# Presentation: 678617

## A Search for Higgs Decaying to WW(*) at DØ

*presented by*
**Amber Jenkins**
**Imperial College London**
***on behalf of the D************ Collaboration***

**Meeting of the Division of Particles and Fields**
** ****University of California, Riverside, August 30th 2004**

## Overview

**The DØ experiment in Run II**
**Why H********WW****(*)****?**
**Event signature**
**Selection criteria**
**Comparison of Monte Carlo and data**
**The ******** x BR(H********WW****(*)****) limit**
**Conclusions**

## The Upgraded DØ Detector

-  Completely new tracking system, inside 2T magnetic field
-  Inner Si vertex detector (SMT) provides b-tagging capability
-  Excellent Run I calorimetry exploited in Run II
-  Upgraded 3-tier trigger and data acquisition system

## Higgs Searches at the Tevatron

-  Search strategy:
**  ****for a light Higgs (M****H ****<135 GeV)**        - use associated WH or ZH production                               - dominant decay is **H********bb**
**  ****for a heavy Higgs (M****H**** >135 GeV)**          - use ggH production                               - dominant decay is **H********WW****(*)****                **-** **the WW leptonic signature is cleaner

**135 GeV**

- HWW(*)

- SM Higgs decay

*For a heavy Higgs H****WW(*) offers a cleaner decay signal*

- Hbb

## Cross-Section Enhancement From Extra Generations

- Extra quark generations could increase production cross section significantly
- Enhancement factor depends on Higgs and quark masses
- A factor of 8.5 is expected for a 4th generation,    m4=320 GeV

- E. Arik et al, SN-ATLAS-2001-006

## HWW(*): Experimental Signature

- Higgs mass reconstruction not possible due to two neutrinos
- Spin correlations suppress background:
-  WW comes from spin 0 Higgs
-  leptons prefer to point in the same direction
- Event signature: 2 high pT leptons + missing ET
- Search for excess in the leptonic decay modes:      	ee, e and 

**W****+**

**e****+**

**W**-

**e**-

****e

****e

**Look for small opening angle between leptons ********(ll)**

## Data and Monte Carlo Samples

- Analysed data collected between April 2002 and September 2003
-  Final integrated luminosities of **177 pb****-1** (ee), **158 pb****-1** (e) and **147 pb****-1** () for each final state
- Removed runs with hardware failures and incomplete luminosity information
- Monte Carlo events were generated using Pythia or ALPGEN followed by a full detector simulation
- rates normalized to NLO cross section values;
- events overlaid with an average of 0.8 minimum bias events.

## Event Selection

- Event selection includes:
- Require two oppositely charged isolated leptons l = e, 
-  ee: pT(e1) > 12 GeV, pT(e2) > 8 GeV
-  epT(e)   > 12 GeV, pT()  > 8 GeV
-   pT(1) > 20 GeV, pT(2) > 10 GeV
- Missing ET greater than:  20 GeV (ee,e); 30 GeV (
- Removal of mass resonances:
- 12 GeV < m(e,e) < 80 GeV
- m GeV and |m()- mZ| > 15 GeV
- Azimuthal opening angle: e,e)e
- Jet veto  rejects energetic jets:
- ee, eT1 < 90 GeV or ET1 < 50 GeV, ET2 < 30 GeV
- :  ET1 < 60 GeV, ET2 < 30 GeV

- Signal acceptance is ~ 0.02 – 0.2 depending on the Higgs mass/final state

-  Beat down Z/*, W+jets, WW & tt backgrounds

## Data vs. Monte Carlo:Opening Angle, e

**After final                    event selection**

**After basic                    event preselection**

**160 GeV Higgs**

- e Final State

## Data vs. Monte Carlo:Dilepton Invariant Mass

**Distributions after basic event preselection**

**160 GeV Higgs**

- ee Final State

-  Final State

## Data vs. Monte Carlo: Missing ET

- ee Final State

-  Final State

**160 GeV Higgs**

**Distributions after basic event preselection**

**E****T****miss**** (GeV)**

## Data vs. Monte Carlo

| Source |  ll’ = e+e-     
L = 177 pb-1 | ll’ = e
L = 158 pb-1 | ll’ = 
L = 147 pb-1 |
| --- | --- | --- | --- |
| tt  blbl’ | 0.06 ± 0.01 | 0.13 ± 0.01 | 0.03 ± 0.003 |
| WZ  ll’ + X | 0.04 ± 0.01 | 0.11 ± 0.01 |  |
|   e+e- | 0.00 ± 0.01 |  |  |
| WW  ll’ | 1.17 ± 0.02 | 2.51 ± 0.05 | 1.28 ± 0.03 |
| W+jets | 1.24 ± 0.07 | 0.34 ± 0.02 |  |
| QCD/W+jets |  |  | 0.02 ± 0.02 |
| QCD | 0.00 ± 0.50 | 0.00 ± 0.20 |  |
| Z/ e+e- | 0.10 ± 0.10 |  |  |
| Z/  |  | 0.00 ± 0.05 | 3.90 ± 0.60 |
| Z/  | 0.00 ± 0.10 | 0.00 ± 0.10 | 0.00 ± 0.00 |
| Total Background Sum | 2.70 ± 0.40 | 3.10 ± 0.30 | 5.30 ± 0.60 |
| Expected Signal for SM Higgs (MH = 160GeV) | 0.073 ± 0.002 | 0.111 ± 0.004 | 0.085 ± 0.001 |
| Data | 2 | 2 | 5 |

## The HWW(*) Cross-Section Limit

- Cross-section limits have been calculated at 95% C.L. in each leptonic channel by counting events
- Combine likelihood functions from each channel to obtain overall result
- Upper limit on  x BR(HWW(*)) set:
- Agrees well with                                                                                                    predictions from                                                                                                     NLO calculations

****** ****x BR(H********WW) lies between**
**6.6 and 40.1 pb, depending**
**on M****H**

**all channels**

## Conclusions

- D**** has performed a search for HWW(*) in leptonic final states using 147-177 pb-1 of Run II data
- Comparison between data and Monte Carlo looks good
- The number of events observed is consistent with expectations from Standard Model backgrounds
- An upper limit on  x BR(HWW(*)) of between 6 and 40 pb has been set
- result is highly consistent between all three channels
- We look forward to improving the measurement with more data and higher statistics.

## Back-up Slides

## SM Higgs Decay Modes

**135 GeV**

- Hbb

- HWW(*)

## Suppressed Couplings to b,

- Occurs beyond the SM in Top Color or Fermiophobic Higgs models

- L. Brucher, R. Santos, hep-ph/9907434

- Increased HWW(*) branching

## Higgs Sensitivity Reach

## Azimuthal Opening Angle: ll

- An example: e+e- final state C

- ain
- background

## Missing ET

- An example: e+e- final state C

- ain
- background