Distinguishing Standard Model Extensions using MonoTop Chirality at the LHC

Transcription

1 Distinguishing Standard Model Extensions using MonoTop Chirality at the LHC Ryan Mueller R. Allahverdi, M. Dalchenko, B. Dutta, A. Florez, Y. Gao, T. Kamon, N. Kolev, R. M. and M. Segura, J. High Energy Phys. 12 (2016) 046. APS April Meeting 2017: Washington, DC, USA, January 28-31, 2017 APS April Meeting 2017 Ryan Mueller

2 2 Why MonoTop BSM Searches? MonoTop: just like it sounds, a final state with one top quark Investigations into monojet/monotop final states are interesting as they: Predicted by various new physics models Separable from the background: have a distinctive final state Not excluded: MonoTop final states remain open MonoTop states are sensitive to couplings to third generation quarks How can we improve MonoTop searches at the LHC?

3 3 Distinguishing Models with Chirality The chirality of the top can distinguish models: Standard Model (SM) single top production: mostly LH BSM top production: often either exclusively LH or RH Big problem: The top chirality is hard to measure in the MonoTop final state!

4 4 Measuring the Final State Chirality RH top quark W boson LH top quark W boson RH b quark LH b quark Top quark decays typically into longitudinal W and b quark: W s coupling to LH current causes the b s momentum in the COM frame will be antiparallel to the boost vice versa for RH top Distinguish with variable R = E(b)/E(t) This method is new to MonoTop searches! Time to test it out.

5 A Quick Detour: The Model and Simulation APS April Meeting 2017 Ryan Mueller

6 6 A RH MonoTop Model minimal SM extension: Χα: heavy iso-singlet color-triplet scalar Ν: singlet fermion DM candidate λ: antisymmetric under i,j Only interacts with RH type quarks

7 7 Final States Single X production: MonoTop 2 quarks Double X production: 2 X final state We are interested in the MonoTop final state

8 MonoTop Signatures APS April Meeting 2017 Ryan Mueller 8

9 9 Technical detals Generation in MadGraph 5 Hadronization in Pythia8 Detector simulation in Delphes 3.2 MLM jet matching b-tagging efficiency: 70% in the barrel part of the detector ( η < 1.2) 60% in the endcaps (1.2 < η < 2.5).

10 10 Event selection non b-jets N >= 2 pt Hadronic > 30 GeV η < 2.5 leptons (e or μ) N = 0 other b-jets N = 1 pt Both > 70 GeV η < 2.5 non b-jets N <= 1 pt > 30 GeV η < 2.5 leptons (e or μ) N = 1 pt Leptonic > 30 GeV η < 2.1 Missing ET m(j,j,b) > 350 GeV < 450 GeV other N(τ) = 0 pt(w) > 50 GeV Δφ(l,b-jet) < 1.7 ΔR > 0.3 Missing ET mt > 350 GeV > 400 GeV

11 Back on Topic: Measuring the Chirality APS April Meeting 2017 Ryan Mueller

12 12 Final state chirality In our model, X decays to RH top In order to demonstrate our ability to measure chirality, we introduce a LH toy model identical to RH model kinematically

13 13 Measuring the Final State Chirality Generator Sim: E(b)/E(t) Delphes sim: Hadronic Channel 20 fb signal cross section and 100 fb^-1 luminosity

14 14 Cut and Count test Count events including background with this cut: RH and LH scenario distinguished by counts Integral of RH Integral of LH Poisson distribution of counts -> calculate CLs

15 15 Discriminating power Integrated Luminosity for 95% CLs Hadronic channel with 20 fb cross section These numbers would most likely be significantly improved with the inclusion of a proper shape analysis

16 16 Conclusion The MonoTop final state is a particularly interesting probe of new physics: predicted to exist by many BSM models different models can be distinguished through the top quark s polarization Simple variable R = E(b)/E(t) is proposed to separate chirality of top quarks. For the first time, we have reconstructed the top quark chirality well enough for use in a single top final state analysis More works needs to be done for highly boosted top quarks (X > 2 TeV) Further polarization analysis may be possible for the leptonic channel through the lepton s kinematics

17 17 Further polarization analysis possibilities Knowing the polarization of the W further helps determine the polarization of the top The polarization of the W boson can be determined from the angular distribution of it s decay products However two sources of MET prevents this from easily being measured What do you do? deep learning e.g. Jacob Searcy et al. Phys. Rev. D 93, Published 27 May 2016 modified kinematic variable like MT2 Both offer only approximations, but still can improve our significance in the harder leptonic channel

18 18 Final state chirality Electronic Muonic Hadronic Delphes simulation with 20 fb signal cross section and 100 fb^-1 luminosity Leptonic: Hadronic:

19 19 Example LH Model SM extension: Χ α : heavy iso-doublet color-triplet scalar Y: iso-doublet fermions Ν: singlet fermion λ antisymmetric under i,j Only interacts with LH handed type quarks