Mu3e

Abstract:

A study of the Higgs boson decaying into bottom quarks (H → bb¯) and charm quarks (H → cc¯) is performed, in the associated production channel of the Higgs boson with a W or Z boson, using 140 fb−1 of proton-proton collision data at s = 13 TeV collected by the ATLAS detector. The individual production of WH and ZH with H → bb¯ is established with observed (expected) significances of 5.3 (5.5) and 4.9 (5.6) standard deviations, respectively. Differential cross-section measurements of the gauge boson transverse momentum within the simplified template cross-section framework are performed in a total of 13 kinematical fiducial regions. The search for the H → cc¯ decay yields an observed (expected) upper limit at 95% confidence level of 11.5 (10.6) times the Standard Model prediction. The results are also used to set constraints on the charm coupling modifier, resulting in |κc| < 4.2 at 95% confidence level. Combining the H → bb¯ and H → cc¯ measurements constrains the absolute value of the ratio of Higgs-charm and Higgs-bottom coupling modifiers (|κc/κb|) to be less than 3.6 at 95% confidence level.

Abstract:

The ITk is a new silicon tracker for the ATLAS experiment designed to increase detector resolution, readout capacity, and radiation hardness, in preparation for the larger number of simultaneous proton–proton interactions at the High Luminosity LHC. This paper presents the first direct measurement of the material budget of an ATLAS ITk pixel module, performed at a testbeam at the CERN Proton Synchrotron via the multiple scattering of low energy positrons within the module volume. Using a four plane telescope of thin monolithic pixel detectors from the MALTA Collaboration, scattering datasets were recorded at a beam energy of 1.2GeV. Kink angle distributions were extracted from tracks derived with and without information from the ITk pixel module, and were fit to extract the RMS scattering angle, which was converted to a fractional radiation length x/X0. The average x/X0 across the module was measured as [0.89±0.01(resolution)±0.01(subtraction)±0.08(beam momentum band)]%, which agrees within uncertainties with an estimate of 0.88% derived from material component expectations.