particle physics seminar
DESCRIPTION
TRANSCRIPT
Tom GaisserOctober 29, 2002
Oxford
Atmospheric neutrinos
• from decay of , K and produced by interactions of cosmic rays in the atmosphere• Up-down symmetric except for geomagnetic effects• Useful beam for neutrino oscillations?
From D. Ayres, A.K. Mann et al.,PR D84 (1984) 902 & Snowmass, 1982
References:• TKG & M. Honda, Ann. Revs. Nucl. Part. Sci. 52 (2002)•TKG, Proc. Neutrino 2002
Tom GaisserOctober 29, 2002
Oxford
Historical contextParticle physics with cosmic rays: pre-1960• Discovery of positron, muon, pion and kaon• Hadronic scaling (Heitler & Janossy, 1949) -- secondary(E) = Zps p(E)• Study of elementary particles by the photographic method Powell, Fowler & Perkins, 1959
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
Two methods:• From muons to parent pions infer neutrinos (Zatsepin & Kuz’min; Perkins)• From primaries to , K and to neutrinos (Cowsik, TKG & Stanev…)• Giles Barr 1986/87
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Tom GaisserOctober 29, 2002
Oxford
Historical context (cont’d)Atmospheric neutrino anomaly - 1986, 1988 …• IMB too few decays (from interactions of ) 1986• Kamioka -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
Need for precise, complete, accurate, 3D calculations• ~ PT / E is large for sub-GeV neutrinos• Bending of muons in geomagnetic field important for from decay• Complicated angular/energy dependence of primaries (AMS measurement)• Use improved primary spectrum and hadroproduction information
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Tom GaisserOctober 29, 2002
Oxford
Outline of talk• Overview of calculations• E < 10 GeV (contained)
– Sources of uncertainty• Primary spectrum• Hadronic interactions
– Comparison of calculations– Geomagnetic effects– 3 D calculations
• High energy ( & e)– Importance of kaons– Calibration of - telescopes – Prompt background
• Summary
Distribution of E for 4 classes of events determines how oscillation effects appear
P() = 1 - sin22 sin2[1.27 m2(eV2) Lkm / EGeV ]
for two-flavor mixing in vacuum
Tom GaisserOctober 29, 2002
Oxford
Overview of the calculation
Tom GaisserOctober 29, 2002
Oxford
Protons
Helium
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 < 100 GeV• +/- 30%, E ~ TeV
Tom GaisserOctober 29, 2002
Oxford
Comparison (using
same event generator)
• sub-GeV flux increases slightly using new flux from AMS & BESS
AMS/BESS
Kamioka
Soudan/SNO
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Tom GaisserOctober 29, 2002
Oxford
Hadronic interactions
• -yields depend most on treatment of production
• Compare 3 calculations:– Bartol (Target)
– Honda et al. (1995: Fritiof; present: Dpmjet3)
– Battistoni et al. (Fluka)
• Uncertainties from interactions ~ +/-15%
Tom GaisserOctober 29, 2002
Oxford
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 – Interactions < 10 GeV are
important
Kamioka
Soudan/SNO
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Tom GaisserOctober 29, 2002
Oxford
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
HARP
P322
Tom GaisserOctober 29, 2002
Oxford
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
N
From cover of “Cosmic Rays” byA.M. Hillas (1972)
Tom GaisserOctober 29, 2002
Oxford
Response functions, sub-GeV • Eprimary ~ 10-20 x E
• Up/down ratio opposite at Kamioka vs Soudan/SNO
Tom GaisserOctober 29, 2002
Oxford
Cutoffs at Super-K
Lipari 3D
HondaBartol
flux, 0.4 < E < 3 GeV
-0.5 < cos() < 0.5
measured by Super-K and compared to 3 calculations
N E S W
Measurement of East-West effect withatmospheric neutrinos--an importantconfirmation of analysis & interpretationof Super-K data as neutrino oscillations
Tom GaisserOctober 29, 2002
Oxford
3-dimensional effects• Characteristic 3D feature:
– excess of near horizon
– shown in top, left panel
– lower panels show directions of 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
Tom GaisserOctober 29, 2002
Oxford
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()/E sets scale
– ~ 0.1 GeV / E
– therefore negligible for E > 1 GeV from M. Honda et al., Phys. Rev. D64 (2001) 053001
Tom GaisserOctober 29, 2002
Oxford
E = 0.3 GeVE = 1 GeV Soudan/SNOKamioka
Path-length dependence
• Path length shorter near horizon on average in 3D case– cos() > 0 only,
– phase space favors nearby interaction scattering to large angle
– 5-10% (E ~0.3-1 GeV)
• Effect not yet included in Super-K analysis
from M. Honda et al., Phys. Rev. D64 (2001) 053001m2L/E …increase m2 1%?
Tom GaisserOctober 29, 2002
Oxford
– 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 > cutoff (S.B. Treiman, 1953)
– trapped for several cycles
– Re-entry rate is low (dashed line)
Is the second spectrum important for atmospheric ?
10 GV
P. Zuccon et al.
Tom GaisserOctober 29, 2002
Oxford
Technical aspects of 3D calculation• Brute force
– Generate showers randomly all over globe
– ~ 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, ~ ?
Tom GaisserOctober 29, 2002
Oxford
Higher energy atmospheric
• Mean E ~ 100 GeV for -induced upward
Tom GaisserOctober 29, 2002
Oxford
High energy ( e.g. )
• Importance of kaons– main source of
> 100 GeV
– p K+ + important
– Charmed analog important for prompt leptons
vertical60 degrees
Tom GaisserOctober 29, 2002
Oxford
Calibration with atmospheric
• MINOS, etc.• Neutrino telescopes
• Example*** of / e
– flavor ratio
– angular dependence
***Note: this is maximal effect:horizontal = 85 - 90 deg in plots
Tom GaisserOctober 29, 2002
Oxford
MINOS: +/- discrimination 1 < E < 70 GeV
a) No Oscillations b) Oscillations: full mixing, m2 = 0.0025eV2
1 GeV contained
10 GeV, contained
External (x 10-4)
Angular distribution of 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
Tom GaisserOctober 29, 2002
Oxford
Vertically upward interactions inside detector
E
E E
Nine angular bins in direction
so-
d/dy ~ const, but d/dy ~ (1-y)2, so oscillates vs E-
Problems: smears effect; statistics too low in MINOS
Tom GaisserOctober 29, 2002
Oxford
Global view of atmospheric spectrum
Prompt
e
Solar
Plot shows sum ofneutrinos + antineutrinos
Slope = 3.7
Slope = 2.7
Uncertainty in levelof charm a potentialproblem for finding diffuse neutrinos
Possible E-2 diffuse astrophysical spectrum (WB bound)
Tom GaisserOctober 29, 2002
Oxford
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
Tom GaisserOctober 29, 2002
Oxford
Summary (low energy)• Evidence for oscillation uses ratios:
– Contained events• ( )data / (e / )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
Tom GaisserOctober 29, 2002
Oxford
Summary (high energy)
• Kaon decays dominate atmospheric , e above 100 GeV
• Well-understood atmospheric , e useful for calibration
• Uncertainty in level of prompt neutrinos (from charm decay) will limit search for diffuse astrophysical neutrinos
Tom GaisserOctober 29, 2002
Oxford
What next?
• Use neutrino fluxes for calibration, etc.– MINOS, SNO, Neutrino telescopes…– Learn about charmed analog of K production
• Finish and use Giles’ 3D scheme
• Incorporate new hadro-production results– HARP below 15 GeV– NA 49, E907 ~ 100 GeV
Tom GaisserOctober 29, 2002
Oxford
Comparison to muons +, - 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 decayed to
Data from CAPRICE, 3D calculation of Engel et al. (2001)
Tom GaisserOctober 29, 2002
Oxford
Solar modulation• Neutron monitors
– well correlated with cosmic-ray flux
– provide continuous monitor
– response like sub-GeV neutrinos with no cutoff
– SNO, Soudan: <20% variation
– Kamioka: <5% (10 %) for downward (upward)
P. Lipari
Tom GaisserOctober 29, 2002
Oxford
a) No Oscillationsb) Oscillations: full mixing m2 = 0.0025 eV2
1 GeV contained
10 GeV, contained
External (x 10-4)
Angular distribution of
Tom GaisserOctober 29, 2002
Oxford
Tom GaisserOctober 29, 2002
Oxford
Soudan 5.9 kT yr
M. Goodman, Neutrino 2002
Electrons
Muons
Black lines: calculated, no oscillation
Blue lines: fitted with oscillations