Methods and problems in low energy neutrino experiments (solar, reactors, geo-) I G. Ranucci ISAPP 2011 International School on Astroparticle physics THE NEUTRINO PHYSICS AND ASTROPHYSICS July 26th - August 5th, 2011 Varenna - Italy Summary of the topics -Neutrino detection overview -Radiochemical methodology -Scintillation methods -Cerenkov approach -Low background implications in low energy neutrino search With examples of applications taken from experiments and geo-neutrinos (anti-ν)ν)ν) (not discussed here) fundamental Neutrino production in the Sun In our star > 99% of the energy is created in this reaction The pp chain reaction The CNO cycle In the Sun < 1% More important in heavier stars There are different steps in which energy (and neutrinos) are produced pp ν νν from: Monocrhomatic ν’s (2 bodies in the final state) pp pep CNO ννν from: 7Be 13 N 8B 15 O hep 17 F Rome - 3 July, 2009 Gioacchino Ranucci - I.N.F.N. Sez. di Milano Neutrino production in the Sun Neutrino energy spectrum as predicted by the Solar Standard Model (SSM) John Norris Bahcall (Dec. 30 , 1934 – Aug. 17 , 2005 ) 7Be: 384 keV (10%) 862 keV (90%) Pep: 1.44 MeV Rome - 3 July, 2009 Gioacchino Ranucci - I.N.F.N. Sez. di Milano Solar neutrino experiments: a more than four decades long saga Radiochemical experiments Homestake (Cl) Gallex/GNO (Ga) Sage (Ga) Real time Cherenkov experiments Kamiokande/Super-Kamiokande SNO Scintillator experiments Borexino Rome - 3 July, 2009 Gioacchino Ranucci - I.N.F.N. Sez. di Milano This is equivalent to find a needle in a haystack Triple strategy Selection of construction materials Pulse shape analysis to reject background pulses Calibrations of the instruments Output (measured neutrino flux) of the Gallex/GNO and Sage experiments compared to the model prediction Important part of the overall methodology: global calibration with a 51 Cr neutrino source Icecube Antares Nemo 1 The angle is cos θ = βn 1 The spectrum has a dependence λ2 Cerenkov light is produced in a pool reactor where the core is submerged in water (Sudbury Neutrino Observatory) νννµ and ννντττ has employed Third phase: helium 3 proportional counters deployed in the detector mainly to cross check results of phase 2 Summary of Signatures in SNO (D 2O) Charged-Current (CC) ν → - e+d e +p+p Ethresh = 1.4 MeV νν ee only Neutral-Current (NC) ν → ν x+d x+n+p 3 ways to Ethresh = 2.2 MeV detect neutrons νν νν νν Equally sensitive to e µµ ττ Elastic Scattering (ES) (D 2O & H 2O) ν - → ν - x+e x+e ν ν x, but enhanced for e Events point away from the sun. The Sudbury Neutrino Observatory: SNO 6800 feet (~2km) underground Acrylic vessel (AV) 12 m diameter 1000 tonnes D 2O ($300 million) 1700 tonnes H 2O inner shielding Creighton mine 5300 tonnes H 2O Sudbury, CA outer shielding - Entire detector Built as a Class 2000 ~9500 PMT’s Clean room - Low Radioactivity Detector materials The heavy water has been returned and development work is in progress on SNO+ with liquid scintillator and 150 Nd additive. An example of a cerenkov event Accurate measurement of physics processes in the SNO detector requires a chain of calibrations and calculations to link the photomultiplier data to a full description of the interaction in terms of energy, direction, and particle type Sources deployed everywhere in the detector volume Three Phases of SNO 3 Pure D 2O Salt He Counters Nov 99 – May 01 Jul 01 – Sep 03 Nov 04 – Nov 06 n + d → t + γ n + 35 Cl → 36 Cl + Σγ n + 3He → t + p (E γ = 6.25 MeV) (E Σγ = 8.6 MeV) proportional counters SNO+ σ = 5330 b enhanced NC rate and PRL 87 , 071301 (2001) separation event-by-event PRL 89 , 011301 (2002) separation PRL 89 , 011302 (2002) PRL 92 , 181301 (2004) PRC 75 , 045502 (2007) PRC 72 , 055502 (2005) PRL 101 , 111301 (2008) archival papers with complete details Gioacchino Ranucci - Rome - 3 July, 2009 I.N.F.N. Sez. di Milano Results of the 3 Phases stat stat + syst Art MacDonald@Neutel 2009 p-value for consistency of NC/CC/ES in the salt & NCD phases + D2O NC(unconstr) is 32.8% Rome - 3 July, 2009 Gioacchino Ranucci - I.N.F.N. Sez. di Milano The two outputs (measured neutrino flux) of the SNO experiment compared to the model prediction For general information The NC and CC measurements from SNO together with the other solar (and KamLAND) experiments proved to be pivotal to determine the values of the oscillation parameters Detection via νννe scattering as third Other example detection method of Cerenkov in SNO detector Background level SuperSuper--KamiokandeKamiokande History inner detector mass: 32kton fiducial mass: 22.5kton 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 SK-I SK-II SK-III SK-IV SK-I Acrylic (front) SK-II SK-III SK-IV + FRP (back) 11146 ID PMTs 5182 ID PMTs 11129 ID PMTs Electronics (40% coverage) (19% coverage) (40% coverage) Upgrade Energy Threshold 5.0 MeV 7.0 MeV 4.5 MeV < 4.0 MeV (total electron energy) work in progress target Background issues 5.0-5.5MeV 5.5-6.0MeV SK-I SK -III -1 0 1 θθθ cos sun 6.0-6.5MeV Fiducial volume is central 13.3kt SK has lower background level in these central 13.3kt throughout the years of operation The two outputs (measured neutrino flux) of Kamiokande/Superkamiokande compared to the model prediction and SNO+ (planned) π Delocalized molecular orbital α β Some examples of scintillator based detectors Borexino (low energy solar neutrino detector) described in the following at length as paradigmatic example of a scscintillatorintillator detector Chooz (reactor neutrino detector) KamLAND (reactor neutrino detector) Planned: SNO+ and LENS.