The Auger Observatory and UHE neutrinos

• Why UHE neutrinos ?

• What is the Auger Observatory ?

• How can it see UHE neutrinos ?

• How to discriminate them ?

• What sensitivity ?

NO-VE 2006 Pierre Billoir, LPNHE Paris, CNRS/univ. Paris 6 and 7 Auger Collaboration P. Billoir, NO-VE 2006 1

UHE neutrinos

• expected from interaction of accelerated particles with photons in the source region or with the CMBR (GZK effect):

relatively soft spectrum

• decay of ultra massive objects:

harder spectrum expected:

UHE photons and neutrinos are a signature of top-down scenarii propagation in straight line: point to the source differences with photons : - propagation over cosmological distances - low probability to produce an observable atmospheric shower Photons and neutrinos:

possible interesting byproducts of the Auger Observatory

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general framework

• n oscillations : ~ equal fluxes of the 3 flavours • assume neutrinos

weakly interacting

, even at UHE • probability of interaction in atmosphere <~ 10 -4

better sensitivity to

n t t

in earth skimming scenario

(

t

emerging within a few degrees from horizontal)

This study: based on Astrop. Phys. 17 (2002) 183 (X. Bertou, P.B., O. Deligny, C. Lachaud, A. Letessier-Selvon) + work on first Auger data (2004-05) (special contribution of Oscar Blanch Bigas) P. Billoir, NO-VE 2006 3

Battery box

Water Cherenkov tanks

GPS antenna Communications antenna Electronics enclosure Solar panels 3 nine inch photomultiplier tubes

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Plastic tank with 12 tons of water

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Optical system (fluorescence telescopes)

corrector lens (aperture x2) 440 PMT camera 1.5° per pixel segmented spherical mirror aperture box shutter filter UV pass safety curtain

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Hybrid detection

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“normal” (nucleic) showers

almost vertical:

thick curved front

muons + electromagnetic very inclined:

thin flat front

High energy muons P. Billoir, NO-VE 2006 14

a real vertical event (20 deg)

Noise !

doublet P. Billoir, NO-VE 2006 15

a real horizontal event (80 deg)

“single” peaks : fast rise + exp. light decay ( t ~ 70 ns)

accidental background signals are similar

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neutrino showers

(distinguishable if almost horizontal)

downgoing

(direct

n

interaction in atmosphere)

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(

upgoing n t t

in earth decay in flight )

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Simulation chain

• inject n t at 0.1, 0.3, 1, 3, …, 100 EeV into earth crust • generate c.c. and n.c interactions (CTEQ4-DIS) , t decay and energy loss • if a t emerges: generate decay in atmosphere

(modes e,

p

,

pp 0

,

ppp 0

,

pp 0 p 0

,

ppp

,

pppp 0 • apply a specific analysis (trigger + selection)

,

pp 0 p • inject the products of decay into AIRES (shower simulation package) • regenerate particles entering the tank from the “ground” output file • simulate the Cherenkov response and FADC traces 0 p 0 +

neutrinos)

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ground spot

decay of an horizontal t of 1 EeV e nn ( almost pure e.m. cascade) pn ( hadronic+e.m. cascade)

injected

t average level of trigger P. Billoir, NO-VE 2006 19

Simulated t p + ( 0.27 EeV) n 400 m above ground P. Billoir, NO-VE 2006 20

Simulated t p + ( 5.1) p 0 (16.1) n 1800 m above ground P. Billoir, NO-VE 2006 21

n

candidate selection

1.

“young” showers

online local triggers (one tank): • threshold : one slot above

Th

(detection of peaks) •

time over threshold

:

N

3 m s above

th

slots within (detection of long signals)

Global condition: at least 3 t. o. th. stations satisfying area/peak > 1.4 * “single” one “central” + one within 1500 m + one within 3000 m

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Trigger efficiency

Fraction of decaying t (

excluding

mnn

channel

) giving a trigger E n = 0.1 EeV E n = 1 EeV 1 km E n = 10 EeV P. Billoir, NO-VE 2006 2 km E n = 100 EeV 23

footprint analysis

Variables defined from the footprint

(in any configuration, even aligned)

• •

length

L and

width

W (major and minor axis of the ellipsoid of inertia)

“speed”

for each pair of stations (distance/difference of time) t i d ij t j P. Billoir, NO-VE 2006 24

n

candidate selection

2. Discriminating variables

Search for

long shaped

configurations, compatible with a front moving

horizontally

at speed c,

well contained

(background: vertical or inclined showers, d/

inside the array D

t > c )

cuts: L/W > 5 0.29 < av. Speed < 0.31 r.m.s. < 0.08

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What can be measured ?

•

direction

: precision better than 2deg

(improving with N stat )

•

energy

: possible lower bound for a given event unknown energy losses - estimation of E shower in interaction/decay chain depends on altitude possible strategy: inject in the simulation chain a spectrum with a given shape deduce from the selected data a level (or an upper bound)

model dependent result

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main sources of systematic errors

•

detection:

triggering/selection efficiency, effective integrated aperture: to be evaluated

(not dominant)

• cross section of neutrinos • energy loss of t in earth: big uncertainty !

bremsstrahlung + pair production: well defined - deep inelastic scattering in photonuclear process: “pessimistic” hypothesis from

Dutta et al, Phys.Rev. D63 (2001) factor of ~5 between low and high estimation of the acceptance P. Billoir, NO-VE 2006 27

Auger sensitivity

TD AGN GRB GZK Points: 1 event / year / decade of energy P. Billoir, NO-VE 2006 28

upper bounds for 1 year of full Auger

(if no candidate) (“pessimistic” hypothesis for t energy loss) Solid: various models from Protheroe (astro-ph/9809144) Dashed: upper bounds at 95 % C.L. for each shape if no candidate P. Billoir, NO-VE 2006 29

summary and perspectives

• the surface array of Auger is sensitive to UHE neutrinos

most promising: earth skimming (decay of

t

in air)

• real data are

clean

• simple criteria allow to reject the background

still room for refinement of criteria…

• constraining upper bounds expected within a few years Ongoing studies: • other criteria to select neutrino candidates • specific trigger to enhance sensitivity at low energy • acceptance calculations • shower energy evaluation • observation with the fluorescence detector • atmospheric n interactions (less horizontal) P. Billoir, NO-VE 2006 30