1. South West Jiaotong University, Sichuan Province，China
Sun Shadow Study in the Quiet
Phase of the Solar Activity with the ARGO-YBJ Experiment
FENGRONG ZHU
South West Jiaotong University, Sichuan Province，China
on behalf of the ARGO-YBJ Collaboration
32ND INTERNATIONAL COSMIC RAY CONFERENCE，BEIJING 2011

2. Outline Content Introduction Data Method Physical analysis
Discussion and Summary

3. Advantage of ARGO-YBJ experiment
Large area:5600m2
Wide FOV: Zenith<50o
Duty cycle: ≥ 85%
Low energy threshold : 300GeV
Long term Stable operation : 4 years

4. Sun shadow study 1957, Concept by Clark
1991, first Sun+Moon shadow(4.9sigma) by CYGNUS
Only several  sun shadows with CASA, Milagro,
SOUDAN2, MACRO, L3+c
Further physics with AS, ARGO-YBJ
AS

5. Sun shadow study ARGO-YBJ Interplanetary Magnetic Field measurement
ApJ ,729(2011)113
Solar activity(this work)
Solar Magnetic Field (Under study)

6. Date: 2008.02---2010.10 Sun shadow observation Event Selection:
Data
Date: Sun shadow observation
Solar quiet phase
Event Selection:
nHit :>=100(5TeV)
Zenith：4.6-50degree
Chi2_cn:<200(ns)2
Distance to the ARGO core:<150m
6o * 6o sky area, 1.06e8Events
11 groups(MJD):
, , , ,
, , , ,
, ,

7. Methods Advantage: Eliminate various detecting
Effects, such as changes in
pressure and temperature.
Limitiation: Small zenith angle
Smooth radius: 1.2degree

8. Sun shadow Vs. Time
X :W-E direction
Y: S-N direction
~1.0e7events
~13

9. Sun shadow Vs. Time
Displacements in the west-east direction of the sun
shadow core
Using reiteration method to fit the deficit event projected along the W-E and N-S direction using the Gaussian distribution , then the most deficit point is the core of the sun shadow.

10. Sun shadow Vs. Time Deficit ratio of the sun shadow:
The ratio of the deficit count
compared to the expected one
A non-dimensional valuable
Independent of the exposure

11. Correlation: correlation probability : 99.99%,
Deficit ratio Vs. Sunspot
correlation probability : 99.99%,
correlation coefficient:-84%

12. Discussion: Displacement Vs. solar polar magnetic field
What factors make the sun shadow shift towards east?
To be removed the geomagnetic effect

13. Discussion and Summary
The Sun shadow as the function of the time
Confirm that the correlation between the deficit ratio of the sunshadow and sunspot(99.99%,-84%)
The Displacements in the west-east direction of the sun shadow maybe have a relation with solar dipole magnetic field ,need to carefully remove geomagnetic field effect