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XXV European Cosmic Ray Symposium, Turin, Sept. 4-9 2016 1 High-energy neutrino astronomy with KM3NeT-ARCA R. Coniglione for the KM3NeT collaboration LNS-INFN, Via S. Sofia 62, 95125 Catania, Italy The KM3NeT/ARCA high energy neutrino telescope is currently under construction in the Mediterranean sea. The detector will consist of two blocks of instrumented structures and will have a size of the order of a cubic-kilometer. In this work the status of the detector, the expected performancetogalacticandextragalacticneutrinosources,theresultsfromprototypesandthefirst deployed lines will be briefly reported. I. INTRODUCTION and flavour composition have not been precisely de- 7 fined. The measurement of the diffuse neutrino flux 1 The KM3NeT collaboration has designed and measured by IceCube with a detector, like ARCA, 0 started the construction of two research infrastruc- with a different fieldof view and a better angular res- 2 tures in the Mediterranean Sea hosting two neutrino olutioncanshedlightontheoriginoftheseneutrinos. n detectors and nodes for Earth and Sea sciences. The Moreover,thelargevisibilityofthegalacticplaneand a twoneutrinodetectorssharethesametechnologybut the good angular resolution, both for track and cas- J havetwodifferentphysicsgoals. KM3NeT/ARCA,to cade events, makes ARCA the ideal instrument to in- 0 be installed off shore the Sicilian coast at a depth of vestigate galactic sources and in general all sources 2 3500 m, aims at the discovery and subsequent obser- located in the southern sky. ] vation of galactic and extragalactic high-energy neu- The performance of the full ARCA detector (2 M trino sources while KM3NeT/ORCA, to be installed buildingblocksof115DUseach)todiffuseandpoint- off shore the French coast at a depth of 2500 m, aims like sources has been extensively studied by means of I . at the determination of the neutrino mass hierarchy Monte Carlo simulations and the results are reported h bymeasuringtheoscillationofatmosphericneutrinos. in Ref. [2]. In the Monte Carlo simulations the detec- p - The main detector elements, namely the optical tor response to particles crossing the detector, their o sensors (Digital Optical Modules - DOM) and the interaction with the medium surrounding the detec- tr detection units (DU), are identical in the two de- tor and subsequent Cherenkov light production, and s tectors. The DUs are arranged in blocks of 115. the detector response in terms of the PMT data sent a [ The granularity of the detectors will be different: toshorehavebeentakenintoaccount. NCandCCin- the KM3NeT/ARCA detector, when completed, will teractions for all the three neutrino flavors have been 1 have an instrumented volume of about 1 km3 while simulated. Background events of atmospheric muons v KM3NeT/ORCA, will be smaller and more densely withalivetime ofaboutthree yearsandatmospheric 9 4 instrumented. In this work the KM3NeT/ARCA de- neutrinos have also been simulated. 8 tector will be briefly described and the current status The sensitivity of the ARCA detector to the neu- 5 and the expected performance of the complete detec- trino flux measured by IceCube has been evaluated 0 tor reported. The KM3NeT/ORCA detector is dis- using both track-like events reconstructed up to 10◦ 1. cussed in [1]. above the horizon and cascade-like events in the full 0 Adetaileddescriptionofthetechnicaldesignofthe angular range. The results of this analysis show that 7 two detectors and their performances are reported in a significance of 5σ can be reached in less than one 1 the KM3NeT Letter Of Intent [2]. year. : v The most intense high energy gamma ray sources i andgenericpoint-likeneutrinoemittershavebeenalso X II. PHYSICS OBJECTIVES AND EXPECTED considered for the estimate of the discovery potential r PERFORMANCES inARCA.Inparticular,theGalacticsourcesRXJ1713 a and Vela X have been considered. The sources have The IceCube observation of a high-energy astro- beensimulatedasextendedhomogeneoussourceswith physical neutrino flux is nowadays very well assessed. the same radius observed in the high energy gamma Different analyses, with sophisticated and different measurements. Neutrino spectra with energy cutoffs methodologies, have proven the existence of an ex- of few TeV have been also assumed. Results from traterrestrial neutrino flux [3–5]. This discovery rep- simulations show that a significance of about 3σ is resentsaturningpointintheastroparticlephysics. In reached in 4 years for the RXJ1713 and in about 2 fact,neutrinosareauniqueprobefortheinvestigation years for the VelaX [2]. Generic point-like neutrino of the hadronic or leptonic origin of the high energy sourceswithaneutrinoenergyspectrumproportional cosmic rays present in the Universe. to E−2 have been considered and compared with the Withtheavailabledatatheoriginoftheseneutrinos correspondent IceCube curve. has not yet been determined and the spectral shape Recently,anewtrackreconstructionwithimproved eConf TBA 2 XXV European Cosmic Ray Symposium, Turin, Sept. 4-9 2016 angularresolution(<0.1◦ forE >100TeVandnear breakout box. ν the intrinsic ν −µ angle for Eν < 10 TeV) and ef- For the deployment, each detection unit is wound ficiency has been developed inside the collaboration. aroundasphericalframewithdiameterofabout2.2m Moreover, a more sophisticated multivariate analysis (Launcher of Optical Modules, LOM), which is posi- has been applied in the analysis of point-like sources tionedontheseabedandthenunwindedwitharotat- todiscriminatesignaleventsfrombackgroundevents. ing upwards movement. At the end of operation the In the neutrino telescopes two different background LOM reaches the sea surface, where it is collected for eventswithdifferentangulardistributionsandenergy reuse. spectra are present: the atmospheric neutrino events Poweranddataaretransferredto/fromtheseafloor and the atmospheric muon events. We have recently infrastructure via a main electro-optic cable. The applied a Random Forest algorithm to our simulated readout of the detectors is based on the “All-data- data, able to distinguish between three different sam- to-shore” concept. ples: two backgrounds samples and a signal sample. The new technical designs have been validated The first very preliminary results show that an im- through different prototypes. A DOM prototype proving of about one year in the RXJ1713 discovery hosted on the ANTARES instrumented line has been at 3σ is achieved. deployedinMay2013andoperatedforoneyear. The results, reported in [6], have proven the validity of the design and the powerful of the single DOM in the III. DETECTOR DESIGN rejection of background events from 40K decay. ADUprototype,hostingthreeDOMswasoperated The observation of high energy neutrinos is possi- for over a year at the KM3NeT-Italy site. From the ble if particles produced in the rare neutrino interac- datacollectedduringthisperiod[7]afastandreliable tions with the matter surrounding the instrumented procedure for the time calibration which exploits 40K volume are detected. To reconstruct the tracks of the decays from the salt in the seawater and the LED secondary particles produced, and from that also the beacons inside the DOM has been tested. neutrino direction and its energy, the arrival times of For the calibration of the PMT responses in the the light collected by optical sensors and their geo- DOM, coincidences of Cherenkov photons from the metrical positions are measured. 40K decay are used. The PMTs time offsets, the rel- Theoptical sensorsare hostedin flexible string-like ative efficiencies and the time spreads are extracted structures, called Detection Units (DUs), anchored with this method with a fast code that can be eas- at the sea floor, kept vertical by buoys and con- ily expanded to the full detector. The time off- nected to shore by an electro-optical cable network. sets between different DOMs are evaluated using the KM3NeT/ARCA consists in two building blocks of nanobeacons mounted inside the optical modules and 115 DUs each one hosting 18 optical sensors, called cross checked with a calibration procedure using the Digital Optical Modules (DOM). The horizontal dis- signals from muons. tancebetweentheDUsisabout90mandthevertical With this time calibration method a precision at distance between adjacent DOMs is 36 m. the level of nanosecond has been reached [7]. Both the DOM and the DU are technologically innovative elements designed and constructed inside the KM3NeT collaboration. The DOM consists of a IV. STATUS 17-inch diameter pressure resistant glass sphere that contains 31 3-inches photomultipliers with low power high-voltage bases and the readout electronics. 19 The ARCA detector, that will consist of two build- PMTs are located in the lower hemisphere and are ing blocks of 115 DUs, when finished will have the down-looking while the remaining 12 PMTs are lo- geometrical volume of about 1 km3. In Figure 1 the cated in the upper hemisphere and are up-looking. footprint of the detector is shown. The DOM contains also three calibration sensors: a Neutrino telescopes, being modular detectors, al- LEDnano-beaconfortimecalibration,acompassand low for staged construction and data analysis. The tiltmeter for orientation calibration and an acoustic KM3NeT-phase1willconsistof24DUsstring-likeand piezo sensor, glued to the inner surface, for position 8 DUs based on a flexible tower design [8, 9] as first calibration. partoftheARCAdetector(seeFigure1)and7string- The DU consists in two parallel ropes to which the like DUs at the French site with a denser distribution DOMs are fixed via a titanium collar. For the power of the optical sensors, representing the first nucleus and data transmission a vertical electro-optical cable, of the ORCA detector. KM3NeT-phase1 has been a pressure balanced, oil-filled, plastic tube that con- funded and the construction and deployments of the tains two copper wires and 18 optical fibres, is at- first strings started. tached to the ropes. At each DOM two power con- The ARCA phase1 detector (24 DUs string-like) ductors and a single fibre are branched out via the when completed will be have a volume of about 0.1 eConf TBA XXV European Cosmic Ray Symposium, Turin, Sept. 4-9 2016 3 KM3NeT/ARCA Phase1 preliminary 1]10-7 -s 2 -m ARCA Phase1 2 years c V ODU2 Ge ANTARES 2007-2015 ODU1 L [ C % 0 9 10-8 F2 E 10-9- 1 - 0.8 - 0.6 - 0.4 - 0.2 0 0.2 0.4 0.6 0.8 1 sin(d ) FIG. 2: ARCA-phase1 (24 strings) sensitivity as a function of the source declination (red line) for one neutrino flavour, for point-like sources with a spectrum E−2 and 2 years of data-taking. For comparison, the most recent (8 yearsofdatataking)sensitivityoftheANTARESdetector (blue line) is also shown. KM3NeT preliminary Inter-DOM Time calibration of DU-2 s] 5 n n [ 4 Nanobeacon o ati 3 Atmospheric muons br FIG. 1: Layout of the two ARCA building blocks. The ali 2 c smchaienmcaatbiclemsiaspalosfotrheepocratbelde.sIcnonbnlaeccktinthgetphoesDitiUonsswainthdtsheae hore 01 s floor network of the ARCA phase-1. The two red circles n- -1 o indicatethepositionsofthetwostringsalreadydeployed. o -2 e t c -3 n e er -4 km3 and will quickly exceed the ANTARES sensitiv- Diff -5 ity. In Figure 2 the sensitivity for point-like source 2-13-24-35-46-57-68-79-810-911-1012-1113-1214-1315-1416-1517-1618-17 DOM pair with spectrum proportional to E−2 for two years of observationtimeisreportedasafunctionofthesource FIG. 3: Time differences between the time offsets esti- declination for ARCA phase1 (red continuos line). mated with the nanobeacons (red points) and muon sig- The sensitivity is evaluated for up-going track events. nals(bluepoints)andthetimeoffsetsestimatedon-shore. Forcomparisonthebestsensitivityforup-goingtrack The dashed lines represent the standard deviation of the events of the ANTARES detector, reached after 8 two distributions. years of observation time, is also reported (blue line). Currently two lines are in operation at Capo Passero site: the first one deployed in December 2015 on-shoretimeoffsetshavebeenestimatedwithalaser and the second one in May 2016 (DU1 and DU2 re- beamduringtheintegrationphaseoftheDU.There- spectivelyinFigure1). Theanalysisofthedatataken sultsshowthatthetwomethodsareinagreementand with the two first lines started and currently the cali- that the difference between the nanobeacons and the bration procedures described in [7] are on-going. laser calibration is about 1.1 ns (standard deviation) Preliminary results of the inter-DOM time calibra- while the calibration with atmospheric muon signals tionperformedwiththenanobeaconsarereportedfor shows is around 1.5 ns. the DU2 in Figure 3 and compared with the calibra- With a very simple analysis of raw data the ex- tion that uses the signals from muons. In particular pected exponential dependence of the atmospheric thedifferenceintimeoftheoff-shoretimeoffsetswith muon rate as function of the depth has been found the time offsets estimated on-shore are reported. The as shown in Figure 4. This dependence has been ob- eConf TBA 4 XXV European Cosmic Ray Symposium, Turin, Sept. 4-9 2016 KM3NeT preliminary V. SUMMARY 0.007 10-fold 11-fold 0.006 No calibration applied 12-fold 0.005 1134--ffoolldd Inthiscontributionthemaintechnicalcomponents Hz]0.004 15-fold and the status of the KM3NeT/ARCA detector has Rate [0.003 been briefly presented. The construction of the de- 0.002 tector, which in its final configuration consists of 2 0.001 building blocks of 115 DUs with a total instrumented 2700 2800 2900 3000 3100 3200 3300 3400 volume of about 1 km3, has begun. The detector sen- Rate [Hz] 111468000000 Depth [m] 2-fold stoitivthiteiedsitffounseeuflturixnomfleuaxseusrefdrombyGIacelaCcutibcesohuarvceesbaenedn 1200 2700 2800 2900 3000 3100 3200 3300 3400 discussed for the full ARCA detector. Depth [m] KM3NeT-Phase1 is fully funded and will consist of 24 strings and 8 towers, at the Italian site near Capo FIG. 4: Dependence of the event rates measured in the Passero(Sicily),and7stringsattheFrenchsite,close DOMs of DU1 as a function of its position with respect to the Toulon coast. From MC simulation has been tothesealevel(depth)fordifferentcoincidencelevels(see estimated that after two years of data taking ARCA text). Continuos lines represent the exponential fit. phase1 will exceed the current ANTARES sensitivity to point-like sources (8 years of data taking). tained imposing cuts on the number of PMTs inside ThefirsttwoDUsoftheARCAdetectorhavebeen the single DOM with signal in a 20 ns time window deployedandcurrentlythecalibrationphaseisongo- (coincidence level). In the bottom panel of Figure 4 ing. Some preliminary results on raw data have been this dependence is reported for low coincidence level herepresentedshowingthefunctionalityofthedetec- (fold=2). The observed flat behaviour is consistent tor. with the expected dependence of events due to 40K. [1] J. Hofesta¨dt for the KM3NeT Coll., “Prospects Ultrahigh-Energy Cosmic-Ray Sources from a Search for measuring the Neutrino Mass Ordering with forNeutrinosabove10PeVwithIceCube”.Phys.Rev. KM3NeT/ORCA”, in this proceeding and in Lett. 117 (2016) 241101 and references therein. arXiv:physics.ins-det/1701.04078. [6] S. Adriań-Mart´ınez et al., KM3NeT Coll., “Deep sea [2] S. Adriań-Mart´ınez et al., KM3NeT Coll., “Letter of tests of a prototype of the KM3NeT digital optical IntentforKM3NeT2.0”,J.Phys.G:Nucl.Part.Phys. module”, Eur. Phys. J. C 74 (2014) 3056. 43 (2016) 084001. [7] S.Adriań-Mart´ınezetal.,KM3NeTColl.,“Theproto- [3] M.G. Aartsen et al., IceCube Coll. “Observation and type detection unit of the km3net detector”. The Eu- Characterization of a Cosmic Muon Neutrino Flux ropean Physical Journal C 76 (2016) 1. from the Northern Hemisphere using six years of Ice- [8] S. Aiello et al., NEMO Coll., “Measurement of Cubedata”.arXiv:astro-ph/1607.08006andreferences the atmospheric muon depth intensity relation with therein. the NEMO Phase-2 tower”. Astroparticle Physics 66 [4] M.G. Aartsen et al., IceCube Coll. “A Combined (2015) 1 maximum-likelihoodanalysisofthehigh-energyastro- [9] S. Adrián-Mart´ınez et al., NEMO Coll., “Long term physical neutrino flux measured with IceCube”. The monitoring of the optical background in the Capo Astrophysical Journal, 809, (2015) 89 and references Passero deep-sea site with the NEMO tower proto- therein. type”,TheEuropeanPhysicalJournalC76(2016)68. [5] M.G. Aartsen et al., IceCube Coll. “Constraints on eConf TBA