Water Tank as the Outer Muon Veto Mingjun Chen

2 Outline  Past work  As the muon veto  MC simulation  Future Plan

3 Schematics of a water tank. ۝ Material of water tank ： PVC Size ： 1m×1m×13m ۝ Shape of two ends ： Winston Cone ۝ Inner wall covered by 1070D Tyvek and Al film with 90% reflectivity ۝ 8-inch photomultipliers installed in two ends as the photons’ collectors ۝ Clean de-ionized water (>10MΩ· cm ) is used ۝ A simple water purification system with 0.1μm filter We built a water tank prototype: Middle point of water tank is set as the origin of coordinate system

4 Water Tank Prototype

5

6  Position Dependent Response of the Water Tank The muons vertically pass through the prototype at the different positions X is the distance from the trigger counters to the PMT at right Effective absorption length of the water tank: 5.74+/-0.29(m) Energy Res. 7%/Sqrt(E(GeV))

7  Angular Dependent Response of the Water Tank The track lengths of all data points are normalized to 1m at x=0.5m Muons pass through the prototype with different angles

8 Elevation: Use water tank as the muon veto

9 Two 8-inch PMTs Al Mirror Reflector 16m Top View: Tyvek

10 Advantages of Water Cherenkov Detector Compared with RPC and plastic scintillator  Good detection efficiency(about 100% theoretically )  Not sensitive to the natural radioactivity of Daya Bay’s rock  Simple machine( the tanks immersed in water)  Very low cost ( Use water as the media)

11 MC simulation  To study the detection efficiency of Cherenkov photons  Based on GEANT4 and including the detailed optical model  The parameters of optical model come from the MC simulation program of the prototype

12 Some parameters of MC simulation program:

13 Number of Detected photoelectrons (m)(m) X is the incident position of the vertical mouns 10 muon

14 Future Plan on the prototype:  Look for new reflector instead of Tyvek For example: reflective paint  Two PMTs installed in each end of water tank  Redesign the optics collection system of two ends ☺Use lens system  Better water purification system