Multicore Cosmic Shower in the ARGO-YBJ experiment Jing Zhao, Xinhua Ma On behalf of the ARGO-YBJ collaboration

outline Physical motivation The ARGO-YBJ experiment The multicore data analysis The Monte carlo simulation Conclusions

Physical motivation The common interpretation of multicore events is jet production, which is essentially produced by the leading particle interactions with ‘air’ target nuclei. Multicore events are good samples to study hadronic interaction models.

The ARGO-YBJ experiment provides a good opportunity Panir Coll., Mt. Fuji Coll. and Chacaltaya Coll., Nucl. Phys. B191(1981)1-25 MEC (mountain emulsion chamber ): the two core of multicore event<40cm. The ARGO-YBJ experiment provides a good opportunity to study the Multicore events in a more precise way.

The ARGO-YBJ experiment bigpad The analog readout (bigpad) started to work from Sep. 2010

Multicore event selection r(m) ρ(m-2) 5.3σ(with trial number) EAS data selection: hit strips > 5000, max ADC count > 10 Multicore event selection : significance > 5σ r12 ~ 3.5 -10 m. 光度学

One real event MEC strip→direction BigPad→density ρmax → core position ρ(particle/m2), r(m)

The multicore data analysis As for the data over four months, we get 3.78×1011 EAS events. After EAS data selection we get 2.53×106 high energy EAS events. After Multicore data selection, 1356 multicore events are found in the selected EAS events, about 10 events/day. 较高初能事例: hit strips > 5000, and max. ADC count > 10 多芯事例选择: significance > 5σ r12 ~ 3.5 -10 m. good linearly dynamic range: The main EAS core > 100 particles /m2 and the second core > 50 particles/m2 above ρFit(r). No BigPad is saturated.

The Monte carlo simulation Corsika QGSJETII primary energy range 1014-1016eV composition: H,He,CNO,MgAlSi,Fe The zenith angle ranges : 0°- 45° azimuthal angle : 0°- 360° observation level : 4300 m a.s.l. (YBJ) considering only the experimental geometry.

The Monte carlo simulation Distribution of difference between dropped core position and position of bigpad with the maximum particle density. Indicate resolution of core position decided by the position of BigPad with the maximum particle density is 0.7m. The MC event reconstruction efficiency. For proton (Fe), detection efficiency is more than 80% above primary energy of 200TeV(500TeV).

an simulation multicore event MC: to get the fine structure and more detaisl of the secondary particles in the cores to understand the mechanism of the generation of multicores. fine structure and more detail of the secondary particles in the cores to understand the mechnism of the genarnation of multicores.

Conclusions ARGO-YBJ data have been analyzed to search for multicore EAS events. A simple Monte carlo simulation has been made to understand properties of air showers,especially multicore events. Next work: More real data and full simulation of the ARGO-YBJ experiment will be obtained to study multicore EAS events in the near future.

Thank you !