Methods and problems in low energy neutrino experiments (solar, reactors, geo-)

I

G. Ranucci

ISAPP 2011International School on Astroparticle physics

THE NEUTRINO PHYSICS AND ASTROPHYSICS

July 26th - August 5th, 2011Varenna - 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- )n

(not discussed here)

fundamental

Rome - 3 July, 2009 Gioacchino Ranucci - I.N.F.N. Sez. di Milano

Neutrino production in the Sun

pp

from: pp

pep 7Be 8B

hep

The pp chain reactionThe CNO cycle

There are different steps in which energy (and neutrinos) are produced

Monocrhomatic ν’s(2 bodies in the final state)

In our star > 99% of the energy is created in this reaction

In the Sun < 1% More important in heavier stars

CNO from: 13N 15O 17F

Rome - 3 July, 2009 Gioacchino Ranucci - I.N.F.N. Sez. di Milano

Neutrino production in the Sun

Neutrino energy spectrum as predicted bythe 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

This is equivalent to find a needle in a haystack

Selection of construction materials

Triple strategy

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 51Cr neutrino source

IcecubeAntaresNemo

The angle is n

1cos

The spectrum has a dependence 21

Cerenkov light is produced in a pool reactor where the core is submerged in water

(Sudbury Neutrino Observatory)

n m and nt

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 (D2O)

Charged-Current (CC)e+d e-+p+pEthresh = 1.4 MeV

e only

Elastic Scattering (ES) (D2O & H2O)x+e- x+e-

x, but enhanced for e Events point away from the sun.

Neutral-Current (NC) x+d x+n+p Ethresh = 2.2 MeV

Equally sensitive to e nm t

3 ways todetect neutrons

Acrylic vessel (AV) 12 m diameter

1700 tonnes H2O inner shielding

1000 tonnes D2O($300 million)

5300 tonnes H2O outer shielding

~9500 PMT’s

Creighton mineSudbury, CA

The Sudbury Neutrino Observatory: SNO6800 feet (~2km) underground

The heavy water has been returned and development work is in progress on SNO+ with liquid scintillator and 150Nd additive.

- Entire detectorBuilt as a Class 2000

Clean room- Low RadioactivityDetector materials

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 typeSources deployed everywhere in the detector volume

Gioacchino Ranucci - I.N.F.N. Sez. di Milano

Rome - 3 July, 2009

3He CountersNov 04 – Nov 06

n 3He t p

proportional counters s = 5330 b

event-by-event separation

PRL 101, 111301 (2008)

Pure D2O

Nov 99 – May 01

n d t g

(Eg = 6.25 MeV)

PRL 87, 071301 (2001)

PRL 89, 011301 (2002)

PRL 89, 011302 (2002)

PRC 75, 045502 (2007)

SaltJul 01 – Sep 03

n 35Cl 36Cl g

(Eg = 8.6 MeV)

enhanced NC rate and separation

PRL 92, 181301 (2004)

PRC 72, 055502 (2005)

Three Phases of SNO

archival papers with complete details

SNO+

stat stat + systResults of the 3 Phases

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

Art MacDonald@Neutel 2009

The two outputs (measured neutrino flux) of the SNO experiment compared to the model prediction

For general informationThe 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

Other example of Cerenkov detector

Detection via ne scattering as third detection method in SNO

Background level

Super-Kamiokande History

11146 ID PMTs(40% coverage)

5182 ID PMTs(19% coverage)

11129 ID PMTs(40% coverage)

EnergyThreshold(total electron energy)

1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009

SK-I SK-II SK-III SK-IV

Acrylic (front)+ FRP (back)

ElectronicsUpgrade

SK-I SK-II SK-III SK-IV

5.0 MeV 7.0 MeV 4.5 MeVwork in progress

< 4.0 MeVtarget

inner detector mass: 32kton fiducial mass: 22.5kton

Background issues5.0-5.5MeV 5.5-6.0MeV

6.0-6.5MeVFiducial volume is central 13.3ktSK has lower background level

in these central 13.3kt throughout the years of operation

SK-ISK-III

cosqsun

1-1 0

The two outputs (measured neutrino flux) of Kamiokande/Superkamiokande compared to the model prediction

and SNO+ (planned)

p

Delocalized molecular orbital

a

b

Some examples of scintillator based detectors

Borexino (low energy solar neutrino detector) described in the following at length as paradigmatic example of a scintillator detector

Chooz (reactor neutrino detector)

KamLAND (reactor neutrino detector)

Planned: SNO+ and LENS