First Results from Borexino Taking Advantage of a

First Results from Borexino “Taking Advantage of a Free Neutrino beam” Rencontres de Moriond Electroweak Session 2008 F. Dalnoki-Veress (Princeton U. ) on behalf of the Borexino Collaboration

Outline of Talk: �Some Background: 40 Yrs of Taking advantage of a Free Neutrino Beam �The Borexino design : Graded Shielding Concept �Background Reduction Techniques �First Results from Borexino Detector Physics Letters B Volume 658, Issue 4, 3 January 2008, Pages 101 -108 �Future Studies 1/4/2022 F. Dalnoki-Veress Princeton University 2

40 Years of SNν Experiments in 1 Slide: �High flux, free, neutrino beam, 100% duty cycle! �Energy production through pp chain: neutrino sources: pp, pep, 7 Be, 8 B, hep �Pep and pp are closely linked (ratio known to <1%) � 8 B measured very precisely by the SNO/K/SK collaborations but very rare � 7 Be never measured before in DE experiments accounting for 7% of flux Neutrino Sources SSM 0. 51 7 Be 8 B pp Expts DE IE Gallex/GNO Ga 0. 33 Ray Davis DE vs IE Cl 0. 30 DIFFERENT EXPTS DIFFERENT THRESHOLDS D 2 O DIFFERENT ν SOURCES �Experiments found an energy dependent flux suppression (different thresholds) �Explanations exhausted neutrino oscillations (vacuum / matter) 1/4/2022 F. Dalnoki-Veress Princeton University 3

Main Goals/Motivations of the Borexino Detector: �Make the first observation of sub-Me. V solar neutrinos in a DE, real-time detecting experiment as opposed to IE experiments �Make a measurement of the flux of Be-7 Neutrinos (to a few % uncertainty) �Chart deviation from the expected flux suppression expected by MSW effect: - Deviations from 7% expected annual change due to orbital eccentricity - Day/Night effects not expected and long term variations - Look for NSI, Mavans, Unparticle Sector unparticles (See talk by Ann Nelson) . 1/4/2022 IE . DE F. Dalnoki-Veress Princeton University 4

The Borexino Collaboration � 70 scientists in 6 countries France: APC Paris Germany: MPIK, TUM Italy: INFN groups: Milano/Ferrara/Genova/Perugia/LNGS Poland: Jagiellonian University, Krakow Russia: Kurchatov Institute, Moscow + JINR Dubna USA: Princeton + VT 1/4/2022 F. Dalnoki-Veress Princeton University 5

µ Assergi, AB Teramo L’Aquila 1/4/2022 F. Dalnoki-Veress Princeton University 6

Borexino Detector: Principle of Graded Shielding Each shielding layer shields against activity from outer layers. The highest radiopurity is naturally at the detector center– see 5 to 1 – concentric outer shells have higher activity 6 Stainless Steel Sphere: ● Scintillator: 278 t PC+PPO (1. 5 g/l) 1 2 3 4 5 Nylon vessels: ~ 1000 m 3 buffer of pc+dmp (light quenched) Water Tank: (125 μm thick) γ and n shield Inner: 4. 25 m μ water Č detector Outer: 5. 50 m 208 PMTs in water (radon barrier) 2100 m 3 Carbon steel plates 1/4/2022 ● 2212 PMTs 20 legs F. Dalnoki-Veress Princeton University 7

Borexino Detector: Requirements for Success �Purification Plants: Distillation plant to remove non-volatile contaminants, filters to remove particulates, nitrogen stripping to remove residual gases. �Piping and Detector Components: All components selected for radiopurity , SS Components electropolished, pickled/passivated, cleaned with detergents, rinsed, and particulate assessed to Mil-Std-1246 < level 30. � Nylon vessels: Ultra low BG producing 1 ct/day/100 t scintillator. Handled and constructed in a class 100 clean room containing Rn-free air. Vessels purged with special LAKN to remove residual gases present in the IV/OV. � CTF: Borexino prototype has allowed careful studies to be made of batches of scintillator �A breath of fresh air will harm the expt! (10 cc will add significant 85 Kr BG) -Leak-tightness 1/4/2022 F. Dalnoki-Veress Princeton University 8

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Borexino Detector: Attention to detail What is so interesting about a couple of VCR joints: Attention to detail 1/4/2022 F. Dalnoki-Veress Princeton University 10

Borexino Detector: Stages of Detector Filling 1 3 LAKN UPW 2 4 LAKN UPW PC UPW Pictures taken with one of 7 cameras attached to SSS 1/4/2022 F. Dalnoki-Veress Princeton University 11

Borexino Detector: Filled May 15 2007 4 2012 PMT PC+PPO PC+DMP 1/4/2022 F. Dalnoki-Veress Princeton University 12

The First Data Set �Results reported are from 47 days of detector live time in 278 t of scintillator (PC+1. 5 g/l PPO). �We measure scintillation light from ν-e elastic scattering: Q (energy), t (position) �Most prominent features in raw data: 14 C, 210 Po, continuous gamma spectrum. Events/(days x 100 tons x 5 photoelectrons) 14 C 210 Po Raw data Predicted 7 Be neutrino signal background from external gamma rays ²No internal calibration sources have yet been deployed

Borexino Data Cuts: Background Compts AN EXAMPLE Y. Kishimoto 2007, TAUP 2007 Kam. LAND Before Purification Fiducial Cut R<4 m ISOTOPES/CUTS Method Rate 14 C Material selection ~14 cps Reduction of det residue < 6 cpd/100 t MS/QC QA 40 K 85 Kr 232 Th 238 U 85 m. Rb 85 Rb [85 m. Rb = 1. 46 s] (β, γ) Eγ=. 514 Me. V <35 cpd/100 t 212 Bi 212 Po 208 Pb [212 Po = 431 ns] (β, α) Eα=8. 8 Me. V < 0. 2 cpd/100 t 214 Bi 214 Po 210 Pb [214 Po = 237 s] (β, α) Eα=7. 7 Me. V < 2 cpd/100 t 85 Kr Tagged decays 218 Po 214 Pb 214 Bi 214 Po Lookback Technique Rn-daughters 222 Rn Ext. γ’s (PMT, IV) FV cut from 4. 25 m to 3 m (100 t) (see slide) 210 Po Gatti Filter statistical separation of β’s and α’s Red factor 105 1/4/2022 F. Dalnoki-Veress Princeton University 14

Fiducial Volume Cut γ‘s Radial Distribution �MC Simulation of external gamma’s plotted as a function of distance From the center of the detector. Ext BG decreases further inward. �Analyse only central 100 t Use 14 C events to determine the radius 100 t corresponds to. �Possible problems: 14 C non-uniformity/ position reconstruction biases /Light yield as a function of Radius etc. . �Conservatively estimate the systematic error to be 25% 1/4/2022

210 Po Presence in Borexino Raw Spectrum 210 Po Peak 210 Bi if 210 Bi & 210 Po in equilibrium Po-210 is coming from another source � 210 Po (α-emitter) present at a rate of 60 cpd/t, 2 orders of magnitude higher than 7 Be ν’s. � 210 Po is out of equilibrium with 210 Pb and 210 Bi! �Polonium chemistry is quite complicated and is not easily removed. This has been confirmed by tests with CTF (Borexino prototype) and also observed by Kam. LAND. �Another scheme is necessary for it’s removal Gatti Filter 1/4/2022 F. Dalnoki-Veress Princeton University 16

210 Po Cut: Gatti Filter �The Gatti Filter is a technique for statistically separating 2 distributions based on whether they are simular to two reference functions. In the case of Borexino, the Gatti Parameter is used to classify events as β-like or α-like. Gatti Parameter Histograms α α �Fits are done to the sum of two Gaussians for every 5 pe Gatti Parameter histogram 1/4/2022 See: Nucl. Instrum. Meth. A 584: 98 -113, 2008 F. Dalnoki-Veress Princeton University 17

Progression of Cuts Raw Spectrum scaled to Fiducial Volume After Rn cuts and FV cuts After α/β separation SSM LMA 7 Be Fit 1/4/2022 F. Dalnoki-Veress Princeton University 18

Final Spectrum After Cuts: 7 Be rate = 47 7 stat 12 sys LMA MSW = 49 4 1/4/2022 No Flavour Change = 75 4 (Cpd/100 tons) F. Dalnoki-Veress Princeton University 19

Future Analyses: pep, SN, Geoν. . ²Pep ν’s closely related to pp (91% of solar ν production) ² Rates lower than 7 Be by an order of magnitude ² 7 Be is a BG! ²Cosmogenic 11 C is a problem but techniques are developed to separate these (C. Galbiati et al. , Phys. Rev. C 71 (2005) 055805). ²Supernova ν’s and geo-neutrinos ² DBD with Nd-150 a possibility 1/4/2022 F. Dalnoki-Veress Princeton University 20

CONCLUSIONS: Technical Achievement: It is possible to construct a real-time, sub-Me. V, k. T scale neutrino detector with backgrounds at the level of DBD searches Dpd/100 t �Physics Achievement: Measured the 7 Be flux to be in agreement with the SSM: 7 Be rate = 47 7 stat 12 sys LMA MSW No FC = 49 4 = 75 4 ² Need to decrease systematic error with calibration source deployments: goal is a <5% uncertainty measurement. 1/4/2022 F. Dalnoki-Veress Princeton University 21

Backup and Recycled Slides

Borexino Data Cuts: Tagged Isotopes ² 222 Rn (U) daughters are removed from the data by using the Lookback Technique: 222 Rn 3. 8 d α 218 Po α 214 Pb 3. 1 m 27 m βγ Tag Bi. Po and look back for all events near Bi. Po in position and time. βγ 214 Po 164 µs 214 Bi m α 20 210 Pb 22 y �Excluding events preceding a 214 Bi. Po coincidence by 3 hours or less, and within 0. 85 m of the 214 Bi. Po events’ spatial locations, lets us eliminate > 90% of these events! 1/4/2022 F. Dalnoki-Veress Princeton University 23

What Next: Geoneutrinos • Anti-neutrinos are produced in Earth’s crust by radioactive decay (of exactly the isotopes that cause problems for us in the detector!) • We can see them via p + e n + e+: – first we see the positron annihilation ( 1. 02 Me. V) – then, with a mean life of ~ 200 s, we see the neutron capture 2. 2 Me. V – The reaction has a energy threshold of mn + me - mp, or 1. 8 Me. V • Expected rate is ~ 10 events/year in 280 tons of scintillator, with a background of reactor anti-neutrinos on the same order due to European nuclear reactors. [Rothschild, Chen and Calaprice, Geophys. Res. Lett. 25 (1998) 1083; ar. Xiv: nucl-ex/9710001] • In principle it is possible to disentangle anti-neutrino rates from reactors, from 232 Th-chain isotopes, and from 238 U-chain isotopes • The amount of radioactivity in the Earth’s crust is not yet very well known, so this data will be welcome! K. Mc. Carty (Princeton) SLAC Seminar 2007

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Pep/CNO Background 1/4/2022 F. Dalnoki-Veress Princeton University 27