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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;
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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;
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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;
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J. Xu,
F. Calaprice,
C. Galbiati,
A. Goretti,
G. Guray,
T. Hohman,
D. Holtz,
A. Ianni,
M. Laubenstein,
B. Loer,
C. Love,
C. J. Martoff,
D. Montanari,
S. Mukhopadhyay,
A. Nelson,
S. D. Rountree,
R. B. Vogelaar, A. Wright
[show abstract]
[hide abstract]
ABSTRACT: The discovery of argon from underground sources with significantly less 39Ar
than atmospheric argon was an important step in the development of
direct-detection dark matter experiments using argon as the active target. We
report on the design and operation of a low background detector with a single
phase liquid argon target that was built to study the 39Ar content of the
underground argon. Underground argon from the Kinder Morgan CO2 plant in
Cortez, Colorado was determined to have less than 0.65% of the 39Ar activity in
atmospheric argon.
04/2012;
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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;
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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
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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
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G. Bellini,
J. Benziger,
S. Bonetti,
M. Buizza Avanzini,
B. Caccianiga,
L. Cadonati,
F. Calaprice,
C. Carraro,
A. Chavarria,
F. Dalnoki-Veress, [......],
R. B. Vogelaar,
F. von Feilitzsch,
J Winter,
M. Wojcik, A. Wright,
M. Wurm,
J Xu,
O. Zaimidoroga,
S. Zavatarelli,
G. Zuzel
Physical Review D, v.82, 1-10 (2010).
-
M. Misiaszek,
G. Bellini,
J. Benziger,
S. Bonetti,
M. B. Avanzini,
B. Caccianiga,
L. Cadonati,
F. Calaprice,
C. Carraro,
A. Chavarria, [......],
R. B. Vogelaar,
F. von Feilitzsch,
J Winter,
M. Wojcik, A. Wright,
M. Wurm,
J. Xun,
O. Zaimidoroga,
S. Zavatarelli,
G. Zuzel
Acta Physica Polonika B, v.41, 1603-1609 (2010).
-
G. Bellini,
J. Benziger,
S. Bonetti,
M. Buizza Avanzini,
B. Caccianiga,
L. Cadonati,
F. Calaprice,
C. Carraro,
A. Chavarria,
A. Chepurnov, [......],
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 report the measurement of ν-e elastic scattering from 8B solar neutrinos with 3 MeV energy threshold by the Borexino detector in Gran Sasso (Italy). The rate of solar neutrino-induced electron scattering events above this energy in Borexino is 0.22±0.04(stat)±0.01(syst) cpd/100 t, which corresponds to Φ8BES=2.4±0.4±0.1×106 cm-2 s-1, in good agreement with measurements from SNO and SuperKamiokaNDE. Assuming the 8B neutrino flux predicted by the high metallicity standard solar model, the average 8B νe survival probability above 3 MeV is measured to be 0.29±0.10. The survival probabilities for 7Be and 8B neutrinos as measured by Borexino differ by 1.9σ. These results are consistent with the prediction of the MSW-LMA solution of a transition in the solar νe survival probability Pee between the low-energy vacuum-driven and the high-energy matter-enhanced solar neutrino oscillation regimes.
Phys. Rev. D. 82(3).
