Search for an exotic decay of the Higgs boson to a pair of light pseudoscalars in proton-proton collisions at 13 TeV and Luminosity measurement in Pb-Pb collisions at 5.02 TeV

In the first part of the thesis, we report the results of a search for exotic decay of a Higgs boson with m$_{H}$ = 125 GeV to a pair of new light bosons, a$_{1}$, where one of the light bosons decays to a pair of muons and the other to a pair of b quarks. Such signatures are predicted in a number of well-motivated extensions of the standard model, including the next-to-minimal supernumerary and generic two-Higgs-doublet models with an additional scalar singlet. A data sample corresponding to an integrated luminosity of 138 fb$^{-1}$ recorded with the CMS detector during 2016-2018 is exploited in $\mu$$\mu$bb final state where no statistically significant excess is observed with respect to the standard model backgrounds for different m$_{a1}$ hypotheses above 15 GeV and below m$_{H}$/2. Upper limits on $B$($H$ → $a$1$a$1 → $\mu$$\mu$bb) are obtained to be (0.17 − 3.3) × 10$^{−4}$ depending on the m$_{a1}$ values. The second part of the thesis includes a study of luminosity measurement using lead-lead (PbPb) collisions at 5.02 TeV in 2015

Recent CMS results on rare heavy flavour decays

Recent results on the B handrons decays from the CMS experiment at the LHC are reported. The observation of the $\mathrm{B}^{0}\to\psi(2\mathrm{S}) \mathrm{K}^{0}_{\mathrm{S}}\pi^{+}\pi^{-}$ and \mathrm{B}^0}_{\mathrm{s}}\to\psi(2\mathrm{S}) \mathrm{K}^{0}_{\mathrm{S}} decays is presented together with the first observation of the $\eta\to\mu^+\mu^-\mu^+\mu^-$ decay and the first observation of the $\Lambda^{0}_{\mathrm{b}}\to \mathrm{J}/\psi\Xi^{-}\mathrm{K}^{+}$ decay. The results are based on data sample collected in pp collisions at 13 TeV

Exotic production and decays of the 125 GeV Higgs – ATLAS

Since its discovery in 2012, the Higgs boson has been recognized as a promising candidate for exploring new physics beyond the Standard Model. The ATLAS collaboration has undertaken extensive efforts to investigate various potential scenarios for new physics. A substantial portion of the ATLAS physics program is devoted to the thorough examination of exotic Higgs phenomena. This paper presents recent studies conducted by the ATLAS collaboration in this endeavor

Yang-Mills, Gravity, and the Double-Copy Connection

Scattering amplitudes in Yang-Mills theory and in gravity have a rich internal structure. I review this structure, and the linear relations relating amplitudes. I also review the double-copy connecting Yang-Mills amplitudes to gravitational amplitudes. I'll discuss some examples of practical applications of the double copy. Time permitting, I will also discuss some of the novel tools used in the search for new relations and additional structure.</p

Long Term Irradiation of an ATLAS NSW SM2 Micromegas Quadruplet Using an AmBe Neutron Source

The NSW Micromegas chambers in the ATLAS forward muon spectrometer are subject to background rates of 15-20 kHz/cm under HL-LHC conditions. Typical anode currents will be around 6 A on an area of 1440 cm in the innermost part closest to the beamline. Due to the late change of the detectorgas from non-ageing Ar:CO2 93:7 to the more HV stable ternary mixture Ar:CO2:isobutane 93:5:2 and the known vulnerability of wire chambers to hydrocarbon containing gas mixtures a three year long ageing study has been performed. At CERN an SM1 and LM2 chamber underwent intense gamma irradiation of 662 keV gammas in GIF++ and an SM2 series module of the NSW Micromegas quadrupets was irradiated at LMU in Munich using a 10 GBq strong AmBe neutron source emitting 6*10e5 MeV n/s as well as 3.5E6 4.4 MeV gammas/s and 3.6E9 60keV gammas/s. Using this cocktail the SM2 chamber was irradiated on a several cm large region with a dose rate well exceeding the HL-LHC equivalent local charge densities for three years. In between the irradiation periods the performance of the SM2 chamber regarding spatial resolution and efficiency on cosmic muon tracking was tested several times. We report on the irradiation and the performance studies of the SM2 Micromegas quadruplet and come to the conclusion that no sign of loss in performance has been observed in contradiction to an earlier experience using drift tube wire chambers

Impact of Time-to-Digital converter thresholds on the precision of HGCAL timing

This note documents a series of simulation studies performed to investigate how precision timing measurement by the high granularity calorimeter (HGCAL) of the Compact Muon Solenoid (CMS) Phase-2 detector may be affected by the time-of-arrival (ToA) time-to-digital converter (TDC) threshold. Particle-level simulations are used to parameterize the expected efficiency and ToA resolution of different TDC thresholds. The parameterizations are then applied at stable particle-level of vector-boson-fusion (VBF) production of a Higgs boson to two photons to illustrate the potential gain of the precision timing on noise and pileup reduction in the HGCAL. An additional study is reported on the potential to correct time offsets due to clock phase jumps

3D Modelling and Transient Simulation of the Superconducting High Order Corrector Magnets for the High Luminosity Upgrade of the LHC

In this work, the superconducting superferric self-protected high order corrector magnets that are part of the High Luminosity Upgrade of the Large Hadron Collider are modelled and quench transient simulations are performed. These magnets include sextupole, octupole, decapole, and dodecapole magnets that were designed and manufactured by LASA (INFN). The purpose of these magnets is to correct the magnetic field errors of the focusing quadrupole magnets in the two main intersection regions in the LHC (ATLAS and CMS). To perform a quench protection analysis, the Python framework STEAM-SDK is used, which is developed at CERN and connects several softwares for (co-)simulation of superconducting magnets by unified models. As part of the modelling, the 3D racetrack geometry of the considered magnets is implemented in the framework and is now available across various STEAM tools. Electromagnetic and thermal transients in the magnets are simulated using STEAM-LEDET, which models 3D thermal diffusion along the conductor and between turns, ohmic loss, and inter-filament coupling loss using the finite difference method. Furthermore, STEAM-SDK is further developed with regard to two automation functions. On the one hand, the parameters of all conductors are to be automatically calculated for each coil individually and adjusted in the model. Secondly, all parameters related to a quench event will be calculated and adjusted in the model on the basis of automatically created measurement files. With this automation, each coil of the HL-LHC HOC magnets will also be adjusted from the design parameters to measured values. Within the context of modelling, several assumptions have to be made, which are validated and justified by appropriate simulations and measurements. Specific aspects such as the quench propagation between coils, the adjustment of the helium cooling or the approximation of the magnetic circuit are addressed. Eleven measurements from training quenches at LASA with different magnets at different current levels are available for validation. Since the initial quench position remains an unknown quantity, a targeted parameter study is performed for this purpose. Furthermore, the occurrence of quench back is investigated and an analysis of the simulated hot-spot temperatures is performed to evaluate the effectiveness of the quench protection strategy. For the different high order corrector magnets, a consistent set of assumptions was found for which the models provide predictive simulation results for all magnets and at different current levels, with almost all simulation results being within the uncertainties of the quench position with respect to quench load

Development of A 16:1 serializer for data transmission at 5 Gbps

Radiation tolerant, high speed and low power serializer ASIC is critical for optical link systems in particle physics experiments. Based on a commercial 0.25 μm silicon-onsapphire CMOS technology, we design a 16:1 serializer with 5 Gbps serial data rate. This ASIC has been submitted for fabrication. The post-layout simulation indicates the deterministic jitter is 54 ps (pk-pk) and random jitter is 3 ps (rms). The power consumption of the serializer is 500 mW. The design details and post layout simulation results are presented in this paper.Radiation tolerant, high speed and low power serializer ASIC is critical for optical link systems in particle physics experiments. Based on a commercial 0.25 μm silicon-onsapphire CMOS technology, we design a 16:1 serializer with 5 Gbps serial data rate. This ASIC has been submitted for fabrication. The post-layout simulation indicates the deterministic jitter is 54 ps (pk-pk) and random jitter is 3 ps (rms). The power consumption of the serializer is 500 mW. The design details and post layout simulation results are presented in this paper.Radiation tolerant, high speed and low power serializer ASIC is critical for optical link systems in particle physics experiments. Based on a commercial 0.25 um silicon-on-sapphire CMOS technology, we design a 16:1 serializer with 5 Gbps serial data rate. This ASIC has been submitted for fabrication. The post-layout simulation indicates the deterministic jitter is 54 ps (pk-pk) and random jitter is 3 ps (rms). The power consumption of the serializer is 500 mW. The design details and post layout simulation results are presented in this paper