1. Constraints to Dark Matter and cosmic ray propagation by the PAMELA space experiment Roberta Sparvoli University of Rome ”Tor Vergata” and INFN

2.  Roberta Sparvoli  October 8th, 2009  Como (Italy) Everything starts with …

3.  Roberta Sparvoli  October 8th, 2009  Como (Italy) Anti-nucleosyntesis WIMP dark-matter annihilation in the galactic halo Background: CR interaction with ISM CR + ISM  p-bar + … Evaporation of primordial black holes and various ideas of theoretical interpretations

4.  Roberta Sparvoli  October 8th, 2009  Como (Italy)

6. CR antimatter Antiprotons Positrons CR + ISM   ± + x   ± + x  e ± + x CR + ISM   0 + x    e ± Propagation dominated by energy losses (inverse Compton & synchrotron radiation) Local origin (@100GeV 90% from <2kpc) ___ Moskalenko & Strong 1998 Positron excess? Charge-dependent solar modulation Solar polarity reversal 1999/2000 Asaoka Y. Et al. 2002 ¯ + C R + I S M  p - b a r + … P r o p a g a t i o n d o m i n a t e d b y n u c l e a r i n t e r a c t i o n s K i n e m a t i c a l t h r e s h o l d : E t h ~ 5. 6 f o r t h e r e a c t i o n Experimental scenario before PAMELA WHAT DO WE NEED TO BETTER UNDERSTAND ? Measurements at higher energies Better knowledge of background High statistics Continuous monitoring of solar modulation Long Duration Flights

7.  Roberta Sparvoli  October 8th, 2009  Como (Italy) PAMELA pre-history

8.  Roberta Sparvoli  October 8th, 2009  Como (Italy) Moscow St. Petersburg Russia Sweden KTH, Stockholm Germany Siegen Italy BariFlorenceFrascatiTriesteNaplesRome CNR, Florence The PAMELA collaboration

9.  Roberta Sparvoli  October 8th, 2009  Como (Italy) p-bar, e + Halo PAMELA Scientific goals

10.  Roberta Sparvoli  October 8th, 2009  Como (Italy) PAMELA design performance energy range particles in 3 years Antiprotons 80 MeV ÷190 GeV O(10 4 ) Positrons 50 MeV ÷ 270 GeV O(10 5 ) Electrons up to 400 GeVO(10 6 ) Protons up to 700 GeVO(10 8 ) Electrons+positrons up to 2 TeV (from calorimeter) Light Nuclei up to 200 GeV/n He/Be/C:O(10 7/4/5 ) Anti-Nuclei search sensitivity of 3x10 -8 in anti-He/He Magnetic curvature & trigger spillover shower containment Maximum detectable rigidity (MDR)

11.  Roberta Sparvoli  October 8th, 2009  Como (Italy) PAMELA detectors GF: 21.5 cm 2 sr Mass: 470 kg Size: 130x70x70 cm 3 Power Budget: 360W Spectrometer microstrip silicon tracking system + permanent magnet It provides: - Magnetic rigidity  R = pc/Ze - Charge sign - Charge value from dE/dx Time-Of-Flight plastic scintillators + PMT: - Trigger - Albedo rejection; - Mass identification up to 1 GeV; - Charge identification from dE/dX. Electromagnetic calorimeter W/Si sampling (16.3 X0, 0.6 λI) - Discrimination e+ / p, anti-p / e - (shower topology) - Direct E measurement for e - Neutron detector 36 He3 counters - High-energy e/h discrimination Main requirements  high-sensitivity antiparticle identification and precise momentum measure + -

12.  Roberta Sparvoli  October 8th, 2009  Como (Italy) The Resurs DK-1 spacecraft

13.  Roberta Sparvoli  October 8th, 2009  Como (Italy)

15. PAMELA milestones Main antenna in NTsOMZ Launch from Baikonur  June 15th 2006, 0800 UTC. ‘First light’  June 21st 2006, 0300 UTC. Detectors operated as expected after launch Different trigger and hardware configurations evaluated  PAMELA in continuous data-taking mode since commissioning phase ended on July 11th 2006 Trigger rate* ~ 25 Hz Fraction of live time* ~ 75% Event size (compressed mode) ~ 5kB 25 Hz x 5 kB/ev  ~ 10 GB/day (*outside radiation belts) Today 1212 days in flight >14 TBytes of raw data downlinked >10 9 triggers recorded and under analysis

16.  Roberta Sparvoli  October 8th, 2009  Como (Italy) Antiproton/positron discrimination energy measurement

17.  Roberta Sparvoli  October 8th, 2009  Como (Italy) Antiparticle selection e-e-e-e- e+e+e+e+ p, d p ‘Electron’ ‘Hadron’

18.  Roberta Sparvoli  October 8th, 2009  Como (Italy) Antiprotons

19.  Roberta Sparvoli  October 8th, 2009  Como (Italy) Analyzed data July 2006 – February 2008 (~500 days) Collected triggers ~10 8 Identified ~ 10 10 6 protons and ~ 1 10 3 antiprotons between 1.5 and 100 GeV ( 100 p-bar above 20 GeV ) Antiproton/proton identification: rigidity (R)  SPE |Z|=1 (dE/dx vs R)  SPE&ToF  vs R consistent with M p  ToF p-bar/p separation (charge sign)  SPE p-bar/e - (and p/e + ) separation  CALO Dominant background  spillover protons: finite deflection resolution of the SPE  wrong assignment of charge-sign @ high energy proton spectrum harder than antiproton  p/p-bar increase for increasing energy (10 3 @1GV 10 4 @100GV)  Required strong SPE selection High-energy antiproton analysis

20.  Roberta Sparvoli  October 8th, 2009  Como (Italy) Proton-spillover background Electrons: efficiently removed by CALO Pions (from interactions in dome) : about 3% in the pbar sample

21.  Roberta Sparvoli  October 8th, 2009  Como (Italy) PAMELA: Antiproton-to-proton ratio PRL 102, 051101 (2009)

22.  Roberta Sparvoli  October 8th, 2009  Como (Italy) PAMELA: Antiproton-to-proton ratio PRL 102, 051101 (2009)

23.  Roberta Sparvoli  October 8th, 2009  Como (Italy) PAMELA: Antiproton-to-proton ratio New (preliminary) data ! Full statistics

24.  Roberta Sparvoli  October 8th, 2009  Como (Italy) PAMELA: Antiproton flux preliminary PAMELA

25.  Roberta Sparvoli  October 8th, 2009  Como (Italy) Positrons

26.  Roberta Sparvoli  October 8th, 2009  Como (Italy) High-energy positron analysis Analyzed data July 2006 – February 2008 (~500 days) Collected triggers ~10 8 Identified ~ 150 10 3 electrons and ~ 9 10 3 positrons between 1.5 and 100 GeV ( 180 positrons above 20 GeV ) Electron/positron identification: rigidity (R)  SPE |Z|=1 (dE/dx=MIP)  SPE&ToF  =1  ToF e - /e + separation (charge sign)  SPE e + /p (and e - /p-bar) separation  CALO Dominant background  interacting protons: fluctuations in hadronic shower development     might mimic pure em showers proton spectrum harder than positron  p/e + increase for increasing energy (10 3 @1GV 10 4 @100GV)  Required strong CALO selection S1 S2 CALO S4 CARD CAS CAT TOF SPE S3 ND

27.  Roberta Sparvoli  October 8th, 2009  Como (Italy) Positron identification with CALO Identification based on: – Shower topology (lateral and longitudinal profile, shower starting point) – Total detected energy (energy-rigidity match) Analysis key points: – Tuning/check of selection criteria with: test-beam data simulation flight data  dE/dx from SPE & neutron yield from ND – Selection of pure proton sample from flight data (“pre-sampler” method): Background-suppression method Background-estimation method Final results make NO USE of test-beam and/or simulation calibrations. The measurement is based only on flight data with the background-estimation method 51 GV positron 80 GV proton

28.  Roberta Sparvoli  October 8th, 2009  Como (Italy) Particle selection after total energy cut and starting point of the shower + - e+e+ e - p (anti p)

29.  Roberta Sparvoli  October 8th, 2009  Como (Italy) PAMELA: Positron fraction NATURE 458, 697, 2009 Solar modulation effects Anomalous increasing ? (Moskalenko & Strong 1998) GALPROP code Plain diffusion model Interstellar spectra

30.  Roberta Sparvoli  October 8th, 2009  Como (Italy) PAMELA: Positron fraction wrt other exp’s NATURE 458, 697, 2009

31.  Roberta Sparvoli  October 8th, 2009  Como (Italy) Different statistical approaches for the bkg Data: July 2006  December 2008

32.  Roberta Sparvoli  October 8th, 2009  Como (Italy) New data + systematic error Data: July 2006  December 2008 In publication on APP !

33.  Roberta Sparvoli  October 8th, 2009  Como (Italy) PAMELA antimatter data: Do we have any antimatter excess in CRs?

34.  Roberta Sparvoli  October 8th, 2009  Como (Italy) Antiproton-to-proton ratio Secondary Production Models No evidence for any antiproton excess NB! Solar modulation Nuclear cross-section … CR + ISM  p-bar + … ~20%  Uncertainty band related to propagation parameters (~10% @10 GeV)  Additional uncertainty of ~25% due to production cs should be considered !!

35.  Roberta Sparvoli  October 8th, 2009  Como (Italy) Positron fraction Secondary Production Models CR + ISM   ± + …   ± + …  e ± + … CR + ISM   0 + …    e ± Increasing positron fraction only if  e -  p > 0.6  unlikely (Serpico 2008) Quite robust evidence for a positron excess

36.  Roberta Sparvoli  October 8th, 2009  Como (Italy) Primary positron sources Dark Matter e + yield depend on the dominant decay channel  LSPs (SUSY) seem disfavored due to suppression of e + e - final states  low yield (relative to p-bar)  soft spectrum from cascade decays  LKPs seem favored because can annihilate directly in e + e -  high yield (relative to p-bar)  hard spectrum with pronounced cutoff @ M LKP (>300 GeV) Boost factor required to have a sizable e + signal  NB: constraints from p-bar data!! Other hypothesys possible and under study (i.e. Minimal DM Model, decaying DM, new gauge bosons, …) LKP -- M= 300 GeV (Hooper & Profumo 2007) More than 150 articles claim DM is discovered !

37.  Roberta Sparvoli  October 8th, 2009  Como (Italy) Example: dark matter

38.  Roberta Sparvoli  October 8th, 2009  Como (Italy) Primary positron sources Astrophysical processes Local pulsars are well-known sites of e + e - pair production (t he spinning B of the pulsars strips e- that emit gammas then converting to pairs trapped in the cloud, accelerated and then escaping at the Poles) :  they can individually and/or coherently contribute to the e + e - galactic flux and explain the PAMELA e + excess (both spectral feature and intensity)  No fine tuning required  if one or few nearby pulsars dominate, anisotropy could be detected in the angular distribution  possibility to discriminate between pulsar and DM origin of e + excess All pulsars (rate = 3.3 / 100 years) (Hooper, Blasi, Seprico 2008)

39.  Roberta Sparvoli  October 8th, 2009  Como (Italy) Example: pulsars

40.  Roberta Sparvoli  October 8th, 2009  Como (Italy) Explanation with supernovae remnants Shaviz and al. astro-ph.HE 0902.0376

41.  Roberta Sparvoli  October 8th, 2009  Como (Italy) Positrons from old SNR’s P. Blasi 0903.2794

42.  Roberta Sparvoli  October 8th, 2009  Como (Italy) Standard Positron Fraction Theoretical Uncertainties T. Delahaye et al., arXiv: 0809.5268v3 γ = 3.54γ = 3.34 Need for high statistics CR measurements

43.  Roberta Sparvoli  October 8th, 2009  Como (Italy) Electrons Any positron source is an electron source too …

44.  Roberta Sparvoli  October 8th, 2009  Como (Italy) Recent claims of (e + +e - ) excess FERMI does not confirm the ATIC bump but finds an excess wrt conventional diffusive models  = 3.0

45.  Roberta Sparvoli  October 8th, 2009  Como (Italy) PAMELA electron flux measurements wrt other experiments Key points wrt other experiments (ATIC, HESS, FERMI) :  Combination of CALO and SPECTROMETER allow energy self- calibration in flight  no dependence on ground calibrations or MC simulations  Very deep CALO (16 X 0 )  containment of the shower maximum beyond 1 TeV  Neutron detector help proton rejection, especially at high energy  No atmospheric contamination  Possibility to disentangle electrons from positrons But..  Smaller acceptance  lower statistics

46.  Roberta Sparvoli  October 8th, 2009  Como (Italy) PAMELA electron flux preliminary

47.  Roberta Sparvoli  October 8th, 2009  Como (Italy) PAMELA electron flux wrt other exp’s preliminary

48.  Roberta Sparvoli  October 8th, 2009  Como (Italy) PAMELA electron flux preliminary Primary source ??? Data ready by the end of the year

49.  Roberta Sparvoli  October 8th, 2009  Como (Italy) Protons, nuclei, …

50.  Roberta Sparvoli  October 8th, 2009  Como (Italy) Galactic protons and Helium fluxes p He preliminary

51.  Roberta Sparvoli  October 8th, 2009  Como (Italy) PAMELA proton and helium fluxes preliminary

52.  Roberta Sparvoli  October 8th, 2009  Como (Italy) Proton flux compared to prev. exp’s

53.  Roberta Sparvoli  October 8th, 2009  Como (Italy) PAMELA secondary/primary nuclei ratios

54.  Roberta Sparvoli  October 8th, 2009  Como (Italy) PAMELA secondary/primary nuclei ratios preliminary

55.  Roberta Sparvoli  October 8th, 2009  Como (Italy) Solar modulation Interstellar spectrum July 2006 August 2007 February 2008 Decreasing solar activity Increasing GCR flux sun-spot number Ground neutron monitor PAMELA (statistical errors only)

56.  Roberta Sparvoli  October 8th, 2009  Como (Italy) Solar modulation

57.  Roberta Sparvoli  October 8th, 2009  Como (Italy) Low energy e + : charge dependent solar modulation effects

58.  Roberta Sparvoli  October 8th, 2009  Como (Italy) A > 0 Positive particles A < 0 ¯ + Charge dependent solar modulation

59.  Roberta Sparvoli  October 8th, 2009  Como (Italy) Summary ~40 14

60.  Roberta Sparvoli  October 8th, 2009  Como (Italy) Summary PAMELA positron fraction alone insufficient to understand the origin of positron excess Additional experimental data will be provided by PAMELA: – e+ fraction @ higher energy (up to 300 GeV) – individual e- and e+ spectra – anisotropy (…maybe) – high energy e + +e - spectrum (up to 2 TV) Complementary information from: – gamma rays – neutrinos PAMELA mission extended to end 2011 ! It will be possible to constrain further the nature of DM and models of cosmic ray propagation in the Galaxy.