# Presentation: 841389

## Higgs Searches at the Tevatron

## Outline

- Introduction
- Tevatron & experiments
- Standard Model (SM) Higgs
- Introduction
- Results
- Low & high mass
- Combination
- Non-SM Higgs
- Minimal Supersymmetric SM
- Prospects & Conclusions

- Results shown use ~1fb-1
- (2fb-1 this summer)

- [ Thanks to all my Tevatron colleagues ]

## Tevatron Performance

- Performance matching design
- 	integrated luminosity of ~8fb-1
- 	by 2009

- this talk

- 2fb-1

- Tevatron continues to perform well
- Over 3fb-1 delivered to
- 	each experiment
- Peak luminosities of ~3 x1032

## CDF and DØ experiments

- Both detectors extensively upgraded for Run IIa
- New silicon vertex detector
- New tracking system
- Upgraded muon chambers
- CDF: New plug calorimeter & ToF

- DØ
- New solenoid & preshowers
- Run IIb: New  inner layer in SMT
- 	& L1 trigger

## Standard Model Higgs

- Introduction
- Constraints on the Higgs
- Higgs Production at Tevatron
- Techniques / status
- Low mass
- I
- I
- I
- High mass
- I
- Combination

## Standard Model Higgs

- Higgs mechanism
- Additional scalar field in SM Lagrangian
- 	 mass to W,Z & leptons
- Predicts neutral, spin 0 boson
- But not its mass
- Direct searches at LEP2
-  *m**H* > 114.4 GeV @95%CL
- Improved mt & mw tighten indirect constraints:
*m**H*  < 144 GeV @ 95%CL (EW fit)
*m**H* < 182 GeV if LEP2 limit included
- 			 A light Higgs is favoured

## SM Higgs Production & Decay

- Small production cross-sections
- 0.1 -1 pb cf WZ, ZZ, single top @~2-4pb
- Branching ratio dictates search
*m**H* < 135 GeV
- gg → H → bb overwhelmed by multijet (QCD) background
- Associated WH & ZH production
- 	with H → bb decay
- Main backgrounds: Wbb, Zbb,
- 	W/Z jj, top, di-boson, QCD
*m**H* > 135 GeV
- gg → H → WW
- Main background: WW

## B-tagging

- Critical for low mass H bb
- Improves S/B by > 10
- Use lifetime information
- Correct for MC / data differences
- Measured at given operating points
- Analyse separately (“tight”)
- 	single & (“loose”) double tags

**CDF: Secondary vertex reconstruction**
-  Neural Net - improves purity
-  Inputs: track multiplicity, *p**T*, vertex
-   decay length, mass, fit
-  **Loose = 50% eff, 1.5 % mistag**
** ****Tight   = 40% eff, 0.5 % mistag**

**D****Ø:**** Neural Net tagger**
-  Secondary vertex & dca based inputs,
-    derived from basic taggers
-  High efficiency, purity
-  **Loose = 70% eff, 4.5% mistag**
** ****Tight   = 50% eff, 0.3% mistag**

## Higgs Sensitivity

- Previous studies
- Sensitivity above
- 	LEP starts at 2fb-1
- 8fb-1: Exclusions
- 	from 115-135GeV
- 	& 145-180GeV
- Now:
- Measuring SM backgrounds (tt, Zbb, Wbb, WZ, ZZ, single top !)
- Optimizing analysis techniques
- 1st combined Higgs limits & comparing to predictions

## Low mass SM Higgs

- Introduction
- Low mass
- I
- I
- I
- High mass
- Combination

- Leptonic decay of W / Z boson
- provides ‘handle’ for event
- H  bb helps reduce SM background

- Highest cross-section
- Use electron and muon channels
- Selection
- Isolated lepton, *p**T* > 20GeV
- Missing *E**T* > 20GeV
- Two jets:
*p**T* > 15GeV (CDF)
*p**T* > 20GeV (DØ)
- Backgrounds
- W+jets, QCD, top, di-boson
- Analyses
- CDF & DØ: Cuts based analyses
- DØ also has a Matrix Element analysis

## Separate 1 “tight” & 
	2 “loose” b-tag channels

No significant excess

Cross section limits derived from  invariant mass distributions

95% CL upper limits (pb):
	mH=115 GeV (SM expected: 0.13 pb)
CDF: 3.4 (2.2) pb obs. (expect.)
DØ:  1.3 (1.1) pb obs. (expect.)

excl / SM~ 8.8 (best expect.)
Moriond ’07 vs ICHEP ’06
OR all triggers
NN b-tagger

- 	2 “loose” b-tag channels
- No significant excess
- Cross section limits derived from  invariant mass distributions
- 95% *CL* upper limits (pb):
*	**m**H**=*115 GeV (SM expected: 0.13 pb)
- CDF: 3.4 (2.2) pb obs. (expect.)
- DØ:  1.3 (1.1) pb obs. (expect.)
- excl / SM~ 8.8 (best expect.)
- Moriond ’07 vs ICHEP ’06
- OR all triggers
- NN b-tagger

- 1 b-tag

- ≥ 2 b-tag

- 1 b-tag

- 2 b-tag

- ICHEP ‘06

- Moriond ‘07

**Notes:**
OR all triggers gives 50% more signal in the muon channel. High eff ~70% using NN btager.
Single and double channels alter combined, as for e and muon channels

## Matrix Element: Use LO ME
 event probability densities 
for signal and background

Optimized for single top
	(will be re-optimized)

Cross section limits derived fromthe per-channel discriminant distributions 

95% CL upper limit (mH=115 GeV)
1.7 (1.2) pb obs. (expect.)

Similar ratio to SM as cuts based analysis (~9)

- Matrix Element: Use LO ME
-  event probability densities
- for signal and background
- Optimized for single top
- 	(will be re-optimized)
- Cross section limits derived fromthe per-channel discriminant distributions
- 95% *CL* upper limit (*m**H**=*115 GeV)
- 1.7 (1.2) pb obs. (expect.)
- Similar ratio to SM as cuts based analysis (~9)

- Matrix element analysis

## Cleanest low mass channel, but low cross section

Selection:
Loose lepton ID
mll ~MZ, opposite charge
Isolated from jets
Two jets: 
pT > 25,15GeV (CDF)
pT > 20GeV (DØ)

Backgrounds:
Z+jets, top, WZ, ZZ, QCD

Analyses (2006)
DØ: ≥ 2 b-tags. Cross-section limits from dijet invariant mass distribution within search window
CDF: 1 b-tag. 2-D NN to discriminate against two largest backgrounds (tt vs. ZH and Z+jets vs. ZH). Limits from NN distribution  

- Cleanest low mass channel, but low cross section
- Selection:
- Loose lepton ID
*m**ll **~M**Z*, opposite charge
- Isolated from jets
- Two jets:
*p**T* > 25,15GeV (CDF)
*p**T* > 20GeV (DØ)
- Backgrounds:
- Z+jets, top, WZ, ZZ, QCD
- Analyses (2006)
- DØ: ≥ 2 b-tags. Cross-section limits from dijet invariant mass distribution within search window
- CDF: 1 b-tag. 2-D NN to discriminate against two largest backgrounds (tt vs. ZH and Z+jets vs. ZH). Limits from NN distribution

**Notes:**
(Zbb irreducible), QCD is multijet

## ’2006’ Results
95% CL upper limits (pb):
	mH=115 GeV (SM expected: 0.08 pb)
DØ:  2.7 (2.8) obs. (expect.)
CDF: 2.2 (1.9) obs. (expect.)
	→ excl / SM~ 23 (best expect.)

- ’2006’ Results
- 95% *CL* upper limits (pb):
*	**m**H**=*115 GeV (SM expected: 0.08 pb)
- DØ:  2.7 (2.8) obs. (expect.)
- CDF: 2.2 (1.9) obs. (expect.)
- 	→ excl / SM~ 23 (best expect.)

- CDF (Moriond QCD ’07)
- Adjust jets to balance
- 	missing *E**T*
- Improved dijet mass
- 	resolution

**Notes:**
Improvement in dijet mass mass resoln from 17% to 10% (eqiv to 30% gain in lumi ??)

## CDF Moriond QCD ’07 cont’d
Additionally - split sample into 1 & 2 b-tags, improved 2D NN 
mH=115 GeV
excl / SM~ 16
Equivalent to x2 more data

- CDF Moriond QCD ’07 cont’d
- Additionally - split sample into 1 & 2 b-tags, improved 2D NN
*m**H**=*115 GeV
- excl / SM~ 16
- Equivalent to x2 more data

- Again clear improvement
- in analyses

**Notes:**
16 – actually both expected and observed. RH plot, upper right bin, S/B = 1/4

## Larger cross-section & acceptance but hard - no visible leptons & only 2 jets in final state
Contribution from WH when l missed

Selection
Two jets
CDF: > 60, 20 GeV; DØ: > 20GeV
Missing ET (Not aligned in  with jets)
CDF: > 75 GeV; DØ: > 50GeV
B-tags
CDF: Separate 1 & 2 b-tag sample; DØ : 1 tight + 1 loose
Veto on isolated leptons, max HT ( =∑ PT)

Backgrounds
Physics: W/Z + jets, di-boson, top – measured with Monte Carlo
Instrumental: Mis-measured missing ET together with QCD jets – determined from data

- Larger cross-section & acceptance but hard - no visible leptons & only 2 jets in final state
- Contribution from WH when l missed
- Selection
- Two jets
- CDF: > 60, 20 GeV; DØ: > 20GeV
- Missing *E**T* (Not aligned in  with jets)
- CDF: > 75 GeV; DØ: > 50GeV
- B-tags
- CDF: Separate 1 & 2 b-tag sample; DØ : 1 tight + 1 loose
- Veto on isolated leptons, max *H**T *( =∑ *P**T*)
- Backgrounds
- Physics: W/Z + jets, di-boson, top – measured with Monte Carlo
- Instrumental: Mis-measured missing *E**T* together with QCD jets – determined from data

**Notes:**
Two jets: CDF: > 60, 20 GeV with eta < 1.1 and 2.4
		 D0 – both within eta < 1.1. 

## CDF (ICHEP’06)
Heavy flavour (h.f.) bkgs 
	from MC
Light jets from mistags, 
	estimated from data
h.f. normalized in control region

DØ (Spring’07)
Define 2 missing energy variables
MHT – measured with jets
MET – direct from calorimeter cells
Asymmetry isolates mis-measured jets 

- CDF (ICHEP’06)
- Heavy flavour (h.f.) bkgs
- 	from MC
- Light jets from mistags,
- 	estimated from data
- h.f. normalized in control region
- DØ (Spring’07)
- Define 2 missing energy variables
- MHT – measured with jets
- MET – direct from calorimeter cells
- Asymmetry isolates mis-measured jets

## Cross section limits derived from
	invariant mass distributions
Set limits for ZH and WH with the
	l unreconstructed
mH=115 GeV
excl / SM~ 10 (best expect.)

- 	invariant mass distributions
- Set limits for ZH and WH with the
- 	l unreconstructed
*m**H**=*115 GeV
- excl / SM~ 10 (best expect.)

## High mass SM Higgs

- Low mass
- High mass
- I
- Combination

- Main search channel for mH > 135GeV

- Use ee, e,  channels
- Signature:
-    High *P**T* opposite sign leptons (10-20GeV)
-    Missing *E**T*

**High mass SM Higgs**

## Analyses: CDF: cuts based (EW ’07), ME (QCD ’07) DØ: cuts based (ICHEP ’06)

Backgrounds
Drell-Yann, QCD, tt, SM WW dominates

Selection
Missing ET >  20GeV, isolation 
Veto on # of jets, HT ( =∑ PT)
mH dependent cuts (PT, mll etc) 
WW from spin 0 Higgs 
Leptons prefer to point in same direction

di-lepton opening angle ll discriminates against dominant WW bkg.
Cross section limit derived from ll distribution (cuts based)

- Analyses: CDF: cuts based (EW ’07), ME (QCD ’07) DØ: cuts based (ICHEP ’06)
- Backgrounds
- Drell-Yann, QCD, tt, SM WW dominates
- Selection
- Missing *E**T* >  20GeV, isolation
- Veto on # of jets, HT ( =∑ *P**T*)
*m**H* dependent cuts (PT, *m**ll* etc)
*WW *from spin 0 Higgs
- Leptons prefer to point in same direction
- di-lepton opening angle ***ll* discriminates against dominant WW bkg.
- Cross section limit derived from ***ll** *distribution (cuts based)

**Notes:**
CDF: Missing ET > mH/4 

## CDF Moriond  QCD ’07
Improved lepton acceptance

Matrix Element approach
Use observed leptons & missing ET (xobs)
Integrate over LO theory predictions 
	for WW, ZZ, W+, W+jet, 10 Higgs masses
Construct LR discriminant from probabilities

Validate LR for background

Limit set by fitting LR distribution

- CDF Moriond  QCD ’07
- Improved lepton acceptance
- Matrix Element approach
- Use observed leptons & missing *E**T* (xobs)
- Integrate over LO theory predictions
- 	for WW, ZZ, W+, W+jet, 10 Higgs masses
- Construct LR discriminant from probabilities
- Validate LR for background
- Limit set by fitting LR distribution

## mH= 160 GeV
CDF result, Matrix Element:
x3.4 (x4.8) obs. (expect.) SM
Cuts based:
x9.2 (6.0) obs. (expect.) SM
DØ cuts based:
x3.7 (4.2) obs. (expect.) SM

4th generation model already excluded for mH = 150 – 185 GeV

*m**H**=* 160 GeV
- CDF result, Matrix Element:
- x3.4 (x4.8) obs. (expect.) SM
- Cuts based:
- x9.2 (6.0) obs. (expect.) SM
- DØ cuts based:
- x3.7 (4.2) obs. (expect.) SM
- 4th generation model already excluded for *m**H **= *150 – 185 GeV

## Combination

- Summer ’06 - 1st Tevatron combination   - Like 1 experiment  with ~1.3fb-1
- Much progress since
- Better sensitivity in all channels
- Advanced analysis techniques
- NN – b-tagging or event selection
- ME methods
- x~2 more luminosity
- Combinations ongoing
- DØ alone now has tighter limits
- Factor of 3 better at low *m**H*
- Better than √L gain

**Notes:**
ICHEP ’06	115    10.4 (obs)  7.6 (exp)			
(TeV)		160      3.9 (obs)  5.0  (exp)

Apr ’07		115     8.4 (obs)  5.9 (exp)
(Dzero)		160     3.7 (obs)  4.2  (exp)

## Non-SM Higgs

- Introduction
- SM Higgs
- Minimal Supersymmetric Standard Model (MSSM)
- Introduction
-  Neutral Higgs bosons () searches
- → 
- b → bbb
- Fermiophobic Higgs
- Prospects & Conclusions

## Higgs bosons in the MSSM 

- In MSSM have 2 Higgs doublets
- Hu (Hd) couple to up- (down-) type fermions
- Ratio of VEV’s: tan = < Hu>/< Hd>
- 5 Higgs particles after the EWSB: h, H, A, H+, H-
- h has to be light: *m**h **< ~*140 GeV
- At tree level, 2 independent parameters: mA and tan
- At large tan :
- Coupling of A, h/H to down-type fermions, e.g. *b*-quark, enhanced wrt SM
- 	 → production amplitude ~tan→ production cross section ~tan2
- h/H & A (denoted by degenerate in mass → further increase in cross-section
- For low & intermediate masses
- Br (→ ) ~10%, Br (→ bb) ~90%

## MSSM Higgs boson production

- Signature
- Higgs decays to 2 ’s
- Further decays of ’s
- 	define final states
- 2 high *P**T* b-jets from
- 	Higgs
- 1 or 2 extra b-quarks
- Search for peak in dijet
- 	invariant mass

-  → 

- Similar overall sensitivities

## Neutral MSSM Higgs  lhad

- Only 1 isolated separated from the
- 	hadronic  with opposite sign
- identification: NN based
- MW < 20 GeV removes most of
- 	 remaining W boson bkg.
- Optimized NNs to separate signal
- 	from bkg.
- CDF e, e+channels)
- Isolated e or separated from hadronic  with opposite sign
- identification: Variable-size cone algorithm
- Jet background suppression:                              GeV
- remove most of W bkg. by cutting on relative directions of the visible  decay products and missing *E**T*

**Neutral MSSM Higgs**** ******** ********l********had**

- Main bkgs.: →(irreducible), W+jets, Z →ee,, multijet, di-boson

## Neutral MSSM Higgs  lhad

- CDF: Limits derived from *m**vis *distribution
- Observed limits weaker than expected due to an excess in data sample, but significance ≤ 2 once all search channels & windows considered
- DØ: Cross-section limits: NNs for the different tau types

- e,

## Neutral MSSM Higgs  lhad

-  ******x **Br ( )
- MSSM parameter
- 	space

**Neutral MSSM Higgs**** ******** ********l********had**

- Use no-mixing & *m**h**max*
-   benchmark scenarios
-  90<*m**A*<200 GeV,
-    tan > 40-60 excluded

## Neutral MSSM Higgs  bb + b[b]

**Neutral MSSM Higgs ******** bb + b[b]**

- DØ: ICHEP ‘06
- ≥ 3 b-tagged jets: *p**T*> 40, 25, 15 GeV
- Invariant mass of 2 leading jets
- 	peaks at Higgs mass
- Backgrounds from data
- Shape estimated from double-tagged
- 	dijet mass spectrum
- Rate normalized outside signal window
- Agreement between data & predicted
- 	background  set upper limits
- Preliminary analysis being optimized

**Events with ****≥****3 ****b-tagged jets**

**Inv. mass of leading jets (GeV)**

- (mA=120, tan=60)

**Signal window**

- 95% CL limits
- 0.9 fb-1

**Notes:**
Rate normalized outside signal window for each point in mA and tan plane

## Fermiophobic Higgs  3 + X

- Some extensions of SM:  coupling of higgs to fermions suppressed
- Search for the channel:
- Cuts
- 3 with ||<1.1, *E**T*1,2,3 > 30, 20, 15 GeV
- Backgrounds
- Jets or electrons misidentified as 
- 	 and direct 3production
- Estimated from data
*H**T* ) > 25GeV
- 0 events seen for 1.1 expected
- 95% CL limit: (hH±) < 25.3fb
- Exclusion  on mass of *h**f* for different
- 	charged Higgs masses (*m**H*±) & tan

**Notes:**
Good photon ID crucial

## Prospects and Conclusions

- Introduction
- SM Higgs
- Non-SM Higgs
- Prospects and
- 	Conclusions

## Prospects – SM Higgs

- Rapid evolution
- Some single channels now as powerful as Tevatron results of ICHEP ’06
- More sensitivity will be gained by
- Larger data sets ( ~ x8 in total)
- Include more channels e.g.  final states
- Improved di-jet mass, b-tagging and simulation
- Improved analyses, especially use of multivariate techniques: e.g. NN, ME and decision trees
- Recent single top and WZ results important step in use of such techniques to extract small signals in large backgrounds
- Need ~3fb-1 to reach 95% exclusion at *m**H*= 115GeV or *m**H* = 160GeV
- Expect updated Tevatron combination for summer ‘07

**Notes:**
Need ~8fb-1 to reach 3 sigma at mh = 115GeV or mh = 160 GeV

## Prospects – MSSM Higgs

- 1st results from 1fb-1 show promising sensitivity
- Similar approach to improvements as for SM Higgs
-  Short term (this summer)
- New  → bb + b[b]
- From both experiments
- New  → bb + b[b]  &
-  →  (& b → b) combination
- Longer term
- Up to *m**A* ~250 GeV for large tan
- Down to tan~20 for low *m**A*
- Or discovery

- 1st combination - low statistics

## Conclusions

- Tevatron and CDF/ DØ experiments performing very well
- Over 2.5 times more data under analysis
- Wide range of Higgs searches performed by CDF & DØ with up to 1 fb-1 Run II data:
- No deviations from SM expectations observed
- No signal observed in MSSM Higgs search, but already powerful!
- Rapid evolution in sensitivity
- Increased use of multivariant techniques
- 1st Tevatron SM combination from Summer ’06
- Some individual channels already have similar limits!
- More work needed to reach desired sensitivity, but clear roadmap
- At *m**H*=115GeV or 160GeV need ~3fb-1 for 95% exclusion, ~8fb-1 for 3
- Updated CDF and DØ combinations soon
- 						Very exciting times ahead!

## And as the last speaker..

- Many thanks to our hosts and the local organising committee

## 

Backup slides

- Backup slides

## Tevatron & DØ 

## DØ B-tagging

**Several mature algorithms used:**
**3 main categories:**
**	****- Soft-lepton tagging**
**	****- Impact Parameter based**
**	****- Secondary Vertex reconstruction**

## B-tagging – (DØ) Certification

- Have MC / data differences – particularly at a hadron machine
- Measure performance on data
- Tag Rate Function (TRF) Parameterized efficiency &
- 	fake-rate as function of pT and η
- Use to correct MC b-tagging rate
- b and c-efficiencies
- Measured using a b-enriched data sample
- Fake-rate
- Measured using QCD data

## DØ B-tagging gains

- Update b-tagging optimization (as compared to Single-Top result)
- Use asymmetric *TIGHT* + *LOOSE* b-tagging thresholds for double-tagged jet sample (*gain ~40% in sensitivity*)
- For WH → lbb, separate orthogonal 2 b-tag and 1 b-tag samples to salvage lost efficiency (*gain ~15% in sensitivity*)

**W+ 2 b-tag control plots**

**Notes:**
Update b-tagging optimization (as compared to Single-Top result) – meaning ????

## SM Summary

**CDF limit (1fb****-1****)**
**Factor above SM**
**Observed (****expected****)**

**D****Ø**** limit**** ****(1fb****-1****)**
**Factor above SM **
**Observed (****expected****)**

**Analysis**

**Z/WH→MET+bb @ 115 ****Technique: M****jj**

**16  (****15****)**

**14  (****9.6****)**

**WH****→****l****n****bb @ 115**
**Technique: M****jj**
**Technique: ME**

**26  (****17****)**
** ****---**

**11  (****8.8****)**
**12  (****9.5****)**

**ZH****→****llbb @ 115**
**Technique: M****jj**
**Technique: NN2D**

**---**
**16  (****16****)**

**23  (****22****)**
**  ****---**

**H****→****WW****→****ll@ 160**
**Technique: ********(l,l)**
**Technique: ME**

**9.2  (****6.0****)**
**3.4  (****4.8****)**

**3.7  (****4.2****)**
**   ****---**

**tan ********< 69 (****47****)**

**tan**** ********< 44 (****54****)**

** ****h****→**** ******** ****@ 160**
******<0, no mixing**

## SM evolution

- Based on DØ current limits, what could we achieve?

**→**** ****need ~3 fb****-1**** to reach 95 % C.L. exclusion**

## MSSM benchmarks

- Five additional parameters due to radiative correction
- MSUSY (parameterizes squark, gaugino masses)
- Xt      (related to the trilinear coupling At → stop mixing)
- M2      (gaugino mass term)
-         (Higgs mass parameter)
- Mgluino (comes in via loops)
- Two common benchmarks
- Max-mixing  - **Higgs boson mass**
**	****m****h**** close to max possible value **
**	****for a given tan******
- No-mixing - **vanishing mixing in **
**	****stop sector ****→ ****small mass **
**	****for h **

## Tau ID

- CDF: Isolation based
- Require 1 or 3 tracks, pT > 1GeV in the isolation cone
- For 3 tracks total charge must be ±1
- pThad > 15 (20) GeV for 1 (3) prongs
- Mhad < 1.8 (2.2) GeV
- Reject electrons via E/p cut
- Validated via W/Z measurements
- Performance
- Efficiency ~ 40-50%
- Jet to tau fake rate ~0.001-0.005

- DØ: 3 NN’s for each tau type
- Validated via Z’s

- Eff(%)

**Notes:**
D0 taus - 1st Tevatron Z cross-section measurement.

## CDF - MSSM Higgs  lhad

- No excess seen
- in this channel

## MSSM evolution