# Presentation: 302094

## Higgs Searches at D0 

- V. Daniel Elvira (Fermilab)                                                 for the D0 Collaboration

## Outline

- <footer>

- WIN’03, October 7th 2003

**Outline**

-  Motivation, previous measurements.
-  Accelerator and D0 detector upgrades, current   performance, prospects.
-  Higgs sensitivity studies (1999, 2003,...)
-  D0 preliminary results related to SM Higgs   searches.  (Non-SM discussed in next talk by G.   Watts).

- _[www-d0.fnal.gov/Run2Physics/higgs](http://www-d0.fnal.gov/Run2Physics/higgs)_**   and follow the link**
**to public documents for more information on the D0 results**

## The search for the Higgs boson is an important part of the Run II Tevatron program.
     Motivation: understand the nature of electroweak symmetry breaking
Direct searches at LEP exclude a SM Higgs below 114.4 GeV at 95% C.L.
A global fit to SM measurements gives limit of mH < 211 GeV (LEP’2003, 95% C.L.)

-      Motivation: understand the nature of electroweak symmetry breaking
- Direct searches at LEP exclude a SM Higgs below 114.4 GeV at 95% C.L.
- A global fit to SM measurements gives limit of m**H **< 211 GeV (LEP’2003, 95% C.L.)

**Introduction**

## Higgs Production I:

- _Low Mass Searches_ (MH < 130 GeV):
- gg H  (H bb)
- qq  W/Z  W/Z +H

- _High Mass Searches_ (MH >150 GeV):
- gg H (WW*)

**Higgs Production I:**

- Gluon fusion
- (large background)

- Associate production

- _Standard_
- _Model_

## Higgs Production

**Higgs Production**

- _Beyond SM_

- In a two Higgs-doublet SUSY model (h**0**,H**0**,A**0**,H**+-**), the b-Higgs coupling is proportional to tan Study _Higgs associated production with two b’s_:

- gg/qq          bbH

-  _Fermiophobic/Topcolor Higgs_ can occur in Type-1 2-doublet Higgs models

- qq      W*/Z*     W/Z+h
- qq      WW*      h

-  _Pair production of double charged Higgs bosons_ (left-right symmetric or triplet models)

- qq     Z *     H**++**H**--**

## Higgs Decay

- gg  H bb  hopeless (H  maybe)
- H(W  l) and H(Z  ll/): best

- H (W  l)(W* l): best
- H WZ* (W l / Z ll)

- bbH (bb)

- W/Z+h (h       )
- WW      h  (h       )

- H**++**H**–-**** **      ++--**   **

- _Low Mass Searches_

- _High Mass Searches_

- _Higgs associated production with two b’s_

- _Fermiophobic Higgs_

- _Pair production of double charged Higgs bosons_

- Need excellent understanding of ,e, , jets, b-tagging,

## The Run II Tevatron

-  Accelerator Improvements: (Main Injector, Recycler, etc.)

- 1.8 TeV

- Luminosity:   100 pb-1  (Run I)
-                      > 4 fb-1 (Run II)

- 220 pb-1 written by DØ to tape before the shutdown

- 1.96 TeV

- D0

- Main Injector

- Tevatron

**The Run II Tevatron**

-  20-30% increase in the SM Higgs cross section

-  Higher c-of-m energy
-  Higher antiproton intensity

- 6x6             36x36 bunches
- 3.6 s          396 ns

- summer results  (<120 pb-1) in this talk

**Notes:**
Where does that 20-30% come from?? Hard to find out!

## The D0 Detector Upgrade

- Added a 2T Magnetic Field

- Track pT, Lepton ID, Jet Calibrations

- New Silicon  & Fiber Tracking Detectors

- Secondary Vertex ID, Tracking

- Preshower Detector

- Improved electron ID

- Trigger/DAQ Upgrade

- Better Efficiency for difficult signals

- Finding the Higgs will require all components of the detector

- Forward Muon Chambers

- Muon Scintilator

**The D0 Detector Upgrade**

- Silicon Tracker

## Detector Characteristics

- Tracking

- Calorimeter

- Muon

- Roman Pots (far forward)

**Detector Characteristics**

- _Tracking_:
- Full SMT & CFT coverage:
-             |****|<2
- Impact parameter      resolution:   15****m
-            (p**Ttrk **> 10 GeV)
- _Calorimetry_:
- _Muons_:

- |****|<4
****x****=0.1x0.1
- EM resol =
- HAD resol=

- |****|<2

## Higgs Sensitivity Study I

- Low mass SM Higgs may be                                                 discovered (5): i.e. 15 fb**-1**                                                                       for a 115 GeV Higgs.
- Assumptions: D0 & CDF data                                            combined, 55% b-tagging                                                  efficiency (central region,                                                       high p**T**), 10% dijet mass                                              resolution.

**Higgs Sensitivity Study I**

*hep-ph/0010338*

## Higgs Sensitivity Study II

**Higgs Sensitivity Study II**

- No systematics !

-  _Discovery_ of low mass SM   Higgs (5) with >8 fb**-1**        for a 115 GeV Higgs     (caveat: systematics,    RunIIb detectors !).
-  _Evidence_ (3 excess) for                 M**H**= 115 GeV with 3 fb**-1**
-  _Exclusion_ of m**H**<130 GeV                        with 4 fb**-1**

- ......and re-evaluated in _2003_, using a detailed detector simulation and the Run IIa data experience.

- _Additions_: fit the entire m**bb **distribution, neural network method for background rejection, use QCD background from data.

- Assumes RunIIb silicon detectors

## Higgs Sensitivity Study II

- _Current D0 performance_: **b-jet tagging eff. ~ 35%**  (encouraging for a 1st of version of our tagging tools ! ) ,  M**bb**~15% (a lot of room for improvement)
- (Sources for improvement: use of solenoid for jet calibration, tracking reconstruction, advanced jet algorithms.)

- With Luminosities 3-8 fb**-1** , the Run II Tevatron will make very important statements about the nature of the Higgs Boson.

- Past experience (LEP, TeV)......we can do better than expected !

## Luminosity Prospects

- LHC commissioning starts

- design (optimistic) base (conservative)

- _Run IIb silicon upgrades cancelled_ (Sep ‘03)
- Layer 0 addition to SMT proposed to compensate b-tagging efficiency losses due to expected degradation in current SMT.

- Higgs sensitivity study using current SMT for the duration of Run II is in progress.

## b-tagging

**B**

- Impact Parameter (d)

- Impact Parameter Significance

- d/(d)

- Hard Scatter

-  Higgs contain b-quark jets
-  b-quark jet contains a   B meson which
- - Has finite life time
- - Travels some    distance from the    vertex before   decaying

**b-tagging**

- Three different algorithms are being developed. Typically based on:

## b-tagging

- Data enhanced in heavy flavor (high p**Trel** )

- Negative Tag

- Positive Tag

**B**

**B**

- Evidence of displaced vertex

- Fold over

**b-tagging**

- Track intersects jet axis before/after the primary vertex

## Jet Lifetime Probability

- The Jet Lifetime Probability (JLIP) algorithm is used to b-tag jets.

- Based on probability of observing the b lifetime from jet tracks with d>0

- For a 1.1% light quark-jet background, b-tag efficiency is 35+/-2%

- DØ Run II Preliminary

## W(e) + jets with b-tagging 

- _Selection_
- W( e****)** **
- Electron (pT > 15 GeV, |****| < 1.1):  calorimeter shower shape, EM fraction, isolation, and E/p matching with an associated track
- Missing ET > 25 GeV
- Jets
- Fixed cone Run II Legacy, R=0.5, algorithm (pT > 20 GeV, |****| < 2.5): quality cuts, *b-tagging **with Jet Lifetime Probability (JLIP) method based impact parameter measurement *
*   **[  Eff = 0.35 x 0.7  (taggability) = 0.24 ]*
- _ __Corrections and Systematics_
-              Include trigger & quality cut efficiencies, jet energy scale,  e,              jets, & ****   corrections to        . QCD bkgnd extracted from data

- Relevant for Higgs searches in WH associated production.
- Test W + jets generators beyond tree-level.

## W(e) + jets with b-tagging 

**W(e********) + jets with b-tagging **

- PYTHIA

- ALPGEN W+2j, W+3j

**Data: W + ******** 2 Jets**

- PYTHIA

- DØ Run II Preliminary

- ALPGEN describes well both shape and normalization

- PYTHIA describes well the inclusive sample.

- In W +  2 Jets, a large disagreement in normalization with PYTHIA is visible.

## W(e) + jets with b-tagging 

- PYTHIA renormalized by a factor 1.85
- ALPGEN by 1.19 (compatible with luminosity and JES error).
- ALPGEN
- describes better the distribution tails.

**W(e********) + jets with b-tagging **

- DØ Run II Preliminary

- DØ Run II Preliminary

- DØ Run II Preliminary

- DØ Run II Preliminary

- PYTHIA

- PYTHIA

- ALPGEN W+2j, W+3j

- ALPGEN W+2j, W+3j

## W(e) + jets with b-tagging 

-  distance between two leading jets & W +  2 Jets (left).  One b-tagged (right). Both well reproduced by ALPGEN.

- ALPGEN

**At least 2 jets above 20 GeV**

**At least 2 jets above 20 GeV**

- ALPGEN

- 92 events are single b-tagged in data compared to 89.5 (28.4 from QCD, 28.4 from W+2j, 7.1 from tt, 3.0 from Wbb, 1.6 single top..)

## W(e) + jets with b-tagging 

- ALPGEN

- ALPGEN

**At least 2 jets above 20 GeV**

**At least 2 jets above 20 GeV**

- 61.6 +/- 6 b-tag events            (after bkgnd. subtraction)
- N**sm**= 41.3 (61.3) PYTHIA (ALPGEN)

- 3 events observed

- Consistent with 5.5 +/- 1.6 expected
- (0.9 from Wbb  &  0.12 from a SM   Higgs M**H**=115 GeV )

## W(e) + jets with b-tagging 

- 95% C.L. upper limit to the Wbb cross section was derived using a Bayesian approach:   33.4 pb

- One of the  3 double-tagged events. Topology is consistent with a top candidate (e, , 2 b-jets,        )

- primary    secondary

- b-jets

- muon

|  | Systematics Errors |
| --- | --- |
| Trigger  | 3% |
| Track Matching | 3% |
| Electron Id/ Reconstruction Efficiency | 3% |
| Electron Energy uncertainty (2%) | 4% |
| Electron Smearing  | 1% |
| Jet Id/ Reconstruction Efficiency | 7% |
| JES Error/ Missing ET/ Smearing | 15% |
| Jet Taggability | 7% |
| JLIP b-Tagging Efficiency | 10% |
| Total | 25% |

## Z(ee/) + jets 

- 2 Electrons

- or

- 2 Muons

- Jets

**Z ******

**Z ******ee

**Z(ee/********) + jets **

- DØ Run II Preliminary

- Z(ee/) + jets combined:    L=34.5 pb**-1**

- Z (ee) cross section:  294 +/- 11 (stat) +/- 8 (sys) +/- 29 (lum) pb
- Z (****) cross section:  261.8 +/- 5 (stat) +/- 8.9 (sys) +/- 26.2 (lum) pb

## Z(ee/) + jets 

- 1st leading jet

- PYTHIA

- 2nd leading jet

- PYTHIA is normalized by area.
- Error includes statistical and systematic uncertainties from luminosity, trigger efficiency, ID, jet energy scale & background

## Z(ee/) + jets 

- DR between 2 jets

**Z(ee/********) + jets **

- #jets in Z+jets

- PYTHIA

- PYTHIA

- PYTHIA

- PYTHIA is normalized by area.
- Error includes statistical and systematic errors from luminosity, trigger efficiency, ID, jet energy scale & background

- Agreement in shape between data and PYTHIA, ...but statistics are too low

## Summary

-  Higgs sensitivity re-evaluated: with luminosities 3-8 fb**-1** , the upgraded     Run II Tevatron experiments will make very important statements about   the nature of the Higgs Boson......
-  ......however silicon upgrades have been cancelled following the lower than   predicted luminosity performance of the Tevatron (4-8 fb**-1 **by 2009).
-  The performance of the D0 detector is encouraging.

-   _Wbb/Zbb preliminary analyses_
-  The W-dijet sample is well described by ALPGEN.
-  The observation of 3 events with at least 2 b-tagged jets is in   agreement with the SM expectation of 4.2 ± 1.2 events.
-  The 95% confidence level upper limit on Wbb cross-section derived   from a double tagged sample is 33.4 pb.

- _General_