UHE photons and neutrinos at the Pierre Auger Observatory

Enrique ZasDepartamento de Física de Partículas &

Instituto Galego de Física de Altas Enerxías,Universidade de Santiago de Compostela, SPAIN

Enrique ZasDepartamento de Física de Partículas

Instituto Galego de Física de Altas EnerxíasUniversidad de Santiago de Compostela

for the Pierre Auger Collaboration

A Hybrid detectorTwo techniques:

Fluorescence (FD)

Particle detector array (SD)

Redundant~ 10% of events are observed with both: wealth of information about shower development & exploit SD

SD

Fluorescence light

E. Zas

FD

Digitised signals: FADC

Time [ns]25 ns time bins

Communicationsantenna

Low consumption electronics

Solar panels

Battery box

3 photomultiplier tubes

Rotomolded plastic tank

12 tons of purified water

GPSSD Units

Calibrated online regularly using signals induced by atmospheric muons

• At detector level– Signal: Number of particles – Start time: timing– Rise time: Sperad of particle arrival – Area over Peak: low for single muons– Structure: jumps -> muon counting ....

• At shower level– Shower size– Direction– Xmax (FD)– Curvature of particle front

Rich SD data: Useful observables which can be correlated with hybrid data

Sig

nal

(V

EM

)

Time (ns)

“Fast & narrow signal” produced by

muonic component

“Slow & broad signal”

produced by EM component

Time (ns)

25 ns time resolution allows distinction between broad and narrow signals

Sig

nal

(V

EM

)

L C, RAV, AAW, EZ (Ap Phys 2004)

Xmax and curvature are related

Xmax

Larger Xmax => larger curvature(smaller radius)

2

2

2

1

z

rzltc

Time delay of first muon (curvature) & average

400

300

200

100

0

200

150

100

50

0

120

80

40

0

80

60

40

20

0

(ns)

600 700

800 870

Apparent for s in hadronic showers

Distance to core

1000 m 1000 m

Risetime also related to Xmaxmuons travel in straight lines

em component straggles

2

2

2

2

2

1

zz

r

z

rRisetime

zTwo main reasons: 1. Z range (production)

1. 2. less delayed than e & Deep showers have more em component

Photon Search

Basis: Xmax discrimination

-induced showers reach maximum deeper in the atmosphere than nucleonic ones

P. Homola for the Auger Collab., ICRC 2009

Use Surface Detector data

Two discriminating observables

• Radius of curvature of shower front

• Time structure of shower front (Risetime)

(both correlated to Xmax)

Rise time is the time it takes to go from 10% to 50% of the total

signal

Sig

nal

(V

EM

)

Time (ns)

50% of integrated signal

Astroparticle Physics 29 (2008) 243-256

Surface Detector

Deviation of Risetime w.r.t. to mean [ units]

Dev

iati

on

of

Cu

rva

ture

w.r

.t. t

o m

ean

[

un

its]

MC photonsData

MC photons

5% Data

Cut: Median of distribution

Principal component analysis

Cut

Direct Xmax search: HybridAstroparticle Physics 27 (2007) 155 & arXiv 0903.1127v2

Quality cuts• More than 6 PMTs • Shower axis distance to highest signal SD station <1.5 km • Reduced 2 (profile fit) <6 and ratio to 2 (line fit) <0.9 • Xmax within field of view

Fiducial volume cuts avoid biasses:

• Zenith> 350 +g1(E) [35+7 @ 1019.7

• Distance to telescope < 24 km +g2(E)• Viewing to shower axis angle >150 (Cherenkov rejection) • E>2, 3, 5 and 10 EeV

Full simulations made (Corsika, QGSJET01, FLUKA): • Fotons • Protons • Iron

Quality cuts

Hybrid

Fiducial volume cuts

Hybrid search: candidates

Cut: Median of the simulated photon Xmax distribution

5% of protons simulated with QGSJET01 above this line

Uncertainties:

(Xmax) ~ 16 g cm-2

(E)/E ~ 22 %

E cand p(Fe)

2 EeV

8 30 (0.3)

3 1 12 (0.2)

5 0 4 (0.1)

10 0 1 (0)

Deepest event observed

3.8%

2.4%3.5% 2.0%

5.1%

31 %

A1, A2 = AGASA

HP = Haverah Park

Y = Yakutsk

Limits on fractions: SD & HybridP. Homola for the Auger Collab., ICRC 2009

Strong constraints on: Super-Heavy DM & Topological Defect models

fraction constrained in Energy - range2 EeV → 40 EeV

Neutrino Search

Cosmic rays at ultra high energy (neutrino?)

V.S. Berezinsky, G.T. Zatsepin

Academy of Sciences of the USSR, Physical Institute, Moscow, Russia

Physics Letters B Vol. 28, Issue 6, pp. 423-424 (1969)

Received: 8 November 1968Published: 6 January 1969

Abstract:

The neutrino spectrum produced by protons on microwave photons is calculated. A spectrum of extensive air shower primaries can have no cut-off at an energy E>3 1019 eV, if the neutrino-nucleon total cross-section rises up to the geometrical one of a nucleon.

Cosmogenic s

• 1969 Inclined showers for neutrino detection Berezinsky, Zatsepin

• 1987 bound with Fly’s Eye Fly’s Eye

• 1991-97 bounds with Tokyo data Halzen, EZ, ...

• 1996 Auger UHE possibilities shown Capelle, Cronin, Parente, EZ

• 1999 Earth skimming effect Fargion / Lettessier-Selvon & Bertou, Billoir

• 2007 First earth skimming experimental bound Auger / HiRes

Selected developments in neutrino search with EAS:

Inclined showers Protons, nuclei, :Shower ’s e+’s and e-’s

do not reach ground level Only muons

vertical atmospheric depth

e+e-

0 2000 4000 6000 8000 10000 12000

Depth (g/cm2)

Inclined hadron Air Showers

Case 2: Earth-skimming

Complex three stage process• Attenuation through Earth and regeneration: NC CC & t CC CC & t decay• CC interaction, t energy loss and no decay• Exit and t decay in the atmosphere

Air shower

Earth

Air shower

Earth

Case 1: down-going

Detection (deep)=>inclined

Upgoing: detection=>inclined)

“Earth skimming”

Low loss => large target volume

Large density: Earth’s crust

Only sensitivity to CC channel

Small zenith angle range (50) (solid angle)

Auger results: PRL 100 (2008) 211101 Jan 04- Aug 07PRD 79 (2009) 102001 Jan 04- Apr 08

Shower•EM + Hadronic •Hadronic •Hadronic• decay

•Hadronic•EM•NO shower• decay

Channel

•CC einteractions

•NC interactions

•CC interactions

•CC the decay

•Resonant einteract

• qq• ee

•

•

Energy Transfer100%25%25%40%

100%25%

50%

Low density targetZenith angle range 750(600?)-900

All channels and flavors. Relative contributions:

x flv3 x 21 x 63 x 43 x 2

6 x 11 x 11 x 11 x 1

“Down-going”

Searching for in data: general criteria

Footprint of the shower on ground compatible with that of an inclined shower: Elongated pattern (large Length over Width). “Speed of propagation of signal” along Length, close to speed of light. Angular reconstruction.

(1) Search for Inclined Showers

D. Gora for the Auger Collab., ICRC 2009

Inclined proton/nuclei showers induced high in the atmosphere: (mainly) of muons at ground.

Neutrinos: inclined showers with broad traces

“Slow & broad signal” produced by EM component

“Fast & narrow signal” produced by muonic component

(2) Search for showers with large electromg component

Selection for earth skimming neutrinos• Trace cleaning (remove random muons) • Inclined

• signal pattern length/width>5 (elongated) • 0.31 m/ns > ground speed > 0.29 m/ns (horizontal)• r.m.s. (ground speed) < 0.08 m/ns (compatible)

• Electromagnetic• >60% of stations satisfy “Offline ToT” (Time over threshod: 13 bins

above 0.2 VEM)• Signal over peak>1.4

• Central trigger condition only to Off Tot stations• Quality trigger (T5)

Selection for down going neutrinos• Only events of 4 or more stations

• Trace cleaning (remove random muons) • Inclined

• signal pattern length/width>3 (elongated) • 0.313 m/ns > ground speed > 0.29 m/ns (horizontal)• r.m.s. (ground speed) < 0.08 m/ns (compatible)• Zenith reconstructed < 750

• Electromagnetic• Fisher discriminant analysis on ten variables (related)

Acceptance (Monte Carlo)

Earth skimming • Earth conversion of to • decay in the atmosphere • extensive air shower• Trigger and identification

efficiency (E, h10km)• detector exposure

(integration over running array)

Down-going• Atmospheric interactions

Down-going neutrino channels

F = a1·var1 +a2·var2

Maximise discrimination power using multivariate analysis (Fisher discriminant).

Very simple idea:– Find “projection line” for maximal hadrons & separation

var2

var1

Simple example in 2D

Neutrinos

HAS

Fisher discriminant analysis

F is a linear combination

)(σ(HAS)σ

FFR

2F

2F

νHAS

2)(

“mean” of F for HAS and neutrinos maximally SEPARATED relative to

Variance of F for HAS Variance of F for neutrinos

Fisher discriminant analysis

F is the linear combination of discriminating variables used maximising the ratio:

Ten discriminating variables:First 4 AOPsFirst 4 (AOPs)2. Product of the first 4 AOPs. An asymmetry parameter: “Mean[early AOP] - Mean[late AOP]”.

Variables for Fisher methodExploit that neutrino showers have: (1) Broad signals in the early part(2) Asymmetry in time spread of signals between early and late parts.

Training data 01Jan04-31Oct07 (black) and Nu showers (red)

Area Over Peak of the first T2 tank AOP Product of the first four T2 tanks

Useful variable: AOP = integrated signal over peak signal

Sig

nal

(V

EM

)

Broad signal Large AOP

Time (ns) Time (ns)

Narrow signal Small AOP

“Early” region “Late” region

Neutrinos interacting deep in the atmosphere

Asymmetry in time spread:

Spread in time of the FADC trace of each station in an event

Real inclined event Simulated down-going neutrino

Attenuation of the EM component of the shower from the earliest to the latest station

early

early (broad signals)

late (narrow signals) late

Each dot represents a station in the event

(μs) (μs)

Sp

read

in t

ime

of

the

sig

na

l [n

s]

Sp

read

in t

ime

of

the

sig

na

l [n

s]

Example distributions:Inclined real events (black) Simulated nu showers (red)

early – late asymmetry parameter of the event

AOP of the 1st tank in the event

Blind search for neutrinos:Data from 01 Jan 04 to 31 Oct 07 used to “train” Fisher method:

• Select the best discriminating observables.

• Set cuts in Fisher variable above which an event is a candidate.

Data from 01Nov07 to 28Feb09 to do a blind search for neutrinos

No neutrino candidates in the search period

Flux limits for a E-2 neutrino spectrum

AUGER limits Down 01Nov07- 28Feb09 Up 01Jan04-28Feb09

K [GeV cm-2 s-1 sr-1] 3.2 x 10-7 4.7 x 10-8

J. Tiffenberg for the Auger Collab., ICRC 2009

COSMOGENIC s