Ultra- High Energy neutrinos at the Pierre Auger Observatory

Transcription

1 Ultra- High Energy neutrinos at the Pierre Auger Observatory Jaime Alvarez- Muñiz Univ. San?ago de Compostela, Spain for the Pierre Auger Collabora?on Very High Energy Par?cle Astronomy Kashiwa, Japan, 19 February 014 1

2 The Pierre Auger Southern Observatory: Malargüe, Mendoza (Argentina) 1600 water Cherenkov tanks 4 Fluorescence Buildings ~ 3000 km 35.5º S, 69.3º W 1400 m a.s.l. (880 g cm-)

3 Main aim of the Pierre Auger Observatory Characteriza?on of energe?c cosmic rays: arrival direc?ons energy spectrum nature of primaries: light, heavy? Informa?on crucial to: disentangle scenarios of UHECR origin determine reason for End of spectrum : a. maximum energy of CR sources? b. propaga?on effects? a. GZK? b. Photodisintegra?on? c. a & b ac?ng together? 3

4 Cosmogenic neutrinos Single flavour -4 p, best fit with Fermi-LAT bound (Ahlers) s -1 sr -1 ] - dn/de [ GeV cm p, FRII & SFR, E = max 0 Fe, FRII & SFR, E max =6 x ev (B. Sarkar) ev (B. Sarkar) p & mixed, SFR & GRB, E =Z x - max ev (Kotera) E E ν Detec?on in EeV range may provide complementary informa?on to direct UHECR detec?on on: UHECR nature (p, mixed, Fe), origin (evolu?on of the sources, maximum energy a^ainable, ) [ev]

5 Auger sensi?vity to UHE neutrinos Auger is not a dedicated neutrino observatory but with the surface detector we have good sensi?vity to UHE neutrinos at EeV energies and above. Challenge: Iden?fying neutrino- induced showers in the dominant background of showers induced by cosmic rays (p & nuclei). The interac?on probability & discrimina?on power is enhanced when looking at inclined showers: θ > 60 o 5

6 Inclined showers & UHE neutrinos Protons & nuclei ini?ate showers high in the atmosphere. Shower front at ground: mainly composed of muons electromagne?c component absorbed in atmosphere. Neutrinos can ini?ate deep showers close to ground. Shower front at ground: electromagne?c + muonic components Searching for neutrinos searching for inclined showers with electromagne?c component ν τ 6

7 Surface Detector (SD) sta?ons ü Sensi?ve to inclined showers. x Not directly sensi?ve to electromagne?c and muonic components. ü Can measure the?me structure of the signals induced by electrons and muons GPS Communications antenna 3 photomultiplier tubes electronics Solar panels Signals are digi?zed with 5 ns?me resolu?on Battery box VEM plastic tank 1 tons of purified water FADC trace Example of signal induced by a muon t (ns) 7

8 Iden?fying νs in data collected at SD With the SD, we can dis?nguish muonic from electromagne?c shower fronts (using the?me structure of the signals in the water Cherenkov sta?ons). signal [VEM] signal [VEM] signal [VEM] 6 4 PMT time [ns] 6 4 PMT time [ns] 6 4 PMT time [ns] signal [VEM] signal [VEM] signal [VEM] PMT time [ns] PMT time [ns] PMT time [ns] 8

9 Iden?fying νs in data collected at SD From the observa?onal point of view, signals extended in?me: Induce Time- over- Threshold (ToT) triggers in the SD sta?ons and/or Trace example: ToT trigger & large AoP Defini?on of Area- over- Peak (AoP) Have large Area- over- Peak value (AoP ~ 1 muonic front) Searching for neutrinos Searching for inclined showers with sta?ons with ToT triggers and/or large AoP 9

10 Sensi?vity to all flavours & channels

11 Methodology: general strategy DATA Monte Carlo Search sample Training sample Neutrino simulations ES or DGH or DGL Blind search for candidates Identification criteria (inclined & deep showers) No candidates Candidates Exposure Discovery: Neutrino flux Upper limit to neutrino flux 11

12 Selec?on of inclined showers: 3 observables (1) Elongated footprint () Apparent velocity V of propaga?on of shower front at ground along major axis L Ver?cal shower Horizontal shower V >> c V ~ c (3) Reconstructed θ 1

13 ν iden?fica?on: Earth- Skimming <AoP> = mean value of Area- over- Peak in the event Events 3 ν candidate if <AoP> > 1.83 Training data Exponential fit Monte Carlo ~ 90% of ν events selected <AoP> Neutrino searches not limited by background! 13

14 ν iden?fica?on: Down- going (75 o, 90 o ) Events Area- over- Peak of various sta?ons along with other observables constructed from AoP combined in a Fisher linear discriminant 4 3 Training data ν Monte Carlo ν candidate if Fisher > 3. 1 ~ 90% of MC ν events selected Fisher Value 14

15 ν iden?fica?on: Down- going (75 o, 90 o ) Events Area- over- Peak of various sta?ons along with other observables constructed from AoP combined in a Fisher linear discriminant 4 3 Training data ν Monte Carlo ν candidate if Fisher > 3. 1 ~ 85% of MC ν events selected Fisher Value 15

16 General strategy DATA Monte Carlo Search sample Training sample Neutrino simulations ES or DGH or DGL Blind search for candidates Identification criteria (inclined & deep showers) No candidates Candidates Exposure Discovery: Neutrino flux Upper limit to neutrino flux 16

17 Unblinding: Opening the box Summary of ν iden?fica?on cuts ν iden?fica?on cuts applied blindly to data: 1 Jan Dec 1 (excluding training data periods) No candidates found in Earth Skimming or Downward- going 17

18 ν search: Earth- Skimming analysis Events 3 ν candidate if <AoP> > 1.83 Search data up to 31 Dec 1 ν Monte Carlo 1 No events above cuts <AoP> 18

19 ν search: Down- going (75 o, 90 o ) Events 4 3 Search data up to 31 Dec 1 ν Monte Carlo 1 ν candidate if Fisher > 3. No events above cuts Fisher Value 19

20 General strategy DATA Monte Carlo Search sample Training sample Neutrino simulations ES or DGH or DGL Blind search for candidates Identification criteria (inclined & deep showers) No candidates Candidates Exposure Discovery: Neutrino flux Upper limit to neutrino flux 0

21 Combined exposure calcula?on: Earth- Skimming + Downgoing (60 o, 75 o ) & (75 o, 90 o ) 1

22 Exposure calcula?on: accoun?ng for a dynamical array Array status in Nov. 007 before construc?on ended (008). Neutrino simulated showers are thrown over a changing array Distance [Km] Distance [Km] 1 Shower fully contained, triggering and iden?fied as a neutrino. Shower outside array not triggering. 3 Shower not fully contained, triggering but not iden?fied as a neutrino. 4 Shower not fully contained, but triggering and iden?fied as a neutrino

23 Exposure: Earth- skimming ν τ 1. Tau neutrino propaga?on and tau produc?on: Dedicated MC for propaga?on of ν τ through the Earth producing emerging tau leptons. Convolute with probability of tau decay in the atmos. (exponen?al). Tau decay products obtained with TAUOLA generator: All decays included 17% BR to muons which are not detected 3. Shower induced by tau decay products simulated with AIRES 4. Detector simula?on performed with Auger Offline package Events E ντ = ev - Energy spectra of emerging τ θ = 90.1 deg. θ = 91. deg. θ = 94.8 deg log (E /ev) τ. TAUOLA 1. ν τ PROPAGATION 3. AIRES Mean Mean Mean OFFLINE 3

24 Exposure: 1 Jan Dec 1 (excluding training data periods) 18 PRELIMINARY s sr ] 17 Exposure [ cm E Sum of all Channels (6 yr of complete Auger) Earth-Skimming o Downward-going 75 < θ < 90 o Downward-going 60 < < 75 [ev] 19 θ 0 o o 4

25 General strategy DATA Monte Carlo Search sample Training sample Neutrino simulations ES or DGH or DGL Blind search for candidates Identification criteria (inclined & deep showers) No candidates Candidates Exposure Discovery: Neutrino flux Upper limit to neutrino flux 5

26 Limits to diffuse flux of UHEν s -1 sr -1 ] - Single flavour (90% CL) -4 dn/de [ GeV cm ν limits IceCube 013 Auger 013 RICE 01 ANITA-II 0 Cosmogenic ν models p, Fermi-LAT bound Fe, FRII & SFR evol. p & mixed Astrophysical sources AGN ν Waxman-Bahcall Pierre Auger PRELIMINARY E E ν dn/de = k E - k ~ 1.3 x 8 GeV cm - s - 1 sr % C.L ev < E < 0 ev 6 [ev]

27 Limits to diffuse flux of UHEν s -1 sr -1 ] - Single flavour (90% CL) -4 dn/de [ GeV cm ν limits IceCube 013 Auger 013 RICE 01 ANITA-II 0 Cosmogenic ν models p, Fermi-LAT bound p, FRII & SFR Fe, FRII & SFR evol. p & mixed Astrophysical sources AGN ν Waxman-Bahcall Pierre Auger PRELIMINARY E E ν [ev] Auger constrains on models with proton primaries & strong FRII evolu?on 7

28 Differen?al limits to diffuse flux of UHEν ] sr -1 s -1 - Single flavour (90% CL) dn/de [ GeV cm ν limits Full IceCube ( yr) Auger (6 yr) ANITA-II (8.5 days) ASHRA NTA (3 yrs) (expected) Cosmogenic ν models p, Fermi-LAT bound Fe, FRII & SFR evol. p & mixed Astrophysical sources AGN ν Waxman-Bahcall Pierre Auger PRELIMINARY E E ν [ev] All limits converted to single flavour and given per half a decade of energy 8

29 Rela?ve contribu?on of different channels to Auger limit PRELIMINARY 9

30 Expected number of events PRELIMINARY 30

31 Exo?c models of UHECR produc?on & limits Many exo?c models ruled out by Auger limits on νs (and photons). ] sr -1 s -1 - Single flavour (90% CL) dn/de [ GeV cm ν limits IceCube 013 Auger 013 RICE 01 ANITA-II 0 Exotic scenarios Z-burst (Kalashev) TD (Sigl) Pierre Auger PRELIMINARY E E ν [ev]

32 Systema?c uncertain?es PRELIMINARY Uncertain?es incorporated in the limit following the well- known Conrad approach. 3

33 Conclusions I Cosmogenic neutrinos at EeV energies provide complementary informa?on on UHECR origin and composi?on at s of EeV. SD of Auger sensi?ve to UHE neutrinos: Easy to iden?fy: inclined showers with broad fronts. Search NOT limited by background but by exposure. Sensi?vity peaks at ~ EeV (peak of cosmogenic neutrino fluxes). 33

34 Conclusions II Physics results from Auger neutrino limits relevant to the origin of UHECR: Limits below Waxman- Bahcall landmark. First shower array to achieve this benchmark. Protons from cosmological sources start to be constrained: p & FRII evolu?on disfavored. Top- down (exo?c) models strongly disfavored (when not excluded). More exposure needed to constrain UHECR produc?on at individual candidate sources. 34

35 Backup 35

36 Inclined showers 36

37 Data vs MC simula?ons W/L Distribution - Events above saturation - Zenith=(80,86 ) 0 0 Events -1 Auger data Proton QGSJET Iron QGSJET Mean RMS Mean RMS Mean RMS Width/Length 37

38 Efficiencies: Down- going (75 o, 90 o ) Trigger and identification efficiency for e CC channel: 87 o - 1 EeV Trigger Eff ID Eff slant depth g/cm ground top of atmosphere 38

39 Efficiencies: Earth- skimming Trigger and iden?fica?on probabili?es as a func?on of shower height h c at km from tau decay point Trigger Efficiency [%] E τ = 17 ev o Trigger ν iden?fica?on Trigger Efficiency [%] E τ = 18 ev Shower height at km from decay [km] Shower height at km from decay [km] Trigger Efficiency [%] E τ = 19 ev Trigger Efficiency [%] E τ = 0 ev Shower height at km from decay [km] Shower height at km from decay [km] 39

40 Point- like sources Frac?on of a day a source at declina?on δ is visible in the angular range of Earth- skimming (90 o, 95 o ) and Down- going (75 o, 90 o ) analysis Auger downward-going Auger Earth-skimming Fraction of a sidereal day [%] Source declination [deg] 40

41 Limits to UHEν: point- like sources Single flavour neutrino limits (90% CL) -5 Auger downward-going Auger Earth-skimming - ) [GeV cm F(E = E s -1 ] -6 k PS -7 E ν from 17 ev to 0 ev Source declination [deg] NOTE: Data from 1 Jan 04 up to 31 May only 41

42 Limits to UHEν from Centaurus A -4 Centaurus A - Single flavour neutrino limits (90% CL) s -1 ] - -5 Auger Downward-going LUNASKA 008 ) [GeV cm F(E -6-7 IceCube 011b Auger Earth-skimming Cuoco 008 = E -8 k PS -9 Kachelriess E [ev] NOTE: Data from 1 Jan 04 up to 31 May only 3 4

43 What if a ν candidate appears? Energy esfmate of a ν candidate: Only the energy of the ν- induced shower (E shower ) can be reconstructed ν flavour cannot be determined & E shower depends on flavour At best a lower bound to E ν because E ν > E shower ν can interact anywhere in atmosphere: E shower determina?on should include shower age No algorithm including age exists so far. Angular reconstrucfon of quasi- horizontal events: Not op?mized for deeply penetra?ng & very inclined showers (> 80 deg.). Angular resolu?on ~ 1- deg. Iden?fica?on of upgoing shower would indicate tau neutrino primary. Auger SD = discovery experiment (a counter of UHE neutrinos). 43