COSMIC RAY COMPOSITION. Towards a measurement of cosmic ray composition in the TeV range with IACTs Henrike Fleischhack for the VERITAS-Collaboration HAP Composition workshop 22.09.2015 Alliance for Astroparticle Physics
Reminder Cosmic Ray Spectrum Beringer et al. [2012]. Henrike Fleischhack CR composition with IACTs 22.09.2015 Seite 2
CRs in Imaging Cherenkov Telescopes Direct Cherenkov (DC) light from primary particle: > Intensity Z 2 sin 2 (θ c ). > Heavy nuclei, eg. iron. > 500 TeV. > Charge resolution 5%. > Aharonian et al. [2007]; Kieda et al. [2001]. Source: Aharonian et al. [2007] Henrike Fleischhack CR composition with IACTs 22.09.2015 Seite 3
Previous Results (H.E.S.S. & VERITAS) > Aharonian et al. [2007]: heavy elements (Z = 25 28), 13 200 TeV. > Wissel [20]: iron, 20 140 TeV. > Spectral shape: ( ) γ E F(E) = φ 0 E 0, see below. > Dominant uncertainties: statistics, atmosphere, hadronic interaction model. > Can we improve on that? E 0 /TeV φ 0 (m 2 s sr TeV) γ H.E.S.S. (QGSJET) 1 (2.2 ± 0.9 ± 0.6) 2 2.62 ± 1 ± 7 H.E.S.S. (SYBILL) 1 (2.9 ± 1.1 ± 0.8) 2 2.76 ± 1 ± 7 VERITAS (QGSJET) 50 (5.8 ± 0.84 ± 1.2) 7 2.84 ± 0.3 ± 0.3 Henrike Fleischhack CR composition with IACTs 22.09.2015 Seite 4
0.04 Previous Results Charge separation normalize 0.06 elements 0.02 > Aharonian et al. [2007] > Select images with direct Cherenkov contribution. > Energy E from shower light > Charge Z from DC light. > heavy elements (Z = 25 28) vs light elements > Fit fraction of heavy elements per energy bin. normalized countrate 1.5 1.3 1.1 < log (E/TeV)< < 1.7 1.5 1.3 data 0.08 0.06 0.04 0.02 0.08 0.06 0.04 0.02 0.08 5 0.06 0.04 0.05 0.02 1.5 1.7 1.3 < log (E/TeV)< 1.7 1.9 1.5 0.2 1.9 1.5 1.7 < log (E/TeV)< 2.3 1.7 1.9 model Fe lightelements 0 0.2 1.9 1.7 < 15 log (E/TeV)< 20 25 2.3 1.9 30 35 40 Z* Source: Aharonian et al. [2007] 0.08 5 Henrike Fleischhack CR composition FIG. with 9: ZIACTs distributions 22.09.2015 of data Seite(open 5 circles) and the fitted SIBYLL model (black boxes) in five energy bands. The 0.06
Template Method for Shower Reconstruction Likelihood fit of telescope images. See eg. [Fleischhack, 2015; Le Bohec et al., 1998] camera y [deg] 0.5 0.4 0.3 0.2 4 3 2 photoelectons per pixel 0 1 0 0.2 0.4 0.6 0.8 1 1.2 1.4 camera x [deg] Example: Iron, Ze=0, Energy=30 TeV, Distance=80 m, First interaction Height=33 km Henrike Fleischhack CR composition with IACTs 22.09.2015 Seite 6
Energy and direction resolution Ze = 0, Offset = 1.0 Ze = 0, Offset = 1.0 likelihood reconstruction standard reconstruction likelihood reconstruction standard reconstruction core resolution [m] (68%) 180 160 140 120 0 80 60 angular resolution [deg] (68%) 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 40 0.2 20 0 VERITAS PRELIMINARY 1 1.5 2 2.5 3 log energy [TeV] 0 VERITAS PRELIMINARY 1 1.5 2 2.5 3 log energy [TeV] > Better reconstruction better identification of DC pixel. > Energy resolution is improved as well. Henrike Fleischhack CR composition with IACTs 22.09.2015 Seite 7
Charge separation > Multivariate analysis combining DC light, image shape,... > Composition measurement possible with this approach. Energy bin 2 (50-0 TeV) events (A.U.) 180 160 background iron 140 120 0 80 60 40 20 VERITAS PRELIMINARY 0-1 -0.8-0.6-0.4-0.2 0 0.2 0.4 0.6 0.8 1 BDT reponse Henrike Fleischhack CR composition with IACTs 22.09.2015 Seite 8
Charge separation > Multivariate analysis combining DC light, image shape,... > Composition measurement possible with this approach. Energy bin 2 (50-0 TeV) events (A.U.) 180 160 140 120 proton helium carbon oxygen magnesium iron 0 80 60 40 20 VERITAS PRELIMINARY 0-1 -0.8-0.6-0.4-0.2 0 0.2 0.4 0.6 0.8 1 BDT reponse Henrike Fleischhack CR composition with IACTs 22.09.2015 Seite 8
Outlook Status and Plans: > Improved measurement of the iron spectrum with VERITAS on the way. > Improved statistics, reconstruction, charge separation, atmospheric modeling. > Systematic uncertainties remain, esp. hadronic interaction models. Future developments? > CTA studies ongoing (see talk by S. Ohm later today). > Would like to image heavy nuclei in DC light. > Would need dedicated instruments: 0 m total mirror diameter, 0.01 pixels/psf. Thank you for the attention! Henrike Fleischhack CR composition with IACTs 22.09.2015 Seite 9
Backup. Henrike Fleischhack CR composition with IACTs 22.09.2015 Seite
Bibliography Aharonian, F. et al. (2007). First ground based measurement of atmospheric Cherenkov light from cosmic rays. Phys.Rev., D75:042004. Beringer, J. et al. (2012). Review of particle physics. Phys. Rev. D, 86. Fleischhack, H. (2015). A template method for measuring the iron spectrum in cosmic rays with cherenkov telescopes. Journal of Physics: Conference Series, 632(1):012009. Kieda, D., Swordy, S., and Wakely, S. (2001). A high resolution method for measuring cosmic ray composition beyond TeV. Astroparticle Physics, 15(3):287 303. Le Bohec, S. et al. (1998). A new analysis method for very high definition imaging atmospheric cherenkov telescopes as applied to the cat telescope. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 416(2-3):425 437. Wissel, S. (20). Observations of Direct Cerenkov Light in Ground-based Telescopes and the Flux of Iron Nuclei at TeV Energies. PhD thesis, University of Chicago. Henrike Fleischhack CR composition with IACTs 22.09.2015 Seite 11