Radovan Milinčić and Predrag Miočinović SLAC International SalSA Workshop, February 3-4, 2005 1

T(CR)3ICTestbed 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

1University of Hawaii at Manoa, Honolulu, Hawaii, USA2 University of California, Los Angeles, California, USA

February 2, 2005

SLAC International SalSA Workshop

Radovan Milinčić and Predrag Miočinović SLAC International SalSA Workshop, February 3-4, 2005 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

Radovan Milinčić and Predrag Miočinović SLAC International SalSA Workshop, February 3-4, 2005 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

Radovan Milinčić and Predrag Miočinović SLAC International SalSA Workshop, February 3-4, 2005 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

Radovan Milinčić and Predrag Miočinović SLAC International SalSA Workshop, February 3-4, 2005 5

• 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.

Experimental Setup

Radovan Milinčić and Predrag Miočinović SLAC International SalSA Workshop, February 3-4, 2005 6

Location UH Manoa campus

Physics Dept.

Salt stack

Radovan Milinčić and Predrag Miočinović SLAC International SalSA Workshop, February 3-4, 2005 7

Antennas• Dual linear polarized bowtie antenna

printed on PCB• Frequency response ~0.2-2.0 GHz

Measurements of beampattern in salt

300 MHz 600 MHz 920 MHz

Radovan Milinčić and Predrag Miočinović SLAC International SalSA Workshop, February 3-4, 2005 8

• 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

Radovan Milinčić and Predrag Miočinović SLAC International SalSA Workshop, February 3-4, 2005 9

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

Radovan Milinčić and Predrag Miočinović SLAC International SalSA Workshop, February 3-4, 2005 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

Radovan Milinčić and Predrag Miočinović SLAC International SalSA Workshop, February 3-4, 2005 11

• 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)

Radovan Milinčić and Predrag Miočinović SLAC International SalSA Workshop, February 3-4, 2005 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

Radovan Milinčić and Predrag Miočinović SLAC International SalSA Workshop, February 3-4, 2005 13

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

Radovan Milinčić and Predrag Miočinović SLAC International SalSA Workshop, February 3-4, 2005 14

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

Radovan Milinčić and Predrag Miočinović SLAC International SalSA Workshop, February 3-4, 2005 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/yr3σ rate 0.5 ev/yr

Radovan Milinčić and Predrag Miočinović SLAC International SalSA Workshop, February 3-4, 2005 16

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

Radovan Milinčić and Predrag Miočinović SLAC International SalSA Workshop, February 3-4, 2005 17

• 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 and200-260 MHz bands

Analysis, cont.

Strategy II:

Radovan Milinčić and Predrag Miočinović SLAC International SalSA Workshop, February 3-4, 2005 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

Radovan Milinčić and Predrag Miočinović SLAC International SalSA Workshop, February 3-4, 2005 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

Radovan Milinčić and Predrag Miočinović SLAC International SalSA Workshop, February 3-4, 2005 20

Testbed on Haleakala