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Spectroscopy of geo-neutrinos from 2056 days of Borexino data
We report an improved geo-neutrino measurement with Borexino from 2056 days
of data taking. The present exposure is
protonyr. Assuming a chondritic Th/U mass ratio of 3.9, we obtain geo-neutrino events. The null
observation of geo-neutrinos with Borexino alone has a probability of (5.9). A geo-neutrino signal from the mantle is
obtained at 98\% C.L. The radiogenic heat production for U and Th from the
present best-fit result is restricted to the range 23-36 TW, taking into
account the uncertainty on the distribution of heat producing elements inside
the Earth.Comment: 4 pages, 4 figure
The Main Results of the Borexino Experiment
The main physical results on the registration of solar neutrinos and the
search for rare processes obtained by the Borexino collaboration to date are
presented.Comment: 8 pages, 8 figgures, To be published as Proceedings of the Third
Annual Large Hadron Collider Physics Conference, St. Petersburg, Russia, 201
Measurement of neutrino flux from the primary proton--proton fusion process in the Sun with Borexino detector
Neutrino produced in a chain of nuclear reactions in the Sun starting from
the fusion of two protons, for the first time has been detected in a real-time
detector in spectrometric mode. The unique properties of the Borexino detector
provided an oppurtunity to disentangle pp-neutrino spectrum from the background
components. A comparison of the total neutrino flux from the Sun with Solar
luminosity in photons provides a test of the stability of the Sun on the
10 years time scale, and sets a strong limit on the power production in
the unknown energy sources in the Sun of no more than 4\% of the total energy
production at 90\% C.L.Comment: 15 pages, 2 tables, 3 figure
Characterization of the LUNA neutron detector array for the measurement of the 13C(α,n)16O reaction
We introduce the LUNA neutron detector array developed for the investigation of the 13C(\u3b1, n)16O reaction towards its astrophysical s-process Gamow peak in the low-background environment of the Laboratori Nazionali del Gran Sasso (LNGS). Eighteen 3He counters are arranged in two different configurations (in a vertical and a horizontal orientation) to optimize neutron detection efficiency, target handling and target cooling over the investigated energy range E\u3b1,lab=300 12400 keV (En=2.2 122.6MeV in emitted neutron energy). As a result of the deep underground location, the passive shielding of the setup and active background suppression using pulse shape discrimination, we reached a total background rate of 1.23\ub10.12 counts/hour. This resulted in an improvement of two orders of magnitude over the state of the art allowing a direct measurement of the 13C(\u3b1, n)16O cross-section down to E\u3b1,lab=300 keV. The absolute neutron detection efficiency of the setup was determined using the 51V(p,n)51Cr reaction and an AmBe radioactive source, and completed with a Geant4 simulation. We determined a (34 \ub1 3)% and (38 \ub1 3)% detection efficiency for the vertical and horizontal configurations, respectively, for En=2.4MeV neutrons
The bottleneck of the CNO burning and the age of the Globular Clusters
The transition between the Main Sequence and the Red Giant Branch in low mass
stars is powered by the onset of the CNO burning, whose bottleneck is the
N(p,O. The LUNA collaboration has recently improved the
low energy measurements of the cross section of this key reaction. We analyse
the impact of the revised reaction rate on the estimate of the Globular
Clusters ages, as derived from the turnoff luminosity. We found that the age of
the oldest Globulars should be increased by about 0.7-1 Gyr with respect to the
current estimates.Comment: Accepte
First direct limit on the 334 keV resonance strength in the Ne({\alpha},{\gamma})Mg reaction
In stars, the fusion of Ne and He may produce either Mg,
with the emission of a neutron, or Mg and a ray. At high
temperature, the () channel dominates, while at low temperature, it
is energetically hampered. The rate of its competitor, the
Ne(,)Mg reaction, and, hence, the minimum
temperature for the () dominance, are controlled by many nuclear
resonances. The strengths of these resonances have hitherto been studied only
indirectly. The present work aims to directly measure the total strength of the
resonance at _{r}334keV (corresponding to
_{x}10949keV in Mg). The data reported here have been
obtained using high intensity He beam from the INFN LUNA 400 kV
underground accelerator, a windowless, recirculating, 99.9% isotopically
enriched Ne gas target, and a 4 bismuth germanate summing
-ray detector. The ultra-low background rate of less than 0.5
counts/day was determined using 67 days of no-beam data and 7 days of
He beam on an inert argon target. The new high-sensitivity setup
allowed to determine the first direct upper limit of 4.010
eV (at 90% confidence level) for the resonance strength. Finally, the
sensitivity of this setup paves the way to study further
Ne(,)Mg resonances at higher energy.Comment: Submitted to Eur. Phys. J.
Underground experimental study finds no evidence of low-energy resonance in the 6Li(p,Îł)7Be reaction
The astrophysical Li6(p,\u3b3)Be7 reaction occurs during Big Bang nucleosynthesis and the pre-main sequence and main sequence phases of stellar evolution. The low-energy trend of its cross section remains uncertain, since different measurements have provided conflicting results. A recent experiment reported a resonancelike structure at center-of-mass energy 195 keV, associated to a positive-parity state of Be7. The existence of such resonance is still a matter of debate. We report a new measurement of the Li6(p,\u3b3)Be7 cross section performed at the Laboratory for Underground Nuclear Astrophysics, covering the center-of-mass energy range E=60-350 keV. Our results rule out the existence of low-energy resonances. The astrophysical S-factor varies smoothly with energy, in agreement with theoretical models
Low-energy resonances in the 18O (p,΄) 19F reaction
Background: Shell hydrogen burning during the asymptotic giant branch (AGB) phase through the oxygen
isotopes has been indicated as a key process that is needed to understand the observed 18O/16O relative abundance
in presolar grains and in stellar atmospheres. This ratio is strongly influenced by the relative strengths of the
reactions 18O(p,\u3b1) 15N and 18O(p,\u3b3 ) 19F in low-mass AGB stars. While the former channel has been the focus
of a large number of measurements, the (p,\u3b3 ) reaction path has only recently received some attention and its
stellar reaction rate over a wide temperature range rests on only one measurement.
Purpose: Our aim is the direct measurement of states in 19F as populated through the reaction 18O(p,\u3b3 ) 19F
to better determine their influence on the astrophysical reaction rate, and more generally to improve the
understanding of the nuclear structure of 19F.
Method: Branchings and resonance strengths were measured in the proton energy range Elab
p = 150\u2013400 keV,
using a high-purity germanium detector inside a massive lead shield. The measurement took place in the ultralow-
background environment of the Laboratory for Underground Nuclear Astrophysics (LUNA) experiment at
the Gran Sasso National Laboratory, leading to a highly increased sensitivity.
Results: The uncertainty of the \u3b3 branchings and strengths was improved for all four resonances in the studied
energy range; many new transitions were observed in the case of the 334 keV resonance, and individual \u3b3 decays
of the 215 keV resonance were measured for the first time. In addition a number of transitions to intermediate
states that decay through \u3b1 emission were identified. The strengths of the observed resonances are generally in
agreement with literature values.
Conclusions: Our measurements substantially confirm previous determinations of the relevant resonance
strengths. Therefore the 18O(p,\u3b3 ) 19F reaction rate does not change with respect to the reaction rate reported
in the compilations commonly adopted in the extant computations of red-giant branch and AGB stellar models.
Nevertheless, our measurements definitely exclude a nonstandard scenario for the fluorine nucleosynthesis and
a nuclear physics solution for the 18O depletion observed in Group 2 oxygen-rich stardust grains
Experimental Detection of the CNO Cycle
Borexino recently reported the first experimental evidence for a CNO neutrino. Since this process accounts for only about 1% of the Sunâs total energy production, the associated neutrino flux is remarkably low compared to that of the pp chain, the dominant hydrogen-burning process. This experimental evidence for the existence of CNO neutrinos was obtained using a highly radio-pure Borexino liquid scintillator. Improvements in the thermal stabilization of the detector over the last five years have allowed us to exploit a method of constraining the rate of 210Bi background. Since the CNO cycle is dominant in massive stars, this result is the first experimental evidence of a major stellar hydrogen-to-helium conversion mechanism in the Universe
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