arXiv subjects

Kai Zuber

Publications and source records attributed to Kai Zuber.

At least 37 records · Page 2Linked to original sources

arXiv2018

Precision Mass Measurement of $^{58-63}$Cr: Nuclear Collectivity towards the \emph{N}=40 Island of Inversion

The neutron-rich isotopes $^{58-63}$Cr were produced for the first time at the ISOLDE facility and their masses were measured with the ISOLTRAP spectrometer. The new values are up to 300 times more precise than those in the literature and indicate significantly different nuclear structure from the new mass-surface trend. A gradual onset of deformation is found in this proton and neutron mid-shell region, which is a gateway to the second island of inversion around \emph{N}=40. In addition to comparisons with density-functional theory and large-scale shell-model calculations, we present predictions from the valence-space formulation of the \emph{ab initio} in-medium similarity renormalization group, the first such results for open-shell chromium isotopes.

nucl-ex↗

arXiv2017

Constraining the $^7$Be($p,γ$)$^8$B $S$-factor with the new precise $^7$Be solar neutrino flux from Borexino

Among the solar fusion reactions, the rate of the $^7$Be($p,γ$)$^8$B reaction is one of the most difficult to determine rates. In a number of previous experiments, its astrophysical $S$-factor has been measured at $E$ = 0.1-2.5 MeV center-of-mass energy. However, no experimental data is available below 0.1 MeV. Thus, an extrapolation to solar energies is necessary, resulting in significant uncertainty for the extrapolated $S$-factor. On the other hand, the measured solar neutrino fluxes are now very precise. Therefore, the problem of the $S$-factor determination is turned around here: Using the measured $^7$Be and $^8$B neutrino fluxes and the Standard Solar Model, the $^7$Be($p,γ$)$^8$B astrophysical $S$-factor is determined at the solar Gamow peak. In addition, the $^3$He($α$,$γ$)$^7$Be $S$-factor is redetermined with a similar method.

astro-ph.SR↗

arXiv2017

Future Experimental Improvement for the Search of LNV Process in $eμ$ Sector

Exploring the leptonic sector in frontier experiments is more of importance nowadays, since the conservation of lepton flavor and total lepton number are not guaranteed anymore in the Standard Model after the discovery of neutrino oscillations. $μ^- + N(A,Z) \rightarrow e^+ + N(A,Z-2)$ conversion in a muonic atom is one of the most promising channels to investigate the lepton number violation process, and the measurement of this process is planned in future $μ^--e^-$ conversion experiments with a muonic atom in a muon-stopping target. This paper discusses how to maximize the experimental sensitivity of the $μ^--e^+$ conversion by introducing the new requirement of the mass relation of $M(A,Z-2)<M(A,Z-1)$, where $M(A,Z)$ is the mass of the muon-stopping target nucleus, to get rid of the background from radiative muon capture. The sensitivity of the $μ^--e^+$ conversion is anticipated to have four orders of magnitude of improvement in forthcoming experiments using a proper target nucleus, which satisfies the mass relation. The most promising isotopes found are $^{40}$Ca and $^{32}$S.

hep-ex↗

arXiv2017

Half-life Expectations for Neutrinoless Double Beta Decay in Standard and Non-Standard Scenarios

We investigate the half-life expectations for neutrinoless double beta decay by applying statistical distributions of neutrino mixing observables, neutrino mass constraints from cosmology and nuclear matrix elements. The analysis is performed in the standard scenario of active Majorana neutrino exchange, when light sterile neutrinos are added, and within TeV-scale left-right symmetric frameworks. The latter two cases correspond to a modified phenomenology of double beta decay for a normal and inverted mass ordering, and thus different discovery potential for future experiments.

hep-ph↗

arXiv2017

High precision half-life measurement of $^{147}$Sm $α$ decay from thin-film sources

An investigation of the α-decay of $^{147}$Sm was performed using an ultra low-background Twin Frisch-Grid Ionisation Chamber (TF-GIC). Four natural samarium samples were produced using pulsed laser deposition in ultra high vacuum. The abundance of the $^{147}$Sm isotope was mea- sured using inductively coupled plasma mass spectrometry. A combined half-life value for 147Sm of $1.079(26)\times{}10^{11}$ years was measured. A search for the α-decay into the first excited state of $^{143}$Nd has been performed using $γ$-spectroscopy, resulting in a lower half-life limit of $T_{1/2} > 3.1 \times{}10^{18}$ years (at 90% C.L.).

nucl-ex↗

arXiv2017

A new precision measurement of the α-decay half-life of 190Pt

A laboratory measurement of the $α$-decay half-life of $^{190}$Pt has been performed using a low background Frisch grid ionisation chamber. A total amount of 216.60(17) mg of natural platinum has been measured for 75.9 days. The resulting half-life is $(4.97\pm0.16)\times 10^{11}$ years, with a total uncertainty of 3.2%. This number is in good agreement with the half-life obtained using the geological comparison method.

nucl-ex↗

arXiv2017

$\boldsymbol{μ^-}$- $\boldsymbol{e^+}$ conversion in upcoming LFV experiments

We present an illustrative discussion of the physics potential of $μ^-$- $e^+$ conversion. We point out that this process, although much less frequently studied than the related but much more popular processes of $μ^-$- $e^-$ conversion and neutrinoless double beta decay, in fact is a promising alternative possibility to detect both lepton flavour and number violation. However, for this goal to be reached, a combined effort of experiments and theory, both in nuclear and particle physics, is necessary to advance. The aim of this paper is to be an "appetiser" to trigger such an initiative.

hep-ph↗

arXiv2016

Results of a search for neutrinoless double-beta decay using the COBRA demonstrator

Neutrinoless double-$β$ decay ($0νββ$ decay) is a hypothetical process that can occur if the neutrino is its own antiparticle. The COBRA collaboration operates a demonstrator to search for these decays at the Laboratori Nazionali del Gran Sasso in Italy using CdZnTe semiconductor detectors. The exposure of $234.7\,$kg\,d considered in this analysis was collected between September 2011 and February 2015. The analysis focuses on the decay of the nuclides $^{114}$Cd, $^{128}$Te, $^{70}$Zn, $^{130}$Te and $^{116}$Cd. A Bayesian analysis is performed to estimate the signal strength of $0νββ$ decay. No signal is observed for any of these nuclides. Therefore, the following half-life limits at 90% credibility are set: $T_{1/2}^{0ν}>1.6\cdot10^{21}\,$yr ($^{114}$Cd), $T_{1/2}^{0ν}>1.9\cdot10^{21}\,$yr ($^{128}Te$), $T_{1/2}^{0ν}>6.8\cdot10^{18}\,$yr ($^{70}$Zn), $T_{1/2}^{0ν}>6.1\cdot10^{21}\,$yr ($^{130}$Te), and $T_{1/2}^{0ν}>1.1\cdot10^{21}\,$yr ($^{116}$Cd).

nucl-ex↗

arXiv2016

Search for the decay of nature's rarest isotope $^{\rm {180m}}$Ta

$^{\rm {180m}}$Ta is the rarest naturally occurring quasi-stable isotope and the longest lived metastable state which is known. Its possible decay via the $β^-$ or the electron capture channel has never been observed. This article presents a search for the decay of $^{\rm {180m}}$Ta with an ultra low background Sandwich HPGe gamma spectrometry setup in the HADES underground laboratory. No signal is observed and improved lower partial half-life limits are set with a Bayesian analysis to $5.8\cdot10^{16}$ yr for the $β^-$ channel and $2.0\cdot10^{17}$ yr for the electron capture channel (90% credibility). The total half-life of $^{\rm {180m}}$Ta is longer than $4.5\cdot10^{16}$ yr. This is more than a factor of two improvement compared to previous searches.

nucl-ex↗

arXiv2016

Letter of Intent: Jinping Neutrino Experiment

Jinping Neutrino Experiment (Jinping) is proposed to significantly improve measurements on solar neutrinos and geoneutrinos in China Jinping Laboratory - a lab with a number of unparalleled features, thickest overburden, lowest reactor neutrino background, etc., which identify it as the world-best low-energy neutrino laboratory. The proposed experiment will have target mass of 4 kilotons of liquid scintillator or water-based liquid scintillator, with a fiducial mass of 2 kilotons for neutrino-electron scattering events and 3 kilotons for inverse-beta interaction events. A number of initial sensitivities studies have been carried out, including on the transition phase for the solar neutrinos oscillation from the vacuum to the matter effect, the discovery of solar neutrinos from the carbon-nitrogen-oxygen (CNO) cycle, the resolution of the high and low metallicity hypotheses, and the unambiguous separation on U and Th cascade decays from the dominant crustal anti-electron neutrinos in China.

physics.ins-det↗

arXiv2016

Solar neutrino interactions with liquid scintillators used for double beta decay experiments

Solar neutrinos interact with double beta decay detectors (DBD) and hence will contribute to backgrounds (BG) for DBD experiments. Background contributions due to solar neutrinos are evaluated for their interactions with atomic electrons and nuclei in liquid scintillation detectors used for DBD experiments. They are shown to be serious backgrounds for high sensitivity DBD experiments to search for the Majorana neutrino masses in the inverted and normal hierarchy regions.

physics.ins-det↗

arXiv2016

Origin of the p-process radionuclides 92Nb and 146Sm in the early Solar System and inferences on the birth of the Sun

The abundances of 92Nb and 146Sm in the early Solar System are determined from meteoritic analysis and their stellar production is attributed to the p process. We investigate if their origin from thermonuclear supernovae deriving from the explosion of white dwarfs with mass above the Chandrasekhar limit is in agreement with the abundance of 53Mn, another radionuclide present in the early Solar System and produced in the same events. A consistent solution for 92Nb and 53Mn cannot be found within the current uncertainties and requires that the 92Nb/92Mo ratio in the early Solar System is at least 50% lower than the current nominal value, which is outside its present error bars. A different solution is to invoke another production site for 92Nb, which we find in the alpha-rich freezeout during core-collapse supernovae from massive stars. Whichever scenario we consider, we find that a relatively long time interval of at least ~10 Myr must have elapsed from when the star-forming region where the Sun was born was isolated from the interstellar medium and the birth of the Sun. This is in agreement with results obtained from radionuclides heavier than iron produced by neutron captures and lends further support to the idea that the Sun was born in a massive star-forming region together with many thousands of stellar siblings.

astro-ph.SR↗

arXiv2016

Silicon photomultiplier readout of a monolithic 270$\times$5$\times$5 cm$^3$ plastic scintillator bar for time of flight applications

The detection of 200-1000 MeV neutrons requires large amounts, $\sim$100 cm, of detector material because of the long nuclear interaction length of these particles. In the example of the NeuLAND neutron time-of-flight detector at FAIR, this is accomplished by using 3000 monolithic scintillator bars of 270$\times$5$\times$5 cm$^3$ size made of a fast plastic. Each bar is read out on the two long ends, and the needed time resolution of $σ_t$ $<$ 150 ps is reached with fast timing photomultipliers. In the present work, it is investigated whether silicon photomultiplier (SiPM) photosensors can be used instead. Experiments with a picosecond laser system were conducted to determine the timing response of the assembly made up of SiPM and preamplifier. The response of the full system including also the scintillator was studied using 30 MeV single electrons provided by the ELBE superconducting electron linac. The ELBE data were matched by a simple Monte Carlo simulation, and they were found to obey an inverse-square-root scaling law. In the electron beam tests, a time resolution of $σ_t$ = 136 ps was reached with a pure SiPM readout, well within the design parameters for NeuLAND.

physics.ins-det↗

arXiv2015

The Dortmund Low Background Facility - Low-Background Gamma Ray Spectrometry with an Artificial Overburden

High-purity germanium (HPGe) detectors used for low-background gamma ray spectrometry are usually operated under either a fairly low overburden of the order of one meter of water equivalent (mw.e.) or a high overburden of the order of 100mw.e. or more, e.g. in specialized underground laboratories. The Dortmund Low Background Facility (DLB) combines the advantages of both approaches. The artificial overburden of 10mw.e. already shields the hadronic component of cosmic rays. The inner shielding, featuring a state-of-the-art neutron shielding and an active muon veto, enables low-background gamma ray spectrometry at an easy-accessible location at the campus of the Technische Universität Dortmund. The integral background count rate between 40keV and 2700keV is 2.528+-0.004counts/kg/minute. This enables activity measurements of primordial radionuclides in the range of some 10mBq/kg within a week of measurement time.

physics.ins-det↗

arXiv2015

Design and performance of an ionisation chamber for the measurement of low alpha-activities

A new ionisation chamber for alpha-spectroscopy has been built from radio-pure materials for the purpose of investigating long lived alpha-decays. The measurement makes use of pulse shape analysis to discriminate between signal and background events. The design and performance of the chamber is described in this paper. A background rate of ($10.9 \pm 0.6$) counts per day in the energy region of 1 MeV to 9 MeV was achieved with a run period of 30.8 days. The background is dominantly produced by radon daughters.

physics.ins-det↗

arXiv2015

Probing flavor models with Ge-76-based experiments on neutrinoless double-beta decay

The physics impact of a staged approach for double-beta decay experiments based on Ge-76 is studied. The scenario considered relies on realistic time schedules envisioned by the GERDA and the MAJORANA collaborations, which are jointly working towards the realization of a future larger scale Ge-76 experiment. Intermediate stages of the experiments are conceived to perform quasi background-free measurements, and different data sets can be reliably combined to maximize the physics outcome. The sensitivity for such a global analysis is presented, with focus on how neutrino flavor models can be probed already with preliminary phases of the experiments. The synergy between theory and experiment yields strong benefits for both sides: the model predictions can be used to sensibly plan the experimental stages, and results from intermediate stages can be used to constrain whole groups of theoretical scenarios. This strategy clearly generates added value to the experimental efforts, while at the same time it allows to achieve valuable physics results as early as possible.

hep-ex↗

arXiv2015

Constraining Big Bang lithium production with recent solar neutrino data

The 3He(α,γ)7Be reaction affects not only the production of 7Li in Big Bang nucleosynthesis, but also the fluxes of 7Be and 8B neutrinos from the Sun. This double role is exploited here to constrain the former by the latter. A number of recent experiments on 3He(α,γ)7Be provide precise cross section data at E = 0.5-1.0 MeV center-of-mass energy. However, there is a scarcity of precise data at Big Bang energies, 0.1-0.5 MeV, and below. This problem can be alleviated, based on precisely calibrated 7Be and 8B neutrino fluxes from the Sun that are now available, assuming the neutrino flavour oscillation framework to be correct. These fluxes and the standard solar model are used here to determine the 3He(alpha,gamma)7Be astrophysical S-factor at the solar Gamow peak, S(23+6-5 keV) = 0.548+/-0.054 keVb. This new data point is then included in a re-evaluation of the 3He(α,γ)7Be S-factor at Big Bang energies, following an approach recently developed for this reaction in the context of solar fusion studies. The re-evaluated S-factor curve is then used to re-determine the 3He(α,γ)7Be thermonuclear reaction rate at Big Bang energies. The predicted primordial lithium abundance is 7Li/H = 5.0e-10, far higher than the Spite plateau.

astro-ph.CO↗

arXiv2014

Stellar origin of the 182Hf cosmochronometer and the presolar history of solar system matter

Among the short-lived radioactive nuclei inferred to be present in the early solar system via meteoritic analyses, there are several heavier than iron whose stellar origin has been poorly understood. In particular, the abundances inferred for 182Hf (half-life = 8.9 million years) and 129I (half-life = 15.7 million years) are in disagreement with each other if both nuclei are produced by the rapid neutron-capture process. Here, we demonstrate that contrary to previous assumption, the slow neutron-capture process in asymptotic giant branch stars produces 182Hf. This has allowed us to date the last rapid and slow neutron-capture events that contaminated the solar system material at roughly 100 million years and 30 million years, respectively, before the formation of the Sun.

astro-ph.SR↗