# Presentation: 435908

## Searches for the Standard Model Higgs at the Tevatron

***presented by***
***Per Jonsson***
***Imperial College London***
***On behalf of the CDF and DØ****** ******Collaborations***

## Outline

*Outline*

**Introduction**
**Higgs ******** bb (low mass)**
**ZH ******** ********bb**
**WH ******** l********bb**
**Higgs ******** WW (high mass)**
**WH ******** WWW**
**H ******** WW**
**Limits:**
**combination**

**36×36 bunches**
**396 ns bunch crossing**

**New results!**

**New result!**

**New result!**

- Only new results since last year’s Moriond are shown

## Tevatron Performance

- Per Jonsson - Imperial College London

*Tevatron Performance*

- Currently in shutdown:
-  Silicon and Trigger upgrades

**Run I**

- 4-8 fb-1 expected by end of 2009

**This talk:**
**261-950pb****-1**

## The DØ  and CDF detectors

- Per Jonsson - Imperial College London

*The DØ  and CDF detectors*

- The Standard Model Higgs Boson is:
-  Key part of Electro-Weak symmetry breaking
-  A scalar with the Higgs mass as the only free parameter
- DØ and CDF constrain the SM Higgs boson mass:
-  Indirectly: Top and W mass measurements
-  Directly: **Search for Higgs boson production**

## EW constraints on Higgs

- Per Jonsson - Imperial College London

*EW constraints on Higgs*

**m****H ****=89 +45 -30 GeV**

**m****H****<175 GeV**** ****@95%CL**
**(< 207 GeV if LEP2 limit incl.)**

- A light Higgs is favored

- 68% CL

- [GeV]

- [GeV]

- LEPEWWG 18/03/06

## SM Higgs Production

*SM Higgs Production*

**Production cross sections are small: 0.1-1 pb depending on m****H****:**
**~1 in 10****12 ****pp events is a Higgs**
**M****H****< 135 GeV: decay to bb**
**gg ********H ********bb ****overwhelmed by QCD background **
**searches can be performed in ****W/Z associated ****production with lower background**
**Best channels:**
**WH********l********bb, ZH************bb**
**M****H ****> 135 GeV: decay to WW**
**gg ********H ********WW****(*)**** ********l****+****l****-******
**WH ********WWW****(*)**** **
**final states can be explored**

- We probably have a Higgs in our data already!

## Backgrounds and Tools

*Backgrounds and Tools*

** ****Lepton identification**
** ****Missing transverse energy**

**Measurements also rely on:**
**Jet reconstruction**
**B-tagging:**
- Use track impact parameter (IP) measurements or secondary vertex reconstruction

**IP**

**Both detectors are delivering the excellent performance needed**

**Understanding and modeling of background is critical:**
**Especially so for advanced analysis techniques**
**Electroweak backgrounds **
**     ****(W, Z, WZ, WW, Top):**
- Monte Carlo distributions normalized to (N)NLO cross sections
**QCD and instrumental background taken from real data control samples**

## Z/ ee + jets

- Comparison of jet multiplicities and distributions in data and MC:
- Pythia 6.319 vs. Sherpa 1.0.6
- Sherpa : Matrix Element + Parton showers, using CKKW algorithm

- Event selection includes:
- Electron pT > 25 GeV, 
- 70 GeV < Mee < 120 GeV

**New result!**

- Sherpa agrees well with data
- upto njet=4

- L=~950 pb-1

- L=~950 pb-1

- For details see Gavin’s
- talk yesterday.

##  ZH bb

* **ZH ******bb*

**Event selection includes:**
**≥ ****1 tagged b-jets**
**Two jets with E****T  ****> 60/25 GeV**
**E****T ****miss**** ****> 70 GeV**
**Backgrounds:**
**W/Z + heavy flavour jets**
**QCD**
**Di-bosons**
**Mis-tagged b-jets**
**Top pairs**

**M****H  ****= 120 GeV, 80 < m****jj ****< 120 GeV**
**6 events observed**
**4.36 +/- 1.02 predicted**
**************pb**

- ET1  = 100.3 GeV
- ET2 = 54.7 GeV
- ETmiss = 144.8 GeV
- Mjj = 82.1 GeV

## Improved event selection includes:
Two acoplanar jets with:
 ET > 20 GeV
ETmiss > 50 GeV
Sum of scalar jet ET < 240 GeV

Separate analysis for single and double b-tagged events:
Increased statistics

**New result!**

- L=261 pb-1

- L=261 pb-1

**1 b-tag**

**2 b-tags**

**Improved event selection includes:**
**Two**** acoplanar**** jets with:**
** ****E****T ****> 20 GeV**
**E****T****miss ****> 50 GeV**
**Sum of scalar jet ****E****T ****< 240 GeV**
**Separate analysis for single and double b-tagged events:**
**Increased statistics**

**m****H ****= 115 GeV,  75 < m****jj**** < 125 GeV:**
**11 events observed**
**9.4 +/- 1.8 predicted**
**************pb**
- Same analysis for WH lbb with missed lepton improves the WH limit

* **ZH ******bb*

## Muon and electron channel combined:
1 or 2 tagged b-jets
electron or muon with pT > 20 GeV 
ETmiss > 20 GeV

**1 or 2 tagged b-jets**
**electron or muon with**** ****p****T**** > 20 GeV **
**E****T****miss ****> 20 GeV**

- Per Jonsson - Imperial College London

-  **Main backgrounds:**
** ****W + jets**
** ****Top pairs**
** ****di-bosons (WW, WZ etc.)**

- e/

- 

- b jet

- b jet

* **WH****l****bb , (l=e,***

## New muon analysis
Re-optimized electron analysis
Separate single and double 
    b-tag analysis 

Event selection includes:
Central isolated e/
 pT > 20 GeV
Missing ET > 25 GeV
≥ two jets: 
ET > 20 GeV, |η| < 2.5
One or two tagged b-jets

Limit from combined channels:
mH = 115 GeV, 85 < mjj < 140 GeV:
6 (32 ST) events observed
9.3 (45.1 ST) predicted
pb

**Re-optimized electron analysis**
**Separate single and double **
**    ****b-tag analysis **
**Event selection includes:**
**Central isolated ****e/******
****** ****p****T ****> 20 GeV**
**Missing E****T**** ****> 25 GeV**
**≥ ****two jets:**** **
**E****T**** > 20 GeV, |η| < 2.5**
**One or two tagged b-jets**
**Limit from combined channels:**
**m****H ****= 115 GeV, 85 < m****jj**** < 140 GeV:**
**6 (32 ST) events observed**
**9.3 (45.1 ST) predicted**
**************pb**

**New result!**

*WH****l****bb, (l=e,***

- Per Jonsson - Imperial College London

**Event selection includes:**
**Two isolated like signed leptons (ee,e******
**p****T ****> 15 GeV**
**E****T****miss ****> 20 GeV**
**************m****H****=115 GeV)********pb**

*WH****WWW**(*)****ll****qq,**** (l=e,***

- Per Jonsson - Imperial College London

- Mainly di-bosons (WZ)

- CDF 194 pb-1

- L=363 pb-1

|  | observed | expected |
| --- | --- | --- |
| ee | 1 | 0.70 +/- 0.08 |
| e | 3 | 4.32 +/- 0.23 |
|  | 2 | 3.72 +/- 0.75 |

## 
Higgs mass reconstruction not possible due to two neutrinos

Employ spin correlations to suppress the background
 (ll) variable is particularly useful
Charged leptons from Higgs are collinear

 Event selection includes:
Two leptons (e/
pT > 20/10 GeV
Missing ET greater than
MH/4
Di-lepton invariant mass
> 16 GeV
< MH/2-5 GeV 

ll distribution fitted to extract 95% CL limit

SM cross section still far away, but 4th generation models getting closer

**Higgs mass reconstruction not possible due to two neutrinos**
**Employ spin correlations to suppress the background**
** ********(ll) variable is particularly useful**
**Charged leptons from Higgs are collinear**
** ****Event selection includes:**
**Two leptons (e/******
**p****T**** > 20/10 GeV**
**Missing E****T**** greater than**
**M****H****/4**
**Di-lepton invariant mass**
**> 16 GeV**
**< M****H****/2-5 GeV**** **
******ll**** distribution fitted to extract 95% CL limit**
**SM cross section still far away, but 4****th**** generation models getting closer**

**m****H****= 130 GeV**

**m****H****= 160 GeV**

*H****WW**(*)****l**+**l**-****, (l=e,***

## L= 950 pb-1

ee and echannels

Event selection includes:
Isolated e/
pT(e1, e2) > 15, 10 GeV
pT(e/1) > 15 GeV,
pT(e/2) > 10 GeV
Missing ET greater than
20 GeV (ee, e)
Veto on
Z resonance
Energetic jets

MH = 120 GeV:
31 events observed
32.7 +/- 2.3 (stat) predicted
Bkg systematic uncertainty: 15%
pb

**L= 950 pb****-1**
**ee and e********channels**
**Event selection includes:**
**Isolated e/******
**p****T****(e****1, ****e****2****) > 15, 10 GeV**
**p****T****(e/********1****) > 15 GeV,**
**p****T****(e/********2****) > 10 GeV**
**Missing E****T**** greater than**
**20 GeV**** (ee, e********)**
**Veto on**
**Z resonance**
**Energetic jets**
**M****H ****= 120 GeV:**
**31 events observed**
**32.7 +/- 2.3 (stat) predicted**
**Bkg systematic uncertainty: 15%**
**************pb**

- Per Jonsson - Imperial College London

**New result!**

- ee

- e

- After cuts

- 160 GeV Higgs (x 10)

*H****WW**(*)****l**+**l**-**** (l=e,***

## Currently a factor 15 away from 
   mH =115 GeV

With L= 2 fb-1, both experiments, NN b-tagging, NN analyses, track-cal jets, increased acceptance, new channels, full cross efficiency, and reduced systematics:
Cross section factor  = 1.2

- Currently **a factor 15** away from
-    mH =115 GeV
- With L= 2 fb-1, both experiments, NN b-tagging, NN analyses, track-cal jets, increased acceptance, new channels, full cross efficiency, and reduced systematics:
**Cross section factor  = 1.2**

**New result!**

*Combined limit*

- New combined limit from all SM Higgs search channels!
- 14 orthogonal search channels (incl. single and double-tag analyses and
-        WH lbb w. missed lepton)
- Full account taken of systematic uncertainties
- High mass region benefits from HWW analyses

## Limits

## Summary

*Summary*

- Many results already and more with increased stats are coming soon!

**The Tevatron and the experiments are performing well**
**A wide range of Standard Model Higgs searches have been performed by both CDF and D0 with up to 1 fb****-1 ****RunII data:**
**No deviation from the SM background expectation observed**
**Work underway to improve sensitivity:**
**First combination of all channels from D0**
**Very exciting prospects for the future:**
**Sensitivity to m**** H ****> 114 GeV**** **** starts at ~2 fb****-1**
**Exclusion up to 180 GeV possible with 8 fb****-1**

## Back-up slides

## SM Higgs Sensitivity

*SM Higgs Sensitivity*

**New Higgs sensitivity study from CDF + DØ in 2003:**

## Major Improvements

- 6x more lumi (2 fb-1 ): 2.4
- We need both CDF and D0: 1.4
- Multivariate analysis: 1.7
- NN b-tagging: 1.35
- Di-jet mass resolution: 1.2
- Additional search channels: 1.15