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The Gran Sasso muon puzzle  [PDF]
Enrique Fernandez-Martinez,Rakhi Mahbubani
Physics , 2012, DOI: 10.1088/1475-7516/2012/07/029
Abstract: We carry out a time-series analysis of the combined data from three experiments measuring the cosmic muon flux at the Gran Sasso laboratory, at a depth of 3800 m.w.e. These data, taken by the MACRO, LVD and Borexino experiments, span a period of over 20 years, and correspond to muons with a threshold energy, at sea level, of around 1.3 TeV. We compare the best-fit period and phase of the full muon data set with the combined DAMA/NaI and DAMA/LIBRA data, which spans the same time period, as a test of the hypothesis that the cosmic ray muon flux is responsible for the annual modulation detected by DAMA. We find in the muon data a large-amplitude fluctuation with a period of around one year, and a phase that is incompatible with that of the DAMA modulation at 5.2 sigmas. Aside from this annual variation, the muon data also contains a further significant modulation with a period between 10 and 11 years and a power well above the 99.9% C.L threshold for noise, whose phase corresponds well with the solar cycle: a surprising observation for such high energy muons. We see no corresponding long-period oscillation in the stratospheric temperature data.
Cosmogenic Backgrounds in Borexino at 3800 m water-equivalent depth  [PDF]
G. Bellini,J. Benziger,D. Bick,G. Bonfini,D. Bravo,M. Buizza Avanzini,B. Caccianiga,L. Cadonati,F. Calaprice,P. Cavalcante,A. Chavarria,A. Chepurnov,D. D'Angelo,S. Davini,A. Derbin,A. Empl,A. Etenko,K. Fomenko,D. Franco,C. Galbiati,S. Gazzana,C. Ghiano,M. Giammarchi,M. G?ger-Neff,A. Goretti,L. Grandi,C. Hagner,E. Hungerford,Aldo Ianni,Andrea Ianni,V. Kobychev,D. Korablev,G. Korga,D. Kryn,M. Laubenstein,T. Lewke,E. Litvinovich,B. Loer,P. Lombardi,F. Lombardi,L. Ludhova,G. Lukyanchenko,I. Machulin,S. Manecki,W. Maneschg,G. Manuzio,Q. Meindl,E. Meroni,L. Miramonti,M. Misiaszek,R. M?llenberg,P. Mosteiro,V. Muratova,L. Oberauer,M. Obolensky,F. Ortica,K. Otis,M. Pallavicini,L. Papp,L. Perasso,S. Perasso,A. Pocar,G. Ranucci,A. Razeto,A. Re,A. Romani,N. Rossi,R. Saldanha,C. Salvo,S. Sch?nert,H. Simgen,M. Skorokhvatov,O. Smirnov,A. Sotnikov,S. Sukhotin,Y. Suvorov,R. Tartaglia,G. Testera,D. Vignaud,R. B. Vogelaar,F. von Feilitzsch,J. Winter,M. Wojcik,A. Wright,M. Wurm,J. Xu,O. Zaimidoroga,S. Zavatarelli,G. Zuzel
Physics , 2013, DOI: 10.1088/1475-7516/2013/08/049
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.
Seasonal modulation in the Borexino cosmic muon signal  [PDF]
Davide D'Angelo,for the Borexino Collaboration
Physics , 2011, DOI: 10.7529/ICRC2011/V04/0510
Abstract: Borexino is an organic liquid scintillator detector located in the underground Gran Sasso National Laboratory (Italy). It is devoted mainly to the real time spectroscopy of low energy solar neutrinos via the elastic scattering on electrons in the target mass. The data taking campaign started in 2007 and led to key measurements of 7}Be and 8B solar neutrinos as well as antineutrinos from the earth (geo-neutrinos) and from nuclear power reactors. Borexino is also a powerful tool for the study of cosmic muons that penetrate the Gran Sasso rock coverage and thereby induced signals such as neutrons and radioactive isotopes which are today of critical importance for upcoming dark matter and neutrino physics experiments. Having reached 4y of continuous data taking we analyze here the muon signal and its possible modulation. The muon flux is measured to be (3.41+-0.01)E-4/m2/s. A modulation of this signal with a yearly period is observed with an amplitude of (1.29+-0.07)% and a phase of (179+-6) d, corresponding to June 28th. Muon rate fluctuations are compared to fluctuations in the atmospheric temperature on a daily base, exploiting the most complete atmospheric data and models available. The distributions are shown to be positively correlated and the effective temperature coefficient is measured to be alpha_T = 0.93 +- 0.04. This result is in good agreement with the expectations of the kaon-inclusive model at the laboratory site and represents an improvement over previous measurements performed at the same depth.
Muon and Cosmogenic Neutron Detection in Borexino  [PDF]
Borexino Collaboration,G. Bellini,J. Benziger,D. Bick,S. Bonetti,M. Buizza Avanzini,B. Caccianiga,L. Cadonati,F. Calaprice,C. Carraro,A. Chavarria,A. Chepurnov,D. D'Angelo,S. Davini,A. Derbin,A. Etenko,F. von Feilitzsch,K. Fomenko,D. Franco,C. Galbiati,S. Gazzana,C. Ghiano,M. Giammarchi,M. Goeger-Neff,A. Goretti,E. Guardincerri,S. Hardy,Aldo Ianni,Andrea Ianni,M. Joyce,V. Kobychev,Y. Koshio,D. Korablev,G. Korga,D. Kryn,M. Laubenstein,C. Lendvai,T. Lewke,E. Litvinovich,B. Loer,F. Lombardi,P. Lombardi,L. Ludhova,I. Machulin,S. Manecki,W. Maneschg,G. Manuzio,Q. Meindl,E. Meroni,L. Miramonti,M. Misiaszek,D. Montanari,V. Muratova,L. Oberauer,M. Obolensky,F. Ortica,M. Pallavicini,L. Papp,L. Perasso,S. Perasso,A. Pocar,R. S. Raghavan,G. Ranucci,A. Razeto,A. Re,A. Romani,D. Rountree,A. Sabelnikov,R. Saldanha,C. Salvo,S. Sch?nert,H. Simgen,M. Skorokhvatov,O. Smirnov,A. Sotnikov,S. Sukhotin,Y. Suvorov,R. Tartaglia,G. Testera,D. Vignaud,R. B. Vogelaar,J. Winter,M. Wojcik,A. Wright,M. Wurm,J. Xu,O. Zaimidoroga,S. Zavatarelli,G. Zuzel
Physics , 2011, DOI: 10.1088/1748-0221/6/05/P05005
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 deg 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.
Measurement of CNGS muon neutrino speed with Borexino  [PDF]
Borexino Collaboration
Physics , 2012, DOI: 10.1016/j.physletb.2012.08.052
Abstract: We have measured the speed of muon neutrinos with the Borexino detector using short-bunch CNGS beams. The final result for the difference in time-of-flight between a =17 GeV muon neutrino and a particle moving at the speed of light in vacuum is {\delta}t = 0.8 \pm 0.7stat \pm 2.9sys ns, well consistent with zero.
Borexino  [PDF]
Lino Miramonti
Physics , 2006,
Abstract: Borexino is a massive calorimetric liquid scintillation detector whose installation has been completed in the underground Gran Sasso Laboratory. The focus of the experiment is on the direct and real time measurement of the flux of neutrinos produced in the $^{7}Be$ electron capture reaction in the Sun. Furthermore, recent studies about the reduction of the $^{11}C$ background through suitable rejection techniques demonstrated the possibility to open an interesting additional observation window in the energy region of the pep and CNO solar neutrinos. Beyond the solar neutrino program, the detector will be also a powerful observatory for antineutrinos from Supernovae, as well as for geoneutrinos, profiting from a very low background from nuclear reactors.
Geoneutrinos in Borexino  [PDF]
Marco G. Giammarchi,Lino Miramonti
Physics , 2006, DOI: 10.1007/s11038-006-9106-6
Abstract: This paper describes the Borexino detector and the high-radiopurity studies and tests that are integral part of the Borexino technology and development. The application of Borexino to the detection and studies of geoneutrinos is discussed.
CNO and pep neutrino spectroscopy in Borexino: Measurement of the deep underground production of cosmogenic 11C in organic liquid scintillator  [PDF]
Borexino Collaboration
Statistics , 2006, DOI: 10.1103/PhysRevC.74.045805
Abstract: Borexino is an experiment for low energy neutrino spectroscopy at the Gran Sasso underground laboratories. It is designed to measure the mono-energetic $^7$Be solar neutrino flux in real time, via neutrino-electron elastic scattering in ultra-pure organic liquid scintillator. Borexino has the potential to also detect neutrinos from the \emph{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 $^{11}$C, produced in reactions induced by the residual cosmic muon flux on $^{12}$C. In the process, a free neutron is almost always produced. $^{11}$C can be tagged on an event by event basis by looking at the three-fold 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 \emph{in situ} muon induced $^{11}$C in a large underground scintillator detector. We measure a $^{11}$C production rate of 0.130 $\pm$ 0.026 (stat) $\pm$ 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 \emph{ab initio} estimations based on the $^{11}$C producing nuclear reactions.
Measurement of Muon Annual Modulation and Muon-Induced Phosphorescence in NaI(Tl) Crystals with DM-Ice17  [PDF]
DM-Ice Collaboration,:,J. Cherwinka,D. Grant,F. Halzen,K. M. Heeger,L. Hsu,A. J. F. Hubbard,A. Karle,M. Kauer,V. A. Kudryavtsev,K. E. Lim,C. Macdonald,R. H. Maruyama,S. Paling,W. Pettus,Z. P. Pierpoint,B. N. Reilly,M. Robinson,P. Sandstrom,N. J. C. Spooner,S. Telfer,L. Yang
Physics , 2015,
Abstract: We report the measurement of muons and muon-induced phosphorescence in DM-Ice17, a NaI(Tl) direct detection dark matter experiment at the South Pole. Muons are identified by the observed pulse shape and large energy deposition of their interaction in the crystals. The measured muon rate in DM-Ice17 is 2.93 +/- 0.04 muons/crystal/day with a modulation amplitude of 12.3 +/- 1.7%, consistent with expectation. Following muon interactions, we observe long-lived phosphorescence in the NaI(Tl) crystals with a decay time of 5.5 +/- 0.5 s. The prompt energy deposited by a muon is correlated to the amount of delayed phosphorescence, the brightest of which consist of tens of millions of photons. As they are distributed over tens of seconds, the rate and timing structure of photon arrivals do not mimic a scintillation signal above 2 keVee. While the properties of phosphorescence vary between individual crystals, the annually-modulating signal observed by DAMA cannot be accounted for by phosphorescence with the characteristics observed in DM-Ice17.
Observation of seasonal variation of atmospheric multiple-muon events in the MINOS Near and Far Detectors  [PDF]
P. Adamson,I. Anghel,A. Aurisano,G. Barr,M. Bishai,A. Blake,G. J. Bock,D. Bogert,S. V. Cao,C. M. Castromonte,S. Childress,J. A. B. Coelho,L. Corwin,. D. Cronin-Hennessy,J. K. de Jong,A. V. Devan,N. E. Devenish,M. V. Diwan,C. O. Escobar,J. J. Evans,E. Falk,G. J. Feldman,M. V. Frohne,H. R. Gallagher,R. A. Gomes,M. C. Goodman,P. Gouffon,N. Graf,R. Gran,K. Grzelak,A. Habig,S. R. Hahn,J. Hartnell,R. Hatcher,A. Holin,J. Huang,J. Hylen,G. M. Irwin,Z. Isvan,C. James,D. Jensen,T. Kafka,S. M. S. Kasahara,G. Koizumi,M. Kordosky,A. Kreymer,K. Lang,J. Ling,P. J. Litchfield,P. Lucas,W. A. Mann,M. L. Marshak,N. Mayer,C. McGivern,M. M. Medeiros,R. Mehdiyev,J. R. Meier,M. D. Messier,W. H. Miller,S. R. Mishra,S. Moed Sher,C. D. Moore,L. Mualem,J. Musser,D. Naples,J. K. Nelson,H. B. Newman,R. J. Nichol,J. A. Nowak,J. O. Connor,M. Orchanian,S. Osprey,R. B. Pahlka,J. Paley,R. B. Patterson,G. Pawloski,A. Perch,S. Phan-Budd,R. K. Plunkett,N. Poonthottathil,X. Qiu,A. Radovic,B. Rebel,C. Rosenfeld,H. A. Rubin,M. C. Sanchez,J. Schneps,A. Schreckenberger,P. Schreiner,R. Sharma,A. Sousa,N. Tagg,R. L. Talaga,J. Thomas,M. A. Thomson,X. Tian,A. Timmons,S. C. Tognini,R. Toner,D. Torretta,J. Urheim,P. Vahle,B. Viren,A. Weber,R. C. Webb,C. White,L. Whitehead,L. H. Whitehead,S. G. Wojcicki,R. Zwaska
Physics , 2015, DOI: 10.1103/PhysRevD.91.112006
Abstract: We report the first observation of seasonal modulations in the rates of cosmic ray multiple-muon events at two underground sites, the MINOS Near Detector with an overburden of 225 mwe, and the MINOS Far Detector site at 2100 mwe. At the deeper site, multiple-muon events with muons separated by more than 8 m exhibit a seasonal rate that peaks during the summer, similar to that of single-muon events. In contrast and unexpectedly, the rate of multiple-muon events with muons separated by less than 5-8 m, and the rate of multiple-muon events in the smaller, shallower Near Detector, exhibit a seasonal rate modulation that peaks in the winter.
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