16 th International Conference on Topics in Astroparticle and Underground Physics 9-13 September 2019 Toyama, Japan Ten years of cosmic muons observation with Borexino Davide D’Angelo on behalf of the Borexino Collaboration Università degli Studi di Milano Istituto Nazionale di Fisica Nucleare, sez. di Milano
Why Borexino? Ø A low energy neutrino detector Ø based on elastic scattering on electrons Ø highly purified organic liquid scintillator Solar neutrinos: 7 Be , 8 B, pep, pp and possibly CNO. See talk by S. Zavatarelli Geo-neutrinos, supernova explosion, neutrino See talk by L. Ludhova magnetic moment, … TAUP 2019 – Borexino Cosmic Muons D. D'Angelo 2
The Borexino Detector Stainless Steel Sphere: 2212 PMTs ● ~ 1000 m 3 buffer of pc+dmp ● Scintillator: (light quenched) 278 t PC+PPO (1.4 g/l) Water Tank: Nylon vessels: γ and n shield (125 μ m thick) μ water Č detector Inner r: 4.25 m 208 PMTs in water Outer r: 5.50 m 2100 m 3 (radon barrier) 3800m w.e. of rock shielding TAUP 2019 – Borexino Cosmic Muons D. D'Angelo 3
Why Borexino? Ø A low energy neutrino detector Ø based on elastic scattering on electrons Ø highly purified organic liquid scintillator Solar neutrinos: 7 Be , 8 B, pep, pp and possibly CNO. Geo-neutrinos, supernova explosion, neutrino magnetic moment, … Ø Also a powerful detector for muons, neutrons and cosmogenic backgrounds. Ø Muon detection occurs with both Inner and Outer detector Spherical detector: no systematics due to angular dependence of the acceptance TAUP 2019 – Borexino Cosmic Muons D. D'Angelo 4
Borexino data taking campaign now May Oct. May Jan temperature 2010 2011 2007 2017 stabilization Purification Preparation Phase 1 Phase 2 CNO 6 cycles of water extr. • 7 Be ν : 1 st observ. + pp ν : 1 st observation (Nature 2014) • Campaign precision; Day/Night seasonal modulation of 7 Be ν • asymm.; Comprehensive measurement of pp- • • pep ν : 1 st observation; chain solar neutrinos: • 8 B ν with low thresh.; Nature 562, 505–510 (2018) • CNO ν : best limit; more details: arXiV:1707.09279, 1709.00756/ • TAUP 2019 – Borexino Cosmic Muons D. D'Angelo 5
Borexino data taking campaign now May Oct. May Jan temperature 2010 2011 2007 2017 stabilization Purification Preparation Phase 1 Phase 2 CNO 6 cycles of water extr. • 7 Be ν : 1 st observ. + pp ν : 1 st observation (Nature 2014) • Campaign precision; Day/Night seasonal modulation of 7 Be ν • asymm.; Comprehensive measurement of pp- • • pep ν : 1 st observation; chain solar neutrinos: • 8 B ν with low thresh.; Nature 562, 505–510 (2018) • CNO ν : best limit; more details: arXiV:1707.09279, 1709.00756 • 10 years observation of cosmogenic muons! TAUP 2019 – Borexino Cosmic Muons D. D'Angelo 6
J ournal of C osmology and A stroparticle P hysics An IOP and SISSA journal JCAP 02 (2019) 046 Modulations of the cosmic muon signal in ten years of Borexino data 16 th May 2007 – 15 th May 2017 CNGS muons (2008-2012) removed 3218 days used The Borexino collaboration no prolonged downtimes Muons crossing both Inner and Outer Detector ◦ efficiency 0.9928(2) Detector cross sections for muons:146 m 2 Total exposure: 4.2 10 5 m 2 d TAUP 2019 – Borexino Cosmic Muons D. D'Angelo 7
10yr muon modulation analysis ] -1 4600 Borexino Muon Data Average Muon Flux [d Seasonal Modulation Fit ✓ 2 π ◆ 4500 I µ ( t ) = I 0 µ + δ I µ cos T ( t − t 0 ) 4400 µ = (3 . 432 ± 0 . 001) · 10 − 4 m − 2 s − 1 x I 0 4300 − 1 ± 4200 ± · is δ I µ = (58 . 9 ± 1 . 9) d − 1 = (1 . 36 ± 0 . 04)% is χ 2 / NDF = 3921 / 3214. 4100 ± 6 σ (Data-Fit)/ 4 d T = (366 . 3 ± 0 . 6) d 2 0 − 2 ± 4 − 6 − 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 ase t 0 = (174 . 8 ± 3 . 8) d. Jun 25 th TAUP 2019 – Borexino Cosmic Muons D. D'Angelo 8
Or folded to 1y ] -1 Period fixed to Average Muon Flux [d 10 yr Borexino Data 4450 Seasonal Modulation Fit 1yr Rate and 4400 amplitude 4350 unchanged Better 4300 determination of 4250 the phase 4200 is χ 2 / NDF = 13702 / 362. Jan Mar May Jul Sep Nov e t 0 = (181 . 7 ± 0 . 4) d, Jul 1 st TAUP 2019 – Borexino Cosmic Muons D. D'Angelo 9
Why a muon seasonal modulation? (in a nutshell) Muons originate from π and K meson decay high in the atmosphere. The muon flux observed underground depends on the fraction of mesons that decay before first interaction Hotter air is less dense leading to reduced interaction chance higher temperature è more visible muons TAUP 2019 – Borexino Cosmic Muons D. D'Angelo 10
Effective atmospheric temperature Normalized Weight ⇤ ∞ 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 ∆ I µ dX α ( X ) ∆ T ( X ) Pressure [hPa] 60 ∆ I µ ∆ T e ff Height [km] = 1 = � T I 0 T 0 ( X ) Normalized Weights Normalized Weights $ + ! 0 I 0 T e ff µ K ) ( ! n n µ 50 Temperature T(X) � N n + W K n =0 ∆ X n T ( X n )( W π n ) T e ff ⇤ 40 10 � N n + W K n =0 ∆ X n ( W π n ) W(X) 30 2 20 10 π ,K ) 2 e � X/ Λ π ,K A 1 (1 � X/ Λ ⇥ π ,K W π ,K ( X ) ⇤ ⇥ + ( ⇥ + 1) B 1 π ,K K ( X )( ⌅ E th cos ⌅ ⇧ / ⇤ π ,K ) 2 10 3 10 only site-related parameter h i 200 210 220 230 240 250 260 270 280 290 300 T [K] , h E thr cos ✓ i = (1 . 34 ± 0 . 18) TeV d A 1 K = 0 . 38 · r K / π , w new from our simulation eter B 1 considers [formerly 1.833 TeV from Grashorn et al. (2010)] TAUP 2019 – Borexino Cosmic Muons D. D'Angelo 11
European Centre for Air temperature data Medium-range Weather Forecast (ECMWF): Temperature [K] ü 4 daily measures: 0h, 6h, 12h, 18h. 230 ECMWF Data ü 37 pressure levels: [1-1000]hPa. Seasonal Modulation Fit 228 ü 1.5km spaced grid 226 ü interpolate to LNGS coordinates 224 10 Deviation from mean (%) 222 8 Temperature 6 220 4 2 218 0 2 216 − 4 − 214 6 − Borexino muon rate − 8 212 − 10 Jul/2014 Dec/2014 Jul/2015 Jan/2016 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 Close agreement also on short scale Time Sudden Stratospheric Warming (SSW): ~1-2w winter maxima due to artic variations cyclone deformations. [Geophys. Res. Lett. 36 L05809 (2009)] TAUP 2019 – Borexino Cosmic Muons D. D'Angelo 12
α T ∆ I µ ∆ T e ff = � T Predicted α T at LNGS: I 0 T e ff µ ↵ T = T @ I µ (%) with some parametrization … . 10 Data I 0 @ T 〉 µ = 0.90 0.02 µ α ± I T 〈 / µ I 5 Δ 1 / ✏ K + A K ( D π /D K ) 2 / ✏ π 1 ↵ T = , D π 1 / ✏ K + A K ( D π /D K ) / ✏ π 0 d A K = 0 . 38 ⇥ r K / π 5 − the product of the t � ✏ π , K D π , K ⌘ 1 . 1 h E thr cos ✓ i + 1 R-value=0.55 � + 1 − 10 − 5 − 4 − 3 − 2 − 1 0 1 2 3 T / T (%) Δ 〈 〉 eff eff Experiment Time period ↵ T Revising the value from 1.833 TeV to 1.34 TeV, Borexino (This work) 2007–2017 0 . 90 ± 0 . 02 Error halved ! the prediction shifts from α T = 0.92 ± 0.02 to Borexino Phase I [6] 2007–2011 0 . 93 ± 0 . 04 α T = 0.895 ± 0.15 GERDA [7] 2010–2013 0 . 96 ± 0 . 05 0 . 91 ± 0 . 05 MACRO [31] 1991–1997 0 . 91 ± 0 . 07 TAUP 2019 – Borexino Cosmic Muons D. D'Angelo 13 LVD [5] 1992–2016 0 . 93 ± 0 . 02
α T T α α α based on r K/ π = 0.149 ± 0.06 literature value 1.4 T T ( ( ) ) α α T T π π ( ( ) ) α α 1.2 T T K K Fit: r Fit: r = 0.08 = 0.08 0.02 0.02 ± ± K/ K/ π π 1 LNGS Weighted Mean AMANDA MINOS 0.8 Ice Cube Barrett Daya Bay EH3 0.6 1 MACRO Borexino Daya Bay EH2 0.95 (This Work) 0.4 Daya Bay EH1 Double Chooz FD 0.9 LVD GERDA II Double Chooz ND Borexino 0.2 (2012) 0.85 GERDA I 0 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 E cos [TeV] 〈 θ 〉 thr TAUP 2019 – Borexino Cosmic Muons D. D'Angelo 14
Kaon/Pion ratio indirect measure comparison with existing measurements 0.98 π T K/ 0.25 α Experimental α Borexino (this work) (p+A ) r T atm MINOS (p+A ) Theoretical α 0.96 T atm 2 IceCube (p+A ) Combined Fit χ atm 0.2 +0.11 NA49 (Pb+Pb) Best Fit Value: r = 0.11 K/ -0.07 π - 0.94 - STAR (Au+Au, K / ) π E735 ( p +p) 0.15 0.92 0.9 0.1 0.88 0.05 0.86 gy p s = (190 ± 28) GeV, 0.84 0 0 0.05 0.1 0.15 0.2 0.25 0.3 3 2 10 10 Atmospheric Kaon to Pion Ratio r duction ratio, we es K/ π s [GeV] √ s computed assuming a fixed nucleon of r K / π = 0 . 11 +0 . 11 − 0 . 07 . target hit by a proton of 18 TeV, � 2 profiles of the B on a fixed nucleon target. Th computed as 10x the simulated gy h E thr i = (1 . 8 ± 0 . 2) TeV , given that cosmic muons TAUP 2019 – Borexino Cosmic Muons D. D'Angelo 15
long term modulation muon flux ] -1 only Average Muon Flux [d Borexino Muon Data 4360 Ampl = (0.34±0.04)% Long-Term Modulation 4350 4340 4330 not in T! 4320 4310 T long =(8.25+0.82)yr 4300 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 TAUP 2019 – Borexino Cosmic Muons D. D'Angelo 16
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