marco g. giammarchi istituto nazionale di fisica nucleare
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Results from Borexino 26th Rencontres de Blois - 2014. Marco G. Giammarchi Istituto Nazionale di Fisica Nucleare Via Celoria 16 – 20133 Milano ( Italy ) [email protected] http://pcgiammarchi.mi.infn.it/giammarchi/. On behalf of the BOREXINO Collaboration - PowerPoint PPT PresentationTRANSCRIPT
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Marco G. GiammarchiIstituto Nazionale di Fisica NucleareVia Celoria 16 – 20133 Milano (Italy)
[email protected]://pcgiammarchi.mi.infn.it/giammarchi/
1. BOREXINO
2. Be-7 flux measurement
3. B-8 measurement
4. pep detection and CNO limit
5. Future
Results from Borexino26th Rencontres de Blois - 2014
1Rencontres de Blois - May 2014
On behalf of the BOREXINO CollaborationReporting on the Solar Results only
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the Borexino Collaboration
UMass Amherst
Milano
Perugia
Princeton
Virginia Tech
Genova
JINR Dubna
HeidelbergMünchen
Kurchatov Moscow
Jagiellonian Kraków
St. Petersburg
Paris
Hamburg
Gran Sasso
Houston
Los Angeles
Moscow
Mainz
TU DresdenNapoli
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We believe we understand the Sunpp-cycle
>99% energy production5 ν species
CNO-cycle <1% energy production
3 ν species
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Neutrinos are produced in several reactions in both cycles
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1. BOREXINO
Borexino is a low background Neutrino Detector for sub-MeV solar Neutrino (and other) studies
Detecting Solar Neutrinos, Geo-neutrinos and other rare phenomena
• Main detection reaction: elastic scattering in a scintillator
• Low interaction rates: 0.1/1 event/day/ton of target mass
• Low energy (mostly <10 MeV, better if <2 MeV)
• Low threshold and low background (radiopurity)
• Underground location to shield from cosmic rays (106 reduction of muon flux)
ee
1. BOREXINO
2. Be-7 flux measurement
3. B-8 measurement
4. pep detection and CNO limit
5. Future
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Abruzzo, Italy120 Km from Rome
LaboratoriNazionali del Gran Sasso
Assergi (AQ)Italy
1400m of rock shielding
~3800 m.w.e.
Borexino Detector and Plants
External Labs
Experimental site
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Water Tank:γ and n shieldμ water Č detector208 PMTs in water2100 m3
2020 legs legs Carbon Steel Plates
Scintillator:270 t PC+PPO (1.4 g/l)
Stainless Steel Sphere:
● 2212 PMTs ● ~ 1000 m3 buffer of
pc+dmp (light queched)
Nylon vessels:(125 μm thick)Inner: 4.25 mOuter: 5.50 m(radon barrier)
The Borexino DetectorNeutrino electron
scattering e > e
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Filling phase of the Borexino detector (2007, Laboratorio del Gran Sasso)
11 m
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Water
Scintillator
Photomultipliers
Nylon Vessels
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,Borexino
Solar Neutrinos: the predicted spectrum
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Study of Solar Neutrinos Solar Neutrino Problem Neutrino Oscillations
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(W. Hiroko’s talk at Neutel 2013)Neutrino Oscillation Solution
0025.00241.0sin
307.0sin
1054.7
132
018.0016.012
2
2526.022.0
212
eVm
Large Mixing Angle + MSW mechanism in the Sun
Global, 3-lepton flavor analysis
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Open Issues
However: before Borexino, only radiochemical experiments could observe solar neutrinos below 1 MeV. Real-time experiments were sensible mostly to > 5 MeV
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2. Be-7 flux measurement
Cross Section 10-44 cm2 (@ 1 MeV)
eLieBe 77
),,( exee xx
Eν = 862 keV (monoenergetic)ΦSSM = 4.8 · 109 ν s-1 cm2
Electron recoil spectrum
νe
νx
1. BOREXINO
2. Be-7 flux measurement
3. B-8 measurement
4. pep detection and CNO limit
5. Future
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1291024.084.4 scmLMA
tdcstat 100/5.10.46 6.15.1
systst 007.00012.0001.0
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3. B-8 measurementAnalysis with 3 MeV thresholdBorexino rate : ≈ 0.2 cpd / (100 tons)Backgrounds: • Muons, Neutrons• External background• Fast cosmogenics• C-10, Be-11• Tl-208,Bi-214
1. BOREXINO
2. Be-7 flux measurement
3. B-8 measurement
4. pep detection and CNO limit
5. Future
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)3(100/)(01.0)(04.022.0 MeVabovetcpdsyststatR
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p + e - + p d + e
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4. pep detection and CNO limit
Pep reaction
Monoenergetic1.44 MeVneutrinos
1. BOREXINO
2. Be-7 flux measurement
3. B-8 measurement
4. pep detection and CNO limit
5. Future
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C-11 reduction strategy:
• Threefold coincidence (muon,neutron,C11)
• Pulse shape discrimination electron/gamma/positron (Ps formation)
• Multivariate fit with also energy and position
12810)3.06.1()( scmLMAMSWpep
)%95(107.7)( 128 CLscmLMAMSWCNO
First pep measurement and the best CNO limit
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Solar neutrino components measured by Borexino
,Borexino
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Solar electron neutrino survival probability as a function of neutrino energyLMA-MSW with standard neutrino interactions
Neutrino Oscillations properties measured by Borexino
Matter Regime
Vacuum Regime
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6. Future (summary)
Borexino Phase II (solar neutrinos):
• pp detection
• CNO study
Cycles of Purification (Water Extraction) :
• Reduce 85Kr and 210Bi affecting the pep and CNO analyses
• Kr background reduced to a negligible rate
• Bi-210 reduced (tens of counts/day 100 tons) and possibly studied by means of the time evolution of Po-210 rate.
1. BOREXINO
2. Be-7 flux measurement
3. B-8 measurement
4. pep detection and CNO limit
5. Future
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CNO detection
CNO reactions are responsible for less than 1% of the Sun energy generation
However, this cycle should be dominant for higher mass stars (higher temperatures)
Given their small flux and low energy, neutrinos from CNO have never been measured directly.
pp detection
They make up more than 90% of the total flux and have never been directly observed.
Main source of background is C-14 and its pileup effect.
C-14 spectral shape and pileup
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2323
Thank you for your attention (& selected bibliography)
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• G. Alimonti et al., Nucl. Instr. & Methods A600 (2009) 568
• C. Arpesella et al., Phys. Lett. B 568 (2008) 101• C. Arpesella et al., Phys. Rev. Lett. 101 (2008) 091302• G. Bellini et al., Phys. Rev. Lett. 107 (2011) 141302• G. Bellini et al., Phys. Lett. B 707 (2012) 22
Detector
Be-7
• G. Bellini et al., Phys. Rev. D 82 (2010) 033006 B-8
• G. Bellini et al., Phys. Lett. B 687 (2010) 299• G. Bellini et al., Phys. Lett. B 722 (2013) 295
Geo ν
• G. Bellini et al., Phys. Rev. Lett 108 (2012) 051302 pep
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Backup Slides
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5. Geoneutrinos
enpe
AntiNeutrinos emitted in beta decays of naturally occurring radioactive isotopes in the Earth’s crust and mantle
Moderate Nuclear Reactors bkgd at LNGS
Detection by Inverse Beta Decay (1.8 MeV thr.)
Unoscillated Geo-nu and nuclear reactor nu
Unoscillated Geo-nu
Positron-Gamma (2.2 MeV) delayed coincidence
1. BOREXINO
2. Be-7 flux measurement
3. B-8 measurement
4. pep detection and CNO limit
5. Geoneutrinos
6. Future
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Search for positron/neutron-capturedelayed coincidences in the Borexino detectorMain background sources:• Li-9, He-8, untagged muons, accidentals………• And of course nuclear reactors• First observation published in 2010
New analysis based on 1353 days of dataPhys. Lett. B 722 (2013) 295
Reactor antineutrinos at LNGS
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1353 days in Borexino: antineutrino geo analysis
Nuclear Reactor component :
Found : 21 events above geo endpoint
Expected : 22.0 +- 1.6
Geoneutrinos vs Reactor neutrinos:
Extreme expectations of BSE (Bulk Silicate Earth) model
Reactor signal expectation
68.27%, 95.45%, 99.73%Confidence level contour plots for geo and reactor neutrinos
(1 TNU = 1 Terrestrial Neutrino Unit = 1 event/year/1032 protons)
Free parameters- Weight of Geo nu- Weight Reactor nu
Th/U = 3.9 fixed(condhritic value)
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TNUSN
TNUSN
reareac
geogeo
3.199.16
0.71.6 5.842.31
)0.128.38(4.43.14
Best fit values:
126
126
106.00.2)(
107.04.2)(
scmTh
scmUGeofluxes
If U,Th contributions are left free: 126
126
101.36.2)(
105.11.2)(
scmTh
scmU
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τ (n capture): ~250μs
nCC 1112
MeVdpn 2.2
eeBC 1111
nγ
μ
τ (11C): ~30min
β11C Production Channels:
[Galbiati et al., Phys. Rev. C71, 055805, 2005]
1. 95.5% with n: (X,X+n) X = γ, n, p, π±, e±, μ.
2. 4.5% invisible : (p,d); (π+,π0+p).
The main background for pep and CNO analysis is 11C, a long lived (τ=30min) cosmogenic β+ emitter with ~1MeV end-point (shifted to 1-2MeV range)
11C rate = (28.5 ± 0.5) cpdexp. pep rate ~ 3cpd
Going for pep and CNO: 11C tagging
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Electron/Positron discrimination due to Ps formation in positron events(D. Franco, G. Consolati and D. Trezzi, Phys. Rev. C 83 (2011) 015504
Going for pep and CNO: positronium
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A. The Cr-51 source, with an activity of ~10 Mci
Obtained by irradiation of Cr-50 .
3-months experiment to be performed in 2015
B. A Ce-144 antineutrino source can be used. Due to the antineutrino tag, the activity could be much smaller, in the 80 kCi range.
C. The Ce-144 source positioned at the center of the detector
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Short distance neutrino Oscillations with BoreXino (SOX)
Experimental anomalies which are difficult to accomodate in a simple 3-flavor scenario
A fourth (sterile) neutrino? («Gallium», «Reactor», «LSND-MiniBoone» anomalies)
Borexino can be used to perform a short baseline experiment with neutrino source
Exploration of parameters in the plane )2sin,( 1422
14 m
L/E of the order of eV2
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PMNS neutrino mixing matrix, analogous to CKM matrix for quarks
Solution of the Solar Neutrino Problem is neutrino oscillation with matter (MSW) effect at Large Mixing Angle (LMA)
Neutrino Oscillations
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