with the Standard Model background predictions
- First attempt to set Cross-Section Limits with DØ  RunII   data has been made
- Work on improving sensitivity is in progress
- Another search for the Higgs                                   with suppressed fermion couplings at DØ                                          (HWWtalk by Peter Tamburelo tomorrow)
- More data is being accumulated
- Stay tuned for new results