Hybrid measurement of CR light component spectrum by using

ARGO-YBJ and WFCTA

Shoushan Zhang on behalf of LHAASO collaboration

and ARGO-YBJ collaboration

IHEP (Institute of High Energy Physics), Beijing, China

32th ICRC, August 11-18, 2011, Beijing, China.

Outline• Motivation

• WFCTA and ARGO experiment introduction

• Data analysis

• Preliminary result

• Summary and discussion

Hybrid measurement

Lateral distribution protoniron

Density ratio: the ratio of particle density at two different shower core distance

Aim: To build an overlap between balloon measurements and ground based experiment for cross-calibration of the experiments.

Motivation

-- ARGO-YBJ: lateral distribution• Density ratio mass sensitive

-- Cherenkov Telescope: longitudinal information • Hillas parameter mass sensitive• Better energy resolution

1. 5m2 spherical mirror；2. Camera: 16x16 PMT array 3. Pixel size 1º, 4. FOV: 14ºx16º.5. Elevation angle: 60º

Wide Field of View Cerenkov Telescope (WFCT)

WFCA @ YBJ

Hybrid observation: WFCA && ARGO

50m

ARGO-YBJ experiment

2. Detector introduction

Start from July 2006Rate： 3.5kHzThreshold： ~ 300 GeVDuty cycle: >86%FOV: 2 sr

ARGO Hall

One of Cherenkov event

Num

ber

of

Fire

d S

trip

sStripsBig pad Strips

Simulation && data selection

Calibration

Component discrimination

Energy reconstruction

Data analysis

Simulation

• Cherenkov simulation : Ray tracing package• ARGO simulation: G4argo

Telescope simulation

Shower simulation• Tool: Corsika6735 + QGSJETII-03 + GHEISHA• Component model: J.R. Horandel (2003)• Primary particles: proton, helium, CNO, MgAlSi, iron• Energy range: 10 TeV – 1PeV• Geometry: the: 20 – 42, phi: 69-111, • Core: +/- 130 m

Geometry reconstruction: From ARGO-YBJ • Core resolution: <3 m @ Nhit > 1000• Angular resolution: < 0.4o @ Nhit > 1000

J.R. Horandel (2003)

Data selection

Cherenkov image cleaning:

• Signal to noise ratio>3.5;• Arrival time information: all triggered pixel should be within a time

window Δt=240 ns;• Rejection isolated pixel.

Data selection: • The stereo data from 2008.12 ~ 2009.03: 314,928• Good weather selection: 213,839 events left (LL. Ma etc. ICRC 2011, poster 1033)• Geometry selection: 20526 -- core position locates in ARGO center carpet: x(-40, 40) m, y (-40, 40) m; -- the 26-34, phi 39 – 55 for full Cherenkov image.

Simulation and data comparison

Log10(total Npe)ρ(20)/ρ(40)

Cherenkov size Density ratio

ARGO-YBJ hit numbers Impact parameter

Cherenkov Telescope CalibrationMethod 1: A calibrated LED is mounted on the center of the mirror to calibrate Cherenkov telescope every day. The transmission of the glass window and reflectivity of the mirrors are not take into.

Method 2: End to end calibration: N2 Laser device, but unfinished. (Yong Zhang etc. ICRC2011, oral 1344)

S.S. Zhang et al., NIM A (2011)

The systematic uncertainty ofthe calibration constant : ~ 7%.

Gain monitor result

20-200TeV Proton helium CNO MgAlSi Iron

Primary 41.0% 26.6% 13.5% 8.2% 9.4%

After cut 65.5% 29.0% 4.4% 1.0% 0.1%

The contamination of heavy component is about 5.5%

Strips

Big pad will be used

Energy distribution of primary and after cut Component discrimination: ARGO density ratio cut

• Impact parameter (Rp): 5m/bin• Log(total Npe) bin: 0.1/bin

Energy reconstruction: look- up table Energy resolution： ~23%Bias: < 5%

WFCTA-ARGO data agree with CREAM and ARGO-YBJ results Direct and ground-based measurements have overlap making

possible the cross-calibration of the experiments. Next steps: Using ARGO-YBJ big pad data and WFCTA to measure

higher energy up to PeV. Hillas parameters to discriminate component

The contamination of heavy component is about 5.5%

Preliminary result

Summary and Discussion Uncertainty

• Calibration: 10% in flux • Atmosphere condition: 12% in flux • Reconstruction: <5% • Mirror reflection: Unfinished• Primary component model: unfinished • Simulation tool: unfinished• Hadronic model: The results of Large Hadron Collider forward (LHCf) experiment

show that none of the hadronic interaction models agree perfectly with the measurements, but QGSJET II-03 show good agreement than the other models (O. Adriani et al., arXiv:1104.5294

Energy resolution: ~23% and bias <5% Preliminary light component energy spectrum:

• 30TeV – 200 TeV, with contamination of heavy component less than 5.5%.

Next step -- Big pad data for higher energy up to PeV;

-- Cherenkov image information such as hillas parameters to discriminate component;-- Uncertainties study: calibration, simulation tool and primary component model.

1) For η>10.94, QGSJET II-03, DPMJET 3.04 and PYTHIA 8.145 showvery good agreement with the experimental result between 0.5 and 1.5TeV,but they predict significantly larger photon yield at high energy >2TeV .2) For η>10.94, SIBYLL 2.1 shows a very good agreement with the experimentalresult for the spectral shape for >0.5TeV, but predicts a photonyield only half of the experimental result over the entire energy range.3) For 8.81<η<8.99, difference in the spectral shape between the experimentaldata and the models is not as large as the case 1), but still a largedeviation at high energy is found for the DPMJET 3.04 and PYTHIA 8.145models.