Charged Higgs Results from Tevatron

Charged Higgs Results from Tevatron

Sudeshna Banerjee

Tata Institute of Fundamental Research

Mumbai, India

For CDF and DØ Collaborations

Fermila

b, Chicago

Beijing

ICHEP04 Beijing, ChinaAug 16, 2004

What are Doubly Charged Higgs How do we look for them at the Tevatron Did we find them What can we say about their properties from

experimental data

What are Doubly Charged Higgs How do we look for them at the Tevatron Did we find them What can we say about their properties from

experimental data??

ICHEP04, Beijing, August 16, 20042Sudeshna Banerjee

Main Injector & Recycler

Tevatron

Booster

p p

DØ

DØDØCDF

CDF

p source

p p

s =1.96 TeV t = 396 ns

Luminosity:4 1031 cm-2s-1 (2003)Projection:8 1031 cm-2s-1 (2004)

Batavia, Illinois

Chicago

REACHED 10

Fermilab


Doubly Charged Higgs Bosons appear in several models L-R Symmetric models, Little Higgs model, MSSM

Higgs fields can be represented as a triplet in L-R symmetric models (along with neutral and singly-charged Higgs)

L-handed and R-handed Higgs fields are possible

In L-R Symmetric models, the Higgs triplets are only one of the Higgs multiplets that break symmetry between L- and R- handed weak interactions at low energy.

SUSY L-R models suggest low mass for a Doubly Charged Higgs (~100 GeV)

Properties of Doubly Charged Higgs

2

2

,0,

,,

,RL

RL

RLRL

RL


Doubly-charged Higgs production cross section is enhanced substantially (~35%) due to NLO corrections.

R-handed H++ cross section is smaller by a factor of ~2 due to different value of coupling of these particles to Z bosons.

W-W Fusion :

q

WW H --++q

_

Small probability

|EW - 1| Is small, experimentally observed

+

H++

q W W-q_

Pair Production :

Dominant Production mode

Cross section independent of Fermionic coupling

* H--q

H++q_

Production of H± ±

M. Spira & M. Mühlleitner, hep-ph/0305288


A typical decay

Couplings like WWH, HHH, HHW and H with hadrons are possible but with very small coupling constants (not considered).

Experimental Signature of H± ± decay

A pair of like sign di-leptons

(Yukawa coupling >10-7)

H--*

q

H++

q_

Decay of H± ±

Contamination from other Standard Model processes is low because of the requirement of two high pT leptons of same sign.


Z with charge misidentification, probable for high pT tracks

Possible Background Decay Channels

Important modes are those which produce like sign leptons

semileptonic decays bb, t t, Z

Hadronic jets

leptonic decays WZ/ZZ

one electron radiates a photon which then converts to e+e-, check for photon conversion vertices.

W + jets

Hadronic jets

Cosmic rays eliminated by demanding that the two muons originate at the beam line coincident in time with each other and with a p p collision.

e eZ

eliminated by demanding isolated muons.


Search Strategy

Choose events triggered with two high pT dileptons.

• electron – energetic EM cluster

• muon – a high pT track matched with a stub in the muon

counter + a MIP trace in the EM calorimeter

Make more stringent selection offline.

Generate signal events in different H±± mass bins covering

the search region.

Generate Monte Carlo samples for different background

decay channels.

Use the same selection criteria on experimental data, signal

and background samples.

If after final selection and background subtraction an excess

is seen in experimental data, a discovery is claimed.

If no excess is seen, a limit on H±± is calculated.


H±± channel (100 % BR assumed)

Offline selection of events :

Two muons, matched to good tracks (pT> 15 GeV)

Calorimeter ET in outer cone around the muon trace should be small pT of tracks around the muon track should be small

< 2.51 (requirement for events with less than 3 muons)

Two of the muons should have the same charge

Preselection

113 pb-1 integrated luminosity used


Search performed by DØ experiment

Isolation

Acolinearity

Like sign requirement

Signal Monte Carlo generation (PYTHIA 6.2) Samples with H±± mass ranging from 80 GeV to 200 GeV are generated in steps of 10 GeV

Total signal efficiency for the above selection = 47.5 % ± 2.5 % (not mass dependent)

All efficiencies derived from dataAll efficiencies derived from data


preselection

preselection + like sign muon requirement

Z events dominate

Effect of Selection criteria (DØ )

b b events dominate

reduces after isolation cut

101 data events

95 b b events


Final Yield (DØ )

like sign requirement

preselection

isolation

acolinearity

+

+

+

Signal (mass = 100 GeV)

Total background

Data

preselection isolation acolinearity like sign

9.4 8.5 7.5 6.5

5254 ± 47 4113 ± 43 368 ± 14 1.5 ± 0.4

5168 4133 378 3


Limit calculation depends on mass distribution for signal and background and experimental mass resolution

CL (signal) = CL (signal+background)/CL(background) 95%

Systematic Uncertainties – MC (27%), theory (10%), Luminosity (6.5%), normalization (5%)

Limit on H± ± Mass (DØ )

(MCLIMIT - T. Junk, Nucl. Instrum. Methods A 434, 435 (1999))

Lower Mass Limit

H±± (R) = 98.2 GeVH±± (L) = 118.4 GeV

Lower Mass Limit

H±± (R) = 98.2 GeVH±± (L) = 118.4 GeV


Search for H± ± (CDF)

Acceptance = (Kinematic + geometric) x trig ID

Leptons are selected in the central region

H++ Acceptance

Search in all dilepton decay channals – e e, e ,

e 242 ± 14 pb-1

e e 235 ± 13 pb-1

240 ± 14 pb-1

Integrated luminosity used


Total background 1.1 ± 0.4 1.5

Observed Events = 1

e e decay channel (CDF)

Backgrounds :

Z e e, one electron radiates a photon which converts to e+e-

Hadronic jets

W + jet

WZ

Low Mass Region High Mass Region

mee < 80 GeV mee > 80 GeV

-0.6+0.9

Expected Number

5.8

mH = 100 GeV


Total Background (e )

Di-lepton mass distributions (CDF)

Backgrounds : Hadromic jets, W+jet, WZ

Total background ( )

Observed Events = 0

High Mass Region

mll > 80 GeV

-0.4+0.5 0.8

0.4 ± 0.2

Low Mass Region

mll < 80 GeV

0.8 ± 0.4

0.4 ± 0.2

Expected Number

mH = 100 GeV

10.1

5.0


No events are found in the high mass regions of e e, e , samples.

Limit on Higgs mass is calculated using Bayesian method with flat prior for signal and Gaussian prior for background and acceptance uncertainties.

Limit Calculation (CDF)

H+ + (R)

H+ + (L) (e e = 133 , e = 115 , = 136) GeV

( = 115) GeV


Promptly Decaying H±±

Summary of mass limits

DØ HL,R ±± Mass limits submitted to Phys. Rev. Lett. in April 2004

(hep-ex/0404015)

CDF HL,R±± Mass limits submitted to Phy. Rev. Lett. in June 2004

(hep-ex/0406073)


No constraint on the lifetime of H±± , can be long

Search for particles with c > 3 m, no decay within the detector They will behave like heavy stable particles, (muons but more ionising)

Measurement of ionization – dE/dx measurement along the charged particle track in tracker and calorimeter.

Background – Advantage is lack of Standard Model decays. Events expected from highly ionizing particles.

• Muons – data from cosmic rays (pure muon sample)

• Electrons – W e Monte Carlo sample

• Hadronic decays for taus from Monte Carlo sample

• QCD contribution calculated from experimental data

Long Lived Doubly Charged Higgs (CDF)

Main process of energy loss is ionization , dE/dx (charge)2


Tracker dE/dx >35 ns

Tracker dE/dx >35 ns

Loose cut :

Tight cut :

Energy (EM) > 0.6 GeV

Energy (Had.) > 4 GeV

Select events which have a good muon track with pT > 18 GeV.Require a second track with pT > 20 GeV offline.

Long Lived Doubly Charged Higgs (CDF)

Use loose cuts for setting mass limitsAnd tight cuts for discovery.

Loose Search Tight Search

Total Background < 10-5 10-6

Data Candidates 0 0



Expected Number10.2 6.6

3.2 2.4100 GeV130 GeV

mH


Mass Limit for Long Lived Higgs

Bayesian upper limit on H±± crosssection

H±± Upper Limit on No. of Signal Events at 95% C.L. for 0 Observed Events Total H±± Acceptance x Integrated Luminosity

=

For a H±± mass of 130 GeV H±± cross section is 0.057 ± 0.0066 ± 0.0030

Mass Limit for Quasi-Stable Doubly charged Higgs is 134 GeVMass Limit for Quasi-Stable Doubly charged Higgs is 134 GeV


• Tevatron has improved the limits on masses of H±±

• There is scope for much more improvement in the coming years

• Tevatron has improved the limits on masses of H±±

• There is scope for much more improvement in the coming years

Conclusions

Prompt Decays

• Limits on L-handed Higgs have gone up to ~ 130 GeV

• Limits on R-handed Higgs have gone up to ~ 113 GeV

• DØ plans to include e e and e modes in future.

Long Lived Higgs

• Limit on Higgs mass is 134 GeV

• Both experiments will redo the analyses with much more luminosity as good data is being collected at a steady rate at the Tevatron.

LEP Results

For both promptly decaying and long lived Higgs

• Mass Limit ~ 100 GeV

Tevatron Results

Documents

Charged Higgs Results from Tevatron