NPAC (Nuclear/Particle/Astro/Cosmo) Forums
Organized by: Prof. Lu Lu
Events on Thursday, November 9th, 2023
- Measurement of the ttH and tH Production Rates in theH to bb Decay Channel at CMS
- Time: 1:00 pm - 2:00 pm
- Place: 5310 CH
- Speaker: Abhisek Datta, UCLA
- Abstract: Associated production of the Higgs boson with a top quark-antiquark pair (𝑡𝑡̅𝐻) provides the best direct probe of the top-Higgs Yukawa coupling at tree-level. Measurement of this coupling is important not only to confirm the predictions made by the Standard Model but also to search for indications of new physics. In this talk, I will present an analysis of 𝑡𝑡̅𝐻 production with the Higgs boson decaying to a 𝑏𝑏̅ pair which has the largest branching fraction. Latest results obtained using pp collision data at the CERN LHC recorded by the CMS experiment at √𝑠 = 13 TeV between 2016 and 2018 corresponding to an integrated luminosity of 138 𝑓𝑏−1 will be shown. One particularly challenging background limiting the precision of this measurement arises from direct 𝑡𝑡̅+𝑏𝑏̅ production. Measurements of both the overall 𝑡𝑡̅𝐻 production rate and in intervals of Higgs boson transverse momentum are performed. Limits are also set on the production rate of a Higgs boson with a single top quark (𝑡𝐻) and on the strength and structure of the top-Higgs coupling from simultaneous measurements of 𝑡𝑡̅𝐻 and 𝑡𝐻 production rates. In order to improve the precision of these measurements in the future, the LHC in the High Luminosity era will be upgraded to deliver instantaneous luminosities much higher than the original design value. ME0 is a new muon sub-detector (using Gas Electron Multiplier technology) that will be added in the far-forward region (2.0<|𝜂|<2.8) of CMS as part of the Phase-2 Upgrade. I will discuss the development of the readout electronics for the ME0 detector, which must be designed to deal with high data rates and be sufficiently radiation hard to operate so close to the beamline.
- Host: Kevin Black
- Exploring New Physics with Background Radiation Fields
- Time: 2:30 pm - 3:30 pm
- Place: 5310 Chamberlin or
- Speaker: Justin Finke, Naval Research Labs
- Abstract: I will explore the following topics: (1) I will discuss modeling the ultraviolet through infrared Extragalactic Background Light (EBL), which is the background light from all of the stars and dust that have existed in the observable universe. This radiation field can absorb gamma-rays to produce electron-positron pairs, and can thus be probed with gamma-ray observations, as well as optical and infrared surveys. I will discuss what we can learn about star formation and other physics from it. (2) I will discuss the brightest gamma-ray burst (GRB) ever observed, GRB 221009A. Fewer very-high energy (VHE) gamma-rays from this GRB are absorbed by the EBL than models predict, which may be an indication of new physics. I will discuss how VHE observations of this GRB can be explained by Lorentz invariance violation (LIV). Lorentz invariance is one of the fundamental symmetries of relativity, and its violation is consistent with some beyond Standard Model theories. (3) Astrophysical gamma-rays can also be absorbed by a much closer source of optical photons than the EBL, namely, by photons from the Sun. I will discuss how observations of absorption of astrophysical gamma-rays by solar photons could be used to probe LIV.
- Host: Abhishek Desai