AMS a cosmic ray experiment in the ISS

Transcription

1 AMS a cosmic ray experiment in the ISS AMS status and results installed on ISS 19 May, 2011 Fernando Barao (fernando.barao@cern.ch) LIP, Instituto Superior Tecnico (Lisbon) Space Particles and Earth (IDPASC, Évora) Oct, 2015 Fernando Barao (1)

2 AMS on ISS: a long journey... STS-91 flight (Jun 98) BESS-POLAR (2004, ) FERMI (June 2008) PAMELA (June 2006) AMS to ISS (16-19 May 2011) Space Particles and Earth (IDPASC, Évora) Oct, 2015 Fernando Barao (2)

3 AMS02 on ISS AMS installed on ISS on 19 May 2011 Space Particles and Earth (IDPASC, Évora) Oct, 2015 Fernando Barao (3)

4 Cosmic Rays and space environment geomagnetic field, heliosphere Space Particles and Earth (IDPASC, Évora) Oct, 2015 Fernando Barao (4)

5 Cosmic ray fluxes p he e e + C p Space Particles and Earth (IDPASC, Évora) Oct, 2015 Fernando Barao (5)

6 AMS02 orbiting earth earth magnetic field - geomagnetic field defines a region of influence to charged cosmic rays - magnetosphere AMS is installed in the International Space Station and orbiting around earth 90 minutes orbit average rate of 700 Hz it is continously passing through different magnetic latitudes (λ) regular temperature variations RICH temperatures Tmax,Tmin <T> outer tracker layers displacement of hundreds of microns Tmax-Tmin corrections needed on detectors response and magnetic field 6 months: 22 May - 26 Nov 2012 Space Particles and Earth (IDPASC, Évora) Oct, 2015 Fernando Barao (6)

7 AMS02 tracker layers shifts short term (orbit) and long term (2 months) shifts of hundreds of micrometers observed on layer 1 and 9 of tracker alignment of tracker external layers is done continuously with a precision of few microns Space Particles and Earth (IDPASC, Évora) Oct, 2015 Fernando Barao (7)

8 CR fluxes: geomagnetic modulation there is a minimal rigidity (pc/ze) - rigidity cutoff - for a primary cosmic ray to be detected near earth transfer function detected proton rates measured at different geomagnetic latitudes drop at the rigidity cutoff values dn 1 t dr Rates vs Rigidity depending on Geomag Lat(θ M ) θ M [0.0;0.1] θ M [0.1;0.2] θ M [0.2;0.3] θ M [0.3;0.4] θ M [0.4;0.5] θ M [0.5;0.6] θ M [0.6;0.7] θ M [0.7;0.8] θ M [0.8;0.9] θ M [0.9;1.0] θ M [1.0;1.1] R(GV) 2 10 galprop Space Particles and Earth (IDPASC, Évora) Oct, 2015 Fernando Barao (8)

9 Cosmic Ray detection AMS detection principles Space Particles and Earth (IDPASC, Évora) Oct, 2015 Fernando Barao (9)

10 AMS02 detector and data AMS is orbiting around earth at around 400 Km of altitude and taking data since May detector: high redundancy on measuring particle observables on every day: around 40 million events gathered 100 GBytes to transfer every day at 10 Mb/s through relay satellites (TDRS) on every year: Triggers (Raw Data) 39 TB Raw Data Volume almost 65 billions of events gathered till now Space Particles and Earth (IDPASC, Évora) Oct, 2015 Fernando Barao (10)

11 AMS02 detector: charge measurement TOF 4 sci layers de/dx Z 2 Si TRACKER 9 Si layers de/dx Z 2 RICH Cerenkov rad N γ Z 2 Space Particles and Earth (IDPASC, Évora) Oct, 2015 Fernando Barao (11)

12 AMS02 detector: Z Tracker and TOF measurements de/dx on Tracker RICH Z rec Space Particles and Earth (IDPASC, Évora) Oct, 2015 Fernando Barao (12)

13 AMS02: β measurement TOF RICH 4 sci layers 4 time samplings t 140 psec (Z=1 (1/β) = 0.04 (Z=1) Cerenkov ring θ c reconstructed β/β 0.12 % (Z=1) γ particle TRDγ(β) sensitive ϕ i em radiation (Xrays) N γ γ e/p separation r i Space Particles and Earth (IDPASC, Évora) Oct, 2015 Fernando Barao (13)

14 AMS02 detector: E, p measurement MAGNET Si TRACKER magnetic field 0.14 T ± separation B/B= 0.09%/ C resolution 10µm (Y) 30µm (X) MDR 2TV (Z=1) ECAL 18 layers 3D showering 17 X 0 2 % resolution Space Particles and Earth (IDPASC, Évora) Oct, 2015 Fernando Barao (14)

15 AMS02 detector: E, p track resolution improves when external layers are used Momentum resolution (Z=1) energy resolution Space Particles and Earth (IDPASC, Évora) Oct, 2015 Fernando Barao (15)

16 AMS results nuclei, B/C, leptons, antiprotons Space Particles and Earth (IDPASC, Évora) Oct, 2015 Fernando Barao (16)

17 AMS02: nuclei Protons are the most abundant charged particles in cosmic rays Knowledge of the precise behavior of the proton spectrum is important in understanding the origin, acceleration, and propagation of cosmic rays Li, Be, B are of secondary origin their study provide information about CR propagation e +, p are of secondary origin and are considered "smoking guns" of Darkmatter good knowledge of primary fluxes and their propagation mechanism is crucial for defining DM reference background spectra downgoing particles β>0.3 data selection positive charge Z selected along particle trajectory TOF, L-1, L2-8 (inner), L9 tracker full tracker level arm (3 m) track quality cuts (χ 2 ) removes bad rigidity meas m rec > 0.5 GeV/c 2 removes interactions on top of ams Space Particles and Earth (IDPASC, Évora) Oct, 2015 Fernando Barao (17)

18 Flux calculation φ(r)= N(R, R+ R) ε(r) Acc(R) T(R) R N number of events ε(r) trigger efficiency T(R) 30 months Acc(R) acceptance (m 2.sr) T(R) exposure time full detector available to primaries, out of SAA, good DAQ,... R rigidity interval ε(r) protons Space Particles and Earth (IDPASC, Évora) Oct, 2015 Fernando Barao (18)

19 protons: results 300 million events progressive hardening of the spectrum above 100 GV γ (0.1 %) R GV (3 %) γ (20-30 %) Space Particles and Earth (IDPASC, Évora) Oct, 2015 Fernando Barao (19)

20 helium: selection charge selection Z=2 is made along all detector the proton background before imposing inner tracker selection is very small (10 4 ) estimated fraction of helium coming from carbon interactions on top of the detector Space Particles and Earth (IDPASC, Évora) Oct, 2015 Fernando Barao (20)

21 helium: results 50 million events progressive hardening of the spectrum above 100 GV p,he comparison R 0.08 Space Particles and Earth (IDPASC, Évora) Oct, 2015 Fernando Barao (21)

22 Li, Be, B produced by spallation lithium and B/C good probes of CR propagation Space Particles and Earth (IDPASC, Évora) Oct, 2015 Fernando Barao (22)

23 Positron data analysis selection primary particle: above cutoff Rig>1.2 R max cuto f f DAQ livetime above 50% (exclude SAA data) quality cuts on ECAL, TRK and TRD tracks tracker and calorimeter shower matching TRD track with min number of hits (15) singly charged particles (0.8 < Z < 1.4) ate least one e.m. shower within fiducial ECAL region backgrounds The shower topology cut (BDT cut >0.3) removes a large fraction of the proton background while keeping the e + signal very abundant protons ( 10 3 ) but with a very different mass and flavour can be discriminated with ECAL, TRK and TRD observables electrons ( 10) wrong-sign reconstructed spill-over effect due to tracker spatial resolution wrong hit-track association due to radiation Space Particles and Earth (IDPASC, Évora) Oct, 2015 Fernando Barao (23)

24 Positron identification with TRD the electron and proton track signal is sampled up to 20 times in TRD P e,p = n Π n i=1 pe,p i p e,p i ( L e = ln ) P e P e +P p : layer probability of an electron or proton signal deposition 90% e ± efficiency TRD estimator: L e,p Space Particles and Earth (IDPASC, Évora) Oct, 2015 Fernando Barao (24)

25 Positron identification with ECAL electron and proton create different "tracks" in electromagnetic calorimeter (ECAL) Boost Decision Tree (BDT) folds the different observables that can distinguish both particles, into one classifier 90% e ± ECAL efficiency E/P>0.75 The ECAL and Tracker detectors ensure a very high proton rejection Re j>10 4 from 3 to 500 GV Space Particles and Earth (IDPASC, Évora) Oct, 2015 Fernando Barao (25)

26 Positron selection The number of positrons in every energy bin is obtained: applying the ECAL shower topology cut (BDT) - energy dependent asking for positive (Q>0) and negative (Q<0) particles counting the number of positrons and electrons obtained from a fit on the two remaining discriminating observables: likelihood TRD estimator and E/p reference spectra from electron and proton testbeam samples wrong-sign events (charge confusion) spectrum taken into account TRD estimator < 0.75 Space Particles and Earth (IDPASC, Évora) Oct, 2015 Fernando Barao (26)

27 Positron fraction e + secondary production is expected to decrease monotonically while results indicate a persistent rise positron fraction starts to increase 8GeV r e += N e + N e ++ N e no particular structure identified a flattening of the positron fraction is observed at high energy 30 months of data (May.11-Nov.13) [ ] GeV Space Particles and Earth (IDPASC, Évora) Oct, 2015 Fernando Barao (27)

28 electron and positron fluxes positron flux above 20 GeV (no effect of solar modulation), the spectral indices for positrons and electrons are significantly different from 20 to 200 GeV, e + is significantly harder than e the increase with energy in the positron fraction is due to the hardening of positron spectrum and not to the softening of the electron spectrum above 10 GeV Space Particles and Earth (IDPASC, Évora) Oct, 2015 Fernando Barao (28)

29 Positron fraction: source needed a minimal fitting model: e+ and e fluxes are parametrized as the sum of individual diffuse power law spectra and the contribution of a single common source (with an energy cutoff) Space Particles and Earth (IDPASC, Évora) Oct, 2015 Fernando Barao (29)

30 positron sources secondary origin the diffuse positron spectrum originates from cosmic rays that undergo inelastic nuclear collisions the charged pions will decay into electrons and positrons the secondary spectra is steeper than the interacting cosmic rays due to energy loss other possible sources reacceleration of positrons inside supernova remnants pulsars dark matter annihilation in the galaxy supernova explosions of massive stars give rise to Pulsars (fast rotating magnetized neutron stars) solar masses R 13 Km electron-positron pairs are produced from sinchroton radiation emitted by electrons extracted from the star Space Particles and Earth (IDPASC, Évora) Oct, 2015 Fernando Barao (30)

31 SNRs and acceleration secondary production takes place in the same region where cosmic rays are being accelerated positrons are produced from primary CRs collisions in the accelerating SNR shock and through diffusion undergo acceleration (P. Blasi, PRL 103, (2009)) the maximum energy attainable E max is a free parameter: physics limit? arxiv (sarkar, 2014) Space Particles and Earth (IDPASC, Évora) Oct, 2015 Fernando Barao (31)

32 Pulsar injection spectrum pulsars g(e)=q 0 ( E0 E ) γ exp ( E/E c ) spectral index 2σ 1σ energy carried by e + arxiv: v1 (Giesen et al., 2015) Space Particles and Earth (IDPASC, Évora) Oct, 2015 Fernando Barao (32)

33 positrons from DM dark matter annihilations can produce electron-positron pairs directly or through q q pairs (hadronization) dark matter must satisfy some conditions to explain observed positron fraction absence of anomalies in antiprotons spectrum requires that the DM particle shall be leptophilic a large boosting factor associated with the DM annihilation (substructures) larger than numerical simulations of large scale structure formation indicate a large cross section (Sommerfeld, Breit-Wigner enhancements...) Space Particles and Earth (IDPASC, Évora) Oct, 2015 Fernando Barao (33)

34 q DM e (E)= 1 σv ( ) ρ(x) 2 dn + 2 m χ i B e+ i de i DM positrons no assumption about underlying DM model different annihilation channels fit to AMS02 positron fraction data arxiv: (Boudaud et al.) <σv> cm 3.s 1 Space Particles and Earth (IDPASC, Évora) Oct, 2015 Fernando Barao (34)

35 Conclusions AMS is up on space since May 2011 gathering aroung 15 billion events per year all detectors working at nominal conditions and performing well nuclei spectra analysis (p, he, li) show a breaking on power law spectra at around 200 GV different diffusion regimes? positron analysis indicates clearly that some "source" acceleration mechanism shall exist SNRs, pulsars, DM? antiproton ratio flat at high energy CR propagation models can explain it for the moment Space Particles and Earth (IDPASC, Évora) Oct, 2015 Fernando Barao (35)

36 Backup slides Space Particles and Earth (IDPASC, Évora) Oct, 2015 Fernando Barao (36)

37 protons: errors sources at 200 GV Trigger 0.2 % Acceptance 1.1 % Unfolding, Rigidity Resolution 0.95 % Rigidity Scale 0.7 % Space Particles and Earth (IDPASC, Évora) Oct, 2015 Fernando Barao (37)