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Higgs & Top at LHeC
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CERN - Tokyo - Liverpool - Johannesburg - Beijing - Hamburg
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Satoshi Kawaguchi presented on the status of electron efficiency
problem in Delphes 3.1.2. He found that the bug in this version
was in the photon reconstruction. Due to this, the LHeC detector card
which was used in our group so far could reconstruct only ~50%
of signal NC Higgs events. However, ATLAS detector card seems
not affected by the bug. The reason is the input for photon definition.
ATLAS uses Calorimter/photons while LHeC uses Calorimter/eflowPhotons.
By modifying our LHeC detector card for Delphes, the electron efficiency
has been recovered to 95%. Repeating the whole analysis with this fix,
he obtained 2sigma sensitivity of 7.47% while the previous result was 12.4%.
Masahiro Tanaka orally mentioned that he will repeat his CC Hbb analysis
using this fix. Probably the signal CC events won't be affected much,
but the background containing true electrons may have been underestimated.
Hao Sun presented an update on his studies published in
arXiv:1602.04670v2 [hep-ph] 25 Feb 2016
on anomalous FCNC Top-Higgs Couplings
- The signal process is the charged current reaction eb --> t ne
with t -> h ubar and with h -> b bbar
- He uses the madgraph@nlo programme with
five flavour scheme PDFs, so b comes out of the proton
- Backgrounds with largest cross sections are multijet
production in neutral currents, after all cuts single top
is largest background source
- Studies are done on parton level (no delphes)
with assumptions on b-tagging and light flavour mistagging
efficiences
- Many kinematic cuts applied on final state to suppress the backgrounds,
e.g. |eta_jet|<2 and requiring >=2 b tags etc.,
TMVA based analysis is also performed
- Example scenarios:
7 TeV on 60 GeV, L=1000fb-1
--> final signal significance ~4
50 TeV on 60 GeV, L=1000fb-1
--> final signal significance ~13
- p.8 shows that with 1ab^-1 lumi one could get at LHeC 1 sigma
limit on BR(t-> uh) <= 0.033% (cut based analysis)
- p.9/10 tables:Comparison to RUN I CMS and ATLAS results
and projected resutlts for run II or High lumi LHC
--> LHeC with lumi of o(1ab^-1) is competitive
for Br(t--> uh), e.g. Br(t-> uh)<0.23% for HL-LHC
Questions:
- Please write on each relevant slide
the beam energies and add somewhere other assumptions such as
b-tag eff and light flavour mistag
- p.8/9/10: confuse 1sigma and 2sigma should be changed
- in general many 1 and 2 sigma level are given, would
be nice to go up to 5 sigma levels
- Prospects for extending studies to detector studies based on Delphes:
--> Uta: correct photon bug and then it could be passed on
- Question: kinematic cuts on jets like |eta_j|<2
are these realistic? --> they help to reduce backgrounds, jets
are often forward(see arxiv Note)
------------------------------
Mukesh Kumar:
study FCNC gamma u --> t at at photon proton collider
- get photon spectrum from electron
- calculated cross section results on pythia level
- wish to finish using delphes detector level.
-> present on one of the next meetings
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