Lepton Flavour Violation effects are predicted in several extensions of the Standard Model at a measurable level. Since the Standard Model background, even including ν oscillations and mixing, is ...completely negligible, the observation of such effects would be a strong evidence for New Physics beyond the Standard Model, while a non observation with high precision experiments would put severe constraints on possible Standard Model extensions. In this talk I review the present status and the future perspectives of the Lepton Flavour Violation experiments involving µ's and discuss the sensitivity improvements which could be obtained from new high intensity machines coupled with high resolution detectors.
The cylindrical drift chamber is the most innovative part of the MEG II detector, the upgraded version of the MEG experiment. The MEG II chamber differs from the MEG one because it is a single volume ...cylindrical structure, instead of a segmented one, chosen to improve its resolutions and efficiency in detecting low energy positrons from muon decays at rest. In this paper, we show the characteristics and performances of this fundamental part of the MEG II apparatus and we discuss the impact of its higher resolution and efficiency on the sensitivity of the MEG II experiment. Because of its innovative structure and high quality resolution and efficiency the MEG II cylindrical drift chamber will be a cornerstone in the development of an ideal tracking detector for future positron-electron collider machines.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
3.
The Cylindrical Drift Chamber of the MEG II experiment Chiappini, M.; Baldini, A.M.; Benmansour, H. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
02/2023, Letnik:
1047
Journal Article
Recenzirano
The MEG experiment at the Paul Scherrer Institut (PSI) represents the state of the art in the search for the charged Lepton Flavor Violating μ+→e+γ decay, setting the most stringent upper limit on ...the BR (μ+→e+γ)≤4.2×10−13 (90% C.L.). An upgrade of MEG, MEG II, was designed, commissioned and recently started the physics data taking. Its goal is to reach a sensitivity level of 6×10−14. In order to reconstruct the positron momentum vector a Cylindrical Drift CHamber (CDCH) with unprecedented peculiarities was built, featuring angular and momentum resolutions at the 6.5 mrad and 100 keV/c level. The CDCH is a 2-meter long, 60 cm in diameter, low-mass, single volume detector with high granularity: 9 layers of 192 drift cells, few mm wide, defined by ∼12000 wires in a stereo configuration for longitudinal hit localization. The filling gas mixture is Helium:Isobutane 90:10. The total radiation length is 1.5×10−3 X0, thus minimizing the Multiple Coulomb Scattering and allowing for a single-hit resolution <120μm. After the assembly at INFN Pisa, the CDCH was transported to PSI and integrated into the MEG II experimental apparatus since 2018. The commissioning phase lasted for the past three years until the operational stability was reached in 2020. The analysis software is continuously developing and the tuning of the reconstruction algorithms is one of the main activities. The latest updates on the positron momentum vector resolutions and tracking efficiency are presented.
Abstract
Ultra-thin metallic anode and cathode wires are frequently
employed in low-mass gaseous detectors for precision experiments,
where the amount of material crossed by charged particles must be
...minimised. We present here the results of an analysis of the
mechanical stress and chemical corrosion effects observed in 40
and 50 μm diameter silver plated aluminum wires
mounted within the volume of the MEG II drift chamber, which caused
the breakage of about one hundred wires (over a total of
≈ 12000). This analysis is based on the careful inspection
of the broken wires by means of optical and electronic microscopes
and on a detailed recording of all breaking incidents. We present a
simple empirical model which relates the number of broken wires to
their exposure time to atmospheric relative humidity and to their
mechanical tension, which is necessary for mechanical stability in
the presence of electrostatic fields of several kV/cm. Finally we
discuss how wire breakages can be avoided or at least strongly
reduced by operating in controlled atmosphere during the mounting
stages of the wires within the drift chamber and by choosing a
25 % thicker wire diameter, which has very small effects on the
detector resolution and efficiency and can be obtained by using a
safer fabrication technique.
Commissioning and preliminary performance of the MEG II drift chamber Chiappini, M.; Chiarello, G.; Baldini, A.M. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
10/2022, Letnik:
1041
Journal Article
Recenzirano
In the quest for Lepton Flavor Violation (LFV) the MEG experiment at the Paul Scherrer Institut (PSI) represents the state of the art in the search for the charged LFV decay μ+→e+γ, setting the most ...stringent upper limit on the BR(μ+→e+γ)≤4.2×10−13 (90% C.L.). An upgrade of MEG, MEG II, was designed and it recently started the physics data taking, with the aim to reach a sensitivity level of 6×10−14. The Cylindrical Drift CHamber (CDCH) is a key detector in order to improve the e+ angular and momentum resolutions at the 6.5 mrad and 100 keV/c level. The CDCH is a low-mass single volume detector with high granularity: 9 layers of 192 drift cells each, few mm wide, defined by 12000 wires in a stereo configuration for longitudinal hit localization. After the assembly, the CDCH was transported to PSI for the commissioning phase and it has been integrated into the MEG II experimental apparatus since 2018. The operational stability was reached in 2020 and the complete readout electronics was tested for the first time in 2021. A preliminary analysis of 2020–2021 data is presented.
Lepton Flavour Violation in the charged lepton sector (CLFV) is forbidden in the Minimal Standard model and strongly suppressed in extensions of the model to include finite neutrino mixing. On the ...other hand, a wide class of Supersymmetric theories, even coupled with Grand Unification models (SUSY-GUT models), predict CLFV processes at a rate within the reach of new experimental searches operated with high resolution detectors at high intensity accelerators. As the Standard model background is negligible, the observation of one or more CLFV events would provide incontrovertible evidence for physics beyond Standard model, while a null effect would severely constrain the set of theory parameters. Therefore, a big experimental effort is currently (and will be for incoming years) accomplished to achieve unprecedented sensitivity on several CLFV processes. In this paper we review past and recent results in this research field, with focus on CLFV channels involving muons and tau's. We present currently operating experiments as well as future projects, with emphasis laid on how sensitivity enhancements are accompanied by improvements on detection techniques. Limitations due to systematic effects are also discussed in detail together with the solutions being adopted to overcome them.
The ultra light Drift Chamber of the MEG II experiment Baldini, A.M.; Cavoto, G.; Cei, F. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
04/2020, Letnik:
958
Journal Article
Recenzirano
Odprti dostop
The MEG experiment at the Paul Scherrer Institute searches for the charged Lepton Flavor Violating μ+→e+γ decay. MEG has already determined in a first data taking phase the world best upper limit on ...the branching ratio: BR(μ+→e+γ)<4.2×10−13 An upgrade of the whole detector has been approved to obtain a substantial increase in sensitivity. Currently MEG is in upgrade phases, this phase involves all the detectors. The new positron tracker is a high transparency single volume, fully stereo cylindrical Drift Chamber (CDCH), immersed in a non uniform longitudinal B-field, with length of 1.93 m, internal radius of 17 cm and external radius of 30 cm. It is composed of 9 concentric layers, divided into 12 identical sector of 16 drift cells. The single drift cell is approximately square, with a 20 μm gold plated W sense wire surrounded by 40 μm silver plated Al field wires in a ratio of 5:1. The total number of wires amounts to 11904 for an equivalent radiation length per track turn of about 1.5x10−3 X0 when the chamber is filled with a gas mixture of helium and iso-butane. Due to the high wire density (12wires∕cm2), the use of the classical feed-through technique as wire anchoring system could hardly be implemented and therefore it was necessary to develop new wiring strategies. The number of wires and the stringent requirements impose the use of an automatic system (wiring robot) to operate the wiring procedures. Several tests have been performed in different prototypes of the drift chamber, exposed to cosmic rays, test beams and radioactive sources, to fulfill the requirement on the spatial resolution to be less than 110 μm. In this paper we describe the CDCH construction and the first tests during the 2018 Engineering Run.
We present a field-programmable gate array (FPGA)-based technique for the on-line identification of highly ionizing particles in a liquid xenon (LXe) detector. The method was developed and ...successfully exploited to select <inline-formula> <tex-math notation="LaTeX">\alpha </tex-math></inline-formula> particles emitted by 241 Am sources submerged in LXe in an overwhelming, mostly beam-related, <inline-formula> <tex-math notation="LaTeX">\gamma </tex-math></inline-formula>-ray background. After revising the main features of xenon and other liquid noble gases as ultra-violet (UV) scintillating media, we describe the algorithm idea and its firmware implementation. We then present the results in terms of efficiency and background suppression for the real-time <inline-formula> <tex-math notation="LaTeX">\alpha </tex-math></inline-formula>-particle tagging and the limits of the MEG trigger configuration. Finally, we show that in MEG II we are going to overcome the main issues and further improve the performances.
The new drift chamber of the MEG II experiment Chiappini, M.; Baldini, A.M.; Cavoto, G. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
08/2019, Letnik:
936
Journal Article
Recenzirano
Odprti dostop
This article presents the MEG II Cylindrical Drift CHamber (CDCH), a key detector for the phase 2 of MEG, which aims at reaching a sensitivity level of the order of 6×10−14 for the charged Lepton ...Flavour Violating μ+→e+γ decay (Calibbi and Signorelli, 2018; Cei and Nicolò, 2014). CDCH is designed to overcome the limitations of the MEG e+ tracker (Baldini et al., 2013) and guarantee the proper operation at high rates with long-term detector stability. CDCH is a low-mass unique volume detector with high granularity: 9 layers of 192 drift cells, few mm wide, defined by ≈12000 wires in a stereo configuration for longitudinal hit localization. The total radiation length is 1.5×10−3X0, thus minimizing the Multiple Coulomb Scattering (MCS) contribution and allowing for a single-hit resolution of 110μm (Baldini et al., 2016) and a momentum resolution of 130 keV/c. CDCH integration into the MEG II experimental apparatus (Baldini et al., 2018) will start in this year.
•The new Cylindrical Drift CHamber (CDCH) is a key detector for the phase 2 of MEG.•CDCH has a single cylindrical volume filled with a low-mass He:Isobutane gas mixture.•High granularity is ensured by 1728 drift cells (few mm wide) divided in 9 layers.•Material budget minimized to 1.5×10−3X0 per track turn to reduce MCS.•CDCH is in the final mechanical and HV test phase before the shipping to PSI.
Low latency serial communication for MEG II trigger system Francesconi, M.; Baldini, A.M.; Cei, F. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
08/2019, Letnik:
936
Journal Article
Recenzirano
In the framework of the upgrade of the MEG experiment a new trigger system with demanding performances in terms of latency was designed. To achieve the goal of 512 ns latency the serial connections ...between trigger boards have been optimized so that they only rely on serial to parallel shift registers for the data flow, minimizing the amount of logic to be crossed by data. A dedicated Finite State Machine (FSM) was designed to select the sampling point of the serial stream with respect to an external precision clock used by both transmitter and receiver. As a proof of concept a 16000 channel weighted waveform sum including pedestal suppression, was computed, resulting in 700 ns of latency.
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