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Development of a radio detection array for the
observation of showers induced by UHE Tau neutrinos
C. Cârloganu, D. Ardouin, Didier Charrier, H. Hongbo, Pascal Lautridou, O.
Martineau-Huynh, V. Niess, O. Ravel, X.-P. Wu, M. Zhao, et al.
To cite this version:
C. Cârloganu, D. Ardouin, Didier Charrier, H. Hongbo, Pascal Lautridou, et al.. Development of a
radio detection array for the observation of showers induced by UHE Tau neutrinos. 44th Rencontres
de Moriond, Feb 2009, La Thuile, Italy. �in2p3-00406960�
by UHE Neutrinos C.C^arloganu a ,onbehalfofD. Ardouin b ,D. Charrier b ,H.Hongbo ,P.Lautridou b ,O. Martineau-Huynh ;d;e ,V.Niess a , O.Ravel b ,X.P.Wu e ,M,Zhao e ,Y.Zhiguo a
Laboratoirede Physique Corpus ulairede ClermontFerrand,IN2P3/CNRS, UniversiteBlaise Pas al, ClermontFerrand,Fran e
b
SUBATECH, Universite de Nantes,IN2P3/CNRS, E ole desMines Nantes,Fran e
Parti leAstrophysi s Center,Instituteof HighEnergy Physi s,Chinese A ademyof S ien e, Beijing, 100049, China
d
Laboratoirede PhysiqueNu leaireetdesHautesEnergies, Universites Paris6-7, IN2P3/CNRS, Paris Cedex 05,Fran e
e
NationalAstronomi al Observatories ,ChineseA ademy ofS ien e,Beijing 100012, China. Therunningradio-dete tor21CMAisbeing urrentlyadaptedfor
sear hes.10287antennas sitalong twohighaltitude valleys, surroundedby mountain hains, inanex eptionally low ele tromagneti noiseenvironment.Firstsmeasurementsobtainedwiththeinsitu,6-antennas prototype,showthegreatpotentialforshowerdete tionofthearray. Preliminarysimulations of the foreseensetup indi atethat anoneyear exposureof 10
13 m 2 ssr for 10 17 eV 's maybeattainableusing80dedi atedantennas.
1 Introdu tion
The probing of the UHE omponent of the far away Universe relies heavily on the dete tion of the UHE neutrinos
1
. Unfortunately, they an be observed only indire tly, through their intera tion with target nu leons. The very low intera tion ross se tion, ombined with the already small uxespredi ted
1
,requiredete tion volumes oftheorder of ubi kilometers. The UHE neutrinosare produ ed either bythe intera tion of the UHE osmi rays within theirsour es, orintheir subsequent intera tions withthe ba kgroundradiation elds. In both ases, tauneutrinos are mu h suppressed at produ tion sin ethey are not a de ay produ t of the dominatingpions. However, approximatelyequal uxesforea h avour are expe ted after traveling osmologi aldistan es to theEarthdueto neutrino avouros illations
2;3 . Thereareseveralrunningexperimentslookingfor
's, asthededi ated neutrinoteles opes ANTARES
4
and I eCube 5
. The extensive air shower (EAS) dete tor AUGER 6
looks for
's whi h enter the Earth just below the horizon and produ e leptons whi h an es ape the Earth;subsequently,the 's de ayin ight intheatmosphere produ es showers visiblebothin theirsurfa earrayand uores en eteles opes. TheAUGER ollaborationshowed a umulated exposures of the order of 310
16 m
2
ssr, whi h allowed them to pla e an upperlimit on the
ux approa hing thetheoreti al predi tionsfortheGZKneutrinos 7
. Lately, two ollaborations, CODALEMA
8
and LOPES 9
, showed the feasibility of radio-dete tionoftheEAS'susingan externaltriggerprovidedbygrounddete tors. Moreover,signal
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Local Sideral Time (h)
Average antenna signal (dB)
Figure1: Left: averageFouriertransformoftheba kgroundnoisefora21CMAantenna. Right: antennasignal averagedover15hoursofdatatakingasafun tionofthelo alsideraltime,peakingtothegala ti radioemission.
of EAS's 8
. An a ura y of the order of the degree was obtained by CODALEMA for the re onstru tion of the arrivaldire tions of radiotransients generated by solar ares. The same re onstru tion method was used for the EAS's. Under theassumption that the EAS's an be measuredby standaloneradiosensors witha dire tion a ura y of theorder of the degree, we presenthereapropositiontolookfor
'susingsome dedi atedsensorsfromanalreadyexisting radio array, 21CMA
10
. It is argued that the experimental site is parti ularlyappropriate for the
dete tion andgenerallyforradiodete tion. Thestatusoftheproje tisshown,aswellas ourexpe tationsforthephysi s outrea h basedon preliminarysimulationsof theexperimental setup.
2 21CMA experiment and the present setup for 21CMA
The 21CMA experiment is situated in the Ulastai Valley, in the Western-China provin e of XinJiang, at 2700 m of altitude. It is the only running experiment dedi ated to re-ionisation studies. The dete tor onsists of 10287 [50-100 MHz℄ log-periodi antennas, distributed over 81 groups of 127 antennas ea h ( alled inthe following pods). It has two arms of 3 and 4 km length,orientedNorth-SouthandEast-Westrespe tively,whi hfollowtwoalmostperpendi ular valleys.
On ea h pod, the analog signals of the 127 antennas are added and ampli ed by 45 dB beforebeingsentoveranopti al bretothe ontrolroom. Priortotheirre ordingondisk,they aredigitised using818-bits ADCs (oneforea h pod),workingsyn hronouslyat 200 MHz.
The rst measurements performed on site showed a unique radio environment: the radio transmittersabove15MHzarequasi-absent(Figure1,left). Thegala ti planethermalemission in the radio waveband is visible after only 15 hours of data taking (Figure 1, right), showing thatthe antennas have thesensitivityrequiered forEASdete tion.
The rst phase of the proje t is meant to prove the prin iple of the EAS dete tion with a self-triggeringarray. SixantennaswerepositionedasseeninFigure2,leftandtriggeredusingan amplitudethresholdsetat6timesthestandarddeviationoftheele troni snoiseand oin ident signalson more thanthree antennas. A triangulationre onstru tionleadsto thesignal origin.
The time alibration of the setup was he ked by re onstru ting a nearby radio sour e of known position. The dispersionofthere onstru ted positionof thesour e(Figure 2,right),is
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radio source position
S−N [ m ]
W−E [ m ]
Figure 2: Left: the positions of the 81 pods in the two valley are shown (thered dots). The6 pods housing oursupplementaryantennasare highlighted by the yellowre tangle. Middle: a lose view ofthe pods. Right: the position of the six antennas (blue stars), the position of the ar used as radio sour e (red ross) and the
re onstru tedorigin ofthesignal (greenandbla kpoints).
3 Simulation Chain
Thedete tionprin iplefor
'sat 21CMAisthefollowing: aUHE,almosthorizontal
, inter-a ts with themountainssurroundingthe antennas. The produ ed an es ape themountains and ifitde ays withinthevalley itprodu esashowerwhi h an be seenbytheantennas. The mountains a t also as shielding against the EAS's due to the osmi ray intera tions in the atmosphere. An angular resolution of degree should prevent ontamination from downgoing CREAS's.
Startingwith adi useneutrino ux,the uxwilldependon thedepth ofmatter rossed, whi his al ulatedfromsatellitedata
11
. The
-nu leonintera tionissimulatedwithPythia 12
. The propagation assumes ontinuous losses
14
and its de ay is simulated with theTAUOLA pa kage
13
. The radio signal is generated following the longitudinal and radial pro les of the shower and it has an exponential fall with the distan e
15
. The typi al ele troni s noise is simulated and the trigger is de ned by three or four oin ident antennas. With a omplete dete tor with 81 antennas (one per pod) the expe ted e e tive surfa e at the trigger level is showninFigure3,left,asfun tionofthein oming
anglewiththelo alverti alforanenergy of 10 19 GeV. It rea hes 3:510 3 m 2 for horizontal
's inthe ase of four oin ident antennas. Onthe right of thesame gure,the a hievable exposure inone year of datatakingis shown as fun tionof thein identneutrino energy.
4 Con lusion
The proje t of using the running 21CMA radio dete tor for
sear hes started in June 2008 and the rstresultsareveryen ouraging. Theradioenvironment isideal: almost noterrestrial noise,themeasurementoftheradiosignalfromthegala ti planeo ersareliable alibrationof theantennasensitivity. A lotof e ortisongoing forthetimeinter- alibrationof theprototype usingknown radiosour es. If learmeasurements of the EASwill be availablebefore summer 2009,theprototypewillbethenupgradedtothefull81antennas. Simulationstudiesshowthat the21CMAlayoutisveryeÆ ientforthedete tion of
'swithenergiesbetween10 16
-10 19
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Figure3: Left: e e tivesurfa eatthetriggerlevelasafun tionofthein oming anglewiththelo alverti al for10
19
GeV . Right: expe tedexposureinoneyearofdatatakingasfun tionofthein identneutrinoenergy. Thedi erent urves orrespondtotriggersrequiring3or4 oin identantennas.
Referen es
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