Moon shadow analysis -- Using ARGO experiment Wang Bo, Zhang Yi, Zhang Jianli, Guo Yiqing, Hu Hongbo Apri for NanJing Meeting

OUTLINE 1. Why to study Moon shadow? 2. Experiment introduction. 3. Data and Reconstruction. 4. Moon shadow Analysis 5. Observation of the steel beam shadow 6. Summary

Why to study the Moon Shadow Cosmic Rays are blocked by the Moon Deficit of cosmic rays in the direction of the Moon angular resolution of the detector  Size of the deficit: angular resolution of the detector pointing error  Position of the deficit: pointing error  Geomagnetic field: energy calibration  Geomagnetic field: proton and antiproton ratio  monitor the long-term stability. The Earth-Moon as a spectrometer

Longitude 90° 31’ 50” East Latitude 30° 06’ 38” North 90 Km North from Lhasa (Tibet) 4300 m above the sea level A strophysical R adiation with G round-based O bservatory Tibet AsgammaARGO YBJ 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 m74 m 111 m Detector Layout 10 Pads = 1 RPC (2.80  1.25 m 2 ) 12 RPC =1 Cluster ( 5.7  7.6 m 2 ) 8 Strips = 1 Pad (56  62 cm 2 ) Layer of RPC covering  5600 m 2 (  92% active surface) cm lead converter + sampling guard-ring time resolution ~ 1 ns space resolution = 6.5  62 cm 2 (1 strip) Central Carpet: 130 Clusters, 1560 RPCs, Strips

EAS space-time structure High space-time granularity + Full coverage technique + High altitude a unique way to study Extensive Air Showers

Shower front axis  curvature core ~20ns ~2ns EAS phenomenology  L tttt atmosphere Detector array Event reconstruction Event Rate:~4000HZ

Reconstruc tion Angular resolution: Core Reconstruction: Liklihood Direction reconstruction: Planar fit+Conical correction, (Robust Method) Event Rate:~4000HZ

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 ) Event Rate:~4000HZ

Data Analysis 1.Selection of data time: Oct. 30, 2006~May Oct. 30, 2006~May Event Cut: 1.)Zenith angle < 50degrees 2.) Core position < 1500m. 3.) sigma< )nHit cut --Equi-Zenith angle method Eliminate various detecting effects, such as changes in pressure and temperature.

Moonshadow for low energy Moon shadow for low energy and high energy's comic ray events For High energy Cosmic RaysFor Low energy Cosmic Rays

System error Using Moon shadow of Different energy 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 shadow

N-S direction system pointing error system pointing error 0.22 in N-S direction N-S direction shift for different nHit 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 calibration Proton/antiproton ratio If for proton: 1.6deg/E(Tev) 1.6deg/E = 38.6 × (nHit) E= × (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 8mm 6mm Fig1Fig2 Fig3 Fig1.The map of normalized hit number ratio, using about ten days’ data taken from tape681 to tape690. 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 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 2.5m m

Summary 1. 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= /1.177*2.2=3.1