Development of ultra-low mass and high-rate capable RPC based on Diamond-Like Carbon electrodes for MEG II experiment

A new type of resistive plate chamber with thin-film electrodes based on diamond-like carbon is under development for background identification in the MEG II experiment. Installed in a low-momentum and high-intensity muon beam, the detector is required to have extremely low mass and a high rate capability. A single-layer prototype detector with 2 cm $\times$ 2 cm size was constructed and evaluated to have a high rate capability of 1 MHz/cm$^2$ low-momentum muons. For a higher rate capability and scalability of the detector size, the electrodes to supply high voltage was segmented by implementing a conductive pattern on diamond-like carbon. Using the new electrodes, a four-layer prototype detector was constructed and evaluated to have a 46% detection efficiency with only a single layer active at a rate of $\cal O$(10 kHz). The result is promising to achieve the required detection efficiency of 90% at a rate of 4 MHz/cm$^2$ with all the layers active.Comment: 5 pages, 8 figures. Contribution to XVI Workshop on Resistive Plate Chambers and Related Detectors (RPC2022), September 26-30 2022. Submitted to Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipmen

Prototype study of 0.1% X00.1\%\,X_0 and MHz/cm2\mathrm{MHz/cm^2} tolerant Resistive Plate Chamber with Diamond-Like Carbon electrodes

A novel Resistive Plate Chamber (RPC) was designed with Diamond-Like Carbon (DLC) electrodes and performance studies were carried out for 384$\,\mathrm{\mu m}$ gap configuration with a $2\,\mathrm{cm}\times2\,\mathrm{cm}$ prototype. The use of thin films coated with DLC enables an ultra-low mass design of $< 0.1\%\,X_0$ with up to a four-layer configuration. At the same time, 42% MIP efficiency, and 180 ps timing resolution per layer were achieved in a measurement performed under a $1\,\mathrm{MHz/cm^2}$ non-MIP charged particle beam. In addition, we propose a further improved design for a $20\,\mathrm{cm}$-scale detector that can achieve 90% four-layer efficiency in an even higher $4\,\mathrm{MHz/cm^2}$ beam. In this paper, we describe the detector design, present the results of performance measurements, and characterize the rate capability of the DLC-based RPCs with a performance projection for an improved design.Comment: 8 page

Towards a New μ→eγ Search with the MEG II Experiment: From Design to Commissioning

The MEG experiment represents the state of the art in the search for the Charged Lepton Flavour Violating µ+ → e+γ decay. With its first phase of operations at the Paul Scherrer Institut (PSI), MEG set the most stringent upper limit on the BR(µ+ → e+γ) ≤ 4.2 × 10−13 at 90% confidence level, imposing one of the tightest constraints on models predicting LFV-enhancements through new physics beyond the Standard Model. An upgrade of the MEG experiment, MEG II, was designed and it is presently in the commissioning phase, aiming at a sensitivity level of 6 × 10−14 . The MEG II experiment relies on a series of upgrades, which include an improvement of the photon detector resolutions, brand new detectors on the positron side with better acceptance, efficiency and performances and new and optimized trigger and DAQ electronics to exploit a muon beam intensity twice as high as that of MEG (7 × 107 µ+/s). This paper presents a complete overview of the MEG II experimental apparatus and the current status of the detector commissioning in view of the physics data taking in the upcoming three years

The trigger system for the MEG II experiment

Intending to improve the current sensitivity on decay by one order of magnitude, the MEG II experiment at Paul Scherrer Institute completed the integration phase in 2021 with all detectors successfully operated throughout the subsequent beamtime. Earlier in 2021, the WaveDAQ integrated Trigger and Data Acquisition (TDAQ) system, developed for the readout of the experiment, was completely commissioned. Receiving almost 9000 channels from the detectors, the MEG II TDAQ system is the largest WaveDAQ deployment so far, proving the scalability of the overall design, from bench-top setup through various smaller-size experiments. We will describe how MEG II trigger system reduces the muon decays at the experiment target down to a 10 Hz event rate by exploiting the signal event characteristics at the online level. The trigger system performs the calorimetric reconstruction of the photon shower and then compares the timing and direction with positron candidates within a 600 ns hard latency time. The first release of the online reconstruction, deployed in 2021, achieved a photon energy resolution at the signal energy of and a coincidence time resolution among the child particles

The trigger system for the MEG II experiment

Intending to improve the current sensitivity on mu -&gt; e gamma decay by one order of magnitude, the MEG II experiment at Paul Scherrer Institute completed the integration phase in 2021 with all detectors successfully operated throughout the subsequent beamtime. Earlier in 2021, the WaveDAQ integrated Trigger and Data Acquisition (TDAQ) system, developed for the readout of the experiment, was completely commissioned. Receiving almost 9000 channels from the detectors, the MEG II TDAQ system is the largest WaveDAQ deployment so far, proving the scalability of the overall design, from bench-top setup through various smaller-size experiments. We will describe how MEG II trigger system reduces the similar to 10(7) muon decays at the experiment target down to a 10 Hz event rate by exploiting the signal event characteristics at the online level. The trigger system performs the calorimetric reconstruction of the photon shower and then compares the timing and direction with positron candidates within a 600 ns hard latency time. The first release of the online reconstruction, deployed in 2021, achieved a 2.4 % photon energy resolution at the signal energy of 52.8 MeV and a similar to 2 ns coincidence time resolution among the child particles

The search for \ub5+ \u2192 e+\u3b3 with 10 1214 sensitivity: The upgrade of the meg experiment

The MEG experiment took data at the Paul Scherrer Institute in the years 2009\u20132013 to test the violation of the lepton flavor conservation law, which originates from an accidental symmetry that the Standard Model of elementary particle physics has, and published the most stringent limit on the charged lepton flavor violating decay \ub5+ \u2192 e+\u3b3: BR(\ub5+ \u2192 e+\u3b3) &lt; 4.2 7 10 1213 at 90% confidence level. The MEG detector has been upgraded in order to reach a sensitivity of 6 7 10 1214 . The basic principle of MEG II is to achieve the highest possible sensitivity using the full muon beam intensity at the Paul Scherrer Institute (7 7 107 muons/s) with an upgraded detector. The main improvements are better rate capability of all sub-detectors and improved resolutions while keeping the same detector concept. In this paper, we present the current status of the preparation, integration and commissioning of the MEG II detector in the recent engineering runs