1. 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)

2. 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 20102 ‾ e/μ + ν cs τ + ν τ  l + ν l ν τ ν τ ‾ ‾ { ‾

3. 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 Paul S MiyagawaHiggs working group meeting, 11 June 20103 ‾ ‾

4. H + cs channel Paul S MiyagawaHiggs working group meeting, 11 June 20104 ‾

5. 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 20105 ‾ 7 TeV PUB

6. 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 Paul S MiyagawaHiggs working group meeting, 11 June 20106 ‾ 1 fb -1 @ 7 TeV B(t  H + b) = 0.1 for signal 7 TeV PUB

7. 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 Paul S MiyagawaHiggs working group meeting, 11 June 20107 ‾ Lepton PtLepton eta Light quark eta 7 TeV/10 TeV

8. 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(tH + b) including total systematic using 1000 pseudo- experiments –Pile-up (~4 extra interactions) evaluated @ 10 TeV Effects negligible except for m H+ ≈ 90 GeV (~3% increase in branching ratio) Paul S MiyagawaHiggs working group meeting, 11 June 20108 ‾ 7 TeV PUB

9. 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 Paul S MiyagawaHiggs working group meeting, 11 June 20109 ‾ 200 pb -1 @ 10 TeV1 fb -1 @ 7 TeV 7 TeV PUB Expected upper limit B(t  H + b) without SF 15.0% 4.8% 3.5% 3.8%

10. H + τ + ν channel Paul S MiyagawaHiggs working group meeting, 11 June 201010

11. 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 10000 toy MC experiments Paul S MiyagawaHiggs working group meeting, 11 June 201011 m T2 H+

12. 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 Paul S MiyagawaHiggs working group meeting, 11 June 201012 1 fb -1 @ 7 TeV B(t  H + b) = 0.1 for signal 7 TeV PUB

13. H + τ + ν: 7 TeV acceptances Paul S MiyagawaHiggs working group meeting, 11 June 201013 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 m T2 H+ –Both distributions look similar

14. 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 Paul S MiyagawaHiggs working group meeting, 11 June 201014 200 pb -1 @ 10 TeV 1 fb -1 @ 7 TeV 7 TeV PUB

15. Results and conclusions Paul S MiyagawaHiggs working group meeting, 11 June 201015

16. 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 201016 7 TeV PUB

17. Backup slides Paul S MiyagawaHiggs working group meeting, 11 June 201017

18. Current Tevatron limits Current best upper limits on branching ratios set by Tevatron Paul S MiyagawaHiggs working group meeting, 11 June 201018

19. H + cs: 10 TeV acceptances Paul S MiyagawaHiggs working group meeting, 11 June 201019 ‾

20. 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 Paul S MiyagawaHiggs working group meeting, 11 June 201020 ‾

21. H + cs: 7 TeV acceptances Paul S MiyagawaHiggs working group meeting, 11 June 201021 ‾

22. H + τ + ν: 10 TeV acceptances Paul S MiyagawaHiggs working group meeting, 11 June 201022

23. H + τ + ν: 7 TeV acceptances Paul S MiyagawaHiggs working group meeting, 11 June 201023

24. H + τ + ν: 7 TeV acceptances Paul S MiyagawaHiggs working group meeting, 11 June 201024

25. 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 10000 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 201025