Short Distance Neutrino Oscillations with BoreXino SOX Borexino - - PowerPoint PPT Presentation

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Short Distance Neutrino Oscillations with BoreXino SOX Borexino - - PowerPoint PPT Presentation

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Short Distance Neutrino Oscillations with BoreXino SOX Borexino experiment Borexino experiment Mainly, a solar neutrino experiment + e - + e - in organic liquid scintillator Very low background obtained with material

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SLIDE 1

Short Distance Neutrino Oscillations with BoreXino SOX

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SLIDE 2

2 Milano 4-4- 2013

Borexino experiment Borexino experiment

  • Mainly, a solar neutrino experiment
  • ν + e- → ν + e- in organic liquid scintillator
  • Very low background obtained with

material screening, shielding and purifications

  • Low energy threshold, good energy resolution,

spatial reconstruction, pulse shape α/β identification

  • but also
  • Very good anti-neutrino detection (e.g. geo-neutrinos)
  • sub-MeV ν e detection: proved by 7Be and pep
  • sensitivity: as low as a few cpd/100 t
  • pep: 3.1 ± 0.6(stat) ± 0.3(sys) cpd/100 t
  • Phys. Rev. Lett. 107, 141302 (2011)
  • Phys. Rev. Lett. 108, 051302 (2012)
  • ν e detection: proved by geo-

neutrinos

  • total background:
  • << 1 events / year in the whole

volume

new

Neutel Venice 2013

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SLIDE 3

3 Milano 4-4- 2013

The detector The detector

Tank

3300 m3 of water 210 PMTs Cherenkov

Principle: “graded shielding”. Pure and pure materials toward the center of the detector Scintillator

270 t PC-PPO

Nylon Vessels

internal: R=4.25 m external: R=5.50 m

PIT

~ 1 m3 available at 8.25 cm from the center

Stainless Steel Sphere

~1300 m3 of liquid support for 2214 PMTs 18 m 16.9 m 13.7 m 8.25 m

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SLIDE 4

4 Milano 4-4- 2013

Borexino background today Borexino background today

  • A significant purification effort done in 2010/2011 to improve

purity further

  • Very effective on 85Kr, good on 210Bi, excellent for 238U and 232Th

p.e.

arbitrary units

  • 85Kr
  • < 8.8 cpd / 100 t
  • 2007-2010: 31.2 ± 5
  • 210Bi
  • 18 ± 4 cpd / 100 t
  • 2007-2010: 41.0 ±

2.8

  • 238U
  • < 9.7 10-19 g/g
  • 232Th
  • < 2.9 10-18 g/g

pp ν region

85Kr very

reduced

sharp 7Be shoulder

210Po peak

decays

days

cpd/100 tons

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SLIDE 5

5 Milano 4-4- 2013

SOX: SOX: S Short distance hort distance ν νe

e

O Oscillations with Bore scillations with BoreX Xino ino

  • Science
  • Motivations
  • Search for sterile neutrinos or other

short distance effects on Pee

and also

  • Measurement of ϑW at low energy (~ 1 MeV)
  • Improved limit on neutrino magnetic moment
  • Measurement of gV e gA at low energy
  • Constraints on neutrino NSI
  • Technology
  • Neutrino source: 51Cr
  • Anti-neutrino source: 144Ce
  • Project
  • SOX-A - 51Cr external
  • SOX-B - 144Ce external
  • SOX-C - 144Ce internal

Funded by the European Research Council with an ERC advanced grant amounting to 3.5 Meuros SOX is the “European”

  • fficial project acronym
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SLIDE 6

6 Milano 4-4- 2013

A long standing idea A long standing idea

  • The idea to deploy a source in Borexino dates back to the

beginning of the project

  • Successfully implemented by Gallex (LNGS) and SAGE (Baksan-

Russia)

  • Recently, revised and re-proposed by many authors to search for

sterile neutrinos

  • N.G. Basov, V. B. Rozanov, JETP 42 (1985)

Borexino proposal, 1991 (Sr90) 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) I.R.Barabanov et al., Astrop. Phys. 8 (1997) Gallex coll. PL B 420 (1998) 114 Done (Cr51) A.Ianni,D.Montanino, Astrop. Phys. 10, 1999 (Cr51 and Sr90) A.Ianni,D.Montanino,G.Scioscia, Eur. Phys. J C8, 1999 (Cr51 and Sr90) 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 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 SOX proposal - ERC 320873 - Feb. 2012 - approved Oct. 2012

a very incomplete list! See White Paper and references therein: arxiv:1204.537 9

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SLIDE 7

7 Milano 4-4- 2013

SOX: the Science case SOX: the Science case

Credit: T. Lasserre

Reactor Anomaly

  • C. Giunti et al. arxiv:1210.5715 (hep-ph)

Gallium Anomaly

  • Eur. Phys. J. C (2013) 73:2345
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SLIDE 8

8 Milano 4-4- 2013

SOX: Three Phases SOX: Three Phases

  • Mission: test the existence of low L/E

ν e and/or ν e anomalies by placing well known artificial sources close to

  • r inside Borexino
  • SOX-A
  • 51Cr source in pit beneath detector
  • 8.25 m from center [2014/2015]
  • SOX-B
  • 144Ce-144Pr source in W.T.
  • PPO everywhere to enhance sensitivity
  • 7.15 m from center [2015/2016]
  • SOX-C
  • 144Ce-144Pr source in the center
  • Only after the end of solar program
  • More effort and more time

[>2017]

pit

tunnel

144Ce

SOX-C

144Ce

SOX-B

51Cr

SOX-A

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SLIDE 9

9 Milano 4-4- 2013

Artificial neutrino sources Artificial neutrino sources

Source Production τ (days) Decay mode Energy [MeV] Mass [kg/MCi] Heat [W/kCi]

51Cr

ν e

Neutron irradiation of

50Cr in reactor

Φn ≳ 5. 1014 cm-2 s-1 40 EC γ 320 keV (10%) 0.746 1.1 0.19

144Ce-144Pr

ν e

Chemical extraction from spent nuclear fuel 411 β- <2.997 5 0.314 7.6

144Ce-144Pr

Detection threshold

144Ce 144Pr

51Cr

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SLIDE 10

10 Milano 4-4- 2013

The tunnel beneath the detector The tunnel beneath the detector

100 cm

Steel Floor of the Water Tank

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SLIDE 11

11 Milano 4-4- 2013

Data analysis: two techniques Data analysis: two techniques

  • Total counts: standard “disappearance” experiment
  • T
  • tal number of events depends on θ14 and (weakly) from Δm214
  • Sensitivity depends on:
  • Statistics (source activity and active volume)
  • Error on activity (in particular) and on efficiency
  • The relatively short life-time of 51Cr yield useful time-events

correlation

  • The background is constant while the signal is not
  • Spatial waves [C.. Grieb et al., Phys. Rev. D75: 093006 (2007)]
  • With expected Δm2 e and ~ 1 MeV energy, the wavelength is

smaller than detector size (~11 m max) and bigger than resolution (~ 15 cm)

  • The distribution of events as a function of distance to source shows

waves

  • Oscillometry analysis →Direct measurement of Δm142 and θ14
  • Very powerful and independent. Does not depend on knowledge of

source activity.

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SLIDE 12

12 Milano 4-4- 2013

Geometry with external source Geometry with external source

  • Volume:
  • Flux and decay
  • Oscillations (one sterile)
  • The number of νe-e- events at distance l from

the source, with detection threshold T1 and maximum recoil energy T2:

N.B.: The distribution of events is not uniform even without oscillations

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SLIDE 13

13 Milano 4-4- 2013

  • Waves may be detected in the distribution of events

as a function of the distance from source

  • With waves, both parameters can be measured

Ideal curves Borexino Background - No fluctuations Full Geant4 simulation - example Borexino Background

Reactor anomaly central value

1 σ 3 σ

Example for SOX-A Example for SOX-A

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SLIDE 14

14 Milano 4-4- 2013

Waves with ν Waves with νe

e and space-energy correlation

and space-energy correlation

Δm2 = 1.0 eV2 sin2(2ϑs) = 0.1 1 year

1 m fiducial cut

  • Space - Energy correlation
  • With the 144Ce-144Pr source (both

external SOX-B and internal SOX-C) global fit exploiting correlation between reconstructed event position and positron energy

Δm2 = 2.0 eV2 sin2(2ϑs) = 0.05 1 year p

  • s

i t r

  • n

e n e r g y ( M e V )

positron energy (MeV) d i s t a n c e f r

  • m

t h e s

  • u

r c e ( m ) d i s t a n c e f r

  • m

t h e s

  • u

r c e ( m )

External

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SLIDE 15

15 d i s t a n c e f r

  • m

t h e s

  • u

r c e ( m )

15 1 2.2

positron energy (MeV)

15

d i s t a n c e f r

  • m

t h e s

  • u

r c e ( m )

1 2.2

positron energy (MeV)

10 1 2.2 10 1 2.2

d i s t a n c e f r

  • m

t h e s

  • u

r c e ( m ) d i s t a n c e f r

  • m

t h e s

  • u

r c e ( m ) positron energy (MeV) positron energy (MeV) Milano 4-4- 2013

External Center More examples of space-energy patterns for More examples of space-energy patterns for 144

144Ce-

Ce-

144 144Pr

Pr

∆m2=2eV2 sin22θ=0.1 ∆m2=6eV2 sin22θ=0.1

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SLIDE 16

16 Milano 4-4- 2013

SOX-A sensitivity SOX-A sensitivity

Reactor+Ga anomaly region

  • SOX-A:
  • 51Cr source at

8.25 m from the center

  • 10 MCi
  • 1% precision in

source activity

  • 1% in FV

determination

  • Phase A can happen any time during next solar neutrino phase
  • 2014/15 is realistic – 3 months of data taking
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SLIDE 17

17 Milano 4-4- 2013

SOX-B sensitivity SOX-B sensitivity

  • SOX-B
  • 144Ce-144Pr source at

7.15 m from the center (in water tank)

  • 75 kCi
  • 1.5% precision in

source activity

  • 2% bin-to-bin error

to include all effects

  • SOX-B can happen any time during next solar neutrino phase
  • 2015/16 is a realistic scenario – 1.5 years of data taking

Reactor+Ga anomaly region

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SLIDE 18

18 Milano 4-4- 2013

SOX-C sensitivity SOX-C sensitivity

  • SOX-C:
  • 144Ce-144Pr source

in the center

  • 75 kCi
  • 1.5% precision in

source activity

  • 2% bin-to-bin error to

include other systematics

  • SOX-C can happen only after the end of solar neutrino phase
  • 2017-2018 is in principle possible – 1.5 years of data taking
  • Reactor+Ga

anomaly region

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SLIDE 19

19 Milano 4-4- 2013

T echnology: T echnology: 51

51Cr source

Cr source

External T must be acceptable Current value: T=90°C Internal T must be below syntherization (750°C) Current value: T=260 °C

51Cr

W

Gallex 1994

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SLIDE 20

20 Milano 4-4- 2013

T echnology: location for T echnology: location for 51

51Cr source

Cr source

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SLIDE 21

21 Milano 4-4- 2013

T echnology: shielding T echnology: shielding

  • Material: DENSIMET-185 ( W 97%, 3% Ni-Fe alloy)
  • Weight: ~ 2 ton
  • Main problem not from 51Cr (low energy photons) but from impurities at

ppm level

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SLIDE 22

22 Milano 4-4- 2013

SOX-C: SOX-C: 144

144Ce source inside detector

Ce source inside detector

  • Very massive source
  • ~ 4 t of shielding
  • Source: spent nuclear fuel from Russia
  • DENSIMET (W) shielding plus

ultra-pure copper layer to reduce background

  • W is very dirty for Borexino
  • γ background is a problem if rate too high
  • random coincidences make background
  • Source deployment to be studied
  • Either from the top or from the bottom
  • PPO everywhere in the SSS to enlarge

active volume (active radius up to 5.5 m)

  • New anti-neutrino trigger
  • Trigger on singles would be too hard, but this is not a problem
  • > 2017 for deployment in within the scintillator
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SLIDE 23

23 Milano 4-4- 2013

Summary Summary

  • We plan to perform an extensive search of sterile neutrinos with

neutrino and anti-neutrino sources

  • SOX-A
  • 51Cr neutrino source (external)
  • Preliminary schedule: 2014/2015
  • SOX-B
  • 144Ce anti-neutrino source

(external)

  • T

entative schedule: 2015/2016 (TBC)

  • SOX-C
  • 144Ce anti-neutrino source

(internal)

  • No schedule (>2017)

SOX-A SOX-B

positron energy (MeV)

positron energy (MeV)

d i s t a n c e f r
  • m
t h e s
  • u
r c e ( m )

d i s t a n c e f r

  • m

t h e s

  • u

r c e ( m )