first results from the dampe mission · • many new spectral features observed with high precision...
TRANSCRIPT
FirstResultsfromtheDAMPEMission
XinWu
DepartmentofNuclearandParticlePhysicsUniversityofGeneva,Switzerland
SeminaratLaboratoire del’Accélérateur Linéaire (LAL)Univ.Paris-Sud, CNRS/IN2P3
June1,2018
2LAL,1/06/2018XinWu
Launched >2yearsago,17/12/2015
Highenergyparticlephysicsexperimentinspace
DAMPE
NeutronDetector(NUD)
PlasticScintillatorDetector (PSD)
Silicon-TungstenTracker(STK)
BGOCalorimeter(BGO)
TheDetector
3XinWu
highenergyγ-ray,electronandcosmicray
nucleitelescope
LAL,1/06/2018
ü Chargemeasurements(PSDandSTK)ü PrecisetrackingwithSistripdetectors(STK)ü Tungstenphotonconvertersintracker(STK)ü Thickimagingcalorimeter(BGOof32X0 )ü Extrahadronrejection(NUD)
�
4XinWu
• OurGalaxyisimmergedinahaloofhighenergychargedparticles(CosmicRays)
– Mainlynucleiconsistentwithstellarmaterial:p(90%),He,C,O,… Fe,…
• Butalsosecondaryions:Li,Be,B,sub-Fe,pbar,…
Whystudyparticlesinspace?
LAL,1/06/2018
• Gamma-rays,neutrinos(notcoveredhere)
– Sourcepointingcapability→gamma-ray/neutrinoastronomy
http://www.srl.caltech.edu/ACE/ACENews/ACENews83.html,2004
Cosmicparticlesaremessengersofhighenergyprocesses(“cosmicparticleaccelerators”)� fundamental
implicationsonastronomy,cosmologyandparticlephysics
NormalizedtoSi=103
• andelectrons,positrons(� 1%)
• Observedparticleswithenergyupto~1020 eV(=100MillionTeV =100EeV)
– UptoPeV,bestmeasuredinspace,abovetheatmosphere,forprecisionandcomposition
EssentialingredientoftheMulti-messengerhighenergyastrophysics
XinWu 5
• In1785Charles-AugustinCoulombobserved isolatedchargeleakingoutinair…
Allstartedwiththeleakingcharge…
… sothere is“radioactivity”intheair,butwheredoesthisradiationcomefrom?
LAL,1/06/2018
• In1896Becquereldiscoveredradioactivity,also…
Electroscopecanbedischargedbyradioactivity!
XinWu 6
• Manysearches ...Elster &Geitel (1899),metalbox;C.T.R.Wilson(1901),railwaytunnel;Wulf (1909),Eiffel tower;Gockel (1910),balloon;Pacini (1911),lake …ledtothediscoverybyV.Hess(1912) inaballoonupto5000m– Conclusiveevidenceofincreasingpenetratingradiationwithrisingaltitude
→extraterrestrialorigin!
TheDiscoveryof“CosmicRadiation”
Spaceparticlephysicswasborn!
Hess,1912
KolhörsterDetector!
Wulf Electroscope
NobelPrize1936forV.HessLAL,1/06/2018
7XinWu
• Auguste Piccarddevelopedapressuredaluminumcabin
– Measuredcosmicraysuptothestratosphere(~16km)in1931
GoingtotheStratosphere
Piccard 1931
Regener,1932
Kolhörster, 1913/14
• ErichRegener extended themeasurement toanaltitudeof28km in1932withsmallunmannedrubber-balloons
LAL,1/06/2018
First“astronauts”!
First“space-lab”!
Studiesofcosmicraysongroundledtothediscoveriesof:positron(1932),muon(1936),chargedpion(1947),K,Λ, Σ, Ξ, … (1950’s)
• Alongseriesofballoonsandsatellites experimentsbasedoncalorimeters,leadingtothehighprecisionDAMPEmission, launchedinDec. 2015
Fromballoonstosatellites andspacestations• Manydiscoverieswithballoonsin1930-40’s
– Geomagneticeffects(1927),CRmainlychargedparticles (1929)�mainlypositivelycharged(1933)�mainlyprotons(1940),heavynucleiobserved(1948)
8LAL,1/06/2018XinWu
• Spaceage:particledetectorswerekeyelementsonfirstsatellites– Sputnik-2:launchedNov.3,1957carried2Geigercounters
• IndicationoftheVanAllenradiationbelt
– Explorer-1(FirstUSsatellite): launchedinJan.1,1958
• DiscoveryoftheVanAllenbeltwithaGeigercounter
• 1960:Fristevidencesofcosmicrayelectrons(~0.5GeV)in2balloonexperiments,withmulti-platecloudchamberandNaI/scintillatorcounters– 1963:Friste+/e− ratio(0.1– 1GeV)withmagnetinballoonexperiments
• Magneticspectrometerscontinueswithballoonsandsatellites, leadingtothehighprecisionAMS-02 experiment, launchedin2011
• Gamma-ray detectiontechnologies successfullydeployedinspace,leadingtothehighprecisionandlargeacceptanceFERMI observatorylaunchedin2008
Particlephysicsinspacehasenteredaprecisionmeasurementera!
Manysurprises!• Spectradonotfollowthesimplepowerlaw,asobservedwithlowerprecisiondata
9LAL,1/06/2018XinWu
• Manynewspectralfeaturesobservedwithhighprecisiondata,reflectingthecomplexnatureofcosmicrays– Particlescanbeproducedfromdifferentsourcesatdifferenttimesatdifferent
distances,withdifferentaccelerationmechanisms,thentravelthroughdifferentpathstotheEarth
• Astrophysicalsources(eg.SNR,Pulsar,AGN)orexoticsources(eg.DM)
• Propagation/secondaryproductioneffects
• Non-exhaustivelistofnewand“unexpected”observations– Cosmicraypositronfraction“anomaly”
– Cosmicrayelectron+positronspectralbreaks
– Protonandlightnucleispectralbreaks
– Flatteningantiprotonfraction
– GeVgamma-rayexcessattheGalacticCenter
– …
Stillalongwayfroma“StandardModelofCosmicRayPhysics”!
10XinWu
• Positronswerethoughttobemainlysecondary� singlepowerlaw
– Secondary:fromcosmicraysinteractingwithInterstellarmedium
Positronfraction“anomaly”
Butelectronandpositionmayhavedifferentcontributingsources�directlylookattheindividual fluxes
LAL,1/06/2018
• Positronsmayhaveaprimarycontribution
– Primary:EMcascadeinpulsarmagneticfieldorthroughpionproductioninshockacceleration(pulsar,SNR),orDM
S.Ting,CERNcolloquium,May24,2018
11XinWu
• AMSdatabothelectronandpositrondonotfollowsimplepowerlaw– Source(s)contribution,ornewpropagationeffect?
Positronandelectronindividualfluxes
Needmoredatatomeasurethecut-offofthepositronsourcecontribution� understand thenatureofthesource(DM?pulsar?Propagation?)
LAL,1/06/2018
S.Ting,CERNcolloquium,May24,2018
Geomagneticeffect
12XinWu
• AMS-02publishedCREspectrumupto1TeV,Fermiupto2TeV
• CREfluxcanalsobemeasuredbythickcalorimetricdetectors(DAMPE,CALET)
– Betterenergyresolutionathighenergy
Electron+positron(CRE)flux
LAL,1/06/2018
Fermi,PRD95,082007(2017)
AMS,PRL113,221102,(2014)
Hardening~30GeVseenbyAMSandFermi
But:Fermilargesystematicerrorduetothincalorimeter,HESSlargesystematicerrorduetoshowermodeling inatmosphereandenergyscale(15%,notshowninfigureabove)
DAMPEwillproducehighstatisticsandprecisemeasurementatmulti-TeV region
Intriguing“features”around1TeV
Protonandlightnucleirigidityspectra,upto~TV
13LAL,1/06/2018XinWu
Thereisageneralsinglepowerlawbreakdownaround200GV!
Acceleration?Propagation?Mixed?
S.Ting,CERNcolloquium,May24,2018
Proton
ProtonandHeliumhighenergyspectra,1- 100TeV
14LAL,1/06/2018XinWu
• 1– 100TeV range:exploredbyCREAM,ATIC,NUCLEON
• Nearfuture:uptoPeV toconnecttoground-basedEASmeasurements
– HERD:onboardChina’sSpaceStation(CSS),~2025
NewmeasurementstocomefromDAMPE,CALETandISS-CREAM
Anotherspectralhardening>1TeV?andasoftening>10TeV?
Cream-III,ApJ 893,5(2017),NUCLEON,JCAP07,020(2017)
15XinWu
• Apowerlawcanresultfromaprocesswithenergyindependentaccelerationrateand energyindependentescapeprobability– Energygainedaftereachacceleration: !" "⁄ = %
– Escapeprobabilitybetweeneachacceleration:&'()• Accelerationprobability:1 − &'()
Whypowerlaw?
• Thedifferential spectrumisthen,-
,.= /0123.×"
6768
• Insteadystate,thenumberofparticleswithenergyabove"9 = ": 1 + % 9:
– <(" > "9) = < 1accelerations + < 1+ 1accelerations + ⋯
= <0 ∑ 1 − &'()NO
NP9 =-Q
RSTU1 − &'()
9
– Thoseescaped(observed):<V2/(" > "9) = &V2/<(" > "9) =N0 1 − &'()9
• Replacenwith1 =XYZ .[ .Q⁄
XYZ 8\]
– <V2/(" > "9) = /0123.×"967, _ = −
XYZ 86RSTU
XYZ 8\]
LAL,1/06/2018Butistheresuchacceleration process intheGalaxy?
16XinWu
• Fermi(1949):CosmicraysareoriginatedandacceleratedprimarilyintheinterstellarspaceoftheGalaxybycollisionsagainstmovingmagneticfields
– Fermimechanism(of2nd order):head-on(gain)morelikelythantail-end(loss)⟹ onaverage<ΔE/E>�β2
cloud
FermiAccelerationandSNR
– SupernovaRemnants(SNRs):plausiblesourceforcosmicraysupto~1015 eV
• CanexplainthebulkofCRenergydensity(~1eV/cm3)iffew%ofthekineticenergyreleasedgoesintotheaccelerationofprotonsandnuclei
ud uu
shock
• (1977-78)Similarmechanism,butmoreefficient,withshocksinspaceplasmas
– Fermimechanismof1st order:particlecrossingbackandforthoftheshockfrontalwaysgainenergy⟹ <ΔE/E>�Δβshock
• Efficient:~1000yearstoreach1014 eV(0.1PeV)
• Universalpowerlaw,independentofparticleenergy!
• Notefficientenough:Takestoolongtoaccelerate
• Needsufficientinjection(initial)energy
• Predictspowerlaw,butnotuniversal
a fewpercentury
βcloud~10−4
βshock~10−2
17XinWu
• Pulsars(fastspinning,highlymagnetizedneutronstarsresultingfromSNexplosions)
– Strongelectricfieldsgeneratedbyrotatingstrongmagneticfields
– Capableofconvertingrotationalkineticenergyintoradioemission(observed), γ-rays(observed), cosmicraysincludinge+e− pairs• Possibleoriginofcosmicraysinthegalactictoextragalactictransitionregion(1015 – 1019 eV)
Pulsars,BinariesandAGNs
• Binarieswithneutronstarorpulsar
– Accretionprocessgenerateshighspeedparticlesfallingintotheaccretiondisk,thenacceleratedinrotatingmagneticfields
• Accelerationto1019 eV possible
• Accretiondisksofcompactobjectsarecommonlyassociatedwithhighlycollimatedrelativisticjets
– Fermiaccelerationinjets(turbulences) associatedwithActiveGalacticNuclei(AGN)couldbetheoriginofextragalacticcosmicrays
`×" =ab
a3
18XinWu
• Cosmicraysdiffuse throughtheinterstellarmedium (ISM)
– Randomscatteringwithdiscontinuitiesoftheinterstellarmagneticfields
• Directionbecomesisotropic;Spectrumismodified:E−γ� E−γ−δ
CosmicRayPropagationinISM
Secondary-to-primaryratiose.g.B/C,areusefultodeterminepropagationparameters!
– InteractionwithambientmaterialinISM(~90%H,10%He)
• Productionofsecondarycosmicrayparticles
• Somearemainlysecondary:Li,Be,B,sub-Fegroup,…
• ChemicalcompositiongiveuniqueinformationonsourcesandpropagationInterestregionofDAMPE
andfuturemissions
LAL,1/06/2018
TheDAMPESatellite
19XinWu
Weight:1450/1850kg(payload/satellite)Power:300/500W(payload/satellite)Readoutchannels:75,916(STK73,728)
Size:1.2mx1.2mx1.0m
LAL,1/06/2018
�EQM,Oct.2014,CERN Integratedsatellite,Sept.2015,Shanghai
20XinWu
TheOrbit
LAL,1/06/2018
• Altitude:500km• Inclination: 97.4065�• Period:95minutes• Orbit:sun-synchronous
• Dec.20:alldetectorspoweredon,excepttheHVforPMTs
• Dec.24:HVon!• Dec.30:stabletriggercondition• Verysmoothoperation since!
LaunchedDec.172015
TheCollaboration• China
– PurpleMountainObservatory,CAS,Nanjing
– UniversityofScienceandTechnologyofChina,Hefei
– InstituteofHighEnergyPhysics,CAS,Beijing
– InstituteofModernPhysics,CAS,Lanzhou
– NationalSpaceScienceCenter,CAS,Beijing
• Switzerland
– UniversityofGeneva,Switzerland
• Italy
– INFNPerugiaandUniversityofPerugia
– INFNBariandUniversityofBari
– INFNLecceandUniversityofSalento
21LAL,1/06/2018XinWu
ScientificobjectivesofDAMPE• PrecisionTeV measurementsinspace
– Measurethehighenergycosmicelectronandgammaspectra– Studyofcosmicrayspectrumandcomposition
– Highenergygammarayastronomy
22
Detectionof1GeV- 10TeVe/γ,100GeV- 100TeV cosmicrayswithexcellentenergyresolution,directionreconstruction (γ)andchargemeasurement
LAL,1/06/2018XinWu
PlasticScintillatorDetector(PSD)
23XinWu LAL,1/06/2018
2 layers(x,y)ofstrips1cmthick,2.8cmwideand88.4cmlongSensitivearea82.5cmx82.5cm,nodeadzone• Stripstaggeredby0.8cm
Readout both ends with PMT, each uses twodynode signals (factor ~40) to extend thedynamic range to cover Z = 1, 26
Silicon-TungstenTracker(STK)
• Outerenvelop1.12mx1.12mx25.2cm
• Detectionarea76x76cm2
• Totalweight:154.8Kg
• Totalpowerconsumption:~85W
24XinWu LAL,1/06/2018
• 12layers(6x,6y)ofsingle-sidedSi stripdetectormountedon7supporttrays
• Tungstenplates(1mmthick)integratedintrays2,3,4(fromthetop)
– Total 0.85X0 forphotonconversion
TheSTKstructure
25XinWu LAL,1/06/2018
73,728channels
768siliconsensors95x95x0.32mm3
1,152ASICs
192ladders
X Layer (22 BGO bars)
Y Layer
14 Layers
BGOCalorimeter(BGO)• 14-layerBGOhodoscope,7x-layers+7y-layers
– BGObar2.5cm�2.5cmx60cm,readoutbothendswithPMT
• Use3dynode(2,5,8)signalstoextendthedynamicrange
– Chargereadout/Trigger:VATA160withdynamicrangeupto12pC
26Totalthickness32X0/1.6λILAL,1/06/2018XinWu
Detectionarea60cm�60cm
BGOreadoutandtrigger
• TA(fastshaping,22channelOR)signalsofVATA160usedfortrigger
– Onlythedynodes5and8ofthetop4andbottom4layers used– Triggermenu:HE(notprescaled), LE,MIP-1,MIP-2,Unbiased
27LAL,1/06/2018XinWu
5x
NeutronDetector(NUD)• 4largeareaboron-dopedplasticscintillators(30cm�30cm�1cm)
– Detectthedelayedthermalneutroncapturesignaltohelpe/hseparation
– Gatingcircuittodetectdelayedsignalwithasettabledelay(0-20µs)afterthetriggerfromtheBGO
28LAL,1/06/2018XinWu
γ + Li+ α → B+ n 710
DAQsystem
29LAL,1/06/2018XinWu
Triggerlatency1µs
3ms fixedDAQdeadtime
• 2crates• Allmoduleswithdouble
redundancy• 16GBmemory
On-groundcalibration
30XinWu
• SeveralweeksatCERNPSandSPSbeamsfromOct.2012– Nov.2015(EQM)– Plusmanycosmicmuondata(FM)
LAL,1/06/2018
Oct.2012Nov.2014
March2015Nov.2015
31XinWu
Electronenergylinearityandresolution
LAL,1/06/2018Goodlinearityandresolution
Goodagreementbetweentestbeamandsimulation
1-20GeV 50-243GeV
ΔE/E<1.2%for>100GeV
NIMA856(2017)11Energycorrection:~6-7%for100GeV – 1TeV
32XinWu
Protonenergyresolution
LAL,1/06/2018
Protonenergycannotbeeasilycorrected.Needunfolding!
Goodagreementbetweentestbeamandsimulation
Noise [ADC counts]0 2 4 6 8 10 12 14 16 18 20
Entri
es
1
10
210
310
410After production
After payload integration
After satellite integration
STKon-groundcalibration• ExtensivelytestedandcalibratedwithparticlebeamsatCERNandwith
cosmicraymuons
• STKremainedinexcellentqualitythrough~6monthsoftransportation,integration,spaceenvironmentaltests,…
– Numberofnoisychannels<0.4%beforelaunch• LargeamountofcosmicdatacollectedtoaligntheSTK
– Excellentpositionresolutionachievedbeforelaunch
• 40– 50µmforverticalentryparticles (requirement75µm)
33XinWu
Numbe
rofchann
els
Noise(ADC) Trackincidenceangle
Positionresolutio
n
LAL,1/06/2018
Chargemeasurementswithbeams• TestwithionfragmentbeamsatCERN
34XinWu LAL,1/06/2018
ChargemeasuredbyPSDChargemeasuredbySTKladders
STKhasbetterresolution atlowZ,butsaturateatZ~ 8
Ar primarybeam Pb primarybeam
STKASICgain
35XinWu
• 15 orbits/day
• ~50Hzaveragetriggerrate
– Mainhighenergytriggerandprescaled lowenergyandMIPtriggers
Particlehitcountsvsorbit
LAL,1/06/2018
36XinWu
• HETtriggerrate20– 60Hz– EventsinSouthAtlanticAnomaly(SAA)
regionsnotused
Triggerrateinorbit
LAL,1/06/2018
3 ObitsthroughSAA
Proc.Sci.(ICRC2017)232(2017)
• Smalltriggerthresholdvariationwithtemperature– ~13ACD(0.04MIP)infull
temperaturerange
Temperature
Triggerthreshold
PSDin-flightcalibration
37XinWu
Pedestalcomparison
LAL,1/06/2018 Proc.Sci.(ICRC2017)168(2017)
Dy5andDy8signalcorrelation
Lightattenuationcalibration,usingSTKtrackforextrapolation
Dy8
Dy5 Singlelayerefficiency
Average~99.5%
PSDbarnumber
38XinWu LAL,1/06/2018
Charge resolution: 1�0.12 for H, 2�0.28 for He
Ni
Fe
SiNe
C OHe
Ca
H
PSDchargemeasurement
Goodstartingpointforprotonandnucleimeasurements
Noise Runs0 100 200 300 400 500 600 700
Num
ber o
f Cha
nnel
s
0
50
100
150
200
250
300
350
400
450
Frac
tion
of T
otal
[%]
0
0.1
0.2
0.3
0.4
0.5
0.6noise>5 ADC10>noise>5 ADCnoise>10 ADC (1 PED run per day)
Dec. 30, 2015 - Feb. 28, 2018
39XinWu
• Detectorstartedingoodshape,Steadilyimprovedinthefirst2yearduetostabilizationeffect
LAL,1/06/2018
• Bulkofnoisecorrelatedwithtemperature
– Verysmalltemperaturecoefficient
• ~0.01ADCper2�,stability�1.4%
• Simplificationforoperation
– datacompressionthresholdsupdatedonlyonceonFeb.22,2016usingaveragenoiseofFeb.13-17,2017
STKNoiseverystablesincelaunch
Rangeofvariation (0.3ADC)moreprecisethan theon-boardpedestalcalculation(2ADC)!
26monthssincelaunch
Numberofnoisychannels<0.28%
Averagenoise2.84-2.87ADC
C
10 20 30 40 50
30
40
50
60
708090
100
200
300x2 x1x3 x6x4 y1x5 y6y2 alignedy3 non-alignedy4y5
) (deg)yθ(xθ
m)
µEf
fect
ive
reso
lutio
n (
• Goodthermal stabilityguaranteedagoodshorttermmechanicalstability
LAL,1/06/2018 40XinWu
STKin-flightalignment
Re-alignevery2weekstocorrectforlongtermshift
Outsidelayerswithlargerextrapolationerrors
Intrinsicpositionresolution40-50µm
Unbiasedhitresidualof12layersbefore/after(re)alignment,asfunctionofincidenceangle
dataof2months
Dec-312015
Jul-012016
Dec-312016
Jul-012017
Dec-312017
Jul-022018
11.11.21.31.41.5
Dec-312015
Jul-012016
Dec-312016
Jul-012017
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Jul-012016
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Jul-012017
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Jul-012017
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11.11.21.31.41.5
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Jul-012016
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Jul-012017
Dec-312017
Jul-022018
11.11.21.31.41.5
° < 10x
Θ < °0 ° < 20x
Θ < °10
° < 30x
Θ < °20 ° < 40x
Θ < °30
° < 50x
Θ < °40 ° > 50xΘ
(Jan
uary
,1st
) 1σ
/ 1σ x1 x2x3 x4x5 x6
LAL,1/06/2018 41XinWu
Residualratioevolution:initialalignment
UsealignmentofJan.2016:traymovementinZdirectionaffectsresolutionoflargeangletracks
<10� 10-20�
>50�
20-30� 30-40�
40-50�
LaunchtoMay2018
Dec-312015
Jul-012016
Dec-312016
Jul-012017
Dec-312017
Jul-022018
11.11.21.31.41.5
Dec-312015
Jul-012016
Dec-312016
Jul-012017
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11.11.21.31.41.5
Dec-312015
Jul-012016
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Jul-012017
Dec-312017
Jul-022018
11.11.21.31.41.5
Dec-312015
Jul-012016
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Jul-012017
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11.11.21.31.41.5
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Jul-012016
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Jul-012017
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11.11.21.31.41.5
Dec-312015
Jul-012016
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Jul-012017
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11.11.21.31.41.5
° < 10x
Θ < °0 ° < 20x
Θ < °10
° < 30x
Θ < °20 ° < 40x
Θ < °30
° < 50x
Θ < °40 ° > 50xΘ
(Jan
uary
,1st
) 1σ
/ 1σ x1 x2x3 x4x5 x6
LAL,1/06/2018 42XinWu
Residualwithalignment:launchtoMay2018
Bi-weeklyupdateofalignmentissufficient,stability~2%
<10� 10-20�
>50�
20-30� 30-40�
40-50�
LaunchtoMay2018
BgoMIPsADC8960_L4_B12_S2Entries 7955Mean 314.9RMS 136.1
/ ndf 2χ 118.8 / 65p0 0.07± 15.84 p1 1.5± 258.8 p2 9.582e+02± 8.061e+04 p3 1.60± 89.62
ADC0 200 400 600 800 1000 1200
Cou
nt
0
50
100
150
200
250
300
BGOin-flightMIPcalibration
43XinWu LAL,1/06/2018
time0 10 20 30 40 50 60 70
Mea
n(M
eV)
1220
1240
1260
1280
1300
1320
01/16 03/16 05/16 07/16 08/16 10/16 12/16 03/17
0.96
0.97
0.98
0.99
1
1.01
1.02
1.03
1.04
Stability of Helium MIPs
31/12/1501/04/1601/07/1630/09/1631/12/1601/04/1701/07/17
MIPs M
PV(AD
C)
520
540
560
580
600
620
Time(Day/Month/Year)31/12/15 01/04/16 01/07/16 30/09/16 31/12/16 01/04/17 01/07/17
C )°Tem
peratu
re(
0
5
10
• “MIP”calibration:ADC→MeVandequalization,useeventsneartheequator,�20�
After“temperaturecorrection”(MIPcalibrationonceperorbit)
Proton“MIP”MPVvstemperature (time)
MPVofaBGObar
Geomagneticcut-offeffectM
IPM
PVsh
ift%
MIPspectrumofaBGObar
ADC
MeV
TotalenergymeanofHeliumMIP
Helium“MIP”meanvstime,stable<1%
MIPenergycalibrationstability
44XinWu LAL,1/06/2018
BGObarCarbonMIPpeak BGObarIronMIPpeak
MIPenergycalibrationstabilityisbetterthan1%
BGOchargeidentificationofMIPevents
Absoluteenergyscalevalidation
45XinWu LAL,1/06/2018
• UseLin1– 1.14,cut-off~13GeV• Measuredcut-offcomparedtoMCsimulation
withIGRF-12modelandback-tracingcode(InternationalGeomagneticReferenceField)
Proc.Sci.(ICRC2017)197(2017)
• Overallenergyscalecanbecheckedwithgeomagneticcut-offeffects– Chargeparticlesdetectedinageomagneticzonehavespecificcut-offintheflux
(deflectionbythemagneticshield)
McIlwain Lshells
Cut-off:13.20GeV(data)vs.13.04GeV(IGRF)
Cdata/Cpred=1.0125�0.0174(stat.)�0.0134(sys.)
Absoluteenergyscale• ~1.25%aboveexpectation• ~2%at1σ level
Notcorrectionapplied,useassystematics
1. Reconstructedenergyspectrum
46XinWu
– Ni:numberofeventsobservedafterfiducial andselection cuts– Bi:numberofestimatedbackground– ei:efficiency ofallselectioncutsappliedafterthefiducialcut– Wi:binwidthinGeV(correctedreconstructedenergy)
Theelectron(e++e−)fluxmeasurement
– StatisticalerrorofNi andsystematic(+statistical)errorsofBi,Ai,εi,T
– Ai:acceptanceofthe“fiducial”cutincm2sr– T:livetimecorrespondingtothedataset(30.12.15-08.06.17,2.8billionsevents)
2. Unfoldingtotrueenergyspectrum– Detailedstudiesshowedsmearingeffectisnegligiblewithcorrectedenergy
(ΔE/E<1.5%above20GeV):
3. Acceptance andlivetimecorrection
4. Errorevaluation
Fouringredients:
LAL,1/06/2018
LAL,1/06/2018XinWu 47
Crosscheckswithindependentanalyses• 3independentanalyseshavebeenperformed,usingdifferent PID(e-p
separation)methods
– Showershape(ζ method):combinelateralandlongitudinalshowershapevariablestooneparameterζ
– Principalcomponentanalysis
– boosteddecisiontree
• Threemethodsgaveveryconsistent(withinthestatisticaluncertainties)resultsofthefinalelectronflux
Theanalysisoftheζ method is presented here
LAL,1/06/2018XinWu 48
Theglobalshowershapevariableζ• Electronshavenarrowerandshortshowers
– Lateralshowershape• sumRms =sumoftheshowerwidthofall14BGOlayers
– Longitudinalshowershape
• F last =ratiooflayerenergytototalBGOenergyofthelastlayerthathasenergy
5.6 TeV electron candidate
LAL,1/06/2018XinWu 49
Theglobalshowershapevariableζ• Electronshavenarrowerandshortshowers
– Lateralshowershape• sumRms =sumoftheshowerwidthofall14BGOlayers
– Longitudinalshowershape
• F last =ratiooflayerenergytototalBGOenergyofthelastlayerthathasenergy
sumRms [mm]
F last
• sumRms andF last arecombinedtoaglobal showervariable
ζ = F last� (sumRms)4 /(8� 106)
0.5– 1TeV0.5– 1TeV
goode/pseparation!
50XinWu
• Fiducialcuts– Defineacceptance
• Trigger:passedtheHighEnergyTrigger(HET)• Selection
– Pre-selection(cleanup)• Removelateralentry,largeshowerandsomeheavynucleiMIPstofacilitatebackgroundextrapolationlater
– Heavynucleiremoval:separatecutsfor2mutuallyexclusivesamples:track-matchedandBGOonly
• Track-matched:removingheavynucleiwithPSDandSTKcharge
• BGO-only:removingheavynucleiwithtop2BGOlayers
– Signalextractionusing theζ variable
Thecutflow
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51XinWu
• 3cutstoensure:– TheparticleenergyiswellcontainedintheBGO– Theparticleisenteringfromthetopofthedetector
• Fiducialcut1– BGOfull-span:showerdirectionextrapolatestowithin28cmfromthe
centeratthetopandthebottomsurfacesoftheBGOinbothXandY
• BGObarlengthis60cm
• Fiducialcut2– Removeevents inwhichtheBGObarwithmaximumenergyinsecond,
thirdandforthlayerisontheoutside(bar0or21)
• Fiducialcut3– Removeeventswithmax.layerenergy/totalenergydeposited>35%
Fiducialcuts
LAL,1/06/2018
Particle energy [GeV]210 310 410
sr]
2Ac
cept
ance
[m
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
Electron MC, fiducial
52XinWu
• Systematicsareevaluatedbycheckingthedata-MCconsistencyincutvariables– Residualdifferencesusedtoestimatesystematicuncertainties
• Totalerror2.2%,flatinenergy.MaincontributionfromtheBGOfull-spancut(2%)– BGOfull-spancutsystematics:thepreciselyreconstructedelectrontrackcan
beusedtoevaluatedtheextrapolationresolutionoftheshowerdirection– Data-MCdifferenceinextrapolationresolution~2mm→2% acceptancechange
Acceptance
~0.31m2sr, relativelyflatvs.energy
AcceptanceisevaluatedwithMC
LAL,1/06/2018
BGO corrected total energy [GeV]210 310
High
Ene
rgy
Trig
ger E
fficie
ncy
0
0.2
0.4
0.6
0.8
1
Data
Electron MC
53XinWu
• Triggerefficiencyisevaluatedfromthepre-scaledLowEnergytrigger
– UnbiasedfortheHighEnergyTrigger,validatedwithMC
– Crosscheckedwiththe(heavily)pre-scaledUnbiasedTrigger
• Theoverallagreement isexcellent.Differenceatlowenergycomesmainlyfromprotoncontaminationwhichhaslowertriggerefficiency
• MCefficiencyusedforfluxcalculation,halfofthedifferenceassystematics → 1.5%at25GeVand1%at2TeV
TriggerEfficiency
Veryhighefficiency,gooddata–MCagreement
LAL,1/06/2018
54XinWu
• Verylooseclean-upcuts– 2cutstoreduce largehadronshowerandlateralentryevents+1cut
toremoveheavynucleiMIPs
• maxRms <100mm– maxRms:themaximumwidthofalllayerswithenergy>1%ofthe
totalenergy
• Numberofhitsinthelastlayer(nBarLayer13)– nBarLayer13<8log(totalE)– 5
• nBarLayer13=numberofbarswithenergy>10MeVinthelastBGOlayer
• Lowenergycleaning cut (foreventswithrawenergy<250GeVonly)– AngulardependentlowercutonsumRms
Preselection
Preselectioncuts are highly efficient for signal (>99.9%), and have negligible (<0.03%) systematics uncertainties
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55XinWu
• Heavynucleicontaminationisnegligibleinthesignalregionindatabecauseoftheirlargeshowershape
• Butheavynucleishouldberemovedinthebackgroundregionofdata
– Bkg regionisusedtonormalize theζ templatefromprotonMC• Differentcutsareusedforeventswithandwithoutatrackmatch
– Track-matched:removingheavynucleiwithPSDandSTKcharge
• PSDbarisidentifiedbyextrapolatingtheSTKtracktothePSD
– BGO-only:removingheavynucleiwithtop2BGOlayers
Heavynucleiremoval
Cutsaredefinedtobe highly efficient for signal (>99%), and have negligible (<0.3%) systematics uncertainties
• Systematicsareevaluatedbydata-MCcomparisonofcutvariables
– Trackingefficiencyhasgooddata-MCagreement(seenextpage)
• Nosystematicassignedsinceevents failedtrackselectiongotothe"BGOonly"category
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XinWu 56
Signalextractionusingtheζ variable• Strategy
– Extractsmoothζ templatesofeachenergybinfromprotonMC,usinginterpolationacrossenergybinstoreducefluctuation,andthenfit
– Ineachenergybinofdata• Fittheprotonζ templatetodatainthebackgroundregion(20<ζ <100)• Subtractthenumberofbkg.inthesignalregion(ζ <8.5)predictedbythefittedtemplatetoobtainthesignal:Si=Ni–Bi
110– 126GeV 1– 1.11TeV 2.29– 2.63TeV
SignificantsignaluptoafewTeV
3examples.Total38binsfrom24GeVto4.57TeV
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Energy [GeV]210 310
Back
grou
nd fr
actio
n [%
]
5
10
15
20
25
30
35
40
45
50
DAMPE CRE selection
XinWu 57
Systematicsofbackgroundestimate• Sourcesofsystematicsconsidered
– Choiceofinterpolationfittingfunction– MCStatisticaluncertaintyininterpolationfit– Choiceofbinningofζ forinterpolationacrossenergybins– Choiceofcontrolregion
– Datastatisticaluncertaintyinthecontrolregionfit• CrosscheckedwiththemethodusingasimpleMCtransferfactor(TF)toscale
eventsfrombackgroundregiontosignalregion
Lowbackgroundfraction(2%- 18%)uptoafewTeV
InterpolationTFmethod
Energy
Numbe
rofbkg
even
tsex
pected
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XinWu 58
Validationoftheprotonζ distribution• Validationwith400GeVprotonsdatatakenattheCERNSPS
– TwoMChadronicmodelsarecompared:QGSPandFTFP
– Data-MChavegoodagreement(withinstatistics)
– Twohadronicmodelshavesimilardistributions
400GeVproton
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XinWu 59
Efficiencyandsystematicsoftheζ cut• Comparetheζ distributionofelectronMCtodataaftersubtractingthe
protonbackground
– Verygoodagreement ingeneral
– Smallenergy-dependent difference :-1.9%at25GeVto8.4%at2TeV
• Confirmedwith250GeVelectronCERNtestbeamdata
– MCefficiencyiscorrectedforthisdifference• Halfofthedifference istakenassystematics
Electron,flightdata144- 251GeV
Electron,testbeam250GeV
ζ distribution
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Energy [GeV]210 310
sr]
2Ef
fect
ive
Acce
ptan
ce [m
0
0.05
0.1
0.15
0.2
0.25
0.3
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0.4
DAMPE CRE selection
XinWu 60
Effectiveacceptanceandsystematics• Sincenounfoldingisneeded, theacceptanceandefficiencycanbe
multipliedtobecomethe“effective acceptance”
– Efficiencyissmoothvs.energy,dropofefficiencyduetotightcut
– Simpletightcut(ζ>8.5)toselectacleansampleforfirstpublication• Validatedwithloose(energydependent) cut→compatibleresults
– Future:multivariateanalysis(ML),Neutrondetector
NUDAD
Cζ
Energy
NUDADCLAL,1/06/2018
61XinWu
Summaryofalluncertainties• Acceptance:2.2%
– maincontributorBGOgeometricalacceptance
• Efficiency:1.8%(25GeV)- 9.4%(4.5TeV)– maincontributors:triggerandζ cut
• (Ni–Bi)”statisticalerror”:ΔNi isstat.,ΔBi issyst.andstat.(frombgk norm.)
– 25GeV:δ(Ni– Bi)=0.32%,negligible
– 2TeV:δ(Ni– Bi)=25.6%,dominatedbyδNi =24.2%(N=17)• T=34913811.6sec,estimatedfilebyfile,removeDAQd.t. (3.0725ms)and
operationaldowntime
– Twoindependentcalculationsagreewithin0.08%
• Totalsystematicsonflux:<10%– 2.8%(25GeV)to9.6%(4.5TeV)
Mostprecise~TeV measurement!
Plus�2%ofabsoluteenergyscaleuncertainty(→~5%shiftinflux)
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62XinWu
Systematicandstatisticaluncertainties
LAL,1/06/2018Statisticalerrordominating at~TeV,canbeimprovedwithmoredata
63XinWu
Nosaturationeffect
LAL,1/06/2018
NosaturationeffectinBGObarsuptomorethan300GeVperbar
Electroncandidates
Energy (GeV)10 210 310 410
)-1G
eV-1
sr-1 s-2
Flux
(m
10−10
9−10
8−10
7−10
6−10
5−10
4−10
3−10
2−10
1−10
1
10DAMPE (2017)
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DAMPEelectron+positron(CRE)flux
~8 ordersofmagnitude!
Energy (GeV)10 210 310 410
)-1G
eV-1
sr-1 s-2
Flux
(m
10−10
9−10
8−10
7−10
6−10
5−10
4−10
3−10
2−10
1−10
1
10DAMPE (2017)
H.E.S.S. (2008)
H.E.S.S. (2009)
AMS-02 (2014)
Fermi-LAT (2017)
CALET (2017)
LAL,1/06/2018XinWu 65
CREfluxcomparison
~8 ordersofmagnitude!
hardtoseethefeatures!
5-20% whereotherexperimentshave
comparableprecisions(<1TeV)
hardtotelldifferences!
Energy (GeV)310
)-1G
eV-1
sr-1 s-2
Flux
(m
10−10
9−10
8−10
7−10
6−10
5−10
4−10
3−10DAMPE (2017)broken power law
single power law
LAL,1/06/2018XinWu 66
Zoominto>100GeV
Abreakaround1TeV isclearlyobserved!
FitwithSmoothlyBrokenPower-Law
Breakatthisordercannotbecausedbytheenergyscaleuncertainty
Energy (GeV)310
)-1G
eV-1
sr-1 s-2
Flux
(m
10−10
9−10
8−10
7−10
6−10
5−10
4−10
3−10DAMPE (2017)
H.E.S.S. (2008)
H.E.S.S. (2009)
AMS-02 (2014)
Fermi-LAT (2017)
CALET (2017)
broken power lawsingle power law
LAL,1/06/2018XinWu 67
Zoominto>100GeV
Afacturearound1TeVisclearlyobserved!
FitwithSmoothlyBrokenPower-Law
AlsoindicatedbyH.E.S.SandCALET
Breakatthisordercannotbecausedbytheenergyscaleuncertainty
Energy (GeV)10 210 310 410
)2G
eV-1
sr-1 s-2
Flu
x (m
× 3 E
50
100
150
200
250
DAMPE (2017)H.E.S.S. (2008)H.E.S.S. (2009)AMS-02 (2014)Fermi-LAT (2017)CALET (2017)
LAL,1/06/2018XinWu 68
ScalingupthefluxbyE3
Easiertoseespectralchanges
Butalsodistortthespectrumandexaggeratefluctuations!
Twofeatureshaveemerged:• ahardeningat~30-50GeV• Abreakat~1TeV
Manyhypotheses→needmoredatafromDAMPE/AMS/CALET,
andHERD!
H.E.S.S:15%energyscaleerrornotincluded
Fermi:extraEdependenterrornotincluded
Energy (GeV)10 210 310 410
)2G
eV-1
sr-1 s-2
Flu
x (m
× 3 E
50
100
150
200
250
H.E.S.S. (2008)
H.E.S.S. (2009)
AMS-02 (2014)
Fermi-LAT (2017)
CALET (2017)
LAL,1/06/2018XinWu 69
ScalingupthefluxbyE3,beforeDAMPE
Easiertoseespectralchanges
Twofeatureshaveemerged:• ahardeningat~30-50GeV• Abreakat~1TeV
Manyhypotheses→needmoredatafromDAMPE/AMS/CALET,
andHERD!
H.E.S.S:15%energyscaleerrornotincluded
Butalsodistortthespectrumandexaggeratefluctuations!
LAL,1/06/2018XinWu 70
LatestAMSresultcompatiblewiththeTeV break
S.Ting,CERNcolloquium,May24,2018
Protonspectrumbeyond10TeV/nucleon
71LAL,1/06/2018XinWu
Anotherspectralhardening>1TeV?andasoftening>20TeV?
DAMPEprotonfluxupto100TeV inprogress
LAL,1/06/2018XinWu 72
PhotondetectionwithDAMPE• Whatarethosetungstenplatesfor? 2-yearskymap
(1– 100GeV)
Next:HERD(HighEnergyRadiationDetectionfacility)
73XinWu
– 5-sidesensitive� ~3 m2sr– Payload~4T(~0.5AMS)
• NextgenerationhighenergyparticledetectoronboardtheChineseSpaceStation– Cosmic-rayphysicsatTeV - PeV,DMsearch,highenergyγ-rayastronomy
– CRsourceidentification, anisotropy,compositon
– SimilartoDAMPE,butwithlargeracceptance
• LYSOcube3Dimagingcalorimeter
• Si/Fibertracker,withconverters
• Anti-coincidencedetector
• Chargemeasurements
~7500LYSOcrystals� 55X0 and3λ !LAL,1/06/2018mainparticipants:CN,IT,CH,launch~2025
LAL,1/06/2018XinWu 74
Conclusions• DAMPEisworkingextremelywellsince launchedmorethan2yearsago
– Apreciseelectron+positronfluxintheTeV regionhasbeenmeasured
• Aclearspectralbreakhasbeenobservedat~1TeV →anewpieceofpuzzletounderstandmanymysteriesincosmicrayphysics!
– Resultsonnucleimeasurements (protonfluxto100TeV!)comingsoon
– Photondetection capabilityisdemonstrated.Needmorestatistics toprofittheexcellentenergyresolutionathighenergy
• Spaceisthenewfrontierofparticlephysics
– Stillanexploratoryscience� groundbreakingmeasurements areexpected
• Experimentallychallengingbutmanyopportunities
– Opportunitiestoapplylatestparticledetection technologiestospace
– Opportunitiestodevelopspecializedandmulti-purposespacedetectorconcepts
– Close interplaybetweenparticlephysics,nuclearphysics,astrophysics,cosmology,solarphysics,spaceweather,spaceradiationdosimetry,planetaryexplorati…
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