Alberto Guglielmi INFN Padova on behalf of the ICARUS Collaboration - PowerPoint PPT Presentation

ICARUS: perspective for Sterile Neutrinos search at FermiLab Alberto Guglielmi INFN Padova on behalf of the ICARUS Collaboration CRIS 2016 Conference, Ischia, July 7 th 2016

The high energy frontier  Neutrino masses and oscillations represent today a main experimental evidence of physics beyond SM. Being the only elementary fermions whose basic properties are still largely unknown, n s are naturally one of the main priorities to complete our knowledge of SM. n s :the most abundant massive particles in the Universe- 336 n /cm 3  The incredible smallness of n masses compared to other elementary fermions points to some specific scenario awaiting to be elucidated. Slide: 2

Persisting anomalies in the neutrino sector  Neutrino oscillations established a coherent picture with mixing of physical n e , n µ , n t with small mass difference. There are however a number of “anomalies” which, if confirmed, could hint at additional 4 th non standard sterile n driving oscillations at small distance with D m 2 new ~1 eV 2 :  Observation of n e excess (1) from n m in LSND (3.8 s effect) and MiniBooNE expts at accelerators;  Anti- n e event signal (2) from near-by nuclear reactors where observed to predicted event rate is R=0.938 ± 0.023 and (3) from Mega-Curie k-capture calibration sources in solar n e expts, R=0.86 ± 0.05;  Data from CMB exps, large scale structure and Lyman- a forest observation, naively bind for 3 massless + 1 massive sterile n to m s <0.26 eV at 95% CL and should effectively exclude sterile neutrino as explanation of LSND anomaly .  If LSND notwithstanding confirmed experimentally, cosmological data will have been proven wrong calling for a re-examine of this entire framework! Slide: 3

The remarkable evolution of n - experiments: the LAr-TPC  Cherenkov radiation detection has been so-far one of key choices for exploring n s with Kt mass water/ice detectors. Unfortunately these detectors don’t permit to identify unambiguously each ionizing track of complex events produced by n s Cathode: E DRIFT = 0.5 kV/cm  As an alternative, Liquid Argon Imaging 1.5m drift technology LAr-TPC, effectively an electronic bubble-chamber, was originally proposed by E E C. Rubbia in 1977 [CERN-EP/77-08]. PMT array  With the continuing efforts of ICARUS Coll. and INFN support, LAr-TPC technology has been taken to full maturity with theT600 3 readout wire arrays detector, 0.76 Kt mass ultrapure liquid argon 0, +/- 60 0 , 3mm pitch installed in Gran Sasso INFN Lab. 3-Dimensional images Time from scintillation light ICARUS T600 is also a technological milestone towards future larger LAr-TPCs, tens of kt as the DUNE project in US. Slide: 4

ICARUS T600 in underground installation at INFN LNGS  ICARUS T600, 0.47 Kt LAr LN2 active mass, concluded in 2013 vessels cryogenics a very successful 3 years long (behind) run at CNGS n beam collecting readout electronics 8.6 x 10 19 pot event stat with T300 T300 a detector live time > 93%.  At the same time ICARUS recorded cosmics for a total 0.73 kty exposure . 2650 CNGS n 2011 2012 events selected ~ 3.4 n /10 17 pot in ~agreement with expects Slide: 5

A key feature of LAr imaging: very long e - mobility  Level of e-negative impurities in LAr must be kept exceptionally low to ensure ~m long drift path of ionization e - signal without attenuation;  New industrial/lab purification methods developped to continuously filter and re-circulate both liquid (100 m 3 /day) and gas (2.5 m 3 /hour) argon;  Electron lifetime measured during ICARUS run at LNGS with cosmic m ’s: t ele >7 ms (~40 p.p.t [O2] eq) → 12% max. charge attenuation on 1.5 m drift. New not-immersed pump on East cryostat since April 4th, 2013: t ele >15 ms! ICARUS demonstrated the effectiveness of single phase LAr-TPC technique, paving the way to huge detectors with ~5 m drift as required for LBNF/DUNE project.

ICARUS LAr-TPC performance  Tracking device: precise ~mm 3 resolution, 3D event topology, accurate ionization measurement;  Global calorimeter: total energy reconstruction E DEP distrib. for by charge integration- excellent accuracy for CNGS events contained events; momentum of non contained m determined via Multiple Coulomb Scattering D p/p ~15% in 0.4-4 GeV/c range;  Measurement of local energy deposition dE/dx : e/ g remarkable separation (0.02 C 0 sampling, C 0 = 14 cm, particle id. by dE/dx vs range):  Low energy electrons: dE/dx (MeV/cm) vs. dE/dx distrib. residual range (cm) for σ (E)/E = 11%/√E(MeV)+2% for real and protons , p,m compared MC m s from  Electromagn etic showers: to Bethe-Bloch curves CNGS events σ (E)/E = 3%/√E(GeV)  Hadron shower (pure LAr): σ (E)/E ≈ 30%/√E(GeV) Slide: 7

Measurement of muon momentum via multiple scattering ● An essential tool to measure the momentum L =4 m of non-contained m s. Initial p from MCS -> ● Algorithm validated on stopping m s, L m >2.5m ( 3 l I in LAr) produced in CNGS n s interactions upstream of T600 and stopping/decaying inside the detector, by comparing p MCS with the corresponding calorimetric p CAL . Some deviations for p >3.5 GeV/c induced by Initial p from calorimetry -> non-perfect planarity of TPC cathode L =4m Ratio MS/calorimetry momentum resolution for effective m track lengths D p/p~15% in 0.4-4 GeV /c momentum range of interest for short/long base-line experiments Slide: 8

Unique feature of ICARUS: e/ g separation, p 0 reconstruction p 0 reconstruction: Ek = 102 ± 10 MeV p πo = 912 ± 26 MeV/c m πo = 127 ± 19 MeV/c² θ θ = 28.0 ± 2.5º Ek = 685 ± 25 MeV Three “ handles ” to separate e/ g : • invariant mass of p 0 • dE/dx : single vs. double m.i.p. Collection • photon conversion separated from Collection primary vertex M gg :133.8 ± 4.4 ± 4 MeV/c 2 2 m.i.p. 1 m.i.p. Induction2 p 0 Crucial for NC rejection Conversion distances in n e-physics 6.9 cm, 2.3 cm

CNGS n e CC identification in ICARUS LAr-TPC ● The unique detection properties of LAr-TPC technique allow to identify unambiguously individual e-events with high efficiency.  The evolution of the actual dE/dx from a single track to an e.m. shower for the electron shower is clearly apparent from individual wires. Single M.I.P Slide: 10

Other CNGS n e interactions Run 11731 Event 4278: Collection Double M.I.P Single M.I.P Zoomed Induction 2 Run 11319 Event 2862: Scheme of 3D reconstruction Collection Slide: 11

Search for anomalous LSND n e events in CNGS  ICARUS searched for n e excess related to L/E n ~1 m/MeV LSND anomaly on CNGS n m beam (~1% intrinsic n e ) in 10-30 GeV E n range at 732 km distance;  At CNGS L/E n ~36.5m/MeV: LSND-like oscillation signal averages to sin 2 (1.27 D m 2 new L /E) ~1/2.Compared to MINOS and T2K, ICARUS operates in a L/E n range where contributions from standard oscillations not yet too relevant.  No excess observed in 7.93 x 10 19 pot sample: 7 n e events compared to 8.5 ± 1.1 expected in absence of LSND-like effect providing 90%CL limit P( n m → n e ) ≤ 3.86 x 10 -3 . The 2650 recorded n events allow searching for possible oscillations also in disappearance, provided the initial n flux at CERN from the associated m measurements.  ICARUS and OPERA restrict allowed parameter to a narrow region D m 2 ~0.5 eV 2 , sin 2 2 q ~0.005 where all the experimental results can be coherently accommodated at 90% C.L. Need for a definitive experiment on sterile n s to clarify all the reported anomalies Slide: 12

Towards automatic neutrino search: atmospheric n  Recorded cosmic events are being filtered by an automatic algorithm rejecting passing muons and selecting events with a multi-prong interaction vertex topology (≥ 2 charged particles, ~30 % of n CC) to identify atmospheric n candidates;  A drastic reduction to 0.5% of events undergoing the next visual scanning has been achieved for multi-prong event topology;  new algorithms looking for clusterized energy deposition maintaining low the fraction of events needing visual scanning and improving the efficiency up to 70% for n eCC are under validation;  3 m -like, 2 e-like within a sample of 12 observed atm. n candidates have been identified so far in 25% of collected statistics (10 ± 2 multi-prong events are expected) Induction 2 Collection Slide: 13

The first observed „LAr TPC” atmospheric n e CC event  Quasi-elastic n eCC with E Dep =2.12 GeV  Clear primary electron initiated (single m.i.p.) shower (2 GeV);  115 MeV proton identified by dE/dx 1 m.i.p. 2 m.i.p. Automatic search for n eCC in GeV range feasible Slide: 14

A second atmospheric n e CC event: low energy 35 cm Downward-going, quasi elastic event: deposited energy: 240 MeV!  dE/dx measured on first wires (2.1 MeV/cm) corresponds to a m.i.p. particle  One short proton track recognized .  Automatic search for n eCC in sub GeV range is feasible too Atmospheric neutrinos cover the energy range of BNB neutrinos at FNAL ! Slide: 15

Additional n e CC events: working progress – new data fltering 0.7 m 0.8 m 0.9 m 0.6 m 0.7 m  Deposited energy ~ 1.9 GeV Electron deposited energy ~ 1.7 GeV;  dE/dx measured on few wires (2 MeV/cm) corresponds to a m.i.p. particle  Very clearly seen in Induction projection; 0.6 m Slide: 16

Additional n e CC event candidate COLL 0.6 m 0.9 m IND2 0.9 m 0.6 m  Deposited energy ~ 440 MeV  Electron deposited energy ~ 270 MeV;  Very clearly seen in Induction projection; To be fully studied Slide: 17