Cosmic Ray Physics at University of Utah

Charlie JuiProfessor of Physics

May 13, 2008

Jui 5/13/2008 2

Outline• Scientific Context and Background• The original Success: The Fly’s Eye• The recent past: High Resolution Fly’s Eye (HiRes)• The present: Telescope Array (TA)• The Future: TA Low Energy Extension (TALE)• External Funding over the last 20 years

Jui 5/13/2008 3

Scientific Context• Between ~1945-~1995, Fundamental Physics was

dominated by the successes of accelerator-based experiments and the Standard Model of particles and fields

• The success of the Standard Model, where essentially all experiments agree with its predictions, has unexpectedly led the field of physics into a blind corner

• This is reminiscent of the situation in the late 1800’s and early 1900’s where the successes of Classical Mechanics, Maxwell’s Theory of Electrodynamics, and Boltzmann’s Statistical theory of thermodynamics made it appears as if Physics was essentially complete, modulo a few loose ends

• Those few loose ends developed into Modern Physics as we know it (Theory of Relativity, Quantum Mechanics)

• Physics is once again at a Critical Juncture

Jui 5/13/2008 4

Loose Ends @ the Start of the 21st Century

• At the start of the 21st Century, some of the most promising loose ends appear at the interface between Particle Physics, and astrophysics & cosmology:

• Some of the most compelling OPEN QUESTIONS in this overlapping region are:– The question of dark matter and energy– The development of the early Universe– The origin of cosmic rays

• The Cosmic Ray group at the University of Utah, established originally by Jack Keuffel in the early 1960’s, has played a leading role in the development of Cosmic Ray Physics in the post-accelerator era

• In particular, the air fluorescence technique, originally developed at Cornell by Kenneth Greisen, was first successfully deployed at the University of Utah.

Jui 5/13/2008 5

The Early Years• The Cosmic Ray

group at University of Utah was founded with the arrival of Jack Keuffel in the 50’s

• The field of High Energy Physics (Particle Physics) traces its origin back to the discovery of exotic particles in cosmic rays

• Early efforts included the neutrino detector in the Park City Mines

Jui 5/13/2008 6

Ultrahigh Energy Cosmic Rays• Since the middle 1970’s, the

cosmic ray group, then led by Prof. George Cassidy, has concentrated on ultrahigh energy (UHE) cosmic rays (single particles with energies > ~1017 eV)

• This Utah group was the first group to have successfully detected UHE cosmic rays using the air fluorescence technique.

• Between 1981-2004, the Fly’s Eye and its successor, the High Resolution Fly’s Eye (HiRes) were the only fluorescence detectors in the world

Jui 5/13/2008 7

Detection of UHE Cosmic Rays• UHE cosmic rays are

extremely rare:– < 1 particle per m2 per

50 years– Direct detection (high-

altitude balloons, satellites, shuttle missions) is impractical

• Traditional techniqueis to detect the extensive air showers by sampling the particles striking Earth– ground array technique– Uses the Earth’s

atmosphere as the detection medium

Jui 5/13/2008 8

Ground Arrays• Since the 1960’s, the

conventionaltechnique for measuring UHE cosmic rays has been to use ground arrays:– Yakutsk– Volcano Ranch– Akeno/AGASA

• Disadvantages:– Essentially measuring

“leakage” from the “calorimeter” (atmos.)

– Model-dependent energy determination

Zatsepin at Yakutsk Linsley at Volcano Ranch

Akeno Giant Air Shower Array (AGASA) in Japan

Jui 5/13/2008 9

Air Fluorescence• An innovative alternative

proposed in the 1960’s was to observe the air shower directly by detecting the UV light emitted in the wake of the charged particles in the shower

• This technique was developed in the 1950’s as a reliable way to estimate the yield from atmospheric nuclear tests (which were banned by 1960?)

• The advantage of the fluorescence technique is that we look directly at the central portion of the shower:– Based on well-understood physics

(quantum electrodynamics)– Can measured longitudinal shower

development “chemical composition”

Jui 5/13/2008 10

Cornell 1967• An early, unsuccessful

attempt at a fluorescence detection was made by the late Prof. Ken Greisenat Cornell– Lacking atmospheric clarity– Insufficient optical aperture

Jui 5/13/2008 11

The Fly’s Eye (1976, 1981-1993)• The first successful test of the

fluorescence technique was made by the Utah group on Thanksgiving day, 1976– Observed fluorescence from an air

shower detected by the Volcano Ranch ground array in New Mexico

• The Utah Cosmic Ray group then received funding to build a full-scale experiment at Dugway, Utah

• The Fly’s Eye operated between 1981-2003

• In 2008 the American Physical Society (APS) awarded Dean Sokolsky and Prof. Cassidy the Panofsky Prize for their breakthrough in the successful development of the air fluorescence detection technique

Jui 5/13/2008 12

The Highest Energy Ever Seen• In 1991, the Fly’s Eye

experiment observed an event with energy of 3.2x1020 eV

• This remains the world recordfor the highest energy ever measured in a particle

• This energy is ~5 times higher than the predicted Greisen-Zatsepin-K’uzmin (GZK) Limit

• At above the GZK threshold (~6x1019 eV), cosmic protons can lose energy in collisions with photons in the Cosmic Microwave Background Radiation (CMBR)

Event Display and Shower Longitudinal Profile of the Highest Energy Cosmic Ray

Jui 5/13/2008 13

The AGASA Result• The Fly’s Eye event was followed between by reports from the AGASA ground array in Japan of an apparent absence of the GZK Cut-off

• The apparent violation of the GZK prediction for a suppression in the cosmic ray flux suggested possibility of new physics, for example:– Violation of Relativity at

high energies– Exotic new particles in

UHECR– Exotic Nearby Sources AGASA UHE Cosmic Ray Energy Spectrum

(June 2003)

Jui 5/13/2008 14

The High Resolution Fly’s EyeHiRes – (1994–2006)

Bigger Mirrors:- collect more light- see fartherSmaller pixels:- better resolution - better signal to noise

Jui 5/13/2008 15

The Advantage of “High” ResolutionHiRes detectors can see

showers up to ~25 milesaway, compared to ~8 miles for the original Fly’s Eye.

HiRes is ~10 times more sensitive than the Fly’s Eye

Total Construction Award from NSF (Utah): $9.9Mbetween 1991-2001 (~$1.0M/yr)

Total Operations Award from NSF (Utah): $15.8Mbetween 1994-2005 (~$1.43M/yr)

8 miles

25 miles

Fly’s Eye

HiRes

Jui 5/13/2008 16

Typical HiRes Event

• Two observatory sites separated by 12.6 km

• ~2×1019eV event seen in 1999• (3× vertical scale)

Jui 5/13/2008 17

Event Movie at 1/500,000 speed

Jui 5/13/2008 18

HiRes Success• Between 1997-2004, HiRes was the largest UHE cosmic ray detector, and the ONLY fluorescence detector in the world.

• 5σ Observation of the GZK Suppression (qualifies in High Energy Physics as a “Discovery”)

• First Observation of the GZK Cut-Off!Published in Physical Review Letters

Jui 5/13/2008 19

The Present: Telescope Array• The core groups of the

AGASA and HiRes experiments have joined forces in the new Telescope Array (TA) Experiment

• Goals of TA (Phase 1):– Combine ground array (AGASA)

and Fluorescence (HiRes) technique to resolve the different results from the two techniques

– Create the largest cosmic ray detector in the Northern Hemisphere

• Phase 2 (TALE)– Extend (to lower energies)

fluorescence/hybrid measurements down to ~1016.5

eV

Jui 5/13/2008 20

Telescope Array

Surface Detector Stations covering (blue diamonds): ~800 km2 Rectangular grid with 1.2km spacing; 3.0 m2 plastic scintillation detectors

Three fluorescence Stations: 12 x 3m dia. mirrors each at Black Rock Mesa (BRM) and Long Ridge (LR), 14x 2m dia. Mirrors at Middle Drum (MD)

Central Laser Facility (CLF): atmospheric monitoring laser seen by all 3 FD

Surface Detectors

LR

MD

BRM

CLF

Jui 5/13/2008 21

Ground Array

• TA Phase-1– Construct 512 surface

detector units– Three Communication

towers for triggering and data transfer, located near FD stations

Jui 5/13/2008 22

Fluorescence Detectors (1)• 3m dia. Mirrors

and new DAQ electronics at BRM & LR

• Built in Japan with trigger and comm. system designed in Utah (J. Smith).

Jui 5/13/2008 23

Fluorescence (2)• 14 refurbished HiRes telescopes

(with PMT clusters and DAQ electronics) instrument the Middle Drum (MD) station

Jui 5/13/2008 24

TA Status: GO!• FD Systems at both BRM and LR

are complete and have been in routine observation since May and June, 2007, respectively

• MD Site completed and began routine observation in November, 2007

• >500 ground array counters are in place and tuned (turned on and have antennae pointed towards one of three communication towers)

• Initial Bio Surveys are complete for the full ground array

• Ground Array in operation since start of 2008 !

Jui 5/13/2008 25

TA Low Energy Extension (TALE)• We have submitted an updated proposal for the low energy extension

(TALE) in the fall of 2007 to the NSF• The proposal will include the construction of new FD site with a total

of 39 fluorescence telescopes situated on SITLA land• The new sites will extend stereo fluorescence observation down to

1016.5 eV

PRELIMINARY

Jui 5/13/2008 26

TALE Tower Detectors• 15 of the 39 TALE

telescopes will be mirrors looking up to 70° (TA mirrors look up to 31°)

• The 15 tower mirrors will also have larger mirrors (4m dia.) requiring more interior space

• The 15 new tower mirrors and their DAQ electronics are not from HiRes

• The tower detector is intended to extend hybrid observations down to 1016.5 eV.

PRELIMINARY

Jui 5/13/2008 27

TALE Surface Detectors• The Tower detector is coupled to an infill surface array :

100 additional counters at 400 m separation• Underground Muon detector array: provides

complementary information on composition to the tower FD

(km)

Jui 5/13/2008 28

NSF TALE Proposal• NSF TALE Construction Proposal: ~$6M

– Amount is the difference between the original 2005 TA proposal and the three year Phase-1 construction grant from NSF (2005-2008)

– Exact cost of the construction and new equipment continues to be refined.

– More collaborators (e.g. Brookhaven Nat. Lab, Russia, S. Korea) are joining we

– Promise of local funding (U. of U., the State of Utah…etc.) for surveying and site preparation will greatly enhance the likelihood of success of the TALE proposal

• Our collaborators are actively seeking TALE funding from China, S. Korea and Taiwan.

Jui 5/13/2008 29

total

0.000

0.500

1.000

1.500

2.000

2.500

3.000

1989

1990

1992

1993

1994

1995

1997

1998

1999

2000

2002

2003

2004

2005

2007

2008

2009

2010

total

Cosmic Ray Group Per Year NSF Funding(incomplete, and does not include

VERITAS or AUGER)

Pending

Fly’s Eye High Resolution Fly’s Eye Telescope Array$M/yr

Jui 5/13/2008 30

cumu

0.000

5.000

10.000

15.000

20.000

25.000

30.000

35.000

40.000

45.000

1985 1990 1995 2000 2005 2010 2015

cumu

Cumulative NSF Funding Since 1989(incomplete, and does not include

VERITAS or AUGER)$M

Year

Pending

High Resolution Fly’s Eye Telescope ArrayFly’s Eye

Jui 5/13/2008 31

Summary• The Cosmic Ray group at University of Utah has played a

unique and dominant role in the Fundamental Area of High Energy Astrophysics– Successful Development (and monopoly until ~2004) of the Air

Fluorescence Technique (Panofsky’ Prize to Sokolsky and Cassidy)– Record for the Highest Energy Particle ever detected (Fly’s Eye

1991)– First Observation of the GZK Suppression ~40 years after its

prediction– The group has brought over $30M of external research funding to the

University of Utah over the last 20 years and continues to be supported at a similar level by the NSF

• This group continues to play a pivotal role in the field both serving as the host institution and providing the scientific leadership for the new Telescope Array Experiment

• A new Low Energy Extension is being proposed which will take this group well into the next decade