Abstract
A search is presented for the associated production of a Higgs boson with a top quark pair in the all-jet final state. Events containing seven or more jets are selected from a sample of proton-proton collisions at sqrt{s}=13 TeV collected with the CMS detector at the LHC in 2016, corresponding to an integrated luminosity of 35.9 fb−1. To separate the mathrm{t}overline{mathrm{t}}mathrm{H} signal from the irreducible mathrm{t}overline{mathrm{t}}+mathrm{b}overline{mathrm{b}} background, the analysis assigns leading order matrix element signal and background probability densities to each event. A likelihood-ratio statistic based on these probability densities is used to extract the signal. The results are provided in terms of an observed ttH signal strength relative to the standard model production cross section μ = σ/σSM, assuming a Higgs boson mass of 125 GeV. The best fit value is widehat{mu}=0.9pm 0.7left(mathrm{stat}right)pm 1.3left(mathrm{syst}right)=0.9pm 1.5left(mathrm{tot}right) , and the observed and expected upper limits are, respectively, μ < 3.8 and < 3.1 at 95% confidence levels.
Highlights
Background estimationThe main backgrounds stem from multijet and tt production associated with additional gluons, light-flavour, charm, or bottom quarks
To verify that the good performance demonstrated in the gluon jet enriched validation region (VR) (QGLR < 0.5) holds in the quark jet enriched signal region (SR) (QGLR > 0.5), we investigate another control region (CR)
Each background contribution is initially normalized to an integrated luminosity of 35.9 fb−1, while the multijet contribution is free to float in the fit
Summary
The central feature of the CMS apparatus is a superconducting solenoid of 6 m internal diameter, providing a magnetic field of 3.8 T. A silicon pixel and strip tracker, a lead tungstate crystal electromagnetic calorimeter (ECAL), and a brass and scintillator hadron calorimeter (HCAL), each composed of a barrel and two end sections, reside within the field volume. Events of interest are selected using a twotiered trigger system [29]. The first level, composed of specialized hardware processors, uses information from the calorimeters and muon detectors to select events at a rate close to 100 kHz, ascertained within a time interval of less than 4 μs. The second level, known as the high-level trigger, consists of a farm of processors running a version of the full event reconstruction software optimized for fast processing, and reduces the event rate to ≈1 kHz before data storage. A more detailed description of the CMS detector, together with a definition of the coordinate system and the kinematic variables, can be found in ref. [30]
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