# Presentation: 805730

## Search for Fermiophobic and Topcolor Higgs in the Diphoton Final States at DØ

**Search for Fermiophobic and Topcolor Higgs in the Diphoton Final States at**** ****D****Ø**

**DPF 2004                August 30                  Riverside, CA**

**Alex Melnitchouk****                     ****University of Mississippi****                             ****for the D****Ø collaboration**

## h Decay Mode in the SM and Beyond. Why  

-  no tree-level H coupling (Higgs boson is neutral)
- Di-photon decays happen via W 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 boson

- 

- (top-quark loop reduces H width by 20-30% due to destructive interference)

## How Can h Decays be Enhanced

- One possibility: suppress fermion decay rates (then the full decay width would only be shared with hWW and HZZ decays)
- In the Standard Model Higgs is responsible for both **Electroweak symmetry breaking (EWSB)** and **fermion masses**
- Higgs-**W,Z**/**fermion** interaction terms                                    in the SM Lagrangian are:                                                                               			              (1/**v**) 2m2WW+W-H                        		                          (1/**v**) m2ZZZH               	                                 (1/**v**) mfH
- Relative strength of **Higgs-W,Z** and **Higgs-fermion** couplings is fixed by **v**                                      (Higgs field vacuum expectation value)
- In a more general situation different sectors of theory  (or different mechanisms) could be responsible for **EWSB** and (some of) **fermion masses** => Higgs couplings to fermions and those to weak gauge bosons can vary independently

## Some Examples of h Enhancement

- Strong dynamics [1] :**                                                    EWSB = via technicolor condensation,**                 fermion masses = via “extended techncolor”
- Generic two Higgs doublet model [2]:                                                    **v1 – W,Z masses**,  v2 – fermion masses
- Top-condensation model + Higgs [3]                                 top and bottom quarks get their masses from the topcolor interaction while **Higgs gives mass to remaining fermions and gauge bosons**
- Topcolor Higgs=(top,vector-like quark )[4]                    Top quark mass from Higgs, other fermion and **W/Z masses -- from other interactions present in the theory**
- Still another possiblity of h enhancement arises when the Higgs field extends into **large extra dimensions** (while fermion and gauge boson fields remain confined to 3D) [5]
-                                                                                                                               [1] E.Farhi (CERN), L. Susskind Phys,.Rept.**74**, 277 (1981)                                                 [2] H.E.Haber et al, Nucl. Phys. **B161**, 493 (1979)                                                         [3] J.D. Wells, Phys. Rev. **D56**,  1504 (1997)                                                                        [4] B.Dobrescu, Phys. Rev**. D63, **015004 (2001)                                                                     [5] L. Hall, C.Kolda, Phys. Lett. **B459**, 213 (1999)

## Major Backgrounds :               Drell-Yan and QCD

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

- e.g.

- e.g.

## A Slice of the DØ Detector. Experimental Signature of a Photon

**Jet**** **

**Photon**

- EM showers

**Electron **

- hadronic                     shower

**                                                                                    ****Photon :  ** EM-like shower in the calorimeter                  	     WITHOUT associated track

**track**

## Analysis Outline

- Select 2 Energetic Photon Objects
- Estimate SM backgrounds:**     **
**      ****-  ****QCD (jj and ********j)**                                                         **-  ****Z/********ee****                                                                 -  **direct di-photons  (PYTHIA MC                                			   with k factor of 1.4)
- Look for a bump                                                           in the diphoton invariant mass spectrum

**Analysis Outline**

- from data with absolute normalization

## 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)
-                                   -- sum of  pT of all tracks                   	                   in a hollow cone of 0.05<R<0.4 around  			     photon candidate must be < 2.0 GeV
-  	                            -- track veto
**EM = Electromagnetic Object (Photon or Electron)** **	**	*

## Event Displays of Candidate 

**Mass = 125.8 GeV**

- 14

##  Di-photon mass spectra,                   Ldt  190pb-1 ( half of the currently available data) 

**Diphoton PT (35 GeV)cut**

## Setting Limits on the Diphoton Branching Fraction 

-  Count di-photons in a mass window
-  Derive Higgs cross section limits using Bayesian Approach
-  Convert to limits on branching fractions
-  Consider two scenarios:
***-- Fermiophobic Higgs                                        ****(does not couple to fermions)                     *Production mechanisms:
- 	1. W/Z associated production               		2. W/Z fusion
***--Topcolor Higgs                                                    ****(**of all** **fermions couples** **only to** top)              *Production mechanisms:
- 	1. W/Z associated production               		2. W/Z fusion                                    		3. gluon fusion

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

## B(h) Limits 

## Neural Net Studies

- Try to use Neural Nets for photon identification to suppress background
- Preliminary studies indicate significant improvement over current EMID
- Plan to incorporate new ID in the analysis

- Neural Net performance curves. Varying training method parameters

## Conclusions

- A Search for the Fermiophobic and Topcolor Higgs boson has been performed in the inclusive  h  X   channel with 190 pb-1 of DØ data collected between April 2002 and September 2003
- In the absence of excess we set limits on the branching fraction
- Limits are comparable with those of DØ Run I
- Work on improving sensitivity is in progress
- More data is being accumulated
- Stay tuned for new results

## Back Up Slides Start Here

## 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

## Identification of a Photon Shower  in the Calorimeter. Isolation

- Photon-induced shower is smaller than quark/gluon shower both transversely and longitudinally

## Photon ID Tools                    (Monte Carlo Distributions)

**EM fraction**

**Isolation ****(previous slide)**

**multi-variable shower shape tool**

- ratio of EM cluster energy deposited in EM calorimeter and total energy

- measure of cluster narrowness

- - layer energy fractions                           -width at shower maximum

## 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

**(Z*)**

**(Z)**

- W/Z associated

- W/Z fusion

- quark-antiquark fusion                      cross-section  is small :
-  Higgs-fermion coupling ~ mf
-   Masses of u,d quarks are small

## DØ Calorimeter

- Uranium/Liquid Argon Sampling Calorimeter
- Three modules: -- Central Calorimeter (CC)                		       -- Two End Calorimeters (EC)

**Unit cell**

- End-View of Central   Calorimeter

## DØ Tracking System

**(0,0,0)**

-   Central Fiber Tracker
-   Silicon Microstrip Tracker

- One-quarter r-z view

- End-View                  of the                  Central Fiber Tracker

## Silicon Tracker.          Longitudinal View

****** ****50 cm**

- Barrel/Disk                         Design:

## Background Estimation Example: Zee

**     ****N****DY****(********)****=********(pp********Z/********+X) ******** ****Br(ee) ******** L****int  ******** A **** ******** ********(trigger)****                                                     ****	****	****                         ******** ********2****(EM) ******** ****[1****- ********(track)] ****2**

-        **N****DY****(ee) **=******(pp********Z/********+X) ******** Br(ee) ******** L****int ******** A ******** ********(trigger)                                    ****	****	****	****           ******** ********2****(EM) ******** ********2****(track)**

**N****DY**(****) **= ****N****DY****(ee)**  **[1****- ********(track)] ****2 ****    ****= **
**	****                    ********2****(track)**

-            **= {****N(ee) - N(misidentified ee)}**  **[1****- ********(track)] ****2**** ****	****	****                                                     ** ******2****(track)**

**                ****= {****N(ee) - N(di-LooseEM)********f ****2****(e)****}**  **[1****- ********(track)] ****2**** ****	****	**                                                          ******2****(track)**

- Electron misidentification rate

-  Tracking efficiency