MEG: Muon to Electron and Gamma Baldini, Alessandro MAssimo; Mori, Toshinori
SciPost physics proceedings,
09/2021
5
Journal Article
Recenzirano
Odprti dostop
The possible existence of the
\mu \rightarrow {e} \gamma
μ
→
e
γ
decay predicted by many new physics scenarios is investigated by
stopping positive muons in a very thin target and measuring emitted
...photons and positrons with the best possible resolutions. Photons are
measured by a 2.7 ton ultra pure liquid xenon detector while positron
trajectories are measured in a specially designed gradient magnetic
field by low-mass drift chambers and precisely timed by scintillation
counters. A first phase of the experiment (MEG) ended in 2016, and
excluded the existence of the decay with branching ratios larger than
4.2 \times 10^{-13}
4.2
×
10
−
13
(90% C.L.). This provides approximately 30~times stronger constraints on
a variety of new physics models than previous experiments. In the second
phase (MEG II), most of the detectors have been upgraded by adopting
up-to-date technologies to improve the search sensitivity by another
order of magnitude down to
\mathcal{O}(10^{-14})
(
10
−
14
)
.
MEG II will perform a search for physics beyond the Standard Model
complementary to high energy collider experiments with compatible or
even higher sensitivity.
Commissioning of liquid xenon gamma-ray detector for MEG II experiment Matsushita, Ayaka; Ban, Sei; Benmansour, Hicham ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
02/2023, Letnik:
1047
Journal Article
Recenzirano
The liquid xenon (LXe) gamma-ray detector in the MEG II experiment measures the energy, position and timing of the gamma-ray from μ+→e+γ, and it is the key to the unprecedented sensitivity of the ...experiment. All the photo sensors of 4092 VUV MPPCs and 668 PMTs were read out for the first time and a physics data collection started in 2021. The detector response was monitored all through the beam time, and the LXe detector operated stably. The timing and energy resolution were measured using the gamma-rays from the π0 decays after charge exchange reaction of charged pions in a liquid hydrogen target. The detector has been successfully commissioned and is ready for the long physics run.
Patients with poorly differentiated endometrial cancer show poor prognosis, and effective molecular target-based therapies are needed. Endometrial cancer cells proliferate depending on the activation ...of HES1 (hairy and enhancer of split-1), which is induced by several pathways, such as the Notch and fibroblast growth factor receptor (FGFR) signaling pathways. In addition, aberrant, ligand-free activation of the FGFR signaling pathway resulting from mutations in FGFR2 was also reported in endometrial cancer. However, a clinical trial showed that there was no difference in the effectiveness of FGFR inhibitors between patients with and without the FGFR2 mutation, suggesting a presence of another signaling pathway for the FGFR activation. Here, we investigated the signaling pathway regulating the expression of HES1 and proliferation of poorly and well-differentiated endometrial cancer cell lines Ishikawa and HEC-50B, respectively. Whereas Ishikawa cells proliferated and expressed HES1 in a Notch signaling-dependent manner, Notch signaling was not involved in HES1 and proliferation of HEC-50B cells. The FGFR inhibitor, NVP-BGJ398, decreased HES1 expression and proliferation of HEC-50B cells; however, HEC50B cells had no mutations in the FGFR2 gene. Instead, HEC-50B cells highly expressed ligands for FGFR2, suggesting that FGFR2 is activated by an autocrine manner, not by ligand-free activation. This autocrine pathway activated Akt downstream of FGFR for cell proliferation. Our findings suggest the usefulness of HES1 as a marker for the proliferation signaling and that FGFR inhibitor may be effective for poorly differentiated endometrial cancers that harbor wild-type FGFR.
We developed two complementary ways to measure the position of SiPMs inside liquid xenon detector for MEG II experiment; one uses laser tools and the other uses an X-ray beam. We measured the ...position of all SiPMs to an accuracy of 320 μm.
•Precise alignment of SiPMs in liquid xenon detector with X-ray and laser.•The SiPM array is scanned with X-ray beam that makes a local energy deposit.•Reconstructed 3D SiPM array from an image taken by a laser scanner.•Reasonable thermal contraction was observed from the comparison.•Consistent shape of the SiPM array measured by two measurements.
The dynamics of methanol and ethanol molecules confined in MCM-41 with pore diameters d = 2.1, 2.8, and 3.7 nm has been investigated by quasi-elastic neutron scattering (QENS) and dielectric ...measurements. Two kinds of adsorbed amounts of liquids were studied: surface-adsorbed and capillary-condensed. The QENS measurements were performed only for methanol at room temperature and revealed that the molecular motions became slower in the following order: bulk, capillary-condensed, and surface-adsorbed liquid. The effect of confinement on the dynamics of capillary-condensed methanol molecules is stronger than in the case of acetonitrile, indicating higher cooperativity of molecular motions in liquid methanol. The dielectric measurements for methanol and ethanol in the frequency range 102−107 Hz and temperature range 120−300 K showed that the molecular motions became slower in the same order as for the QENS measurements. The slowest molecular motions of surface-adsorbed liquid must result from strong interaction between liquid molecules and the pore surface, which was demonstrated by adsorption isotherm and Fourier transform infrared spectra measurements. The slow molecular motions of capillary-condensed liquid can be explained by the influence of slow molecules near the pore surface through the cooperativity of molecular motions and/or formation of an ordered structure possibly due to van der Waals interactions between hydrogen-bonded chains.
A silver-ion-exchanged HZSM-5 zeolite sample (Ag(H)ZSM-5) evacuated at 573 K exhibited prominent catalytic behavior in the partial oxidation of CH
4 at temperatures above 573 K, exceeding the ...performance of Ag/SiO
2⋅Al
2O
3 and Ag/SiO
2 catalysts. From the infrared (IR) and X-ray absorption fine structure (XAFS) spectra, as well as the dioxygen adsorption measurement, it was concluded that the simultaneous existence of Ag
+ ions and small clusters of Ag particles leads to the partial oxidation of methane. Taking the magnitude of the formation enthalpy (per oxygen atom) of Ag
2O (
Δ
H
=
26
kJ
/
mol
) into consideration, we propose the interpretation that the dioxygen activated on small Ag metal clusters formed in ZSM-5 elaborates a surface oxide layer on small Ag clusters and the thus-formed species is simultaneously and easily decomposed at 573 K or above, and the oxygen activated in this way on the Ag metal spills over and can react with methane that has been activated by the Ag
+ ions exchanged in ZSM-5, resulting in the high catalytic activity of the Ag(H)ZSM-5 sample in the partial oxidation of methane. This interpretation is also well evidenced by XAFS and IR data. It is anticipated that this material has the potential to be a promising catalyst in the conversion of natural gas into higher value-added chemicals and fuels.
AgZSM-5 exhibited prominent catalytic behavior in the partial oxidation of CH
4 to CO and H
2 above 573 K and has a potential for acting as the catalyst for the conversion of abundant gases into valuable chemicals.
A peculiar N2 adsorption was found on a copper-ion-exchanged MFI-type zeolite (CuMFI); the N2 adsorption was established within 20 s at 300 K. Related to this fact, the bond dissociation energy of ...NN in a stable Cu+−NN species in CuMFI was, for the first time, evaluated to be 9.11 eV from the characteristic bands at 2295, 2654, and 4553 cm−1, which correspond to the fundamental, combination, and overtone vibrations of NN adsorbed on Cu+ of CuMFI, respectively. The vibrational frequency of Cu+−N in the Cu+−NN formed in CuMFI was also determined to be ∼360 cm−1, together with the energy for the formation of a Cu+−N bond; the Cu+−NN species is stable enough to maintain a N2 molecule on MFI at 300 K. DFT calculations reasonably explain the experimental data and also the N2 adsorption model based on the three-coordinate Cu+ site in CuMFI.
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