Muon Flux Measurements and Simulation at CJPL Zhi ZENG CDEX Collaboration Symposium of the Sino-German GDT Cooperation Tübingen, Apr. 2013

Contents 1.Introduction 2.Muon Flux Measurement 3.Muon Flux Simulation 4.Muon Background in CJPL 5.Summary

1.Introdution Muon Flux Measurements and Simulation at CJPL 第3页第3页

The position of the Jinping tunnel 第4页第4页

Profile of Jinping Tunnel 第5页第5页 Elevation/m Tunnel length/m CJPL Tunnel Jinping Mountain Elevation/m Yalong River （ East ） Yalong River （ west ）

CJPL Site 第6页第6页 Traffic Tunnel A Traffic Tunnel B CJPL Entrance Main Hall Total Volume

Muon Background in DM Exp. Muon penetration; Neutrons produced by muon interactions; Gammas produced by muon interactions; Muon capture reactions(not important) 第7页第7页

2. MUON FLUX MEASUREMENT Muon Flux Measurements and Simulation at CJPL 第8页第8页

Detector &Electronic system 第9页第9页 A telescope system consisting of 2 groups, both of them is composed of 3 plastic scintillation detectors. The signal from PMT is fanned into 2 channels: One fed into a 100MHz bandwidth FADC module, the other sent to logic OR modules after discriminated and stretched. A signal generator as a random trigger for dead time study also contribute system trigger gate. FADC converts the whole analog pulses to digital signals, which written into storage for offline analysis by DAQ program. 20 cm 1.0m×0.5m×0.05m

Muon event selected: Pulse Shape Discrimination(PSD) 第 10 页 Muon energy deposit >= 10MeV in 5cm thickness detector, while gamma deposit energy <3MeV Distribution s of the pulse amplitudefollow Landau distribution Cut threshold: 5000 FADC unit (1) The pulse amplitude threshold in PSD Test result on the ground

第 11 页 (2) The rise/fall time distribution in PSD rise time distribution fall time distribution The acceptance regions for rise time and fall time are ns and ns respectively. Noise events that fall out of these regions are th us discarded. Muon event selected: Pulse Shape Discrimination(PSD)

第 12 页 Muon event selected: Restriction of triple-coincidence Fan In/Out PMT Disc. Logic OR FADC Counter 5cm 20 cm Trigger Logic AND Pulses from all the 3 detectors in the same group should pass through the pulse shape constraint and the amplitude threshold.

Muon Flux measurement correction 第 13 页 (1) Dead time correction factor: >99.9% Using signal generator, serving as random trigger, produces periodic pulses which are independent of physics events. Dead time correction factor: Defined as the ratio of recorded number to generated number of random trigger events; Dead time correction factor: measured, higher than 99.9%.

第 14 页 Muon Flux measurement correction (2) Edge effect correction: 93.4% Edge effect:Muon would pass the edge of the top or bottom scintillators but penetrate the whole thickness of the middle one. in thes cases, these events would not pass pulse amplitude threshold selected. using Monte Carlo method to calculate the correction factor, it is 93.4%. edge effect illustration

Muon Flux measurement correction 第 15 页 (3) detection efficiency correction (4) solid angle correction muon Flux: number of triple-coincident events

第 16 页

Muon Flux Measurement in CJPL Nov to Dec. 2011, 231 days measurement, 28 events from two groups are pass all the constrain. After correction, get Muon flux in CJPL*: (2.0 ±0.4) × cm -2 s -1 * the solid angle correction in CJPL is set to 1.0 for the angle distribution underground is unkown 第 17 页

第 18 页

3. MUON FLUX SIMULATION Muon Flux Measurements and Simulation at CJPL 第 19 页

Incident Muon Energy Spectrum Assumption ： muon energy spectrum on the top of Jinping mountain (~4000 m) like that at sea level 第 20 页 Fig.1 Muon momentum spectrum distribution of two different angles at sea level [2] Gaisser Equation: :Muon energy on sea level(GeV)

Computational Model and program Assumption: CJPL lies in a hemisphere MUSIC: muon transportation 第 21 页 Fig. 2 Schematic of the mountain and CJPL’s location Muon energy threshold: Muon energy 860GeV~10 4 GeV, integral muon flux in the ground is about 4.84×10 -8 cm -2 s -1.

Simulation results by MUSIC Average energy of residual muon : ～ 370GeV Muon survival probability: 7.65×10 -3 Muon flux in CJPL with ： 3.17× cm -2 s -1 (simulation) 2.0× cm -2 s -1 (measurement ） 第 22 页 Fig.3 Simulation results of residual muon flux

第 23 页 Google Earth map for the elevation of Jinping Mount. voxeled JInping Mount in GEANT Google Elevation API pixel: 201*301 CJPL CJPL average rock overburden/m exact simulation is processing! polar angle/deg.

4. MUON BACKGROUND IN CJPL Muon Flux Measurements and Simulation at CJPL 第 24 页

Neutron by Muon with FLUKA 第 25 页 Incident Muons Rock Air Concrete Schematic of computational model for secondary particles caused by muon Neutron >20MeV neutron < 20MeV Neutron yield by muons(n/μ): (total). --->20MeV: <20MeV: × cm -2 s -1 Neutron flux (by muon):

Gamma by Muon with FLUKA 第 26 页 Incident Muons Rock Air Concrete Schematic of computational model for secondary particles caused by muon Gamma yield by muons: p/μ Gamma flux by muon : 1.57×10 -8 cm -2 s -1

5. Summary Muon Flux Measurements and Simulation at CJPL 第 27 页

underground Labs in the world 第 28 页 Underground Lab Rock Depth (m) Muon Flux (m -2 ·s -1 ) neutron flux by muon (m -2 ·s -1 ) Boulby UK ×10 -4 [3] 8.70× -6 [4] Canfranc ， Spain 850(2~4)×10 -3 [3] （ 1.73±0.91 ） ×10 -5 [5] Modane ， French ×10 -5 [3] 5.6×10 -2 [3] Gran Sasso, Italy ×10 -4 [3] 3.78×10 -2 [3] Baksan,Russia ±0.19×10 -5 [3] 1.4×10 -3 （ E>1.0MeV ） [3] Kamiokande, Japan ×10 -3 [3] （ 8.25±0.58 ） ×10 -2 （ thermol ） [3] （ 11. 5±1.2 ） ×10 -2 （ non-thermol ） [3] SNO,CA ×10 -6 [3] 4.7×10 -2 （ thermol ） [3] 4.6×10 -2 （ fast ） [3] Soudan, US ×10 -3 [3] - DUSEL,US ×10 -5 [6] - CJPL, China ×10 -6 （ simulation ） 2.0×10 -6 （ measurement ） 8.37×10 -7 （ simulation ）

第 29 页 中国锦屏地下实验室建设 及暗物质实验工作总结汇报会 Thanks ！

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