Exploring the Cosmos with the Amanda/IceCube ν Observatory

Transcription

1 Exploring the Cosmos with the Amanda/IceCube ν Observatory Nick van Eijndhoven A. Achterberg, M.R. Duvoort, J. Heise, N. Langer, G. t Hooft Department of Physics and Astronomy, Utrecht University Princetonplein 5, NL-3584 CC Utrecht, The Netherlands nick@phys.uu.nl nick Overview Cosmic rays 1 Possible high-energy sources 7 Observation of high-energy photons 8 Hunting for neutrinos 11 The Amanda experiment 13 The IceCube Neutrino Observatory 29 Outlook 35

2 Cosmic rays Observations : Charge leaks slowly from capacitors Effect is smaller when shielded Idea : Air gets ionised by charged particles Where do these particles come from? From outer space (Hess 1912) What sort of particles are these? Cosmic ray experiments Nikhef, 02-dec-2005 Physics Colloquium 1 Nick van Eijndhoven

3 Cosmic rays Cosmic ray spectra Below 1 GeV Solar modulation At higher energies we observe Proportions of major components relatively constant with energy Iron seems to be special dn de E 2.7 Boron spectrum falls steeper B is a spallation product of C and O Secondary (e.g. spallation) nuclei steeper than primaries sec./prim. decreases as energy increases High E rays diffuse out of galaxy faster What is the maximum energy? Nikhef, 02-dec-2005 Physics Colloquium 2 Nick van Eijndhoven

4 Cosmic rays E 2.7 scaled flux Spectral features observed (knee, ankle) E limits of different cosmic accelerators? What are these cosmic accelerator sites? Rather large uncertainties in flux Due to different exp. and models (see later) What is the cosmic acceleration mechanism? Nikhef, 02-dec-2005 Physics Colloquium 3 Nick van Eijndhoven

5 Cosmic rays Shock wave acceleration Shock front due to an explosive event Number of particles with energy above E Thin matter sheet with v > v sound N(> E) P k stay bulk motion ( v) after the shock = (1 P esc) n P esc Let a particle enter downstream of the shock and pass the front Energy gain E = αe (α v/c) May backscatter downstream again process may be repeated Multy-step particle acceleration Start energy E 0 and escape prob. P esc After n encounters : E n = E 0 (1 + α) n n = ln(e/e 0) to reach energy E ln(1+α) and P stay = (1 P esc ) n k=n Resulting in a spectrum N(> E) 1 P esc ( E E 0 ) β where β = ln(1 P esc) ln(1+α) P esc α Indeed a powerlaw spectrum is obtained! Note : P esc is related to mean free path Spectral slope β (σ density) 1 Where do we find shock waves? Nikhef, 02-dec-2005 Physics Colloquium 4 Nick van Eijndhoven

6 Cosmic rays Supernova blast waves Moving charge in static magnetic field p ZeB Gyroradius r = ( p B) ( p ) 1 TeV = Z ( ) ( B r 1 G 1 m Shock wave : extra factor (Γβ) shock Accelerator of size R Origin of cosmic rays ) Particles escape when r > R E max Typical values : B µg R 10 pc Protons : E max PeV ( knee ) At fixed r E Z = ZE proton E > 10 7 TeV r > R galaxy Extra-galactic origin What causes the slope change and ankle? Change in composition? How can E > ev exist? (GZK) Modification of cross sections? (LHC) Incorrect energy determination? Nikhef, 02-dec-2005 Physics Colloquium 5 Nick van Eijndhoven

7 Cosmic rays Analysis of cosmic ray cascades Only sec. from atm. interactions observed A dependence (composition) Properties of shower development Multidim. (N e, N µ ) shower analysis 1. At prim. vertex : π, K, Λ, Ξ, D, At shower maximum : large N e 3. After max. : meson decays µ, ν µ 4. Even later : µ decays e, ν e, ν µ With increasing primary E Maximum closer to detector (D max ) D max from e.g. fluorescence meas. Larger sec. energies longer lifetimes N e /N µ increases N e /N µ (E/A) α (α > 0) N e A(E/A) β (β > α) N µ A α/β N 1 α/β e Heavy primaries Muon rich showers Set scale limits by p and Fe N e /N µ (and D max ) A E Quantitative analysis MC needed Large discrepancies between various models Data needed to validate/tune models CERN-LHC might provide insight here Physics E(Z) or cascade E(A) effect? Nikhef, 02-dec-2005 Physics Colloquium 6 Nick van Eijndhoven

8 Possible high-energy sources Generic AGN (GRB) picture Processes in the jet Acceleration via shock waves in the jets Jet directed to us Blazar Markarian 421 and 501 High-energy photons and neutrinos Nikhef, 02-dec-2005 Physics Colloquium 7 Nick van Eijndhoven

9 Observation of high-energy photons Compton Gamma Ray Observatory COMPTEL (sky maps, spectroscopy) Compton Telescope Wide field 1-30 MeV EGRET (AGN, GRBs, Pulsars) Energetic Gamma Ray Exp. Telescope Wide field 20 MeV - 30 GeV OSSE (X-ray sources, QSO spectra, SNe) Oscillating Scintillation Spectrometer Exp. Narrow field ( ) 50 kev - 10 MeV BATSE (All sky monitor, GRBs) Burst and Transient Source Experiment Wide field (8 elements) 20 kev - 30 MeV Nikhef, 02-dec-2005 Physics Colloquium 8 Nick van Eijndhoven

10 Observation of high-energy photons The WHIPPLE gamma ray telescope Ground based (Arizona, USA) Reflective 10 meter diameter dish Cerenkov radiation from air showers Field of view : 3 0 Shower energy 100 GeV - 10 TeV Nikhef, 02-dec-2005 Physics Colloquium 9 Nick van Eijndhoven

11 Observation of high-energy photons Observations of Markarian 421 Markarian 421 : AGN at a distance of about 100 Mpc (z = 0.031). Discovered in 1991 by TeV gamma rays (Nature 160 (1992) 477). Observed by EGRET ( ) and Whipple : Flare at may (ApJ 438 (1995) L59. ApJS 94 (1994) 551.) EGRET (E γ > 100 MeV) : constant flux of (1.7 ± 0.3) 10 7 photons cm 2 s 1 Whipple (E γ > 250 GeV) : average flux of (2.3 ± 0.3) photons cm 2 s 1 Flux during 1994 flare : (2.1 ± 0.3) photons cm 2 s 1 Can the fireball model be probed? in other words : Can we indicate hadronic processes in these objects? Nikhef, 02-dec-2005 Physics Colloquium 10 Nick van Eijndhoven

12 Hunting for neutrinos Neutrino production mechanism All produced leptons about same energy E ν 4%E p 400 TeV Photons from π 0 decays E γ 10%E p 1 PeV E γ degraded in dense medium (Compton and γγ e + e ) High energy : ν µ flux comparable to γ flux See talk of Francis (Phys. Rep. 258 (1995) 173) production threshold : E γ 10 ev (UV photons) Point sources with high-energy γ and ν flux Can we identify them in the sky? Nikhef, 02-dec-2005 Physics Colloquium 11 Nick van Eijndhoven

13 Hunting for neutrinos Neutrino detection mechanism < α > / E ν (E ν in TeV) Directional info from detected µ On average E µ E ν E ν spectrum might be investigated ν cross section σ tot /E 10 fb GeV 1 high-e ν interactions inside detector Better energy measurement Main background Atmospheric muons Take upgoing µ need good time resol. Softer spectrum use E threshold Atmospheric ν (CR charm production) Cross sections not known at CR energies Can very likely be measured al LHC (Alice) Nikhef, 02-dec-2005 Physics Colloquium 12 Nick van Eijndhoven

14 The Amanda experiment Nikhef, 02-dec-2005 Physics Colloquium 13 Nick van Eijndhoven

15 The Amanda experiment Amanda A ( ) 0.8 1km 4 strings 73/80 8 PMTs (d=10 m) gain 10 8 noise 1500 Hz λ abs 300 m at 0.8 km ( 400 nm) Eff. λ scat cm ( m) bubbles air hydrate Xtalls 1450 m Amanda B ( ) km 10 4 m 2 10 strings 289/302 8 PMTs gain 10 9 noise 400 Hz σ τ 5 ns λ abs 150 m (dust) Eff. λ scat 24 m (no bubbles) Amanda II ( ) 10 5 m PMTs (19 strings) λ abs > 200 m (less dust > 2 km) Eff. λ scat > 40 m ϑ 3 0 Nikhef, 02-dec-2005 Physics Colloquium 14 Nick van Eijndhoven

16 The Amanda experiment The two Amanda DAQ systems The standard µdaq (since 1997) TDCs record arrival time of PMT pulses Only max. 8 leading edges per trigger ADCs record max. of PMT amplitude Only 1 (peak) amplitude per event Dynamic range extends to N pe 30 Measured in time window of 2 µs Hardware based trigger logic (DMADD) (Discriminator and Multiplicity ADDer) Transient Waveform Recorders (since 2003) FADCs (12 bit, 100 MHz) record complete PMT waveform Integrated charges of all PMT pulses Dynamic range extends to N pe 100 Measured in time window of µs Software based trigger logic Allows for more complex triggers Easy integration with IceCube ATWD Nikhef, 02-dec-2005 Physics Colloquium 15 Nick van Eijndhoven

17 The Amanda experiment The Amanda basic trigger systems The standard µdaq trigger Trigger criteria Mult. M 24 record event M < 24+local coinc. record event Local coincidence (string) trigger Next neighbour on same string fired Rate : 100 Hz 1 TB/year Mostly atmospheric muons Deadtime 15% The new TWR trigger Uses DMADD as source (for testing) Trigger criteria M 18 record event M < 18+local coinc. record event Local coincidence trigger 1 hit OM within 90 m N 1hit + + N pair no. local coinc. pairs N 1hit > 5 or N pair > 8 record event Rate : 195 Hz 15 TB/year (Huffman compression) Deadtime 0.015% Nikhef, 02-dec-2005 Physics Colloquium 16 Nick van Eijndhoven

18 The Amanda experiment Graphical representation of the Amanda basic trigger systems TWR system has performed very well (ICRC2005) µdaq will be phased out Further upgrade/tuning of TWR-DAQ Reduce min. multiplicity Reduce energy threshold New pattern recognition algorithms (a la local coinc.) to remove background Send trigger signals to IceCube Full integration into IceCube DAQ Nikhef, 02-dec-2005 Physics Colloquium 17 Nick van Eijndhoven

19 The Amanda experiment Upgoing µ in Amanda Low noise and scattering at large depths Good directional information Ready for (astroparticle)physics Atmospheric neutrinos oscillations? Study multi-muon showers Supernova watch Search for pointsources Correlations with GRB events Pilot project for larger (km 3 ) detectors IceCube+IceTop Nikhef, 02-dec-2005 Physics Colloquium 18 Nick van Eijndhoven

20 The Amanda experiment Reconstruction ingredients Level 0 (trigger N ch > 16) Hit cleaning (noise removal) Track ansatz from first guesses Level 1 (N direct > 2) Level 2 (track length > 75 m) further selection levels max. likelihood for µ track yields direction (up-down) angular cuts etc... Focus on upgoing muons What has been observed so far? ApJ 583 (2003) 1040 & ICRC2005 Skyviewer 815 events and potential sources Excesses above atm. background? Can we identify pointsources? Blind optimisation of signal/background Need a description of the background Need a signal flux estimate Point-source search with optimised cuts Nikhef, 02-dec-2005 Physics Colloquium 19 Nick van Eijndhoven

21 The Amanda experiment Monte Carlo simulation to model the background Use observed cosmic ray spectrum to simulate atmospheric µ and ν background Hadronic interactions : CORSIKA-QGSJET Muon propagation : MUDEDX Checked against data at each selection level Fair description for optimising cuts Nikhef, 02-dec-2005 Physics Colloquium 20 Nick van Eijndhoven

22 The Amanda experiment Cosmic neutrino flux estimate Shock wave acceleration : dn de = αe 2 cm 2 s 1 sr 1 GeV 1 (α = constant) E. Waxman, Astrophys. J. 452 (1995) L1 E. Waxman and J. Bahcal, Phys. Rev. D59 (1999) A. Achterberg et al., Mon. Not. Roy. Astron. Soc. 328 (2001) 393 EGRET : Mrk 421 γ spectral index (1.9 ± 0.1) (agrees with model) High-E ν and γ fluxes comparable Use Mrk 421 γ data to determine α N = αe 2 de = [ αe 1] E max E min EGRET : E γ > 100 MeV dω = sr N γ = (1.7 ± 0.3) 10 7 cm 2 s 1 Whipple : E γ > 250 GeV dω = sr N γ = (2.3 ± 0.3) cm 2 s 1 α E = (1.3 ± 0.2) 10 7 α W = (1.7 ± 0.3) 10 7 cm 2 s 1 sr 1 GeV Benchmark cosmic ν flux : E 2 dn de = 10 7 cm 2 s 1 sr 1 GeV Nikhef, 02-dec-2005 Physics Colloquium 21 Nick van Eijndhoven

23 The Amanda experiment Point-source signal/background optimisation Use hardness of spectra via N ch cut Signal E 2 Bkg E 3 Use angular resolution of Amanda Small bin cuts Bkg, but keeps the signal Simulate signal from E 2 ν spectrum True and rec. µ angular difference (Ψ) Angular bins as small as 4 0 may be used Optimise to maintain good statistics Nikhef, 02-dec-2005 Physics Colloquium 22 Nick van Eijndhoven

24 The Amanda experiment Amanda point-source analysis Look for event clustering in angular bins Optimal size of search bins Excess of 5σ over Bkg Discovery Upward fluct. of Bkg : P ( of 1-sided norm. Gaussian > 5σ) N 0 min. # obs. events for 5σ effect Bkg. expectation : < n b > µ For a discovery (n obs N 0 ) we need : n=n 0 P DF bkg (n µ) Assume Poisson distr. for the background P DF bkg (n µ) = µn e µ n! Slices of in declination Construct bins with equal solid angle 30 bins at horizon 3 at δ = non-overlapping bins Detector located at South Pole Equal, time-indep. sky coverage for all δ Investigation of bin i in decl. slice δ j (NvE, W.Wetzels NIM A482 (2002) 513) µ i < n obs > in all other bins in δ j Significance ξ i 10 log(p i ) with P i (n n obs,i ) = µn i e µ i n! n=n obs,i Nikhef, 02-dec-2005 Physics Colloquium 23 Nick van Eijndhoven

25 The Amanda experiment Background fluctuation estimate (NvE, W.Wetzels NIM A482 (2002) 513) Randomise r.a. coord. of the data events Re-calculate the ξ i again Prevent bin-edge effects Re-analyse with shifted grid ( 1 2 bin) Point-source candidates should show Large significance value Large data/bkg ratio Largest observed ξ value : % prob. to be random Bkg fluctuation No evidence for a point-source Absence of signal ν flux limit But we observed something else... Nikhef, 02-dec-2005 Physics Colloquium 24 Nick van Eijndhoven

26 The Amanda experiment Orphan Gamma-Ray flares observed for 1ES Hegra (E γ > 2 TeV) observations Whipple (E γ > 600 GeV) data Amanda analysis : Frequentist approach Blind analysis used to determine sensitivity Investigate deviations from expected Bkg Otherwise : stat. evaluation impossible 2 ν events observed in flare period A-posteriori analysis in 2 0 bin Observation violates blindness principle Wait for new data Nikhef, 02-dec-2005 Physics Colloquium 25 Nick van Eijndhoven

27 The Amanda experiment Minimum flux which can be detected Flux limit determination Consider a source model flux Φ s providing a signal expectation < n s > N 0 minimum # observed events for a 5σ significance Scale Φ s such that < n s > + < n b >= N 0 yields minimum detectable flux Φ 5σ Flux upper limit In case NO events are observed above background provide upper limit for source model G.Feldman & R.Cousins, Phys. Rev. D57 (1998) 3873 Generic method based on < n b > to quantify the sensitivity of an experiment by providing µ cl maximum # of events that can be excluded at a given confidence level Experiment can constrain any model that predicts at least < n s >= µ cl signal events Assume arbitrary source spectrum Φ s predicting < n s > signals µ 90 90% confidence level flux limit Φ 90 = Φ s < n s > Nikhef, 02-dec-2005 Physics Colloquium 26 Nick van Eijndhoven

28 The Amanda experiment Flux measurements involve N obs, Area, T exposure, Efficiencies Need for Monte Carlo simulations A eff (E µ ) signal rate/incident flux Need to fold-in several effects Φ source, σ cc νn (E ν) and det. response Energy-averaged effective area < A eff > (10 GeV - 10 PeV) Nikhef, 02-dec-2005 Physics Colloquium 27 Nick van Eijndhoven

29 The Amanda experiment Pointsource with a flux Φ s and signal expectation < n s > µ 90 90% c.l. limit Φ 90 = Φ s < n s > Energy-averaged 90% c.l. flux limit µ 90 Φ 90 = T live ε bin < A eff > ε bin accounts for angular resolution and possible non-central location of source Flux limits for an E 2 source spectrum Amanda-B10 data : ϑ = 4 0 T live = days Amanda-II : ϑ = 3 0 IceCube : ϑ = 1 0 T live 1 year T live 1 year 90% c.l. flux limits Atm. ν fluxes for 3 0 and 1 0 Quest for larger detectors Nikhef, 02-dec-2005 Physics Colloquium 28 Nick van Eijndhoven

30 The IceCube Neutrino Observatory Nikhef, 02-dec-2005 Physics Colloquium 29 Nick van Eijndhoven

31 The IceCube Neutrino Observatory Instrumented volume of 1 km 3 80 strings of 60 modules each Amanda will form an integral part of it Nikhef, 02-dec-2005 Physics Colloquium 30 Nick van Eijndhoven

32 The IceCube Neutrino Observatory Nikhef, 02-dec-2005 Physics Colloquium 31 Nick van Eijndhoven

33 The IceCube Neutrino Observatory Use Monte Carlo simulation to determine expected signals in IceCube Same sim. and reco. procedures as for Amanda Angular resolution of 1 0 Benchmark cosmic ν flux to model source signal : E 2 dn de = 10 7 cm 2 s 1 sr 1 GeV Resulting ν induced muons in IceCube Different curves : various levels of event selection (Astropart. Phys. 20 (2004) 507) Signal/background ratio is energy dependent Optimise by N ch and angular bin Nikhef, 02-dec-2005 Physics Colloquium 32 Nick van Eijndhoven

34 The IceCube Neutrino Observatory Multiplicity dependence at level 2 We can investigate flux limits like before (Use worst case charm contribution) Obtain 90% c.l. flux upper limit Φ 90 Recall : Scaling of model flux Φ s minimum detectable flux Φ 5σ If a Φ 5σ source is present : Atm. ν uncertainty due to charm Within a 1 0 circular angular bin N ch > 30 provides tolerable signal/bkg Introduces 1 TeV energy threshold Probability P 5σ to have n obs N 0 n=n 0 P (n < n s > + < n b >) Underlying signal strength not always produces a 5σ significance, but... we can determine the signal strength such that P 5σ gets close to certainty (e.g. needed flux to obtain P 5σ = 80%, 90%, 95%,...) Nikhef, 02-dec-2005 Physics Colloquium 33 Nick van Eijndhoven

35 The IceCube Neutrino Observatory IceCube E 2 flux limits Sensitivity to various source models after 3 years of data taking Nikhef, 02-dec-2005 Physics Colloquium 34 Nick van Eijndhoven

36 Outlook Heading towards the discovery of neutrino pointsources in coming years IceCube new readout technology : ATWD Records photon arrival-time profile Width distance Height N pe Better angular resolution (< ) Improved energy determination Cleaner samples (larger statistics) Surface array IceTop Calibration on downgoing muons Study of CR showers (composition) Operation coincides with SWIFT mission Trigger for transient (GRB) phenomena IceCube deployment scheme (2005) Year : Strings : First light : feb 2005 Dwarf Amanda in 2007 Nikhef, 02-dec-2005 Physics Colloquium 35 Nick van Eijndhoven

37 Outlook Nikhef, 02-dec-2005 Physics Colloquium 36 Nick van Eijndhoven

38 Outlook Nikhef, 02-dec-2005 Physics Colloquium 37 Nick van Eijndhoven

39 Outlook Nikhef, 02-dec-2005 Physics Colloquium 38 Nick van Eijndhoven

40 Outlook Nikhef, 02-dec-2005 Physics Colloquium 39 Nick van Eijndhoven

41 Outlook Nikhef, 02-dec-2005 Physics Colloquium 40 Nick van Eijndhoven

42 Outlook Nikhef, 02-dec-2005 Physics Colloquium 41 Nick van Eijndhoven

43 Outlook Nikhef, 02-dec-2005 Physics Colloquium 42 Nick van Eijndhoven

44 Outlook Nikhef, 02-dec-2005 Physics Colloquium 43 Nick van Eijndhoven

45 Outlook Real IceCube+IceTop event 07-feb-2005 Nikhef, 02-dec-2005 Physics Colloquium 44 Nick van Eijndhoven

46 Outlook Amanda triggered combi-event Nikhef, 02-dec-2005 Physics Colloquium 45 Nick van Eijndhoven

47 Outlook String 21 triggered event Nikhef, 02-dec-2005 Physics Colloquium 46 Nick van Eijndhoven

48 Outlook Nikhef, 02-dec-2005 Physics Colloquium 47 Nick van Eijndhoven

49 Outlook Nikhef, 02-dec-2005 Physics Colloquium 48 Nick van Eijndhoven