[Paper Review] DAMPE space mission: first data

F. Gargano|arXiv (Cornell University)|Jan 18, 2017

Dark Matter and Cosmic Phenomena3 citations

TL;DR

The DAMPE space mission, launched in December 2015, measures cosmic ray spectra with high precision from tens of GeV to 100 TeV using a large acceptance (0.3 m²sr), deep BGO calorimeter (32 radiation lengths), and multi-layered detectors for electron/proton separation. First on-orbit data show excellent detector performance, with leptonic showers distinguished from hadronic backgrounds using shape parameters and neutron detection, achieving a rejection power >10⁵ for protons.

ABSTRACT

The DAMPE (DArk Matter Particle Explorer) satellite was launched on December 17, 2015 and started its data taking operation a few days later. DAMPE has a large geometric factor ($\sim~0.3\ m^2\ sr$) and provides good tracking, calorimetric and charge measurements for electrons, gammas rays and nuclei. This will allow precise measurement of cosmic ray spectra from tens of $GeV$ up to about $100\ TeV$. In particular, the energy region between $1-100\ TeV$ will be explored with higher precision compared to previous experiments. The various subdetectors allow an efficient identification of the electron signal over the large (mainly proton-induced) background. As a result, the all-electron spectrum will be measured with excellent resolution from few $GeV$ up to few $TeV$, thus giving the opportunity to identify possible contribution of nearby sources. A report on the mission goals and status is presented, together with the on-orbit detector performance and the first data coming from space.

Motivation & Objective

• To measure the all-electron spectrum from few GeV to several TeV with unprecedented energy resolution and low background.
• To identify potential dark matter signatures through precise measurements of high-energy electrons and positrons.
• To study cosmic ray composition and energy spectra up to 100 TeV, including boron/carbon ratios and spectral hardenings.
• To achieve high rejection of hadronic backgrounds using combined calorimeter, tracking, and neutron detection techniques.
• To validate the performance of the DAMPE detector system in orbit and ensure long-term stability for 3+ years of science operations.

Proposed method

• The DAMPE satellite uses a plastic scintillator array (PSD) for charge measurement and anti-coincidence, enabling Z identification up to Z=26.
• A silicon-tungsten tracker (STK) with 12 planes and 3 tungsten converter layers provides precise particle track reconstruction and gamma-ray pair conversion.
• A 32 radiation length BGO calorimeter with 308 scintillator bars measures shower profile and energy deposition with high resolution, enabling electromagnetic vs. hadronic shower separation.
• A neutron detector (NUD) based on ¹⁰B-loaded plastic scintillators detects thermalized neutrons from hadronic showers, enhancing hadron rejection.
• A shape parameter Fᵢ = spreadᵢ × (Eᵢ/E_tot) is computed from BGO layer profiles to distinguish leptonic from hadronic showers.
• On-orbit calibration and data transmission are performed with 70 Hz trigger rate, using timestamped event packaging and daily data output of ~100 GB after reconstruction.

Experimental results

Research questions

• RQ1 Can DAMPE achieve electron/proton separation with a rejection power exceeding 10⁵ in the 1–100 TeV energy range?
• RQ2 What is the precision of the all-electron spectrum measurement from 10 GeV to several TeV, and can it reveal spectral features from nearby astrophysical sources?
• RQ3 How well does the DAMPE detector system perform in orbit, particularly in energy calibration, pointing accuracy, and background suppression?
• RQ4 To what extent can the BGO calorimeter and NUD system improve hadronic shower rejection compared to previous experiments?
• RQ5 What are the expected measurements of the boron/carbon ratio and cosmic ray spectra over 3 years of operation?

Key findings

• The DAMPE detector system is operating stably in orbit with performance parameters (temperature, noise, spatial resolution, efficiency) matching pre-launch expectations.
• The absolute energy scale of the BGO calorimeter has been validated using the geomagnetic cutoff, confirming accurate energy calibration.
• The absolute pointing accuracy of the instrument has been successfully verified through on-orbit data.
• A preliminary high-energy sky map based on 165 days of photon data shows the correct positions of major gamma-ray sources.
• The charge measurement for cosmic rays up to iron (Z=26) was successfully demonstrated with only 10 days of data, showing clear separation of elements.
• Preliminary results show electron/proton separation with a rejection power exceeding 10⁵ using shape parameters from the last two BGO layers (layers 13 and 14).