Search for Higgs boson and observation of Z boson through their decay into a charm quark-antiquark pair in boosted topologies in proton-proton collisions at $\sqrt{s}$ = 13 TeV

TL;DR

This paper reports a search for the Higgs boson decaying into charm quark pairs in boosted topologies at 13 TeV, using CMS data, with a novel charm tagging method validated by observing Z to charm decays.

Contribution

It introduces a deep neural network charm tagging technique for boosted Higgs decays and validates it by observing Z to charm decays at high transverse momentum.

Findings

First observation of Z to charm in high pT regime

Set upper limits on Higgs to charm decay rate

Validated charm tagging with SM Z decay measurement

Abstract

A search for the standard model (SM) Higgs boson (H) produced with transverse momentum greater than 450 GeV and decaying to a charm quark-antiquark ($\mathrm{c\bar{c}}$) pair is presented. The search is performed using proton-proton collision data collected at $\sqrt{s}$ = 13 TeV by the CMS experiment at the LHC, corresponding to an integrated luminosity of 138 fb$^{-1}$. Boosted H $\to$ $\mathrm{c\bar{c}}$ decay products are reconstructed as a single large-radius jet and identified using a deep neural network charm tagging technique. The method is validated by measuring the Z $\to$ $\mathrm{c\bar{c}}$ decay process, which is observed in association with jets at high $p_\mathrm{T}$ for the first time with a signal strength of 1.00 $_{-0.14}^{+0.17}$ (syst) $\pm$ 0.08 (theo) $\pm$ 0.06 (stat), defined as the ratio of the observed process rate to the standard model expectation. The observed (expected) upper limit on $\sigma$(H) $\mathcal{B}$(H $\to$ $\mathrm{c\bar{c}}$) is set at 47 (39) times the SM prediction at 95% confidence level.