Abstract
A search for the dimuon decay of the Standard Model (SM) Higgs boson is performed using data corresponding to an integrated luminosity of 139 fb−1 collected with the ATLAS detector in Run 2 pp collisions at s=13 TeV at the Large Hadron Collider. The observed (expected) significance over the background-only hypothesis for a Higgs boson with a mass of 125.09 GeV is 2.0σ (1.7σ). The observed upper limit on the cross section times branching ratio for pp→H→μμ is 2.2 times the SM prediction at 95% confidence level, while the expected limit on a H→μμ signal assuming the absence (presence) of a SM signal is 1.1 (2.0). The best-fit value of the signal strength parameter, defined as the ratio of the observed signal yield to the one expected in the SM, is μ=1.2±0.6.
Highlights
Background events from the DrellYan (DY) Z /γ ∗ → μμ process were generated with Sherpa 2.2.1 [77] using NLO-accurate matrix elements for up to two partons, and leading order (LO)-accurate matrix elements for up to four partons calculated with the Comix [78] and OpenLoops [79,80] libraries and the NNPDF3.0 NNLO set
This paper presents an improved search for the dimuon decay of the Higgs boson using the full pp collision dataset recorded with the A√TLAS detector in the LHC Run 2 period, spanning 2015 to 2018 at s = 13 TeV, corresponding to an integrated luminosity of about 139 fb−1
Number of events observed in the mμμ = 120–130 GeV window in data, the number of signal events expected in the Standard Model (SM) (SSM), and events from signal (S = μ × SSM) and background (B) as derived from the combined fit to the data with a signal strength parameter of μ = 1.2
Summary
The ATLAS detector [18,19] covers nearly the entire solid angle around the collision point. It consists of an inner tracking detector surrounded by a thin superconducting solenoid, electromagnetic and hadronic calorimeters, and a muon spectrometer incorporating three large superconducting toroid magnets. The ATLAS detector [18,19] covers nearly the entire solid angle around the collision point.1 It consists of an inner tracking detector surrounded by a thin superconducting solenoid, electromagnetic and hadronic calorimeters, and a muon spectrometer incorporating three large superconducting toroid magnets. A high-granularity silicon pixel detector covers the vertex region and typically provides four measurements per track. It is surrounded by a silicon microstrip tracker, which typically provides four measurement points per track. The muon spectrometer (MS) comprises separate trigger and high-precision tracking chambers measuring the deflection of muons in a magnetic field generated by the superconducting aircore toroids. This is followed by a softwarebased high-level trigger which runs algorithms similar to those in the offline reconstruction software, reducing the event rate to approximately 1 kHz from the maximum L1 rate of 100 kHz
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