T(CR)3IC Testbed for Coherent Radio Cherenkov Radiation from Cosmic-Ray Induced Cascades

Transcription

1 T(CR)3IC Testbed for Coherent Radio Cherenkov Radiation from Cosmic-Ray Induced Cascades R. Milinčić1, P. Gorham1, C. Hebert1, S. Matsuno1, P. Miočinović1, M. Rosen1, D. Saltzberg2, G. Varner1 1 University of Hawaii at Manoa, Honolulu, Hawaii, USA 2 University of California, Los Angeles, California, USA SLAC International SalSA Workshop February 3,

2 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 2

3 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 3

4 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 4

5 Experimental Setup 20,000 kg of synthetic rock-salt placed in the rectangular wooden box. index of refraction n = 2.4; θc = 65 specific density ρ = 2.08 g/cm3 radiation length Xo = 13.5 cm critical energy EC = 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. 5

6 Location UH Manoa campus Salt stack Physics Dept. 6

7 Antennas Dual linear polarized bowtie antenna printed on PCB Frequency response ~ GHz Measurements of beampattern in salt 300 MHz 600 MHz 920 MHz 7

8 Antenna setup 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 8

9 Trigger Trigger is based on MACRO scintillator counters -liquid scintillator with index of refraction n = 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 9

10 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 10

11 RF readout (old) 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 (3 GHz bandwidth) Sampling rate 2.5 GS/s 11

12 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 residual switch noise switch edges 50 ns 12

13 RF readout (new) RF readout through a custom, low-power digitizer chip (STRAW2) mounted on cpci card (ANITA/SalSA prototype) 12 RF channels per card sampling rate 2.12 GS/sec, 250 samples per waveform 13

14 RF readout (new) cont. Taking data with new system since Aug 26, 2004 Improvement in RF data quality We fully capture particle transit window (~ 60 ns) Downside: - lower bandwidth - larger digitizer noise ~120 ns 14

15 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 15

16 Analysis Preliminary analysis of data collected with old RF readout shows that strong switch noise is complicating signal extraction (i.e. do it later), so concentrate on new RF readout data 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 yet Bowtie response to Askaryan pulse 16

17 Analysis, cont. Strategy II: To improve our 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 for selected events 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; MHz and MHz bands 17

18 Summary The testbed experiment has been operating since July 26th 2002, and since Aug 26th 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 18

19 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 19

20 Testbed on Haleakala 20