WhatWWhatWhhaatt areaarearree CosmicCCosmicCoossmmiicc Rays?!RRays?!Raayyss??!! By Hayanon Translated by Y. Noda and Y. Kamide Supervised by Y. Muraki p+Pb 5-8 TeV 4 - Cosmic Rays" QCD processes in ! - Extensive air showers" - Interplay between CR Physics Cosmic Rays air showers" and accelerators" Alessia Tricomi University and INFN Catania, Italy - The LHCf experiments" What are Cosmics Rays" Electromagnetic radiation:"Radio" """""""IR" Astronomy" """""""Visible" """""""UV" Astrophysics" """""""X" """""""#" " Charged particles:" ""p" TinyTiny mysteriousmysterious particlesparticles areare comingcoming -" allall thethe wayway throughthrough """""""e spacespace toto Earth.Earth. """""""e+" Subjects"""" of this talk" p """""""Nuclei " """""""Antinuclei?" TheyThey areare """""""???" cosmiccosmic rayrays!s! " Neutral particles: " ""$" Hooray, What are you """""""???" I got it! looking at, Mirubo? "" Alessia Tricomi - University and INFN Catania" Robotic dog, Mirubo. Cosmic rays! Mol, science- loving girl. 1 Brief history of Cosmic Rays Detecton" Hess discovers cosmic rays" 1912" 1925" Quasi-isotropy" Auger discovered" extensive air showers" 1938" (E = 1015 eV!)" First experiment" to detect EAS 1946" " Giant EAS array detectors" Nowadays" based on hybrid tecnique" Alessia Tricomi - University and INFN Catania" Primary cosmic rays Φ ∝ E−2.7 Deviations from this power law § knee (4.1015 eV) Region 1 Region 2 § ankle (5.1018 eV) 109 eV 1015 eV Change in composition ↓ From ↓light to heavy 1015 eV 1021 eV Very different techniques are necessary to cover these huge differences of: o Fluxes o Energies GZK cut-off? LHC Beam Energy LHC CM Energy Alessia Tricomi - University and INFN Catania CR Detection Direct measurements Indirect measurements Alessia Tricomi - University and INFN Catania 5 HE-UHECR What do cosmic Primary cosmic rays consist of? rays, the cosmic What particles rays coming from outer space, are do they have? P mostly protons. primary cosmic rays They collide with the Earth‛s atmosphere and decay into secondary pion gamma cosmic rays. ray secondary cosmic rays muon electron I have got it! Cosmic rays on the Earth‛s surface are tiny particles produced by energetic protons. Alessia Tricomi - University and INFN Catania 7 Air Shower simulation Air Shower simulation Electrons Air Shower simulation Muons Air Shower simulation Hadrons Indirect measurements If the energy of the CR is too big to be directly measured, indirect measurements are necessary. The atmosphere is used as ‘PASSIVE CALORIMETER’ Object of the measurements: 1. Charged particles: μ±, e±, p (Extended Air Shower detectors, EAS) 2. Cherenkov light 3. Fluorescence light Charged component: EAS vs Atmospheric Depth Analytic shower model AnalyticSimplified Showermodel [Heitler Model]: shower – developmentEM Showers governed by X0 Simplifiede- loses model[1 - 1/e] [ Heitler= 63% ]:of energy in 1 Xo (Brems.) the mean free path of a γ is 9/7 Xo (pair prod.) shower development governed by X0! Lead%%absorbers%in%cloud%chamber% e- loses [1 - 1/e] = 63% of energy in 1 X (Brems.) " Assume: 0 " E > Ec : no energyAssume: loss by" ionization/excitation E >E E <c: Enoc :energy energy loss loss by only ionization/excitation via ionization/excitation" E < Ec: energy loss only via ionization/excitation" Simple shower model: Simplet shower model:" After shower max is reached: • 2 particles after t [X0] only ionization, Compton, photo-electric - •2 X/each& particles with energy after E/2t='t /& splittings" - each with energy E /2t" • Stops if E < critical 0energy εC - stops if E < E • Number of particlesC" N = E/εC - •number Maximum of particles at Nmax = E0/EC" 7 - Maximum at Xmax=&ln2(E0/EC)" This model is reasonably valid for EM showers" ~ roughly valid for Hadronic showers " Alessia Tricomi - University and INFN Catania COSMIC RAYS AND EXTENSIVE AIR SHOWERS Lab energy. The cosmic ray spectrum is shown in Fig. 1. The figure indicates the energy range where the cosmic ray spectrum is measured directly by balloon and satellite experiments. When the energy starts to exceed significantly 1,000 GeV the cosmic ray flux is too small and the cosmic rays are measured by the showers they generate in the atmosphere. There are di↵erent types of air shower detectors: Air shower arrays consist of particle detectors that are spaced at di↵erent distances from • each other depending on the energy range of the detectors. If the design is for detection of 106 GeV air showers the distance between detectors is several tens of meters. In the Auger southern observatory, which aims at shower energy exceeding 109 GeV the distance between detectors is 1,500 m. The shower arrays trigger when several detectors fire in coincidence. The reconstruction of the primary energy depends heavily of the hadronic interaction model that is used by the detector Monte Carlo simulation. Air Cherenkov detectors detect the Cherenkov light emitted by the shower charged par- • ticles (mainly electrons and positrons) in the atmosphere. Most of the light comes when the shower is at maximum. Fluorescent detectors detect the fluorescent light from the Nitrogen atoms in the atmo- • sphere that are excited by the ionisation of the shower charged particles. Unlike the Cherenkov light the fluorescent light is isotropic. High energy showers can be observed from as far as 40 km away. Fluorescent detectors integrate over the shower longitudinal development to estimate the primary particle energy after adding the invisible energy, contained in high energy particles and neutrinos. Di↵erent observational methods are now combined as in the case of the southern Auger obser- vatory and the new Telescope Array detector. 2 Rough Estimates of the Shower Parameters As mentioned earlier, shower Monte Carlo calculations are used for calculations of the efficiency of the detectors and estimations of its e↵ective area. The main features of the air shower development can be understood on the basis of the toy model of the shower development created by Heitler [1]. Heitler assumed that the shower consists of one type of particles. At each interaction length λ two new particles are created each one of them carrying 1/2 of the energy. This continues until the Analyticparticle energy Showeris less than the Modelcritical energy – HadronicEc under which Showersparticles do not interact. The maximum number of particles in the cascade is then Nmax = E0/Ec. The depth of maximum is proportional to the logarithm of the ratio of the primary and the critical energies E /E : X = λ log (E /E ) . 0 c max Heitler2 model0 c is reasonably valid for EM showers TSandTANEV only roughly valid Hadronic cascades forare mhadronicuch more complicated showers but one can still use Heitler’s approach to derive approximate expressions for some shower parameters. Assuming that the air shower development depends only on the first cosmic rayAssume:interaction, one can estimate the depth of the shower maximum in- theOnlyatmosphere the firstas interaction[2] contribute to shower size 2(1 Kel)E0 Xmax = X0 ln − + λN (E0) , (1) and the number of electrons at Xmax as ( m /3)" h i 0 max 1 m (1 Kel)E0 Ne = h i − , (2) 2 3 "0 m is the effective meson multiplicity where m is the e↵ective meson multiplicity and the 1/3 factor accounts for the multiplicity of Kel is the elasticity coefficient of the first neutral mesons. Kel is the elasticitinteractiony co e(roughlyfficient ½of) the first interaction (roughly 1/2) and ✏0 is the critical energy of the electrons in air (81 MeV). Replacing the primary energy E0 with ε0=Ec of the electrons in air (81 MeV) E0/A (the mass of a nucleus) one can derive the expressions for showers initiated by primary nuclei. The conclusions are that Xmax in such show273ers is smaller (showers develop higher in A p the atmosphere): Xmax = Xmax X0 ln A and the muon/electron ratio in showers initiated 1 β − by nuclei is higher by A − (β = 0.85) than in proton showers. These two parameters are most often used in studies of the cosmic ray chemical composition. After this short introduction it is important to remember thatAlessia Tricomicosmic - Universityra andy INFNsho Cataniawer experiments are observations, rather than experiments in the accelerator experiment sense. We have no idea of the energy and type of the primary particle or of the first interaction point in the atmosphere. We have to measure as many shower parameters as possible, compare them to Monte Carlo calculations, and derive the energy and composition of the primary particles. This not easy because of the large inherent fluctuations in the shower development. Figure 2 shows the shower longitudinal profiles of ten simulated proton showers of primary energy 105 GeV and their average. 1 10 5GeV 0.8 0 0.6 / E e N 0.4 0.2 0 0 200 400 600 800 1000 Depth, g/cm2 Figure 2: Shower profiles of ten simulated proton showers. The average shower profiles is shown with the points. For this reason the reconstruction of individual showers is quite uncertain and we have to work with large statistical samples in the investigation of the cosmic ray energy spectrum and composition. 274 Analytic Shower Model – Hadronic Showers Heitler model is reasonably valid for EM showers and only roughly valid for hadronic showers Assume: - Only the first interaction contribute to shower size - Superposition principle is valid à Nucleus with iron 14 50 km mass A and energy E0 is equivalent to A nucleons E=10 eV nucleus with energy E0/A proton CORSIKA Simulation 40 km p Xmax =X max−X0lnA QGSJET/EGS4 30 km 1−β p Nμ/Ne=A (Nμ/Ne) 20 km e/ γ 10 km µ h Alessia Tricomi