Antonis LeisosKM3NeT Design Study the calibration principle using atmospheric showers construction and performance of the prototype detector station Monte Carlo Studies XXV Workshop on Recent Developments in High Energy Physics & CosmologyNTUA Greece 28 - 31 March 2007 Calibration systems and methods for underwater neutrino telescopeG. Bourlis, E. P. Christopoulou, N. Fragoulis, N. Gizani, A. Leisos, S. E. Tzamarias, A. Tsirigotis, B. Verganelakis

SPASE air shower arrays calibration of AMANDA angular resolution and pointing ! resolution Amanda-B10 ~ 3.5spase-amanda

The General IdeaAngular offsetEfficiencyResolutionPositionPhysics ? (ex. ICETOP)C.R. compositionUHE - Horizontal ShowersVeto atmospheric background Study background

~4km~20kmIsotropic on the top of the atmosphere BUT

Pierre Auger: M. Are et al. Ast.Part. 14: 109-120 2000Haverah Park (www.ast.leeds.ac.uk/haverah/havpark.html): 12km2 effective area and 2 coverage in for 10 years operation less than 100 detected showers with NESTOR: muon flux @ 4000m

The ConceptFloating stations

HELYCON StationGPSScintillator-PMTScintillator-PMTScintillator-PMTDAQ~20 m 1 m2 Single Station Set-UpTriangulation Shower DirectionScintillator-PMT4(1W/counter)+30W(PC+electronics)

The HELYCON Detector ModuleScintillator 2Scintillator 3GPS timestampStation ServerScintillator 3

Simulation ToolsCORSIKA(Extensive Air ShowerSimulation)GEANT4(Scintillation, WLS & PMT response)Fast Simulation also availableNumber of particles to the groundEnergy: 105 GeV 5 105 GeV

Simulation ToolsDAQSIM(DAQ Simulation)HOUANA(Analysis & Track Reconstruction)Time (ns)Height (mV)Zentih (degrees)

Simulation ToolsGEANT4Muon Propagation to KM3HOU-KM3Muon track (s) reconstruction

Monte Carlo Studies- Outlook 1014 - 51015 eVE~ 1014 - 51015 eV: 2500 showers/m2/yearSingle station detection: 351m2 effective area (depends on geometry and selection cuts)Multi-Station: separation 1016 eV: 1 shower/m2/yearTO BE STUDIED

35% of the detected showers include a muon which arrives at the Neutrino Telescope (depth 4000m) with an energy >300GeVGeneral Remark: 3 stations operating for 10 days can identify an angular offset with an accuracy of 0.15o

Monte Carlo StudiesDepends on: Detector separation Selection criteria Shower directionTypical ValuesNo cut: = 4.5Total Collected Charge > 10 mips: =2.22Total Collected Charge > 25 mips: =1.33Total Collected Charge > 30 mips: =1.2

Atmospheric shower simulation by CORSIKA - muon transportation to the detector DEPTH by GEANT4 - Sea-Top Detector detailed simulation GEANT4_HOUPRELIMINARYrec-trueAngular Resolution inSingle Shower Reconstruction

Monte Carlo StudiesReconstruction efficiencyResolution (degrees)Three Stations Working Independently for 10 daysSingle Station: 4 detectors (1m2 plastic scintillator), 20 m distance between the detectors, three out of four selection trigger

PRELIMINARY

Proposed Detectordt=019m19m5m1 m2 Scintillation Counterdt1dt2dt3

Multi-Station Operation Monte Carlo Studies in ProgressTime Spread (ns)Total collected charge [pe]First coming particles

Timing vs Pulse HightSlewingResolution

Time corrections

Consistent EstimationsMinuit Minimization

Detection EfficiencyEfficiencyEventsA hit is considered when there is more than 4 mips deposited charge

Muon Propagation trackkm3Geant Simulation(propagation & Energy Loss)Accepted if muon with E>2TeV goes through km3Muon Track Reconstruction(A. Tsirigotis talk)Zenith angle < 13 deg

Muon Propagation

Primary Zenith Angle Resolution Deposited Charge per counter > 4 mips Number of Hits > 10

Primary Azimuth and Space angle Resolution

Charge parameterizationAGASA parameterization (S. Yoshida et al., J Phys. G: Nucl. Part. Phys. 20,651 (1994)Parameters depend on (, , primary)Mean particle density registered by an active counter

Primary Impact determination

Effective Area~ 30 showers per day reconstructed at the surface and in the deep sea

ConclusionsThe operation of 3 stations (16 counters) for 10 days will provide:

The determination of a possible offset with an accuracy ~ 0.05 degThe determination of the absolute position with an accuracy ~ 0.6 mEfficiency vs Energy and Zenith angleResolution

I am going to present you the work of our group concerning the calibration system we have proposed for the Kilometer cube Neutrino Telescope which is going to be deployed in the Mediterranean Sea. The system is based on the sea level detection of low energy atmospheric showers that also trigger the v-Telescope at a depth of about 4000 meters.

This is the Outline of this talk: First I will describe the calibration principle using atmospheric showers, then I will show you a few transparencies concerning the construction and the performance of the prototype detectors already running at the our lab and finally I will concentrate in the Monte Carlo studies and show what we can expect to achieve with this calibration system. The idea is actually stolen from the SPASE-AMANDA project at the Antarctic sea. The AMANDA detector is an array of Photomultiplier tubes buried in the ice at a depth of 2 thousand meters. These photomultiplier tubes detect the Cherenkov light emitted by energetic muons that passing by. These muons may come from a neutrino interaction or more often these are atmospheric muons that penetrate to the detector depth.The Spase scintillation array consists of 120 scintillator counters positioned at the surface. It detects cosmic air showers in order to study the shower properties like energy, primary mass, age etc) but it also serves as a calibration module for the AMANDA detector.The concept is that some of the reconstructed showers will also trigger the AMANDA array and a direct comparison can be made. This way SPASE measured the AMANDA B10 reconstruction accuracy and also indicated a zenith angle offset of the neutrino detector of about 1.5 degrees.

The general idea of such a calibration module is that a significant percentage of the reconstructed atmospheric showers contain very energetic muons that can penetrate to the detector depth and thus they can be reconstructed by the neutrino telescope.By comparing the reconstructed muon track with the reconstructed shower direction one can estimate in principle:The possible angular offset of the telescopeThe efficiency of the telescopeThe angular resolution and The absolute position of the telescope.In addition such an array can study the Cosmic ray physics, the UHE neutrinos be detecting Horizontal showers or it can be used to veto the atmospheric muon background.That is what actually ICETOP will do, the surface partner of the ICECUBE in the Antarctic sea.Unfortunately this can not be done for a deep sea -Telescope which will probably be deployed at a depth of about 4000 meters at a distance of about 20 kilometers from the shore. The reason is that despite that the primary cosmic ray flux is isotropic at the top of the atmosphere, due to the slant depth the zenith angle distribution is modulated according to this law with a of about 10 which means that inclined showers are very rare.So such an array at the shore is practically useless for calibration purposesFor example In Piere Auger Laboratory the expected flux of showers with energy above the knee and for zenith angles grater than 80 degrees is about 1.4 showers/year for an instrumented area of 4 thousand kilometer square.In haverah Park after 10 years of operation only 100 showers were detected with zenith angles grater than 80 degrees , while the muon flux at 4000 meter deep measured by the NESTOR collaboration demonstrates that muon tracks above 60 degrees are very rare. So the concept of our proposal is that we could use floating stations above the detector for small periods of time.

We propose a minimum of 3 stations each one with at least 16 square meters of scintillator counters to operate for at least 10 days continuously.The counters of the station are the ones currently used by the HELYCON detector array. The HELYCON array is a research and education purpose detector which is planned to be operated in the area of Patras city It consists of stations positioned at the roof of high schools or public buildings each one with 4 scintillator counters and a GPS for absolute synchronisation.The counters are positioned at a typical distance with each other of about 20 meters and are controlled by a central DAQ hosted in a Personal Computer.

The detection principle is based on the almost true fact that the shower front of particles is a plane perpendicular to the shower axis moving with the speed of light. Then by triangulation the azimuth and the zenith shower angle can be reconstructed with at least 3 active counters. The HELYCON detector module consists of 160 scintillating tiles covering an area of about 1 m2. The light produced by the scintillator is guided to a single PMT with 96 Wavelength shifting fibers. The electronic pulses are acquired from the DAQ board which also timestamps the event using a Motorrola timing module. A lot of work has been carried out in order to develop accurate and efficient simulation tools for the analysis. For the generation of the Atmospheric air showers we use the well known Corsika generation code. For demonstration in this plot you can see the number of particles that reach the ground for low energy showers.Then for the particles that hit the detector modules, we simulate the production of scintillation the role of the WLS fibers and the PMT response using the the Geant4 simulation Package. Due to the large number of particles we have also developed a fast simulation version with the appropiate parameterizations. The next step is to simulate the Data Acquisition system, the trigger formation and the digitization. For example here you can see the generated waveform due to some particle hits.Finally the determination of the shower parameters is performed with the Analysis and Reconstruction program which produces plots histograms etc. For the need of the calibration system the simulation code includes also the propagation of the muons to the sea depth of 4000 meters taking into account all the possible muon interactions and especially the production of the Cherenkov light that is collected from the PMTs.Finally we use the muon reconstruction code in order to reconstruct the muon track parameters namely the zenith and azimuth angle ans the psuedovertex position odf the track.You have already seen the very good agreement of the Monte Carlo simulation with the experimental data so I will skip that section and give you the results of the simulation for a HELYCON station of 4 counters using low energy air showers just above the threshold which is 10 to 14 eV. The effective area for such a detector is 351 square meters for very loose cuts resulting in a rate of 2500 events per day. Almost 35 percent of these events include a muon which arrives at the neutrino Telescope and if you use 3 such detectors for a period of 10 days then you can estimate a possible n-Telescope offset of about 0.15 degrees.For demonstration in this slide you can see the resolution of such a station for 4 different cuts to the total collected charge.Starting from 4.5 degrees you can go down to 1.2 degrees if you demand total collected charge grater than 30 mips.You should have in mind that when you apply hard cuts you improve the resoluion but you loose in statistics, so in this plot you can see the zenith angle resolution offset as a function with the minimum total collected charge concluding that the resolution can be up to 0.15 degrrees.I remind you that these results concern 3 station HELYCON detectors, that is 4 counters per station at a distance od 20 meters between them.The accuracy can be better if you increase the number of counters and decrease the spacing between them.In the rest of this talk I will refer to this station of 16 nodes with 5 meter spacing. The reconstruction procedure is simple. Assuming that these bullets here are the detectors you measure the time difference of these hits with respect to the hit of a specific detector and minimise the corresponding chi square function.The reconstruction procedure assumes that the shower particle front is a plane moving with the speed of light but in real life this is not trueAs you can see in this picture the shower front is not a plane but it is curved so particles far from the shower core are delayed.In addition away from the shower core as the particle density drops the time spread of the particles is bigger giving rise to the possiblity that the first particle is not close to the curved shower front. That is called thickness and it is demonstrated in this plot. The lower the collected charge the bigger the time spread.This facts must be taken into account in order to apply the needed corrections.As far as the detector concerns the timing is disturbed due to slewing. The variation of the arrival time with respect to the pulse height. We have studied slewing and found that for particle densities above 4 mips per square meter the resolution reaches a plato of about 1.3 ns.Finally we have parameterized the delay and the delay spread due to the thickness with respect to the collected charge.As you can see as the deposited charge is increased, the delay spread reaches a constant value which is actually the spread due to sllweing.If we apply all these corrections and take into account the corresponding errors we cheked the procedure by calculating the time residuals of the detector hits.As you can see they are distributed according to a normal distibution with mean zero and sigma unity.We have also checked the consistency of the fitting procedure by calculating the Xchi square probability of 2 statistics R and lamda.R is the difference of the chi square function calculated for the true and the estimated parameter values whilst Lamda is mahalanobis distance of the generated and the estimated parameter values.In both case the chi square probability with 2 dgrees of freddom is constant prooving that the method is unbiased an the error estimation correct.In this plot you can see the distribution of the active counters per shower and next The efficiency of the reconstruction with respect to the distance from the shower core.The detector can reconstruct showers which can be up to 60 meters far away Coming back to the calibration, only a portion of the reconstructed showers are usefull.Specifically we accept showers wich contain a muon with energy grater than 2 TeV with a direction towards the km3 detector.The most efficient position of the platform is found to be just above the v-telescope restricting us to showers with zenith angle less than 13 degrees. For these showers we have calculated the muon shower space angle and the zenith angle difference and we found to be 1.5 and 1.2 degrees respectivelyAs I have already mentiond the accuracy of determining the shower zenith angle depends on the selection cuts we apply.In this analysis we asked for more than 4 mips per counter and more than 10 hits resulting in an accuracy of 1.2 degrees.The azimuth angle resolution is limited to 14 degrees but remember we speak for almost vertical showers so we expect that the phi resolution is poor.Concering the space angle between true and estimated shower direction, the mean value is 1.5 degrees.One step further in the reconstruction analysis includes the deterimnation of the shower impact point.The impact point can be estimated by measuring the particle density distribution wit respect to the perpendicular core distance. This distribution can be parametrised according to the AGASA formulaWhere the parameters depend on the zenith angle the primary mass and the energy of the shower.However the mean lateral distribution for all energies and zenith angles can be parameterized with respect to the perpendicular distance from the shower coreAs you can see in these plots the mean particle density registered by an active counter as well as the rms value can be fitted very well. Consequently the impact point can be estimated with an accuracy of about 10 meters for the standard selecion cuts we apply.Of course the resolution can be incresed as it is demonstarted in this plot by asking more collected charge.Finally we have calculated the effective area with respect to the energy of the primary particle and convoluted with the defferential flux of the cosmic rays, we end up with about 30 showers per day reconstructed at he surface and in the deep sea. So..The conclusion is that the operation of 3 such stations for 10 days will provide:The determination of a possible offset with an accuracy ~ 0.05 degThe determination of the absolute position of the -detector with an accuracy ~ 0.6 m

Calibration system and assuming that the n-Telescope resolution in determining the zenith angle of a muon track is about 0.1 degrees and the impact about 2 meters,