Borexino Source Experiment G. Ranucci On behalf of the Borexino - - PowerPoint PPT Presentation

Borexino Source Experiment

• G. Ranucci

On behalf of the Borexino Collaboration SNAC11,Blacksburg, VA 27 September 2011

Gioacchino Ranucci ‐ SNAC11 27/09/2011

The idea to use a neutrino source in Borexino d i th d d i t d t and in other underground experiments dates back to at least 20 years

– N.G.Basov,V.B.Rozanov, JETP 42 (1985) – Borexino proposal, 1991 (Sr90) Bx J N Bahcall PI Krastev E Lisi Phys Lett B348:121 123 1995 – J.N.Bahcall,P.I.Krastev,E.Lisi, Phys.Lett.B348:121‐123,1995 – N.Ferrari,G.Fiorentini,B.Ricci, Phys. Lett B 387, 1996 (Cr51) Bx – I.R.Barabanov et al., Astrop. Phys. 8 (1997) G ll ll PL B 420 (1998) 114 D (C 51) – Gallex coll. PL B 420 (1998) 114 Done (Cr51) – A.Ianni,D.Montanino, Astrop. Phys. 10, 1999 (Cr51 and Sr90) Bx – A.Ianni,D.Montanino,G.Scioscia, Eur. Phys. J C8, 1999 (Cr51 and Sr90) Bx – SAGE coll. PRC 59 (1999) 2246 Done (Cr51 and Ar37) – SAGE coll. PRC 73 (2006) 045805 – C.Grieb,J.Link,R.S.Raghavan, Phys.Rev.D75:093006,2007 g y – V.N.Gravrin et al., arXiv: nucl‐ex:1006.2103 – C.Giunti,M.Laveder, Phys.Rev.D82:113009,2010 – C.Giunti,M.Laveder, arXiv:1012.4356 C.Giunti,M.Laveder, arXiv:1012.4356

Gioacchino Ranucci ‐ SNAC11 27/09/2011

The physics case with a source experiment

• Neutrino magnetic moment
• Neutrino‐electron non standard interactions
• Probe ν

e weak couplings at 1 MeV scale

• Probe νe‐ e weak couplings at 1 MeV scale
• Probe sterile neutrinos at 1eV scale
• Probe neutrino vs anti‐neutrino oscillations on

10m scale 10m scale

Gioacchino Ranucci ‐ SNAC11 27/09/2011

Anomalies/hints for Δm 2 ≅1eV2 Anomalies/hints for Δm ≅1eV

/ Workshop on Beyond Three Family Neutrino Oscillations a) The LSND/Miniboone (anti‐ν and ν) anomalies b) The reactor anomaly arXiv:1101.2755 sin22θee=0.1 Δm2=0.4 eV2 R t l l i Family Neutrino Oscillations LNGS 3‐4 May 2011 Rate only analysis sin22θee=0.1 Δm2=1.5 eV2 Rate+shape c) The Gallium anomaly R=0.86 from Gallex and Sage source tests arXiv1006.3244 Giunti and Laveder sin22θee=0.5 Δm2=2.24 eV2 d) Indications from cosmology and BBN of more than 3 neutrinos

Gioacchino Ranucci ‐ SNAC11 27/09/2011

Borexino at Gran Sasso: low energy neutrino real time detection

Scintillator:

Stainless Steel Sphere: 2212 photomultipliers 1350

3

Scintillator: 270 t PC+PPO in a 150 μm thick nylon vessel

1350 m3

Design based on the N l l principle of graded shielding

Water Tank: γ and n shield μ water Č detector

Nylon vessels: Inner: 4.25 m Outer: 5.50 m

μ water Č detector 208 PMTs in water 2100 m3

Neutrino electron

20 legs

scattering ν e −> ν e

Gioacchino Ranucci - SNAC11

20 legs

Carbon steel plates

27/09/2011

Gioacchino Ranucci - SNAC11

UMass

27/09/2011

Borexino achievements

High precision (better than 5%) 7Be flux 7Be day night (absence) 7 Be day‐night (absence) Unambiguous geo‐neutrino detection 8 Be with a 3 MeV threshold First indication of pep solar neutrinos and tight upper limit

• n CNO neutrinos (Borexino talks at the recent TAUP)

All above thanks to the accurate energy‐position calibration of the detector volume detector volume The perfect knowledge of the detector performances witnessed by this impressive list of achievements is the solid ground upon which this impressive list of achievements is the solid ground upon which the proposal for the source test in Borexino is built

Gioacchino Ranucci ‐ SNAC11 27/09/2011

7Be Solar neutrinos in Borexino

hep‐ex/1104 1816v1 hep‐ex/1104.1816v1

7Be = 46.0 ± 1.5 cpd/100 tons

+1.6 p / ‐1.5

210Bi

Bi pep & CNO

85Kr

pp Now removed! pp

Gioacchino Ranucci ‐ SNAC11 27/09/2011

Solar neutrino survival probability p y

“Ultimate” validation of the MSW‐LMA survival probability curve

Gioacchino Ranucci ‐ SNAC11 27/09/2011

Position and energy calibration

• On and off axis

calibrations sources

• Rn, AmBe

Rn, AmBe

• 57Co, 139Ce, 208Hg, 85Sr,

54Mn 65Zn 40K 60Co

Mn, Zn, K, Co

The knowledge of the detector and The knowledge of the detector and

• f its performance makes it the ideal

“environment” for a series of source test to shed light on the hints of a test to shed light on the hints of a new neutrino oscillation mass scale involving steriles Initially external location, later in the Initially external location, later in the center

Gioacchino Ranucci ‐ SNAC11 27/09/2011

Source location in Borexino Source location in Borexino

A d th WT

• A: underneath WT

– D=825 cm – No change to present g p configuration

• B: inside WT

00

B C

– D = 700 cm – Need to remove shielding water g

• C: center

– Major change l – Remove inner vessels – To be done at the end of solar Neutrino physics eut

• p ys cs

A

Gioacchino Ranucci ‐ SNAC11 27/09/2011

Source position A Source position A

Gioacchino Ranucci ‐ SNAC11 27/09/2011

Gioacchino Ranucci ‐ SNAC11 27/09/2011

Sources

Activity: several 1000 ν evts within 1 year E >250 keV (14C background) E >250 keV ( C background) Half-life ≥1 month Compact Limited heat Limited heat Efficient shielding Low impurities level

Gioacchino Ranucci ‐ SNAC11 27/09/2011

Proposed at the workshop Beyond 3 ν at Gran Sasso in May and in arXiv:1107.2335 y

Gioacchino Ranucci ‐ SNAC11 27/09/2011

51Cr

Originally proposed by h Raju Raghavan

~36 kg of 38% enriched 50Cr g 190 W/MCi from 320 keV γ’s

7μSv/h (must be < 200)

Done two times for Gallex at 35 MW reactor

2 1

SAGE coll., PRC 59 (1999) 2246 Gallex coll., PL B 420 (1998)

with effective thermal neutrons flux of ~5.4E13 cm‐2s‐1 ~1.8 MCi

Gioacchino Ranucci ‐ SNAC11 27/09/2011

Transport container

Gioacchino Ranucci ‐ SNAC11 27/09/2011

Cr51 Gallex source Cr51 Gallex source

Gioacchino Ranucci ‐ SNAC11 27/09/2011

Gioacchino Ranucci ‐ SNAC11 27/09/2011

The case of νe

51Cr source in Borexino

The case of νe Cr source in Borexino

Bi th210 Bismuth210 CNO Source events CNO Be7 Wi d 0 250 0 700 K V Window 0.250‐0.700 KeV Background : solar neutrinos + Bismuth210

Gioacchino Ranucci ‐ SNAC11 27/09/2011

37Ar ν source

Ar νe source

37 37Ar(τ=50.55 days)

813 keV (9.8%) 811 keV (90.2%)

37Cl From irradiation of CaO using fast neutrons 40Ca(n,α)37Ar ~16 W/MCi from 2.6 keV X‐rays Used in SAGE with ~0.4 MCi

Gaseous source Mentioned here for “historical” reasons

SAGE coll., PRC 73 (2006) 045805

Gioacchino Ranucci ‐ SNAC11 27/09/2011

90Sr‐90Y

e

ν

source

τSr= 28.79 years τY= 3.8 days

90Sr

Inverse beta decay <E>=2±0 2MeV <E> 2±0.2MeV <σ>=7.2⋅10‐45cm2

90Y

Product of nuclear fission Used in thermoelectric generators

7.25 kg/MCi ~6700 W/MCi

Used in thermoelectric generators Known technology for 0.2 MCi sources

6700 W/MCi including Bremsstrahlung

Gioacchino Ranucci ‐ SNAC11 27/09/2011

Gioacchino Ranucci ‐ SNAC11 27/09/2011

3

Gioacchino Ranucci ‐ SNAC11 27/09/2011

120

Spatial profile of detected events for a monoenergetic source (Cr51) in the tunnel

100

Δm2 sin22θ 8 0 07

80

8 0.07 1 0.1

60

no oscillation

Ideal case

40

Ideal case no spatial resolution no background

20 400 500 600 700 800 900 1000 1100 1200 1300 1400

Cmfrom the source

Gioacchino Ranucci ‐ SNAC11 27/09/2011

How to exploit the rate and waves information Oscillometry measurements

Standard way to convey the predicted sensitivity of an oscillation ‐Standard way to convey the predicted sensitivity of an oscillation experiment

• Exclusion plots exploiting

Exclusion plots exploiting

• Rate only (usual approach)
• Rate plus waves (specificity of the present case)
• Obtained through the likelihood ratio method, testing

against the oscillation hypothesis simulated data which instead are produced unaffected by oscillations instead are produced unaffected by oscillations

• Practically derived by comparing the corresponding χ2

(average data with no oscillation ‐ model with oscillation) ( g ) with the desired quantile (90%, 99%, 99.73%) of the χ2 distribution with two degrees of freedom

Gioacchino Ranucci ‐ SNAC11 27/09/2011

‐Complementary, less used approach:

• Discovery plots to determine the existence of the effect,

exploiting again only the rate or the rate+waves combination Obt i d th h th lik lih d ti th d b t

• Obtained through the likelihood ratio method, but

testing against the no oscillation hypothesis simulated data which instead are produced as simulated data which instead are produced as affected by oscillations

• Practically derived by comparing corresponding χ2

(average data with oscillation ‐ model with no

• scillation) with the desired quantile (90%, 99%,

99 73%) f th

2di t ib ti

ith t d f 99.73%) of the χ2 distribution with two degrees of freedom

• The determination of the oscillation parameters is
• The determination of the oscillation parameters is

also carried out

• Exclusion and discovery contours are practically

similar ‐At high Δm2 effectively rate only analysis (in both cases)

Exclusion plots

Cr51 Sr90 Ce144 ‐In the tunnel (A) and (in some cases) in the center (C). B is very similar to A ‐Detector characteristics affecting the sensitivity of the measure S ti l l ti b t 15 Spatial resolution ‐ about 15 cm Systematic error on spatial reconstruction (Fiducial Volume systematic error) 1% Background S l i d Bi h f b 40 d Solar neutrinos and Bismuth for ν source about 40 events per day Geo and reactor anti‐ν (a dozen of events per year) for anti‐ν source The precision of the knowledge of the source intensity is another systematic error ‐The precision of the knowledge of the source intensity is another systematic error assumed 1%

Gioacchino Ranucci ‐ SNAC11 27/09/2011

10

90% C.L.

At high Solar+KamLAN Cr51 10 Mci (2 expositions) T l (d 825 )

90

Δm2 the fast

• scillations

D constraints accounting for the θ13 ≠ 0 f h T2K 1 Tunnel (d=825 cm) 200 days 1% err. source intensity 1% err FV

% C.L.. e

are smeared by the detector from the T2K result

• A. Palazzo

Δm2 1% err. FV

xcluded

detector spatial resolution ⇒ arXiv:1105.170 5 and talk at TAUP 0.1 Reactor anomaly Joint Reactor+Ga anomaly ⇒ effectively rate‐only analysis TAUP Rate + waves Rate only Joint Reactor+Ga anomaly analysis Here and in 0 01 the following Δm2 in unit eV2 0.01 0.001 0.01 0.1 1 sin22θ

10

99% C.L. Cr51 10 Mci (2 expositions) T l (d 825 )

90% C

1

Tunnel (d=825 cm) 200 days 1% err. source intensity 1% err FV

C.L.. excl

0.1

Δm2 1% err. FV

uded

Reactor anomaly Rate + waves

0.01

Rate + waves Rate only

0.001 0.001 0.01 0.1 1

sin22θ

Gioacchino Ranucci ‐ SNAC11 27/09/2011

Cr51 in the center

1.4

Enhanced sensitivity

1 1.2

due both to the pattern Oscillation waves

0.8 1

and the increased number of

0.6

events

0 2 0.4

Resolution effect non gaussianity at center

0.2 100 200 300 400 500 600

Distance from the center

Gioacchino Ranucci ‐ SNAC11 27/09/2011

10

90% C.L.

9

The effect on the exclusion

1

Cr51 10 Mci (2 expositions) Center

90% C.L..

the exclusion plot of the enhanced sensitivity in

1

200 days 1% err. source intensity 1% err. FV

excluded

sensitivity in the center location is striking, the

0.1

Δm2

d

g, reactor anomaly region would Reactor anomaly Joint Reactor+Ga anomaly be fully covered.

0.01

Rate + waves Rate only Technically very challenging ‐ size and

0.001 0 001 0 01 0 1 1

g g shielding (320 keV γ’s and γ’s from impurities) issues – more plausible 0.001

0.01 0.1 1

sin22θ to deploy the anti‐ν source

Gioacchino Ranucci ‐ SNAC11 27/09/2011

Sr90 source – oscillation probability as function of distance and energy

0 5 0 1 Δm2 θ

1 1.005

0.5 0.1

0.99 0.995 0 9 0.98 0.985 0 965 0.97 0.975 0.955 0.96 0.965 200 400 600 800 1000 1200 1400 1600

Cm from the source location The different curves correspond to energies ranging from 1.8 to 2.28 MeV A twofold energy‐distance approach is needed For simplicity here we have integrated over the energy

4 50E 02

Sr90 source –event spatial profile variation over the energy interval 1.8 to 2.28 MeV

4.00E‐02 4.50E‐02 3.00E‐02 3.50E‐02 2.50E‐02 1.50E‐02 2.00E‐02 5.00E‐03 1.00E‐02 0.00E+00 5.00E 03 200 400 600 800 1000 1200 1400 1600 1800

Distance from the source (cm)

Gioacchino Ranucci ‐ SNAC11 27/09/2011

Δm2=1 sin22θ =0.2 Δm2=2 sin22θ =0.1

Sr90 source – expected event spatial profile after energy integration over energy

ude (a.u.)

Sr90 in the

ude (a.u.)

Sr90 in the

Amplitu

tunnel

Amplitu

tunnel

500 1000 1500 2000 Distance from the source (cm) 500 1000 1500 2000 Distance from the source (cm)

Δm2=1 sin22θ =0.1 Δm2=0.1 sin22θ =0.2

itude (a.u.)

Sr90 in the tunnel

litude (a.u.)

Sr90 in the tunnel

Ampli Ampl 500 1000 1500 2000 Distance from the source (cm) 500 1000 1500 2000 Distance from the source (cm)

Gioacchino Ranucci ‐ SNAC11 27/09/2011

Sr90 Advantages

Background free measure (delayed coincidence) Background free measure (delayed coincidence) Higher counting rate due to the possibility to exploit the full volume, in this case the FV error can be ignored (the following plots in which the FV error is maintained are (the following plots in which the FV error is maintained are therefore conservative) – the coincidence technique makes it suited to be located in the center Future scalability: in a post solar phase of the experiment the h b f ll d h ll entire sphere can be filled with scintillator Issues to be considered : heat dissipation and bremmstralung background – shielding and “shadowing” around the center

Gioacchino Ranucci ‐ SNAC11 27/09/2011

10

90% C.L. Sr90 1 Mci Tunnel (d=825 cm) 365 days

90% C.

1

365 days 1% err. source intensity 1% err. FV

.L.. exclu

0.1

Δm2

ded

Reactor anomaly Joint Ga+Reactor anomaly

0.01

Rate + waves Rate only y

0.001 0.001 0.01 0.1 1 0.001 0.01 0.1 1

sin22θ

Gioacchino Ranucci ‐ SNAC11 27/09/2011

10

90% C.L. Realistically the FV b

1

Sr90 1 Mci Tunnel (d=825 cm) 365 days

90% C.

FV error can be ignored due to the delayed coincidence

1

365 days 1% err. source intensity

.L.. exclu

coincidence measurement. The 90% reactor

0.1

Δm2

ded

reactor anomaly region is almost fully covered

0 01

Reactor anomaly Joint Ga+ Reactor anomaly fully covered

0.01

Rate + waves Rate only y

0.001 0.001 0.01 0.1 1

Rate only sin22θ

Gioacchino Ranucci ‐ SNAC11 27/09/2011

10

99% C.L. “Decent”

1

Sr90 1 Mci Tunnel (d=825 cm) 365 days

90% C.L

Decent sensitivity even at 99% C.L. Further improvable

1

1% err. source intensity 1% err. FV

L.. exclud

improvable ignoring the FV error

0.1

Δm2

ed

Reactor anomaly Rate + waves

0.01

Rate only

0.001 0.001 0.01 0.1 1 0.001 0.01 0.1 1

sin22θ

Gioacchino Ranucci ‐ SNAC11 27/09/2011

Sr90 in the center

7 00E 03

The averaging effect over the energy range is less important than for the external location

6.00E‐03 7.00E‐03 6.00E‐03 7.00E‐03 4.00E‐03 5.00E‐03 Energy lower limit Energy range 4.00E‐03 5.00E‐03 2.00E‐03 3.00E‐03 Energy range upper limit Middle energy range 2 00E‐03 3.00E‐03

No oscillation Energy

1.00E‐03 2.00E 03 No oscillation 1.00E‐03 2.00E 03

gy averaged

0.00E+00 100 200 300 400 500 600

cm from the center

0.00E+00 100 200 300 400 500 600

cm from the source Δm2 =2 sin22θ=0.1

Gioacchino Ranucci ‐ SNAC11 27/09/2011

10

90% C.L.

90

1

Sr90 1 Mci Center 365 days

% C.L.. e

Potential improveme nts w.r.t.

1

365 days 1% err. source intensity 1% err. FV

xcluded

this plot: a)No FV error b) d d

0.1

Δm2 b) Extended data taking time (three ) Reactor anomaly Joint Reactor+Ga anomaly years) c) Entire SS sphere filled with

0.01

Rate + waves Rate only y filled with scintillator

0.001 0.001 0.01 0.1 1

sin22θ

Gioacchino Ranucci ‐ SNAC11 27/09/2011

10

99% C.L.

90

Sr90 1 Mci Center 365 d

0% C.L.. e

Extremely good sensitivity

1

365 days 1% err. source intensity 1% err. FV

excluded

also at the 99% C.L.

0.1

Δm2

d

Reactor anomaly R t

0.01

Rate + waves Rate only

0.001 0 001 0 01 0 1 1 0.001 0.01 0.1 1

sin22θ

Gioacchino Ranucci ‐ SNAC11 27/09/2011

106Ru‐106Rh

e

ν

source

τRu= 539 days τRh=29.8 s

106Ru 106

Inverse beta decay <E>=2 5±0 2 MeV

106Rh

<E>=2.5±0.2 MeV <σ>=89.2⋅10‐45cm2

Product of nuclear fission

l

Ad S 90 l i i ff d bl

Similar option: Ce144 – Pr144

Gioacchino Ranucci ‐ SNAC11

Advantage w.r.t. Sr90: lower activity affordable

27/09/2011

Following the concepts devised in arXiv:1107.2335

Gioacchino Ranucci ‐ SNAC11

W+Cu shield

27/09/2011

Gioacchino Ranucci ‐ SNAC11 27/09/2011

100

90% C.L. With a Ce144 50 kCi

90% C.

t a “modest” source activity a

10

Ce144 50 kCi Center 365 days 1% err. source intensity

.L.. exclu

y good sensitivity reach is

1

Δm2 1% err. source intensity 1% err. FV

ded

anyhow ensured Joint Reactor+Ga anomaly

0.1

Reactor anomaly Rate+waves

0.01 0.001 0.01 0.1 1

sin22θ

Gioacchino Ranucci ‐ SNAC11 27/09/2011

100

99% C.L. Ce144 50 kCi

90%

….. Even at

10

Ce144 50 kCi Center 365 days 1% err. source intensity

C.L.. exc

99% C.L.

1

Δm2 1% err. source intensity 1% err. FV

luded

Joint Reactor+Ga anomaly 90% C.L.

0.1

Reactor anomaly Rate + waves

0.01 0.001 0.01 0.1 1

sin22θ

Gioacchino Ranucci ‐ SNAC11 27/09/2011

100

90% C.L. Ce144 50 kCi Tunnel (d=825 cm) 365 days

9

A reach capability

10

1% err. source intensity 1% err. FV

90% C.L..

p y at some level even if located

1

Δm2 Reactor anomaly

excluded

externally

0.1

Joint Reactor+Ga anomaly

d

Rate + waves

0.01 0.001 0.01 0.1 1

Sin22θ

Gioacchino Ranucci ‐ SNAC11 27/09/2011

Discovery curves

Likelihood ratio test statistics to identify the oscillation effect , if exists

) ( l 2 n

• scillatio

no L − ) ( ) ( ln 2 n

• scillatio

L n

• scillatio

no L t − =

Example from a specific simulation case: Δm2=1 sin22θ=0.2 “Blind” search over Δm2 and sin22θ

160

Cr51 10 MCi Δm2=1 sin22θ=0.2

200

Cr51 10 MCi Δm2=1 sin22θ=0 2

80 100 120 140 atistic t 100 150

Cr51 10 MCi Δm =1 sin 2θ=0.2

20 40 60 80 test sta 50 100 2 4 6 8 10 Δm2 0.2 0.4 0.6 0.8 1 1.2 sin22θ

Oscillation effect unambiguously detected True parameters correctly identified

Gioacchino Ranucci ‐ SNAC11 27/09/2011

Why consider explicitly the discovery

Eligio Lisi talk at TAUP 2011

discovery scenario? It provides a more suitable more suitable framework to address the i request coming from the community to illustrate the sensitivity of the proposed p p experiments to an existing effect in term of effect in term of actual discovery capability

Gioacchino Ranucci ‐ SNAC11 27/09/2011

Limiting factor of the discovery capability Since the maximum of the test statistic t over the spanned region of the

• scillation parameters is the criterion to define a discovery, the corresponding

limiting factor is represented by the distribution of t when actually there is no

• scillation (this is equivalent to the noise distribution in a signal‐over‐noise

Th MC distributions

0.3

Δm2=5

sin22θ=0.11

search)

The no

• scillation

curve follows closely the

0.2 0.25

sin22θ=0.2 no oscillation i 2 θ

closely the expected ideal χ2 (2) distribution

0.1 0.15

3σ threshold

sin22θ=0.05

distribution

0.05

The threshold is set in this example for a

When t is found above the threshold “discovery” is declared. For a Δ

2 h b

d b h d d d

5 10 15 20 25 30 35 40 45

t=‐2ln(Lnum/Lden)

p three sigma detection

given Δm2 the boundary between the no discovery and discovery regions of the parameter sin22θ is its specific value at which discovery happens 50% of the times, e.g. 0.11 in this example

Example of individual simulations – Cr51 in position B h fi ll l d i The fit allows also to determine precisely the oscillation parameters

Gioacchino Ranucci ‐ SNAC11 27/09/2011

Other simulations – Sr90 at the center

G d i h h l i l ill i Good agreement with the analytical oscillation curves

Gioacchino Ranucci ‐ SNAC11 27/09/2011

10

51Cr Discovery plot

In Cr51 10 MCi Tunnel (d=825 cm) 200 days

90%

practice the discovery

1

m2 200 days 1% err. source intensity 1% err FV

% C.L.. ex

y plot does not differ from the

0.1

Δm 1% err. FV

xcluded

exclusion plot for the same Reactor + Ga 90% C.L. C.L.

0.01

3 sigma discovery plot Reactor anomaly 90%

0.001 0.001 0.01 0.1 1

Reactor anomaly 99% Sin22θ

Gioacchino Ranucci ‐ SNAC11 27/09/2011

100

144Ce discovery plot

Ce144 50 kCi Center

90% C.

The superior performance f th ti

10

365 days 1% err. source intensity 1% FV

L.. exclud

• f the anti‐ν

source in the center is confirmed

1

Δm2 1% err. FV

ded

confirmed Δ Joint reactor+Ga anomaly 90% C.L.

0.1

actor anomaly 99% C.L. reactor anomaly 90% C.L.

0.01

y 3 sigma discovery plot

0.001 0.01 0.1 1

Sin22θ

Gioacchino Ranucci ‐ SNAC11 27/09/2011

10

Discovery plots – only shape analysis vs. rate + shape

51Cr 10MCi IP 200 days 3σ CL

90% exc

1

2

1% FV 1% Source

luded

0.1

Δm2 51Cr – 10 MCi – external

3 sigma rate+waves

0.01 0.001 0.001 0.01 0.1 1

Sin22θ Sin22θ Gioacchino Ranucci ‐ SNAC11 27/09/2011

Status of the material for the Cr51 source and investigations in progress

The isotopically enriched Cr (40% Cr50) material is stored at Saclay in form of small chips for a total of 35.5 Kg It is perfectly suited to undergo a new irradiation We are currently in contact with Michel Cribier and the Saclay group in order to bring back the material to Italy. It will be stored in a special location while waiting for the new irradiation campaign : Forli’ – company Protex SPA Shipping company : MIT nucleare – the same Company can do the transportation after the irradiation (it will be needed a special Transport Container ) ( p p ) We have contacted the LNGS “expert for handling of radioactive material” Luciano Lembo (involved also in the Gallex calibration) to discuss both the issues Luciano Lembo (involved also in the Gallex calibration) to discuss both the issues connected with the transportation of the a) inert and b) activated Cr material: transport regulations and authorizations – complex but addressable matter

Gioacchino Ranucci ‐ SNAC11 27/09/2011

Search of an irradiation facility

Research reactor

• A) High thermal neutron flux throughout the entire target ideally 1E15

/ / n/cm2/sec

• B) Enough space to accommodate the material
• C) Flexible enough to allow the reconfiguration of the core

The Siloe’ reactor at Grenoble met this requirements, but it is no longer available, no other suitable reactors available in France We visited the Delft reactor (Netherland) which meets the requirements B and C, but not A – cost would have been very limited but not A cost would have been very limited We visited the Petten reactor (Netherland) , promising, complete feasibility evaluation being started evaluation being started Possibility in USA : the “Advanced Test Reactor” at Idaho National Laboratory, f i fl h i d l l featuring neutron fluxes at the required level

Gioacchino Ranucci ‐ SNAC11 27/09/2011

Further considerations Further considerations

Opportunities in Russia are being investigated as well – additional transportation difficulties Starting point GNO 2001 proposal for transportation difficulties ‐ Starting point GNO 2001 proposal for irradiation at SM3 reactor of Dimitrovgrad ‐ cost estimate was 1.3 M$

• f dollars – “kick off” meeting in Moscow at the beginning of July

More investigations required for the anti‐ν sources: Sr90 can be available from the Companies who separate it from the other fissions products‐ Experience in Russia (heating equipments upto 1993) The same consideration apply to the very recent proposal of Ru106 and Ce144 sources Joint (with potential suppliers) feasibility studies of the source preparation and delivery to be started imminently

Gioacchino Ranucci ‐ SNAC11 27/09/2011

Conclusions

Borexino is in a very favorable position to address the “hot” topic of possible short baseline νe disappearance due to oscillation to sterile via a series of neutrino source tests, through which perform powerful oscillometry measurements exclusion and discovery plots In a first step a totally non invasive measurement can be performed by deploying externally a source in the Tunnel underneath the Water Tank specifically prepared for this purpose during the construction of the detector affording already an for this purpose during the construction of the detector, affording already an interesting sensitivity limit capable to address the Gallium anomaly and to start the “exploration” of the reactor anomaly Alternative for the first phase: source immersed in water in the Water Tank In the post solar phase scenario the source(s) can be deployed in the center and the target volume increased achieving the ultimate sensitivity capable to cover a wide target volume increased achieving the ultimate sensitivity capable to cover a wide region of the oscillation parameter plane, thus fully addressing the reactor anomaly indication We have started the investigation for the source(s) preparation and procurement. For Cr51 Gallex experience and GNO proposal of 2001 Opportunity for LNGS to maintain and strengthen the leadership role gained Opportunity for LNGS to maintain and strengthen the leadership role gained through the Gallex—GNO and Borexino results in the solar neutrino sector

Gioacchino Ranucci ‐ SNAC11 27/09/2011