particle physics seminar

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


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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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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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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


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Overview of the calculation


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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


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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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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%


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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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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


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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

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From cover of “Cosmic Rays” byA.M. Hillas (1972)


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Response functions, sub-GeV • Eprimary ~ 10-20 x E

• Up/down ratio opposite at Kamioka vs Soudan/SNO


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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


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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


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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


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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%?


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– 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.


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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, ~ ?


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Higher energy atmospheric

• Mean E ~ 100 GeV for -induced upward


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High energy ( e.g. )

• Importance of kaons– main source of

> 100 GeV

– p K+ + important

– Charmed analog important for prompt leptons

vertical60 degrees


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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


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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


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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


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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)


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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


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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


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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


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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


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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)


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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


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a) No Oscillationsb) Oscillations: full mixing m2 = 0.0025 eV2

1 GeV contained

10 GeV, contained

External (x 10-4)

Angular distribution of


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Soudan 5.9 kT yr

M. Goodman, Neutrino 2002

Electrons

Muons

Black lines: calculated, no oscillation

Blue lines: fitted with oscillations

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