Transcript ppt file - Department of Physics & Astronomy at the University of Utah

SLAC E-165
Fluorescence from Air in Showers
(FLASH)
J. Belz1, Z. Cao2, P. Chen3*, C. Field3, P. Huentemeyer2,
W-Y. P. Hwang4, R. Iverson3, C.C.H. Jui2, T. Kamae3, G.-L. Lin4,
E.C. Loh2, K. Martens2, J.N. Matthews2, W.R. Nelson3, J.S.T. Ng3,
A. Odian3, K. Reil3, J.D. Smith2, P. Sokolsky2*, R.W. Springer2,
S.B. Thomas2, G.B. Thomson5, D. Walz3
1University
of Montana, Missoula, Montana
2University of Utah, Salt Lake City, Utah
3Stanford Linear Accelerator Center, Stanford University, CA
4Center for Cosmology and Particle Astrophysics (CosPA), Taiwan
5Rutgers University, Piscataway, New Jersey
* Collaboration Spokespersons
MOTIVATIONS
• Discrepancy in the UHECR spectrum
AGASA
HiRes
• Future experiments: Auger, OWL, EUSO, etc.
FLUORESCENCE ISSUES
• Detailed shape of the fluorescence spectrum
– Photon scattering during propagation sensitive to wavelength
– Fluorescence spectrum exhibits structures on the order of 10nm
• Pressure dependence of the fluorescence yield
– Detailed exploration below 100 torr (or above 15 km) important to spacebased detectors such as EUSO and OWL
• Effects of impurities on fluorescence yield
– Impurity composition, e.g., CO2, Ar and H2O, above 20 km is neither
stable nor well known.
– There may even be surprises in the fluorescence yield at high altitude
• Effects of electron energy distribution on yield
– A significant fraction of energy in an EAS is carried by energy <1 MeV
– Fluorescence efficiency inthis energy range is poorly known
MEASURING FLUORESCENCE AT SLAC
• Extensive Air Showers (EAS) are
predominantly a superposition of EM subshowers.
• Important N2 transition (2P) not accessible
by proton excitation; only e-beam can do it.
• FFTB beam-line provides energy equivalent
showers from ~1015 to ~1020 eV.
– 108-1010 electrons/pulse at 28.5 GeV.
– 2% of electron pulse bremsstrahlung option.
OBJECTIVES
• Spectrally resolved measurement of
fluorescence yield to better than 10%.
• Investigate effects of electron energy.
• Study effects of atmospheric impurities.
• Observe showering of electron pulses in
air equivalent substance (Al2O3) with
energy equivalents around 1018 eV.
PROGRAM
• Gas Composition
– N2/O2 dependence, and Ar, CO2, H2O impurities
• Pressure Dependence
– Yield versus Pressure down to 10 torr
• Energy Dependence
– Yield versus electron energy distribution down to
100keV
• Fluorescence Spectrum
– Resolve individual bands using narrow band filters or
spectrometer.
• Pulse Width
– Pressure dependence of fluorescence decay time for
each spectral band
THIN TARGET STAGE
• Pass electron beam through a thin-windowed
air chamber.
– Measure the total fluorescence yield in air.
– Measure the yield over wide range of pressures at
and below atmospheric.
– Measure emission spectrum using narrow band
filters or spectrometer.
– Effects of N2 concentration. Pure N2 to air. Also
H2O, CO2, Ar, etc.
THICK TARGET STAGE
• Pass electron beam through varying
amounts of showering material (Al2O3).
– Is fluorescence proportional to dE/dx?
– What are the contributions of low-energy
(<1 MeV) electrons?
– Can existing shower models (EGS, GEANT,
CORSIKA) correctly predict fluorescence
light?
– How does the fluorescence yield in an air
shower track the shower development?
THICK TARGET SHOWER
DEVELOPMENT
BREMSSTRAHLUNG BEAM OPTION
CORSIKA AIR SHOWERS
SYSTEMATIC UNCERTAINTIES
• Defining the yield as Y = n /(x ne)
– n  Number of photons
– x  Distance of travel
– ne  Number of e– (and e+)
• We intend to measure Y and dY/d to better
than 10%.
SYSTEMATIC UNCERTAINTIES
• Beam charge should be measurable by the
beam toroids to better than 2%.
– When showering the beam, the beam energy
will also affect the number of particles in the
shower. This should be determined to better
than 0.5%.
– If a bremsstrahlung beam is used the
contribution of the converter foil thickness
uncertainty should be less than 1%.
SYSTEMATIC UNCERTAINTIES
• The uncertainties in showering 3%.
– Uncertainty in simulations and transition effects
from dense target to air 2%.
– Uncertainty in amount of showering material of
1-1.5%.
SYSTEMATIC UNCERTAINTIES
• Detector systematic uncertainties of 5.4%.
– PMT calibration uncertainty of 5%.
– Cable and ADC uncertainty of 2%.
• Detector Optics 4% (thin) 6.5 % (thick).
– Wide band filters and mirrors (1%).
– Narrow band filter transmission (3%).
SYSTEMATIC UNCERTAINTIES
• Beam charge should be measurable by the
beam toroids to better than 2%.
• The uncertainties in showering 3%.
• Detector systematic uncertainties of 5.4%.
• Detector Optics 4% (thin) 6.5 % (thick).
• Total systematic uncertainty of 7-9%.
SYSTEMATIC UNCERTAINTIES
Beam
Showering
Detector
System
Optical
System
Total
Thin Target
Thick Target
2%
2.2%
-
3%
5.4%
5.4%
4%
6.5%
7%
9.2%
THIN TARGET SETUP
• Thin target stage
requires the 28.5
GeV beam to
deliver 108-109 eper pulse.
• Located in the
FFTB tunnel.
THIN TARGET AIR CHAMBER
LEDs
PMTs
LED
PMT
THICK TARGET SETUP
• Thick target stage requires the 28.5 GeV
beam to deliver 107-108 e- per pulse.
• Alternatively, the FFTB bremsstrahlung
beam can be used to select 2% of a larger
pulse beam.
• The layers of Al2O3 must be remotely
moveable to allow changing of shower
depth observed.
THICK TARGET SHOWER WIDTH
THICK TARGET SETUP
E-165 PLAN SUMMARY
• Thin Target
–
–
–
–
Pressure variations
Fluorescence Spectrum
Linearity of fluorescence with beam charge.
Impurities.
E-165 PLAN SUMMARY
• Thick Target
– Shower depth variations.
– N2/O2 variations.
– Fluorescence spectrum.
CONCLUSION
• FLASH aims to achieve an accuracy of 10% in the
total fluorescence yield and individual spectral lines.
• Verify energy dependence of yield down to ~100keV.
• Both thin target and thick target approaches will be
invoked.
• Dependence of yield and spectrum on pressure and
atmospheric impurities will be measured.
• Shower developments equivalent to ~1018 eV will be
measured at various depths and compared with codes.
• We hope that FLASH will help to shed light on the
apparent differences between HiRes and AGASA, and
provide reliable information for future fluorescencebased UHECR experiments.