sensitivity prospects for light charged higgs at 7 tev j.l. lane, p.s. miyagawa, u.k. yang...

Sensitivity Prospects forLight Charged Higgs at 7 TeV

J.L. Lane, P.S. Miyagawa, U.K. Yang (Manchester)M. Klemetti, C.T. Potter (McGill)

P. Mal (Arizona)A. Ferrari (Uppsala)

Light charged Higgs• Charged Higgs bosons predicted in extensions of SM with more than one Higgs

doublet (e.g. MSSM)• Discovery of charged Higgs boson would be definite signal for new physics

beyond SM• Light H+ (mH+ < mtop) produced primarily through top decays tH+b

– H+τ+ν dominant for tanβ > 3– H+cs significant for low tanβ

• ttbar event topology with one W replaced by H+

– Remaining W decays leptonically• Two H+ decay channels considered

– H+cs (semileptonic)– H+τ+ν with τ decaying leptonically (dilepton)

Paul S Miyagawa Higgs working group meeting, 11 June 2010 2

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Present status• Sensitivity studies at 10 TeV with 200 pb-1; searches

for H+τ+ν and H+cs– ATL-PHYS-INT-2009-105 approved– ATL-COM-PHYS-2010-193 (PUB note) under PC action

• Approval talk in Higgs WG meeting, 15 April 2010

• Sensitivity studies at 7 TeV with 1 fb-1

– Assume same acceptances and systematics, scale cross sections and luminosity, re-evaluate upper limits

– Checked assumption on acceptances and systematics– ATL-PHYS-INT-2010-060 approved

• ATLAS Sensitivity Prospects for Light Charged Higgs Bosons in the H+cs and H+τν Decay Channels with Simulated LHC Data at 7 TeV


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H+cs channel


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H+cs: analysis method• Signature

– 1 lepton (Pt > 20 GeV, |η| < 2.5)– 4 jets (Et > 20 GeV, |η| < 2.5, 2 b-tagged)– Missing Et (> 20 GeV)– High-Pt lepton trigger

• Shape analysis study– Look for second peak in W mass (di-jet) distribution– Improve di-jet mass using kinematic χ2 fitter to constrain kinematics of ttbar system– Produce templates for signal and backgrounds to extract B(tH+b), Ntt, Nnon-tt bkgds using

binned maximum likelihood fit

• Extract upper limit on B(tH+b) using 1000 pseudo-experiments


2 pTi, fit pT

i,meas 2

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UE ,meas 2

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H+cs: expected event rate @ 7 TeV• As first step, assumed same acceptances and systematics

as at 10 TeV– Scaled cross sections and luminosities

• Checked acceptances at generator level for H+ + SM ttbar background– Acceptances increased by 4-7%– Scale factor (SF) applied to number of expected events


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1 fb-1 @ 7 TeVB(tH+b) = 0.1 for signal

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H+cs: 7 TeV acceptances

• Compared Pt, eta distributions for lepton + 4 quarks in event– Pt distributions look similar– eta distributions more central @ 7 TeV– Results in higher acceptances (4-7%) from eta cut


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Lepton Pt Lepton eta Light quark eta

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H+cs: 7 TeV systematics• Estimated impact of systematics for 130 GeV H+ @ 7 TeV

– Varied each source of systematic error by ±1σ– Recalculated acceptances and di-jet mass distributions– Repeated signal extraction using perturbed acceptances and distributions to

evaluate new upper limit• Consistent with results @ 10 TeV

– Valid to use 10 TeV total systematic numbers for all H+ masses– Re-evaluate B(tH+b) including total systematic using 1000 pseudo-

experiments

– Pile-up (~4 extra interactions) evaluated @ 10 TeV• Effects negligible except for mH+ ≈ 90 GeV (~3% increase in branching ratio)


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H+cs: 7 TeV final limits• Expected limits @ 7 TeV much better than Tevatron

– Also better than ATLAS @ 10 TeV with 200 pb-1

– Effect of acceptance scale factor is very small


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200 pb-1 @ 10 TeV 1 fb-1 @ 7 TeV

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Expected upper limit B(tH+b) without SF 15.0% 4.8% 3.5% 3.8%

H+τ+ν channel


H+τ+ν: analysis method• Signature

– 2 opposite charge leptons (leading Pt > 20 GeV, 2nd Pt > 10 GeV, |η| < 2.5)

– large MET from 4+ neutrinos (> 50 GeV)– 2 jets (Et > 15 GeV, |η| < 5, ≥ 1 b-tag)– High-Pt lepton trigger

• Essentially an event counting analysis– Define new analysis variables

• Helicity angle cosθ* between lepton and b-jet in W rest frame

• Generalized transverse mass mT2H+

• Provide some power to distinguish W and H+ decays• mT2

H+ can provide estimate of H+ mass– Normalize backgrounds from data using

sidebands– Estimate portion of non-ttbar background using

tag-and-probe• Upper limits on B(tH+b) calculated by

– Evaluated using 10000 toy MC experimentsPaul S Miyagawa Higgs working group meeting, 11 June 2010 11

mT2H+

sigint

bgobs

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H+τ+ν: expected event rate @ 7 TeV• As first step, assumed same acceptances and systematics

as at 10 TeV– Scaled cross sections and luminosities

• Checked acceptances at generator level for 130 GeV H+ + SM ttbar background– Acceptances changed by 3-4%; effect is negligible


1 fb-1 @ 7 TeVB(tH+b) = 0.1 for signal

7 T

eV

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H+τ+ν: 7 TeV acceptances


• Compared pT, eta distributions for 2 leptons + 2 b-quarks in event– pT distributions look

similar– eta distributions more

central @ 7 TeV• Also compared cosθ* and

mT2H+

– Both distributions look similar

H+τ+ν: 7 TeV sensitivities + limits• Sensitivities @ 7 TeV with 1 fb-1 calculated

assuming Tevatron upper limits

• Upper limits evaluated assuming no signal– Much better than Tevatron– Also better than ATLAS @ 10 TeV with 200 pb-1


200 pb-1 @ 10 TeV 1 fb-1 @ 7 TeV

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Results and conclusions


Results and conclusions• ATLAS sensitivity to light charged Higgs evaluated for 7 TeV

with 1 fb-1 based on 10 TeV results

• Almost factor of 2 improvement in Tevatron limits• Better limits than 10 TeV with 200 pb-1Paul S Miyagawa Higgs working group meeting, 11 June 2010 16

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Backup slides


Current Tevatron limits

• Current best upper limits on branching ratios set by Tevatron




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H+cs: 7 TeV acceptances• Different changes in acceptance between signal and background

due to different kinematics– Kinematics of leptonic top (lepton + b-quark) should be the same– Differences attributed to differences in MC generator (Pythia for signal,

MC@NLO for SM ttbar)– Use MC@NLO scale factor for leptonic side to adjust overall acceptance

scale factor


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H+τ+ν: 7 TeV sensitivity estimation• Assuming no signal beyond SM, B(tH+b) calculated according to

– Input parameters: Nobs, Nbg, εsig

• Evaluate upper limit on branching ratio using 10000 toy MC experiments– Vary each input parameter according to Gaussian distribution

• Width of Nobs distribution is Poisson uncertainty √Nobs

• Widths of Nbg and εsig determined by MC statistics and systematic uncertainties– Calculate branching ratio for each toy MC– 95% CL upper limit defined where integral of branching ratio distribution

reaches 95% positive area


sigint

bgobs

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sensitivity prospects for light charged higgs at 7 tev j.l. lane, p.s. miyagawa, u.k. yang...

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