Gordana Milutinovic-Dumbelovic Vinca Institute of Nuclear Sciences, Belgrade Ivanka Bozovic-Jelisavcic, Strahinja Lukic, Mila Pandurovic Branching ratio measurement of the SM-like Higgs decay into μ + μ - at 1.4 TeV CLIC CLIC Workshop, February 3-7, 2014, CERN, Geneva

Overview 2 Motivation for the measurement ILD detector for CLIC Electron tagging in the forward region Signal and background processes Event selection and MV analysis Method of the measurement Conclusions CLIC Workshop 2014, Gordana Milutinovic-Dumbelovic

Motivation for the measurement 3 Higgs BRs measurements are potential probe for the New Physics (i.e. models that could possibly extend SM Higgs sector impact Higgs couplings to EW bosons and/or Higgs Yukawa couplings ) Challenging measurement due to low signal yield (predicted BR( )  ) : Background has to be efficiently suppressed Requires excellent momentum resolution i.e. in the barrel, as foreseen in CLIC CDR CLIC Workshop 2014, Gordana Milutinovic-Dumbelovic

ILD detector for CLIC 4 CLIC Workshop 2014, Gordana Milutinovic-Dumbelovic -Iron yoke instrumented with 9 active layers for μ identification average p T resolution in the barrel region, on the signal sample Muon p T reconstruction translates into m(μμ) mass width  statistical uncertainty of the measurement

Electron tagging in the forward region 5 - If escapes at very small angles, undetected electron can mimic missing energy signature of the signal - Forward region below ~ 7 deg is instrumented with calorimeters to (among others) tag (high-energy) electron - However, detectors are overflowed with background from incoherent pairs - Electron is tagged if reconstructed shower energy deviates for 4  from the pair depositions in the layer with maximal deposition - In order to reduce coincidence with Bhabha events, polar angle of the rec. shower is required > 30 mrad CLIC Workshop 2014, Gordana Milutinovic-Dumbelovic

Signal and background processes 6 Signal Background CLIC Workshop 2014, Gordana Milutinovic-Dumbelovic

Signal and background processes 7 -The most important kinematical property of signal is missing energy. - Process with the same signature like and give irreducible background (even after MVA) - Processes like and with low- angle electron in the final state can be dealt with in MVA + electron tagging - We added the full simulation of background including now the overlay of resulting in a change of Evis distribution (reduced MVA separation) CLIC Workshop 2014, Gordana Milutinovic-Dumbelovic

Signal and background processes 8 CLIC Workshop 2014, Gordana Milutinovic-Dumbelovic ProcessN events A A A Including a cut of 100GeV <M( )<140GeV and requiring a minimal polar angle for both muons of 8°.

Event selection and MV analysis ab -1 corresponding to 4 years operation with 50% data taking efficiency. - Pre-selection: - two reconstructed muons, ( ) GeV - di-muon mass window - absence of a E>200 GeV electron at on side of the FWD calorimeters – electron tagging CLIC Workshop 2014, Gordana Milutinovic-Dumbelovic ProcessRejection by direct tagging Rejection including coincident Bhabha events 17%24% 11%17% 0.2%7%

MVA 10 CLIC Workshop 2014, Gordana Milutinovic-Dumbelovic - TMVA input (E vis, p T (  ), p T (  1 )+p T (  2 ),  (  ), cos  *,  (  )). - BDT is trained on:

Background suppression with MVA 11 CLIC Workshop 2014, Gordana Milutinovic-Dumbelovic - BDT cut corresponds to the minimal relative statistical error maximization of significance or purity∙efficiency - MVA selection efficiency is 40% for signal. - Overall signal efficiency is 33%. BDT>0.064

12 - is reduced about 3 orders of magnitude - E mis signature background irreducibly present Before - after MVA CLIC Workshop 2014, Gordana Milutinovic-Dumbelovic

Signal and background PDFs Method of the measurement 13 Fully simulated, as large as possible, samples of signal and background to extract PDFs CLIC Workshop 2014, Gordana Milutinovic-Dumbelovic SIGNAL ALL BACKGROUND

Method of the measurement 14 Pseudo-experiments based on randomly sampled fully simulated signal events + backgrounds generated with PDFs Expected shape of data (signal + background) for each Toy MC is fitted with f to extract number of signal N s Toy MC experiments CLIC Workshop 2014, Gordana Milutinovic-Dumbelovic

Method of the measurement Toy MC experiments is performed to extract statistical uncertainty and check the pull distribution - RMS from Ns distribution give us statistical uncertainty of the measurement - Pull distribution confirms adequate description of signal and background with PDFs CLIC Workshop 2014, Gordana Milutinovic-Dumbelovic Statistical uncertainty

Results - Uncertainty of the measurement is dominated by the small statistics of signal and by the backgrounds with (true) missing energy. - One should not that no polarization is included that can boost statistics by a factor 2. - Uncertainty of the g H  (12%) is estimated assuming uncertainties of g HWW and  H as in the Snowmass paper. - Processes and has to be treated in EPA for low momentum transferred by the exchanged photon. In that kinematical region electron is substituted by a quasi-real photon. 16 CLIC Workshop 2014, Gordana Milutinovic-Dumbelovic NsNs 26±10 εsεs 33% σ WWH ×BR( ) 0.05 fb δ(σ WWH ×BR( )) 36% BR( ) (2.0±0.7)×10 -4

Conclusion 17 H→ μ + μ - analysis at 1.4 TeV completes Higgs BRs studies at CLIC energy stages. All relevant backgrounds are considered as well as a realistic electron tagging performance in the forward region. It has been shown that BR(H→ μ + μ - ) can be measured with a statistical accuracy of order of 30+ percent (the exact number will be provided after we introduce EPA) Uncertainty of the measurement is dominated by the small statistics of signal and by the backgrounds with (true) missing energy. CLIC Workshop 2014, Gordana Milutinovic-Dumbelovic

18 BACKUP

Systematics 19 - Peak luminosity (estimated to be determined within ~1.4 permille at 3 TeV CLIC - Systematic uncertainty of the signal count is relatively insensitive to the accuracy of the p T resolution - Uncertainties of the polar angle resolution and muon identification efficiency are expected to be at the percent level as at LEP - Coincidence with Bhabha events with 10ns (20 BX) time stamping is found to be 7% CLIC Workshop 2014, Gordana Milutinovic-Dumbelovic