1. Radovan Milinčić and Predrag Miočinović SLAC International SalSA Workshop, February 3-4, 20051 T(CR) 3 IC Testbed for Coherent Radio Cherenkov Radiation from Cosmic-Ray Induced Cascades R. Milinčić 1, P. Gorham 1, C. Hebert 1, S. Matsuno 1, P. Miočinović 1, M. Rosen 1, D. Saltzberg 2, G. Varner 1 1 University of Hawaii at Manoa, Honolulu, Hawaii, USA 2 University of California, Los Angeles, California, USA February 2, 2005 SLAC International SalSA Workshop

2. Radovan Milinčić and Predrag Miočinović SLAC International SalSA Workshop, February 3-4, 20052 Outline Motivation Experimental setup - antennas in salt - trigger and reconstruction of the particle track Analysis - MC calculations - threshold and SNR estimates - single event vs. coherent signal addition Summary and Outlook

3. Radovan Milinčić and Predrag Miočinović SLAC International SalSA Workshop, February 3-4, 20053 Motivation Detecting the first coherent radio Cherenkov signal of natural origin Exploration of Askaryan effect in rock salt in broad range of energies Evaluating potential of rock salt as a medium for detection of UHE particles, e.g. salt domes

4. Radovan Milinčić and Predrag Miočinović SLAC International SalSA Workshop, February 3-4, 20054 Experiment Target material: 20 tons of synthetic rock salt - rock salt blocks, weighing 22.7 kg each - purity of the salt: 93-96% Bowtie antennas embedded in salt and amplified by cable TV technology Computer controlled waveform readout Camac-based trigger from MACRO particle counters

5. Radovan Milinčić and Predrag Miočinović SLAC International SalSA Workshop, February 3-4, 20055 20,000 kg of synthetic rock-salt placed in the rectangular wooden box. –index of refraction n = 2.4; θ C = 65° –specific density ρ = 2.08 g/cm 3 –radiation length Xo = 13.5 cm –critical energy E C = 52.6 MeV dimensions of the box 12 x 1.2 x 0.8 m interior walls covered with thin zinc plated steel sheets two rows of antennas were placed on the lowest layer of salt blocks. 3 MACRO counters track charged particles as a trigger for antenna readout. Experimental Setup

6. Radovan Milinčić and Predrag Miočinović SLAC International SalSA Workshop, February 3-4, 20056 Location UH Manoa campus Physics Dept. Salt stack

7. Radovan Milinčić and Predrag Miočinović SLAC International SalSA Workshop, February 3-4, 20057 Antennas Dual linear polarized bowtie antenna printed on PCB Frequency response ~0.2-2.0 GHz Measurements of beampattern in salt 300 MHz 600 MHz920 MHz

8. Radovan Milinčić and Predrag Miočinović SLAC International SalSA Workshop, February 3-4, 20058 Antenna array configuration –antenna diameter is 20 cm. –the angle of antenna is 60° –antenna orientation toward the array axis is 45° –4 antenna channels of same polarization mixed into one signal channel –total of 48 channels Antenna setup

9. Radovan Milinčić and Predrag Miočinović SLAC International SalSA Workshop, February 3-4, 20059 Trigger Trigger is based on MACRO scintillator counters - liquid scintillator with index of refraction n = 1.55 -in tree layer (12 m long, 0.7 m wide, 0.3 m tall) -total of twelve (30.5 cm diameter) PMTs face the scintillator from both sides of the layers Trigger threshold set to 100 GeV muons; requires larger particle multiplicity in lower two counters Trigger rate ~2500/day

10. Radovan Milinčić and Predrag Miočinović SLAC International SalSA Workshop, February 3-4, 200510 Particle track reconstruction Two dimensional reconstruction of particle track is based on PMT timing For each trigger, all RF signal channels are read out, as well as full PMT signal information

11. Radovan Milinčić and Predrag Miočinović SLAC International SalSA Workshop, February 3-4, 200511 6 oscilloscope channels are used to record 48 RF signals Thus 8 different signals recorded by each oscilloscope channel. Time Division Multiplexing module records all 8 signals with one oscilloscope channel. – Signals recorded with 2 Tektronix TDS 684 real time digital sampling oscilloscopes. – Sampling rate 2.5 Gs/s. RF readout (old)

12. Radovan Milinčić and Predrag Miočinović SLAC International SalSA Workshop, February 3-4, 200512 RF readout (old) cont. switches used for multiplexing introduced a very large noise additionally, cable delays attenuated signal, requiring additional amplification stage resulting waveforms had reduced noise-free time window 330 days of data recorded in this way

13. Radovan Milinčić and Predrag Miočinović SLAC International SalSA Workshop, February 3-4, 200513 RF readout (new) RF readout through a custom, low-power digitizer chip (STRAW2) mounted on cPCI card 12 RF channels per card sampling rate 2.12 GS/sec, 250 samples per waveform

14. Radovan Milinčić and Predrag Miočinović SLAC International SalSA Workshop, February 3-4, 200514 RF readout (new) cont. Taking data with new system since Aug 26, 2004 Great improvement in RF data quality We fully capture particle transit window

15. Radovan Milinčić and Predrag Miočinović SLAC International SalSA Workshop, February 3-4, 200515 MC expectations –polarization characteristics of 4 in 1 hybrid antenna pulses. –the test measurement was done in SLAC Final Focus Test Beam facility –based on measured signal strength, 1σ threshold for cascade energy is 1.8 TeV –Total expected event rate is 12.7 events/yr –2σ rate 2.3 ev/yr 3σ rate 0.5 ev/yr

16. Radovan Milinčić and Predrag Miočinović SLAC International SalSA Workshop, February 3-4, 200516 Analysis Preliminary analysis of data collected with old RF readout shows that switch noise is dominating and any signal extraction with be very difficult at best (i.e. do it later) Strategy I: build matching filter based on SLAC measurements of bowtie response to Askaryan pulse + lab measured system response scan all events for coincident pulses consistent with expected shape analyzed 2 months of data, but no clear candidates Bowtie response to Askaryan pulse

17. Radovan Milinčić and Predrag Miočinović SLAC International SalSA Workshop, February 3-4, 200517 To reduce our threshold sensitivity, coherently add RF data; i.e. add subthreshold events in order to boost SNR Look for statistical increase in RF power seen by antennas inside Cherenkov cone when compared to antennas outside of the cone In progress, no results to report –currently limited by RFI from UHF TV station and KTUH 90.3FM, Hawaii’s only alternative –need to digitally filter out RFI; 50-95 MHz and 200-260 MHz bands Analysis, cont. Strategy II:

18. Radovan Milinčić and Predrag Miočinović SLAC International SalSA Workshop, February 3-4, 200518 Summary The testbed experiment has been operating since July 26 th 2002, and since Aug 26 th 2004 with an improved RF readout Built on a shoestring budget ($40-50k), but proving to be essential for hardware development platform for both ANITA and SalSA Motivated by a good physics goal, not just a technology tesbed

19. Radovan Milinčić and Predrag Miočinović SLAC International SalSA Workshop, February 3-4, 200519 Outlook Several significant improvements possible –More quiet even better RF readout possible with new chips place experiment further away from RF noise pollution more stable amplifiers; CATV technology is adequate, but not optimal –Higher move to higher ground for increased particle flux –Bigger Increase volume of instrumented salt

20. Radovan Milinčić and Predrag Miočinović SLAC International SalSA Workshop, February 3-4, 200520 Testbed on Haleakala