Precise Measurement of the Absolute Yield of Fluorescence Photons in Atmospheric Gases

📝 Abstract

We have performed a measurement of the absolute yield of fluorescence photons at the Fermilab Test Beam. A systematic uncertainty at 5% level was achieved by the use of Cherenkov radiation as a reference calibration light source. A cross-check was performed by an independent calibration using a laser light source. A significant improvement on the energy scale uncertainty of Ultra-High Energy Cosmic Rays is expected.

💡 Analysis

We have performed a measurement of the absolute yield of fluorescence photons at the Fermilab Test Beam. A systematic uncertainty at 5% level was achieved by the use of Cherenkov radiation as a reference calibration light source. A cross-check was performed by an independent calibration using a laser light source. A significant improvement on the energy scale uncertainty of Ultra-High Energy Cosmic Rays is expected.

📄 Content

arXiv:1101.3799v1 [astro-ph.IM] 19 Jan 2011 Precise Measurement of the Absolute Yield of Fluorescence Photons in Atmospheric Gases AIRFLY Collaboration: M. Avea, M. Boh´aˇcov´abc, K. Daumillera, P. Di Carlod, C. Di Giulioe, P. Facal San Luisb∗, D. Gonzalesf, C. Hojvatg, J. R. H¨orandelh, M. Hrabovsk´yi, M. Iarlorid, B. Keilhauera, H. Klagesa, M. Kleifgesj, F. Kuehng, M. Monasorb, L. Noˇzkac, M. Palatkac, S. Petrerad, P. Priviterab, J. Ridkyc, V. Rizid, B. Rouill´e d’Orfeuilb, F. Salamidaa, P. Schov´anekc, R. ˇSmidaa, H. Spinkak, A. Ulrichl, V. Verzie, C. Williamsb aKarlsruhe Institute of Technology, IK, Postfach 6980, D - 76021 Karlsruhe, Germany bUniversity of Chicago, Enrico Fermi Institute & Kavli Institute for Cosmological Physics, 5640 S. Ellis Ave., Chicago, IL 60637, USA cInstitute of Physics of the Academy of Sciences of the Czech Republic, Na Slovance 2, CZ-182 21 Praha 8, Czech Republic dDipartimento di Fisica dell’Universita de l’Aquila and INFN, Via Vetoio, I-67010 Coppito, Aquila, Italy eDipartimento di Fisica dell’Universita di Roma Tor Vergata and Sezione INFN, Via della Ricerca Scientifica, I-00133 Roma, Italy fKarlsruhe Institute of Technology, IEKP, Postfach 3640, D - 76021 Karlsruhe, Germany gFermi National Accelerator Laboratory, Batavia, IL 60510, USA hIMAPP, Radboud University Nijmegen, 6500 GL Nijmegen, The Netherlands iPalacky University, RCATM, Olomuc, Czech Republic jKarlsruhe Institute of Technology, IPE, Postfach 3640, D - 76021 Karlsruhe, Germany kArgonne National Laboratory, Argonne, IL 60439, USA lPhysik Department E12, Technische Universit¨at Muenchen, James Franck Str. 1, D-85748 Garching, Germany We have performed a measurement of the absolute yield of fluorescence photons at the Fermilab Test Beam. A systematic uncertainty at 5% level was achieved by the use of Cherenkov radiation as a reference calibration light source. A cross-check was performed by an independent calibration using a laser light source. A significant improvement on the energy scale uncertainty of Ultra-High Energy Cosmic Rays is expected.

1. Introduction Fluorescence detection of Ultra High Energy Cosmic Rays (UHECRs) is a well established technique, pioneered by Fly’s Eye [1], and today ∗Corresponding author: facal@kicp.uchicago.edu an integral part of the Pierre Auger [2] and the Telescope Array [3] experiments. Excitation of the atmospheric nitrogen by the charged parti- cles in the extensive air shower induces the emis- sion of fluorescence photons, mostly in the 300- 400 nm range. A Fluorescence Detector (FD) 1 2 records this radiation to infer the cosmic ray en- ergy and the particle type. For this purpose, the fluorescence light yield from the charged parti- cles in the shower must be known for every emis- sion point along the shower axis. A correction is then applied to account for atmospheric effects between the shower and the telescope, enabling an accurate, quasi-calorimetric, primary energy determination. The uncertainty on the fluorescence light yield is one of the main systematic uncertainties on the cosmic ray energy determination by experiments that employ the fluorescence technique (e.g. 14% over a total 22% uncertainty for the Pierre Auger experiment). The AIRFLY collaboration has al- ready performed a very precise measurement of the fluorescence spectrum and its pressure de- pendence [4], as well as the dependence of the emission on the temperature and humidity [5]. AIRFLY measurements over electron kinetic en- ergies ranging from keV to GeV using several ac- celerators have also proven the proportionality of the fluorescence yield with the electron energy de- posit [6]. The final step in the precise characterization of the nitrogen fluorescence light emission is the measurement the absolute value of the yield for the main emission line at 337 nm. The AIRFLY strategy to reduce the systematic uncertainties is to calibrate the experimental apparatus in situ, using photons emitted by a well know process: Cherenkov radiation [7]. A second calibration method, with nearly independent systematic un- certainty, is based an absolutely calibrated laser light source. In this paper, we present prelimi- nary results from a series of dedicated measure- ments at the Fermi National Accelerator Labora- tory (Fermilab).
2. Experimental method The measurements were performed at the Fer- milab Test Beam Facility. Most of the mea- surements were carried out using the 120 GeV proton beam, extracted from the Main Injector. Secondary beams of 32 GeV pions and 8 GeV positrons were also used. A sketch of the apparatus is shown in Fig. Figure 1. Layout of the experimental apparatus used at the Fermilab Meson Test Beam Figure 2. AIRFLY chamber with the integrating sphere fitted inside. 3 Figure 3. The integrating sphere used in the mea- surements. The diffusive coating applied to the interior can be seen through two of the ports.

A fluorescence chamber made of a 3 mm thick stainless steel was placed in the beam path, wit

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