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.
The MEG II experiment, based at the Paul Scherrer Institut in Switzerland, reports the result of a search for the decay
μ
+
→
e
+
γ
from data taken in the first physics run in 2021. No excess of ...events over the expected background is observed, yielding an upper limit on the branching ratio of
B
(
μ
+
→
e
+
γ
)
<
7.5
×
10
-
13
(90% CL). The combination of this result and the limit obtained by MEG gives
B
(
μ
+
→
e
+
γ
)
<
3.1
×
10
-
13
(90% CL), which is the most stringent limit to date. A ten-fold larger sample of data is being collected during the years 2022–2023, and data-taking will continue in the coming years.
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, Volume:
1047
Journal Article
Peer reviewed
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.
Operation and performance of the MEG II detector Afanaciev, K.; Baldini, A. M.; Ban, S. ...
The European physical journal. C, Particles and fields,
02/2024, Volume:
84, Issue:
2
Journal Article
Peer reviewed
Open access
The MEG II experiment, located at the Paul Scherrer Institut (PSI) in Switzerland, is the successor to the MEG experiment, which completed data taking in 2013. MEG II started fully operational data ...taking in 2021, with the goal of improving the sensitivity of the
μ
+
→
e
+
γ
decay down to
∼
6
×
10
-
14
almost an order of magnitude better than the current limit. In this paper, we describe the operation and performance of the experiment and give a new estimate of its sensitivity versus data acquisition time.
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, Volume:
1041
Journal Article
Peer reviewed
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.
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, Volume:
958
Journal Article
Peer reviewed
Open access
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.
The cross section of the process e + e − → π + π − has been measured in the center-of-mass energy range from 0.32 to 1.2 GeV with the CMD-3 detector at the electron-positron collider VEPP-2000. The ...measurement is based on an integrated luminosity of about 88 pb − 1 , of which 62 pb − 1 represent a complete dataset collected by CMD-3 at center-of-mass energies below 1 GeV. In the dominant region near the ρ resonance a systematic uncertainty of 0.7% was achieved. The implications of the presented results for the evaluation of the hadronic contribution to the anomalous magnetic moment of the muon are discussed. Published by the American Physical Society 2024
The Mu2e experiment at Fermilab searches for the charged-lepton flavor violating (CLFV) conversion of a negative muon into an electron in the field of an aluminum nucleus, with a distinctive ...signature of a monoenergetic electron of energy slightly below the muon rest mass (104.967 MeV). The Mu2e goal is to improve by four orders of magnitude the search sensitivity with respect to the previous experiments. Any observation of a CLFV signal will be a clear indication of new physics. The Mu2e detector is composed of a tracker, an electromagnetic calorimeter, and an external veto for cosmic rays surrounding the solenoid. The calorimeter plays an important role in providing particle identification capabilities, a fast online trigger filter, a seed for track reconstruction while working in vacuum, in the presence of 1-T axial magnetic field and in a harsh radiation environment. The calorimeter requirements are to provide a large acceptance for 100-MeV electrons and reach at these energies: 1) a time resolution better than 0.5 ns; 2) an energy resolution <10%; and 3) a position resolution of 1 cm. The calorimeter design consists of two disks, each one made of 674-undoped cesium iodine crystals read by two large area arrays of UV-extended silicon photomultipliers (SiPMs). We report here the construction and the test of the Module-0 prototype. The Module-0 has been exposed to an electron beam in the energy range around 100 MeV at the Beam Test Facility in Frascati. Preliminary results of timing and energy resolution at normal incidence are shown. A discussion of the technical aspects of the calorimeter engineering is also reported in this paper.
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, Volume:
936
Journal Article
Peer reviewed
Open access
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.
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