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1
2
Outline
- TA Low Energy extension (TALE) Fluorescence Detector (FD).
- Spectrum Data Set.
- Spectrum / Aperture Calculation
- Energy Spectrum
- Summary.
Cosmic Rays Energy Spectrum from PeV to EeV energies measured by - - PowerPoint PPT Presentation
Cosmic Rays Energy Spectrum from PeV to EeV energies measured by - - PowerPoint PPT Presentation
Cosmic Rays Energy Spectrum from PeV to EeV energies measured by the TALE Detector Tareq AbuZayyad University of Utah for The Telescope Array Collaboration 35 th ICRC (2017) Bexco, Busan, Korea 19 July 2017 1 Outline TA L ow E nergy
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TA Low Energy Extension (TALE)
10 new telescopes to look higher in the sky (31-59o) to see shower development to much lower energies Infjll surface detector array
- f more densely packed
surface detectors (lower energy threshold)
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TALE FD Telescopes / Camera
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Middle Drum TA/TALE Viewing Range
- TAMD + TALE
- 14 lower pointing
telescopes make up TA (Middle Drum) Detector.
- 10 higher pointing
telescopes make up the TA- Low Energy extension Fluorescence Detector (Rings 3 & 4).
- TALE telescopes equipped
with (HiRes2) FADC electronics.
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Track-like Cherenkov Event
A Cherenkov
event seen in two TALE telescopes
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TALE FD Data collection period
TALE FD data collected from 06/20/2014 to 03/31/2016 (22 months) is used. Only good weather data: Good weather selection “clear overhead” + “no haze” A comparison of event data rates vs. MC expectation is used to determine periods of significant attenuation due to haze. Total on-time 1080.0 hours.
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Data Division (Event energy/type)
Once an observed event is reconstructed it can be placed
into one of three subsets:
Cherenkov dominated events (C'kov > 75% of total) Fluorescence dominated events (Scin. > 75% of total) Mixed signal events (All other events).
The three subsets span different but overlapping energy
ranges.
Different, appropriate, event selection criteria (quality
cuts) are applied to each set.
A combined set is used to measure the energy spectrum.
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Event subsets
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Spectrum Calculation
Aperture Calculation (Simulation):
Shower library created with CONEX and QGSJetII-03
Mixed Composition following the H4a model ...
Alternative: Fit to observed xmax distributions.
Detector simulation:
Hourly atmospheric profile (GDAS).
Actual Mirror live-times (for each data part)
Nightly PMT Gains from DB ( UVLED data collected at the start of the run )
Average Sky Noise background (no time dependence.)
Average Aerosols.
Event reconstruction:
Monocular (profile constrained fit)
Nightly gain calibration.
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Aperture Calculation (Composition Dependence)
Performing Data / MC comparisons, it was found that
the MC (H4a, QGSJetII-03) xmax distributions are not in good agreement with the data (for most energies).
To achieve agreement, we modified the composition
(fractions of different primaries) in the MC.
For Each Energy Bin: Fit the xmax distribution to four
independent components: pr, he, cno, and fe.
Note that the resulting primary fractions (composition)
depends on our choice of hadronic interaction model.
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Aperture Calculation (Composition Dependence)
A change in the composition assumption can affect the
spectrum in two ways:
Affects aperture estimation (especially at E < ~1016 eV) Affects event energy assignment (Ecal → Etot); different missing
energy correction for different primaries.
Combined effect will be a change in the overall
normalization.
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Example Fit Result
Example xmax dist. Fit. Ecal 1016.5-1016.6 eV Black points: TALE data. Magenta points: H4a MC
(QGSJetII-03)
Red histogram: Fit to data.
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Data/MC before and after fjt
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Energy Spectrum (1)
Using fits to TALE
xmax distributions
Spectral breaks:
slopes before/after and energy are indicated on the figure.
Errors are statistical
errors from fitting routine.
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Energy Spectrum(2)
Effect of changing
composition assumption.
GST composition
by re-weighting H4a MC.
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Energy Spectrum (3)
Comparison to
- ther experiments.
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Energy Spectrum (4)
Comparison to other
experiments.
Connection to
UHECR (TA SD Energy Spectrum)
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Summary
We presented a measurement of the cosmic rays energy
spectrum using data from TALE FD.
We made use of TALE measured xmax distributions to
infer a model independent input composition for aperture calculation and event missing energy assignment.
The measured spectrum spans the energy range from
1015.4 – 1018.4 eV, using a combined set of Cherenkov/Fluorescence and mixed signal events.
Two features are observed:
a hardening of the spectrum at an energy of ~1016.25 eV. a steepening of the spectrum at an energy of ~1017.05 eV.
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Backup Slides
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TALE Event Reconstruction
Event reconstruction entails reconstructing:
Shower geometry Shower profile/energy.
Cerenkov events are reconstructed as monocular events. Profile constrained Geometry Fit (PCGF) method
(developed and used for the HiRes-I analysis) is adapted for TALE:
Unlike for HiRes-I, the shower xmax parameter is fixed
- nly at the start of the fit but is turned into a free fit
parameter at a later step in the reconstruction process.
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TALE FD Exposure
~1017 eV
threshold for air fluorescence detection.
~1018 eV the fact
- nly high