P. BernardiniSeptember 10, 2006

ARGO-YBJ experiment

andTeV gamma astronomy

ARGO-YBJ detector

Cosmic rays

VHE -astronomy

Conclusions

YangBaJing (Tibet, China)

High Altitude Cosmic RayLaboratory (4300 m a.s.l.)

Longitude 90° 31’ 50” EastLatitude 30° 06’ 38” North

Astrophysical Radiation Ground-based Observatory

-ray astronomy Gamma Ray Burst physics Cosmic Ray physics Sun and Eliosphere physics

Detector layout

10 Pads = 1 RPC (2.80 1.25 m2)

78 m

111 m

99 m

74 m

12 RPC = 1 cluster ( 5.7 7.6 m2 ) 8 Strips = 1 Pad

(56 62 cm2) 42 clusters

104 clusters130 cluste

rs

BIGPAD

ADC

RPC

Read-out ofthe charge induced on“Big Pads”

Layer (95% active surface) of

Resistive Plate Chambers (RPC),

covering a large area (5800 m2)

+ sampling guard ring

+ 0.5 cm lead as -converter

December 2004 42 clusters January 2006 104 clusters June 2006 130 clusters

guard-ring under construction

Fall 2006: 154 clusters in data-taking

lead transport by means of the new Tibetan railway

Summer 2007: fully operative

Time Resolution (ns)

1 ns level

t (ns) HV (kV)

7.3 kV

HV (kV)

RPC layout & performance

• Bakelite RPC (5 1011 m)• Operation in streamer mode• Ar (15%) Isobuthane (10%) TFE (75%)• Efficiency >95 % at 7.5 kV (10 kV at s.l.)• Time resolution ~1 ns

Off-line Time Calibration & Angular Resolution Real events are used to calibrate the detector

(offline procedure in agreement with sampling hardware procedure) Measured angular resolution (even-odd method) in agreement with expected resolution

after

befor

e

residuals

= 0.09 ns

Final configuration

Longitudinal EAS

development

(Corsika simulation)

Primary energy: 1000 TeV

Proton

Iron

Argo-YBJ altitude

Main detector features and performance

Resistive Plate Chambers (RPC) as active elements

Space information from Strips ( pixel 6.5 62 cm2 )

Time information from 8-strip Pads ( resolution 1 ns)

Large area ( 11000 m2 ) and full coverage ( 5800 m2 )

High altitude (4300 m a.s.l.)

Pointing accuracy ( < 0.5°)

Detailed space-time image of the shower front

Detection of small shower (low threshold energy)

Field of View and duty-cycle 100%continuous monitoring of

the skyin the range -10°< <70°

Operation modes

Shower mode

Detection of Extensive Air Showers (direction, size, core …)

Trigger requirement: minimum number of fired pads

20 fired pads on the central carpet: rate ~5 kHz

Aims :cosmic-ray physics (threshold : few TeV)VHE -astronomy (threshold ~300 GeV) search for gamma-ray bursts

Scaler mode

counting rate (n 1,2,3,4) for each cluster, averaged in 0.5 s

Aims: detector and environment monitorflaring phenomena (GRB, solar flares) with a threshold of few GeV

Detector Control System

RPC current Barometric pressure

Temperature

Relative humidity

Continuous monitor of many detector and site parameters

EAS arrival times• Agreement with Poissonian statistics• Dead time and spurious effects are under control

Distribution of time differencebetween consecutive events

Distribution of event-multiplicityin a time window of 1 s

Unprecedented

view of showers

74 m

60 m

90 m

120 ns

Cosmic rayswith ARGO-

YBJ

Measurements

Size as Hit multiplicity (pad & strip)

Analog read-out of RPC pulse charges

Lateral density profile

Shower space-time morphology

Angular distributions (azimuth, zenith)

..... Energy spectrum

Chemical composition

Proton cross section

Check of the hadron interaction models

.....

Flux vs strip size

Lateral density profile

By means of the RPC analog measurement, a further extension is possible up to thousand TeV31 m

3500 particles

35 m

Energy up to hundreds of TeV by using the strip size

~10% systematic error on Ns

Comparison of ARGO-data with JACEE and RUNJOB spectra

“Bridge” between direct and indirect measurements

Flux versus strip size

(data and simulations)

High space/time granularity permits unprecedeted studies

on the EAS phenomenology(different topologies and time structures)

Very energetic shower

Evidence of strong conical shape in small showers

showerfront

show

er a

xis

shower core

Study of the time thicknessof the shower front

conical fit Average time residuals vs distance from the core

resid

ual

(ns)

core distance (m)

200<Nhit<500

DataSimulation (1-30 TeV)with Corsika + QGSjet

Azimuth () distribution

Expected behaviour in the angular range where the overburden atmosphereincreases as 1/cos

xo vertical depth (606 g/cm2 at YBJ)

attenuation length of showers

Deviations from this behaviour (sec - 1 > 1) due to misreconstructed events andhorizontal air showers

/ xαwith

1θ sec α exp I I

0

0

Fit: I0 = (165 ± 9) s-1 sr-1

= 5.6 ± 0.1

k is determined by simulations (interaction model dependent),selecting energy and age ranges by means of the actualexperimental observables

Flux attenuation and p-Air cross section

x0

1secexp )( 0

0 xII

Measurement of the flux attenuation

for fixed energies (and shower ages)

p-Air p-p]/[104.2][

2

INT4

INT

cmgmb

k

Airp

p-Air cross section… ARGO-YBJ approach

This analysis is a first test of such technique… to be employed in unexplored energy regions

R70 radius of circle including 70% of hits

Event selection based on

(a) “shower size” as Nhit (pad multiplicity)

(b) core reconstructed in a fiducial area (30 x 30 m2)

(c) constraints on shower density profile and extension (R70 < 20 m)

data = (81.3 ± 0.6) g/cm2 data

= (76 ± 2) g/cm2

(sec -1) distributions

Full Monte Carlo simulation of proton showersCorsika + QGSjet, detector response,trigger and analysis chain used for real data

Energy

estimate

Nhit<500 Nhit>500

<Ep>= 3.67 ± 0.04 TeV <Ep>= 14.3 ± 0.2 TeV

QGSjet from with 104.2

][ ]/[ k

4

2

Airp

Airp mbcmg

MC = (75.4 ± 0.8) g/cm2 MC

= (71 ± 1) g/cm2

k-factor

evaluation

k = 0.96 ± 0.05 k = 0.97 ± 0.05

p-N cross section

Hit numbers <E> (TeV) k p-Air (mb) p-N (mb)

< 500 3.67 ± 0.04 0.96 ± 0.05 283 ± 15 40 ± 4

> 500 14.3 ± 0.2 0.97 ± 0.05 307 ± 20 47 ± 5

VHE gamma astronomy

Exciting results in -astronomyMany important discoveries from Imaging

Atmospheric Cerenkov Telescopes (HESS, MAGIC and so on)

new sources in the Galactic Plane (SNR, PWN …) source in the Galactic Center new Active Galactic Nuclei many sources have been

mapped (spectrum) SNRs as VHE -radiation sources and sites of cosmic-ray production

HESS survey of the Galactic plane

LSI+61 303Micro-Quasar

1ES1218 (z=0.18)New Source

PG 1553 (Z>0.25) New source

Some sources detected by MAGIC

Complementary measurements Sky survey looking for emission from unknown gamma-sources

Monitor variable sources (i.e. variable luminosity of Mrk 421)

Improve the sensitivity to flaring sources and GRB’s

Probe structures larger than Cerenkov telescope Field of View

Ground-based detectors with:

- large effective area- high angular resolution- duty-cycle close to 100%- wide Field of View

The energy threshold of sampling EAS arrays is too high (tens of TeV)

The high altitude and the full coverageallow to lower the energy threshold

large exposure(FoV time)}

MilagroWater-Cerenkov EAS

detector (2630 m a.s.l.)located near Los Alamos

5000 m2 pond with an external array of 175 water tanks

First PMT layer under 1.5 m of waterSecond PMT layer under 8 m of water (sensitive to hadronic component of the shower, used for background rejection)

HAWC

Cygnus Region

Mrk 421

Crab Nebula

Energy threshold ~2 TeV

Angular Resolut. ~0.5°

ARGO-YBj approach

Lower energy threshold as an effect of the altitude ( ~300 GeV)

Continuous monitoring of the entire overhead sky (FoV duty-cycle

100%)

Angular resolution (<0.5°)

Search for point-like or extended sources looking for flux excess in proper angular bins

Increase the flux sensitivity with the /h discrimination (space-time pattern of the showers)

Npad > 500 <E> ~ 20 TeV

West East

So

uth

N

ort

h Observed significance:

n = 3.9

Expected significance:

n = 4.0

The measured deficit size (0.6°±0.3°) is compatible with the simulated Moon

size (0.4°)

Observed event deficit compatible

with the expected one

The Moon shadow

Implementing /h discrimination (I)

The photon signal is statistically identified by looking for an excess,

from a given direction, over a background due to charged cosmic

rays

The study of the shower space-time pattern can allow /h

discrimination and then larger sensitivity

Encouraging results from

Multiscale analysis + ANN

Photon Shower Proton Shower

Implementing /h discrimination (II)

Results obtained with different algorithmsbased on the analysis of the shower imageMultiscale shower image analysis Shower topology and Lat. Dens. Funct.

/h discrimination

First results with 42 clusters

( 0.6 billion events in 1000 hours live time )

Mkn 421

Mkn 501Crab

The distributionof the standard deviations

do not show any excessfor this small sample

Search for GRB’sThe data collected in scaler mode (E > 1 GeV) are

analyzed searching for possible high energy tails of GRBs

The search is performed on satellite-triggered bursts

( Three sigma cut )

ARGO-YBJ

EAS-TOP

Chacaltaya

The ARGO sensitivity to GRB’s (42 clusters) Fluence limits for HETE/Swift observed GRBs

ConclusionsARGO-YBJ

The detector is almost completed (presently 130/154 clusters in data taking)

Data analysis shows good performance in shower reconstruction

First results in cosmic ray physics. Promising extension to unexplored Ep regions. In the future, check of the hadronic interaction models. Contributions to atmospheric neutrino study ?

-astronomy

The -sky is more and more crowded

Atmospheric Cerenkov and full-coverage EAS detectors are complementary to detect steady and transient, point-like and extended -sources, to discover where and how cosmic rays (and neutrinos) are produced

The contribution of ARGO-YBJ is beyond the corner