Proposta di misura oscillazioni neutriniche a breve distanza con

Proposta di misura oscillazioni neutriniche a breve distanza con Borexino A. Ianni, M. Pallavicini, G. Ranucci per la Collaborazione Borexino CSN2,Frascati 27 Giugno 2011

The idea to use a neutrino source in Borexino and in other underground dexperiments dt dates back to at least 20 years N.G.Basov,V.B.Rozanov, JETP 42 (1985) Borexino proposal, 1991 JNBahcallPI J.N.Bahcall,P.I.Krastev,E.Lisi, KrastevELisi Phys.Lett.B348:121 123,1995 123 1995 N.Ferrari,G.Fiorentini,B.Ricci, Phys. Lett B 387, 1996 I.R.Barabanov et al., Astrop. Phys. 8 (1997) Gll Gallex coll. PL B 420 (1998) 114 Done A.Ianni,D.Montanino, Astrop. Phys. 10, 1999 A.Ianni,D.Montanino,G.Scioscia, Eur. Phys. J C8, 1999 SAGE coll. PRC 59 (1999) 2246 Done SAGE coll. PRC 73 (2006) 045805 C.Grieb,J.Link,R.S.Raghavan, Phys.Rev.D75:093006,2007 V.N.Gravrin et al., arxiv: nucl ex:1006.2103 C.Giunti,M.Laveder, Phys.Rev.D82:113009,2010 C.Giunti,M.Laveder, arxiv:1012.4356

The physics case with a source experiment Neutrino magnetic moment Neutrino electron non standard interactions Probe ν e e weak couplings at 1 MeV scale Probe sterile neutrinos at 1eV scale Probe neutrino vs anti neutrino oscillations on 10m scale

Anomalies/hints for Δm 2 1eV 2 a) The LSND/Miniboone (anti ν and ν) anomalies b) The reactor anomaly arxiv:1101.2755 sin 2 2θ ee =0.1 Δm 2 =0.4 ev 2 Rt Rate only analysis sin 2 2θ ee =0.1 Δm 2 =1.5 ev 2 Rate+shape Workshop on Beyond Three Family Neutrino Oscillations LNGS 3 4 May 2011 c) The Gallium anomaly R=0.86 from Gallex and Sage source tests arxiv1006.3244 Giunti and Laveder sin 2 2θ ee =0.5 Δm 2 =2.24 ev 2 d) Indications from cosmology of more than 3 neutrinos Other possible anomaly : difference in Minos between ν and anti ν oscillation parameters?

Source location in Borexino A: underneath thwt D=825 cm No changetopresent configuration B: inside WT D= 700 cm Need to remove shielding water C: center Major change Remove inner vessels To be done at the end of solar Neutrino physics yscs C A B

Source position A

Borexino new results and achievements (last meeting of the committee) High precision (better than 5%) 7 Be flux 7 Be day night (absence) Accurate energy position calibration ofthedetectorvolume The perfect knowledge of the detector performances witnessed by these latest achievements is the solid ground upon which the proposal for the sources test in Borexino is built

7 Be Solar neutrinos in Borexino hep ex/1104.1816v11816v1 7 Be = 46.0 ± 1.5 +1.6 cpd/100 tons 1.5 pp 85 Kr removed! 210 Bi pep & CNO

Three neutrino mixing global fit with Borexino with Borexino Day night measurement

Solar neutrino survival probability Ultimate validation of the MSW LMA survival probability curve

Position and energy calibration On and off axis calibrations sources Rn, AmBe 57 Co, 139 Ce, 208 Hg, 85Sr, 54 Mn, 65 Zn, 40 K, 60 Co The knowledge of the detector and of its performance makes it the ideal environment for a series of source test to shed light on the hints of a new neutrino oscillation mass scale involving steriles Initiallyexternal location, later inthe center

Sources Activity: several 1000 ν evts within 1 year E >250 kev ( 14 C background) Half-life 1 month Compact Limited heat Efficient shielding Low impurities level

51Cr Originally proposed by Raju Raghavan ~36 kg of 38% enriched 50Cr 190 W/MCi from 320 kev 7μSv/h (must be < 200) SAGE coll., PRC 59 (1999) 2246 Gallex coll., PL B 420 (1998) Done two times for Gallex at 35 MW reactor with effective thermal neutrons flux of ~5.4E13 cm 2 2s 1 1 ~1.8 MCi

Transport container

Cr51 Gallex source

The case of ν 51 e Cr source in Borexino Bismuth210 CNO Source events Be7 Window 0.250 0.700 0 KV KeV Background : solar neutrinos + Bismuth210

37 Ar ν e source 37 Ar(τ=50.55 days) 37 Cl 813 kev (9.8%) 811 kev (90.2%) From irradiation of CaO using fast neutrons 40 Ca(n,α) 37 Ar ~16 W/MCi from 2.6 kev X rays Used in SAGE with ~0.4 MCi SAGE coll., PRC 73 (2006) 045805

90Sr 90Y ν e source τ Sr = 28.79 years τ Y = 3.8 days 90 Sr Inverse beta decay ν e ν e <E>=2±0 2±0.2MeV2MeV <σ>=7.2 10 45 cm 2 90 Y 7.25 kg/mci Product of nuclear fission ~6700 W/MCi Used in thermoelectric generators including Bremsstrahlung Known technology for 0.2 MCi sources

106Ru 106Rh ν e source 106 Ru τ Ru = 539 days τ Rh =29.8 s 106 Rh Inverse beta decay <E>=2.5±0.2 2MeV <σ>=89.2 10 45 cm 2 Similar option: Ce144 Pr144 Product of nuclear fission

Spatial profile of detected events for a monoenergetic 120 source (Cr51) in the tunnel 100 80 Δm 2 sin 2 2θ 8 0.07 007 1 0.1 60 no oscillation 40 Ideal case no spatial resolution no background 20 0 400 500 600 700 800 900 1000 1100 1200 1300 1400 Cmfrom the source

How to exploit the rate and waves information Oscillometry measurements In Incase of no detection of anyeffect upon performing the measurement Exclusion plotsexploiting orate only orate plus waves ocomputed through a χ 2 method In case the effect exists, through the wave analysis: Determination of the existence of the effect (how many sigma) Determination of the oscillation parameters The sensitivity of the experiment can be assessed via discovery plots base on the likelihood ratio At high Δm 2 only rate analysis

Cr51 Exclusion plots Sr90 Ru106 In the tunnel (A) and (in some cases) in the center (C). B is very similar to A Detector characteristics affecting the sensitivity of the measure Spatial resolution about 15 cm Systematic error on spatial reconstruction (Fiducial Volume systematic error) 1% Background Solar neutrinos and Bismuth for ν source about 40 events per day Geo and reactor anti ν (a dozen of events per year) for anti ν source The precision of the knowledge of the source intensity is another systematic error assumed 1%

At high Δm 2 the fast oscillations are smeared by the detector spatial resolution effectively rate only analysis Log 10 Δm 2 To the best of our knowledge first example of exclusion plot done via the oscillometry analysis 1 0 1 2 3 90% C.L. Cr51 10 Mci (2 expositions) Tunnel (d=825 cm) 200 days 1% err. source intensity 1% err. FV Reactor anomaly best fit Reactor anomaly Rt Rate + waves Rate only The Gallium anomaly is on the right side of the Reactor anomaly 2 σ ex xcluded 3 2 Log 1 0 10 sin 2 2θ Solar+KamLAN Dconstraints for θ 13 =0 From arxiv:1105.17 17 05 A. Palazzo The excluded region would further extend toward the left for θ 13 0 T2K result

Correlation of the sterile mixing angle with θ 13 from arxiv:1105.1705 1705 A. Palazzo The excluded area shown in the previous (and following) exclusion plot(s) corresponds to this point N l f θ (T2K) Non zero values of θ 13 (T2K) cause the extension of the excluded area

1 99% C.L. Lo og 10 Δm 2 Cr51 10 Mci (2 expositions) Tunnel (d=825 cm) 0 200 days 1% err. source intensity 1% err. FV 1 Reactor anomaly Rt Rate+ waves 2 Rate only 2 σ exclud ded 3 3 2 1 0 Log 10 sin 2 2θ

Cr51 in the center Enhanced sensitivity due both to the pattern and the increased number of events 1.4 1.2 1 0.8 0.6 Oscillation waves 0.4 0.2 Resolution effect non gaussianity at center 0 0 100 200 300 400 500 600 0 100 200 300 400 500 600 Distance from the center

The effect on the exclusion plot of the enhanced sensitivity in the center location is striking, the reactor anomaly region would be fully covered. Log 10 Δm 2 1 0 1 90% C.L. Cr51 10 Mci (2 expositions) Center 200 days 1% err. source intensity 1% err. FV Reactor anomaly 2 σ exc cluded Rate + waves 2 Rate only 3 3 2 1 0 Log 10 sin 2 2θ

1 99% C.L. 0 Cr51 10 Mci (2 expositions) Center 200 days 1% err. source intensity 1% err. FV 2 σ exclu uded og 10 Δm 2 Lo 1 Reactor anomaly 2 Rate + waves Rate only 3 3 2 1 0 Log 10 sin 2 2θ

1.005 1 0.995 0.99 0.985 0.98 09 0.975 0.97 0.965 0.96 Sr90 source oscillation probability as function of distance and energy Δm 2 θ 05 0.5 01 0.1 0.955 0 200 400 600 800 1000 1200 1400 1600 Cm from the source location The different curves correspond to energies ranging from 1.8 to 2.28 MeV A twofold energy distance approach is needed For simplicity here we have integrated over the energy

Sr90 source event spatial profile variation over the energy interval 1.8 to 2.28 MeV 4.50E 02 4.00E 02 3.50E 02 3.00E 02 2.50E 02 2.00E 02 1.50E 02 02 1.00E 02 5.00E 03 0.00E+00 0 200 400 600 800 1000 1200 1400 1600 1800 Distance from the source (cm)

Sr90 source expected event spatial profile after energy integration over energy Δm 2 =1 sin 2 2θ =0.2 Δm 2 =2 sin 2 2θ =0.1 ude (a.u.) Amplit Sr90 in the tunnel Amplit tude (a.u.) Sr90 in the tunnel 0 0 500 1000 1500 2000 0 0 500 1000 1500 2000 Distance from the source (cm) Distance from the source (cm) Δm 2 =1 sin 2 2θ =0.1 Δm 2 =0.1 sin 2 2θ =0.2 itude (a.u.) Ampli Sr90 in the tunnel Amp plitude (a.u.) Sr90 in the tunnel 0 0 0 500 1000 1500 2000 0 500 1000 1500 2000 Distance from the source (cm) Distance from the source (cm)

Sr90 Advantages Background freemeasure (delayed coincidence) Higher counting rate due to the possibility to exploit the full volume, in this case the FV error can be ignored (the following plots in which the FV error is maintained are therefore conservative) Future scalability: in a post solar phase of the experiment the entire sphere can be filled with scintillator ill Issues to be considered : heat dissipation and internal Issues to be considered : heat dissipation and internal bremmstralung background

1 90% C.L. Sr90 1 Mci Tunnel (d=825 cm) 0 365 days 1% err. source intensity 1% err. FV 2 σ excluded og 10 Δm 2 Lo 1 Reactor anomaly 2 Rate + waves Rate only 3 33 22 11 0 Log 10 sin 2 2θ

1 Realistically the FV error can be ignored due to the delayed coincidence 0 measurement. The 90% reactor anomaly region 1 is almost fully covered Log 10 Δm 2 22 90% C.L. Sr90 1 Mci Tunnel (d=825 cm) 365 days 1% err. source intensity Reactor anomaly Rate + waves Rate only 2 σ excluded 3 3 2 1 0 Log 10 sin 2 2θ

1 99% C.L. 0 Sr90 1 Mci Tunnel (d=825 cm) 365 days 1% err. source intensity 1% err. FV 2 σ exclud ded Log 10 Δm 2 1 Reactor anomaly 2 Rate + waves Rate only 3 33 22 11 0 Log 10 sin 2 2θ

1 Again, realistically ignoring the FV error, the excluded 0 region can be increased 99% C.L. Sr90 1 Mci Tunnel (d=825 cm) 365 days 1% err. Source intensity 2 σ ex xcluded og 10 Δm 2 Lo 1 2 Reactor anomaly Rate + waves Rate only 3 3 2 1 0 Log 10 sin 2 2θ

Sr90 in the center The averaging effect over the energy range is less important than for the external location 7.00E 03 03 6.00E 03 5.00E 03 4.00E 03 3.00E 03 2.00E 03 03 1.00E 03 Energy lower limit Energy range upper limit Middle energy range No oscillation 7.00E 03 6.00E 03 5.00E 03 4.00E 03 3.00E 03 No oscillation 2.00E 0303 Energy 1.00E 03 averaged 0.00E+00 0 100 200 300 400 500 600 cm from the center Δm 2 =2 sin 2 2θ=0.1 0.00E+00 0 100 200 300 400 500 600 cm from the source

1 Further improvement w.r.t. this plot: a)no FV error 0 b) Extended data taking time (three years) 1 c) Entire SS sphere filled with scintillator Log 10 Δm 2 2 90% C.L. Sr90 1 Mci Center 365 days 1% err. source intensity 1% err. FV Reactor anomaly Rate + waves Rate only 2 σ exc cluded 3 3 2 1 0 Log 10 sin 2 2θ

1 0 99% C.L. Sr90 1 Mci Center 365 days 1% err. source intensity 1% err. FV 2 σ exclude ed Log 10 Δm 2 1 Reactor anomaly 22 Rate + waves Rate only 3 3 2 1 0 Log 10 sin 2 2θ

1 Ru106 first attempt. In principle a Ru106 sources located 0 externally tests completely the 90% reactor anomaly region Lo og 10 Δm 2 1 90% C.L. Ru106 1 MCi Tunnel (d=825 cm) 365 days 1% err. source intensity Reactor anomaly 2 σ excl uded 2 Rate + waves Rate only 33 3 2 1 0 Log 10 sin 2 2θ

1 99% C.L. Is it possible to use the Ru106 1 Mci Ruthenium to Tunnel (d=825 cm) realize a 365 days lower activity ii 0 1% err. source intensity source? One can try a 100 kci source in the center. We have not 1 done this attempt, yet. Reactor anomaly Other suggestion Rate + waves from the 2 French group Rate only Ce144. og 10 Δm 2 L 2 σ exc cluded 3 3 2 1 0 Log 10 sin 2 2θ

Discovery curves Likelihood ratio test statistics to identify the oscillation effect, if exists t L ( no oscillation ) = 2ln L( oscillation) 0.3 The no oscillation curve follows closely the expected ideal χ 2 (2) distribution 0.25 0.2 0.15 Δm 2 =1 sin 2 2θ=0.07 MC distributions 0.1 Δm 2 =1 0.05 sin 2 2θ=0.2 0 0 20 40 60 80 100 120 2ln (Lnum/Lden) The distance between the mean value of the signal induced MC distributions and the no oscillation curve gives the sigmas for the discovery

Example of simulation Cr51 in position B h fi ll l d i The fit allows also to determine precisely the oscillation parameters

Other simulations Sr90 at the center Good agreement with ihthe analytical loscillation i curves

Discovery plot only shape analysis 1 0 90% C.L. 2 σ exclu uded 1 51 Cr 10 MCi external 2 3 To the best of our knowledge first example of discovery plot done via the oscillometry analysis 3 2 1 0

Discovery plot 1 90% C.L. 0 2 σ exclud ed 1 51 Cr 5 MCi center 2 3 3 2 1 0

Sr90 in the center 1 year 1 0 90% C.L. CL 2 σ excl uded 1 2 3 3 2 1 0

Sr90 in the center 3 years 1 0 90% C.L. CL 2 σ excl luded 1 2 3 3 2 1 0

Neutrino vs antineutrino sensitivity 2 σ excluded

Status of the material for the Cr51 source and investigations in progress The isotopically enriched Cr (40% Cr50) material is stored at Saclay in form of small chips for a total of 35.5 Kg It is perfectly suited to undergo a new irradiation We are currently in contact with Michel Cribier and the Saclay group in order to bring back the material to Italy. It will be stored in a special location while waiting for the new irradiation campaign : Forli company Protex SPA cost 1500 euro/year Shipping company : MIT nucleare cost 4100 euro the same Company can do the transportation after the irradiation (it will be needed a special Transport Container ) We have contacted the LNGS esperto qualificato Luciano Lembo to discuss both the issues connected with the transportation of the a) inert and b) activated Crmaterial: transport regulations andauthorizations authorizations complex but addressable matter

Search of an irradiation facility Research reactor A) High thermal neutron flux throughout the entire target ideally 10E15 n/cm2/sec B) Enough space to accommodate the material C) Flexible enough to allow the reconfiguration of the core The Siloe reactor at Grenoble met this requirements, but it is no longer available, no other suitable reactors available in France We visited the Delft reactor (Netherland) which meets the requirements B and C, but not A cost would have been very limited We plan to visit the Petten reactor (Netherland) which features the first requirement, we would like to understand what about B and C Opportunities in Russia to be investigated as well additional transportation difficulties Starting point GNO 2001proposal for irradiation at SM3 reactor of Dimitrovgrad cost estimate was 1.3 M$ of dollars planned meeting in Moscow this week

Further considerations Cost sharing: the Paris APC and Saclay CEA groups and the Munich groupexpressed their interest in this physics opportunity, theywould therefore contribute to the cost Other possible source of funding: Europe More investigations required for the anti ν sources: Sr90 can be available from the Companies who separate it from the other fissions products, can be purchased? Experience in France and Russia (heating equipments) The same considerations apply to the very recent proposal p of Ru106 and Ce144 sources In the financial requests for 2012 we will include a request at the level In the financial requests for 2012 we will include a request at the level of some tens of keuros for the feasibility studies of the source test(s)

Conclusions Borexino is in a very favorable position to address the hot topic of possible short baseline ν e disappearance due to oscillation to sterile via a series of neutrino source tests, through which perform powerful oscillometry measurements exclusion and discovery plots In a first step a totally non invasive measurement can be performed by deploying externally a source in the Tunnel underneath the Water Tank specifically prepared for this purpose during the construction of the detector, affording already an interesting sensitivity limit capable to address the Gallium anomaly and to start the exploration of the reactor anomaly Alternative for the first phase: source immersed in water in the Water Tank In the post solar phase scenario the source(s) can be deployed in the center and the target volume increased achieving the ultimate sensitivity capable to cover a wide region of the oscillation parameter plane, thus fully addressing the reactor anomaly indication We have started the investigation for the source(s) preparation and procurement. For Cr51 Gallex experience and GNO proposal of 2001 Opportunity for INFN and LNGS to maintain and strengthen the leadership role gained through the Gallex GNO and Borexino results in the solar neutrino sector

Back up slides

LSND and MiniBooNE LSND Appearance: L/E ~ (25 35 m)/(20 53 MeV) ~ 0.5 2m/MeV Electron anti neutrino candidates: 87.9±22.4±6.0 (3.8σ) P μe = 0.264±0.067±0.045 MiniBooNE Appearance: L/E ~ 1Km/1GeV Neutrino mode: no evidence of oscillations above 450MeV Low energy (200 450 MeV) excess: 128.8±20.4±38.3 (3.0σ) Possible explanationfrom SBL disappearance Giunti, Laveder, PRD 82, 053005 (2010) Anti neutrino mode: 20.9±14.0 exces sevent p value of nullhypothesis = 0.5% p value for 2νoscillation hypothesis = 9% Oscillation hypothesis better at 99.5% C.L. L/E

Reactoranomaly A re evaluationof the expected anti neutrino fluxfromreactorshasgiven a newboostto the possibilityof 1 2 sterile neutrino scenarios G.Mention et al., Reactor Anomaly, arxiv:1101.2755 J.Kopp,M.Maltoni and T.Schwetz, Are thereneutrinos at the ev scale?arxiv:1103.4570

Reactoranomaly: 2ν oscillationhypothesis No oscillationhypothesisrejected at 98.6% C.L.

Adaptedfrom C. Giunti at Beyond3ν 2011

Adaptedfrom C. Giunti at Beyond3ν 2011

1 0 90% C.L. Sr90 1 Mci Tunnel (d=825 cm) 365 days 1% err. source intensity 1% err. FV Log 10 Δm 2 1 22 3 Reactor anomaly Rate + waves Rate only Rate + waves Aldo Rate only Aldo 3 2 1 0 Log 10 sin 2 2θ