# Presentation: 662452

## Moriond 2004, La Thuile, Italy                                             March 28 – April 4, 2004

**Standard Model Higgs searches at**
**the Tevatron**
**Avto Kharchilava**
**University of Notre Dame**
**For the CDF and DØ Collaborations**

## Outline

**Introduction**
**Tevatron in Run II**
**CDF and DØ detectors**
**DØ: limits on Wbb/WH**
**CDF: limits on WH production**
**DØ: ********(Z+b)/********(Z+j) ratio**
**DØ: H********WW****(*)********l****+****l****-**** searches**
**Summary**

**Thanks to**
- Accelerator team for good performance of the Tevatron in 2004
- CDF and DØ colleagues for their contribution to these studies

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

- Avto Kharchilava

- Moriond'04

## Tevatron: current and projected performance

- Avto Kharchilava

- Moriond'04

## The SM Higgs production cross sections

- Production cross sections are small 1 - 0.1 pb depending on the MH
- Hbb decays are dominant at    MH 135 GeV
- searches can be performed in W/Z associated production to handle backgrounds
- HWW(*)l+l- final states can be explored at higher masses
- Light Higgs preferred by global fit
- MH < 211 GeV at 95% C.L.
- LEP limit from direct searches
- MH > 114.4 GeV at 95% C.L.
**We may have Higgs in our data !**

- Avto Kharchilava

- Moriond'04

## The upgraded CDF and DØ detectors

- New
- silicon detector
- drift chamber
- TOF PID system
- Upgraded
- calorimeter, muon system
- DAQ/trigger
- displaced-vtx trigger

- New (tracking in B-field)
- silicon detector
- fiber tracker
- Upgraded
- muon system, calorimeter
- DAQ/trigger
- (displaced-vtx trigger soon)

**Higgs searches demand**
**all of these ...**

- Avto Kharchilava

- Moriond'04

## b-jet tagging

- Performance being improved

**b-jet tagging**

- Essential for Hbb searches
- DØ in Run II has joined CDF
- Can make use of the track impact parameter (IP) measurements or secondary vertex reconstruction
**CDF:** performance of sec. vtx.  algorithm (after kinematics cuts)
**~50% b-tag** efficiency for **~0.6%** light quark **mis-tag** rate in **|******** < 2**

- Both experiments are demonstrating good b-tagging capabilities

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- Moriond'04

## DØ: W(e)bb associated production (1)

- Event selection include
- Central isolated e pT > 20 GeV
- Missing ET > 25 GeV
- ≥ two jets: ET > 20 GeV, || < 2.5
- 2587 evts. in Lint=174 pb-1 of data

- Good understanding of data

- Simulations with Alpgen plus Pythia through detailed detector response
- Cross sections normalized to MCFM NLO calculations

- Avto Kharchilava

- Moriond'04

## DØ: W(e)bb associated production (2)

- Observe 8, expect 8.3±2.2
- Bkgd. dominated by top evts.

- Require jets to be tagged
- Exercise various b-tag algorithms
- All yield consistent results

- Good agreement between data and MC in both cases

- Avto Kharchilava

- Moriond'04

## DØ: W(e)bb associated production (3)

- Suppress the top production by requiring exactly two jets
- Observe **2 evts**., expect **2.5±0.5**
- Sample composition

- Set limits on production of
******(Wbb) < 20.3 pb**
******(WH)B(H********bb) < 12.4 pb      ****	****	****for M****H**** = 115 GeV**
**	**at 95% C.L.
- Systematics studies for Wbb
- (Systematics smaller for WH)

| Wbb | Wc(c) | Wjj | tt+t | Others |
| --- | --- | --- | --- | --- |
| 1.4±0.4 | 0.3±0.1 | 0.1±0.03 | 0.6±0.2 | 0.1±0.03 |

| Source | Uncertainty
 (%) |
| --- | --- |
| Jet energy scale | 17 |
| b-tagging | 11 |
| Trigger & e ID | 5 |
| EM scale | 5 |
| MC simulations | 15 |
| Total | 26 |

- Avto Kharchilava

- Moriond'04

## CDF: W(e/)H(b) associated production (1)

- Event selection include
- Central isolated e/ pT > 20 GeV
- Missing ET > 20 GeV
- Two jets: ET > 15 GeV, || < 2
- Veto
- Di-lepton, extra jet, etc.
-  Observe 2072 events in data
- Simulations performed with Alpgen plus Herwig passed through detailed detector response

- Good agreement between
- data and MC

- Avto Kharchilava

- Moriond'04

## CDF: W(e/)H(b) associated production (2)

- Enrich the b-content of events
- Require at least one b-tagged jet
-  Observe 62 events in data
-  Expect 61 ± 5 events
- Main contributions to the bkgd.
- Expect 0.3 evts from Higgs
- Signal acceptance of ~ 1.8% for
- MH = 110 – 130 GeV

- Again, good agreement between
- data and MC

| Mistags | Wc(c) | Wbb | QCD | top |
| --- | --- | --- | --- | --- |
| 14 | 13 | 12 | 10 | 9 |

- Avto Kharchilava

- Moriond'04

## CDF: W(e/)H(b) associated production (3)

- Set limits on the Higgs production cross section times branching fr.:
******×B < 5 pb**
- Systematics studies

- Exceeds CDF’s Run I limit ******×B < 14 – 19 pb**
- for **M****H**** = 70 – 120 GeV**      PRL 79, 3819 (1997)

| Source | Uncertainty
 (%) |
| --- | --- |
| ISR / FSR | 19 |
| Secondary vertex | 8.6 |
| Lepton ID | 5 |
| Jet energy scale | 3 |
| PDF | 1 |
| Trigger | 0.7 |
| Total | 22 |

- Expect improvements due to
- Better di-jet mass resolution
- More sophisticated analysis techniques

- Avto Kharchilava

- Moriond'04

## Motivation
Background to ZH production
Benchmark for SUSY Higgs production via gbbh
Probes PDF of the b-quark

Examples of ZQ (Zj) LO diagrams

Measure cross section ratio
(Z+b)/(Z+j)
Many uncertainties cancel

- Background to ZH production
- Benchmark for SUSY Higgs production via gbbh
- Probes PDF of the b-quark
- Examples of ZQ (Zj) LO diagrams
- Measure cross section ratio
******(Z+b)/********(Z+j)**
- Many uncertainties cancel

**DØ: Z(********ee/********)b associated production (1)**

- Data correspond to integrated lumi. of 184 (ee), 152 () pb-1
- Event selection include
- Isolated e with pT > 15/20 GeV, || < 2.5/2.0
- Z peak for signal, side bands for bkgd. evaluations
- Jet ET > 20 GeV, || < 2.5
- At least one b-tagged jet
- Simulations performed with Pythia or Alpgen plus Pythia passed through detailed detector response
- Cross sections normalized to data
- Relative b- and c-quark content as given by MCFM NLO calculations

- Avto Kharchilava

- Moriond'04

## DØ: Z(ee/)b associated production (2)

- Transverse energy spectrum of b-tagged jets
- QCD and mistag bkgd. estimated from data
- MC: Pythia Zb normalized to data

- Measure cross section ratio Z+b/Z+j
**  ****0.024 ± 0.005 (stat)               (syst)**
- Theory: **~0.02    **        hep-ph/0312024
- Systematics studies

| Source | Uncertainty
 (%) |
| --- | --- |
| Jet tagging | 16 |
| Jet energy scale | 11 |
| Bkgd. estimation | 6 |
| (Z+c)/(Z+b) | 3 |
| Total | 20 |

**+ 0.005**
**–** **0.004**

- Avto Kharchilava

- Moriond'04

## DØ: H  WW(*)  l+l- final states; l = e,  (1)

**DØ: H ******** WW****(*********) ******** l****+****l****-******** final states; l = e, ******** (1)**

- Event selection include
- Isolated e/
- pT(e1) > 12 GeV, pT(e2) > 8 GeV
- pT(e/1) > 12 GeV, pT(e/2) > 8 GeV
- pT(1) > 20 GeV, pT(2) > 10 GeV
- Missing ET greater than
- 20 GeV (ee, e); 30 GeV ()
- Veto on
- Z resonance
- Energetic jets
- Simulations done with Pythia passed through detailed detector response
- Rates normalized to NLO cross section values
- Data correspond to integrated lumi. of
- ~ 180 (ee), 160 (e) and 150 () pb-1

**Data vs MC after**
**evt. preselection**

- Avto Kharchilava

- Moriond'04

## DØ: H  WW(*)  l+l- final states; l=e,  (2)

- Employ spin correlations to suppress the bkgd.
- (ll) variable is particularly useful
- Leptons from Higgs tend to be collinear

**DØ: H ******** WW****(*********) ******** l****+****l****-******** final states; l=e, ******** (2)**

- Azimuthal angle between e and 
- (after event pre-selection)

**Higgs of 160 GeV**

- Good agreement between data and MC in all
- final states, and all variables examined so far

- Avto Kharchilava

- Moriond'04

## DØ: H  WW(*)  l+l- final states; l=e,  (3)

- Dominant bkgd. in e sample

**DØ: H ******** WW****(*********) ******** l****+****l****-******** final states; l=e, ******** (3)**

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

| WW | W+jets | WZ | tt |
| --- | --- | --- | --- |
| 2.51±0.05 | 0.34±0.02 | 0.11±0.01 | 0.13±0.01 |

|  | ee | e |  |
| --- | --- | --- | --- |
| Observed | 2 | 2 | 5 |
| Expected | 2.7±0.4 | 3.1±0.3 | 5.3±0.6 |

- Excluded cross section times
- Branching Ratio at 95% C.L.

**Higgs of 160 GeV**

- Avto Kharchilava

- Moriond'04

## Summary

- Hunting for Higgs at the Tevatron Run II has begun !
- Recent improvements of the Tevatron performance are encouraging
- Upgraded CDF and DØ detectors are producing the world class physics results
- Understanding of the background processes to the Higgs production is gradually improving
- Limits set on Wbb, WH and HWW(*) productions are unmatched or superior to Run I
**Higgs searches will form a central part of the Tevatron physics program**

- Avto Kharchilava

- Moriond'04