-
G. Bellini,
J. Benziger,
D. Bick,
G. Bonfini,
D. Bravo,
M. Buizza Avanzini,
B. Caccianiga,
L. Cadonati,
F. Calaprice,
P. Cavalcante, [......],
R. B. Vogelaar,
F. von Feilitzsch,
J. Winter,
M. Wojcik,
A. Wright,
M. Wurm,
J. Xu,
O. Zaimidoroga,
S. Zavatarelli,
G. Zuzel
[show abstract]
[hide abstract]
ABSTRACT: The solar neutrino experiment Borexino, which is located in the Gran Sasso
underground laboratories, is in a unique position to study muon-induced
backgrounds in an organic liquid scintillator. In this study, a large sample of
cosmic muons is identified and tracked by a muon veto detector external to the
liquid scintillator, and by the specific light patterns observed when muons
cross the scintillator volume. The yield of muon-induced neutrons is found to
be Yn =(3.10+-0.11)10-4 n/({\mu} (g/cm2)). The distance profile between the
parent muon track and the neutron capture point has the average value {\lambda}
= (81.5 +- 2.7)cm. Additionally the yields of a number of cosmogenic
radioisotopes are measured for 12N, 12B, 8He, 9C, 9Li, 8B, 6He, 8Li, 11Be, 10C
and 11C. All results are compared with Monte Carlo simulation predictions using
the Fluka and Geant4 packages. General agreement between data and simulation is
observed for the cosmogenic production yields with a few exceptions, the most
prominent case being 11C yield for which both codes return about 50% lower
values. The predicted {\mu}-n distance profile and the neutron multiplicity
distribution are found to be overall consistent with data.
04/2013;
-
G. Bellini,
J. Benziger,
D. Bick,
G. Bonfini,
D. Bravo,
M. Buizza Avanzini,
B. Caccianiga,
L. Cadonati,
F. Calaprice,
P. Cavalcante, [......],
R. B. Vogelaar,
F. von Feilitzsch,
J. Winter,
M. Wojcik,
A. Wright,
M. Wurm,
J. Xu,
O. Zaimidoroga,
S. Zavatarelli,
G. Zuzel
[show abstract]
[hide abstract]
ABSTRACT: We present a measurement of the geo--neutrino signal obtained from 1353 days
of data with the Borexino detector at Laboratori Nazionali del Gran Sasso in
Italy. With a fiducial exposure of (3.69 $\pm$ 0.16) $\times$ $10^{31}$ proton
$\times$ year after all selection cuts and background subtraction, we detected
(14.3 $\pm$ 4.4) geo-neutrino events assuming a fixed chondritic mass Th/U
ratio of 3.9. This corresponds to a geo-neutrino signal $S_{geo}$ = (38.8 $\pm$
12.0) TNU with just a 6 $\times$ $10^{-6}$ probability for a null geo-neutrino
measurement. With U and Th left as free parameters in the fit, the relative
signals are $S_{\mathrm{Th}}$ = (10.6 $\pm$ 12.7) TNU and $S_\mathrm{U}$ =
(26.5 $\pm$ 19.5) TNU. Borexino data alone are compatible with a mantle
geo--neutrino signal of (15.4 $\pm$ 12.3) TNU, while a combined analysis with
the KamLAND data allows to extract a mantle signal of (14.1 $\pm$ 8.1) TNU. Our
measurement of a reactor anti--neutrino signal $S_{react}$ =
84.5$^{+19.3}_{-18.9}$ TNU is in agreement with expectations in the presence of
neutrino oscillations.
03/2013;
-
Borexino Collaboration,
G. Bellini,
J. Benziger,
D. Bick,
G. Bonfini,
D. Bravo,
M. Buizza Avanzini,
B. Caccianiga,
L. Cadonati,
F. Calaprice, [......],
F. von Feilitzsch,
J. Winter,
M. Wojcik,
A. Wright,
M. Wurm,
G. Xhixha,
J. Xu,
O. Zaimidoroga,
S. Zavatarelli,
G. Zuzel
[show abstract]
[hide abstract]
ABSTRACT: We have studied the alpha decays of 214Po into 210Pb and of 212Po into 208Pb
tagged by the coincidence with the preceding beta decays from 214Bi and 212Bi,
respectively. The employed 222Rn, 232Th, and 220Rn sources were sealed inside
quartz vials and inserted in the Counting Test Facility at the underground Gran
Sasso National Laboratory in Italy. We find that the mean lifetime of 214Po is
(236.00 +- 0.42(stat) +- 0.15(syst)) \mu s and that of 212Po is (425.1 +-
0.9(stat) +- 1.2(syst)) ns. Our results, obtained from data with
signal-to-background ratio larger than 1000, reduce the overall uncertainties
and are compatible with previous measurements.
12/2012;
-
Borexino collaboration,
H. Back,
G. Bellini,
J. Benziger,
D. Bick,
G. Bonfini,
D. Bravo,
M. Buizza Avanzini,
B. Caccianiga,
L. Cadonati, [......],
D. Vignaud,
R. B. Vogelaar,
J. Winter,
M. Wojcik,
A. Wright,
M. Wurm,
J. Xu,
O. Zaimidoroga,
S. Zavatarelli,
G. Zuzel
[show abstract]
[hide abstract]
ABSTRACT: Borexino was the first experiment to detect solar neutrinos in real-time in
the sub-MeV region. In order to achieve high precision in the determination of
neutrino rates, the detector design includes an internal and an external
calibration system. This paper describes both calibration systems and the
calibration campaigns that were carried out in the period between 2008 and
2011. We discuss some of the results and show that the calibration procedures
preserved the radiopurity of the scintillator. The calibrations provided a
detailed understanding of the detector response and led to a significant
reduction of the systematic uncertainties in the Borexino measurements.
07/2012;
-
L. Ludhova,
G. Bellini,
J. Benziger,
D. Bick,
G. Bonfini,
D. Bravo,
M. Buizza Avanzini,
B. Caccianiga,
L. Cadonati,
F. Calaprice, [......],
R. B. Vogelaar,
F. Von Feilitzsch,
J. Winter,
M. Wojcik,
A. Wright,
M. Wurm,
J. Xu,
O. Zaimidoroga,
S. Zavatarelli,
G. Zuzel
[show abstract]
[hide abstract]
ABSTRACT: Borexino is a large-volume liquid scintillator detector installed in the
underground halls of the Laboratori Nazionali del Gran Sasso in Italy. After
several years of construction, data taking started in May 2007. The Borexino
phase I ended after about three years of data taking. Borexino provided the
first real time measurement of the $^{7}$Be solar neutrino interaction rate
with accuracy better than 5% and confirmed the absence of its day-night
asymmetry with 1.4% precision. This latter Borexino results alone rejects the
LOW region of solar neutrino oscillation parameters at more than 8.5 $\sigma$
C.L. Combined with the other solar neutrino data, Borexino measurements isolate
the MSW-LMA solution of neutrino oscillations without assuming CPT invariance
in the neutrino sector. Borexino has also directly observed solar neutrinos in
the 1.0-1.5 MeV energy range, leading to the first direct evidence of the $pep$
solar neutrino signal and the strongest constraint of the CNO solar neutrino
flux up to date. Borexino provided the measurement of the solar $^{8}$B
neutrino rate with 3 MeV energy threshold.
05/2012;
-
G. Bellini,
J. Benziger,
D. Bick,
G. Bonfini,
D. Bravo,
M. Buizza Avanzini,
B. Caccianiga,
L. Cadonati,
F. Calaprice,
C. Carraro, [......],
R. B. Vogelaar,
F. von Feilitzsch,
J. Winter,
M. Wojcik,
A. Wright,
M. Wurm,
J. Xu,
O. Zaimidoroga,
S. Zavatarelli,
G. Zuzel
[show abstract]
[hide abstract]
ABSTRACT: A search for 5.5 MeV solar axions produced in the p+d→3He+A (5.5 MeV) reaction was performed using the Borexino detector. The Compton conversion of axions to photons, A+e→e+γ; the axioelectric effect, A+e+Z→e+Z; the decay of axions into two photons, A→2γ; and inverse Primakoff conversion on nuclei, A+Z→γ+Z, are considered. Model-independent limits on axion-electron (gAe), axion-photon (gAγ), and isovector axion-nucleon (g3AN) couplings are obtained: |gAe×g3AN|≤5.5×10-13 and |gAγ×g3AN|≤4.6×10-11 GeV-1 at mA<1 MeV (90% confidence level). These limits are 2–4 orders of magnitude stronger than those obtained in previous laboratory-based experiments using nuclear reactors and accelerators.
Phys. Rev. D. 05/2012; 85(9).
-
D. Akimov,
T. Alexander,
D. Alton,
K. Arisaka,
H. O. Back,
P. Beltrame,
J. Benziger,
A. Bolozdynya,
G. Bonfini,
A. Brigatti, [......],
H. Wang,
S. Westerdale,
M. Wojcik,
A. Wright,
J. Xu,
C. Yang,
S. Zavatarelli,
M. Zehfus,
W. Zhong,
G. Zuzel
[show abstract]
[hide abstract]
ABSTRACT: As part of the DarkSide program of direct dark matter searches using liquid
argon TPCs, a prototype detector with an active volume containing 10 kg of
liquid argon, DarkSide-10, was built and operated underground in the Gran Sasso
National Laboratory in Italy. A critically important parameter for such devices
is the scintillation light yield, as photon statistics limits the rejection of
electron-recoil backgrounds by pulse shape discrimination. We have measured the
light yield of DarkSide-10 using the readily-identifiable full-absorption peaks
from gamma ray sources combined with single-photoelectron calibrations using
low-occupancy laser pulses. For gamma lines of energies in the range 122-1275
keV, we get consistent light yields averaging 8.887\pm0.003(stat)\pm0.444(sys)
p.e./keV_ee. With additional purification, the light yield measured at 511 keV
increased to 9.142\pm0.006(stat) p.e./keV_ee.
04/2012;
-
G. Bellini,
J. Benziger,
D. Bick,
G. Bonfini,
D. Bravo,
M. Buizza Avanzini,
B. Caccianiga,
L. Cadonati,
F. Calaprice,
C. Carraro, [......],
D. Vignaud,
R. B. Vogelaar,
J. Winter,
M. Wojcik,
A. Wright,
M. Wurm,
J. Xu,
O. Zaimidoroga,
S. Zavatarelli,
G. Zuzel
[show abstract]
[hide abstract]
ABSTRACT: We have measured the muon flux at the underground Gran Sasso National
Laboratory (3800 m w.e.) to be (3.41 \pm 0.01) \times 10-4m-2s-1 using four
years of Borexino data. A modulation of this signal is observed with a period
of (366\pm3) days and a relative amplitude of (1.29 \pm 0.07)%. The measured
phase is (179 \pm 6) days, corresponding to a maximum on the 28th of June.
Using the most complete atmospheric data models available, muon rate
fluctuations are shown to be positively correlated with atmospheric
temperature, with an effective coefficient {\alpha}T = 0.93 \pm 0.04. This
result represents the most precise study of the muon flux modulation for this
site and is in good agreement with expectations.
02/2012;
-
G Bellini,
J Benziger,
D Bick,
S Bonetti,
G Bonfini,
D Bravo,
M Buizza Avanzini,
B Caccianiga,
L Cadonati,
F Calaprice, [......],
R B Vogelaar,
F von Feilitzsch,
J Winter,
M Wojcik,
A Wright,
M Wurm,
J Xu,
O Zaimidoroga,
S Zavatarelli,
G Zuzel
[show abstract]
[hide abstract]
ABSTRACT: We observed, for the first time, solar neutrinos in the 1.0-1.5 MeV energy range. We determined the rate of pep solar neutrino interactions in Borexino to be 3.1±0.6{stat}±0.3{syst} counts/(day·100 ton). Assuming the pep neutrino flux predicted by the standard solar model, we obtained a constraint on the CNO solar neutrino interaction rate of <7.9 counts/(day·100 ton) (95% C.L.). The absence of the solar neutrino signal is disfavored at 99.97% C.L., while the absence of the pep signal is disfavored at 98% C.L. The necessary sensitivity was achieved by adopting data analysis techniques for the rejection of cosmogenic {11}C, the dominant background in the 1-2 MeV region. Assuming the Mikheyev-Smirnov-Wolfenstein large mixing angle solution to solar neutrino oscillations, these values correspond to solar neutrino fluxes of (1.6±0.3)×10{8} cm{-2} s^{-1} and <7.7×10{8} cm{-2} s{-1} (95% C.L.), respectively, in agreement with both the high and low metallicity standard solar models. These results represent the first direct evidence of the pep neutrino signal and the strongest constraint of the CNO solar neutrino flux to date.
Physical Review Letters 02/2012; 108(5):051302. · 7.37 Impact Factor
-
G Testera,
G Bellini,
J Benziger,
D Bick,
S Bonetti,
G Bonfini,
B Caccianiga,
L Cadonati,
F Calaprice,
C Carraro, [......], R Tartaglia,
D Vignaud,
R B Vogelaar,
F Feilitzsch,
J Winter,
M Wojcik,
M Wurm,
O Zaimidoroga,
S Zavatarelli,
G Zuzel
[show abstract]
[hide abstract]
ABSTRACT: We report the direct measurement of the Be-7 solar neutrino signal rate performed with the Borexino detector at the Laboratori Nazionali del Gran Sasso and the search for a day-night asymmetry of this interaction rate. The interaction rate of the 0.862 MeV Be-7 neutrinos is 46 +/- 1.6(stat)(-1.6)(+1.5)(syst) counts/(day . 100 ton). The hypothesis of no oscillation for this solar neutrinos is inconsistent with our measurement at the 5.8 sigma C.L Our result is the first direct measurement of solar neutrinos with an accuracy better than 5%. We report the survival probability for solar v(e) in the transition region between matter-enhanced and vacuum-driven oscillations. The measured day night asymmetry is A(dn) = 0.001 +/- 0.012 (stat) +/- 0.007 (syst), in agreement with the predicition of MSW-LMA neutrino [13] oscillations. This result discourages MSW oscillations with mixing parameters in the LOW region at more than 8.5 sigma, meaning that this region is, for the first time, strongly rejected without the assumption of CPT symmetry. The result can also be used to constrain some neutrino oscillation scenarios involving new physics. (C) 2012 Elsevier B.V. All rights reserved.
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/2012; 692:258-261. · 1.21 Impact Factor
-
G Bellini,
J Benziger,
D Bick,
S Bonetti,
G Bonfini,
Buizza M Avanzini,
B Caccianiga,
L Cadonati,
F Calaprice,
C Carraro, [......],
D Vignaud,
R B Vogelaar,
J Winter,
M Wojcik,
A Wright,
M Wurm,
J Xu,
O Zaimidoroga,
S Zavatarelli,
G Zuzel
[show abstract]
[hide abstract]
ABSTRACT: We report the result of a search for a day-night asymmetry in the Be-7 solar neutrino interaction rate in the Borexino detector at the Laboratori Nazionali del Gran Sasso (LNGS) in Italy. The measured asymmetry is A(dn) = 0.001 +/- 0.012 (stat) +/- 0.007 (syst), in agreement with the prediction of MSW-LMA solution for neutrino oscillations. This result disfavors MSW oscillations with mixing parameters in the LOW region at more than 8.5 sigma. This region is, for the first time, strongly disfavored without the use of reactor anti-neutrino data and therefore the assumption of CPT symmetry. The result can also be used to constrain some neutrino oscillation scenarios involving new physics. (C) 2011 Elsevier B.V. All rights reserved.
Physics Letters B 01/2012; 707(1):22-26. · 3.95 Impact Factor
-
G Bellini,
J Benziger,
D Bick,
S Bonetti,
G Bonfini,
M Buizza Avanzini,
B Caccianiga,
L Cadonati,
F Calaprice,
C Carraro, [......],
R B Vogelaar,
F von Feilitzsch,
J Winter,
M Wojcik,
A Wright,
M Wurm,
J Xu,
O Zaimidoroga,
S Zavatarelli,
G Zuzel
[show abstract]
[hide abstract]
ABSTRACT: The rate of neutrino-electron elastic scattering interactions from 862 keV (7)Be solar neutrinos in Borexino is determined to be 46.0±1.5(stat)(-1.6)(+1.5)(syst) counts/(day·100 ton). This corresponds to a ν(e)-equivalent (7)Be solar neutrino flux of (3.10±0.15)×10(9) cm(-2) s(-1) and, under the assumption of ν(e) transition to other active neutrino flavours, yields an electron neutrino survival probability of 0.51±0.07 at 862 keV. The no flavor change hypothesis is ruled out at 5.0 σ. A global solar neutrino analysis with free fluxes determines Φ(pp)=6.06(-0.06)(+0.02)×10(10) cm(-2) s(-1) and Φ(CNO)<1.3×10(9) cm(-2) s(-1) (95% C.L.). These results significantly improve the precision with which the Mikheyev-Smirnov-Wolfenstein large mixing angle neutrino oscillation model is experimentally tested at low energy.
Physical Review Letters 09/2011; 107(14):141302. · 7.37 Impact Factor
-
G Bellini,
J Benziger,
D Bick,
S Bonetti,
M Buizza Avanzini,
B Caccianiga,
L Cadonati,
F Calaprice,
C Carraro,
A Chavarria, [......],
D Vignaud,
R B Vogelaar,
J Winter,
M Wojcik,
A Wright,
M Wurm,
J Xu,
O Zaimidoroga,
S Zavatarelli,
G Zuzel
[show abstract]
[hide abstract]
ABSTRACT: Borexino, a liquid scintillator detector at LNGS, is designed for the detection of neutrinos and antineutrinos from the Sun, supernovae, nuclear reactors, and the Earth. The feeble nature of these signals requires a strong suppression of backgrounds below a few MeV. Very low intrinsic radiogenic contamination of all detector components needs to be accompanied by the efficient identification of muons and of muon-induced backgrounds. Muons produce unstable nuclei by spallation processes along their trajectory through the detector whose decays can mimic the expected signals; for isotopes with half-lives longer than a few seconds, the dead time induced by a muon-related veto becomes unacceptably long, unless its application can be restricted to a sub-volume along the muon track. Consequently, not only the identification of muons with very high efficiency but also a precise reconstruction of their tracks is of primary importance for the physics program of the experiment. The Borexino inner detector is surrounded by an outer water-Cherenkov detector that plays a fundamental role in accomplishing this task. The detector design principles and their implementation are described. The strategies adopted to identify muons are reviewed and their efficiency is evaluated. The overall muon veto efficiency is found to be 99.992 % or better. Ad-hoc track reconstruction algorithms developed are presented. Their performance is tested against muon events of known direction such as those from the CNGS neutrino beam, test tracks available from a dedicated External Muon Tracker and cosmic muons whose angular distribution reflects the local overburden profile. The achieved angular resolution is ~ 3°-5° and the lateral resolution is ~ 35-50 cm, depending on the impact parameter of the crossing muon. The methods implemented to efficiently tag cosmogenic neutrons are also presented.
Journal of Instrumentation 05/2011; 6(05):P05005. · 1.87 Impact Factor
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C Arpesella,
H O Back,
M Balata,
G Bellini,
J Benziger,
S Bonetti,
A Brigatti,
B Caccianiga,
L Cadonati,
F Calaprice, [......],
S Vitale,
R B Vogelaar,
F von Feilitzsch,
R von Hentig,
T von Hentig,
M Wojcik,
M Wurm,
O Zaimidoroga,
S Zavatarelli,
G Zuzel
[show abstract]
[hide abstract]
ABSTRACT: We report the direct measurement of the 7Be solar neutrino signal rate performed with the Borexino detector at the Laboratori Nazionali del Gran Sasso. The interaction rate of the 0.862 MeV 7Be neutrinos is 49+/-3stat+/-4syst counts/(day.100 ton). The hypothesis of no oscillation for 7Be solar neutrinos is inconsistent with our measurement at the 4sigma C.L. Our result is the first direct measurement of the survival probability for solar nu(e) in the transition region between matter-enhanced and vacuum-driven oscillations. The measurement improves the experimental determination of the flux of 7Be, pp, and CNO solar nu(e), and the limit on the effective neutrino magnetic moment using solar neutrinos.
Physical Review Letters 09/2008; 101(9):091302. · 7.37 Impact Factor
-
G Bellini,
J Benziger,
S Bonetti,
B Caccianiga,
F Calaprice,
F Dalnoki-Veress,
D D'Angelo,
H de Kerret,
A Derbin,
A Etenko, [......],
V Tarasenkov, R Tartaglia,
G Testera,
D Vignaud,
R B Vogelaar,
F von Feilitzsch,
M Wojcik,
O Zaimidoroga,
S Zavatarelli,
G Zuzel
[show abstract]
[hide abstract]
ABSTRACT: The Borexino experiment started the data taking may 15th 2007. It is until now the only experiment able to detect in real time neutrino interactions below 2 MeV. This is due to the very high radio-purity reached by the detector, more than one order of magnitude better than the goal of the design. The detector allows the single fluxes of low energy solar neutrinos to be determined from all sources not previously studied: 7Be, pep, CNO and hopefully pp. Here the first measurement of the 7Be, obtained from the first 47.6 live days of data taking, is presented.
Journal of Physics Conference Series 07/2008; 120(5):052006.
-
C Galbiati,
D Acosta-Kane,
R Acciarri,
O Amaize,
M Antonello,
B Baibussinov,
M B Ceolin,
C J Ballentine,
R Bansal,
L Basgall, [......],
E Segreto,
A Shirley,
A M Szelc, R Tartaglia,
T Tesileanu,
S Ventura,
C Vignoli,
C Visnjic,
R Vondrasek,
A Yushkov
[show abstract]
[hide abstract]
ABSTRACT: We report on the first measurement of 39Ar in argon from underground natural gas reservoirs. The gas stored in the US National Helium Reserve was found to contain a low level of 39Ar. The ratio of 39Ar to stable argon was found to be ≤4×10-17 (84% C.L.), less than 5% the value in atmospheric argon (39Ar/Ar=8×10-16). The total quantity of argon currently stored in the National Helium Reserve is estimated at 1000 tons. 39Ar represents one of the most important backgrounds in argon detectors for WIMP dark matter searches. The findings reported demonstrate the possibility of constructing large multi-ton argon detectors with low radioactivity suitable for WIMP dark matter searches.
Journal of Physics Conference Series 07/2008; 120(4):042015.
-
M Pallavicini,
G Bellini,
J Benziger,
S Bonetti,
B Caccianiga,
F Calaprice,
F Dalnoki-Veress,
D D'Angelo,
H de Kerret,
A Derbin, [......],
V Tarasenkov, R Tartaglia,
G Testera,
D Vignaud,
R B Vogelaar,
F von Feilitzsch,
M Wojcik,
O Zaimidoroga,
S Zavatarelli,
G Zuzel (on behalf of the Borexino Collaboration
[show abstract]
[hide abstract]
ABSTRACT: The Borexino experiment has begun data taking in May 2007 after a long R&D work and preparation. The liquid scintillator purity exceeds even optimistic expectations, and the first detection of 7Be solar neutrinos has been possible after less than two months of data taking. This note shows briefly which are the main issues that were addressed in order to obtain such an extreme radiopurity, the detector performance and a few details concerning this first result.
Journal of Physics Conference Series 07/2008; 120(5):052017.
-
D Acosta-Kane,
R Acciarri,
O Amaize,
M Antonello,
B Baibussinov,
M Baldo Ceolin,
C J Ballentine,
R Bansal,
L Basgall,
A Bazarko, [......],
E Segreto,
A Shirley,
A M Szelc, R Tartaglia,
T Tesileanu,
S Ventura,
C Vignoli,
C Visnjic,
R Vondrasek,
A Yushkov
[show abstract]
[hide abstract]
ABSTRACT: We report on the first measurement of 39 Ar in argon from underground natural gas reservoirs. The gas stored in the US National Helium Reserve was found to contain a low level of 39 Ar. The ratio of 39 Ar to stable argon was found to be ≤4×10 −17 (84% C.L.), less than 5% the value in atmospheric argon (39 Ar/Ar=8×10 −16). The total quantity of argon currently stored in the National Helium Reserve is estimated at 1000 tons. 39 Ar represents one of the most important backgrounds in argon detectors for WIMP dark matter searches. The findings reported demonstrate the possibility of constructing large multi-ton argon detectors with low radioactivity suitable for WIMP dark matter searches.
01/2008;
-
G. Bellini,
J. Benziger,
S. Bonetti,
B. Caccianiga,
F. Calaprice,
F. Dalnoki-Veress,
D. D’Angelo,
H. de Kerret,
A. Derbin,
A. Etenko, [......], R. Tartaglia,
G. Testera,
D. Vignaud,
F. von Feilitzsch,
R.B. Vogelaar,
M. Wojcik,
O. Zaimidoroga,
S. Zavatarelli,
G. Zuzel,
The Borexino Collaboration
[show abstract]
[hide abstract]
ABSTRACT: Results of background measurements with a prototype of the Borexino detector were used to search for 478 keV solar axions
emitted in the M1-transitions of 7Li*. The Compton conversion of axion to a photon A+e→e+γ, axioelectric effect A+e+Z→e+Z, decay of axion in two photons A→2γ and
Primakoff conversion on nuclei A+Z→γ+Z are considered. The upper limit on constants of interaction of axion with electrons,
photons and nucleons – gAegAN≤(1.0–2.4)×10-10 at mA≤450 keV and gAγgAN≤5×10-9 GeV-1 at mA≤10 keV are obtained (90%c.l.). For heavy axions with mass at 100<mA<400 keV the limits gAe<(0.7–2.0)×10-8 and gAγ<10-9–10-8 are obtained in assumption that gAN depends on mA as for KSVZ axion model. These limits are stronger than obtained in previous laboratory-based experiments using nuclear reactor
and artificial radioactive sources.
European Physical Journal C 01/2008; 54(1):61-72. · 3.63 Impact Factor
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H. Back,
M. Balata,
G. Bellini,
J. Benziger,
S. Bonetti,
B. Caccianiga,
F. Calaprice,
D. D'Angelo,
A. de Bellefon,
H. de Kerret, [......],
Y. Suvorov,
V. Tarasenkov, R. Tartaglia,
D. Vignaud,
R. B. Vogelaar,
F. Von Feilitzsch,
V. Vyrodov,
M. Wójcik,
O. Zaimidoroga,
G. Zuzel
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ABSTRACT: Borexino is an experiment for low-energy neutrino spectroscopy at the Gran Sasso underground laboratories. It is designed to measure the monoenergetic 7Be solar neutrino flux in real time, via neutrino-electron elastic scattering in an ultrapure organic liquid scintillator. Borexino has the potential to also detect neutrinos from the pep fusion process and the CNO cycle. For this measurement to be possible, radioactive contamination in the detector must be kept extremely low. Once sufficiently clean conditions are met, the main background source is 11C, produced in reactions induced by the residual cosmic muon flux on 12C. In the process, a free neutron is almost always produced. 11C can be tagged on an event-by-event basis by looking at the threefold coincidence with the parent muon track and the subsequent neutron capture on protons. This coincidence method has been implemented on the Borexino Counting Test Facility data. We report on the first event-by-event identification of in situ muon-induced 11C in a large underground scintillator detector. We measure a 11C production rate of 0.130 ± 0.026(stat) ± 0.014(syst) day-1 ton-1, in agreement with predictions from both experimental studies performed with a muon beam on a scintillator target and ab initio estimations based on the 11C producing nuclear reactions.
Phys. Rev. C. 10/2006; 74(4).
