Charged Higgs Results from Tevatron
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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
ICHEP04, Beijing, August 16, 20043Sudeshna Banerjee
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
ICHEP04, Beijing, August 16, 20044Sudeshna Banerjee
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
ICHEP04, Beijing, August 16, 20045Sudeshna Banerjee
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.
ICHEP04, Beijing, August 16, 20046Sudeshna Banerjee
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
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.
ICHEP04, Beijing, August 16, 20047Sudeshna Banerjee
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.
ICHEP04, Beijing, August 16, 20048Sudeshna Banerjee
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
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
ICHEP04, Beijing, August 16, 20049Sudeshna Banerjee
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
ICHEP04, Beijing, August 16, 200410Sudeshna Banerjee
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
ICHEP04, Beijing, August 16, 200411Sudeshna Banerjee
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
ICHEP04, Beijing, August 16, 200412Sudeshna Banerjee
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
ICHEP04, Beijing, August 16, 200413Sudeshna Banerjee
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
ICHEP04, Beijing, August 16, 200414Sudeshna Banerjee
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
ICHEP04, Beijing, August 16, 200415Sudeshna Banerjee
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
ICHEP04, Beijing, August 16, 200416Sudeshna Banerjee
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)
ICHEP04, Beijing, August 16, 200417Sudeshna Banerjee
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
ICHEP04, Beijing, August 16, 200418Sudeshna Banerjee
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
206 pb-1 integrated luminosity used
206 pb-1 integrated luminosity used
Expected Number10.2 6.6
3.2 2.4100 GeV130 GeV
mH
ICHEP04, Beijing, August 16, 200419Sudeshna Banerjee
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
ICHEP04, Beijing, August 16, 200420Sudeshna Banerjee
• 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
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