Heaven-Sent Neutrino Interactions From TeV to PeV

Transcription

1 Heaven-Sent Neutrino Interactions From TeV to PeV Mauricio Bustamante Niels Bohr Institute, University of Copenhagen UCL HEP Seminar London, December 08, 2017

2 Two seemingly unrelated questions 1 Where are the most energetic particles coming from? 2 What is the structure of matter at the smallest scales? 2

3 Symmetry Magazine

4 Heaven-Sent Neutrino Interactions From TeV to PeV Mauricio Bustamante Niels Bohr Institute, University of Copenhagen UCL HEP Seminar London, December 08, 2017

5 Neutrinos interactions are weak... but we are persistent At center-of-mass energy of 1 GeV: σpp ~ cm2 σγp ~ cm2 σνp ~ cm2 5

6 Particle Data Group 6

7 Accelerator experiments Particle Data Group 7

8 Accelerator experiments One recent measurement (COHERENT) Particle Data Group 8

9 Accelerator experiments One recent measurement (COHERENT) No measurements until now! Particle Data Group 9

10 Accelerator experiments One recent measurement (COHERENT) Particle Data Group 1

11 Particle Data Group 1

12 Quasi-elastic scattering: νl + n l - + p νl + p l + + n Particle Data Group 1

13 Quasi-elastic scattering: νl + n l - + p νl + p l + + n Resonant scattering: νl + N l- + N* l- + π + N Particle Data Group 1

14 Quasi-elastic scattering: νl + n l - + p νl + p l + + n Deep inelastic scattering: νl + N l - + X νl + N l + + X Resonant scattering: νl + N l- + N* l- + π + N Particle Data Group 1

15 How does DIS probe nucleon structure? What you see Beneath the hood (Plus the equivalent neutral-current process (Z-exchange)) Giunti & Kim, Fundamentals of Neutrino Physics & Astrophysics 15

16 Fermilab Today

17 Peeking inside a proton 17

18 Extrapolating the cross section to high energies 18

19 Extrapolating the cross section to high energies SM 19

20 Extrapolating the cross section to high energies SM + PDFs 20

21 Extrapolating the cross section to high energies SM + = PDFs 21

22 What can we measure now and later? MB & A. Connolly,

23 What can we measure now and later? MB & A. Connolly,

24 Neutrino, interrupted 24

25 Neutrino, interrupted Isotropic fux of high-energy neutrinos 25

26 Neutrino, interrupted Isotropic fux of high-energy neutrinos IceCube 26

27 Neutrino, interrupted 27

28 Neutrino, interrupted 28

29 Measuring the high-energy cross section 29

30 Measuring the high-energy cross section 30

31 Measuring the high-energy cross section 31

32 A feel for the in-earth attenuation Earth matter density Neutrino-nucleon cross section (Preliminary Reference Earth Model) + 32

33 A feel for the in-earth attenuation = 33

34 34

35 Downgoing Upgoing 35

36 Transparent Earth e-τ ~ 1 Downgoing Upgoing 36

37 Downgoing Upgoing Opaque Earth e-τ ~ 0 37

38 IceCube What is it? Km3 in-ice Cherenkov detector in Antarctica >5000 PMTs at km of depth Sensitive to neutrino energies > 10 GeV 38

39 How does IceCube see neutrinos? 39

40 Shower (IceCube event #22)

41 Track (IceCube event #15)

42 What has IceCube found so far (6 years)? 42

43 What has IceCube found so far (6 years)? 80 contained events between 18 TeV 2 PeV (16 atm. neutrinos, 25 atm. muons) C. Kopper, ICRC

44 What has IceCube found so far (6 years)? 80 contained events between 18 TeV 2 PeV (16 atm. neutrinos, 25 atm. muons) Astrophysical ν fux detected at > 7σ (Normalization ok, but steep spectrum) C. Kopper, ICRC

45 What has IceCube found so far (6 years)? Arrival directions compatible with isotropy C. Kopper, ICRC

46 What has IceCube found so far (6 years)? Arrival directions compatible with isotropy Post-trial p-value: 77% C. Kopper, ICRC

47 What has IceCube found so far (6 years)? Flavor composition compatible with equal proportion of each favor M. Usner, ICRC

48 Contained vs. uncontained νn interactions Contained events Uncontained events μ νμ IceCube μ νe ντ Starting track νμ Shower Through-going muon Pro: Clean determination of Eν Pro: Lots of events (~10k used) Con: Few events (<100) Con: Uncertain estimates of Eν Ref.: MB & A. Connolly, Ref.: IceCube, Nature 2017,

49 Cross section from contained events σνn varies with neutrino energy use events where Eν is well-reconstructed These are IceCube High-Energy Starting Events (HESE): νn interaction occurs inside the detector Showers: completely contained in the detector (Edep Eν) Tracks: partially contained (Edep < Eν) We use the 58 publicly available HESE showers (6-year sample) HESE tracks could be used but we would need non-public data to reconstruct Eν without bias 49

50 MB & A. Connolly,

51 Downgoing events constrain (fux x cross section) MB & A. Connolly,

52 Upgoing events constrain the cross section Downgoing events constrain (fux x cross section) MB & A. Connolly,

53 MB & A. Connolly,

54 Energy too low: Nν,up and Nν,down comparable MB & A. Connolly,

55 Energy too high: fux too low, no upgoing events MB & A. Connolly,

56 Goldilocks region MB & A. Connolly,

57 Bin-by-bin analysis TeV (3 showers) TeV (20 showers) TeV (18 showers) TeV (17 showers) 57

58 Sensitivity to σ in each bin 58

59 The fne print High-energy ν s: astrophysical (isotropic) + atmospheric (anisotropic) We take into account the shape of the atmospheric contribution The shape of the astrophysical ν energy spectrum is still uncertain We take a E-γ spectrum in narrow energy bins NC showers are sub-dominant to CC showers, but they are indistinguishable Following Standard-Model predictions, we take σnc = σcc/3 IceCube does not distinguish ν from ν, and their cross-sections are diferent We assume equal fuxes, expected from production via pp collisions We assume the avg. ratio <σνn/σνn> in each bin known, from SM predictions The favor composition of astrophysical neutrinos is still uncertain We assume equal fux of each favor, compatible with theory and observations 59

60 What goes into the (likelihood) mix? Inside each energy bin, we freely vary Nast (showers from astrophysical neutrinos) Natm (showers from atmospheric neutrinos) γ (astrophysical spectral index) σcc (neutrino-nucleon charged-current cross section) For each combination, we generate the angular and energy shower spectrum and compare it to the observed HESE spectrum via a likelihood Maximum likelihood yields σcc (marginalized over nuisance parameters) Bins are independent of each other there are no (signifcant) cross-bin correlations 60

61 What goes into the (likelihood) mix? Inside each energy bin, we freely vary Nast (showers from astrophysical neutrinos) Natm (showers from atmospheric neutrinos) γ (astrophysical spectral index) σcc (neutrino-nucleon charged-current cross section) Including detector resolution (10% in energy, 15 in direction) For each combination, we generate the angular and energy shower spectrum and compare it to the observed HESE spectrum via a likelihood Maximum likelihood yields σcc (marginalized over nuisance parameters) Bins are independent of each other there are no (signifcant) cross-bin correlations 61

62 Our result MB & A. Connolly,

63 Extending cross section measurements MB & A. Connolly,

64 Extending cross section measurements MB & A. Connolly,

65 Extending cross section measurements MB & A. Connolly,

66 How to do better / more? Currently, we are statistics-limited Solvable with more data from IceCube, IceCube-Gen2, KM3NeT Large errors in arrival direction (~10 ) give errors in attenuation Solvable with ongoing IceCube improvements + KM3NeT Charged-current + neutral-current cross sections are indistinguishable Solvable (?) with muon and neutron echoes (Li, MB, Beacom 16) Cannot separate ν from ν Wait to detect Glashow resonance (~6.3 PeV), sensitive only to νe Use starting tracks / through-going muons Doable / done by IceCube (more next) 66

67 Using through-going muons instead Use ~104 through-going muons Measured: deμ/dx Inferred: Eμ deμ/dx From simulations (uncertain): most likely Eν given Eμ Fit the ratio σobs/σsm (stat.)-0.43 (syst.) All events grouped in a single energy bin TeV IceCube, Nature,

68 Summary: fundamental physics with astrophysical ν We extracted the neutrino-nucleon cross section from 18 TeV to 2 PeV Previously known up to 350 GeV Found consistency with Standard-Model predictions Errors are still large due to statistics and astrophysical unknowns But both will be improved in the future Neutrino telescopes can probe fundamental particle physics (cross section, favor composition, anisotropies) 68

69 Quo vadis: IceCube vs. ANITA/ARA/ARIANNA 69

70 Quo vadis: IceCube vs. ANITA/ARA/ARIANNA Test predictions of deep inelastic scattering down to PDFs at x ~ 10-4 (known) 70

71 Quo vadis: IceCube vs. ANITA/ARA/ARIANNA Opportunity to test unprobed nucleon structure down to x < 10-5 (known) 71

72 Backup slides

73 Marginalized cross section in each bin MB & A. Connolly,

74 Neutrino zenith angle distribution Figure by Jakob Van Santen ICRC