Liquid Xenon Calorimeter Research Articles

A liquid hydrogen target to fully characterize the new MEG II liquid xenon calorimeter

The MEG II experiment aims to improve the sensitivity to μ+→e+γ down to 6×10−14, surpassing the 4.2×10−13 UL by MEG. To achieve this sensitivity the detector performances need to be assessed and monitored via dedicated calibrations. To calibrate the Liquid Xenon Calorimeter near the signal energy (52.8 MeV), photons are produced through the Charge EXchange (CEX) process π−p→nπ0(→γγ). Here we present the liquid Hydrogen target used for the CEX run 2021, during the first MEG II physics run.

Novel X-ray scanning technique for in-situ alignment of photo-detectors in the MEGII calorimeter

We describe and show results of a novel technique to measure with high precision the positions of photodetectors installed in the upgraded liquid xenon calorimeter of the MEG II experiment. The measurement was done by detecting the signal in individual photo-detectors as the front surface of the calorimeter was scanned in axial (Z) and azimuthal (ϕ) directions with a precisely controlled, thin, collimated beam of X-rays obtained from a 57Co X-ray source. The measurements were made when the calorimeter was cold and operational, under which conditions they could not otherwise be made. This technique is used to check for changes in the photodetector positions due to the effects of cooling and thermal cycling of the support structure and to provide a reference between the positions of the operational photodetectors and alignment markers on the cryostat exterior. The use of an essentially monochromatic X-ray source allowed ancillary measurements of photodetector properties, including pulse shape, relative gain, and variation in response over the photodetector surface. Measurement uncertainties below 0.6 mm in Z and 0.7 mrad in ϕ have been achieved, well within the requirements for the MEG II performance.

Charged particle identification with the liquid xenon calorimeter of the CMD-3 detector

The paper describes a method of the charged particle identification, developed for the CMD-3 detector, installed at the VEPP-2000 e+e− collider. The method is based on application of boosted decision trees classifiers, trained for the optimal separation of electrons, muons, pions and kaons in the momentum range from 100 to 1200MeV/c. The input variables for the classifiers are linear combinations of the energy depositions of charged particles in 12 layers of the liquid xenon calorimeter of the CMD-3. The event samples for training of the classifiers are taken from the simulation. Various issues of the calorimeter strip channels response simulation and their calibration are considered. Application of the method is illustrated by the examples of separation of the e+e−(γ) and π+π−(γ) final states and of selection of the K+K− final state at high energies.

Measurement of the Cross Section for the Process $$\boldsymbol{e^{+}e^{-}\to K^{+}K^{-}}$$ with the CMD-3 Detector

Preliminary results of measurement of the cross section for the process $$e^{+}e^{-}\to K^{+}K^{-}$$ in the range of c.m. energies between 1.075 and 1.975 GeV are presented. An analysis was performed on the basis of an integrated luminosity of 62.9 pb $${}^{-1}$$ accumulated by employing the CMD-3 detector within the experimental runs of 2019. The suppression of the background from the processes $$e^{+}e^{-}\to e^{+}e^{-}(\gamma)$$ , $$\mu^{+}\mu^{-}(\gamma)$$ , and $$\pi^{+}\pi^{-}(\gamma)$$ and the background of cosmic-ray muons was accomplished with the aid of information about specific energy losses of charged particles in the layers of the liquid xenon calorimeter of the CMD-3 detector. The preliminary results of the present measurement of the $$e^{+}e^{-}\to K^{+}K^{-}$$ cross section are in reasonable agreement with the results of earlier measurements and have a commensurate statistical precision.

Charged particle identification using the liquid Xenon calorimeter of the CMD-3 detector

Abstract This paper describes a currently being developed procedure of the charged particle identification for CMD-3 detector, installed at the VEPP-2000 collider. The procedure is based on the application of the boosted decision trees classification method, and uses as input variables the specific energy losses of charged particles in the 14 layers of the liquid Xenon calorimeter. The performance of the procedure is demonstrated by an example of the extraction of events of e + e − → K + K − ( γ ) process in the center of mass energy range from 1.28 to 1.65 GeV.

MEG II liquid xenon scintillation calorimeter to detect 52.8 MeV [formula omitted] with large area VUV-sensitive MPPCs

The MEG II experiment will search for new physics like SUSY-GUT/SUSY-seesaw through the lepton flavor violating μ+→e+γ decay with ten times better sensitivity than the MEG experiment. The MEG experiment published the result of B(μ+→e+γ)<4.2×10−13 at 90% C.L. in 2016, which was thirty times better result than the previous limit. Because the sensitivity of the MEG experiment was already limited by accidental backgrounds, the MEG detector must be upgraded to reach one order of magnitude better sensitivity.The MEG experiment utilized 846 2 inch PMTs to detect scintillation light in a 900 L liquid xenon gamma calorimeter. On the γ incident face, 216 2 inch PMTs will be replaced with 4092 12 × 12 mm2 MPPCs to improve the energy and position resolution for γ events which interact near the incident face due to finer granularity and better uniformity of the scintillation light collection efficiency. We are now constructing the MEG II liquid xenon calorimeter. The detector calibration, purification, monitoring, and commissioning are in progress. Here the detector status will be described together with the expected detector performance.

Charged particle identification with the liquid Xenon calorimeter of the CMD-3 detector

This paper describes a procedure of particle identification with the liquid Xenon calorimeter of the CMD-3 detector currently being developed. The procedure uses the boosted decision tree classification method with specific energy losses of charged particles in the liquid Xenon calorimeter as input variables. The efficiency of the procedure is illustrated by an example of the measurement of the cross section of the process e+e−→K+K− in the center-of-mass energy range from 1.8 to 2.0 GeV.

Energy calibration of the barrel calorimeter of the CMD-3 detector

The VEPP-2000 e+e− collider has been operated in the Budker Institute of Nuclear Physics since 2010. Experiments are carried out with two detectors CMD-3 and SND. The calorimetry at the CMD-3 detector is based on three subsystems, two coaxial barrel calorimeters—Liquid Xenon calorimeter and crystal CsI calorimeter, and end cap calorimeter with BGO crystals. This paper describes the procedures of the energy calibration of the combined barrel calorimeter of the CMD-3 detector.

Processing of the signals from the Liquid Xenon Calorimeter for timing measurements

One of the goals of the Cryogenic Magnetic Detector at Budker Institute of Nuclear Physics SB RAS (Novosibirsk, Russia) is a study of hadron production in electron-positron collisions near threshold. The neutron-antineutron pair production events can be detected only by the calorimeters. In the barrel calorimeter the antineutron annihilation typically occurs about 5 ns or later after the beams crossing. For identification of such events it is necessary to measure the time of flight of particles to the LXe-calorimeter with an accuracy of about a few nanoseconds. The LXe-calorimeter consists of 14 layers of ionization chambers with two readout: anode and cathode. The duration of charge collection to the anodes is about 4.5 μs, while the required accuracy of measuring of the signal arrival time is less than 1/1000 of that (i.e. 4.5 ns). Besides, the signals' shapes differ substantially from event to event, so the signal arrival time is measured in two stages. In the paper we describ the development of the special electronics which performs waveform digitization and the on-line measurement of signals' arrival times and amplitudes.

Liquid xenon calorimeter for MEG II experiment with VUV-sensitive MPPCs

The MEG II experiment is an upgrade of the MEG experiment to search for the charged lepton flavor violating decay of muon, μ+→e+γ. The MEG II experiment is expected to reach a branching ratio sensitivity of 4×10−14, which is one order of magnitude better than the sensitivity of the current MEG experiment. The performance of the liquid xenon (LXe) γ-ray detector will be greatly improved with a highly granular scintillation readout realized by replacing 216 photomultiplier tubes (PMTs) on the γ-ray entrance face with 4092 Multi-Pixel Photon Counters (MPPCs). For this purpose, we have developed a new type of MPPC which is sensitive to the LXe scintillation light in vacuum ultraviolet (VUV) range, in collaboration with Hamamatsu Photonics K.K. We have measured the performance of the MPPC in LXe, and an excellent performance has been confirmed including high photon detection efficiency (>15%) for LXe scintillation light. An excellent performance of the LXe detector has been confirmed by Monte Carlo simulations based on the measured properties of the MPPC. The construction of the detector is in progress, aiming to start physics data taking in 2017.

Calorimetry of the CMD-3 detector

CMD-3 is a general purpose detector designed to study e+e− annihilation into hadrons. It is mounted at VEPP-2000 collider which operates in the wide energy range, Ec.m.s=0.32−2GeV. The calorimetry at the detector is based on three subsystems: closest to the beam pipe barrel Liquid Xenon calorimeter, outer barrel calorimeter based on CsI scintillation crystals and the endcap calorimeter made of BGO scintillation crystals. We describe the structure of the calorimeters, their electronics and the energy calibration procedures.

Barrel calorimeter of the CMD-3 detector

The structure of the barrel calorimeter of the CMD-3 detector is presented in this work. The procedure of energy calibration of the calorimeter and the method of photon energy restoration are described. The distinctive feature of this barrel calorimeter is its combined structure; it is composed of two coaxial subsystems: a liquid xenon calorimeter and a crystalline CsI calorimeter. The calorimeter spatial resolution of the photon conversion point is about 2 mm, which corresponds to an angular resolution of ∼6 mrad. The energy resolution of the calorimeter is about 8% for photons with energy of 200 MeV and 4% for photons with energy of 1 GeV.

Upgrade of the MEG liquid xenon calorimeter with VUV-light sensitive large area SiPMs

The MEG experiment searches for the muon lepton flavor violating decay, μ+→e+γ. An upgrade of the experiment is ongoing, aiming at reaching a sensitivity of Br(μ+→e+γ)=4×10−14, an order of magnitude better than the sensitivity of the current MEG. To achieve this goal, all of the detectors are being upgraded. In MEG, the energy, position and timing of the gamma ray were measured by a liquid Xe calorimeter, which consists of 900l of liquid Xe and 846 2-in. round-shaped photo-multiplier tubes (PMTs). In the upgrade, the granularity at the gamma ray incident face will be improved by replacing 216 PMTs with 4092 SiPMs (MPPCs) with an active area of 12×12mm2 each. The energy resolution for the gamma ray is expected to improve by a factor of 2, because the efficiency to collect scintillation light will become more uniform. The position resolution is also expected to improve by a factor of 2. In collaboration with Hamamatsu Photonics K.K., we have successfully developed a high performance MPPC for our detector. It has excellent photon detection efficiency for the liquid xenon scintillation light in VUV range. The size of the chips is large so that it can cover large area with a manageable number of readout channels. The characteristics of the MPPCs are being tested in liquid Xe, and also at the room temperature. The results of the tests will be presented, together with the expected performance of the upgraded detector.

A liquid hydrogen target for the calibration of the MEG and MEG II liquid xenon calorimeter

We designed, built and operated a liquid hydrogen target for the calibration of the liquid xenon calorimeter of the MEG experiment. The target was used throughout the entire data taking period, from 2008 to 2013 and it is being refurbished and partly re-designed to be integrated and used in the MEG-II experiment.

CsI calorimeter of the CMD-3 detector

The VEPP-2000 e+e− collider has been operated at Budker Institute of Nuclear Physics since 2010. The experiments are performed with two detectors CMD-3 and SND. The calorimetry at the CMD-3 detector is based on three subsystems, two coaxial barrel calorimeters—Liquid Xenon Calorimeter and crystal CsI calorimeter, and endcap calorimeter with BGO crystals. This paper describes the CsI calorimeter of the CMD-3 detector. The calorimeter design, its electronics and calibration procedures are discussed.

Combined Liquid Xenon and crystal CsI calorimeter of the CMD-3 detector

The barrel electromagnetic calorimeter of the CMD-3 detector consists of two subsystems: the Liquid Xenon calorimeter and the calorimeter based on CsI scintillation crystals. Its structure and main characteristics are presented. The energy calibration procedures of the combined calorimeter are described.

The LXe calorimeter and the pixelated timing counter in the MEG II experiment

The MEG experiment is to look for a lepton flavor violating μ+→e+γ decay with an unprecedented sensitivity, and we set an upper limit of the branching ratio for this decay, 5.7 × 10−13 at 90% C.L. in 2013 which is a twenty times more stringent limit than the previous experiment, MEGA. Since the sensitivity improvement was limited by the accidental background, we have considered the major detector upgrade. A proposal was submitted to PSI committee, and was approved in 2013, which aims at a sensitivity enhancement of one order of magnitude compared with the current MEG experiment. Here mainly two components of the MEG detector will be introduced, a γ-ray calorimeter with 900 L of liquid xenon (LXe), and a pixelated timing counter. The LXe detector will be improved by increasing the granularity at the incident face, by replacing the current PMTs with a larger number of smaller photosensors (MPPC) and optimizing the photosensor layout also on the lateral faces. A new highly segmented, fast timing counter array will replace the old system to allow improved timing resolution capabilities.

Processing of the Liquid Xenon calorimeter's signals for timing measurements

One of the goals of the Cryogenic Magnetic Detector at Budker Institute of Nuclear Physics SB RAS (Novosibirsk, Russia) is a study of nucleons production in electron-positron collisions near threshold. The neutron-antineutron pair production events can be detected only by the calorimeters. In the barrel calorimeter the antineutron annihilation typically occurs by 5 ns or later after beams crossing. For identification of such events it is necessary to measure the time of flight of particles to the LXe-calorimeter with accuracy of about 3 ns. The LXe-calorimeter consists of 14 layers of ionization chambers with anode and cathode readout. The duration of charge collection to the anodes is about 4.5 mks, while the required accuracy of measuring of the signal arrival time is less than 1/1000 of that. Besides, the signals' shapes differ substantially from event to event, so the signal arrival time is measured in two stages. At the first stage, the signal arrival time is determined with an accuracy of 1–2 discretization periods, and initial values of parameters for subsequent fitting procedure are calculated. At the second stage, the signal arrival time is determined with the required accuracy by means of fitting of the signal waveform with a template waveform. To implement that, a special electronics has been developed which performs waveform digitization and On-Line measurement of signals' arrival times and amplitudes.

Status of the Liquid Xenon calorimeter of the CMD-3 detector

Since 2010 the CMD-3 detector has been collecting data at the e+e− collider VEPP-2000 at Budker Institute of Nuclear Physics. CMD-3 is a general purpose detector designed to study e+e− annihilation into hadrons in the wide energy range √s = 0.3−2GeV. The barrel electromagnetic calorimeter of the detector has a thickness equal to 13.5X0 and consists of two subsystems: closest to the beam pipe is the Liquid Xenon calorimeter (LXe) and the outer one is based on CsI scintillation crystals (CsI). The design of the LXe calorimeter and its current performance are presented.

Barrel calorimeter of the CMD-3 detector

Since 2010 the CMD-3 detector has been collecting data at the e+e− collider VEPP-2000 at Budker Institute of Nuclear Physics. CMD-3 is a general purpose detector designed to study e+e− annihilation into hadrons in the wide energy range s=0.3–2GeV. The CMD-3 barrel electromagnetic calorimeter consists of two subsystems: closest to the beam pipe is the Liquid Xenon calorimeter and the outer one is based on CsI scintillation crystals. The design of the calorimeter and its current performance are presented.