Sensitivity Prospects for Light 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 + (m H+ < m top ) produced primarily through top decays tH + 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 MiyagawaHiggs working group meeting, 11 June ‾ e/μ + ν cs τ + ν τ  l + ν l ν τ ν τ ‾ ‾ { ‾

Present status Sensitivity studies at 10 TeV with 200 pb -1 ; searches for H + τ + ν and H + cs –ATL-PHYS-INT approved –ATL-COM-PHYS (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 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 Paul S MiyagawaHiggs working group meeting, 11 June ‾ ‾

H + cs channel Paul S MiyagawaHiggs working group meeting, 11 June ‾

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 χ 2 fitter to constrain kinematics of ttbar system –Produce templates for signal and backgrounds to extract B(tH + b), N tt, N non-tt bkgds using binned maximum likelihood fit Extract upper limit on B(tH + b) using 1000 pseudo-experiments Paul S MiyagawaHiggs working group meeting, 11 June ‾ 7 TeV PUB

H + cs: expected event 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 Paul S MiyagawaHiggs working group meeting, 11 June ‾ 1 fb 7 TeV B(t  H + b) = 0.1 for signal 7 TeV PUB

H + cs: 7 TeV acceptances Compared Pt, eta distributions for lepton + 4 quarks in event –Pt distributions look similar –eta distributions more 7 TeV –Results in higher acceptances (4-7%) from eta cut Paul S MiyagawaHiggs working group meeting, 11 June ‾ Lepton PtLepton eta Light quark eta 7 TeV/10 TeV

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 10 TeV –Valid to use 10 TeV total systematic numbers for all H + masses –Re-evaluate B(tH + b) including total systematic using 1000 pseudo- experiments –Pile-up (~4 extra interactions) 10 TeV Effects negligible except for m H+ ≈ 90 GeV (~3% increase in branching ratio) Paul S MiyagawaHiggs working group meeting, 11 June ‾ 7 TeV PUB

H + cs: 7 TeV final limits Expected 7 TeV much better than Tevatron –Also better than 10 TeV with 200 pb -1 –Effect of acceptance scale factor is very small Paul S MiyagawaHiggs working group meeting, 11 June ‾ 200 pb 10 TeV1 fb 7 TeV 7 TeV PUB Expected upper limit B(t  H + b) without SF 15.0% 4.8% 3.5% 3.8%

H + τ + ν channel Paul S MiyagawaHiggs working group meeting, 11 June

H + τ + ν: analysis method Signature –2 opposite charge leptons (leading Pt > 20 GeV, 2 nd 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 m T2 H+ Provide some power to distinguish W and H + decays m T2 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(tH + b) calculated by –Evaluated using toy MC experiments Paul S MiyagawaHiggs working group meeting, 11 June m T2 H+

H + τ + ν: expected event 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 Paul S MiyagawaHiggs working group meeting, 11 June fb 7 TeV B(t  H + b) = 0.1 for signal 7 TeV PUB

H + τ + ν: 7 TeV acceptances Paul S MiyagawaHiggs working group meeting, 11 June Compared pT, eta distributions for 2 leptons + 2 b-quarks in event –pT distributions look similar –eta distributions more 7 TeV Also compared cosθ * and m T2 H+ –Both distributions look similar

H + τ + ν: 7 TeV sensitivities + limits 7 TeV with 1 fb -1 calculated assuming Tevatron upper limits Upper limits evaluated assuming no signal –Much better than Tevatron –Also better than 10 TeV with 200 pb -1 Paul S MiyagawaHiggs working group meeting, 11 June pb 10 TeV 1 fb 7 TeV 7 TeV PUB

Results and conclusions Paul S MiyagawaHiggs working group meeting, 11 June

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 -1 Paul S MiyagawaHiggs working group meeting, 11 June TeV PUB

Backup slides Paul S MiyagawaHiggs working group meeting, 11 June

Current Tevatron limits Current best upper limits on branching ratios set by Tevatron Paul S MiyagawaHiggs working group meeting, 11 June

H + cs: 10 TeV acceptances Paul S MiyagawaHiggs working group meeting, 11 June ‾

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, for SM ttbar) –Use scale factor for leptonic side to adjust overall acceptance scale factor Paul S MiyagawaHiggs working group meeting, 11 June ‾

H + cs: 7 TeV acceptances Paul S MiyagawaHiggs working group meeting, 11 June ‾

H + τ + ν: 10 TeV acceptances Paul S MiyagawaHiggs working group meeting, 11 June

H + τ + ν: 7 TeV acceptances Paul S MiyagawaHiggs working group meeting, 11 June

H + τ + ν: 7 TeV acceptances Paul S MiyagawaHiggs working group meeting, 11 June

H + τ + ν: 7 TeV sensitivity estimation Assuming no signal beyond SM, B(tH + b) calculated according to –Input parameters: N obs, N bg, ε sig Evaluate upper limit on branching ratio using toy MC experiments –Vary each input parameter according to Gaussian distribution Width of N obs distribution is Poisson uncertainty √N obs Widths of N bg and ε sig 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 Paul S MiyagawaHiggs working group meeting, 11 June