Atmospheric muons & neutrinos in neutrino telescopes

Transcription

1 Atmospheric muons & neutrinos in neutrino telescopes Neutrino oscillations Muon & neutrino beams Muons & neutrinos underground Berlin, 1 October 2009 Tom Gaisser 1

2 Atmospheric neutrinos Produced by cosmic-ray interactions Last component of secondary cosmic radiation to be measured Close genetic relation with muons p + A π ± (K ± ) + other hadrons π ± (K ± ) µ ± + ν µ (ν µ ) µ ± e ± + ν µ (ν µ ) + ν e (ν e ) e µ p π ν µ ν e ν µ Berlin, 1 October 2009 Tom Gaisser 2

3 Historical context Detection of atmospheric neutrinos Markov (1960) suggests Cherenkov light in deep lake or ocean to detect atmospheric ν interactions for neutrino physics Greisen (1960) suggests water Cherenkov detector in deep mine as a neutrino telescope for extraterrestrial neutrinos First recorded events in deep mines with electronic detectors, 1965: CWI detector (Reines et al.); KGF detector (Menon, Miyake et al.) Two methods for calculating atmospheric neutrinos: From muons to parent pions infer neutrinos (Markov & Zheleznykh, 1961; Perkins) From primaries to π, K and µ to neutrinos (Cowsik, 1965 and most later calculations) Essential features known since 1961: Markov & Zheleznykh, Zatsepin & Kuz min Monte Carlo calculations follow second method Stability of matter: search for proton decay, 1980 s ν background for p-decay IMB & Kamioka -- water Cherenkov detectors ν KGF, NUSEX, Frejus, Soudan -- iron tracking calorimeters µ Principal background is interactions of atmospheric neutrinos ν Need to calculate flux of atmospheric neutrinos e Berlin, 1 October 2009 Tom Gaisser

4 Historical context (cont d) Atmospheric neutrino anomaly , 1988 IMB too few µ decays (from interactions of ν µ ) 1986 Kamioka µ-like / e-like ratio too small. Neutrino oscillations first explicitly suggested in 1988 Kamioka paper IMB stopping / through-going consistent with no oscillations (1992) Hint of pathlength dependence from Kamioka, Fukuda et al., 1994 Discovery of atmospheric neutrino oscillations by S-K Super-K: Evidence for neutrino oscillations at Neutriino 98 Subsequent increasingly detailed analyses from Super-K: ν µ ν τ Confirming evidence from MACRO, Soudan, K2K, MINOS Analyses based on ratios comparing to 1D calculations Compare up vs down Parallel discovery of oscillations of Solar neutrinos Homestake , SAGE, Gallex chemistry counting expts. Kamioka, Super-K, SNO higher energy with directionality ν e ( ν µ, ν τ ) Berlin, 1 October 2009 Tom Gaisser 4

5 p Atmospheric neutrino beam Cosmic-ray protons produce neutrinos in atmosphere ν µ /ν e ~ 2 for E ν < GeV Up-down symmetric Oscillation theory: Characteristic length (E/δm 2 ) related to δm 2 = m 12 m 2 2 Mixing strength (sin 2 2θ) Compare 2 pathlengths Upward: 10,000 km Downward: km P(ν µ ν τ ) = sin 2 2θ sin 2 ( 1.27 L(km) δm2 (ev 2 ) ) E ν (GeV) Berlin, 1 October 2009 Tom Gaisser 5 e ν µ µ π ν e ν µ Wolfenstein; Mikheyev & Smirnov

6 Classes of atmospheric ν events Contained (any direction) ν-induced µ (from below) µ e (or µ) External events Plot is for Super-K but the classification is generic Contained events ν e (or ν µ ) Berlin, 1 October 2009 Tom Gaisser 6 ν µ

7 Number of Events Number of Events Number of Events Super-K atmospheric neutrino data (hep-ex/ ) Sub-GeV e-like P < 400 MeV/c Sub-GeV µ-like P < 400 MeV/c Sub-GeV e-like Sub-GeV µ-like P > 400 MeV/c P > 400 MeV/c CC ν e CC ν µ Multi-GeV e-like Multi-GeV µ-like multi-ring 400 Upward through-going µ 100 Multi-GeV µ-like Berlin, October Tom Gaisser cosθ cosθ cosθ multi-ring Sub-GeV µ-like PC Upward stopping µ cosθ 1489day FC+PC data day upward going muon data

8 Atmospheric ν ν µ ν τ, δm 2 = 2.5 x 10-3 ev 2 maximal mixing Solar neutrinos ν e {ν µ,ν τ }, δm 2 ~ 10-4 ev 2 large mixing 3-flavor mixing Yumiko Takenaga, ICRC2007 Flavor state ν α ) = Σ i U αi ν i ), where ν i ) is a mass eigenstate U = C 23 S S 23 C 23 C 13 0 S S 13 0 C 13 C 12 S S 12 C atmospheric C 13 ~ 1 small solar Berlin, 1 October 2009 Tom Gaisser 8 S 13

9 High-energy Neutrino telescopes Large volume--coarse instrumentation--high energy (> TeV) as compared to Super-K with 40% photo-cathode over 0.05 Mton Berlin, 1 October 2009 Tom Gaisser 9

10 Detecting neutrinos in H 2 0 Proposed by Greisen, Markov in 1960 Heritage: DUMAND IMB Kamiokande Super-K SNO ANTARES IceCube Berlin, 1 October 2009 Tom Gaisser 10

11 The neutrino landscape Expected flux of relic supernova neutrinos ν e Lines show atmospheric neutrinos + antineutrinos ν µ Astrophysical neutrinos (WB bound / 2 for osc) Solar ν Prompt ν Slope = 3.7 RPQM for prompt ν from charm Bugaev et al., PRD58 (1998) Slope = 2.7 Cosmogenic neutrinos Berlin, 1 October 2009 Tom Gaisser 11

12 The The atmosphere atmosphere (exponential approximation) Pressure = X v = X o exp{ -h v / h o }, where h o = 6.4 km for X v < 200 g / cm 2 and X 0 = 1030 g / cm 2 Density = ρ = -dx v / dh v = X v / h o X v ~ p = ρrt h o ~ RT Berlin, 1 October 2009 Tom Gaisser 12

13 Cascade equations For hadronic cascades in the atmosphere X = depth into atmosphere λ = Interaction length d = decay length F ji ( E i,e j ) has no explicit dimension, so F F(ξ) ξ = E i /E j & F(E i,e j ) de j / E i F(ξ) dξ / ξ 2 Small scaling violations from m i, Λ QCD ~ GeV, etc Still a remarkably useful approximation Berlin, 1 October 2009 Tom Gaisser 13

14 EAS Boundary conditions Boundary condition for inclusive flux Berlin, 1 October 2009 Tom Gaisser 14

15 Uncorrelated fluxes in Example: flux of nucleons Approximate: λ ~ constant, leading nucleon only atmosphere Separate X-X and E-dependence; E try factorized solution, N(E,X) = f (E) g(x), f (E) ~ E (γ+1) Separation constant Λ N describes attenuation of nucleons in atmosphere Berlin, 1 October 2009 Tom Gaisser 15

16 Nucleon fluxes in atmosphere Evaluate Λ N : Flux of nucleons: N(E, X) = N(E, 0) x exp{-x/λ N } K fixed by primary spectrum at X = 0 Berlin, 1 October 2009 Tom Gaisser 16

17 Comparison to proton fluxes Account for p n CAPRICE98 (E. Mocchiutti,, thesis) Berlin, 1 October 2009 Tom Gaisser 17

18 π ± in the atmosphere pion decay probability π decay or interaction more probable for E < ε π or E > ε π = 115 GeV Berlin, 1 October 2009 Tom Gaisser 18

19 π ± (K ± ) in the atmosphere Low-energy limit: E π < ε π ~ 115 GeV Berlin, 1 October 2009 Tom Gaisser 19

20 π ± (K ± ) in the atmosphere High-energy limit: E π > ε π ~ 115 GeV Spectrum of decaying pions one power steeper for E π >> ε π Berlin, 1 October 2009 Tom Gaisser 20

21 µ and ν µ in the atmosphere To calculate spectra of µ and ν Multiply Π(E,X) by pion decay probability Include contribution of kaons Dominant source of neutrinos Integrate over kinematics of π µ + ν µ and K µ + ν µ Integrate over the atmosphere (X) Good description of data Berlin, 1 October 2009 Tom Gaisser 21

22 2-body decays of π ± and K ± π+ µ + + ν µ 99.99% K + µ + + ν µ 63.44% also for negative mesons to produce anti-neutrinos In rest frame of parent µ and ν have equal and opposite 3 momentum p CM energy of neutrino = p = p = E ν * = (M 2 µ 2 ) / (2 M) CM energy of muon = p 2 + µ 2 = E µ * = (M 2 + µ 2 ) / (2 M) M = mass of parent meson, µ = mass of muon For both µ and ν : E LAB = γ E* + β γ p cos(θ) Berlin, 1 October 2009 Tom Gaisser 22

23 Momentum distributions for π, K E LAB = γ E* + β γ p cos(θ) γ = E M / M and assume E LAB >> M so β 1 Then (E* - p) / M < E LAB / E M < (E* + p) / M because -1 < cos(θ) < 1 Also, decay is isotropic in rest frame so dn / d cos(θ) = constant But d E LAB = d cos(q), so dn / d E LAB = constant Normalization requires exactly one µ or ν so the normalization gives (constant) -1 = E M ( 1 r ) where r = µ 2 / M 2 for both µ and ν Note: r π = while r K = , an important difference! Berlin, 1 October 2009 Tom Gaisser 23

24 Compare µ and ν Berlin, 1 October 2009 Tom Gaisser 24

25 µ and ν µ differ only by kinematics of π ± and K ± decay Berlin, 1 October 2009 Tom Gaisser 25

26 Spectrum-weighted moments (γ-1) Z ab ξ F ab (ξ) dξ Berlin, 1 October 2009 Tom Gaisser 26

27 Interaction vs. decay X v = 100 g / cm 2 at 15 km altitude which is comparable to interaction lengths of hadrons in air Relative magnitude of λ i and d i = X cosθ ( E / ε i ) determines competition between interaction and decay Berlin, 1 October 2009 Tom Gaisser 27

28 High-energy atmospheric neutrinos Primary cosmic-ray spectrum (nucleons) Nucleons produce pions kaons Kaons produce most ν µ for 100 GeV < E ν < 100 TeV charmed hadrons that decay to neutrinos Eventually prompt ν from charm decay dominate,.but what energy? Berlin, 1 October 2009 Tom Gaisser 28

29 Importance of kaons at high E Importance of kaons main source of ν > 100 GeV p K + + Λ important Charmed analog important for prompt leptons at higher energy vertical 60 degrees Berlin, 1 October 2009 Tom Gaisser 29

30 Neutrinos from kaons Critical energies determine where spectrum changes, but A Kν / A πν and A Cν / A Kν determine magnitudes New information from MINOS relevant to ν µ with E > TeV Berlin, 1 October 2009 Tom Gaisser 30

31 Electron neutrinos K + π 0 ν e e ± ( B.R. 5% ) K L0 π ± ν e e ( B.R. 41% ) Kaons important for ν e down to ~10 GeV Berlin, 1 October 2009 Tom Gaisser 31

32 TeV µ + /µ - with MINOS far detector 100 to 400 GeV at depth > TeV at production x Increase in charge ratio shows p K + Λ is important 1.27 x 1.37 Forward process s-quark recombines with leading di-quark Similar process for Λ c? Increased contribution from kaons at high energy Berlin, 1 October 2009 Tom Gaisser 32

33 MINOS fit ratios of Z-factors Z-factors assumed constant for E > 10 GeV Energy dependence of charge ratio comes from increasing contribution of kaons in TeV range coupled with fact that charge asymmetry is larger for kaon production than for pion production Same effect larger for ν µ / ν µ because kaons dominate Berlin, 1 October 2009 Tom Gaisser 33

34 Atmospheric neutrinos harder spectrum from kaons? AMANDA atmospheric neutrino arxiv: v1 Re-analysis of Super-K Gonzalez-Garcia, Maltoni, Rojo JHEP 2007 Berlin, 1 October 2009 Tom Gaisser 34

35 Signature of charm: θ dependence For ε K < E cos(θ) < ε c, conventional neutrinos ~ sec(θ), but prompt neutrinos independent of angle Uncertain charm component most important near the vertical Berlin, 1 October 2009 Tom Gaisser 35

36 Neutrinos from charm Main source of atmospheric ν for E ν >???? > 20 TeV Large uncertainty in normalization! Gelmini, Gondolo, Varieschi PRD 67, (2003) Berlin, 1 October 2009 Tom Gaisser 36

37 Muons & Neutrinos underground Muon average energy loss: from Reviews of Particle Physics, Cosmic Rays Critical energy: Berlin, 1 October 2009 Tom Gaisser 37

38 µ energy spectrum underground Average relation between energy at surface and energy underground Shallow: Deep: Berlin, 1 October 2009 Tom Gaisser 38

39 High-energy, deep muons Berlin, 1 October 2009 Tom Gaisser 39

40 Differential and integral spectrum of Differential atmospheric muons Integral Energy loss: E µ (surface) = exp{ b X } ( E µ +ε ) - ε Set E µ = ε { exp[ b X ] - 1 } in Integral flux to get depth intensity curve Berlin, 1 October 2009 Tom Gaisser 40

41 Plot shows dn µ / dln(e µ ) Berlin, 1 October 2009 Tom Gaisser 41

42 Detecting neutrinos Rate = Neutrino flux x Absorption in Earth x Neutrino cross section x Size of detector x Range of muon (for ν µ ) (Range favors ν µ channel) Probability to detect ν µ -induced µ Berlin, 1 October 2009 Tom Gaisser 42

43 Neutrino effective area Rate: = φ ν (E ν )A eff (E ν )de ν Earth absorption Starts TeV Biggest effect near vertical Higher energy ν s absorbed at larger angles Berlin, 1 October 2009 Tom Gaisser 43

44 Neutrino-induced muons Berlin, 1 October 2009 Tom Gaisser 44

45 Atmospheric muons (shape only) Atmospheric Berlin, 1 October 2009 Tom Gaisser 45

46 Muons in ν telescopes Downward atmospheric muons Neutrino-induced muons from all directions SNO at 6000 m.w.e. depth Million to 1 background to signal from above. Use Earth as filter; look for neurtinos from below. Berlin, 1 October 2009 Tom Gaisser 46

47 Muons in IceCube Downward atmospheric muons Neutrino-induced muons from all directions IceCube P. Berghaus et al., ISVHECRI-08 also HE1.5 Crossover at ~85 for shallow detectors ~75 for deepest Mediterranean site Berlin, 1 October 2009 Tom Gaisser 47 47

48 Atmospheric µ and ν in IceCube Extended energy reach of km 3 detector preliminary Patrick Berkhaus, ICRC 2009 Dmitry Chirkin, ICRC 2009 Currently limited by systematics Berlin, 1 October 2009 Tom Gaisser 48

49 Deep muons as a probe of weather in the stratosphere Barrett et al. MACRO MINOS far detector Sudden stratospheric warmings observed IceCube Interesting because of unique seasonal features of the upper atmosphere over Antarctica related to ozone hole Decay probability ~ T: h 0 ~ RT pion decay probability Berlin, 1 October 2009 Tom Gaisser 49

50 Berlin, 1 October 2009 Tom Gaisser 50