1. CERN Summer Student Lecture Program
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

2. Motivation for the t 𝒕 H 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 ( 𝑌 𝑡 ~1).
Indirect constraints to the top-Higgs Yukawa coupling 𝑌 𝑡 from loop diagrams where the top quark contribute to gg→𝐻 production and H → 𝛾𝛾 decay, but assuming no new particles.
Directly probe top-Higgs coupling through t 𝑡 H production mechanism.
Large deviation from SM Higgs coupling could be explained by some BSM models with enhanced t 𝑡 H production without changing the Higgs Branching Ratio (Vector-like, heavy top partner, Compositeness, RS, little Higgs) .

3. The t 𝒕 H process
Considering s / 𝑏 , we have ≈ 2 times
the sensitivity for the same integrand luminosity.
Multi-Lepton final states are good compromise between Branching Ratio and signature

4. 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

5. How do we want to contribute
We want to reduce t t +jets background, keeping high t t H efficiency
I 𝐏 𝟑𝐃 - the distance of closer approach between lepton quark and Primary Vertex(PV)
I P 3D should be small – for Signal(t t H lepton)
I P 3D should be higher – for Background(t t lepton)
Signed IP-is defined considering the direction of IP along the jet direction

6. Distribution of IP 3D values
< cm
< cm
Eff(signal)
0.9375
0.977
Eff(background)
0.6095
0.714
Eff(signal)/Eff(background)
1.538
1.368
Signed IP
< cm
< 0.01 cm
Eff(signal)
0.9375
0.977
Eff(background)
0.601
0.688
Eff(signal)/Eff(background)
1.5599
1.420
Both variables are discriminating,
Using the sign in IP can provide additional information

7. 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