In a 2016 paper, an anomaly in the internal pair creation on the
M1
transition depopulating the 18.15 MeV isoscalar 1+ state on 8Be was observed. This could be explained by the creation and ...subsequent decay of a new boson, with mass
m
X
c
2
= 16.70 MeV. Further experiments of the same transition with an improved and independent setup were performed, which constrained the mass of the X17 boson (
m
X
c2) and its branching ratio relative to the γ-decay of the 8Be excited state (
B
X
), to
m
X
c
2
= 17.01(16) MeV and
B
X
= 6(1) 10−6, respectively. Using the latter setup, the
e
+
e
− pairs depopulating the 21 MeV
J
π = 0
−
0
+
transition in 4He were investigated and a resonance in the angular correlation of the pairs was observed, which could be explained by the same X17 particle, with mass
m
X
c
2
= 16.98 ± 0.16(stat) ± 0.20(syst) MeV.
An electron–positron pair spectrometer has been designed and constructed for the simultaneous measurement of energy- and angular correlations of e+e- pairs. Experimental results are obtained over a ...wide angular range for high-energy transitions in 16O, 12C and 8Be. The results showed that the angular correlations between 50 and 180°of the e+e- pairs in the energy range between 6 and 18MeV can be determined with sufficient resolution and efficiency in good agreement with the GEANT simulations.
Recently, we observed an anomalous peak-like excess of internal e+e− pairs at around 140° for the M1 transition depopulating the 18.15 MeV isoscalar 1+ state in 8Be. The deviation from the ...theoretical prediction can be described by GEANT simulations assuming the creation and subsequent decay of a new, light boson with a mass of 16.7 MeV/c2. In order to reduce the possible systematic errors from the experimenntal data, we re-investigated the 8Be anomaly with an improved setup and confirmed the anomaly within the statistical uncertainties. We also studied the angular correlation of the electron-positron pairs created in the M0 transition depopulating the 21.01 MeV 0− state in 4He, and observed an anomalous excess of e+e− pairs at a significantly smaller angle of 115°. Since the transition energy was higher in this case, the observed anomaly could be described by assuming the creation and subsequent decay of the same light particle in the simulations.
Gamow-Teller (GT) transitions in atomic nuclei are sensitive to both nuclear shell structure and effective residual interactions. The nuclear GT excitations were studied for the mass number A = 42, ...46, 50, and 54 "f-shell" nuclei in ((3)He, t) charge-exchange reactions. In the (42)Ca → (42)Sc reaction, most of the GT strength is concentrated in the lowest excited state at 0.6 MeV, suggesting the existence of a low-energy GT phonon excitation. As A increases, a high-energy GT phonon excitation develops in the 6-11 MeV region. In the (54)Fe → (54)Co reaction, the high-energy GT phonon excitation mainly carries the GT strength. The existence of these two GT phonon excitations are attributed to the 2 fermionic degrees of freedom in nuclei.
Abstract
The matter radius of the doubly magic
$$^{56}$$
56
Ni was extracted from a measurement of the differential cross section by employing, for the first time, elastic proton scattering in ...inverse kinematics with a radioactive beam at
$$E_{kin}=390.2$$
E
kin
=
390.2
MeV/nucleon circulating in a storage ring and passing an internal hydrogen gas-jet target with a revolution frequency of around 2 MHz. The novel experimental scheme is based on UHV-compatible Si detectors operated as active vacuum windows, which were implemented in the ESR storage ring at GSI. A matter radius
$$<r_{m}^{2}>^{1/2}=3.74^{+0.03}_{-0.06}$$
<
r
m
2
>
1
/
2
=
3
.
74
-
0.06
+
0.03
fm was extracted for the doubly-magic self-conjugate nucleus
$$^{56}$$
56
Ni.
A new light particle is being born Krasznahorkay, A.J.; Begala, M.; Csatlós, M. ...
Journal of physics. Conference series,
12/2022, Letnik:
2391, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Abstract
A few years ago we observed anomalous electron-positron angular correlations for the 18.15 MeV M1 transition of
8
Be. This was interpreted as the creation and decay of an intermediate ...bosonic particle with a mass of
m
0
c
2
=16.70±0.35(stat )±0.5(sys) MeV, which is now called X17. The possible relation of the X17 boson to the dark matter problem triggered an enormous interest in the wider physics community. We also observed a similar anomaly in
4
He, which could be described also by the creation and subsequent decay of the same X17 particle. Very recently, the
11
B proton capture reaction was used for exciting the 17.2 MeV broad (Γ=1.15 MeV) resonance in
12
C and studying their internal pair creation decay. Anomalies were observed in the angular correlation of the electron-positron pairs, which together with the
8
Be and
4
He data provides kinematic evidence for the X17 particle and supports their vector boson and fifth force explanation.
A new technique developed for measuring nuclear reactions at low momentum transfer with stored beams in inverse kinematics was successfully used to study isoscalar giant resonances. The experiment ...was carried out at the experimental heavy-ion storage ring (ESR) at the GSI facility using a stored 58Ni beam at 100 MeV/u and an internal helium gas-jet target. In these measurements, inelastically scattered α-recoils at very forward center-of-mass angles (θcm≤1.5°) were detected with a dedicated setup, including ultra-high vacuum compatible detectors. Experimental results indicate a dominant contribution of the isoscalar giant monopole resonance at this very forward angular range. It was found that the monopole contribution exhausts 79−11+12% of the energy-weighted sum rule (EWSR), which agrees with measurements performed in normal kinematics. This opens up the opportunity to investigate the giant resonances in a large domain of unstable and exotic nuclei in the near future. It is a fundamental milestone towards new nuclear reaction studies with stored ion beams.
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