BELLINI

BOREXINO

Breakthrough in Low Energy Neutrinos

R. S. Raghavan

Virginia Tech Milano, March 23 2009

SSM Prediction

Directly measured so far

Directly

measuredThe New Frontier

SSM Prediction

Directly measured so far

Directly

measuredThe New Frontier

SSM: 4 p 4He

I: p+pd+ e+ + νe (0-0.42 MeV)

II. 7Be 7Li + νe (o.862 MeV)

III 8B 2α + e- + νe (0-15 MeV)

Direct Measurements--only 8B

Kamiokande, SK, SNO

1988—BOREX –NUEX in 11B

1991-Proposal for 7Be

BOREXINO

1976 Proposal for pp

LENS

Borexino LENS

SNO

SK

Radioactivity WAll

BEFORE BOREXINO: After Ga and Kam I B8 nus found: but no Be if SSM holds~~Paradox —What is the matter with Be in Sun?

Radiochemical NOT enough—

Need LO Energy Spectroscopy!

SN in the 1990’s

More intrinsic Motivation for 7Be

•Backbone of the pp chain

•Text book case for nu oscillations

But Be is well below the Radioactivity Wall:

Urgent problem to breakthrough the Wall

Basic Reaction: Nu-electron scattering

νx + e νx + e

Flavor mixed Electron in

Scintillator Recoil Electron

SIGNAL !

BUT: Spectral Signature: Distinct Compton Edge

for monochromatic neutrinos from 7 Be and pep

( see arrows in Fig). No edge for continua.

Background at low energies due to all

sources must be suppressed well below the

solar signal ! Major assests for Be

, Signal Rate, Monoenergetic Nuspectral

Signature—Seasonal Variation from Orbital

eccentricity

Ultrapurity and ultra-low contamination

- U,Th < 10-16 g/g; 14C< 10-18 g/g

Laboratory scale purity data not enough

CTF –5 ton scle

Signal carries NO TAG !!

Detection Method

1988 --Start Borex Project

Start Chemistry of Ultrapurity in Bell Labs

May 1988 First Borex collaboration meeting at Bell Lab-with Blessing of

Arno Penzias

1989—Discovery of ultra-low solubility (~10-17 g/g) of U, Th

in organic liquids ----Antonio di Bari & RSR

Ultrapurification of 100 L –10-15 g/g—Volterra Expt –Radiocarbon—106 depletion needed—only possibility petrochemicals

-Demonstrate that 14C in Natural Gas petrochemical 14C/12C < 10-18

First EvidenceAccc. Mass Spec measurement—Bell Labs+ Univ. Toronto

3 MeV radioacivity WALL broken through for LE neutrinos--

Go for 7Be instead of 8B ( ―test‖ phase of BOREX Borexino! )

Need only a ―small‖ detector~100 tons BOREXINO—little Borex

-1992-- Sufficient experimental data for proposal for CTF (Counting Test Facility

as pre-test for BOREXINO

BOREXBOREXINO

Change of Focus: 8B 7Be

CTF Major Goals:

Dress Rehearsal of OBSERVABLE ultra-purity & low energy

spectroscopyin ton-scale scintillation detector —never done before

Intrinsic sources — Contamination of migrating sources

Bgd from external sources, PMT’s, detector materials, rock, neutrons-----

Spectroscopy at low and v. low energies (--20 keV )

Stability of operations—energy, spatial resolution

Removal of Alphas from actinides even at high purity

via pulse shape spectroscopy

alphas

electrons

Polonium, Krypton—

The “last” obstacles exposed by the CTF

not foreseen In earlier design considerations

Po: Reduced by strict avoidance of

Radon—extreme airtightness

meticulous Cleaning of Rn daughters

—Still not completely solved but

Only minimized enough for seeing Be because

of superior energy resolution and alpha-beta

discrimination

Kr: airtightness <10-8 bar cm3 s-1 Use Very Low Argon Krypton Nitrogen --LAKN—

for all purification, liquid handling etc.

Ar: 0.01 ppm in Nitrogen

Kr: 0.02 ppt in Nitrogen

High Purity Nitrogen:

222Rn < 0.3 μBq/m3

Taken From:

Solar Neutrinos—

From puzzle to

Paradox

Review by

RSR Science ’95

Discussing

―where have all Be

in the sun GONE?

(Became folk song)

Burning question

After Gallex resul:

Imperative to directly

measure Be7

Picture of CTF detector

CTF RESULTS—Major Success

U/Th ~10--16 g/g

C14 <2x10-18 /C12

Energy Resolution Satisfactory and Expected by Monte Carlo

Spectroscopy down to 20 keV—C14 beta (E<156 keV) spectral shape

Vast experience in radon control, contamination pathways …..

CTF taught us every thing and more

Discovered unforeseen sources of contaminants

Po: Reduced by strict avoidance of

Radon—extreme airtightnessmeticulous cleaning of Rn daughters

—Still not completely solved but

Only minimized enough for seeing Be because

of superior energy resolution and alpha-beta discrimination

Kr: airtightness <10-8 bar cm3 s-1

Use Very Low Argon Krypton Nitrogen --LAKN—

for all purification, liquid handling etc.

Then the roof fell in.

Small release of scintillator liquid into outside stream

Environmental emergency

Experiment quarantined for 3 years for installation of

Safety measures by National Agencies and Tunnel

Authorities

Collaboratioin showed extraordinary strength and

Continued together ---

On to Borexino experiment

Science Problem Recognized ultrapurity

Practical Detector Next ultra- Engineering

Magical Mystery Tour of Borexino Engineering

First Technical Breakthrough—Concept to Reality of Scintillator Containment

Try out of Bxino Nylon vessels in Palmer Stadium, Princeton

Borexino Full !

The starting point:

no cut spectrum

14C dominates

below 200 KeV

210Po NOT in

eq. with 210Pb

Mainly external

γs and cosmos

After muon cut

Clear 7Be shoulder

After

FV cuts

β’s α’s

C11 (cosmo)?

Po alphas

Be Be

Analysis-crucial role of spectroscopic power

Po

Po removed

by α-β disc.

Kr

Bi210+CNO

7Be ν Rate:

192 days

Rate consistent with Standard Solar

and MSW-LMA Nu oscillation models

Expect to reduce the systematic

error (Mainly from determination

of Fiducial Mass) via Source

Calibration of Detector (VT led)

49±3stat±4syst counts/(d·100 t).

Solar Neutrinos

Improve statistical precision (and reduce systematics

Aim5% precision of flux 3% hopefully finally

Clean up C-11 Cosmogenic events by neutron tagging

Wait for Po decay (2 years 6 half lives)

New Data on pep neutrinos (variant of pp neutrinos)

CNO in the sun—Discovery experiment on Chemical

composition of light elements in the sun

Solve current mystery

Get Be-7 nu flux to 5%3%?

CNO flux to ~10-15%

pep nu flux to 15%?

Recent analysis shows that the sun

may have 30-50% LESS C, N, O….

Opacities changed, Fluxes changed

significantly

Above all agreement with

helioseismology destroyed.

Crisis===Solution—Measure CNO

flux

Borexino, LENS

The New Solar Neutrino Problem!—

C, N, O in the Sun?

1. Non-standard Weak Interactions

Look at the Recoil Electron Profile

The shape as used so far is the result of averaging over

angular distributions of CC and NC interactions

i.e νe + e (CC) and νμ,τ +e (NC).

The sun emits substantial flux of τau-neutrinos!!

Poser: If the τau-coupling constant is different from standard V-A, then the

angular distribution is different, thus the averaged

recoil electron profile is changed—can probe this in Borexino data

if the Po and Kr problems are cleaned up

Be Be

Analysis

Po Po removed

by α-β disc.

Observed recoil profile

Standard universal V-A profile

Deviation of recoil profile via

Nonstandard tau couplings

Berezhiani, RSR, Rossi

hep-ph/ 0111138

standard Shape can be obtained

from artificial nu source (planned)

which emits ONLY νe

β α

P=0.5 P=0.5 P=0.5

Std Model NSI єeR : NSI єτR

-0.3 0.6 -0.3 0.4

3. Geophysics Antineutrinos from the earth—very low fluxes can be detected

Borexino site has little antineutrino bgd compared to KamLAND

Kamland and Borexino located geophysically different sites

4. Neutrinoless Double beta decay

Noble gases have high solubility in organic liquids

Xe, an excellent candidate for 0nubb studies has 2 wt% in PC

Can put 2tons of Xe in BOREXINO

Ton-scale 0nubb search for the first time

-Detector is ready –needs only to optimize existing puming systems

Energy of onubb signal at 2.5 MeV well outside SN spectrum

Already know background rates at these energies are very low

In any case target in-target out measurements allow no uncertainty of Bgd

Scintillation performance Unaffected—High resolution achieved (500 pe/MeV)

Expected nu mass sensitivity <0.1 meV with enriched Xe

Competitive—FAST –can be down quicker than any other planned expt

MOST EXCITING PROSPECT WITH BOREXINO

Major Background in 0nuBB window

2nuBB bgd

Cosmogenics—10C

Ext Bgd

Int Bgd

dBB signal window

Ultimately we hope to achieve

dBB sensitivity

<mν> ~ 100 meV

Solar Nu’s –Contd:

Model independent fluxes

Borexino & LENS

Borexino Signal

(CC + NC) νe+ νx

LENS Signal

(CC) ) νe only

Possibility of obtaining solar neutrino

Fluxes independent of Solar models

THAT IS WHERE WE ARE GOING!