Atmospheric Neutrinos

1. Atmospheric Neutrinos Nature’s neutrino beam Tom Gaisser

2. Outline • History • Phenomenology • of the atmospheric neutrino beam • and relation to atmospheric muons • Hadronic interactions • K/pi ratio • Production of charm • Atmospheric leptons in neutrino telescopes Tom Gaisser

3. Lines show atmospheric neutrinos + antineutrinos • Astrophysical neutrinos • harder spectrum • point sources nm ne Solar n RPQM for prompt n from charm Bugaev et al., PRD58 (1998) 054001 Slope = 2.7 Prompt n Slope = 3.7 The neutrino landscape • Atmospheric neutrinos: • background • calibration Relic SN n Tom Gaisser

4. Detect relic n from supernovae: Kaplinghat, Steigman & Walker, PR D62 (2000) 043001 Tom Gaisser

5. Stopped m below threshold ne interactions Current limits from Super-K • Limit is from ne + p  n + e+ • Neutron not detected in current Super-K • Backgrounds: • atmospheric ne and ne • solar ne and reactor ne • atmospheric nm  m (Em < 50 MeV) Tom Gaisser

6. Improvement with tagged neutron Beacom & Vagins, PRL 93 (2004) 171101 Prescribe gadolinium additive to detect neutrons and select anti-ne only Tom Gaisser

7. p p m e ne nm nm Atmospheric neutrinos • Produced by cosmic-ray interactions • Last component of secondary cosmic radiation to be measured • Close genetic relation with muons • p + A  p± (K±) + other hadrons • p± (K±)  m± + nm (nm) • m±  e± + nm (nm) + ne (ne) Tom Gaisser

8. Historical context • Detection of atmospheric neutrinos • Markov (1960) suggests Cherenkov light in deep lake or ocean to • detect atmospheric n 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 p, K and m 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 • IMB & Kamioka -- water Cherenkov detectors • KGF, NUSEX, Frejus, Soudan-- iron tracking calorimeters • Principal background is interactions of atmospheric neutrinos • Need to calculate flux of atmospheric neutrinos Tom Gaisser

9. Historical context (cont’d) • Atmospheric neutrino anomaly - 1986, 1988 … • IMB too few m decays (from interactions of nm) 1986 • Kamioka m-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: nm  nt • 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 1968-1995, SAGE, Gallex … chemistry counting expts. • Kamioka, Super-K, SNO … higher energy with directionality • ne ( nm, nt ) Tom Gaisser

10. p p m e nm ne nm ( ) 1.27 L(km) dm2(eV2) En(GeV) P(nmnt) = sin22q sin2 Atmospheric neutrino beam • Cosmic-ray protons produce neutrinos in atmosphere • nm/ne ~ 2 for En < GeV • Up-down symmetric • Oscillation theory: • Characteristic length (E/dm2) • related to dm2 =m12 – m22 • Mixing strength (sin22q) • Compare 2 pathlengths • Upward: 10,000 km • Downward: 10 – 20 km Wolfenstein; Mikheyev & Smirnov Tom Gaisser

11. e (or m) ne (or nm) nm Classes of atmospheric n events m Contained (any direction) n-induced m (from below) External events Plot is for Super-K but the classification is generic Contained events Tom Gaisser

12. Super-K atmospheric neutrino data (hep-ex/0501064) CC ne CC nm 1489day FC+PC data + 1646day upward going muon data Tom Gaisser

13. 0 0 • 0 C23 S23 • 0 -S23 C23 C13 0 S13 0 1 0 -S13 0 C13 C12 S12 0 -S12 C12 0 0 0 1 U = “atmospheric” “solar” C13 ~ 1 S13 small Atmospheric n nm nt, dm2 = 2.5 x 10-3 eV2 maximal mixing Solar neutrinos ne{nm,nt}, dm2 ~ 10-4 eV2 large mixing Yumiko Takenaga, ICRC2007 3-flavor mixing Flavor state | na ) = Si Uai | ni ), where | ni ) is a mass eigenstate Tom Gaisser

14. Primary cosmic-ray spectrum (nucleons) Nucleons produce pions kaons charmed hadrons that decay to neutrinos High-energy atmospheric neutrinos Tom Gaisser

15. Branching ratio moment of decay Spectrum-weighted moment of hadron production For example, for Factors in atmospheric n beam For each parent i = p±, K±, charm: Tom Gaisser

16. Account for m energy loss Account for m decay Similar analysis for atmosphericm Analytic approximation works well! Tom Gaisser

17. Energy spectrum of atmospheric muons and neutrinos • At low energy, Fn,m has same spectral index at production as primary spectrum • Fn,m becomes steeper by one power of energy at high energy • Critical energy depends on zenith angle: Ecritical = ei / cosq Tom Gaisser

18. Neutrinos from kaons Critical energies determine where spectrum changes, but AKn / Apn and ACn / AKn determine magnitudes New information from MINOS relevant to nm with E > TeV Tom Gaisser

19. Energy-angle dependence by parent type Neutrinos Muons Plots show fraction of n & m from p±, K±, charm q = 0 q = 60o Tom Gaisser

20. x 1.37 x 1.27 TeV m+/m- with MINOS far detector • 100 to 400 GeV at depth  > TeV at production • Increase in charge ratio shows • p  K+L is important • Forward process • s-quark recombines with leading di-quark • Similar process for Lc? Increased contribution from kaons at high energy Tom Gaisser

21. 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 nm / nm because kaons dominate MINOS fit ratios of Z-factors Tom Gaisser

22. Atmospheric neutrinos – harder spectrum from kaons? Re-analysis of Super-K Gonzalez-Garcia, Maltoni, Rojo JHEP 2007 AMANDA atmospheric neutrino Phys.Rev D79 (2009) 102005 (The blue shaded region is the same as the green band on the right.) Tom Gaisser

23. FNAL E-781 (SELEX) Large asymmetry of Lc+ / Lc- production in baryon beams: p  Lc+ favored with hard spectrum in xF Tom Gaisser

24. Signature of charm: q dependence For eK < E cos(q) < ec , conventional neutrinos ~ sec(q) , but “prompt” neutrinos independent of angle Uncertain charm component most important near the vertical Tom Gaisser

25. Questions: • How much intrinsic charm? (Brodsky et al.) • What is the magnitude of ZNcharm ? • My analytic estimate: ZNcharm ≈ 5 x 10-4 • Normalized to ISR inclusive spectra in Lykasov et al., arXiv:0909.5061 • RQPM model: ZNcharm ≈ 10-3 • E.V. Bugaev et al., Phys. Rev. D58 (1998) 054001 • Perturbative QCD • Values vary among calculations, generally lower estimates • Example: ZNcharm ≈ 1.5 x 10-4 • Enberg, Reno & Sarcevic, Phys. Rev. D78 (2008) 043005 Tom Gaisser

26. RQPM Parameterization QCD range Multiply differential spectrum x E3 to display transition to prompt leptons Prompt m and n Tom Gaisser

27. m+ + m- nm + nm prompt Experimental challenge: Must measure change of slope of a steep spectrum with low statistics and fluctuations in energy deposited Tom Gaisser

28. Detecting neutrinos in H20Proposed by Greisen, Markov in 1960 • Heritage: • DUMAND • IMB • Kamiokande Super-K ANTARES SNO Neutrino must interact to be detected IceCube Tom Gaisser

29. 125 m IceCube: n telescope& cosmic-ray detector Seattle Tom Gaisser July 2, 2009 Tom Gaisser Photo: James Roth 17-12-2007

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

31. Muons in IceCube Downward atmospheric muons Neutrino-induced muons from all directions IceCube  P. Berghaus et al., ISVHECRI-08 also HE1.5 ~75° for deepest Mediterranean site Crossover at ~85° for shallow detectors Tom Gaisser 31

32. preliminary Atmospheric m and n in IceCubeExtended energy reach of km3 detector Dmitry Chirkin, ICRC 2009 Currently limited by systematics Patrick Berkhaus, ICRC 2009 Tom Gaisser

33. Looking for diffuse fluxes above the background of atmospheric neutrinos Sean Grullon Parallel session Tom Gaisser

34. +75° +60° +45° +30° +15° 24h 0h -15° -30° -45° -log10 p -log10 p R. Lauer, Heidelberg Workshop, Jan09 arXiv:0903.5434 Paper accepted for PRL 9 November 2009 Tom Gaisser

35. IceCube 40 Juan Antonio Aguilar TeV PA 2009 Tom Gaisser

36. Jon Dumm, IceCube, ICRC2009 Tom Gaisser

37. Shadow of the Moon with muons in IceCube Tom Gaisser

38. Cosmic-ray anisotropy with IceCube muons Compare IceCube measurements of the Southern sky with previous results in the North Abbasi, Desiati for IceCube at ICRC2009 Tom Gaisser

39. Monitoring the Universe • Look for correlation with variable sources • e.g. AGN flares • Externally triggered searches (GRB) • Neutrino alerts (e.g. optical follow-up) • 2 or more n from same direction in Dt • Alerts to ROTSE-III from IceCube since Oct. 2008 • Alerts to TAROT from Antares since May 2009 • Sudden excess in counting rate (IceCube) • Send SN alert to SNEWS • Monitoring rates in surface detectors • IceTop, Auger • Solar particle events, modulation of galactic cosmic rays Tom Gaisser

40. pion decay probability 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: • h0 ~ RT Tom Gaisser

41. Tom Gaisser

42. Cosmic-ray physics with IceCube Use ratio of deep muons to shower size for composition Tom Gaisser Photo: James Roth 17/12/07

43. Cosmic-ray physics with IceCube • Goal: • Composition, & spectrum • 1015 – 1018 eV • Use coincident events • Look for transition to extra-galactic cosmic rays IceTop 59 (plus 14 stations installed 09/10) Tom Gaisser

44. Drilling operations 6 strings deployed so far this season. 18-20 planned. 28 tanks installed and freezing Tom Gaisser

45. Extras Tom Gaisser

46. Electron neutrinos K+ p0ne e± ( B.R. 5% ) KL0 p±ne e( B.R. 41% ) Kaons important for ne down to ~10 GeV Tom Gaisser

47. Uncertainty in atmospheric n • Any uncertainty in atmospheric neutrino background limits sensitivity of search for diffuse supernova neutrino background • Primarily interested in shape • Steep spectrum for DSNB as compared to • Hard spectrum of atmospheric neutrinos Tom Gaisser

48. A C B C/A B/A Comparison of 3 calculations used by Super-K( Note: En > 100 MeV in most calculations) Y. Ashi et al. (Super-K Collaboration) Phys. Rev. D71 (2005) 112005 Tom Gaisser

49. Low energy (10 – 100 MeV ) Note: most neutrinos with En < 50 MeV are from decay of muons stopped in atmosphere Gaisser & Stanev, Proc 24th ICRC, Rome (1995) Tom Gaisser

50. Calculations of anti-ne background 10-100 MeV • Note dependence • on phase of solar • cycle: • 10 – 20% variation • similar to response • of neutron monitors FLUKA10-100 MeV Battistoni et al.(2004): http://www.mi.infn.it/~battist/neutrino.html Tom Gaisser