# Presentation: 222519

## Measurement of the Fluorescence Yield for UHECR study

- Gwenaëlle LEFEUVRE
- APC – Collège de France

## Cosmic Rays
Fluorescence
Yield Measurements

**Fluorescence**
**Yield Measurements**

## Ultra-High Energy Cosmic Rays

**Ultra-High Energy Cosmic Rays**

**Energy max. ?**
**Nature ?**
**Origin ?**
**Processes ?**

**Notes:**
On the right : zoom on the UHE region, beyond 10^18 eV. FLux multiplied by E^3 so the variations to the law in E^-3 are well seen.
Blue points : AGASA’s results. It detects muons and electrons in the end of the shower thanks to an array of ground detectors.

Black & red points : HiRes’ results. It detects the fluorescence emitted on the passage of charged particles with telescopes.

Black curve : theoretical curve. Predicts the suppression of the flux around 10^20 eV.It is the GZK cut. Only HiRes’ results seem to agree with this prediction.

## The need of an accurate energy

**15 % in energy ****	****	****     almost 40 % in flux * E****3**** !**

## Air shower

**Air shower**

**some 10****3**** hadrons**
**some 10****9**** electrons**

**Electromagnetic **
**part : **
**90 % of **
**total energy !**

**Cosmic ray**

**Nuclei**

**Cosmic ray**

**Fluorescence**
**(isotropic)**

**Cerenkov cone**

**Charged **
**particles**

**Notes:**
 1st interaction with a nucleus of the atmosphere. Hadronic reaction, producing almost only pions : 2/3 charged, 1/3 neutral.
 Charge pions => other hadronic reactions until they don’t have energy enough to interact. Then they disintergrate into muons that reach the ground.
 Neutral pions => initiate each an electromagnetic shower. Along the shower, the elmg part is 90% of the total energy.
 Charged pions also produce light emission : Cerenkov, directionnal, and fluorescence, isotrope.
 Fluorescence looks like a plain disk moving at light speed, with a diameter equal to the tranverse size of the shower

## Detecting the UHECR

**Detecting the UHECR**

**Sampling**
-  **extrapolation of cross sections**
** ****AGASA, Auger**

**Fluorescence**
-  **development of the shower**
** ****HiRes, Auger, EUSO**

**Today**** : ****Auger**
**calibration of surface detector**
**by fluorescence**

## What is the fluorescence ?

**What is the fluorescence ?**

- e-sh  + N2 	    e- + N2+* + e-sh

**Excitation**

- e- + N2+	N2*

- e-  + N2 	e- + N2*

**Bunner, PhD thesis, 1967**

**Notes:**
Fluorescence is the emission in UV of molecular nitrogen, following an excitation or a ionization.
They can be due to a shower electorn or a secondary electron, ejected from a molecule during another ionization.

## Fluorescence spectrum

**Fluorescence spectrum**

**(Ulrich, Airlight workshop, 2003)**

** ****« Dry air » (80 % N****2****, 20% O****2****), 1 bar**
**after correction of spectrometer response**
** ****electron gun, 10****13**** e****-****/s**

**      ****Wavelength**

**Intensity (rel. unit.)**

**Notes:**
 electron gun & grating spectrometer
 relative spectrum because of the very low energy of electrons
 important dispersion when passing through the window, then diffusion and stopping. Impossible to know the distance.	

## De-excitation of nitrogen

** ****Radiation **
** ****Internal **
** ****Collision**
** ****Recombination : O****2**

**Null pressure**

**f(P, T)**

**Pressure (hPa)**

_**photons / e**__**-**__** / meter**_

## US-Standard 76 atmosphere

**US-Standard 76 atmosphere**

**Density**

**Pressure**

**Temperature**

## Yield variation with altitude

**Yield variation with altitude**

**Models**

**Measurements**

**Notes:**
 each curve is a model. Measurements made at atm P & normalized at z=0 of Us-Std.	
 Measurements don’t seem compatible. But they are, taking into account the uncertainty of 13 % 

## Yield variation with altitude

**Yield variation with altitude**

**13.5 %**

**Notes:**
 each curve is a model. Measurements made at atm P & normalized at z=0 of Us-Std.	
 Measurements don’t seem compatible. But they are, taking into account the uncertainty of 13 % 

## Already, my result...

## Objectives

**Absolute yield in [300, 430] nm with the best accuracy possible**
**Absolute fluorescence spectrum**

**To achieve this : **
**need an ****accurate**** and absolute **
**calibration of the detectors**

## the setup

**the setup**

## the setup

**the setup**

**370 MBq**

## the setup

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**the setup**

**BG3 (Schott)**

**wavelength (nm)**

**Transmission (%)**

## the setup

**the setup**

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**the setup**

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**the setup**

## Slide 26