1. Highligth on the past, present and future of the Borexino project
Gemma Testera (INFN Genova)
On behalf of the Borexino Collaboration
LNGS Sept. 5th, 2014
Gemma Testera (INFN Ge) - LNGS Sept. 5th, 2014

3. Borexino: scientific phases
2010
2007
May
2010
May
2011
Oct.
2015
~Feb.
2015
~Nov.
2017
~mid.
??? ~
now
PHASE 1
Purifications
5% 7Be n measurement
absence of 7Be day night
low threshold 8B
first pep detection
best upper limit on CNO
geon measurement
muons, cosmogenics
limit on rare processes
evidence of 7Be n seasonal modulation
calibration
PHASE 2
more geon results
background reduction
In progress now pp
seas. results (preliminary)
more precise 7Be, 8B. pep (in progress)
Rare processes
SOX, sterile n
+ distillation (under discussion)
calibration
more purification tests
temperature stabilization
PHASE 3
CNO
Gemma Testera (INFN Ge) - LNGS Sept. 5th, 2014

4. and expected interaction rates in Borexino
Solar n spectrum
and expected interaction rates in Borexino
Expected rates in Borexino n
Diff % pp
0.8
pep
2.1
7Be
8.8 8B
17.7
13N
26.7
15O
30.0
17F
38.4
Precise solar n measurement may discriminate between solar models
CNO : high potential discovery… the most difficult to detect!
7Be : high precision needed
CNO
Gemma Testera (INFN Ge) - LNGS Sept. 5th, 2014

5. Solar n and ne survival probability Pee: MSW and Non Standard Interactions (NSI)
MaVan models
Non standard forward scattering
LMA and standard model 1 10
NSI between n and electrons modify Pee vs E (MSW)
NSI affects the shape of the elastic scattering cross section (see next slides)
S.K. Agarwalla et al JHEP (2012)
PRD 88: (2013)
Long range interactions 1 10
Gemma Testera (INFN Ge) - LNGS Sept. 5th, 2014

6. Borexino: real time n detector with liquid scintillator
Stainless Steel Sphere:
R = 6.75 m
2212 PMTs
Scintillator:
270 t PC+PPO (1.5 g/l)
in a 150 mm thick
inner nylon vessel (R = 4.25 m)
n detection:
elastic scattering on electrons
Buffer region:
PC+DMP quencher
4.25 m < R < 6.75 m
anti-n detection:
Inverse Beta Decay (IBD)
Water Tank:
g and n shield
m water Č detector
208 PMTs in water
“prompt signal”
e+: energy loss + annihilation
(2 g 511 KeV each)
“delayed signal”
n capture on H after thermalization; 2.2 g
The smallest radioactive background of all the neutrino detectors:
9-10 orders of magnitude smaller than the every-day environment
Gemma Testera (INFN Ge) - LNGS Sept. 5th 2014

7. Real time solar n detectionpp
pep
7Be
CNO 8B
8B detect en. thres.
(Lowest)
(1010 cm-2 s-1)
(109 cm-2 s-1)
(108 cm-2 s-1)
(108 cm-2 s-1)
(106 cm-2 s-1)
2.344 ±
ne equiv (1.4%) SK
3.5 MeV
SNO
5.25 ±
Total active2 n (3.8%)
3.5 MeV
Kamland
3.26 ± 0.5 (15%)
ne equiv8
2.77 ± 0.26± 0.32
ne equiv (15%)
5.5 MeV
Borexino
6.6 ± 0.7 (10.6%)
LMA-MSW
included7
3.10 ± 0.15 (5%)
ne equiv6
1.6 ± 0.3 (19%)
LMA-MSW
included5
< 7.7
LMA-MSW
included5
2.4 ± 0.4 ± 0.1
ne equiv (17%)
3. MeV
1) Y. Koshio (SK Coll.) Neutrino 2014 talk
2) B. Aharmim et al (SNO Coll.) Phys. Rev. C (2013)
3) S. Abe et al (Kamland Collaboration) Phys. Rev. C (2011)
4) G. Bellini et al (Borexino Collaboration) Phys. Rev. D 82, 3 (033006) 2010
5) G. Bellini et al., (Borexino Collaboration) Phys. Rev. Lett. 108 (2012)
6) G. Bellini et al., (Borexino Collaboration) Phys. Rev. Lett. 107 (2011)
7) G. Bellini et al. (Borexino Collaboration) Nature (2014)
8) A. Gando et al. (Kamland Collaboration) arxiv: v1 (May2014)

8. How do we see n in Borexino?
G. Bellini et al., Phys Rec D (2014)
How do we see n in Borexino?
No direction: key tool in the SNO and SK analysis
Energy (from number of PMT hits or phe) : - high energy resolution and fit of the energy spectra
- recognize the signal on the basis of the spectral shape
- need very low background!
Position reconstruction (from PMT time) : - definition of the Fiducial Volume (from the PMT time meas.)
- distinguish signal from back on the basis of the spatial distribution
of the events
Pulse shape discrimination: distinguish signal and back on the basis of the time profile of the emitted light
+ explore time and space correlations between events to remove or evaluate background
(214Bi-214Po, 212Bi-212Po, 85Kr, 11C 3 fold coincidence, muon daugthers)
In situ calibration with radiocative sources + accurate detector modeling (Monte Carlo and analytical models)
Gemma Testera (INFN Ge) - LNGS Sept. 5th, 2014

9. Fiducial Volume error: +0.5 -1.3%
PHASE 1: position reconstruction calibration (from PMT time measurements)
Rn source deployed in 182 positions
True position with laser light and CCD
The position resolution as a function of the energy
The accuracy of the absolute position reconstruction:
difference between true and reconstructed source position
Vertical coordinate z y x
x coordinate (and similar for y)
Mean: cm
Rms : cm
1MeV
Fiducial Volume error: %
10 1MeV (electron equiv)
Gemma Testera (INFN Ge) - LNGS Sept. 5th 2014

10. PHASE 1: energy (PMT hits or phe) calibration
Energy calibration: g sources in the center
Data and MC
214Po source (from Rn) in 182 positions: difference between
data and MC
Inside the FV
R<3m X
R>3m
The energy scale
in the FV
Energy resolution
≈500 phe/MeV (electron equivalent)
Quenching determined from calibration data

11. PHASE 1: pulse shape discrimination
Distribution of the parameter (Gatti filter) used
to discriminate a from b
The time profile of the emitted light for a and b
1) a b
(obtained with time
tagged 214Bi-214Po)
2) b+ b-
11C decays by b+
e+ slow down, capture e-,
Lifetime in the liquid is few ns
e+ scintillation delayed
(compared to e-)

12. Phase I solar n results : 5% accuracy on 7Be n interaction rate
G. Bellini et al., Borexino Collaboration, Phys. Rev. Lett. 107 (2011)
Use of PSD to subtract
the 210Po peak
11C
210Bi
ne flux reduction
5 s evidence of oscillation
Theor. uncertainty on 7Be flux : 7%
Gemma Testera (INFN Ge) - LNGS Sept. 5th, 2014

13. Physics implication of the solar n Borexino results: high and low metallicity solar models
High met. (1s)
Low met. (1s)
Data
Gemma Testera (INFN Ge) - LNGS Sept. 5th 2014

14. Phase I solar n results : absence of day night asymmetry for 7Be n interaction rate
ne regeneration by interaction with e: D/N effect is a consequence of MSW
not expected for 7Be in the LMA-MSW model
large effect expected in the “LOW” solution (excluded by solar exp + Kamland)
no contradiction with the recent SK results
G. Bellini et al., Borexino Collaboration, Phys. Lett. B707 (2012) 22.
Solar data alone select the LMA-MSW
if one includes the Borexino D/N result
(no use of CPT)
LMA-MSW
LMA-MSW
Day time
Night time
All solar n
without Bx
without Kamland
All solar n
with Bx
without Kamland
Gemma Testera (INFN Ge) - LNGS Sept. 5th, 2014

15. Phase I solar n results : first pep n detection and best limit on CNO
pep signal is ten time lower than 7Be
About 3cpd/100t
CNO: rate similar to pep
G. Bellini et al., Borexino Collaboration, Phys. Rev. Lett. 108 (2012)
pep
7Be
11C
210Bi
CNO
Ext back
Most important background
11C :
210Bi :
External background (g from PMT):
Play against external background
calib. with external 232Th source
Monte Carlo simulation
Include the radial distribution of events in the fit
The effect of the 3 fold coinc.
Play against 11C
3 fold coinc
Pulse shape param in the fit
The eec
Residual 11C: cpd/100t
(9+-1)% of the original value
48.5% of the original exposure preserved
Gemma Testera (INFN Ge) - LNGS Sept. 5th, 2014

16. Phase I solar n results : first pep n detection and best limit on CNO
G. Bellini et al., Borexino Collaboration, Phys. Rev. Lett. 108 (2012)
210Bi cpd/100t
CNO
210Bi
CNO cpd/100t
Sensitivity to CNO limited by 210Bi: similar spectral shape
5.24 High Met; 3.76 Low Met.)
Gemma Testera (INFN Ge) - LNGS Sept. 5th 2014

17. PHASE I solar n results : 8B flux with the lowest energy threshld
208Tl (from the 232Th decay chain) limits the energy threshold
low signal rate (Borexino is small…)
G. Bellini et al., Borexino Collaboration,PRD (2010)
3 MeV electron energy threshold:
the lowest !
Gemma Testera (INFN Ge) - LNGS Sept. 5th, 2014

18. Purification of the scintillator : (between phase 1 and 2)
6 purication cycles
Water extraction
Nitrogen stripping
(May )
238U (from 214Bi-Po)
< g/g 95% C.L.
PHASE 1: g/g
Arbitray units
232Th (from 212Bi-Po)
< g/g 95% C.L.
PHASE 1: g/g
85Kr (from spectral fit)
< 7 cpd/100t 95% C.L.
PHASE 1: 30.4±5.3±1.5
210Bi (from spectral fit)
25±2 cpd/100t
PHASE 1: 41.8±2.8
210Po
102 cpd/100t
PHASE 1: 104 cpd/100t
Gemma Testera (INFN Ge) - LNGS Sept. 5th 2014

19. Phase II solar n results : pp neutrinos !!!
See the Oleg’s talk
Gemma Testera (INFN Ge) - LNGS Sept. 5th, 2014

20. Borexino Solar Neutrino results and the oscillation physics
Gemma Testera (INFN Ge) - LNGS Sept. 5th 2014

21. More about Non Standard Interactions (NSI)
NSI change the ne-e differential elastic scattering cross section
Bounds on the parameters with PHASE 1 data
better limits are expected with reduced background and more statistics
S.K. Agarwalla et al JHEP (2012)
Gemma Testera (INFN Ge) - LNGS Sept. 5th, 2014

22. Expected oscillation amplitute of 7Be n signal:
Phase I (and preliminary for PHASE 2) solar n results : annual modulation of the 7Be n signal
Expected oscillation amplitute of 7Be n signal:
6.8% peak-to-peak
max flux: Jan. 3rd
47.5
e=0.0167
7Be n cpd/100t 46
44.5
Time (years)
Counts in a
energy region dominated by 210Bi
Spectral fit in sub-periods: too large stat. errors
Analysis method:
Select a proper energy region,
group data in time bins and search for a periodical component
Enlarge the fiducial volume (with respect to the 7Be flux meas.)
3 methods (consistent results)
Fit of the rate vs time
Lomb Scargle analysis
Empirical Mode Decomposition
G. Bellini et al., Phys Rec D (2014)
Gemma Testera (INFN Ge) - LNGS Sept. 5th, 2014

23. PHASE 1: annual modulation of the 7Be n signal
Difficult analysis in PHASE 1 due to unstable 210Bi
G. Bellini et al., Borexino Collaboration, Phys. Rev. C (2014) ?????.
best fit 1s 2s
expected value
Gemma Testera (INFN Ge) - LNGS Sept. 5th 2014

24. PHASE 2: annual modulation of the 7Be n signal (preliminary results)
7Be signal and background: annual modulation
210Bi time stability in PHASE 2
Expected time curve
Preliminary
Gemma Testera (INFN Ge) - LNGS Sept. 5th, 2014

25. Dreaming about CNO neutrinos……..
1) Reduce 210Bi by purification: partially achieved
2) Infer the 210Bi activity from the 210Po vs time
210Bi-210Po out of equilibrium: we see an high 210 Po rate
210Pb
210Bi
210Po
206Pb
b (63 KeV) b a
stable
T1/2=22y
5 days
138 days
Look at the 210Po time decay: the rate at regime is due to 210Bi
F. Villante et al.,Phys. Lett. B 701 (2011)
Simulation: 100 t X 1 year, typical Borexino rates
Needed:
210Po activity not too high: actual values are OK
stable conditions for long time (1-2 years..)
no 210Po sources
Standard spectral fit
Constrain on 210Bi rate
due to 210Po time decay

26. Studies of the 210Po decay Temperature of the Hall
Temperature on top of the SSS
210Po of the vessel
moves inside the IV
due to convection
induced by temperature changes
Solutions under discussion
210Po in the Fiducial Volume
Temperature at the bottom of the SSS
July2014
Gemma Testera (INFN Ge) - LNGS Sept. 5th 2014

27. Not only solar n! Geo-n in Borexino: anti ne from inside the Earth
Energy spectrum of geon neutrinos
En>1.8 MeV
Low flux: 3 order of magnitude less than 7Be solar n!
Clean signature by IBD
Geon: they probe the U,Th content of the Earth (no K)
Multidisciplinary research: particle physics&geophysics
reactor
geon
Likelihood fit: geov + reactor
Event selection and results
Search for coincidence (energy, time and space cuts)
Large Fiducial Volume: distance from the vessel <25 cm
Exposure ±26 ton year
46 candidates
geo n events
reactor events
33.3±2.4 expected reactor events
0.70± others back
No geon signal: rejected at 4.5 s C.L.
geon
reactors
1MeV≈ 500 p.e.

28. Geon : implications about Earth models
For each element (U,Th) the expecetd geon signal S in one site on the Earth’s surface is the sum of 3 contributions
It depends on local geology
We are interested in the Mantle contribution which is related to the U,Th mass (or radiogenic heat) in a model dependent way (red and blue plot)
TNU=1ev/ (y protons)
Borexino results
LOC (TNU)
ROC (TNU)
DATA (TNU)
MANTLE
(TNU)
U+Th (TW)
Kamland
17.7±1.4
7.3±1.4
31.1±7.3
6.1±7.6
13±9
Borexino
9.7±1.3
13.7 ±2.5
38.8±12.0
15.4±12.3
23±14
Data not yet precise enough to select Earth models
New multidisciplinary area, large interest from the geo- community
Mantle (BX+Kamland) TNU (1s)
Gemma Testera (INFN Ge) - LNGS Sept. 5th 2014

29. Not only solar n! Search for sterile-n in Borexino (SOX)
Experimental hints for sterile neutrinos
Several unexpected signals at 3 s level:
Accelerator anomaly (3.8 s)
LSND and MiniBoone
Excess of low energy ne events from a nm beam
Appearance signal at a new short baseline?
Gallium anomaly (2.8 s)
Calibration runs with radiocative sources in Gallex/SAGe
Deficit of the detected ne R=
Reactor anomaly (2.5 s)
Re-evaluation of reactor antine spectra
Rate deficit at short baseline (10-100m) R=
Disapperance of electron neutrinos into sterile neutrinos??
Light sterile neutrinos: a white paper Xiv:
Gemma Testera (INFN Ge) - LNGS Sept. 5th, 2014

30. Dm214 (eV2) Add 2 new parameters sin2(2 q14)
Plot taken from arxiv (2013) (Opera collaboration)
Gemma Testera (INFN Ge) - LNGS Sept. 5th 2014

31. n and anti-n neutrino sources to search for sterile n signal
SOX: Short distance neutrino Oscillations with BoreXino)
SOX A:
Source below Borexino: 8.25 m from the center
No changes in the detector
We are working on two sources:
51Cr n e source
44Ce anti- n e (in collaboration with Saclay group)
End 2015: start data taking with 44Ce
8.25 m
Oscillation lenght of the order of the Borexino size

32. Gemma Testera (INFN Ge) - LNGS Sept. 5th 2014

33. The SOX signal
1) Disappearance: - need accurate calibration of the source activity
- measure heat (calorimeter) with 1-2% accuracy
(in construction)
2) See spatial oscillations of the source count rate
51Cr source: example with
Gemma Testera (INFN Ge) - LNGS Sept. 5th, 2014

34. The expected sensitivity
sin2(2 q14)
sin2(2 q14)

35. Summary, conclusions and perspectives
Borexino is the only real time experiment who detected n over all the solar spectrum
The results are relevant to both solar physics and neutrino physics
PHASE 2 with lower background than PHASE 1 almost concluded: data analysis in progress
7Be (going toward % accuracy)
pep 8B
seasonal modulation
geo n
several rare processes
….while waiting for a Supernova all the time
! First pp neutrinos detection in real time !
A new calibration is scheduled for the beginning of 2015: needed to reduce the uncertainties
Effort in progress toward the CNO detection :
we need stable conditions
control of the temperature
further purification of the scintillator (under discussion within the collaboration)
Sterile n search with radiocative source: start soon (end 2015)
Gemma Testera (INFN Ge) - LNGS Sept. 5th 2014