Underground laboratories

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1 State-of-the-art in underground physics experiments (Borexino) Dr. Matthias Laubenstein (on behalf of the Borexino collaboration) Laboratori Nazionali del Gran Sasso IALY Synergies in Low Background Radiation echniques University of Minnesota Minneapolis MN, USA July 25 th, 2005 Underground laboratories HALL B ICARUS LVD DAMA Gerda Borexino OPERA HALL C CRESS2 CUORICINO LBL-2 HDMS GENIUS-F LBL-1 HALL A July 25th, 2005 SiLBR - Minneapolis 2 1

2 SSM Neutrino Spectrum on Earth July 25th, 2005 SiLBR - Minneapolis 3 Low Energy Solar neutrinos q Low energy solar neutrinos a MUS! q Asks for BIG experimental effort q Low energy (<1 MeV) asks for scintillation techniques (upcoming experiments) q Borexino collaboration has addressed important milestones: CF showed for the first time that organic liquid scintillators have the right radiopurity q For low energy on the road liquid noble gases and metal loaded organic scintillators July 25th, 2005 SiLBR - Minneapolis 4 2

3 Organic liquid scintillators: 1. ρ~1g/cm 3 (efficient self shielding), ~10 4 photons/mev, 5% energy 1MeV, sigma ~ 1 MeV for vertex reconstruction 2. Expected 1.3 ev/day/ton for pp and 0.5 for 7 Be in full energy range t target mass for pp gives about 10 counts/day 4. ONLY ES channel (rely on detection of single electron) C (β w/ 156keV) limits low energy sensitivity to only 7 Be with achieved 14 C/ 12 C~10-18 (~0.2 Bq/ton background below end-point) U, 232 h, 40 K, 85 Kr, 39 Ar, 210 Pb sources of important background 7. Needed U,h < 1mBq/ton to get S/B>1 possible! 8. Needed ~0.5 µbq (Kr,Ar)/m 3 of N 2 possible! 9. Needed 210 Pb < 1 mbq/ton rely on distillation of scintillator! 10. Deep location to measure pep and avoid cosmogenic 11 C background: expected 0.03 pep/day/ton vs Gran Sasso depth; a factor 100 SNO! July 25th, 2005 SiLBR - Minneapolis 5 What about solar neutrinos? Find smoking-gun for LMA q q use low energy solar neutrinos or Mton detector measure day-night asymmetry est new physics from neutrino interactions with low energy neutrino q in the Sun with low energy neutrinos in a high density matter q Light sterile neutrino q Neutrino magnetic moment (< µ B ) q Flavour changing interactions with sub-weak strength est solar physics with sub-mev solar neutrinos q Neutrino luminosity = light luminosity q ime variation in the Sun with neutrinos (neutrinos bring information from the interior of the Sun in ~real time!) q CNO luminosity (predicted 1.5%, measured < 6%) July 25th, 2005 SiLBR - Minneapolis 6 3

4 More q Neutrinos from the Earth q Neutrinos from supernovae in the galaxy q Relic supernovae neutrinos July 25th, 2005 SiLBR - Minneapolis 7 Goals for Borexino q Measure 7 Be solar neutrinos q Smoking gun for LMA (Yes/No) q Search for sub-dominant effect with new physics q With 5% 7 Be measurement test solar standard model better than 1% q Study CNO luminosity and pep neutrinos q ime variation of solar signal, neutrino magnetic moment q Neutrino from the Earth q Neutrino form supernovae July 25th, 2005 SiLBR - Minneapolis 8 4

5 Counting est Facility (CF) CF is the prototype of Borexino. Its main goal was to verify the capability to reach the very low-levels of contamination needed for Borexino CF campaigns 1. CF1: CF2: 2000 (PXE) 3. CF3: 2001 still ongoing 100 PMs ~ 4 tons of scintillator 4.5 m thickness of water shield Muon-veto detector 14 C/ 12 C ~ (measured: (1.94 ± 0.09) )) 238 U ~ g/g (measured: (3.5 ± 1.3) ) g/g, Rn daughters) 232 h ~10-16 g/g (measured: ( ) ) g/g) CF high mass and very low levels of background contamination make it a unique detector to search for rare or forbidden processes with high sensitivity July 25th, 2005 SiLBR - Minneapolis 9 July 25th, 2005 SiLBR - Minneapolis 10 5

6 July 25th, 2005 SiLBR - Minneapolis 11 July 25th, 2005 SiLBR - Minneapolis 12 6

7 204 days of livetime Whole 4-ton mass Radial cut at 70cm for Reconstructed events Radial cut at 60cm for Reconstructed events 1 MeV July 25th, 2005 SiLBR - Minneapolis U decay chain by courtesy of Dr. G. Heusser mass spectrometry gamma active nuclides sub chains highly volatile (delayed coincidence) tagging also from atmospheric deposition if Rn can escape, (plate out activity) otherwise Rn and Ra included July 25th, 2005 SiLBR - Minneapolis 14 7

8 by courtesy of Dr. G. Heusser 232 h decay chain mass spectrometry gamma active nuclides 8 sub chain tagging tagging if Rn can escape, (plate out activity) otherwise Rn and the progenitors up to 228 h included July 25th, 2005 SiLBR - Minneapolis 15 Radioassay techniques for primordial U/h decay chains and K Ge-spectroscopy Comparison of Rn emanation assay Neutron activation Liquid scintillation counting Mass spectrometry (ICP-MS; A-MS) suited for γ emitting nuclides 226 Ra, 228 h primordial parents α emitting nuclides primordial parents Graphite furnace Atom Adsorption Sp. primordial parents Roentgen Exitation Analysis Alpha spectroscopy primordial parents 210 Po, α emitting nuclides difficult to compare since each method has its special application July 25th, 2005 SiLBR - Minneapolis 16 8

9 Neutron activation analysis n + 41 K 42 K β h 42 Ca, σ th = 1.2 b (1.2 b) n h 233 h β 22.3 m 233 Pa β 27.0 d 233 U, σ th = 6.1 b (7.8 b) n U 239 U β 23.5 m 239 Np β 2.36 d 239 Pu, σ th = 2.3 b (7.9 b) Sizable cross sections and long enough half lives for delayed counting July 25th, 2005 SiLBR - Minneapolis 17 NAA (U Munich) 239 Np β + 1/2 = 193 ns 106 kev γ γ s + conv. electron 239 Pu 0.19 µbq/kg 8x10-4 µbq/kg 1x10-4 µbq/kg July 25th, 2005 SiLBR - Minneapolis 18 9

10 α concentration of Rn b proportional counting sensitivity = f(procedure blank) M. Laubenstein, Y. Zakharov W. Rau, B. Freudiger H. Simgen, Ch. Buck, G. Zuzel H 2 O N 2 emanation July 25th, 2005 SiLBR - Minneapolis Rn ( 226 Ra) assay with proportional counting efficiency for internal counting (> 15 kev): 148 % background: counts per day about 30 µbq 222 Rn easily detectable (monitoring) Ray Davis Jr. type miniture counter Extract Rn from large quatities of water, nitrogen and as an emanation signal of subsystems of BOREXINO H 2 O: 1 mbq Ra/m 3 Reached sensitivities: surface mbq/rn/m 3 nitrogen: 0.5 µbq/m 3 µbq/m2 emanation July 25th, 2005 SiLBR - Minneapolis 20 10

11 Measuring procedure for Ar and Kr Pipes baked out and flushed with nitrogen for some days VCR flange Metal-sealed valves gas Pipette Sample volume: ~1 ccm Sample purification Mass spectrometer liquid Dewar (200 L) with liquid nitrogen G. Zuzel H. Simgen bubbler [Bq/ m 3 ] N Kr conc. in air, BMU Ann. Rep.02 July 25th, 2005 SiLBR - Minneapolis Nitrogen plant of BOREXINO activity in nitrogen [µbq/kg] nitrogen sample 39 Ar a) 85 Kr a) 222 Rn b) RPN 2 Borexino HPN 2 Borexino HPN 2 Borexino liq.extr. < 0.3 Linde Worms (7.0) SOL Mantua (7.0) Westfalen Hörstel (6.0) required air ~1.1x10 4 ~1.2x10 6 ~1x10 7 a) measured by rare-gas MS; 1 ppm Ar = 1.19 µbq/kg; 1 ppt Kr = 1.03µBq/kg 11.5 l 2 kg Carbo - Act b) measured by concentration and proportional counting July 25th, 2005 SiLBR - Minneapolis 22 11

12 method suited for sensitivity for U/h Ge-spectroscopy* γ emitting nuclides µbq/kg Rn emanation assay 226 Ra, 228 h µbq/kg Neutron activation primordial parents µbq/kg Liquid scintillation counting α emitting nuclides 1 mbq/kg Mass spectrometry (ICP-MS; A-MS) primordial parents µbq/kg Graphite furnace Atom Adsorption Sp. primordial parents µbq/kg Roentgen Exitation Analysis primordial parents 10 mbq/kg Alpha spectroscopy 210 Po, α emitting nuclides 1 mbq/kg * Needs counting time of several weeks to several month Best see Borexino Collaboration, Arpesella, C. et al., Measurements of extremely low radioactivity levels in Borexino, Astrop. Phys. 18 (2002) 1-25 July 25th, 2005 SiLBR - Minneapolis 23 Published articles on CF data (CF2) 1. Search for electron decay mode e γ + ν with prototype of Borexino detector published on Physics Letters B 525 (2002) Study of neutrino electromagnetic properties with the prototype of the Borexino detector published on Physics Letters B 563 (2003) New limits on nucleon decay into invisible channels with the Borexino CF published on Physics Letters B 563 (2003) New experimental limits on heavy neutrino mixing in 8 B-decay obtained with the Borexino CF published on JEP Lett. Vol. 78 No 5 (2003) New experimental limits on violation of the Pauli Exclusion Principle obtained with the Borexino CF published on European Physical Journal C37 (2004) 421 July 25th, 2005 SiLBR - Minneapolis 24 12

13 General remarks concerning data analysis Energy reconstruction is obtained by summing the collected photoelectrons in the event; Position reconstruction is obtained by a maximum likelihood fit to time of arrival of the photons to each PM; Particle identification is obtained via pulse-shape discrimination methods; Photon yield is determined by a fit to the 14 C shape; it has been found to be around ~350 pe/mev for 100 PM; Light quenching at low energy causes a deviation from linearity between emitted light and deposited energy. his effect has been included in the interpretation of the energy spectrum (following Birks parametrization ) July 25th, 2005 SiLBR - Minneapolis 25 Background spectrum in CF /(kg kev yr) he energy spectrum of the background counts in CF is dominated by 14 C at low energy ( <200 kev); Ar, Kr (up to ~700 kev); 238 U and 232 h daughters (up to ~3 MeV); external 40 K (peak at 1.4 MeV + continuum); Muons mainly affect the very high energy region of the spectrum and can be effectively removed with the muon-veto detector July 25th, 2005 SiLBR - Minneapolis 26 13

14 Search for electron decay mode e with the CF γ + ν Non-conservation of electric charge would lead to electron decay via two processes: e γ + ν, e ν + ν + ν We look for the 256 kev γ coming from the e γ + ν decay; A fit is performed to curve D between kev including the contributions of: 14 C spectrum shape ; Residual linear background (U,h,Ar,Kr) Response function of the detector to a 256 kev γ estimated with Montecarlo methods; τ > 4.6 x yr (90% C.L.) his result improves by a factor two the previous best bound on electron stability set on the same decay channel by DAMA July 25th, 2005 SiLBR - Minneapolis 27 Study of neutrino electromagnetic properties with the CF Neutrino-electron scattering is the most sensitive test for neutrino magnetic moment search. he differential cross-section is the sum of weak and electromagnetic terms 2 dσ weak 2 2 ( ) e eme dσ e,eν = 4σ 0 gl + gr 1 glgr ( ) 2 de Eν 2E ν em e,eν = π r0µ υ de e Eν At low energy ( e << E ν ) their ratio is proportional to 1/ e and the sensitivity to the µ ν increases; An energy region between ( )keV is selected to maximize the statistical significance of the effect and to minimize the systematic related to background; A fit is performed to the energy spectrum including contributions from 14 C, other radioactive background (assumed to be linear) and solar (pp and 7 Be) neutrino scattering on electrons with µ ν as free parameter July 25th, 2005 SiLBR - Minneapolis 28 14

15 32.1 days of data taking in the CF2 campaign; µ ν < 5.5x µ B (90% C.L.) 1. e-ν scattering C spectrum 3. Linear background July 25th, 2005 SiLBR - Minneapolis 29 New limits on nucleon decay into invisible channels with the CF Many extensions of the Standard Model foresee B and L violation and predict the decay of protons and nucleons bounded in nuclei; Nucleon decays to strongly or electromagnetically interacting particles have been investigated by several experiments (IMB, Superk and so on). Limits on the lifetime of these processes are currently in the range of years; Limits concerning nucleon decays to invisible particles (neutrinos, majorons and so on) are a few orders of magnitude lower; In CF it is possible to investigate the decays of N or NN occurring inside 12 C, 13 C (scintillator) and 16 O (water); hese decays would produce daughter nuclei such as 11 C, 10 C, 12 B, 11 Be, 14 O Detecting in the scintillator volume the characteristic radioactive decays of these daughters would be a signature of N or NN decay; July 25th, 2005 SiLBR - Minneapolis 30 15

16 Initial Decay Daughter nucleus 12 6 C n p nn pn pp C B C B Be 1 / 2 stable 1/ 2 stable 1/ 2 = 20.38m = 19.20s = 1.6x β (99.76%);EC(0.24%); Q = 1.982MeV + β ; Q = 3.651MeV yr β ; Q = 0.556MeV 13 6 C n p nn pn pp C B C B Be stable 1 / 2 1 / 2 stable 1 / 2 = 20.4ms = 20.38m = 13.8s β ; Q = 13.37MeV + β (99.76%);EC(0.24%); Q = 1.982MeV β ; Q = MeV 16 8 O n p nn pn pp O N O N C stable stable 1 / 2 1 / 2 = 122s = 70.60s = 5730yr + β (99.89%);EC(0.11%); Q = 2.754MeV + β ; Q = 5.145MeV β ; Q = 0.156MeV July 25th, SiLBR - Minneapolis / 2 New limits on nucleon decay into invisible channels (continued) he experimental data do not show evidence for decays of the daughter nuclei; Limits on the nucleon decay can be set conservatively assuming that all the events falling in appropriate energy window were due to the decay under study; τ(n τ(p τ(nn τ(pp invisible) > 1.8 x yr (90%C.L.) invisible) > 1.1 x yr (90%C.L.) invisible) > 4.9 x yr (90%C.L.) invisible) > 5.0 x yr (90%C.L.) world s best limits July 25th, 2005 SiLBR - Minneapolis 32 16

17 New experimental limits on violation of the Pauli Exclusion Principle obtained with the CF Pauli Esclusion Principle has been tested for n, p in 12 C and 16 O nuclei contained in the CF scintillator and water buffer; he idea is to search for γ, n, p and/or α emitted in a non-paulian transition of 1P-shell nucleons to the filled 1S 1/2 shell; τ ( 12 C τ ( 16 O τ ( 12 C τ ( 12 C τ ( 12 C τ ( 12 C τ ( 12 C 12 C + γ) > 2.2 x y (90% C.L.) 16 O + γ) > 2.1 x y (90% C.L.) 11 B + p) > 5.0 x y (90% C.L.) 11 C + n) > 3.7 x y (90% C.L.) 7 Be + α) > 6.1 x y (90% C.L.) 12 B + e + +ν) > 7.7 x y (90% C.L.) 12 N +e - +ν) > 7.6 x y (90% C.L.) July 25th, 2005 SiLBR - Minneapolis 33 New experimental limits on heavy neutrino mixing in 8 B- decay obtained with the CF If heavy neutrinos ν H with m > 2 m e are emitted in 8 B reaction in the sun then decays like ν H ν L + e + + e - should be observed; he rate of this decay depends on the heavy neutrino mass and on the mixing parameter U eh between heavy neutrino and the positron Exploiting the fact that after applying the µ-veto cut the CF data show no events for E>4.5 Mev 2 U - eh Limits can be set in the m νh parameter space; For neutrino mass region between 4-10 MeV the obtained limits are stronger than those obtained in previous experiments using accelerators and reactors July 25th, 2005 SiLBR - Minneapolis 34 17

18 BOREXINO he BOREXINO experiment is designed for the real time detections of solar neutrinos via elastic scattering of the νe on electrons. he threshold energy is 0.25 MeV and allows to study the monoenergetic neutrinos (0.86 MeV), so called 7Be-neutrinos. 300 t of liquid scintillator (PC (1,2,4)-trimetylbenzene + PPO (2,5) diphenyloxazole 1.5 g/l) 2200 photomultipliers 2500 t ultrapure water 40 evt/d according to the Standard Solar Model Water ank (Stainless Steel) diametre 18 m, height 16.9 m he inner sphere (diametre 13.7 m) is supporting the PMs. Contains purified PC. Outside of the sphere there is ultrapure water. Nylon Vessel Diametre 8.5 m, thickness 100µm Collab.: Italy, France, USA, Germany, Hungary, Russia, Belgium, Poland, Canada July 25th, 2005 SiLBR - Minneapolis 35 July 25th, 2005 SiLBR - Minneapolis 36 18

19 Borexino at Gran Sasso Laboratory 100 t target mass of C 9 H 12 scintillator (pseudocumene) + 1.5g/l PPO ~10,000 photons/mev (400phe - /MeV) Energy resolution= 5%@1MeV Background studies carried out with a 4 t prototype, the Counting est Facility Main background issues: 210 Pb, 39 Ar, 85 Kr Elastic scattering 1/R 2 signature due to Earth s eccentricity: in 2 yr 3σ measurement Compton like threshold signature for 7 Be neutrinos spectroscopy Expected ~30 events/day in [0.25,0.8] kev Expected sensitivity for pep neutrinos July 25th, 2005 SiLBR - Minneapolis 37 Conclusions q Borexino R&D and CF showed the feasibility to measure sub-mev solar neutrinos q Sub-MeV neutrinos seems a BIG opportunity q Borexino a unique opportunity for the near future July 25th, 2005 SiLBR - Minneapolis 38 19