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

Outline Content Introduction Data Method Physical analysis Discussion and Summary

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

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

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

Date: 2008.02---2010.10 Sun shadow observation Event Selection: Data Date: 2008.02---2010.10 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): 54510-54598, 54599-54649, 54650-54704,54705-54831, 54832-54942,54943-54998,54999-55036,55037-55196, 55197-55319,55320-55384,55385-55478

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

Sun shadow Vs. Time 54510-54598 54599-54649 54650-54704 54705-54831 54832-54942 54943-54998 55037-55196 54999-55036 X :W-E direction Y: S-N direction ~1.0e7events ~13 55197-55319 55320-55384 55385-55478

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.

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

Correlation: correlation probability : 99.99%, Deficit ratio Vs. Sunspot http://solarscience.msfc.nasa.gov/SunspotCycle.shtml correlation probability : 99.99%, correlation coefficient:-84%

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

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