First detection of solar neutrinos
from the CNO cycle with Borexino
Nicola Rossi

Laboratori Nazionali del Gran Sasso (INFN)pp vs CNO Competition
pp chain(99%)

Dominant in the sun
Tcore ~ 15 x 106 K

4H → He + 2e- +2 ve

CNO cycle(1%)

Solar neutrinos: astro & particle physics- dominant in stars 1.3 heavier
than Sun- crucial for the solar
metallicity problem (Z>He) :2High (HZ) vs Low (LZ)The BOREXINO detector

Laboratori Nazionali del Gran Sasso – INFN (Hall C)
Rock: 3.800 m w.e. – muon flux ~ 1 m-2h-13

The Borexino detector
Nylon vessell
125 μm of radioupurenylon

Stainless steal sphere13.7 m of diameter,
1300 m3 ofpseudocumene
Nylon outer vessel
PC+DMP

Scintillator

Buffer

Water Cherenkov veto
208 PMTs, diameter
18m, 2000 m3 of water

Water

Detection principle :Inner vesseltarget: 300 ton of
scintillator PC+PPO

Internal PMTs
2212 (nominal), 8”,
35% optical coverage
4Borexino’s pictures

During the construction

Now, after the thermal insulation

From monitoring camera

5

Water Extraction and Borexino radiopurity
Key procedure
for CNO quest[1 cpd/100t ~ 0.1 nBq/kg]

Bi85
Kr210
Po210

Before[cpd/100t]~40~30>2000

After[cpd/100t]~10~5<30(decaying)U<9.5x10-20 g/g (95%CL) ,232
Th < 5.7x10-19 g/g (95%CL),
39
Ar, 40K << 1 cpd/100t
238

Six cycles of water extraction
from mid-2010 to mid-2011

Expected CNO ~ 3-5 cpd/100t

6

(Solar) results from Borexino (2018)
Borexino has produced its
results in three experimental
phases, alternated withhardware improvements

NeutrinosReferences

Rate [cpd/100t]

Flux [cm-2s-1]

pp

Nature 2014, Nature 2018, PRD 2019

(134±10)-10+6(6.1±0.5)-0.5+0.3x1010

Be

PLB 2008, PRL 2011, Nature 2018, PRD 2019(48.3±1.1)-0.7+0.4(4.99±0.11)-0.08+0.06x109

pep

PRL 2012, Nature 2018, PRD 2019(2.43±0.36)-0.22+0.15 [HZ]

(1.27±0.19)-0.12+0.08x108 [HZ]B

PRD 2010, Nature 2018, PRD 2020

0.223-0.022+0.021

5.68-0.41-0.03+0.39+0.03x106

hep

Nature 2018, PRD 2020

<0.002 (90% CL)<1.8x105 (90% CL)

CNO

PRL 2010, Nature 2018 (upper limit)<8.1 (95% CL)<7.9x108 (95%CL)

78

Before 2020:- Precise measurement of thepp-chain fluxes- best experimental limit onCNO
7

Implications of Borexino results

Precise measurements era:

Pee survival probability with Borexino data only!

Probing the MSW-LMA
scenario
Low metallicity disfavored at 1.8 σ
8The CNO Strategy
Borexino spectrum after all data selection criteria

CNO <> pep <> 210Bi correlation

Region of interest for the CNO

210BiCNO
pep

Strategy:
1. independent constraint of pep
2. independent constraint and 210Bi (upper limit)

1. the “pep” constraint → 1.4%
Solar solar luminosity, pp/pep ratio,
existing solar neutrino, and oscillation
parameters

92. the “210Bi” constraint
THERMAL INSULATIONPROGRAM

Exploiting the A=210 chain
through secular equilibrium

Warm airfrom roomventilation(~20°C)

Diffusion:
Very slow
D ~ 10-9 m2/s
(diffusion coefficient)

BOREXINO
Water Tank

Heat sink 6°C(Hall C floor)

Convection:
210
Po from the outerregions

Idea: vertical gradient

2014: temperatureprobesMid-2015: insulation
start
Late 2015: water
recirculation systemshut down
2016: active temperature
control system (ATCS)
Early 2019: change ofthe ATCS set point
Late 2019: Hall C - ACTS
10

Thermal Insulation
Before the thermal insulation(Mid-2015)

Temperature probes
Temperature
evolution during thethermal insulation
campaign

After the thermal insulation(Beginning of 2016)11

Effects on Po migration
210

The Low Polonium Field

Minimum at z ~ 80 cm, Compatible with numerical fluid dynamics simulations
210
Po activity: R(minimum) = R(210Bi) + R(Vessel)
R(Vessel) > 0 → Upper limit → lower limit for CNO (anti-correlation)
Bi < (11.5 ± 1.0) cpd/100t (stat + sys) Systematic uncertainty (uniformity): 0.8 cpd/100
Final constraint: 210Bi < (11.5 ± 1.3) cpd/100t

12

CNO neutrino analysis
Main ingredients in the spectralanalysis:A) pep 1.4%
Gaussian penalty
B) 210Bi 11%
Semi-Gaussian penalty
1. Multivariate Montecarlo Fit
2. Counting Analysis (RoI)
Analytical modelling(consistency check)
CNO optimized RoI

13

Final results about CNO

Systematics: Response, resolution, spectral shapes and LY: σL = -0.5, σR= +0.6 (5.1 σ significance)
Hypothesis CNO=0 excluded at 5.0 σ (99%CL) Model compatibility: 0.5σ (HZ), 1.3σ (LZ)
Result (68% CL stat + sys) = 7.2 -1.7+3.0 cpd/100t
LZ disfavored at 2.1 σ including other fluxes from pp-chain (Borexino only)14

Updating the table with CNO neutrinos
Neutrinos

References

Rate[cpd/100t]

Flux[cm-2s-1]

pp

Nature 2014, Nature 2018,PRD 2019134±10-10+6(6.1±0.5-0.5+0.3)x1010

7Be

PLB 2008, PRL 2011,
Nature 2018, PRD 2019(48.3±1.1)0.7+0.4(4.99±0.11-0.08+0.06)x109

pep

PRL 2012, Nature 2018
PRD 2019(2.43±0.36)-0.22+0.15 [HZ]
(2.65±0.36)-0.24+0.15[LZ](1.27±0.19-0.12+0.08)x108 [HZ]
(1.39±0.19-0.12+0.08)x108[LZ]

8B

PRD 2010, Nature 2018,
PRD 2020

0.223-0.022+0.021(5.68-0.41-0.03+0.39+0.03)x106

hep

Nature 2018, PRD 2020

<0.002 (90% CL)<1.8x105 (90% CL)

CNO

Nature 2020 (THIS WORK)

7.2-1.7+3.0

7.0-2.0+3.0x108
15Thank youvery much!

G. & V. Cocconi Prize
2021 - EPS

16