Tom Gaisser

1
Atmospheric neutrinos

• n from decay of p, K and m produced by
  interactions of cosmic rays in the atmosphere
• Up-down symmetric except for geomagnetic effects
• Useful beam for neutrino oscillations?

• References
• TKG M. Honda, Ann. Revs.
• Nucl. Part. Sci. 52 (2002)
• TKG, Proc. Neutrino 2002

From D. Ayres, A.K. Mann et al., PR D84 (1984)
902 Snowmass, 1982
2
Historical context

• Particle physics with cosmic rays pre-1960
• Discovery of positron, muon, pion and kaon
• Hadronic scaling (Heitler Janossy, 1949) --
  Fsecondary(E) Zps Fp(E)
• Study of elementary particles by the
  photographic method
• Powell, Fowler Perkins, 1959

• Stability of matter search for proton decay,
  1980s
• 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

• Two methods
• From muons to parent pions infer neutrinos
  (Zatsepin Kuzmin Perkins)
• From primaries to p, K and m to neutrinos
  (Cowsik, TKG Stanev)
• Giles Barr 1986/87

3
Historical context (contd)

• 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

• Discovery of neutrino oscillations
• Super-K Evidence for neutrino oscillations
  at Neutriino 98
• Subsequent increasingly detailed analyses from
  Super-K 1998
• Confirming evidence from MACRO and Soudan
• SNO results on oscillations of solar neutrinos
• Analyses based on ratios comparing to 1D
  calculations

nm

• Need for precise, complete, accurate, 3D
  calculations
• Q PT / E is large for sub-GeV neutrinos
• Bending of muons in geomagnetic field important
  for n from m decay
• Complicated angular/energy dependence of
  primaries (AMS measurement)
• Use improved primary spectrum and
  hadroproduction information

4
Outline of talk

• Overview of calculations
• En lt 10 GeV (contained)
• Sources of uncertainty
• Primary spectrum
• Hadronic interactions
• Comparison of calculations
• Geomagnetic effects
• 3 D calculations
• High energy (nm? m ne)
• Importance of kaons
• Calibration of n - telescopes
• Prompt background
• Summary

Distribution of En for 4
classes of events determines
how oscillation effects appear P(nm--gtnm) 1 -
sin22q sin21.27 dm2(eV2) Lkm / EGeV
for two-flavor mixing in vacuum
5
Overview of the calculation
6
Primary spectrum

• Largest source of overall uncertainty
• 1995 experiments differ by 50 (see lines)
• Present AMS, BESS within 5 for protons
• discrepancy for He larger, but He only 20 of
  nucleon flux
• overall range (neglect highest and lowest)
• /-15, E lt 100 GeV
• /- 30, E TeV

7
Comparison (using same event generator)

• sub-GeV flux increases slightly using new flux
  from AMS BESS

8
Hadronic interactions

• n-yields depend most on treatment of p
  production
• Compare 3 calculations
• Bartol (Target)
• Honda et al. (1995 Fritiof present Dpmjet3)
• Battistoni et al. (Fluka)
• Uncertainties from interactions /-15

9
Comparison (using same flux)

• New calculations lower than old, e.g.
• Target-2.1/ -1
• Dpmjet3 / HKKM
• 3 new calculations agree at Kamioka but not for
  Soudan/SNO
• Larger uncertainty at high geomagnetic l
• Interactions lt 10 GeV are important

10
New hadro-production data

• Diagram
• Lego plot shows phase space weighting for sub-GeV
  events
• Bars show existing data
• New sources of data
• HARP
• NA49 (P322)
• E907

11
Geomagnetic cutoffs E-W effect as a consistency
check

• Picture shows
• 20 GeV protons in geomagnetic equatorial plane
• arrive from West and from near the vertical
• but not from East
• Comparison to data
• provides consistency test of data analysis

From cover of Cosmic Rays by A.M. Hillas (1972)
12
Response functions, sub-GeV n

• Eprimary 10-20 x En
• Up/down ratio opposite at Kamioka vs Soudan/SNO

13
Cutoffs at Super-K
Measurement of East-West effect with atmospheric
neutrinos--an important confirmation of analysis
interpretation of Super-K data as neutrino
oscillations

• n flux, 0.4 lt En lt 3 GeV
• -0.5 lt cos(q) lt 0.5
• measured by Super-K and
  compared to 3 calculations

14
3-dimensional effects

• Characteristic 3D feature
• excess of n near horizon
• shown in top, left panel
• lower panels show directions of m and e
• cannot see 3D effect directly however
• Horizontal excess is associated with a change in
  path-length distribution

From Battistoni et al., Astropart. Phys. 12
(2000) 315
15
3-D effects at Super-K

• 3D--1D comparison (pink--blue/green) at Kamioka
• Dip near horizon
• due to high local horizontal cutoffs
• Size of effect
• pT(p)/Ep sets scale
• 0.1 GeV / En
• therefore negligible for En gt 1 GeV

from M. Honda et al., Phys. Rev. D64 (2001)
053001
16
Path-length dependence

• Path length shorter near horizon on average in 3D
  case
• cos(q) gt 0 only,
• phase space favors nearby interaction scattering
  to large angle
• 5-10 (En 0.3-1 GeV)
• Effect not yet included in Super-K analysis

from M. Honda et al., Phys. Rev. D64 (2001)
053001
17
Is the second spectrum important for atmospheric
n?

• Cosmic-ray albedo beautifully measured by AMS at
  380 km
• Biggest effect near geomagnetic equator (vertical
  cutoff 10 GV)
• Albedo sub-cutoff protons from grazing
  interactions of cosmic rays gt cutoff (S.B.
  Treiman, 1953)
• trapped for several cycles
• Re-entry rate is low (dashed line)

18
Technical aspects of 3D calculation

• Brute force
• Generate showers randomly all over globe
• e Adetector/Aearth 10-10
• Use large Aeff
• Lipari, Waltham
• Neglect bending in geomagnetic field
• Battistoni et al.
• DST approach two passes
• Giles Barr et al.
• Equivalent to brute force but with higher
  efficiency, e ?

19
Higher energy atmospheric n

• Mean En 100 GeV for n-induced upward m

20
High energy ( e.g. nm ? m )

• Importance of kaons
• main source of n gt 100 GeV
• p ? K L important
• Charmed analog important for prompt leptons

21
Calibration with atmospheric n

• MINOS, etc.
• Neutrino telescopes
• Example of nm / ne
• flavor ratio
• angular dependence

Note this is maximal effect horizontal 85
- 90 deg in plots
22
MINOS m/m- discrimination 1 lt Em lt 70 GeV

• Events in 5 yr w / wo osc.
• Contained 400 / 260
• Contained - 620 / 440
• External 160 / 120
• External - 400 / 280

TKG Todor Stanev astr0-ph/0210512
23
Problems qnm smears effect statistics too low
in MINOS
Em
Em
En
Nine angular bins in n direction
Vertically upward interactions inside detector
24
Global view of atmospheric n spectrum
Uncertainty in level of charm a potential problem
for finding diffuse neutrinos
25
Uncertainties absolute normalization

• Primary spectrum
• /- 10 up to 100 GeV (using AMS, BESS only)
• /- 20 below 100 GeV, /- 30 TeV (all data)
• Note lack of measurements in TeV range
• Hadronic interactions
• /- 15 below 100 GeV
• 1D o.k. for comparing calculations and for
  tracking effects of uncertainties in input
• Other sources at per cent level
• (local terrain, seasonal variations, anisotropy
  outside heliosphere)
• New measurements HARP, E907, P322
• Uncertainty in sn

26
Summary (low energy)

• Evidence for n oscillation uses ratios
• Contained events
• (ne / nm )data / (ne / nm )calculated
• upward / downward
• Neutrino-induced upward muons
• stopping / through-going
• vertical / horizontal
• Broad response functions minimize dependence on
  slope of primary spectrum
• Uncertainties tend to cancel in comparison of
  ratios
• Observation of geomagnetic effects confirms
  experiment interpretation

27
Summary (high energy)

• Kaon decays dominate atmospheric nm, ne above
  100 GeV
• Well-understood atmospheric nm, ne useful for
  calibration
• Uncertainty in level of prompt neutrinos (from
  charm decay) will limit search for diffuse
  astrophysical neutrinos

28
What next?

• Use neutrino fluxes for calibration, etc.
• MINOS, SNO, Neutrino telescopes
• Learn about charmed analog of KL production
• Finish and use Giles 3D scheme
• Incorporate new hadro-production results
• HARP below 15 GeV
• NA 49, E907 100 GeV

29
Comparison to muons

• m, m- vs atmospheric depth
• newer measurements lower by 10-15 than earlier
• comparison not completely internally consistent
• ascent vs float
• balloons rise rapidly
• fraction detected is small compared to m decayed
  to n

Data from CAPRICE, 3D calculation of Engel et al.
(2001)
30
Solar modulation

• Neutron monitors
• well correlated with cosmic-ray flux
• provide continuous monitor
• response like sub-GeV neutrinos with no cutoff
• SNO, Soudan lt20 variation
• Kamioka lt5 (10 ) for downward (upward)

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Soudan 5.9 kT yr
Black lines calculated, no
oscillation Blue lines fitted with oscillations