Moon shadow analysis --Using ARGO experiment

Wang Bo, Zhang Yi, Zhang Jianli, Guo Yiqing, Hu HongboWang Bo, Zhang Yi, Zhang Jianli, Guo Yiqing, Hu Hongbo

Apri. 27 2008 for NanJing Meeting wangb@ihep.ac.cn

OUTLINE1. Why to study Moon shadow?

2. Experiment introduction.3. Data and Reconstruction.4. Moon shadow Analysis5. Observation of the steel beam shadow6. Summary

Why to study the Moon Why to study the Moon ShadowShadow

Cosmic Rays are blocked by the Moon

Deficit of cosmic rays in the direction of the Moon

Size of the deficit: angular angular resolution of the detectorresolution of the detector

Position of the deficit: pointing pointing errorerror

Geomagnetic field:Geomagnetic field: energy energy calibrationcalibration

Geomagnetic field: Geomagnetic field: proton proton and antiproton ratioand antiproton ratio

monitor the long-term monitor the long-term stability.stability.

The Earth-Moon as a spectrometer

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

90 Km North from Lhasa (Tibet)

4300 m above the sea level

Astrophysical Radiation withGround-based Observatory

Tibet Asgamma ARGO

YBJ Experiment In TibetYBJ Experiment In Tibet

large field of view (> 2 sr)

high duty cycle

full coverage of RPC

high altitude (4300m a.s.l)energy threshold: ~100GeV

high granularity imaging of the shower front by a uniform carpet of RPC

Experimental Hall

RPC chamber

Cluster

78 m

99 m

74 m

111 m

Detector Layout

10 Pads = 1 RPC (2.80 1.25 m2)

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

(56 62 cm2)

Layer of RPC covering 5600 m2

( 92% active surface)+ 0.5 cm lead converter+ sampling guard-ring

time resolution ~ 1 nsspace resolution = 6.5 62 cm2 (1 strip)

Central Carpet:130 Clusters, 1560 RPCs, 124800 Strips

EAS space-time structureEAS space-time structureHigh space-time granularity+ Full coverage technique

+ High altitude

a unique way to study Extensive Air Showers

Shower frontShower front

axisaxis

curvaturecurvature

corecore

~20ns~20ns

~2ns~2ns

EAS EAS phenomenologyphenomenology

L

tt

atmosphere

Detector Detector arrayarray

Event reconstructionEvent Rate:~4000HZ

ReconstruReconstructionction

Angular resolution:

Core Reconstruction: Liklihood Core Reconstruction: Liklihood

Direction reconstruction: Planar fit+Conical correction, Direction reconstruction: Planar fit+Conical correction,

(Robust Method)(Robust Method)

Event Rate:~4000HZ

Data Data

Moon time in each month:2007_05: 84.3(hours) 2007_04: 95.6 (hours)2007_03: 99.8(hours) 2007_02: 77.6(hours)2007_01: 110.5(hours) 2006_12: 95.9(hours)2006_11: 112.8(hours)

Data: (Oct. 30, 2006~May. 31 2007)

Event Rate:~4000HZ

Data Analysis Data Analysis 1.Selection of data time: 1.Selection of data time: Oct. 30, 2006~May. 31 2007 Oct. 30, 2006~May. 31 2007

2.Event Cut: 1.)Zenith angle < 50degrees 2.) Core position < 1500m. 3.) sigma<200. 4.)nHit cut

--Equi-Zenith angle method

Eliminate various detecting effects, such as changes in pressure and temperature.

MoonMoon shadow for low energy shadow for low energy and high energy's comic ray eventsand high energy's comic ray events

For High energy Cosmic RaysFor Low energy Cosmic Rays

System error Using Moon shadow of Different energy System error Using Moon shadow of Different energy

1. N-S pointing error:Moon shadow center of N-S direction: 1. N-S pointing error:Moon shadow center of N-S direction: N-S displacement of the Moon shadow center are unaffected due to the ~0 of the geomagnetic

field in E-W .

2.E-W pointing error:

.It is difficult to determine the right position of moon shadow in low nhit due to geomagnetic field

influence.. but we can using Moon shadow center of high nHit,For example, nHit>2000

Explanation of Projection Analysis to obtain Moon Shadow position

～ Corresponding to

MC Optimized distance

Obtain Center of Moon shadowObtain Center of Moon shadow

N-S direction system pointing error

system pointing error0.22 in N-S direction

N-S direction shift for different nHit

Different nHit ranges:Different nHit ranges: 0~60, 60~100, 100~200, 200~500, 500~2000, 2000~0~60, 60~100, 100~200, 200~500, 500~2000, 2000~

HIGHT nHits>2000

W-E direction system pointing error :~0.027 with nHit>2000

The system pointing error in E-W 0.03!?

Using the characteristic: Energy calibrationEnergy calibration Proton/antiproton ratio

If for proton: 1.6deg/E(Tev)

1.6deg/E = 38.6× (nHit) -0.92

E=0.0415×

(nHit)0.92

West-East shift of the center of Moon shadow

W-E direction shift for different nHit

Next work: 1. MC confirm to absolutely calibrate the cosmic ray's energy 2. Increase the data to analyze the Proton/antiproton

The shadow along W-E direction

20cm

35cm

8mm6mm

Fig1 Fig2

Fig3 Fig1.The map of normalized hit number ratio , using about ten days’ data taken

from tape681 to tape690.

normalizediR ( 1)S

Fig2 The radio map selecting the normalized radio 3 times the deviation less than the mean value.

Fig3 The radio map selecting the normalized radio 3 times the deviation less than the mean value.

So the W-E direction steel beam Shadows are observed cleary.

The shadow along S-N directionThe shadow along S-N direction

Fig1.The map of normalized hit number ratio ,using about ten days’ data taken from tape681 to tape690.

Fig1 Fig2

Fig3

Fig2 The radio map selecting the normalized radio 3 times the deviation less than the mean value.

Fig3 The radio map selecting the normalized radio 3 times the deviation less than the mean value.

So the S-N direction steel beam Shadows are also observed. Because the steel beam size, it is not as clear as W-E direction.

6mm

22cm 2.5mm

SummarySummary1. ARGO-YBJ is almost completed, and runing steadily. Data shows good performance in shower reconstruction

2. Very clear Moon shadow is obtained using ARGO-YBJ data

3. By moon shadow analysis, the system error is about 0.22degrees in S-N direction and 0.03degrees in W-E direction.

4. The Steel beam Shadow is clearly observed Using ARGO data.

5. Interesting physics results are coming. For example: Mrk421, Crab and so on

So system pointing error:

Pointing error N-S direction:0.22

Pointing error W-S direction:0.03

Total error:~0.2

Azimuth angle distribution and N-S direction system error?

So shift a certian degrees(0.2?) of Zenith

direction or characteristic plane(with its

normal direction to zenith)

Considering the geomagnetic field, etc.

uniform??

Rotating 0.2Deg.

Rotating 0.2Deg

Optimum angular radius(Gaussian function)

1.585/1.177*2.6=3.5

1.585/1.177*2.2=3.1