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