Mechanical Design of an Electromagnetic Calorimeter Prototype for a Future Muon Collider

Measurement of physics processes at new energy frontier experiments requires excellent spatial, time, and energy resolutions to resolve the structure of collimated high-energy jets. In a future Muon Collider, beam-induced backgrounds (BIB) represent the main challenge in the design of the detectors and of the event reconstruction algorithms. The technology and the design of the calorimeters should be chosen to reduce the effect of the BIB, while keeping good physics performance. Several requirements can be inferred: (i) high granularity to reduce the overlap of BIB particles in the same calorimeter cell; (ii) excellent timing (of the order of 100 ps) to reduce the out-of-time component of the BIB; (iii) longitudinal segmentation to distinguish the signal showers from the fake showers produced by the BIB. Moreover, the calorimeter should operate in a very harsh radiation environment, withstanding yearly a neutron flux of 1014 n1MeV/cm2 and a dose of 100 krad. Our proposal consists of a semi-homogeneous electromagnetic calorimeter based on Lead Fluoride Crystals (PbF2) readout by surface-mount UV-extended Silicon Photomultipliers (SiPMs): the Crilin calorimeter. In this paper, we report the mechanical design for the development of a small-scale prototype, consisting of 2 layers of 3 × 3 crystals

True muonium resonant production at e+e−e^+e^- colliders with standard crossing angle

True muonium ($\mu^+\mu^-$) is the heaviest and smallest bound state not involving quantum chromodynamics, after true tauonium ($\tau^+\tau^-$) and mu-tauonium ($\mu^\pm\tau^\mp$). Unlike atoms containing $\tau$ particles, the muon lifetime is long enough to allow observation of true muonium (TM) decays and transitions. One of the proposed methods to observe the spin 1 fundamental state of TM, which has the smallest lifetime among TM spin 1 states, was to build an $e^+e^-$ collider with a large crossing angle ($\theta \sim 30^\circ$) in order to provide TM with a large boost and detect its decay vertex in $e^+ e^-$. The following paper will instead show that TM excited states ($n\geq2$) can be observed in relatively large quantities ($\mathcal{O}$(10)/month) at a feasible $e^+e^-$ collider with standard crossing angles, after setting their center-of-mass energy to the TM mass ($\sim2m_{\mu}=211.4$ MeV)

True muonium resonant production at e + e − colliders with standard crossing angle

True muonium (TM) (mu (+) mu (-)) is the heaviest and smallest bound state not containing hadrons, after TM (tau (+ )tau( -)) and mu-tauonium (mu( +/-) tau (sic)). One of the proposed methods to observe the spin 1 fundamental state of TM, which has the smallest lifetime among TM spin 1 states, was to build an e (+) e( -) collider with a large crossing angle (theta similar to 30(degrees)) in order to provide TM with a large boost and detect its decay vertex in e + e -. The following paper will instead show that TM excited states can be observed in relatively large quantities ( O (10)/month) at a e (+) e (-) collider with standard crossing angle, after setting their center-of-mass energy to the TM mass (similar to 2m mu = 211.4 MeV)

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

The Mu2e Crystal Calorimeter: An Overview

The Mu2e experiment at Fermilab will search for the standard model-forbidden, charged lepton flavour-violating conversion of a negative muon into an electron in the field of an aluminium nucleus. The distinctive signal signature is represented by a mono-energetic electron with an energy near the muon's rest mass. The experiment aims to improve the current single-event sensitivity by four orders of magnitude by means of a high-intensity pulsed muon beam and a high-precision tracking system. The electromagnetic calorimeter complements the tracker by providing high rejection power in muon to electron identification and a seed for track reconstruction while working in vacuum in presence of a 1 T axial magnetic field and in a harsh radiation environment. For 100 MeV electrons, the calorimeter should achieve: (a) a time resolution better than 0.5 ns, (b) an energy resolution <10%, and (c) a position resolution of 1 cm. The calorimeter design consists of two disks, each loaded with 674 undoped CsI crystals read out by two large-area arrays of UV-extended SiPMs and custom analogue and digital electronics. We describe here the status of construction for all calorimeter components and the performance measurements conducted on the large-sized prototype with electron beams and minimum ionizing particles at a cosmic ray test stand. A discussion of the calorimeter's engineering aspects and the on-going assembly is also reported

Mu2e Crystal Calorimeter Readout Electronics: Design and Characterisation

The Mu2e experiment at Fermi National Accelerator Laboratory will search for the charged-lepton flavour-violating neutrinoless conversion of negative muons into electrons in the Coulomb field of an Al nucleus. The conversion electron with a monoenergetic 104.967 MeV signature will be identified by a complementary measurement carried out by a high-resolution tracker and an electromagnetic calorimeter, improving by four orders of magnitude the current single-event sensitivity. The calorimeter—composed of 1348 pure CsI crystals arranged in two annular disks—has a high granularity, 10% energy resolution and 500 ps timing resolution for 100 MeV electrons. The readout, based on large-area UV-extended SiPMs, features a fully custom readout chain, from the analogue front-end electronics to the digitisation boards. The readout electronics design was validated for operation in vacuum and under magnetic fields. An extensive radiation hardness certification campaign certified the FEE design for doses up to 100 krad and 1012 n1MeVeq/cm2 and for single-event effects. A final vertical slice test on the final readout chain was carried out with cosmic rays on a large-scale calorimeter prototype

Development, construction and qualification tests of the mechanical structures of the electromagnetic calorimeter of the Mu2e experiment at Fermilab

The "muon-to-electron conversion" (Mu2e) experiment at Fermilab will search for the charged lepton flavour violating neutrino-less coherent conversion of a muon into an electron in the field of an aluminum nucleus. The electromagnetic calorimeter is one of the three Mu2e detectors. The hostile Mu2e operational conditions, in terms of radiation levels (total ionizing dose of QR krad and a neutron fluence of 5x10-10 n/cm2 @ Q MeVeq (Si)/y), magnetic field intensity (1 T) and vacuum level (10−4 Torr) have posed tight constraints on the design of the detector mechanical structures and materials choice. In this report the mechanical overall description of the calorimeter is presented, such as the qualification tests performed during the construction of its components and the realized technological choices

Towards a muon collider

A muon collider would enable the big jump ahead in energy reach that is needed for a fruitful exploration of fundamental interactions. The challenges of producing muon collisions at high luminosity and 10 TeV centre of mass energy are being investigated by the recently-formed International Muon Collider Collaboration. This Review summarises the status and the recent advances on muon colliders design, physics and detector studies. The aim is to provide a global perspective of the field and to outline directions for future work

Towards a Muon Collider

A muon collider would enable the big jump ahead in energy reach that is needed for a fruitful exploration of fundamental interactions. The challenges of producing muon collisions at high luminosity and 10 TeV centre of mass energy are being investigated by the recently-formed International Muon Collider Collaboration. This Review summarises the status and the recent advances on muon colliders design, physics and detector studies. The aim is to provide a global perspective of the field and to outline directions for future work.Comment: 118 pages, 103 figure