ComprehensiveComprehensive measurementmeasurement ofof pp-chainpp-chain solarsolar neutrinosneutrinos withwith BorexinoBorexino Mariia Redchuk on behalf of the Borexino collaboration 11.07.2019 EPS-HEP2019 1 Institut für Kernphysik, Forschungszentrum Jülich, Germany 2 III. Physikalisches Institut B, RWTH Aachen, Germany Ghent, Belgium ComprehensiveComprehensive measurementmeasurement ofof pp-chainpp-chain solarsolar neutrinosneutrinos withwith BorexinoBorexino Mariia Redchuk on behalf of the Borexino collaboration 11.07.2019 EPS-HEP2019 1 Institut für Kernphysik, Forschungszentrum Jülich, Germany 2 III. Physikalisches Institut B, RWTH Aachen, Germany Ghent, Belgium OUTLINE 3 ComprehensiveComprehensive measurementmeasurement ofof pp-chainpp-chain solarsolar neutrinosneutrinos withwith BorexinoBorexino 1. What are solarsolar neutrinosneutrinos? 2. What is BorexinoBorexino? 3. What did we measuremeasure and how? 4. What are the implications? 5. What’s next? 6. Summary OUTLINE 4 1. What are solarsolar neutrinosneutrinos? 2. What is Borexino? 3. What did we measure and how? 4. What are the implications? 5. What’s next? 6. Summary WHAT ARE SOLAR NEUTRINOS? 5
• Fusion reactions that convert 99% of the solar energy p → 4He produce ν
Intense natural ν beam • Study ν using the sun → oscillation parameters → MSW-LMA (matter effect)
Direct probe of the sun’s core • Study the sun using ν → fusion rates → metallicity WHAT ARE SOLAR NEUTRINOS? 6 Alternative way to convert p → 4He, closed-loop catalyzed CNO chain Has never been experimentally observed Expected to be the main source of energy in heavier stars < 1% solar energy
Credit: Wikimedia Commons WHAT ARE SOLAR NEUTRINOS? 7
Solar metallicity High M Low M abundance of elements heavier than He
Metallicity → opacity of the solar plasma → central T°C → ν fluxes
Different fluxes are predicted by different Standard Solar Models Metallicity is fundamental but still poorly understood!
N. Vinyoles et al., “A new Generation of Standard Solar Models,” Astrophys. J., vol. 835, no. 2, p. 202 (2017) OUTLINE 8
1. What are solarsolar neutrinosneutrinos? 2. What is BorexinoBorexino? 3. What did we measure and how? 4. What are the implications? 5. What’s next? 6. Summary WHAT IS BOREXINO? 9 Borexino Credit: Google Maps the world's most radio-pure liquid scintillator detector ItalyItaly ● 3800m water equivalent GERDA CUORE the largest ● μ suppressed by factor ~106 underground research center Credit: Laboratori Nazionali in the world del Gran Sasso LNGSLNGS WHAT IS BOREXINO? 10 ● ~200 μ PMTs 50 keV @ 1 MeV water tank Nylon 12 cm @ 1 MeV vessels ~500 p.e./MeV
● Lowest energy threshold
Buffer ● Stainless Unprecedented steel sphere radiopurity ▸ high purity materials
Fiducial ▸ volume Using Fiducial Volume ~2000 internal PMTs ▸ Purification campaign
[for scale] the best for solar neutrinos WHAT IS BOREXINO? 11 before
Nylon vessels after
Inner detector PMTs OUTLINE 12
1. What are solarsolar neutrinosneutrinos? 2. What is BorexinoBorexino? 3. What did we measuremeasure and how? 4. What are the implications? 5. What’s next? 6. Summary WHAT DID WE MEASURE? 13 Comprehensive measurement of pp-chain solar neutrinos with Borexino M. Agostini et al., (Borexino Collaboration), Nature, 562, 505 (2018)
All measurements have improved precision
▸ pp → 9.5% ▸ 7Be → 2.7% × 2 more precise than theory ▸ 8B → 8% ▸ pep → 16% > 5σ discovery ▸ hep → 90% CL upper limit NEW! ▸ CNO → 95% CL upper limit most stringent so far HOW DID WE DO IT? 14 Theory: Data: ν spectra ν + backgrounds
neutrino fit & background rates HOW DID WE DO IT? 15 Theory: Data: ν spectra ν + backgrounds
Compton shoulder
neutrino fit & background rates HOW DID WE DO IT? 16 LER LER → pp, pep, 7Be; CNO (0.19 - 2.93 MeV) First simultaneous extraction of HER pp, pep and 7Be rates
HER → 8B; hep (3.2 - 16 MeV) Lowest energy threshold
Some backgrounds can be measured independently and constrained HER and LER have different backgrounds Low energy region analysis
Phase I Phase II
08 10 11 16 20 20 20 20 purification
High energy region analysis HOW DID WE DO IT? 17 no cuts LER data selection 9 14 9.9 C effi 92 ci % enc µ and y µ daughter cut 210Po Fiducial Volume cut 11C Three-fold coincidence cut
(250 μs) (29.4 min) (2.2 MeV) HOW DID WE DO IT? 18 LER multivariate fit TFC TFC subtracted tagged 8% 11C 92% 11C ~64% exposure ~36% exposure HOW DID WE DO IT? 19 radial pulse shape
TFC-sub TFC-tag HOW DID WE DO IT? 20 HER-I HER-II
3.2 – 5.7 MeV 5.7 - 16 MeV Background: natural radioactivity Background: external γ rays
HER data selection: ● Independent radial fits ● neutron cut ● × 3 increase in target mass, × 10 increase in exposure ● fast cosmogenics cut ● No assumption on Eν energy spectrum! ● 10C cut → no dependence on Pee(Eν) 214 ● Bi-Po cut → probe deviations from MSW OUTLINE 21
1. What are solarsolar neutrinosneutrinos? 2. What is BorexinoBorexino? 3. What did we measuremeasure and how? 4. What are the implications? 5. What’s next? 6. Summary WHAT ARE THE IMPLICATIONS? 22 Real time picture of the core of the sun
→ total power from the nuclear reactions: L = 3.89 ± 0.42 x 1033 erg s-1 compatible with photon output L = 3.846 ± 0.015 x 1033 erg s-1
Credit: NASA/SDO → experimentally confirm nuclear origin of the solar power best precision by a single solar-ν experiment → proves the sun has been in thermodynamic equilibrium over 105 years time scale WHAT ARE THE IMPLICATIONS? 23 Relative intensity of pp-I and pp-II
Theoretical prediction:
RI/II(HM) = 0.180 ± 0.011
RI/II(LM) = 0.161 ± 0.010
New experimental result: R = 0.178 ± 0.027
→ compatible with expected values WHAT ARE THE IMPLICATIONS? 24 7Be and 8B have the largest difference in HZ/LZ ) e B 7 ( f
f(8B) → weak hint towards high metallicity WHAT ARE THE IMPLICATIONS? 25 y t
i vacuum l matter i matter
b dominated dominated a b o r p
l a v i v r u s
e ν
transition
→ region
e ν
Borexino is the only experiment that can probe the νe survival probability in both vacuum and matter dominated regions Disfavour vacuum oscillations at 95% CL OUTLINE 26
1. What are solarsolar neutrinosneutrinos? 2. What is BorexinoBorexino? 3. What did we measuremeasure and how? 4. What are the implications? 5. What’s next? 6. Summary WHAT’S NEXT? 27
Phase I Phase II Phase III
08 10 11 16 20 20 20 20 new trigger system purification CNOCNO νν measurement can solve the metallicity puzzle 210Bi Challenges: pep ● CNO Extremely low rate ● Shape similar to 210Bi and pep WHAT’S NEXT? → TOWARDS CNOCNO 28 Constrain the rate of 210Bi (β)) by measuring 210Po (α)) (the only α → event by event basis) 32y 7.23d 199.1d Sensitivity studies 210PbPb → 210BiBi → 210PoPo → 206PbPb with toy MC → possibility 210 to get a CNO measurement ● Disentangle vessel Po contamination between 2 and 4σ (not in equilibrium)
● thermal convection stabilization
thermal north insulation
south OUTLINE 29
1. What are solarsolar neutrinosneutrinos? 2. What is BorexinoBorexino? 3. What did we measuremeasure and how? 4. What are the implications? 5. What’s next?
6. Summary SUMMARY 30
● Solar νs are a useful tool to probe solar models and neutrino physics
● The Borexino detector is perfect for solar neutrino analysis due to its radiopurity
● New Nature publication by Borexino reports a comprehensive study of the pp-chain νs with improved precision: pp (9.5%), 7Be (2.7%), 8B (8%), pep (16%), hep (90% CL up. lim.)
● It was done using extensive Borexino dataset and a multivariate fit approach
● The results show a weak hint towards the high metallicity hypothesis, exclude vacuum oscillations with 95% CL
● Sensitivity studies show promising perspective for the CNO ν measurement 31 BorexinoBorexino CollaborationCollaboration
University of Technische Universität Houston München
Universität Hamburg
SKOBELTSYN INSTITUTE OF NUCLEAR PHYSICS Joint Institute for Nuclear LOMONOSOV MOSCOW STATE UNIVERSITY Research 32
Thanks for listening! Backup PREVIOUS AND NEW RESULTS 34
Neutrino Previous New (2018)
+6 pp 144 ± 13 ± 10 → 11.5% (2014) 134 ± 10 − 10 → 9.5%
7 + 0.4 Be 48.3 ± 2.0 ± 0.9 → 4.5% (2014) 48.3 ± 1.1 − 0.7 → 2.7%
+0.15 2.43 ± 0.36 − 0.22 → 16.5% (HZ) pep 3.1 ± 0.6 ± 0.3 → 21.5% (2014) +0.15 2.35 ± 0.36 − 0.24 → 15.5% (LZ)
8 +0.015+ 0.006 B 0.22 ± 0.04 ± 0.01 → 18.5% (2010) 0.223 − 0.016 − 0.006 → 7.5%
CNO < 12 at 95% CL (2014) < 8.1 at 95%CL
hep – < 0.002 at 90%CL → NEW! SOLAR NEUTRINO RESULTS 35
● pep are the only ν that show difference in HZ/LZ ● CNO limit is identical for HZ or LZ assumption on pp/pep constraint TOWARDS CNO MEASUREMENT 36
α and β have different hit time distributions
214Bi(β)) 214Po(α)) Multi-Layer Perceptron variable to discriminate between α and β THE SOLAR METALLICITY PUZZLE 37
metallicity High M Low M High M Low M ) s l a t e m (
Helioseismology (surface seismic waves) → low M agrees less
Solar surface composition → lower than assumed before BOREXINO STRUCTURE 38 Outer Nylon vessels detector Shield from Water tank (2100t) PMTs and SSS Shield + μ veto Barrier for Rn ~200 PMTs Create buffer
Stainless Steel Buffer Sphere Diluted LS R = 6.85m Inner Vessel Inner detector R = 4.25m ~2000 PMTs ~280t LS
● 3800m water Fiducial volume equivalent ~70t ● 50 keV @ 1 MeV Software cut [for scale] Remove noise ● 12 cm @ 1 MeV ● 551 pe/MeV HER AND LER INFORMATION 39 Low energy region analysis (0.19 - 2.93 MeV)
Phase I Phase II
08 10 11 16 20 20 20 20 purification
High energy region analysis (3.2 - 16 MeV) HER → 8B; hep LER → pp, pep and 7Be; CNO;
● not sensitive to low 8B is constrained to the value from HER energy backgrounds 7 ● pp, pep and Be: CNO is constrained to HZ/LZ ● Whole IV (280 t) is → 2 results for pep for HZ/LZ, the rest no used (+ z-cut in HER-I), difference unlike LER which uses ● CNO limit: pp/pep ratio is constrained (HZ/LZ) Fiducial Volume (70t) ● hep limit: counting analysis COMPTON & DETECTOR RESPONSE 40 ν spectra
recoiled e- spectra The electron takes a fraction of the ν energy → Compton shoulder
The PDFs for the fit are constructed in two ways (part of systematics)
● MC simulation of all the processes (tuned on calibration data) ● Analytical description of the detector response, some nuisance parameters are free in the fit ENERGY ESTIMATORS 41
# of hits (photons) # of triggered PMTs # of photoelectrons (charge) Monte Carlo method: simulate detector response Analytical method: DIFFERENT FIT METHODS 42 Monte Carlo Analytical Detector response Full simulation Describe mathematically + light yield Free Rates of signal and + 6 response function parameters background parameters More free parameters Cons Cannot account for → unknown variations more correlations
Tuning done on ● More flexible Pros calibration data ● dark noise convolution
independent of analysis ● 14 data easier to deal with C SYSTEMATICS 44 MSW-LMA (MATTER EFFECT) 45
energy independent
mixing angle in matter, depends on Eν NEUTRINO SPECTRA 46
U. F. Katz and C. Spiering, “High-Energy Neutrino Astrophysics: Status and Perspectives,” Prog. Part. Nucl. Phys., vol. 67, pp. 651–704, 2012 DOI: 10.1016/j.ppnp.2011.12.001