Study of Requirements and performances of the electromagnetic calorimeter for the Mu2e experiment at FermiLab

The aim of the Mu2e experiment is to measure the ratio between the rate of the neutrinoless, coherent conversion of muons into electrons in the field of a nucleus, and the rate of ordinary muon capture on the nucleus: Rμe = μ− +A(Z,N)→e− +A(Z,N) . (1) μ− +A(Z,N)→νμ +A(Z−1,N) The muon conversion represents a powerful process to search for charged lepton flavor violation (CLFV). Thus far no CLFV interaction has been observed expe- rimentally; the current best experimental limit on muon-to-electron conversion is from the SINDRUM II experiment, using a gold target: Rμe < 6.1 × 10−13 @ 90% C.L. . Mu2e Experiment will collect ∼ 5.76 × 10−17 stopped muons in three years of runs so to reach a sensitivity of ∼ 10−17 (four order of magnitude better than SINDRUM II). The experiment set-up consists of three main magnets: 1) a Pro- duction Solenoid, where a 8 GeV proton beam impact on a Tungstate target to produce π−, 2) a Transport Solenoid, where the μ−’s, resulting from the π− decays,  are filtered, 3) a Detector Solenoid (DS), where μ−’s are stopped in an Al targets. Possible electrons resulting from a muon conversion are identified by two different detectors operating inside the DS field. The detectors are: a Straw Tubes Tracker, measuring the electron momentum, and a LYSO Crystal Calorimeter, expected to measure its energy. If an orbiting μ− converts, a 105 MeV electron is produced: therefore the conversion signature is an isolated electron with the energy of a muon. For this reason the tracker is required to have high momentum resolution (≈ 150 keV). The calorimeter is needed to help the rejection of different backgrounds and also to check the reliability of the electron track reconstruction. For these puposes the calorimeter must have an excellent energy resolution at 100 MeV (less than 3%), a good spatial resolution on the track impact point (≈ 1 cm), and 1 nsec time resolution. This thesis is devoted to verify that the proposed crystal calorimeter is capable to fulfill all these requirements. This check is done by means of Monte Carlo si- mulations within the Mu2e framework and using recent experimental results from studies on the LYSO crystals. Finally a calculation of the Mu2e sensitivity is also shown for a “calorimeter stand alone” configuration, i.e. without any information from the tracker

Crilin: A Semi-Homogeneous Calorimeter for a Future Muon Collider

Calorimeters, as other detectors, have to face the increasing performance demands of the new energy frontier experiments. For a future Muon Collider the main challenge is given by the Beam Induced Background that may pose limitations to the physics performance. However, it is possible to reduce the BIB impact by exploiting some of its characteristics by ensuring high granularity, excellent timing, longitudinal segmentation and good energy resolution. The proposed design, the Crilin calorimeter, is an alternative semi-homogeneous ECAL barrel for the Muon Collider based on Lead Fluoride Crystals (PbF2) with a surface-mount UV-extended Silicon Photomultipliers (SiPMs) readout with an optimized design for a future Muon Collider

Progress status for the Mu2e calorimeter system

The Mu2e experiment at FNAL aims to measure the charged-lepton flavor violating neutrinoless conversion of a negative muon into an electron. The conversion results in a monochromatic electron with an energy slightly below the muon rest mass (104.97 MeV). The calorimeter should confirm that the candidates reconstructed by the extremely precise tracker system are indeed conversion electrons while performing a powerful μ/e particle identification. Moreover, it should also provide a high level trigger for the experiment independently from the tracker system. The calorimeter should also be able to keep functionality in an environment where the background delivers a dose of ~ 10 krad/year in the hottest area and to work in the presence of 1 T axial magnetic field. These requirements translate in the design of a calorimeter with large acceptance, good energy resolution O(5%) and a reasonable position (time) resolution of ~ < 1 cm (<0.5ns). The baseline version of the calorimeter is composed by two disks of inner (outer) radius of 351 (660) mm filled by 1860 hexagonal BaF2 crystals of 20 cm length. Each crystal is readout by two large area APD's. In this paper, we summarize the experimental tests done so far as well as the simulation studies in the Mu2e environment

Applications and Techniques for Fast Machine Learning in Science

In this community review report, we discuss applications and techniques for fast machine learning (ML) in science - the concept of integrating powerful ML methods into the real-time experimental data processing loop to accelerate scientific discovery. The material for the report builds on two workshops held by the Fast ML for Science community and covers three main areas: applications for fast ML across a number of scientific domains; techniques for training and implementing performant and resource-efficient ML algorithms; and computing architectures, platforms, and technologies for deploying these algorithms. We also present overlapping challenges across the multiple scientific domains where common solutions can be found. This community report is intended to give plenty of examples and inspiration for scientific discovery through integrated and accelerated ML solutions. This is followed by a high-level overview and organization of technical advances, including an abundance of pointers to source material, which can enable these breakthroughs

Lepton Flavor Universality measurements

We present the current status of the measurements performed by ATLAS and CMS related to the Lepton Flavor Universality tests

The Mu2e crystal calorimeter and improvements in the µN->eN search sensitivity

The Mu2e experiment will search for Charged Lepton Flavor Violation (CLFV) looking at the conversion of a muon into an electron in the field of an aluminum nucleus. About 7 · 10^17 muons, provided by a dedicated muon beam line in con- struction at the Fermi National Accelarator Laboratory (Fermilab), will be stopped in 3 years in the Aluminum target. The corresponding single event sensitivity will be 2.5 · 10^−17[1]. The Standard Model of particle physics, even extendend to include the finite neu- trino masses, predicts the ratio Rμe between muon conversions and muon nuclear captures to be ∼ 10^−52 [2]. Several extensions of the Standard Model predict Rμe to be in the range of 10^−14 − 10^−18 [3]. The current best experimental limit, set by the SINDRUM II experiment is 7 · 10^−13 @ 90% CL [4]. The Mu2e experiment plans to improve this experimental limit by four order of magnitude to test many of the possible extensions of the Standard Model. To reach this ambitious goal, the Mu2e experiment is expected to use an intense pulsed muon beam, and rely on a detector system composed of a straw tube tracker and a calorimeter made of pure CsI crystals. The calorimeter plays a central role in the Mu2e measurement, providing particle identification capabilities that are necessary for rejecting two of the most dan- gerous background sources that can mimic the μN → eN conversion electron: cosmic muons and p ̄ induced background. The calorimeter information allows also to improve the tracking performance. Thanks to a calorimeter-seeded track finder algorithm, it is possible to increase the track reconstruction efficiency, and make it more robust with respect to the occupancy level. Expected performances of the calorimeter have been studied in a beam test at the Beam Test Facility in Frascati (Rome, Italy). A reduced scale calorimeter prototype has been exposed to an electron beam, with energy varying from 80 to 140 MeV, for measuring the timing resolution and validate the Monte Carlo prediction. A timing resolution σt < 200 ps @ 100 MeV has been obtained. Combination of the background rejection performance, and the improvements in the track reconstruction, have then been combined in the calculation of the expected Mu2e sensitivity

Search for rare and LFV decays of the Higgs boson with the ATLAS detector

The Standard Model predicts several rare Higgs boson decay channels, among which are the decays to a Z boson and a photon, to a low-mass lepton pair and a photon, and to a meson and photon. The observation of some of these decays could open the possibility of studying the CP and coupling properties of the Higgs boson in a complementary way to other analyses. In addition, lepton-flavour-violating decays of the observed Higgs boson are searched for, where on observation would be a clear sign of physics effects beyond the Standard Model. Several results for decays based on pp collision data collected at 13 TeV will be presented

Searches for CLFV at ATLAS and CMS

Searches for charged lepton flavor violation in ATLAS and CM

Introduction to Charged Lepton Flavour Violation

Neutrino masses are evidence of lepton flavour violation, but no violation in the interactions among the charged leptons has been observed yet. Many models of Physics Beyond the Standard Model (BSM) predict Charged Lepton Flavour Violation (CLFV) in a wide spectrum of processes with rates in reach of upcoming experiments. The experimental searches that provide the current best limits on the CLFV searches are reviewed, with a particular emphasis on the muon-based experiments that give the most stringent constraints on BSM parameter space. The next generation of muon-based experiments (MEG-II, Mu2e, COMET, Mu3e) aim to reach improvements by many orders of magnitude w.r.t. the current best limits, thanks to several technological advancements. We review popular heavy BSM theories, and we present state-of-the-art calculations of the predicted CLFV branching ratios, focusing on the more sensitive $\mu\to e$ sector