The DAMPE satellite has been successfully launched in orbit on December 2015. The science goals of the mission include the study of high energy cosmic ray electrons, photons, protons and nuclei in a wide energy range: 109 − 1014 eV. A report on the mission status will be presented, together with on-orbit detector performance and first data coming from space

A. Capone

A. Morselli

Accardo

Adriani

Azzarello

Chang

G. Rodriguez Fernandez

Ivan De Mitri

Kobayashi

Panov

Zhang

EPJ Web of Conferences

Undetermined

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The DAMPE experiment: first data from space

De Mitri Ivan

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The DAMPE experiment: first data from spaceIvan De Mitri1,2,a (on behalf of the DAMPE Collaboration)1Dip.to di Matematica e Fisica "E. De Giorgi", Università del Salento, Via per Arnesano, I-73100, Lecce, Italy2Istituto Nazionale di Fisica Nucleare (INFN), Sezione di Lecce, Via per Arnesano, I-73100, Lecce, ItalyAbstract. The DAMPE satellite has been successfully launched in orbit on December2015. The science goals of the mission include the study of high energy cosmic rayelectrons, photons, protons and nuclei in a wide energy range: 109 − 1014 eV. A reporton the mission status will be presented, together with on-orbit detector performance andfirst data coming from space.1 IntroductionThe DAMPE (DArk Matter Particle Explorer) satellite was launched on December 17, 2015 and isin smooth data taking since few days after. Data from various subdetectors allow an efficient iden-tification of the electron signal over the large (mainly proton-induced) background. As a result, theall-electron spectrum will be measured with excellent resolution from few GeV up to few TeV, thusgiving the opportunity to cleary observe a cutoff and/or identify a possible contribution of nearbysources. Moreover the study of cosmic ray (CR) electrons and high energy photons will allow an in-direct search for dark matter signatures. Even if primarily optimized to collect electrons and gammas,DAMPE provides good tracking, calorimetric and charge measurements also in case of protons andnuclei. This will allow precise measurement of CR protons and nuclei energy spectra from few GeVup to about hundreds TeV. The high energy region will be explored with better precision comparedto previous experiments: spectral indexes for individual species could then be well measured and theobserved hardenings around 250GeV/n could be studied and better quantified.2 The DAMPE detectorDAMPE consists of a Plastic Scintillator strip Detector (PSD) that serves as anti-coincidence andcharge detector, a Silicon-Tungsten tracKer (STK) to reconstruct the direction (and charge) of incidentparticles, a BGO imaging calorimeter (BGO) of about 32 radiation lengths that measures the energywith high resolution and distinguishes between electrons and protons, and a NeUtron Detector (NUD)that can further increase the hadronic shower rejection power (see Fig. 1).The PSD is designed to measure the charge (Z) of incident high-energy particles, up to Z = 26,by looking at the energy release due to ionization process, that is approximately proportional to Z2. Ithas a 825 × 825mm2 active area made by organic plastic scintillators. Only light materials have beenae-mail: ivan.demitri@le.infn.it  DOI: 10.1051/, 0 (2017) 713602010136 epjconf/201EPJ Web of ConferencesRICAP162010   © The Authors,  published  by EDP Sciences.  This  is  an  open  access  article  distributed  under  the  terms  of the Creative Commons Attribution License 4.0 (http://creativecommons.org/licenses/by/4.0/). Figure 1. Structure diagram (left) and 3D view (right) of the DAMPE detector.DAMPE Figure 2. Comparison of the DAMPE STK featureswith other detectors.X Layer (22 BGO bars)Y Layer14 LayersFigure 3. 3D view of the DAMPE BGO scintillatorcalorimeter.used in the mechanical structure, in order to avoid initiating electromagnetic showers before the STK.It is arranged in a double layer configuration and has in total 82 detector modules. Each module ismade by a long plastic scintillator bar of 825mm with a 28 × 10mm2 cross section and is read outby two PMTs at each end. The modules are staggered by 8mm in the layer, and the bars in the twolayers are perpendicular, resulting in a overall efficiency of 99.75% . A double dynode readout foreach PMT has been implemented in order to cover a wide range, namely from 0.1 to 1400 times theenergy released by a Minimum Ionizing Particle (MIP), with an overlap region for calibration.The Silicon-Tungsten tracKer is devoted to the precise reconstruction of the particle track. It ismade by twelve position-sensitive silicon detector planes (six planes for the x-coordinate, six planesfor the y-coordinate). Three layers of tungsten are inserted in between the silicon x − y planes (2,3, and 4) to convert gamma rays in electron-positron pairs. The specifications of STK are given inTable 1 and a comparison with other experiments is shown in Fig. 2 looking at active area and numberof channels. The tracking resolution is expected to be 0.2◦. The STK analog readout can also providean independent measurement of the incident particle charge, at least up to medium mass nuclei. It isa compact system where readout and power supply electronics are mounted on the sides [2, 5].The BGO calorimeter is devoted to measure the energy deposition of incident particles and toreconstruct the shower profile. Moreover the trigger of the whole DAMPE system is based on thesignals from the BGO and the shower profile is fundamental to distinguish between electromagneticand hadronic showers. The calorimeter is composed of 308 BGO crystal bars (2.5 × 2.5 × 60 cm3 isthe volume of each single bar). The crystals are optically isolated from each other and are arranged  DOI: 10.1051/, 0 (2017) 713602010136 epjconf/201EPJ Web of ConferencesRICAP162010 2Table 1. Main STK specifications.Active area of each silicon layer 0.5534m2Silicon thickness 320 μmSilicon strip pitch 121 μmTungsten thickness 1mmDepth (rad. lengths) 0.976Power consumption 82.7WMass 154.8 kgTable 2. Main BGO specifications.Active area 60 × 60 cm2Depth (rad. len.) 32Sampling > 90%Long. segmentation 14 layersLat. segmentation ∼ 1 Molière radiushorizontally in 14 layers each made by 22 bars (Fig. 3). The bars of a layer are ortogonal to thoseof the following one in order to reconstruct the particle path in both views (x − z and y − z). Thetotal vertical depth of the calorimeter is about 32 radiation lengths and 1.6 nuclear interaction lengths.This unprecedented depth ensures that almost 100% of the energy of electrons and γ-rays is depositedin the calorimeter, and about 40% in the case of protons anad nuclei. The high energy limits of theDAMPE measurement ranges (about few TeV for electrons/photons and hundreds TeV for nuclei,depending on the their fluxes) are manly determined by its very large geometric factor, which is about0.3m2 sr for hadrons and even larger for electrons/photons. Table 2 summarizes the key parameters ofBGO calorimeter. Each crystal element is read out by two PMTs, mounted on both ends of the crystal.The measured light asymmetry allows to further estimate where the energy has been deposited alongthe BGO bar. In order to cover a very large dynamic range (2 × 106), the signals are collected fromthree different dynodes covering different ranges on each side.Typically hadron-induced showers produce roughly one order of magnitude more neutrons thanelectron-induced showers. The neutrons quickly thermalize in the BGO calorimeter and their activitycan be detected by a suitable NeUtron Detector (NUD, see Fig. 1) within few μs, thus providing afurther tool to distinguish the types of high-energy showers. The NUD is made by four boron-loadedplastics, each with a set of PMTs and related electronics. Indeed neutrons entering the boron-loadedscintillator undergo a capture process (namely 10B + n → 7Li + α + γ), whose probability is inverselyproportional to their velocity, within an average capture time that is inversely proportional to the10B loading. The scintilators are wrapped with a layer of aluminium film for photon reflection, andanchored in an aluminium alloy framework. The space between plastic scintillators and the framework(1mm on each side) has been filled with silicone rubber to relieve the vibration during the launch ofthe satellite.3 Ground tests and on-orbit operationAn extensive Monte Carlo simulation activity was done during R&D phase in order to find a propercompromise between physics goals and limitations on geometry, power consumption and weight.DAMPE performances were verified by a series of beam tests at CERN with electrons, photons, pions,protons and nuclear fragments. The wide energy range of the electron beams and the high-purity of theproton beams were sufficient to check energy resolution (Fig. 4), linearity and e/p separation. Also abeam of argon fragments was used for testing the detector response to nuclei. Details of the test-beamresults as well as the features of the qualification module can be found in [1–6]. Furthermore manytests (namely energy response to MIPs, efficiencies, detector alignment, etc.) have been performedduring different stages of the DAMPE assembly using a large samples of CR mouns at ground.After launch, the spacecraft entered a sky-survey mode immediately and a dedicated-calibrationof the detector was performed in two weeks. The calibration included the determination of pedestals,  DOI: 10.1051/, 0 (2017) 713602010136 epjconf/201EPJ Web of ConferencesRICAP162010 3Figure 4. Linearity and resolution of the DAMPE BGO calorimeter for electromagnetic showers: comparison ofbeam test data with simulations [3].Figure 5. Detected counting rate vs latitude and lon-gitude (arbitary units on the color palette). The SouthAtlantic Anomaly is clearly visible.Figure 6. MIP peak in the BGO calorimeter: com-parison of simulation with on-orbit data.response to MIPs, alignment, and timing. By comparing on-orbit data with simulations and on-groundtests we can conclude that the detector is working very well. The satellite is on a solar-synchrous orbitlasting 95 minutes. The pedestal calibration is performed twice per orbit and the global trigger rate iskept at ∼ 60Hz by using different pre-scale for unbiased and low-energy triggers at different latitudes(see Fig. 5 and [2]). Data are packaged with timestamp and transmitted to ground at a rate of about 5millions events per day corresponding to ∼ 15GB/day, that increases up to ∼ 100GB/day after offlinereconstruction.4 First on-orbit data and expected performancesThe DAMPE detector started taking physics data very soon after the launch. The performance pa-rameters (temperature, noise, spatial resolution, efficiency) are very stable and very close to whatexpected. The absolute energy measurement has been checked by using the geomagnetic cut-off andit results well calibrated. Also the absolute pointing has been successfully verified. Indeed the photondata collected in 165 days were enough to draw a preliminary high-energy sky-map where the maingamma-sources are visible in the proper positions. Fig. 6 shows the MIP peak reconstructed with theenergy released in the BGO crystals. It is evident the agreement with the distribution derived from thesimulation. The energy released in the PSD allows measuring the particle charge and distinguishingthe different nuclei in the CR flux. Figs. 7 and 8 show preliminary results of these measurements for  DOI: 10.1051/, 0 (2017) 713602010136 epjconf/201EPJ Web of ConferencesRICAP162010 4PSD high gain readout proton helium                                  Figure 7. Preliminary distribution for light CR com-ponent as measured in the DAMPE PSD.HistTotPsdMean_StkTrkEntries  2946099Mean    2.174RMS      2.47Charge 0 5 10 15 20 25 30Counts110210310410510     Figure 8. Preliminary Z measurement up to iron withthe DAMP PSD.             sum of spreads (mm) F 13 + F 14    (mm) e± protons Figure 9. Preliminary result about e/p separation (seetext). The background on the right is due to CRs en-tering the satellite from the sides.DAMPE in 3 years Simulation assuming        AMS-02 power law spectrum         + cut-off + nearby sources Figure 10. All-electron spectrum. The red dots rep-resent the possible DAMPE measurement in 3 years.the light component (H and He) and for the full range up to iron (1 ≤ Z ≤ 26), respectively, for a firstsample of on-orbit data.The measurement of the electron (plus positron) flux is one of the main goal of the DAMPEmission. The shower development in the BGO provides the tool to distinguish leptons from hadrons.Among others, a shape parameter has been defined: Fi = spreadi × EiEtot , where i is the index of theBGO layer (1 ≤ i ≤ 14), spreadi is the shower width in a given layer, Ei and Etot are the energyon the single i-th layer and on all the calorimenet, respectively. Using the shape parameters on thelast BGO layers (13, 14) it is possible to separate leptons from hadrons with a very large rejectionpower (preliminary results in Fig. 9). The rejection capability will be further enhanced by means ofthe NUD.The DAMPE detector is expected to take data for more than 3 years. This time interval is suf-ficient to deeply investigate many open questions in galactic CR studies. In Fig. 10 the possibleDAMPE measurement of the so called "all-electron" spectrum in 3 years is shown. Given the excel-lent resolution, spectral features like a possible cut-off at about 1 TeV or a flux increase due to nearbyastrophysical sources or dark matter signatures [7], could be well detected.Many experiments [8–11] observed a discrepant hardening of the CR elemental spectra at about250GeV/n. This is another interesting topic related to CR origin and propagation. Due to its verylarge geometric factor, DAMPE will be able to significantly reduce statistical uncertainties in thebreak region and give a precise measurements on the high energy spectral index of each nuclear  DOI: 10.1051/, 0 (2017) 713602010136 epjconf/201EPJ Web of ConferencesRICAP162010 5Figure 11. Proton (left) and helium (right) spectra in the range 10GeV - 10 TeV. The red dots indicate the possibleDAMPEmeasurement (for an exposure of 0.3m2 sr yr) assuming the AMS-02 data fit and its extrapolation to highenergy.species (see Fig. 11). Moreover the large exposure will allow extending energy spectra measurementsfor protons and nuclei up to hundreds TeV. This also apply quantities like the boron-to-carbon ratio,that could be well measured up to about 10 TeV/n.5 ConclusionsThe DArk Matter Particle Explorer (DAMPE) is a space mission supported by the strategic spaceprojects of the Chinese Academy of Sciences with the contribution of Swiss and Italian (namelyINFN and MIUR) institutions. The rocket has been successfully launched on December 17, 2015 andDAMPE presently flies regularly on a sun-synchronous orbit at the altitude of about 500 km. Fourdifferent detectors are arranged on the satellite: a plastic scintillator array (PSD), a silicon-tungstentracker (STK), a BGO calorimeter and a neutron detector (NUD). They are devoted to measure thefluxes of charged CRs (electrons, protons and heavier nuclei), to study high energy gamma rays fromastrophysical sources and to search for indirect dark-matter signatures. The main technical featuresof the detectors and a short review of the first preliminary results have been presented.References[1] J. Chang, Chinese J. Space Science 34 (2014) 550[2] G. Ambrosi et al. (DAMPE Collaboration), "The DAMPE mission", to be submitted[3] Z. Zhang et al., Nuclear Instrum. & Meth. in Phys. Res. A836 (2016) 98[4] V. Gallo et al., Proc. of the 34th Intern. Cosmic Ray Conference (2015) 1199[5] P. Azzarello et al., Nuclear Instrum. & Methods A 831 (2016) 378[6] Z. Zhang et al., Nuclear Instrum. & Methods A 836 (2016) 98[7] T. Kobayashi et al., The Astrophys. Jour. 601 (2004) 340 ; D. Grasso et al., Astroparticle Physics32 (2009) 140[8] A.D. Panov et al., Bull. Russ. Acad. Sci. 71 (2007) 494[9] H.S. Ahn et al., Astrophys. J. Lett. 714 (2010) L89; Y.S. Yoon et al., Astrophys. J. 728 (2011) 122[10] O. Adriani et al., Science 332 (2011) 69[11] L. Accardo et al., Phys. Rev. Lett. 114 (2015) 171103  DOI: 10.1051/, 0 (2017) 713602010136 epjconf/201EPJ Web of ConferencesRICAP162010 6

EDP Sciences OAI-PMH repository (1.2.0)

The DAMPE satellite has been successfully launched in orbit on December
2015. The science goals of the mission include the study of high energy cosmic ray
electrons, photons, protons and nuclei in a wide energy range: 10^9 − 10^14 eV. A report
on the mission status will be presented, together with on-orbit detector performance and
first data coming from space

De Mitri, Ivan

Archivio Istituzionale della Ricerca- Università del Salento

English

The DAMPE experiment: First data from space

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The DAMPE experiment: first data from space

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