A. Boletti

The CMS detector will be upgraded for the HL-LHC to include a MIP Timing Detector (MTD). The MTD will consist of barrel and endcap timing layers, BTL and ETL respectively, providing precision timing of charged particles. The BTL sensors are based on LYSO:Ce scintillation crystals coupled to SiPMs with TOFHIR2 ASICs for the front-end readout. A resolution of 30-60 ps for MIP signals at a rate of 2.5 Mhit/s per channel is expected along the HL-LHC lifetime. We present an overview of the TOFHIR2 requirements and design, simulation results and measurements with TOFHIR2 ASICs. The measurements of TOFHIR2 associated to sensor modules were performed in different test setups using internal test pulses or blue and UV laser pulses emulating the signals expected in the experiment. The measurements show a time resolution of 24 ps initially during Beginning of Operation (BoO) and 58 ps at End of Operation (EoO) conditions, matching well the BTL requirements. We also showed that the time resolution is stable up to the highest expected MIP rate. Extensive radiation tests were performed, both with x-rays and heavy ions, showing that TOFHIR2 is not affected by the radiation environment during the experiment lifetime.

The CMS Detector will be upgraded for the High-Luminosity LHC to include a MIP Timing Detector (MTD). The MTD will consist of barrel and endcap timing layers, BTL and ETL, respectively, providing precision timing of charged particles. The BTL sensors are based on LYSO:Ce scintillating crystals coupled to SiPMs that are read out by TOFHIR2 ASICs in the front-end system. A resolution of 30 ps for MIP signals is expected at the beginning of HL-LHC operation degrading to 60 ps at the end of operation due to the SiPMs radiation damage. Relative to the first version of the front-end ASIC, TOFHIR2X implements improved circuitry for mitigation of the SiPM dark current noise as well as a new current mode discriminator. We present an overview of the TOFHIR2 requirements and design, simulation results and the first measurements with TOFHIR2X silicon samples coupled to LYSO/SiPM prototype sensors.

The CMS drift tubes (DT) muon detector, built for withstanding the LHC expected integrated and instantaneous luminosities, will be used also in the High Luminosity LHC (HL-LHC) at a 5 times larger instantaneous luminosity and, consequently, much higher levels of radiation, reaching about 10 times the LHC integrated luminosity. Initial irradiation tests of a spare DT chamber at the CERN gamma irradiation facility (GIF++), at large (∼ O(100)) acceleration factor, showed ageing effects resulting in a degradation of the DT cell performance. However, full CMS simulations have shown almost no impact in the muon reconstruction efficiency over the full barrel acceptance and for the full integrated luminosity. A second spare DT chamber was moved inside the GIF++ bunker in October 2017. The chamber was being irradiated at lower acceleration factors, and only 2 out of the 12 layers of the chamber were switched at working voltage when the radioactive source was active, being the other layers in standby. In this way the other non-aged layers are used as reference and as a precise and unbiased telescope of muon tracks for the efficiency computation of the aged layers of the chamber, when set at working voltage for measurements. An integrated dose equivalent to two times the expected integrated luminosity of the HL-LHC run has been absorbed by this second spare DT chamber and the final impact on the muon reconstruction efficiency is under study. Direct inspection of some extracted aged anode wires presented a melted resistive deposition of materials. Investigation on the outgassing of cell materials and of the gas components used at the GIF++ are underway. Strategies to mitigate the ageing effects are also being developed. From the long irradiation measurements of the second spare DT chamber, the effects of radiation in the performance of the DTs expected during the HL-LHC run will be presented.

The rare flavour-changing neutral current decays of the B mesons are among the most sensitive laboratories to probe the Standard Model and indirectly search for physics beyond it.In this report, a complete review of the analyses of the rare → ℓℓ decays performed by the CMS Collaboration is presented.In particular, three decays have been studied: 0 → * 0 , + → + , and + → * + .Finally, the projection of the analysis of the 0 → * 0 decay channel to the HL-LHC data-taking is presented.

During the High Luminosity LHC, the Drift Tube chambers installed in the CMS detector need to operate with an integrated dose ten times higher than expected at the LHC due to the increase in integrated luminosity from 300 fb-1 to 3000 fb-1. Irradiations have been performed to assess the performance of the detector under such conditions and to characterize the radiation aging of the detector. The presented analysis focuses on the behaviour of the high voltage currents and the dose measurements needed to extrapolate the results to High Luminosity conditions, using data from the photon irradiation campaign at GIF++ in 2016 as well as the efficiency analysis from the irradiation campaign started in 2017. Although the single-wire loss of high voltage gain observed of 70% is very high, the muon reconstruction efficiency is expected to decrease less than 20% during the full duration of High Luminosity LHC in the areas under highest irradiation.

The results of analyses involving rare decays of B mesons, performed using the data collect by the CMS experiment in pp collisions at √ s = 7 TeV and 8 TeV, are presented.Firstly, the angular analysis of the decay B 0 → K * µ + µ -with the 2012 data is introduced.The forward-backward asymmetry of the muons, the K * longitudinal polarization fraction, and the differential branching fraction are determined as a function of the dimuon invariant mass squared.The results are in good agreement with the standard model expectations.Then, the analysis of the B 0 s → µ + µ -and B 0 → µ + µ -rare decays is presented.An excess is found for the B 0 s decay and the measurement B(B 0 s → µ + µ -) = (3.0+1.0 -0.9 ) × 10 -9 is performed.No significant excess is found for the B 0 decay and the upper limit B(B 0 → µ + µ -) < 1.1 × 10 -9 at 95 % confidence level is set.

In this paper we present an analog circuit for the new MIP Timing Detector of the CMS experiment at CERN, featuring, for the first time, a silicon implementation of the Differential Leading Edge Discriminating technique to suppress SiPM dark noise. This technique also stabilizes the baseline, leading to a time resolution of 25 ps at beginning of life and 55 ps at end of life while dissipating less than 4 mW. The full analog front-end ASIC has 32 channels and has been designed in a CMOS 130 nm technology with a total die area of 8.5 x 5.2 mm2. The radiation tolerance of this design has been confirmed by radiation tests.

The large instantaneous luminosity delivered by LHC to the CMS experiment in Run 2 is an important opportunity for the study of rare B-hadron decays, like $\mathrm{B}^0_{(s)}\to\mu\mu$ and $\mathrm{B}^0\to\mathrm{K}^{*0}\mu\mu$. The main drawback of this luminosity increase is that the trigger selections need to be tighter, in order to fit the rate of recorded events in the limits imposed by the available computer resources. This constraint imposes a challenge in the development of new trigger tools and algorithms, optimized to keep high acceptance on signal events while reducing the rate of collected background events, both at Level-1 Trigger (L1T) and at High-Level Trigger (HLT).

The flavour changing neutral current decays are interesting probes for new physics searches. The angular distributions of $b \to s \ell^+ \ell^-$ transition processes of both $\mathrm{B}^0 \to \mathrm{K}^{*0} \mu^ +\mu^-$ and $\mathrm{B}^{+} \to \mathrm{K}^{+} \mu^+\mu^-$ decays are studied using a sample of proton-proton collisions at $\sqrt{s} = 8~\mathrm{TeV}$ collected with the CMS detector at the LHC, corresponding to an integrated luminosity of $20.5~\mathrm{fb}^{-1}$. Angular analyses are performed to determine the angular parameters $P_1$ and $P_5'$ for $\mathrm{B}^0 \to \mathrm{K}^{*0} \mu^ +\mu^-$ and $A_{FB}$ and $F_{H}$ parameters for $\mathrm{B}^{+} \to \mathrm{K}^{+} \mu^+\mu^-$, as functions of the dimuon invariant mass squared. All the measurements are consistent with the standard model predictions.

The flavour changing neutral current decays are interesting probes for new physics searches. The angular distributions of $b \to s \ell^+ \ell^-$ transition processes of both $\mathrm{B}^0 \to \mathrm{K}^{*0} \mu^ +\mu^-$ and $\mathrm{B}^{+} \to \mathrm{K}^{+} \mu^+\mu^-$ decays are studied using a sample of proton-proton collisions at $\sqrt{s} = 8~\mathrm{TeV}$ collected with the CMS detector at the LHC, corresponding to an integrated luminosity of $20.5~\mathrm{fb}^{-1}$. Angular analyses are performed to determine the angular parameters $P_1$ and $P_5'$ for $\mathrm{B}^0 \to \mathrm{K}^{*0} \mu^ +\mu^-$ and $A_{FB}$ and $F_{H}$ parameters for $\mathrm{B}^{+} \to \mathrm{K}^{+} \mu^+\mu^-$, as functions of the dimuon invariant mass squared. All the measurements are consistent with the standard model predictions. In addition, the projections for the sensitivity of the measurement of the $P_5'$ parameter in the $\mathrm{B}^0 \to \mathrm{K}^{*0} \mu^ +\mu^-$ angular analysis at the High-Luminosity LHC is reported.

To sustain and extend its discovery potential, the Large Hadron Collider (LHC) will undergo a major upgrade in the coming years, referred to as High Luminosity LHC (HLLHC), aimed to increase its instantaneous luminosity, 5 times larger than the designed limit, and, consequently leading to high levels of radiation, with the goal to collect 10 times larger the original designed integrated luminosity. The drift tube chambers (DT) of CMS muon detector system is built to proficiently measure and trigger on muons in the harsh radiation environment expected during the HL-LHC era. Ageing studies are performed at the CERNs gamma ray irradiation facility (GIF++) by measuring the muon hit efficiency of these detectors at various LHC operation conditions. One such irradiation campaign was started in October 2017, when a spare MB2 chamber moved inside the bunker and irradiated at lower acceleration factors. Two out of twelve layers of the DT chamber were operated while being irradiated with the radioactive source and then their muon hit efficiency was calculated in coincidence with other ten layers which were kept on the standby. The chamber absorbed an integrated dose equivalent to two times the expected integrated luminosity of the HL-LHC. Investigation on the outgassing of cell materials and of the gas components used at the GIF++ are underway and strategies to mitigate the aging effects are also being developed. The effect of radiation on the performance of DT chamber and its impact on the overall muon reconstruction efficiency expected during the HL-LHC are presented.

The flavour-changing neutral current decays are interesting probes for new physics searches.The angular distributions of the B + → K * + µ + µ -decay is studied using a sample of proton-proton collisions at √ s = 8 TeV collected with the CMS detector at the LHC, corresponding to an integrated luminosity of 20.5 fb -1 .An angular analysis is performed to determine the longitudinal polarisation fraction and the muon forward-backward asymmetry, as functions of the dimuon invariant mass squared.All the measurements are consistent with the standard model predictions.In addition, the projections for the sensitivity of the measurement of the P 5 parameter in the B 0 → K * 0 µ + µ -angular analysis that is foreseen to be performed on the data that CMS will collect at the High-Luminosity LHC is reported.

The search and study of rare decays of B hadrons and of the lepton are among the most promising approaches of putting the Standard Model of particle physics to the test.In recent years, the study of these decays, and in particular of flavour-changing neutral current decays → ℓℓ, helped shed light on a set of tensions in the data with respect to theoretical predictions for branching ratios, angular distributions and lepton flavour universality.In this work, the most recent results in the study of rare heavy-flavour decays at the Large Hadron Collider experiments are presented.