MEG Upgrade Proposal

Abstract: We propose the continuation of the MEG experiment to search for the charged lepton flavour violating decay (cLFV) \mu \to e \gamma, based on an upgrade of the experiment, which aims for a sensitivity enhancement of one order of magnitude compared to the final MEG result, down to the $6 \times 10^{-14}$ level. The key features of this new MEG upgrade are an increased rate capability of all detectors to enable running at the intensity frontier and improved energy, angular and timing resolutions, for both the positron and photon arms of the detector. On the positron-side a new low-mass, single volume, high granularity tracker is envisaged, in combination with a new highly segmented, fast timing counter array, to track positron from a thinner stopping target. The photon-arm, with the largest liquid xenon (LXe) detector in the world, totalling 900 l, will also be improved by increasing the granularity at the incident face, by replacing the current photomultiplier tubes (PMTs) with a larger number of smaller photosensors and optimizing the photosensor layout also on the lateral faces. A new DAQ scheme involving the implementation of a new combined readout board capable of integrating the diverse functions of digitization, trigger capability and splitter functionality into one condensed unit, is also under development. We describe here the status of the MEG experiment, the scientific merits of the upgrade and the experimental methods we plan to use.

MEG Upgrade Proposal: A Comprehensive Evaluation

The paper "MEG Upgrade Proposal" presents a detailed plan for the improvement of the MEG experiment, which originally targets the search for the lepton flavor violating decay $\mu^+ \rightarrow e^+ \gamma$. The proposed upgrade is motivated by the desire to enhance the experimental sensitivity by a significant margin, thereby enabling the exploration of this rare decay with unprecedented precision.

Scientific Context and Motivation

The MEG experiment, housed at PSI, is central to the investigation of physics beyond the Standard Model (SM), particularly through the study of lepton flavor violation which the SM does not accommodate. The current limit set by MEG is $4.2 \times 10^{-13}$. The upgrade aims to delve further into potential new physics by reducing the statistical and systematic uncertainties that presently constrain the experiment.

Core Components of the Upgrade

The proposal methodically outlines key features of the upgrade, encompassing advancements in multiple areas:

1. Beam Line and Target: Improvements are planned for the muon target to optimize beam properties and reduce background noise. The document elaborates on how refinements in the beam steering and targeting systems can enhance muon yield while minimizing unwanted interactions.
2. Positron Tracker: An upgraded positron tracker is proposed to achieve better spatial resolution and timing precision. The integration of new tracking technologies will lead to superior rejection of background signals and increased efficiency in identifying signal events.
3. Photon Calorimeter: The photon detection capabilities are set to be improved with a revamped calorimeter design. Enhanced resolution and efficiency in detecting $\gamma$ photons are central to increasing the overall sensitivity of the MEG experiment.
4. Trigger and DAQ: The plan involves comprehensive updates to the Data Acquisition (DAQ) systems and trigger mechanisms. These updates are crucial for handling the increased data throughput and obtaining faster, more reliable event reconstruction.

Expected Outcomes and Implications

The final sensitivity goals aim for limits on $\mu^+ \rightarrow e^+ \gamma$ of approximately $6 \times 10^{-14}$, representing a nearly tenfold improvement. This leap in sensitivity could critically influence theoretical models, potentially constraining or ruling out various extensions to the SM.

The upgrade not only pushes forward the technical boundaries of particle physics experiments but also has broader implications for the field. By detecting rare decay processes with greater precision, the initiative helps refine our understanding of particle interactions at fundamental levels. Furthermore, a more stringent limit on lepton flavor violation would inform the design of subsequent experiments globally, aligning with research agendas focused on searching for new physics.

Budget and Timeline

The paper discusses budgetary allocations and outlines responsibilities among participating institutions. A detailed timeline is provided, projecting systematic improvements and adherence to a structured schedule to ensure timely completion.

Conclusion

Overall, the MEG upgrade proposal represents a significant advancement for the field, with the potential to contribute deep insights into lepton flavor violation and new physics. The methodological rigor and anticipated sensitivity enhancements foster optimism for future developments. Should unforeseen challenges arise, the project's robust framework provides confidence in mitigating risks without jeopardizing scientific objectives.