Latest Results and Prospects for Higgs Searches at the Tevatron

Andy Haas

DØ / ATLAS

Columbia University

with results from the
DØ and CDF Collaborations*

Saclay/Orsay Seminars

March 10-11, 2008

*Mostly from Moriond EW 2008
(last week)

Outline

Standard Model Higgs searches

Low mass

High mass

Improvements

Prospects

MSSM Higgs searches

Other Higgs searches

µ+

µ-

b-jet

b-jet

MET

The Standard Model

3 families of matter

3 forces

“gauge symmetries”:
U(1)Y x SU(2)L x SU(3)C

Massive W,Z gauge bosons

Scalar Higgs field, non-zero VEV

W,Z get masses through “Higgs mechanism”

Fermions can get Yukawa masses:

Higgs boson: excitation of the Higgs field

Scalar boson

Couplings specified

Unknown mass: mH

Higgs Mass Constraints

EW variables sensitive to mH
via radiative corrections:

LEP II direct: mH>114.4 GeV

mH<144 GeV

(at 95% CL)

mH<182 GeV (including direct limit)

The Tevatron at Fermilab

Running (again) since ~2003

p-pbar, sqrt(s)=1.96 TeV

Record luminosity: 2.9e32 cm-2s-1 !

Expect 6 fb-1 by '09 (maybe 8 fb-1 by '10)

DØ

Jan. '03

~90% data taking efficiency

3.4 fb-1

3.0 fb-1

CDF

Needle in a Haystack

Higgs has small cross-section at the Tevatron

Couples weakly to light quarks in the proton!

Large backgrounds from

Jets

W,Z + jets

ttbar

WW, WZ, ZZ

Higgs Production at the Tevatron

Higgs Mass (GeV)

gluon fusion

time

Higgs Production at the Tevatron

gluon fusion

Higgs Mass (GeV)

Vector-boson
fusion

time

Higgs Production at the Tevatron

Associated
production

Higgs Mass (GeV)

time

Higgs Decays

Coupling  fermion mass

Main channels:

WW* (high mass)

bb, ττ (low mass)

Need good b-jet tagging!

Main Higgs Analyses

pp→H

pp→WH

pp→ZH

H→WW*→
ee/eµ/µµ+MET

W/Z+H→W/Z+WW*→
l+l- l+ / l+l+jj + MET

H→bb

WH→Wbb→
e/µ+bb

ZH→Zbb→
ee/µµ+bb

MET+bb

H→bb, ττ

(low mass)

H→WW*
(high mass)

Main Higgs Analyses

H→bb, ττ

(low mass)

H→WW*
(high mass)

pp→WH

pp→ZH

H→WW*→
ee/eµ/µµ+MET

WH→Wbb→
e/µ+bb

pp→H

ZH→Zbb→
ee/µµ+bb

MET+bb

H→bb

W/Z+H→W/Z+WW*→
l+l- l+ / l+l+jj + MET

b-Jet Tagging

B hadrons are “long”-lived

Reconstruct charged particles tracks

Reconstruct “vertices” where tracks overlap

Identify jets with:

Large impact parameter significance tracks

Large decay length significance vertices

~3mm

IP significance = IP / σ(IP)

µ+

µ-

b-jet

b-jet

MET

Outer
Tracker

Silicon Tracker

(high-resolution)

Simulated

ZH→μμbb

event

Silicon
Tracker

Beampipe

r=1.6 cm

Secondary

Vertex

(r=0.3 cm)

Beampipe
r=1.6 cm

b-Jet Tagging

Many variables with
separation power:

Secondary vertex:
Decay-length significance
# tracks on vertex
# vertices
mass
chi2/dof

Jet:
# high IP sig. tracks
combined light-jet probability

...

Vertex DL
significance

# vertex tracks

# high IP tracks

~3mm

IP significance = IP / σ(IP)

Neural Network b-Jet Tagging

Train NN on simulated events

Optimized inputs, training method, network topology

Test NN eff. and fake rate using data

NN Output

Cut-based
b-jet tagging
algorithm

NN b-jet tagging

algorithm

Equivalent to 2.5x as much data

for a double-b-tag analysis!

WH-> l nu b b (l=e,mu)

Signal
(x10)

Signal (x10)

Dijete mass+: Inv. mass plus an extra loose jet (ET>12,|η|<2.4) if within ΔR<0.9 of one of the tight jets

New

WH-> l nu b b (l=e,mu)

WH-> l nu b b (l=e,mu)

WH-> l nu b b (l=e,mu)

New

ZH-> l l b b (l=e,mu)

*Summer 2007 results

1.1/fb

ZH-> nu nu b b

pre-tag
asymm.

New

ZH-> nu nu b b

New

Run IIa

Run IIb

ZH-> nu nu b b

New

WH/ZH/VBF/ggH -> ττ + 2 jets

NEW!

WH/ZH/VBF/ggH -> ττ + 2 jets

NEW!

Main Higgs Analyses

H→bb, ττ

(low mass)

H→WW*
(high mass)

pp→WH

pp→ZH

H→WW*→
ee/eµ/µµ+MET

WH→Wbb→
e/µ+bb

W/Z+H→W/Z+WW*→
l+l- l+ / l+l+jj + MET

pp→H

ZH→Zbb→
ee/µµ+bb

MET+bb

H→bb

H -> WW* -> l l (l=e,mu)

H -> WW* -> l l (l=e,mu)

H -> WW* -> l l (l=e,mu)

NEW!

Signal (x10)

New

H -> WW* -> l l (l=e,mu)

New

H -> WW* -> l l (l=e,mu)

NEW!

Now also using H->WW vs. WW ME calculation as input to NN

NN trained for each Higgs mass in
5 Gev steps, for each channel

Full output used for setting limits

NN

H -> WW* -> l l (l=e,mu)

NEW!

Observed Limit / SM ~ 2.1

Expected Limit / SM ~ 2.4

New

DØ excluding from 140-200 GeV

Sensitive up to ~260 GeV by 2010

4th generation

H production

9x more gg->H production!

4th Generation

NEW!

(Also will be sensitive to
fermiophobic Higgs...)

WH -> W WW* -> l± l± +X (l=e,mu)

~20xSM

SM Higgs Combinations

NEW!

3.1e (2.0o)

6.0e (9.6o)

2.4e (2.2o)

5.5e (6.4o)

New things not in CDF combination yet:

WH -> lvbb: +200pb-1,
1tag improvement, forward electrons

ZH -> vvbb: data driven QCD

H -> : 2.0fb-1

1.6e (1.1o) !

3.3e (5.1o)

Improvements underway:

Di-jet mass resolution

Lepton efficiency

Further improvements in analysis technique

Better multivariate
techniques

Better b-tagging

D0/CDF SM Higgs Combination

Burning Hot!

Di-jet Mass Resolution

Undertaking a major effort to improve
jet energy resolution

Add “pre-shower” energy

Correct for jet “width”

Track-based corrections

(H1-style) cell energy weighting

Multiple jet-cone sizes

0.5 less sensitive to noise,
pileup, overlap

0.7 captures more jet energy

Jet-by-jet showering /
FSR correction

0.5 cone

0.7 cone

Pre-shower

Sensitivity Estimates

Di-jet mass resolution (20%)

Lepton efficiency (10% / lepton)

Improved analyses (20%)

Matrix Element (20%)

Better b-tagging

Semi-leptonic tagging (5%)

Silicon Layer-0 (8%)

Should be sensitive to
mH=160 GeV ~now

Sensitive to SM Higgs up to 200 GeV by 2010

2007

2.4 fb-1

Higgs Mass (GeV)

Why is the Higgs so Light?

The Higgs mass is unstable

Large radiative corrections
(it's a scalar)

Hierarchy problem:

mH << mGUT

mH

Why is the Higgs so Light?

New physics: Supersymmetry !

Particles come in fermion-boson pairs

Corrections to Higgs mass nearly cancel,
if boson and fermion masses are similar

Higgs Bosons in the MSSM

Two Higgs doublet fields

Hu(Hd) couple to up(down)-type fermions

tanβ = <Hu>/<Hd>

5 particles after EWSB

h, H, A, H+, H-

h must be light, <~135 GeV

At large tanβ, coupling of A, h/H to down-type fermions (b, τ) is enhanced

Cross-section proportional to tan2β

Branching ratio: bb~90%, ττ~10%

b(h/H,A)→bbb

(h/H,A)→bb swamped by QCD background

Look for associated b production

Require at least 3 b-tagged jets

Signal:

Invariant mass of leading jets is peaked at mA

Backgrounds (determined from data):

Shape based on the double
b-tagged data sample

Corrected for kinematic bias
from the 3rd b-tag

Events with >=3
b-tagged jets

0.9 fb-1

Inv. mass of leading jets (GeV)

(mA=120, tanβ=60)

New

b(h/H,A)→bbb

New result for Moriond QCD 08, using 1.9 fb-1

Search in mass of two lead jets, m12

Backgrounds are events with two true b-tags, and a b/c/fake tag

Characteristic m12 spectra for each

Start from bb+jet sample (corrected double-tags), weight events by flavor hypothesis

Correct bbb and bcb shapes for double/triple-tag selection bias

Largest systematic error

Fit the observed m12 spectrum with the backgrounds and a Higgs shape

New

b(h/H,A)→bττ

344 pb-1 (update in progress!)

Best S/B of all three MSSM analyses, but lowest cross-section x BR

Select ττ(→μ) events, normalize to Z→ττ peak

Require >=1 b-tagged jet, with pT>15 GeV

Multijet (QCD) background measured using like-sign data

single-π-like τ

rho-like τ

3-prong τ

MSSM Higgs Limits

bH→bbb

bH→bττ

New D0 result soon!

H→ττ

New

MSSM Prospects

Results from the first 1-2/fb of data show very promising sensitivity

By 2010...

Exclude

up to mA~300 GeV for high tanβ

down to tanβ~30 for low mA

Or make a discovery!

New results on H+ coming soon!

Other Higgs Searches

Showing results 1 through 47 (of 47 total)
for ti:(Higgs AND Decay) and year 2008

4. arXiv:0801.4554 [ps, pdf, other]

Title: Nonstandard Higgs Boson Decays

5. arXiv:0801.3456 [ps, pdf, other]

Title: Higgs boson decays to four fermions through an abelian hidden sector

13. arXiv:0711.3361 [ps, pdf, other]

Title: Higgs Boson Decays into Single Photon plus Unparticle

18. arXiv:0710.5331 [ps, pdf, other]

Title: Higgs boson decays in the Complex MSSM

19. arXiv:0710.4923 [ps, pdf, other]

Title: Di-photon Higgs Decay in SUSY with CP Violation

21. arXiv:0710.4591 [ps, pdf, other]

Title: Nonstandard Higgs Decays with Visible and Missing Energy

24. arXiv:0710.0340 [ps, pdf, other]

Title: Di-photon Higgs decay in the MSSM with explicit CP violation

31. arXiv:0708.1939 [ps, pdf, other]

Title: Effect of Charged Scalar Loops on Photonic Decays of a Fermiophobic Higgs

34. arXiv:0708.0248 [ps, pdf, other]

Title: Higgs decays in supersymmetric models with light neutralinos

36. arXiv:0707.3152 [ps, pdf, other]

Title: New Physics Effects in Higgs Decay to Tau Leptons

37. arXiv:0707.1591 [ps, pdf, other]

Title: Invisibly decaying Higgs boson in the Littlest Higgs model with T-parity

39. arXiv:0706.1732 [ps, pdf, other]

Title: GeV Seesaw, Accidentally Small Neutrino Masses, and Higgs Decays to Neutrinos

tau

tau

tau
e

tau
mu

Other Higgs Searches

No shortage of new models!

Cover some general signatures we are sensitive to:

Doubly charged Higgs

Enhanced decays to photons

Others are harder, but on the way:

Invisible Higgs

CP-violating Higgs

Higgs->aa->4τ

...

MET

9 GeV

H++

Models with H++

Left-right symmetric models

Higgs triplet

Little Higgs

Analysis Overview

1.1 fb-1

3 ’s with:
PT>15 GeV
||<2.0

>=1  pair with:
M>30 GeV/c2;
<2.5 rad

Results

Background: 3.10.5

Data: 3 events

Result:

HR > 127 GeV

HL > 150 GeV

H→γγ

Could be large H→γγ BR: “fermiophobic”

Top-color models

LED theories

MSSM: Hbb suppressed by 1-loop corrections

Select 2 isolated photons, ET>25 GeV

QCD jet fakes estimated using the shower-shape correlations between
the 2 photons (“matrix method”)

Also contributes to SM Higgs search!

New

Conclusions

The Tevatron is closing in on the SM Higgs

Sensitive at 160 GeV this summer

Sensitive to SM Higgs up to 200 GeV by 2010

Also looking for Higgs in the MSSM and other plausible models

Already exploring new parameter space

The LHC starts this year (?!)

SM Higgs boson by ~2011?

Tevatron

LHC

7x Tevatron energy

~100x the luminosity

Backup

Precision EW Constraints

EW variables sensitive to mH via radiative corrections:

LEP II: mH>114.4 GeV

mH<97 GeV

(at 95% CL)

(leptonic only)

LEP @ CERN in 2000

Circular e+ e- collider

Maximum E of 200-210 GeV

Look for e+ e- -> Z+H(->bb)

Slight excess around 115 GeV

Higgs mass > 114.4 GeV

A good, but not the
only variable...

Loose

Medium

Tight

Limit Setting

Systematic Uncertainties

Luminosity, 6.1%

Lepton ID, 2%

Background cross-
sections, 5-30%

QCD estimation, 20%

Jet-energy scale*

b-tagging*

*Affects shape of NN output
as well as normalization

Matrix Elements

Calculate “cross-section” for an observed event to be from Z+bb or Z+(H->bb)

Use MC integration methods

Include as inputs to NN

ZH

Z+bb

µ

Jet

MET = µ1+µ2+j1+j2+σ(MET)

Tracking

Silicon Microstrip Tracker

Central Fiber Tracker

IP resolution

γ→e+e-

Layer 0 of Silicon Tracker

Silicon detectors mounted just outside the beampipe

Installed fall '06

Better track impact-parameter resolution
-> Better b-jet tagging

Effect of Layer 0

in recent data

IP Resolution (um)

pT (GeV)

Layer 0 being inserted into the silicon tracker

b-Tagging Measurement

System 8 method:

Correlation coefficients, measured in MC:

Muon Acceptance

|eta|=2

|eta|=1

Bottom “holes”

ZH→µµbb
mH = 115 GeV

Muon eta

20% of Z's with
one muon |eta|>2

Use tracker:
good acceptance to |eta|~3.5

Tau ID

H+V→γγ+X

Associated Fermiophobic Higgs

Analysis overview

1.1 fb-1;

2 ’s with: ET>25 GeV, ||<1.1, M>65 GeV

Two regions

Signal: qT>35 GeV

Control: qT<35 GeV

Backgrounds: , j, jj

LEP: mH>109.7 GeV

Ref.) CDF SECVTX btag

More Plots : H   Channel

March 2nd 2008 :: Low Mass Higgs Search :: Kohei Yorita (U. of Chicago)

More Plots : H   Channel

CDF 3b Channel

Old Combinations

H -> WW* -> l l (l=e,mu)

New

SM Higgs Combinations

6x SM

3x SM

6x SM

3x SM

D0/CDF SM Higgs Combination

Observed limit: 1.4x SM !

4x SM

2x SM

Limit / SM cross-section

New Tevatron combination coming very very soon!

Improvements underway:

Di-jet mass resolution

Lepton efficiency

Further improvements in analysis technique

Better multivariate
techniques

Better b-tagging

Dmitri Denisov, ICHEP04, August 21 2004

UIowa Colloquium

November 13, 2006

Andy Haas

2004-07-07T15:59:13