# Ultra High Energy Cosmic Rays 2018

Oct 8 – 12, 2018
Ecole Supérieure de Chimie, Paris
Europe/Paris timezone

## Measurements of UHECR Mass Composition by Telescope Array

Oct 9, 2018, 9:50 AM
20m
Friedel Amphitheater (Ecole Supérieure de Chimie, Paris)

### Friedel Amphitheater

#### Ecole Supérieure de Chimie, Paris

Chimie ParisTech École Nationale Supérieure de Chimie de Paris 11, rue Pierre et Marie Curie 75231 PARIS Cedex 05
INVITED

### Speaker

William Hanlon (University of Utah)

### Description

Telescope Array (TA) has recently published results of nearly nine years of $X_{\mathrm{max}}$ observations providing it's highest statistics measurement of UHECR mass composition to date for energies exceeding $10^{18.2}$ eV. This analysis measured agreement of observed data with results expected for four different single elements. Instead of relying only on the first and second moments of $X_{\mathrm{max}}$ distributions, we have employed a morphological test of agreement between data and Monte Carlo to allow for systematic uncertainties in data and in current UHECR hadronic models. Results of this latest analysis and implications of UHECR composition observed by TA will be presented. TA can utilize different analysis methods to understand composition as both a crosscheck on results and as a tool to understand systematics affecting $X_{\mathrm{max}}$ measurements. The different analysis efforts underway at TA to understand composition will also be discussed.

### Primary author

William Hanlon (University of Utah)