Fluorescence Efficiency
Measured by FLASH at SLAC
-Preliminary ResultsJ.N. Matthews
for the FLASH Collaboration
J.N. Matthews, ICRR 2/2004
FLuorescence in Air SHowers
(FLASH)
T. Abu-Zayyad1, J. Belz2, D. Bergman5, Z. Cao1, F.Y. Chang4, P. Chen3*,
C.C. Chen4, C.W. Chen4, C. Field3, P. Huentemeyer1, W-Y. P. Hwang4,
R. Iverson3, C.C.H. Jui1, G.-L. Lin4, E.C. Loh1, K. Martens1, J.N. Matthews1,
J.S.T. Ng3, A. Odian3, K. Reil3, J.D. Smith1, P. Sokolsky1*, R.W. Springer1,
S.B. Thomas1, G.B. Thomson5, D. Walz3, A. Zech5
1University
2University
of Utah, Salt Lake City, Utah
of Montana, Missoula, Montana
3Stanford
Linear Accelerator Center, Stanford University, CA
4Center for Cosmology and Particle Astrophysics (CosPA), Taiwan
5Rutgers University, Piscataway, New Jersey
* Collaboration Spokespersons
J.N. Matthews, ICRR 2/2004
Outline
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Air Fluorescence and UHECRs
“The Problem”
FLASH
The Detector
Some Measurements
Future
J.N. Matthews, ICRR 2/2004
Air Fluorescence
AGASA and other
ground array
experiments which
sample the distribution
of charged particles on
the Earth’s surface
HiRes (and now Auger)
makes use of the
atmosphere as its
calorimeter
a) The primary cosmic ray particle collides with air nucleus leading to
b) a cascade of secondary particles, which in turn
c) have more collisions producing a shower of a billion or more
particles.
As the charged particles pass through the atmosphere, they excite the
gas causing it to fluoresce. An ultra-violet track develops at the
speed of light….
J.N. Matthews, ICRR 2/2004
Air Fluorescence Technique
• Particle cascade dissipates much
of its energy exciting and ionizing
air molecules
• Fluorescence light emission is
emitted isotropically
• Exited nitrogen molecules
fluoresce in the near UV with
emission line spectrum (roughly
80% of light is emitted between
300 and 450 nm)
• Intensity is proportional to the
number of charged particles
J.N. Matthews, ICRR 2/2004
A HiRes Event
Air fluorescence
generated by
the EAS is
collected
enabling
observation of
shower
development
from beginning
to end
• HiRes 2
• HiRes 1
J.N. Matthews, ICRR 2/2004
Fluorescence Spectra
• Remarkable agreement
between all the spectra
measured by
fluorescence detectors
(including the “hybrid”
HiRes-Prototype/MIA)
J.N. Matthews, ICRR 2/2004
The Problem:
However, between the two
experiments with the greatest
exposures at the highest
energies
HiRes: fluorescence
and
AGAGA: ground array
there is an offset
Perhaps - at least partly - due
to energy scale
J.N. Matthews, ICRR 2/2004
Energy Spectrum
 AGASA energy
scaled by 0.79
J.N. Matthews, ICRR 2/2004
HiRes Systematic Uncertainties
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PMT calibration: 10%
Fluorescence yield: 10%
Unobserved energy: 5%
Atmospheric absorption: most sensitive to vertical
aerosol optical depth (VAOD)
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–
–
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Mean VAOD = 0.04
VAOD RMS = 0.02
VAOD systematic is smaller.
Modify MC and analysis programs to use VAOD = 0.02 and
0.06, reanalyze.
– J(E) changes by 15%
• Total systematic uncertainty = 21%
J.N. Matthews, ICRR 2/2004
Fluorescence efficiency is the foundation for
our belief that we are measuring “energy”
Current Understanding:
• Bunner (1967), Kakimoto et al.(1995) Nagano et al.( 2003)
indicates ~10-15% systematic errors in overall yield and
larger errors in individual spectral lines.
• Non-linear effects possible due to λ4 dependence of
atmospheric attenuation: at 30 km, event energy can
change by 25% if 390 nm line intensity changes by 40%.
• Pressure dependence not well measured esp. P<100 Torr
• Previous measurements show Y proportional to dE/dx, but
no measurements 100 keV – 1 MeV
J.N. Matthews, ICRR 2/2004
SLAC E-165: FLASH
FLuorescence in Air SHowers
• Motivation:
– Reduce the systematic uncertainty in energy
reconstruction of UHECRs for detectors using the
fluorescence technique.
– Shed some light on the discrepancy between
fluorescence and ground array experiments.
• Goals:
– Building on the work of Bunner, Kakimoto and Nagano,
we wish to further reduce the uncertainties in this
measurement.
– Measure the total fluorescence yield and resolve the
spectral shape to better then 10%.
J.N. Matthews, ICRR 2/2004
E-165: Experiment Plan
• A two stage experiment:
– thin target - to study gas composition and pressure effects
– thick target – to study effects of particle energy and shower age
• A thin target test run was held in 2002 and a first data
run was collected in the fall of 2003
• The thick target stage is expected to run summer 2004.
• A third run is approved allowing us to address any
systematic issues which arise.
J.N. Matthews, ICRR 2/2004
E-165 Experimental Design
Thin Target Stage
• Opposing UV LED
calibration source.
• Remotely controllable
filter wheel.
• Post filter UV LED
calibration sources (4)
• Signal PMT.
• 2 orthogonal arms
J.N. Matthews, ICRR 2/2004
E-165 Experimental Design
Thin Target Stage
• Electron beam passes
(5x107-5x109 e-/pulse)
through a gas chamber.
1x1 – 2x2 mm beam spot.
• 1 cm gap well defined by
interior tubes.
• Interior blackened and
baffled.
• HiRes PMTs used to
measure the fluorescence
signal.
J.N. Matthews, ICRR 2/2004
E-165 Experimental Design
Thin Target Stage
• 15 positions of the filter wheel were used.
– HiRes filter glass (band pass 300-400 nm).
– Open and black.
– 337, 355, 390, 380, 395, 400, 315, 375,
330/325, 370, 425 and 296 nm narrow
band (10 nm) filters.
– 425 nm (20 nm FWHM) filter
J.N. Matthews, ICRR 2/2004
E-165 Experimental Design
Thin Target Stage
J.N. Matthews, ICRR 2/2004
Monitoring Measurements
• Measured
– Beam charge with a torroid – monitored for
linearity with yield
– Beam position and size (transition radiator
and CCD)
– Vessel pressure and temperature
– Gas composition
– Background levels (blind PMTs and black
filter)
J.N. Matthews, ICRR 2/2004
Beam Charge Monitoring
x 1010 e-
J.N. Matthews, ICRR 2/2004
Beam Spot Monitor
J.N. Matthews, ICRR 2/2004
PMT Stability to LED (2.2%)
J.N. Matthews, ICRR 2/2004
HV Stability (0.04%).
PMTGAIN=eV
With 6.
J.N. Matthews, ICRR 2/2004
E-165 September 2003 Run
Experimental Program
• Measure the fluorescence yield for pure N2, dry air,
and humid (SLAC) air.
• Repeat the measurement for each filter.
• Measurements were made at several pressures
(10, 25, 50, 100, 250, 500, and 750 torr).
• Measure spectrum of N2, dry, and humid air using
spectrograph.
• Confirm linearity with beam charge and perform
tests relevant to future runs, such as ability to run
with <= 107 e- per pulse.
J.N. Matthews, ICRR 2/2004
E-165 September 2003 Run
Preliminary Results
• Full pressure
sweep was
taken for
each narrow
band filter.
J.N. Matthews, ICRR 2/2004
E-165 September 2003 Run
Fluorescence Spectrum Using Filters
P = 750 torr
Do NOT expect this
to look like Bunner
spectrum.
J.N. Matthews, ICRR 2/2004
E-165 September 2003 Run
Fluorescence Spectrum Using Filters
P > 200 torr
Note: Error bars
are statistical
(tiny), range of
background
subtraction (small
except
faint lines) and
10% for absolute
in toroid (relative
extremely small).
J.N. Matthews, ICRR 2/2004
E-165 September 2003 Run
Effect of Humidity
P > 200 torr
Signals ~5%
lower than dry
M. Fraga
(Airlight Wkshop)
gives at 94%
for 1% H2O.
SLAC Air is
~1.3 % H2O.
lower but
within error.
J.N. Matthews, ICRR 2/2004
E-165 Spectrograph
6 nm resolution from grating
32 anodes
J.N. Matthews, ICRR 2/2004
E-165 September 2003 Run
Spectrum via Spectrograph
J.N. Matthews, ICRR 2/2004
E-165 September 2003 Run
Spectrum via Spectrograph
J.N. Matthews, ICRR 2/2004
E-165 September 2003 Run
“To Do” List
• Apply additional data analysis filters based on
the Beam Spot Monitor.
• Calibration of detector arms.
• Absolute toroid calibration.
• Correction to gains vs time based on LED
tracking.
• Spectrograph data normalized to beam charge.
• Full study of systematic errors.
J.N. Matthews, ICRR 2/2004
E-165 Future Runs
• We have two more runs scheduled for
summer of 2004. The first run will be our
thick target run.
• The third run may be a simultaneous run
of thin target, thick target and
spectrograph system.
J.N. Matthews, ICRR 2/2004
E-165 Experimental Design
Thick Target Stage
• 107 e- showering at 30 GeV
approximately reproduces a
3x1017 eV UHECR shower
(near shower max).
• Shower the FFTB beam in a
range (1, 3, 7, & 11 rad lengths)
of shower depths in air
“equivalent” material (Al2O3).
• Any effects from the change in eenergy distribution?
• Does the signal deviate from
dE/dx?
• Do shower models correctly
predict the fluorescence signal?
J.N. Matthews, ICRR 2/2004
Conclusions
• We have measured the spectrum and yield of air
fluorescence. The shape and yield are in the
right ball park.
• We expect to resolve the spectral shape very
well with our combined method of narrow band
filters and spectrograph.
• Work on calibration and systematics is ongoing.
(The Hard Part)
J.N. Matthews, ICRR 2/2004
J.N. Matthews, ICRR 2/2004
J.N. Matthews, ICRR 2/2004
J.N. Matthews, ICRR 2/2004