Study of new variables for the search of the Higgs boson coupled to top

quarks in the multi-lepton final state

Student: Shahriyar Jafarzade (Institute of Radiation Problems, Azerbaijan)

Supervisor: Dr. Francesco Romeo (Institute of High Energy Physics, Beijing)

CERN Summer Student Lecture Program

Motivation for the tH search

• After the new boson discovery (Higgs like), focus on measuring its other properties {coupling to fermions, gauge bosons and itself}.• The Top quark is mostly strongly-coupled SM particle (~1).• Indirect constraints to the top-Higgs Yukawa coupling from loop

diagrams where the top quark contribute to ggproduction and H decay, but assuming no new particles.• Directly probe top-Higgs coupling through tH production

mechanism.• Large deviation from SM Higgs coupling could be explained by

some BSM models with enhanced tH production without changing the Higgs Branching Ratio (Vector-like, heavy top partner, Compositeness, RS, little Higgs) .

The tH process

Considering s / , we have 2 times the sensitivity for the same integrand luminosity.

Multi-Lepton final states are good compromise between Branching Ratio and signature

Results from the 8 TeV measurement within CMS

We select the events with same-sign di-lepton plus jets (b-jets)

Tt + jets dominates and Non-prompt leptons from b hadrons contaminate lepton selection in TtH, H Multi Lepton section

How do we want to contribute

We want to reduce t+jets background, keeping high tH efficiency

• I - the distance of closer approach between lepton quark and Primary Vertex(PV)

• I should be small – for Signal(tH lepton)

• I should be higher – for Background(t lepton)

• Signed IP-is defined considering the direction of IP along the jet direction

Distribution of IP 3D values

Both variables are discriminating, Using the sign in IP can provide additional information

IP < 0.00826 cm

< 0.015 cm

Eff(signal) 0.9375 0.977Eff(background) 0.6095 0.714Eff(signal)/Eff(background) 1.538 1.368

Signed IP < 0.0059 cm

< 0.01 cm

Eff(signal) 0.9375 0.977

Eff(background) 0.601 0.688

Eff(signal)/Eff(background) 1.5599 1.420

Summary and conclusion

Searching for a Higgs-like particle associated with two tops is important to evaluate its coupling

The multi-lepton final state provide a good compromise between clean signature and Branching Ratio

One of the main source of background is due to leptons from heavy flavor decay in tt+jets processes

IP are useful observables for selecting signal leptons

We have investigated the use of signed IP and shown promising preliminary results

This variable can be used in the analysis, provided good discrimination when used with the other variables and good Monte- Carlo modeling of data

The signed IP can be considered also for all the IP variants : 3D, 2D, value, and significance