Timmermans, C

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29th International Cosmic Ray Conference Pune (2005) 6, 345348Setup and first results of the HiSPARC experimentC. Timmermans on behalf of the HiSPARC collaborationNIKHEF and Radboud University Nijmegen, the NetherlandsPresenter: C. Timmermans (c.timmermans@hef.ru.nl), net-timmermans-C-abs1-he13-oralIn Nijmegen, a high school array is being constructed since 2001. The educational aim of this experiment is tohave high school students participate in a true scientific undertaking. This Nijmegen Area High School Array(NAHSA) currently consists of eight stations located in a relatively compact area. This NAHSA initiativeforms the seed of a national experiment called HiSPARC (High School Project on Astrophysical Researchwith Cosmics), which currently consists of five clusters of detector stations centered around scientific institutesin Amsterdam, Groningen, Leiden, Utrecht and Nijmegen. In 2004 HiSPARC won the international ALTRANfoundation for innovation award. Within HiSPARC, high school students build and operate the detector locatedat their high school and have full access to all the HiSPARC data through the internet. The data consists ofthe full digital scope traces of the signals from both scintillator detectors that make up a station. The setup ofan individual station as well as the setup of a cluster will be discussed. The results from analysis, includingenergy estimates, of coincidences from two and three stations within the Nijmegen cluster will be presented,as well as the largest events we have recorded so far in Amsterdam and Nijmegen.1. Experimental SetupHiSPARC is a national Dutch initiative, which aims to build a large national network of cosmic ray detectorson high schools. The goal is twofold. HiSPARC wants to create enthusiasm within high school students andteachers for the exact sciences by having them participate in a scientific experiment. Furthermore, HiSPARCwants to be a scientific experiment, investigating cosmic rays at energies between 10 and 	 eV. As ascientific experiment, new features are added with respect to previous detectors. Firstly, Flash-ADC readout isused for every single detector station. Secondly, the cosmic ray detector is organized in clusters, with typicaldistances between clusters of about 50 km. This will allow a search for long range correlations and would evenallow for particle-interferometry should correlations be found. Each of these clusters consists of an array ofparticle detectors and is centered around a scientific institute which provides the local organization and support.Representatives from the clusters meet regularly for national coordination.1.1 An individual stationThe active elements of an individual station, located at a high school or scientific institute, consists of twoplates of scintillator with an effective area of 0.5 m  each. The thickness of these plates vary, but our baselineis 2 cm thick BICRON BC408 scintillator. The produced light is guided, using a fish-tail lightguide, into aphototube (Electron Tubes 9125 SB) The detector is glued together and wrapped in aluminum foil and blackpond foil by high school students. Afterward each complete detector station, including PM and electronics iscalibrated and tested by high school students at the scientific institute before installation at school.The signals of the individual tubes are sent to a custom made coincidence unit, which creates a trigger whenboth PMs give a signal within 1  s. The trigger is sent to a GPS unit (Trimble, ACUTIME 2000) and a digitaloscilloscope (PicoScope ADC 212). The coincidence unit, GPS and flash ADC will be replaced by custommade electronics, which is designed by ALTRAN as part of the 2004 ALTRAN award. Using a LabView pro-gram the oscilloscope traces of both scintillator plates is being read out and combined with the GPS timestampfor each trigger. Each scope trace lasts 5  s, and is binned in 20 ns units. Each station takes several triggers346 C. TimmermansFigure 1. High school students assembling a detector.per minute. The data of all the individual stations is sent to a central server, where the combination betweenstations take place as well as further analysis.2. The first resultsThe HiSPARC experiment started in Nijmegen, where the first stations got built in 2001 under the nameNAHSA. The first results originate from the Nijmegen cluster, which is most advanced with respect to dataanalysis. The setup of this cluster has been simulated, using the AGASA particle density distribution [1], as-suming a Poissonian distribution of particles around the average number of expected particles at each detectorplate. The AGASA density distribution has been scaled down by a factor of 2 to account for the altitude differ-ence between Akeno and the Netherlands. We keep track of the uptime of each station by checking for periodswithout data and by checking the dead-time after each trigger, as can be seen in Figure 2. Using the measuredparticle flux [2] from other experiments, an absolute prediction for the number of coincident events betweenschools can be found. In Figure 2 this prediction is compared to actual measurements, which are corrected forrandom coincidences.Using the same particle density distribution, it is possible to estimate the energy of events that triggered at leastthree stations. However, with a few assumptions, a lower limit of the energy can be given for events triggeredby two stations only. The assumption being that the energy is minimal, thus the shower comes in as vertical aspossible and the shower core lies on the line connecting the stations. As the energy spectrum is steeply falling,this actually gives a reasonable estimate of the most probable energy. The reconstructed energy spectrum iscompared to the simulation and the agreement can be seen in Figure 3. Again, the simulation is normalizedto the total uptime of the corresponding combination of stations. The right hand side of Figure 3 shows themeasured and simulated energy distribution for events which are triggered in the three nearest stations. ForSetup and rst results of the HiSPARC experiment 347Figure 2. Left: the uptime distribution of detector 1 during 2003. Right: the number of measured and expected coinci-dences between stations as function of distance.these events an energy estimate can be given, assuming the correctness of the simulation, without any additionalassumptions.3. The highest energy eventsThe highest energy events are those that trigger detectors at the largest distances. Both in Amsterdam andNijmegen events have been found that trigger detectors at more than one kilometer distance. The largest eventsso far are triggered in three stations. On February 4th 2005 an event was seen in Amsterdam, where thedistances between detectors were 845, 1216 and 1535 m, and on March 19 2005 an event was recorded inNijmegen, where the distances were 988, 2477 and 2780 m. The energy of the latter event has been estimatedto be almost  eV. Using the data, the chance probability of the occurrence of this triple coincidencehas been estimated to be less than . For both of these events, the data shows multiple peaks in mosttraces, indicating that the distance between detector and shower core is large.4. Conclusion and outlookCurrently about 35 stations are operational in 5 clusters in the Netherlands. Tools for taking data and analyzingthe results exist and are being improved. Next, the data taking will be optimized and more stations will beadded. Furthermore, better and cheaper electronics will be used. This will allow more high school students tocome in contact with this exciting field of research. Apart from the expansion of HiSPARC, we are also activein organizing a european wide collaboration between the high school array initiatives. Meetings between348 C. TimmermansFigure 3. Left: Energy estimate from coincident events at a distance of 500 m. Right: Threefold coincidences where thedistances between detectors are 520, 800 and 1038 m.representatives of these arrays are taking place. Furthermore, we collaborate with the outreach aspects of theLOFAR radio antenna array which is being constructed in the Netherlands. This has resulted in the LORUNexperiment in which radio antennas are combined with particle detector information in Nijmegen [3]References[1] M. Takeda et al., Astroparticle Physics 19, 447 (2003).[2] M. Nagano and A. A. Watson, Rev. Mod. Phys. 72, 689 (2000).[3] A. Nigl et al., these proceedings.

Setup and first results of the HiSPARC experiment

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