# Presentation: 250161

## Higgs Results from DØ

*presented by*
**Per Jonsson**
**Imperial College London**
**On behalf of the D*****Ø****** ******Collaboration***

** ****Hadron Collider Physics 2004**
**Michigan State University, East Lansing, June 14-18, 2004**

## Outline

**Introduction**
**Tevatron**
**D****Ø**** detector**
**Higgs production/sensitivity**
**Standard Model Higgs**
**Limits on Wbb/WH**
** ********(Z+b)/********(Z+j) ratio**
**H********WW****(*)********l****+****l****-******** searches**
**Higgs Beyond the Standard Model**
**Limits on neutral SUSY Higgs at high tan******
**Limits on non-SM h************ production**
**Limits on H****++****/H****--**
**Summary**

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

- Thanks to all colleagues for their contribution to these studies

- Per Jonsson - Imperial College London

- HCP 04

## Tevatron Performance(1)

- Per Jonsson - Imperial College London

- HCP 04

## Tevatron Performance (2)

- 

- 

- FY 04 integrated lumi

- Per Jonsson - Imperial College London

- HCP 04

## The upgraded DØ detector

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

- Needed for Higgs searches!

- Per Jonsson - Imperial College London

- HCP 04

## EW constraints on Higgs

- MH  constrained in the Standard Model

**Direct searches at LEP2:**
**M****H****>114.4 GeV**** @95%CL**

- 

**Old Top mass combination:**

**New Top mass combination using new D****Ø Run I**** measurement:**

- Per Jonsson - Imperial College London

- HCP 04

## SM Higgs Production

**Production cross sections are small: 0.1-1 pb depending on M****H**
**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****-******** final states can be explored**
**clean, but small branching**

- We may have Higgs in our data already!

- Per Jonsson - Imperial College London

- HCP 04

## SM Higgs Sensitivity

**New Higgs sensitivity study from**** CDF + D****Ø in 2003:**

**Statistical power only****Systematics not included**

**Improved sensitivity from refined analysis and detailed simulation**

- The SM Higgs is a challenge, understanding of bkgs critical!

- Per Jonsson - Imperial College London

- HCP 04

## Higgs Beyond the Standard Model

**Larger cross sections and/or cleaner search topologies**
**MSSM**
**5 physical Higgses:**
**Two CP-even scalars: h (lighter, SM-like) H (heavier)**
**CP-odd scalar: A**
**Charged Higgs pair: H****±**** **
**At tree-level, two free parameters:**
**Ratio of vacuum expectation values: ****tan********u********d**
**One Higgs mass: ****m****A**
**Other possibilities:**
**Left-Right Symmetric, Higgs Triplet models: Doubly Charged Higgs**
**SM extensions which suppress fermion couplings**
**Fermio-phobic or TopColor Higgs**

**MSSM Higgs Main Decays**
**h/H/A********bb ~ 90%**
**h/H/A************ ~ 10%**
**H****+************ ~ 100% (tan********>1)**

**Enhanced ******** over H****SM****bb**
**(prop. to tan****2******** **

- Per Jonsson - Imperial College London

- HCP 04

## B-jet tagging

- demonstrated good b-tagging capability up to |******<**2.5

**Essential for H********bb searches**
**New for DØ in Run II**

**b-tagging efficiency vs light quark mis-tag rate**

- Performance being improved

** ****Use track impact parameter **
**(IP) measurements or secondary **
**vertex reconstruction**
** ****Several algorithms available**

- Per Jonsson - Imperial College London

- HCP 04

## W(e)bb production (1)

**Motivation:**
**Background to WH production**
**Event selection includes:**
**Central isolated ****e, p****T ****> 20 GeV**
**Missing E****T**** ****> 25 GeV**
**≥ ****two jets:**** ****E****T**** > 20 GeV, |****η****| < 2.5**
**2587 evts. in L****int****=174 pb****-1**** of data**

**Simulations with Alpgen and Pythia through detailed detector response**
**Cross sections normalized to MCFM NLO calculations**

- Good understanding of data

- Per Jonsson - Imperial College London

- HCP 04

## W(e)bb production(2)

- Require jets to be b-tagged:
**use different b-tag algorithms**
**consistent results with all**

**Observe 8, expect 8.3±2.2**
**Background dominated by top events**

- Good agreement between data
-  and MC in both cases

- Per Jonsson - Imperial College London

- HCP 04

## W(e)bb production (3)

**Exactly two jets: suppress top production**
**Observe ****2 events****, expect ****2.5±0.5**
**Sample composition:**

| Source | Uncertainty(%) |
| --- | --- |
| Jet energy scale | 14 |
| Jet ID | 7 |
| b-tagging | 11 |
| Trigger & e ID | 5 |
| EM scale | 5 |
| MC simulations | 15 |
| Total | 26 |

**Systematics studies for Wbb:**

**Set limit on production of:**
******(Wbb) < 20.3 pb**
******(WH)xBr(H********bb) < 12.4 pb ****for M****H**** = 115 GeV at 95% C.L.**

**(Systematics smaller for WH)**

| Wbb | Wc(c) | Wjj | tt+t | Others |
| --- | --- | --- | --- | --- |
| 1.4±0.4 | 0.3±0.1 | 0.10±0.03 | 0.6±0.2 | 0.10±0.03 |

- Per Jonsson - Imperial College London

- HCP 04

## Z(eeb associated production (1)

**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:**

**Data correspond to integrated luminosity of ****184 (ee), 152 (********) pb****-1**
**Event selection includes:**
**Isolated ****e/******** with ****p****T ****> 15/20 GeV,**** ****|********| < 2.5/2.0**
**Z peak for signal, side bands for background evaluation**
**Jet ****E****T**** > 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**

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

- Per Jonsson - Imperial College London

- HCP 04

## Z(eeb production (2)

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

**Measured cross section ratio Z+b/Z+j: **
**0.024 ± 0.005 (stat)             (syst)**
**Theory: ****~0.02****     ****hep-ph/031202**
**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 **

- Per Jonsson - Imperial College London

- HCP 04

## HWW(*)l+l- (l=e,

**Event selection includes:**
**Isolated e/******
**p****T****(e****1****) > 12 GeV, p****T****(e****2****) > 8 GeV**
**p****T****(e/********1****) > 12 GeV, p****T****(e/********2****) > 8 GeV**
**p****T****(********1****) > 20 GeV, p****T****(********2****) > 10 GeV**
**Missing E****T**** 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**
**preselection**

- Per Jonsson - Imperial College London

- HCP 04

## HWW(*)l+l- (l=e,

**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**

- Good agreement between data and MC

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

**Higgs of 160 GeV**

- Per Jonsson - Imperial College London

- HCP 04

## HWW(*)l+l- (l=e,

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

**Number of events after selection**

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

** ****Dominant Background in e********sample**

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

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

**Higgs of 160 GeV**

- Per Jonsson - Imperial College London

- HCP 04

## Neutral Higgs Bosons at High tan in Multi-jet Events

**Event Selection:**
**Multi-jet data sample **
**At least 3 jets:****E****T**** cuts on jets are optimized separately for different Higgs mass points, and for min. # jets required in the event**
****** ****3 b-tagged jets**
**Look for signal in the invariant mass spectrum from the ****two leading b-tagged jets**
**Simulations performed with Pythia or Alpgen plus Pythia passed through detailed detector response**
**Data correspond to integrated lumi. ****of ****131pb****-1**

- (**=h,H,A)

- BR(             ) ~ 90%

- (Higgs signal at 95% C.L. exclusion limit)

**Dijet Mass**

- Per Jonsson - Imperial College London

- HCP 04

## Neutral Higgs Bosons at High tan in Multi-jet Events

- Signal acceptance is ~ 0.2 – 1.5% depending on the Higgs mass/**# **of jets

- Per Jonsson - Imperial College London

- HCP 04

## Search for Non-SM Light Higgs in h

- Small in the SM
- Some extensions of SM contain Higgs w/ large B(h)
- Fermiophobic Higgs : does not couple to fermions
- Topcolor Higgs : couple to top (only non-zero fermion coupling)

- Data correspond to integrated lumi. of 191 pb-1
- Event selection:
-  2 Isolated  with pT > 25 GeV, ||<1.05 (CC) or
-      1.5<||<2.4 (EC)
-  pT > 35 GeV

** ****Dominant uncertainty in background **
**estimation is the measurement of ******** **
**mis-ID rate (~30%)**

- Per Jonsson - Imperial College London

- HCP 04

## Search for Non-SM Light Higgs in h

- No clear evidence of excess
- Perform counting experiments on optimized sliding mass window to set limit on B(h) as function of Mh

- Per Jonsson - Imperial College London

- HCP 04

## H++/H--   Search(1)

**H****++****/H****--**** appear in LR symmetric and Higgs triplet models:**
**Leading order pair-production:**
**     ****qq********Z/****************H****++****H****—**
**Dominant decay mode: like-signed leptons**
**Same sign muon decays contain low SM background:**
**clean environment for new physics search**
**Select di-muon triggered events **
**muon identification requirements: **
**Isolated muons with an associated track from the central tracking system. The muon momentum is taken as the central track momentum **
**Muons are required to have **
**      ****P****T**** > 15 GeV and ******** < 2**

**Di-muon mass spectra at various steps of the event selection procedure **

- Per Jonsson - Imperial College London

- HCP 04

## H++/H-- Search (2)

**2 candidates in L=107 pb****-1****, expected bkg of 0.34 from SM**
**Search assumes the H****±±**** branching ratio to like-sign muons to be 100%**
**Confidence level of the signal as a function of the H****±±**** mass, for left- and right-handed Higgs bosons **

- MH> 116 GeV

- MH> 95 GeV

- D**Ø** Run II prel.

- D**Ø** Run II prel.

- Per Jonsson - Imperial College London

- HCP 04

## Summary

**The hunt for Higgs in DØ Run II data is on!**
**The upgraded DØ***** *****detector is producing world class results**
**Understanding of background processes progressing **
**Result summary:**
******(Wbb)< 20 pb **
******(WH)xBr(H********bb) < 12 pb (W********e********)**
******(Z+b)/ ********(Z+j) = 0.024 ± 0.005 (stat)             (syst)**
**limits set on ********(H)xBr(H********WW****(*)****)**
**Search for Neutral Higgs in MSSM:**
**excludes A/h/H for masses 90-150 GeV at high tanβ (>~100)**
**Search for h********:**
**Limits are set for the Branching Ratio vs Mass for both Fermiophobic and TopColor models**
**H****++**** Search: **
**Lower mass limits of 116 and 95 GeV for H****L******** and H****R******** decays to ******
**Limits set are unmatched or superior to Run I**

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

**+ 0.005**
**– ****0.004**

- Per Jonsson - Imperial College London

- HCP 04

- Extra slides...

- Per Jonsson - Imperial College London

- HCP 04

## W(e)bb production (3)

- W Transverse mass of 2 tagged events, keep events with 25GeV<MT(W)<125 GeV

**We observed ****5 events****, expect ****6.9 ******** 1.8 events**
**Set limits on production of ********(Wbb) < 20.3 pb****  at 95% C.L.**

- Per Jonsson - Imperial College London

- HCP 04

## W(e)bb production (4)

**Suppress top production by requiring exactly two jets**
**Observe ****2 events****, expect ****2.5±0.5**
**Sample composition:**

| 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 |

-   **Requiring each jet to be tagged by all of the **
**   ****3 b-tagging**** algorithms reduces the background:**
** ****Observe 2 events, expect 0.3****±0.1 (Background) + 0.6±0.2 Wbb (Signal)**

**Probability(B)=0.04; Probability(S+B)=0.23**
**Standard Model without Wbb disfavored at 2 ******** level**

- Per Jonsson - Imperial College London

- HCP 04

## W(e)H(bb) production

**Observe ****2 events****, expect ****2.5±0.5**
**With 85 GeV< Dijet Mass<135 GeV : **
**0 events**
**0.54 ****± 0.14 expect background**
**0.03 ± 0.01 WH**

| Source | Uncertainty(%) |
| --- | --- |
| Jet energy scale | 14 |
| Jet ID | 7 |
| b-tagging | 11 |
| Trigger & e ID | 5 |
| EM scale | 5 |
| MC simulations | 15 |
| Total | 26 |

- Systematics studies for Wbb:

**Set limit on production of **
******(WH)xBr(H********bb) < 12.4 pb ****for M****H**** = 115 GeV at 95% C.L.**

**(Systematics smaller for WH)**

- Per Jonsson - Imperial College London

- HCP 04

## Views of high dijet mass (220 GeV) Wbb(WH) candidate

- ETmiss

- Vertex view of the 2nd candidate (48 GeV)

- Per Jonsson - Imperial College London

- HCP 04