Some Thoughts on Laboratory Astrophysics for UHE Cosmic

Rays

Pierre SokolskyUniversity of UtahSABRE Workshop

SLAC, March, 2006

UHE Cosmic Ray detection(N, gamma, neutrino)

• Indirect - Extensive Air Shower in atmosphere or solid/liquid.

• Energy not directly measured - surrogate such as air fluorescence, cherenkov radiation, radio emission, electron/muon density at surface is measured instead

• Depending on surrogate, calibration or validation of detailed modeling of EAS cascade is required.

Eamples from UHECR experiments

• HiRes• Auger• Telescope Array

Detector Design• Each HiRes detector unit

(“mirror”) consists of:– spherical mirror w/ 3.72m2

unobstructed collection area

– 16x16 array (hexagonally close-packed) of PMT pixels each viewing 1°cone of sky: giving ×5 improvement in S:N over FE (5° pixels)

– UV-transmitting filter to reduce sky+ambient background light

– Steel housing (2 mirrors each) with motorized garage doors

HiRes Monocular & Prelim Stereo Spectra

(Stereo Normalized to Monocular)

Pierre Auger Observatory Surface Array1600 detector stations1.5 km spacing3000 km2

Fluorescence Detectors4 Telescope enclosures6 Telescopes per

enclosure24 Telescopes total

Principle of Hybrid Detection

Air Fluorescence Air Fluorescence DetectorDetector

Ground Array

e±

μ±

10km~ 27Xo~ 11λI

MC Simulation of 1019 eV Proton Shower

EM Only

EM + Muon

TA

Auger Surface Array Detector Station

Communicationsantenna

Electronics enclosure

3 – nine inchphotomultipliertubes

Solar panels

Plastic tank with12 tons of water

Battery box

GPS antenna

TA

Shower Development – 320 EeV event detected by monocular Fly’s Eye

Fly’s Eye“Big Event”

Example Hybrid Event

Θ~ 30º, ~ 8 EeV

x [km]10 15 20 25 30

y [k

m]

8

10

12

14

16

18

20

22

24

26

28

]2slant depth [g/cm400 500 600 700 800 900

)]2d

E/d

X [

GeV

/(g

/cm

2

4

6

8

10

12

14

16

18

20

610×

azimuth [deg]60 65 70 75 80 85 90

elev

atio

n [

deg

]

5

10

15

20

25

30

Some Examples of Expts. Requiring Calibration

• Atmospheric Fluorescence - Fly’s Eye, HiRes, Auger fluorescence detector, TA fluorescence detectors, OWL-like detectors

• Askarian effect - microwave Cherenkov emission in ice or salt - ANITA, Salsa

• Atmospheric radio emission by EAS

Comparison of HiRes, AGASA and Auger (prelim)Spectra - Is it the energy scale, stupid?

Blue triangles AGASACircles - HiResMonoPurple trianglesAuger (prelim)

Flourescence Yield, Al Bunner’sThesis - circa 1967

The E-165 Thin Target Experimental Setup:

Spectral Shape of Fluorescence• Use SLAC FFTB e- beam• Bunch energy = 1018 eV.• Measure total and spectral

fluorescence yield.

FLASH Thin Target Results

Photons per m

eter per electron

FLASH Thin Target Results

Photons per m

eter per electron

Thin Target Summary

• The total and spectrally resolved air fluorescence yield has been measured using 28.5 GeV electrons

• The overall uncertainty of the total yield measurement is ~10%

• The preliminary E-165 total yield result agrees with the previous T-461 measurement:

Results of T 461:astro-ph/0506741SLAC-PUB-11254

Thick Target Run Motivation

• Strategy: produce a shower with similar characteristics to electromagnetic airshower in the lab.

• Test observed yields against EGS and GEANT simulations, predicted energy loss curves.

Thick Target Fluorescence Vessel and Ion Chamber

• Goal: Sum fluorescence light produced in a “slice” of an EM shower.

• Reduce scattered and non-fluorescence (Cherenkov) contributions to collected light

• Reduce backgrounds from stray particles hitting light detectors

• Drop-in mechanical shutter, (background studies) and filter holder.

•

Direct Detection of Shower Particles: Ion Chamber

• Direct measurement of ionization produced by beam particles.

• Collected simultaneously with fluorescence data; important crosscheck of data and simulation.

Detailed shower simulation

• 2 radiation length block partially interacts with shower particles.

• Reduces particle/light yield at 4, 8, and 12 r.l.

• Well simulated (ion chamber).

• Second order effect in fluorescence vessel: Albedoproduces optical background

hard to simulate!

Signal vs Shower Depth

• Five series of runs overlaid on this plot

• Variations consistent with statistics

• Very stable method!– ±0.8% at 6 r.l.– ±7% at 14 r.l.

Comparison to GEANT 3.2

• Check hypothesis that fluorescence yield is proportional to energy deposition.

• Plot fluorescence signal and GEANT energy deposition at 2, 6, 10, 14 radiation lengths.

• Excellent agreement: ±1%

Longitudinal Fluorescence Profile• Corrections applied

to light yields at 4, 8, 12 radiation lengths

• Fit dE/dT shower max at 5.5 radiation lengths agrees well with critical energy model prediction.

• Curve:

• Using band-pass filters, we can isolate the contributions of several different wavelength bands to the overall light yield.• Shape of fluorescence profile unchanged

Filter Band“None” 310 < λ < 400 nm

OF2 370 < λ < 400 nmKG3 330 < λ < 390 nmU360 330 < λ < 380 nm

Conclusion

• It’s NOT the Fluorescence energy scale, stupid!

• Excellent agreement with Nagano et al., • Effect on CR of using new numbers is

miniscule.• Other experiments (McFly, AirLight) in

progress.

Radio signal from AskarianEffect

• Askarian predicted development of coherent Cherenkov radiation in microwave region due to effective dipole produced by charge separation in EAS.

• First confirmation of effect at SLAC in sand and then salt - Peter Gorham, David Saltzberg et al.

SLAC has been a leader in calibration experiments

FFTB!• LPM effect• Askarian effect• FLASH - air fluorescence

Are there other such?

• Follow-up on FLASH - increase precision, effects of impurities

• ANITA radio detection efficiency tests• Validation of low energy electromagnetic shower

codes at large Moliere radii.• Atmospheric EAS radio detection - what is the

balance of Askarian vs Earth’s magnetic field effects? - Possible controlled experiment producing shower in dense material with B field?

FLASH Thin Target Results

Red: humid air

Photons per m

eter per electron

Radio signals from EAS in Air

• Mechanism is Askarian + curvature of charged particles in Earth’s B field (coherent geosynchrotron radiation).

• Exact balance not well known• First convincing demonstration by French and

German groups (LOPES with Kascade-Grande, CODALEMA) - coincidence with particle ground arrays.

• May be the next big step??

Some Examples of Experiments that require simulations

• Measurement of lateral distribution of electrons and muons in EAS - AGASA, Auger ground array, TA ground array.

• At lower energies near the knee of the CR spectrum, interpretation of Kaskade electron and muon data depends critically on hadronic models

• Validation that longitudinal EAS development can be accurately measured by fluorescence or radio.

• Understanding relation of energy measured by fluorescence vs electron/muon lateral distribution

• Atmospheric neutrino background for UHE neutrino experiments ( prompt particle production)

Issues, continued

• Low energy shower modeling validation- GEANT, FLUKA predictions for e, gamma and hadron subshowers - very significant for understanding muon content of EAS, even at EHE

• High energy interaction models - pp cross-section, p-air cross section- pion and kaon multiplicities, forward direction physics - important for Xmax composition measurement

Impact of other accelerator measurements

• Xmax fluorescence measurement measures composition of CR if hadronic model is reliable.

• Need better bounds on parameters in these modelsthis is primarily a high-energy problem

• Problem of apparent excess of low-energy muonsin EAS - pion physics not well modeled? Both a high energy and a low energy problem!

• UHE hadronic models - QGSJet, Sybill

Better understanding of:

• P-p cross section at highest energies• P-Air and N-Air cross sections• Secondary hadron inelasticity and

multiplicity• Very small x behavior of proton form

factors• Validation of models at LHC and at low

energies

eVmbsyssysstatAirpin

5.1810at )(11)(39)(17456 −+±=−σ

HiRes Measurement

• HiRes: eVmbsyssysstatAirpin

5.1810at )(11)(39)(17456 −+±=−σ

Muon multiplicity problem

• Ground arrays typically use density near 1 km to estimate energy - muons are significant here, particularly for water tanks.

• Muon multiplicity typically is larger experimentally than even Fe simulations would predict - more like Pb or U - makes composition measurement difficult

• What are inadequacies of hadronic models? Is the simulation technology itself flawed? Thinning etc.

Detector ResponseAGASA Auger-SD

μ± e± γ

~1GeV ~10MeV ~10MeV

10MeV ~10MeV ~1MeV

Energy Deposit

μ± e± γ

~1GeV ~10MeV ~10MeV

240MeV ~10MeV ~10MeV

1.2m Water5cm Plastic

Energy Spectrum(10EeV Vertical Proton, r=1km)

Electrons

Gammas

Muons

1MeV 10MeV 100MeV

Water Tank: Aperture vs. Zenith

NeutrinoEM ShowerDominant

MuonDominant

MuonOnly

New possibilities

• LHC forward experiments proposed -TOTEM,etc.• Need significant interaction between Cosmic Ray

community and particle physics community for these to be useful

• Major effort in this direction at ISVHECRI 2006 in Wuhei, China this summer - bring major players together.

• RHIC - RIKEN workshop at Brookhaven this fall on nuclear effects.

Conclusions

• Calibration experiments continue to be very important for UHECR -FFTB and now SABRE remain critical venues for such experiments.

• Collaboration with particle physicists on forward scattering physics at LHC is growing. Much remains to be done. BJ is no longer the lone voice in the wilderness!

• Collaboration with Nuclear community also growing in importance.

• Progress in UHECR REQUIRES “Laboratory Astrophysics” in the broadest sense.