RubenConceiçãoP.Assis,U.BarresdeAlmeida,A.Blanco,A.DeAngelis,

P.Fonte,L.Lopes,G.Matthiae,M.Pimenta,R.Shellard,B.Tomé

RICAP,Rome,June23rd 2016

LATTES:anewgamma-raydetectorconceptforSouthAmerica

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Currentexperimentalstatus

2

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CurrentSituation

3

• NowideFoVexperimentto:

– SurveytheGalacticCenter(GC)

– Exploretheenergyregionof100GeV

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MAGICCrab

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LHAASO

Crab

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Requirements

4

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Argo

CTA

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HESS

LHAASO

MAGICCrab

• BuildanEASarrayexperiment:

– LocatedintheSouthHemisphere

– Lowenergythreshold:

• Highaltitude

• Nextgenerationdetectorconcept

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Solution

5

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Argo

CTA

Fermi

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HESS

LHAASO

MAGICCrab

• BuildanEASarrayexperiment:

– LocatedintheSouthHemisphere

– Lowenergythreshold:

• Highaltitude

• Nextgenerationdetectorconcept

LATTES6

LATTES @ ALMA siteLarge Array Telescope for Tracking Energetic Sources

• Planned site:• Atacama LargeMillimeter Array site

• Chajnantor plateau• 5200 meters altitude in north Chile• Good position to survey theGalactic Center

LATTESconcept

7

LATTES station

PbRPC

WCD

– Thinleadplate(Pb)• 5.6mm(one radiation lenght)

– ResistivePlateChambers (RPC)• 2RPCsperstation• EachRPCwith4x4readoutpads

– WaterCherenkovDetector (WCD)• 2PMTs(diameter:15cm)• Dimensions:1.5mx3mx0.5m

LATTESconcept

8

• Hybriddetector:– Thinleadplate

• Toconvertthesecondaryphotons• Improvegeometric reconstruction

– ResistivePlatesChamber• Sensitivetochargedparticles• Goodtimeandspatialresolution• Improvegeometricreconstruction• Exploreshowerparticlepatternsatground

– WaterCherenkovDetector• Sensitivetosecondaryphotonsandchargedparticles

• Measureenergyflowatground• Improvetriggercapability• Improvegamma/hadrondiscrimination

LATTESstation1.5mx3mx0.5m

LATTEScorearray30x60stations100x100m2

Signal/p.e.)Σ(10

Log1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

(# R

PC h

its)

10Lo

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1−

0

1

2

3

41TeV500GeV100GeV

photonproton

1TeV500GeV100GeV

photonproton

1TeV500GeV100GeV

photonproton

1TeV500GeV100GeV

photonproton

1TeV500GeV100GeV

photonproton

1TeV500GeV100GeV

photonproton

LATTES:complementary

9

• Combineddetection:– Lowertheenergythreshold

• Improvethetriggerconditions(WCD)

– Enabledetectorinter-calibrations• Energycalibrationcanbeusedtocontroldetectorsystematicuncertainties

• CheckMonteCarlosimulationsperformance

– Enhancegamma/hadrondiscrimination• Exploreshowercharacteristics• AccesstoArgo/HAWCdiscriminationtechniques

)hits

(N10

log1− 0 1

(Sig

nal/p

.e)

10lo

g

0

2

4

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abilit

y

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No hits

mean

100GeV photons

WCDvs RPC(stationlevel)

• LATTESperfomance:• Triggerefficiency• EnergyReconstruction• GeometricReconstruction• Gamma-hadrondiscrimination

• LATTESsensitivity

SimulationFramework

11

• Completeend-to-endsimulationchaintoevaluateLATTESperformance– ShowerssimulatedusingCORSIKA

– DetectorlayoutandsimulationperformedbyGeant4

– LATTESsim:IntegratedtoolkittostudyandoptimizeLATTESperformance

ShowerSimulation

DetectorSimulation

Analysis/Reconstruction

• Fixed energies: 104 showers were simulated in energysteps between 30 GeV and 100 GeV; for energies between100 GeV and 1 TeV, 103 showers were produced. Themaximum distance of the random core with respect to thecenter of the array is set according to the energy of theprimary, varying between 200 m for E0 = 30 GeV and600 m for an initial energy E0 = 1 TeV.

• Continuous energy spectrum: the minimum energy is10 GeV for the photons and 40 GeV for the protons; themaximum energy is 5 TeV. About 2 ⇥ 103 showers wereused for each primary, with the core generated inside anarea of (110 ⇥ 110) m2.

E [GeV]210 310 410 510 610

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) in

10pa

rticl

esN

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o x 1 oCosmic rays in 1

Crab

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(> E

) o

x 1

o 1C

R (>

E) /

NC

rab

N

5−10

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3−10

2−10

1−10

Figure 4: Top: Signal above a given energy on a surface of 10000 m2, integratedover 1 second: Crab (solid line) and background from charged cosmic rayswithin one square degree (dashed line). Bottom: ratio signal/background fromthe above plot.

Once atmospheric showers have been simulated and the in-formation of the electrons and photons reaching a height of5200 m a.s.l. is recorded, we simulate the response of the detec-tor. For the simulation of the response of the detector units, theGEANT4 [23, 24] toolkit is used. The wavelength dependenceof the relevant optical parameters, such as the photomultiplier’squantum e�ciency, the water absorption length and the reflec-tivity of the walls, is accounted for in the simulation.

In order to evaluate the performance of the detector, we con-sider a source with an emission energy distribution like the CrabNebula.

[GeV]0E210 310

]2Ef

fect

ive

Area

[m

1

10

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310

410

510

Photon (trigger only)

Proton (trigger only)

Photon (trigger + selection)

Proton (trigger + selection)

Figure 5: E↵ective area at trigger level (solid curves) and after the cuts used forthe shower direction reconstruction (dashed curves), separately for gamma-ray-and proton-initiated showers.

The Crab Nebula is a nearby (⇠ 2 kpc away) pulsar windnebula and the first source detected in VHE gamma-rays [25].Moreover, it is the brightest steady VHE gamma-ray source,therefore it has become the so-called standard candle in VHEgamma-ray astronomy. Recent observation of flares in the GeVrange [26, 27] have however shown that occasionally the Crabflux can vary.

The stationary flux from the Crab Nebula follows, accordingto the measurements from MAGIC [28], a law

dN�dE' 3.23⇥10�11

✓ ETeV

◆�2.47�0.24( ETeV )

TeV�1s�1cm�2 .(1)

For the spectral energy distribution of background cosmicrays we have used the expression

dNdE' 1.8 ⇥ 104

✓ EGeV

◆�2.7GeV�1s�1sr�1m�2 ; (2)

the approximation is valid from some 10 GeV to about 1 PeV.The number of photons from Crab per m2 per second above

a given threshold are shown in Fig. 4, and compared to thebackground from cosmic rays in a square degree.

The photon and proton showers, simulated with an energyspectrum with index -1.0, are weighted by E0 ⇥ f (E0), where fis the di↵erential energy spectrum in Eqs. 1 and 2, respectively,and E0 is the energy of the primary particle.

5. Estimated performance

5.1. E↵ective area at the trigger level

We use a trigger selection which requires that at least threestations have detected a signal; the trigger condition for eachstation requires at least 5 photoelectrons in either photomul-tiplier. The e↵ective area at trigger level, i.e., the integral ofthe surface times the trigger e�ciency, is shown in Fig. 5 forgamma-ray and proton initiated showers.

5

Triggerefficiency

12

• UseWCDstationstotrigger atlowenergies– Triggercondition

• Station:requiremorethan5p.e. ineachPMT• Event:require3triggeredstations

– EffectiveAreaof1000m2 at 100GeV!(after quality cuts)

Energyreconstruction

13

• Useasenergyestimator thetotalsignal recordedbyWCDs• Energyresolutionbelow100%evenat100GeV

– Dominatedbytheshowerfluctuations

[p.e.]totS210 310 410 510 610

[GeV

]0E

210

310

410

E [GeV]210 310

[deg

],6

8θσ

0

0.5

1

1.5

2

Figure 6: Angular resolution for gamma-ray primaries with zenith angle ✓ =10�, as a function of the energy. The points were fitted to the functional formk/p

E.

5.2. Angular resolutionWe reconstruct the arrival direction of the particle initiating

the shower from the positions and the arrival times of particlesin the stations; we assume a time resolution of �t = 1 ns, whichcan be achieved by present RPCs with a standard electronics. Inorder to improve the angular reconstruction it is required thatthe event has at least 10 active RPC pads. We compare thereconstructed angle with the angle in the simulation, and wecalculate the 68% containment angle, �✓,68. The results as afunction of the reconstructed energy are shown in Fig. 6. Fromthis figure it is possible to see that a reasonable resolution, betterthan 2�, can be achieved at energies around 100 GeV.

5.3. E↵ective area at the reconstruction levelAfter the event selection for the shower direction reconstruc-

tion, we further require that the direction of gamma showers iswithin the 68% containment radius defined by the angular res-olution. The e↵ective area after these cuts is shown in Fig. 5,for proton-initiated showers and for gamma-initiated showers.

5.4. Energy estimateThe shower energy is reconstructed from the total signal, de-

fined as the sum of the number of photoelectrons in all WCDstations. A calibration curve is obtained using the photon sim-ulation with the Crab spectrum, by plotting the median of thegenerated photon energies in each bin of measured signal, as afunction of the median of the measured signal. The dependenceappears approximately linear for E0 > 300 GeV.

The non-linearity, defined as the relative di↵erence betweenthe median of the reconstructed and true energies assuming thecalibration constant computed for E0 > 300 GeV, is shown inFig. 7, top, as a function of the reconstructed energy.

The reconstructed energy follows quite well a log-normaldistribution as a function of the generated energy. The en-ergy resolution was thus calculated by fitting the distributionof ln(E/E0) with a Gaussian function; the relative resolution isshown in Fig. 7, bottom. The resolution on the reconstructedphoton energy depends both on the detector resolution and onthe fluctuations in the shower development.

E [GeV]210 310

0)/E 0

(E-E

0.5−

0

0.5

E [GeV]210 310

) 0(E

/Eσ

0

0.5

1

1.5

Figure 7: Top: Non-linearity in the reconstructed energy, for photons with aspectral energy distribution as for Crab nebula. Bottom: Resolution in the re-constructed energy, for the same sample of photon-initiated showers.

5.5. Hadron background suppression

The hybrid configuration of the detector units allows to com-bine the background rejection techniques used by ARGO andHAWC [12, 15]. Large signals in WCDs away from the coreare mostly due to isolated muons, a characteristic signature ofshowers initiated by hadrons. In addition, the RPCs on topprovide important additional information about the structure ofisolated energetic particle clusters, which allows to further im-prove the gamma-hadron discrimination. The development of ahadron rejection algorithm, which combines the information ofthe two sub-dectectors is out of the scope of this article. Con-servatively, no background rejection was considered below 200GeV, and above this energy the performance of HAWC [28] wasassumed.

5.6. Significance of the Crab signal

Gamma-initiated events have been selected within the angu-lar window defined by the cone with half-aperture equal to theangular resolution for photons. The cosmic-ray background hasbeen calculated for the same window, assuming an isotropicflux. The event rate in each bin of reconstructed energy, beforebackground suppression, is shown in the top plot of Fig. 8.

We then computed the number of events for one year of ef-fective time, after applying the hadron suppression e�ciencycurves; the result is shown separately for signal and background

6

E0 ! Simulated energyE ! Reconstructed energy

EnergyResolutionEnergyCalibration

Geometricreconstruction

14

E [GeV]210 310

[deg

],6

8θσ

0

0.5

1

1.5

2

Figure 6: Angular resolution for gamma-ray primaries with zenith angle ✓ =10�, as a function of the energy. The points were fitted to the functional formk/p

E.

5.2. Angular resolutionWe reconstruct the arrival direction of the particle initiating

the shower from the positions and the arrival times of particlesin the stations; we assume a time resolution of �t = 1 ns, whichcan be achieved by present RPCs with a standard electronics. Inorder to improve the angular reconstruction it is required thatthe event has at least 10 active RPC pads. We compare thereconstructed angle with the angle in the simulation, and wecalculate the 68% containment angle, �✓,68. The results as afunction of the reconstructed energy are shown in Fig. 6. Fromthis figure it is possible to see that a reasonable resolution, betterthan 2�, can be achieved at energies around 100 GeV.

5.3. E↵ective area at the reconstruction levelAfter the event selection for the shower direction reconstruc-

tion, we further require that the direction of gamma showers iswithin the 68% containment radius defined by the angular res-olution. The e↵ective area after these cuts is shown in Fig. 5,for proton-initiated showers and for gamma-initiated showers.

5.4. Energy estimateThe shower energy is reconstructed from the total signal, de-

fined as the sum of the number of photoelectrons in all WCDstations. A calibration curve is obtained using the photon sim-ulation with the Crab spectrum, by plotting the median of thegenerated photon energies in each bin of measured signal, as afunction of the median of the measured signal. The dependenceappears approximately linear for E0 > 300 GeV.

The non-linearity, defined as the relative di↵erence betweenthe median of the reconstructed and true energies assuming thecalibration constant computed for E0 > 300 GeV, is shown inFig. 7, top, as a function of the reconstructed energy.

The reconstructed energy follows quite well a log-normaldistribution as a function of the generated energy. The en-ergy resolution was thus calculated by fitting the distributionof ln(E/E0) with a Gaussian function; the relative resolution isshown in Fig. 7, bottom. The resolution on the reconstructedphoton energy depends both on the detector resolution and onthe fluctuations in the shower development.

E [GeV]210 310

0)/E 0

(E-E

0.5−

0

0.5

E [GeV]210 310

) 0(E

/Eσ

0

0.5

1

1.5

Figure 7: Top: Non-linearity in the reconstructed energy, for photons with aspectral energy distribution as for Crab nebula. Bottom: Resolution in the re-constructed energy, for the same sample of photon-initiated showers.

5.5. Hadron background suppression

The hybrid configuration of the detector units allows to com-bine the background rejection techniques used by ARGO andHAWC [12, 15]. Large signals in WCDs away from the coreare mostly due to isolated muons, a characteristic signature ofshowers initiated by hadrons. In addition, the RPCs on topprovide important additional information about the structure ofisolated energetic particle clusters, which allows to further im-prove the gamma-hadron discrimination. The development of ahadron rejection algorithm, which combines the information ofthe two sub-dectectors is out of the scope of this article. Con-servatively, no background rejection was considered below 200GeV, and above this energy the performance of HAWC [28] wasassumed.

5.6. Significance of the Crab signal

Gamma-initiated events have been selected within the angu-lar window defined by the cone with half-aperture equal to theangular resolution for photons. The cosmic-ray background hasbeen calculated for the same window, assuming an isotropicflux. The event rate in each bin of reconstructed energy, beforebackground suppression, is shown in the top plot of Fig. 8.

We then computed the number of events for one year of ef-fective time, after applying the hadron suppression e�ciencycurves; the result is shown separately for signal and background

6

• Showergeometryreconstruction doneusingRPChittime• TakeadvantageofRPCshighspatialandtimeresolution

– Consideratimeresolutionof1ns• Useshowerfrontplaneapproximation• Requiremorethat10hitsintheRPCs

– Angularresolutionbelow2deg evenfor50GeVshowers

� � showers; ✓ = 10

�

• LATTESperformance:• Triggerefficiency• EnergyReconstruction• GeometricReconstruction• Gamma-hadrondiscrimination

• Fornowuseaconservativeapproach:• Below300GeVdon’tconsideranydiscrimination• Above300GeVuseHAWCdiscriminationcurve

• LATTESsensitivity

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/dE

[erg

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2 E

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10% Crab

1% Crab

LATTESHAWC-300Fermi 1 year

LATTESsensitivity

16

Differentialsensitivitytosteadysourcesinoneyear

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) [cm

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25 Crab

Crab

LATTESphysicsopportunities

17

• Many interesting scientific goals:– Dark matter searches at the center of the galaxy– Study transient phenomena

• LATTEScandetect a25Crab sourceat 3sigmain1minute

DMdensityprofile

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]-1

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dN

/dE

[erg

cm

2 E

13−10

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9−10

100% Crab

10% Crab

1% Crab

LATTESHAWC-300Fermi 1 year

LATTESathigherenergies

18

• Thesensitivityscaleswiththearrayarea

• Itcouldbeextendedtoreachhigherenergies withanexternalcoronaofsparsedetectors

Summary

19

• LATTES:gammaraywidefieldofviewexperimentatSouthAmerica– ComplementaryprojecttoCTAtosurveythecenterofthegalaxy

– Nextgenerationgamma-rayexperiment(hybrid)– Goodsensitivityatlowenergies(100GeV)• Coverthegapbetweensatelitte andgroundbasedmeasurements

– Powerfultooltotriggerobservationsofvariablesourceandtodetecttransients

R.Conceição 14

Acknowledgments

BACKUPSLIDES

LATTES 21

Reconstructionofshowergeometry

LATTES 22

• UseRPChittimeinformationtoreconstructtheshower– Takeadvantageofhighspatialandtimeresolution

• Showergeometryreconstruction:– Useshowerfrontplaneapproximation

– Analyticalprocedure– Applytriggerconditions– Applycut onthenumberofregisteredhits bytheRPCs

CHAPTER 3. PIERRE AUGER OBSERVATORY

Figure 3.7: SD trigger e�ciency as a function of Monte Carlo energy E for proton(circles), iron (triangles) and photon primaries (squares) and zenith angle integratedup to 60� . Lines are drawn only to guide the eyes. Taken from [92].

(a) Shower front plane approximation. (b) Shower front parabolic approximation.

Figure 3.8: Shower front reaching the SD tanks.

72

[deg]recθ0 20 40 60 80

hits

RPC

N

10

210Entries 422Mean x 21.14Mean y 11.98RMS x 6.974RMS y 12.54

Entries 422Mean x 21.14Mean y 11.98RMS x 6.974RMS y 12.54

Contributionstothegeometricreconstruction

23

E [GeV]200 400 600 800 1000

[deg

]θσ

0.5

1

1.5

= 10 degθ

Hits - All

Hits - Charged

Hits - Photons

• Photons retainahighercorrelationwiththeshowergeometrythanchargedparticles

• CouldwemeasurephotonswiththeRPCinstead?

RPC

Water Calorimeter

electron

LATTES24

LATTES station baseline concept

muon

Pb

photon

VERITAS

HESS

MAGIC

HAWC

ARGO

VERITAS

BuiltIACTBuilt ArrayPlanned IACTPlanned Array

CTA

CTALHASSO

VERITAS

HESS

MAGIC

HAWC

ARGO

VERITAS

BuiltIACTBuilt ArrayPlanned IACTPlanned Array

LATTES

Strategiesforprimarydiscrimination

LATTES 27

Exploredifferencesinshowerdevelopment

1.1 The Physics of Air Showers

Fig. 1.3: Comparison of the shower development for a leptonic and a hadronic shower(taken from [3]). While the electromagnetic shower (left side) shows only asmall lateral spread compared to its longitudinal extension, the hadronic shower(right side) is quite a lot more extended and also more irregular in shape.

1.1.3 Cherenkov Emission

Cherenkov photons are emitted whenever a charged particle moves through a medium witha velocity v greater than the local speed of light c

0 = c/n (where n denotes the refractiveindex of the medium). The charged particle polarizes the atoms along its path whichemit photons when returning to their equilibrium state. For velocities smaller than thespeed of light the electromagnetic radiation interferes destructively, while for v > c

0 theinterference is additive (See Figure 1.4). This e↵ect is equivalent to the shock front of asupersonic boom. All photons are emmited in a cone with an opening angle of:

#

C

= arccosc

0

v

= arccos1

n�

with � =v

c

.

Since the particles in air showers travel at highly relativistic velocities they emit Cherenkovlight which can be measured by ground-based telescopes. The requirement v > c

0 leads toa threshold energy, above which particles with mass m

0

emit Cherenkov photons:

E

th

=m

0

c

2

p1� n

�2

.

Since E

th

/ m

0

, most of the Cherenkov radiation is emitted by leightweight particles suchas electrons and positrons. Concerning the opening angle of the Cherenkov cone emittedby a shower, one has to take into account that the refractive index of air varies with itsdensity ⇢, which is a function of the height above sea level z. The deviation ⌘ of therefractive index from 1 (⌘ = n� 1) is proportional to the density:

⌘ / ⇢(z) ⇡ ⇢

0

exp(�z/z

⇢

) (1.6)

9

Strategiesforprimarydiscrimination

LATTES 28

• Hitpatternatground– Hitsfromhadronicshowersare

moresparsethaningammainducedshowers

– RPCdetectors– ExploredbytheARGO

collaboration• Searchforenergeticclustersfar

fromtheshowercore– Presentonlyinhadronic

showers– WaterCherenkovDetectors– ExploredbytheHAWC

collaboration• Combinebothstrategiesusingan

hybriddetector:LATTES– Workon-going…

1.1 The Physics of Air Showers

Fig. 1.3: Comparison of the shower development for a leptonic and a hadronic shower(taken from [3]). While the electromagnetic shower (left side) shows only asmall lateral spread compared to its longitudinal extension, the hadronic shower(right side) is quite a lot more extended and also more irregular in shape.

1.1.3 Cherenkov Emission

Cherenkov photons are emitted whenever a charged particle moves through a medium witha velocity v greater than the local speed of light c

0 = c/n (where n denotes the refractiveindex of the medium). The charged particle polarizes the atoms along its path whichemit photons when returning to their equilibrium state. For velocities smaller than thespeed of light the electromagnetic radiation interferes destructively, while for v > c

0 theinterference is additive (See Figure 1.4). This e↵ect is equivalent to the shock front of asupersonic boom. All photons are emmited in a cone with an opening angle of:

#

C

= arccosc

0

v

= arccos1

n�

with � =v

c

.

Since the particles in air showers travel at highly relativistic velocities they emit Cherenkovlight which can be measured by ground-based telescopes. The requirement v > c

0 leads toa threshold energy, above which particles with mass m

0

emit Cherenkov photons:

E

th

=m

0

c

2

p1� n

�2

.

Since E

th

/ m

0

, most of the Cherenkov radiation is emitted by leightweight particles suchas electrons and positrons. Concerning the opening angle of the Cherenkov cone emittedby a shower, one has to take into account that the refractive index of air varies with itsdensity ⇢, which is a function of the height above sea level z. The deviation ⌘ of therefractive index from 1 (⌘ = n� 1) is proportional to the density:

⌘ / ⇢(z) ⇡ ⇢

0

exp(�z/z

⇢

) (1.6)

9

ExploringtheWCD

LATTES 29

• Whatshouldwelookfor?– Lookforenergeticclustersfarfromtheshowercore– Above40m

log(E/GeV)4− 2− 0 2

Parti

cles

per

Sho

wer

3−10

2−10

1−10

1

10

210 All particlesgammaselectronsmuonshadrons

All Particles Spectrum (r > 40 m)

log(E/GeV)4− 2− 0 2

Parti

cles

per

Sho

wer

3−10

2−10

1−10

1

10

All particlesgammaselectronsmuonshadrons

All Particles Spectrum (r > 40 m)

Gammashowers Protonshowers

5 TeV

/p.e.)WCD

(signal10

log0 1 2 3

entri

es [a

.u.]

0

50

100photon - E = 200 GeV

proton - E = 500 GeV

proton - E = 1 TeV

LATTEShotteststation

LATTES 30

• SignalofthehottestWCDstation– above40m fromtheshowercore– withonlyonehitintheRPC

/p.e.)WCD

(signal10

log0 1 2 3

Nor

mal

ized

Cum

ulat

ive

0

0.5

1photon - E = 200 GeV

proton - E = 500 GeV

proton - E = 1 TeV

LATTESintegratedsensitivity

LATTES 31

events in the bottom plot of Fig. 8. One year of e↵ective timecorresponds to 7.9⇥106 seconds, assuming a duty cycle of 25%(which corresponds to the average fraction of time at which asource culminating at zenith is seen within an angle of 30� fromzenith).

The significance of a detection in terms of number of stan-dard deviations n� can be calculated with a simplified for-mula n� ' Nexcess/

pNbkg, where Nexcess is the number of ex-

cess events, and Nbkg is the background estimate, wheneverNexcess ⌧ Nbkg. The significance of the Crab signal for oneyear is also shown in the bottom plot of Fig. 8.

E [GeV]210 310

]-1

Even

ts [s

5−10

4−10

3−10

2−10

1−10

1

10Cosmic rays

Crab

E [GeV]210 310

Even

ts a

fter 1

yea

r

210

310

410

510

610

710

810

210 310

bkg

N/

exce

ssN

10

20

30

40

50Cosmic rays

Crab

Crab significance

Figure 8: Top: Signal from Crab (solid line) and background from chargedcosmic rays (dashed line) per second after the cuts in the 1� angular region,before the background rejection. The error bars are the statistical error ⇥ 10.Bottom: Signal from Crab (solid line) and background (dashed line) in oneyear of e↵ective time after all cuts. The Crab significance, expressed as theratio between the signal and the square root of the background, is also shown.

5.7. Sensitivity for a steady source

To evaluate the performance of the detector, we compute itsdi↵erential sensitivity, i.e. we investigate the sensitivity in nar-row bins of energy (4 bins per decade). We compute the sensi-tivity as the flux of a source giving Nexcess/

pNbkg = 5 after 1

year of e↵ective observation time for a source visible for 1/4 ofthe time (this roughly corresponds to the visibility of the Galac-tic Centre from the Southern tropic).

The result is shown in Fig. 9, and compared with the one-year sensitivities of Fermi and HAWC.

E [GeV]210 310

]-1

s-2

dN

/dE

[erg

cm

2 E

13−10

12−10

11−10

10−10

9−10

100% Crab

10% Crab

1% Crab

This detectorHAWC-300Fermi 1 year

Figure 9: Di↵erential sensitivity. We compute the flux of the source in a givenenergy range for which Nexcess/

pNbkg = 5, Nexcess > 10, after 1 year of time (a

25% diuty cycle has been assumed). 4 bins per decade in estimated energy areused. For comparison, fractions of the Crab Nebula spectrum are plotted withthe thin dashed gray lines.

E [GeV]210 310

]-1

s-2

F(>E

) [cm

13−10

12−10

11−10

10−10

9−10100% Crab

10% Crab

1% Crab

Figure 10: Integral sensitivity, defined as the flux of a source above a givenenergy for which Nexcess/

pNbkg = 5 after 1 year; it is assumed that the SED

is proportional to the SED of Crab Nebula. For comparison, fractions of theintegral Crab Nebula spectrum are plotted with the thin, dashed, gray lines.

The di↵erential sensitivity is independent of the spectral en-ergy distribution (SED) of the emitting source. To compute thetotal sensitivity one must assume a SED; from this assumption,one can compute an integral sensitivity.

We compute the integral sensitivity as the flux of a sourcewith a SED proportional to the SED of Crab Nebula givingNexcess/

pNbkg = 5 after 1 year, and integrating all energies

above a given energy. The integral sensitivity is shown inFig. 10.

5.8. Sensitivity to transient phenomena

To evaluate the capability of the detector to study sourceswith a fast luminosity variability in time, as well as to observefast transient phenomena, we computed the integral sensitivityfor a time window of one minute. Demanding a 3 sigma levelabove background we estimated a sensitivity of 25 Crab unitsabove 100 GeV.

7

events in the bottom plot of Fig. 8. One year of e↵ective timecorresponds to 7.9⇥106 seconds, assuming a duty cycle of 25%(which corresponds to the average fraction of time at which asource culminating at zenith is seen within an angle of 30� fromzenith).

The significance of a detection in terms of number of stan-dard deviations n� can be calculated with a simplified for-mula n� ' Nexcess/

pNbkg, where Nexcess is the number of ex-

cess events, and Nbkg is the background estimate, wheneverNexcess ⌧ Nbkg. The significance of the Crab signal for oneyear is also shown in the bottom plot of Fig. 8.

E [GeV]210 310

]-1

Even

ts [s

5−10

4−10

3−10

2−10

1−10

1

10Cosmic rays

Crab

E [GeV]210 310

Even

ts a

fter 1

yea

r

210

310

410

510

610

710

810

210 310

bkg

N/

exce

ssN

10

20

30

40

50Cosmic rays

Crab

Crab significance

Figure 8: Top: Signal from Crab (solid line) and background from chargedcosmic rays (dashed line) per second after the cuts in the 1� angular region,before the background rejection. Bottom: Signal from Crab (solid line) andbackground (dashed line) in one year of e↵ective time after all cuts. The Crabsignificance, expressed as the ratio between the signal and the square root ofthe background, is also shown.

5.7. Sensitivity for a steady source

To evaluate the performance of the detector, we compute itsdi↵erential sensitivity, i.e. we investigate the sensitivity in nar-row bins of energy (4 bins per decade). We compute the sensi-tivity as the flux of a source giving Nexcess/

pNbkg = 5 after 1

year of e↵ective observation time for a source visible for 1/4 ofthe time (this roughly corresponds to the visibility of the Galac-tic Centre from the Southern tropic).

The result is shown in Fig. 9, and compared with the one-year sensitivities of Fermi and HAWC.

E [GeV]210 310

]-1

s-2

dN

/dE

[erg

cm

2 E

13−10

12−10

11−10

10−10

9−10

100% Crab

10% Crab

1% Crab

This detectorHAWC-300Fermi 1 year

Figure 9: Di↵erential sensitivity. We compute the flux of the source in a givenenergy range for which Nexcess/

pNbkg = 5, Nexcess > 10, after 1 year of time (a

25% duty cycle has been assumed). 4 bins per decade in estimated energy areused. For comparison, fractions of the Crab Nebula spectrum are plotted withthe thin dashed gray lines.

E [GeV]210 310

]-1

s-2

F(>E

) [cm

13−10

12−10

11−10

10−10

9−10100% Crab

10% Crab

1% Crab

Figure 10: Integral sensitivity, defined as the flux of a source above a givenenergy for which Nexcess/

pNbkg = 5 after 1 year; it is assumed that the SED

is proportional to the SED of Crab Nebula. For comparison, fractions of theintegral Crab Nebula spectrum are plotted with the thin, dashed, gray lines.

The di↵erential sensitivity is independent of the spectral en-ergy distribution (SED) of the emitting source. To compute thetotal sensitivity one must assume a SED; from this assumption,one can compute an integral sensitivity.

We compute the integral sensitivity as the flux of a sourcewith a SED proportional to the SED of Crab Nebula givingNexcess/

pNbkg = 5 after 1 year, and integrating all energies

above a given energy. The integral sensitivity is shown inFig. 10.

5.8. Sensitivity to transient phenomena

To evaluate the capability of the detector to study sourceswith a fast luminosity variability in time, as well as to observefast transient phenomena, we computed the integral sensitivityfor a time window of one minute. Demanding a 3 sigma levelabove background we estimated a sensitivity of 25 Crab unitsabove 100 GeV.

7

LATTESexpecteventsfromCrab

LATTES 32

events in the bottom plot of Fig. 8. One year of e↵ective timecorresponds to 7.9⇥106 seconds, assuming a duty cycle of 25%(which corresponds to the average fraction of time at which asource culminating at zenith is seen within an angle of 30� fromzenith).

The significance of a detection in terms of number of stan-dard deviations n� can be calculated with a simplified for-mula n� ' Nexcess/

pNbkg, where Nexcess is the number of ex-

cess events, and Nbkg is the background estimate, wheneverNexcess ⌧ Nbkg. The significance of the Crab signal for oneyear is also shown in the bottom plot of Fig. 8.

E [GeV]210 310

]-1

Even

ts [s

5−10

4−10

3−10

2−10

1−10

1

10Cosmic rays

Crab

E [GeV]210 310

Even

ts a

fter 1

yea

r

210

310

410

510

610

710

810

210 310

bkg

N/

exce

ssN

10

20

30

40

50Cosmic rays

Crab

Crab significance

Figure 8: Top: Signal from Crab (solid line) and background from chargedcosmic rays (dashed line) per second after the cuts in the 1� angular region,before the background rejection. Bottom: Signal from Crab (solid line) andbackground (dashed line) in one year of e↵ective time after all cuts. The Crabsignificance, expressed as the ratio between the signal and the square root ofthe background, is also shown.

5.7. Sensitivity for a steady source

To evaluate the performance of the detector, we compute itsdi↵erential sensitivity, i.e. we investigate the sensitivity in nar-row bins of energy (4 bins per decade). We compute the sensi-tivity as the flux of a source giving Nexcess/

pNbkg = 5 after 1

year of e↵ective observation time for a source visible for 1/4 ofthe time (this roughly corresponds to the visibility of the Galac-tic Centre from the Southern tropic).

The result is shown in Fig. 9, and compared with the one-year sensitivities of Fermi and HAWC.

E [GeV]210 310

]-1

s-2

dN

/dE

[erg

cm

2 E

13−10

12−10

11−10

10−10

9−10

100% Crab

10% Crab

1% Crab

This detectorHAWC-300Fermi 1 year

Figure 9: Di↵erential sensitivity. We compute the flux of the source in a givenenergy range for which Nexcess/

pNbkg = 5, Nexcess > 10, after 1 year of time (a

25% duty cycle has been assumed). 4 bins per decade in estimated energy areused. For comparison, fractions of the Crab Nebula spectrum are plotted withthe thin dashed gray lines.

E [GeV]210 310

]-1

s-2

F(>E

) [cm

13−10

12−10

11−10

10−10

9−10100% Crab

10% Crab

1% Crab

Figure 10: Integral sensitivity, defined as the flux of a source above a givenenergy for which Nexcess/

pNbkg = 5 after 1 year; it is assumed that the SED

is proportional to the SED of Crab Nebula. For comparison, fractions of theintegral Crab Nebula spectrum are plotted with the thin, dashed, gray lines.

The di↵erential sensitivity is independent of the spectral en-ergy distribution (SED) of the emitting source. To compute thetotal sensitivity one must assume a SED; from this assumption,one can compute an integral sensitivity.

We compute the integral sensitivity as the flux of a sourcewith a SED proportional to the SED of Crab Nebula givingNexcess/

pNbkg = 5 after 1 year, and integrating all energies

above a given energy. The integral sensitivity is shown inFig. 10.

5.8. Sensitivity to transient phenomena

To evaluate the capability of the detector to study sourceswith a fast luminosity variability in time, as well as to observefast transient phenomena, we computed the integral sensitivityfor a time window of one minute. Demanding a 3 sigma levelabove background we estimated a sensitivity of 25 Crab unitsabove 100 GeV.

7

RPCs• Gaseousdetector• Planargeometry• uniform electricalfieldimposed.• High resistiveplatesinbetweenthe

electrodeslimittheavalanchecurrent.

• Signalispickedupbytheinductionoftheavalancheinthereadoutpads.

Streamermode

Avalanchemode

ResistivePlateChamber