What is the W b anti-b, Z b anti-b or t anti-t b anti-b irreducible background to the light Higgs boson searches at LHC?

The W b anti-b, Z b anti-b and t anti-t b anti-b production at LHC are irreducible backgrounds for possible observability of the Standard Model (SM) and Minimal Supersymmetric Standard Model (MSSM) light Higgs boson respectively in the associated WH, ZH and t anti-t H production followed by the H -> b anti-b decay. We present a comparison of the background estimates as obtained with (a) complete massive matrix element implemented in AcerMC Monte Carlo generator and (b) PYTHIA implementation of the inclusive W, Z, and t anti-t production, followed by the parton showering mechanism. Both approaches lead to a production of the final state of interest, but differ in the approximations used. We concentrate on the comparison of these approaches for the background to the light Higgs boson searches at LHC.Comment: EPJC Referee's comments adde

MSSM Higgs searches in multi-b-jet final states at the LHC

This paper discusses the possibility to observe a signal from MSSM Higgs boson decays into final states containing four b-jets. Two specific channels are considered: bbH and bbA production with H,A -->bb, for large values of mH, mA and tan(beta), and H-->hh-->bbbb decays for 150 GeV < mH < 2 and for low values of tan(beta). Both channels are difficult to extract because of the very large reducible and irreducible QCD backgrounds. Even with an ultimate integrated luminosity, expected per LHC experiment, of 3*10**5 pb**-1, the region of the MSSM parameter space covered by these channels does not extend the reach beyond that accessible to other channels that were studied in the past. Nevertheless, their observation would help in constraining the couplings and branching ratios of the MSSM Higgs bosons

Deep learning approach to the Higgs boson CP measurement in H to tau tau decay and associated systematics

The H to tau tau decays form the prime channel for the measurement of the Higgs boson state and tests of the CP invariance of Higgs boson couplings. A previous study has shown the viability of deep learning techniques for the measurement. In this paper, the study is expanded. Effects due to the partial modelling of experimental effects are discussed. Furthermore, systematics due to ? decay modelling for complex cascade decays to tau^pm to a_1^pm nu_tau to rho^0 pi^pm nu_tau to 3pi^\pm nu_tau are also addressed. Various parameterisations are considered using low-energy collision data.Comment: 13 pages, 4 figure

QCD

We discuss issues of QCD at the LHC including parton distributions, Monte Carlo event generators, the available next-to-leading order calculations, resummation, photon production, small x physics, double parton scattering, and backgrounds to Higgs production.Comment: 115 pages, Latex, 47 figures, to appear in the Report of the ``1999 CERN Workshop on SM Physics (and more) at the LHC'', S. Catani, M. Dittmar, D. Soper, W.J. Stirling, S. Tapprogge (convenors

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements