WbLS measurements at BNL

Transcription

1 WbLS measurements at BNL David Jaffe 1 BNL cohort: L.J.Bignell, D.Beznosko, M.V.Diwan, S.Hans, S.Kettell, R.Rosero, H.Themann, B.Viren, E.Worcester, M.Yeh, C.Zhang 1 / 16

2 Light production in water, LS & WbLS 1. Čerenkov (point source 2, directional, prompt) 1.1 Light yield is calculable: N (path length) N 0 (sin 2 θ C ) 1.2 Spectrum LY(λ) 1 λ β 2 n(λ) 2 2. Scintillation (point source, isotropic, extended in time) 2.1 Light yield proportional to energy deposit, modulo quenching. Must be measured. 2.2 Narrow spectrum 3. Absorption & re-emission (possibly diffuse source, isotropic, extended in time) 3.1 Optical γ from Čerenkov or scintillation can be absorbed & re-emitted by medium 3.2 Has potential to shift Č γ from VUV to visible to a typical photodetector (eg. bialkalai PMT) LY for these processes is comparable for % concentration WbLS. Disentangling them and understanding the details of λ-dependence is tedious. 2 As opposed to diffuse source 2 / 16

3 λ-dependence (arbitrary norm. except absorption length) 0 WbLSEAbsorptionELengthEl1/mmQ CerenkovEEmissionESpectrumyE475EMeVEProtons WbLSEEmission 1 PhotomultiplierEQuantumEEfficiency CerenkovEEmissionESpectrumyE2EGeVEProtons Wavelength (nm) 3 / 16

4 Measurements at BNL The following pages have details of two sets of measurements in a low energy proton beam. 1. NSRL 3 run 12C: Light yield measured for water, LS, 0.4% and 1% WbLS, investigate quenching. Result: LY approximately linear with LS concentration 2. NSRL run 13A: Absolutely calibrate 1% WbLS LY against Čerenkov LY Result: LY of 1% WbLS is 1 optical photons/mev (±% uncertainty) Goals: 1. Determine increase in sensitivity of a SK-like detector with WbLS to p K + ν. 2. Disentangle competing light production processes. 3 NASA Space Radiation Laboratory at BNL, of course. 4 / 16

5 Early MC estimate of p K + ν sensitivity with 1%-WbLS-based detector Projected Sensitivity Lifetime Sensitivity (90% C.L.) p "! + K Super-K WbLS 22.5 kt Year τ(p K + ν) > 2 34 y at 90% C.L. in years 5 / 16

6 NSRL12C Beam setup (identical liquids in each tub) Not to scale Reflectivity>95% PTFE tub T1 Reflectivity<% Al tub T2 A1 A2 15cm 15cm Proton beam H1 H2 H3 VC 0.635cm 0.635cm H1,H2,H3 plastic scint. hodoscope 2cmX2cmX0.5cm Trigger: H1 H2 T1,T2 Hamamatsu R PMTs CAEN V1729A FADC 12bit,1GSPS NSRL beam monitor: A1 A2 A1 (A2) is 1cm 2 (2 cm 2 ), 2mm thick plastic scint. 6 / 16

7 NSRL12C: PTFE tub with PMT 7 / 16

8 NSRL12C: Incident and deposited energies (MeV) Incident Incident Energy Beam β energy deposited energy T1 T2 T1 T2 T1 T2 Sample Water, WbLS LS Water, WbLS LS Water, WbLS LS p K + ν: β K = 0.57 T p = 2MeV T p = 475MeV is just above proton Čerenkov threshold T p = 2000MeV minimum-ionizing (max NSRL beam energy) Calculated incident velocities, incident and deposited energies in MeV for T1 (PTFE tub) and T2 (Aluminum tub) using NIST s proton stopping power and range tables (PSTAR). Estimated uncertainty is a few MeV. 8 / 16

9 12C results: LY vs deposited energy T1_Charge(PE)/Edep(MeV) vs Edep(MeV) T2_Charge(PE)/Edep(MeV) vs Edep(MeV) T1_Charge(PE)/Edep(MeV) 2 1 T2_Charge(PE)/Edep(MeV) water wbls1 wbls2 ls -2 wbls1 wbls2 ls Edep(MeV) White PTFE tub. PE/MeV vs MeV deposited Edep(MeV) Black PTFE-coated Al tub. PE/MeV vs MeV deposited. 9 / 16

10 12C results: Normalized PE/MeV vs LS concentration Normed PE/MeV vs LS-concentration(%) [Water at 0.001% for plot] Normed PE/MeV LY approximately proportional to concentration for 2, 475 MeV MeV shows effect of Čerenkov contribution T T1 T2 2 T2 475 T LS-concentration(%) [Water at 0.001% for plot] PE/MeV (normalized to LS PE/MeV) vs LS concentration for proton beam data. / 16

11 Table of results Ratio(%) to 0% concentration Conc 2 MeV 475 MeV 2000 MeV (%) T1 T2 T1 T2 T1 T ± ± ± ± ± ± ± ± ± ± ± ± ±.80 0 ± ±.68 0 ±.22 0 ± T1 (white PTFE) 2 MeV LS inaccurate: PMT saturated 2. T2 (black PTFE) water data unreliable: PMT re-positioned MeV data complicated by Čerenkov contribution 11 / 16

12 Compare NSRL12C and Compton-edge data Normed Light Yield vs concentration(%) [Water at 0.001% for plot] Normed Light Yield T1 475 Normed PE/MeV vs LS-concentration(%) [Wa T Normed PE/MeV vs LS-concentration(%) [W T2 2 Normed PE/MeV vs LS-concentration(%) [Wa T2 475 Normed PE/MeV vs LS-concentration(%) [Wa T Normed PE/MeV vs LS-concentration(%) [W Normalized LY vs LAB concentration in CX Normalized LY vs LAB concentration in WbLS concentration(%) [Water at 0.001% for plot] Compare relative light yield of proton beam data with preliminary Compton-edge data for WbLS and LAB in cyclohexane(cx). 1. In WbLS, light yield is proportional to concentration. 2. In cyclohexane, light yield is higher at low concentrations. 12 / 16

13 , NSRL13A setup schematic PRODUCED BY AN AUTODESK EDUCATIONAL PRODUCT * $ - PRODUCED BY AN AUTODESK EDUCATIONAL PRODUCT $./01,*'2,31..,' External 2 2 cm 2 plastic scintillator hodoscopes define beam into yellow region. 2. Dimensions selected so that Č ring from incident proton fully illuminates downstream PMT. 3. Liquids: water and 1% WbLS 4. Beam energies: 475 and 2000 MeV 5. Detector can be rotated by 180 for systematics control. 6. Detector is black ABS plastic, reflectivity < % 13 / 16

14 NSRL13A expected and actual results Beam Expected Actual (in photo-electrons) Energy PMT PMT PMTA PMTB PMTB PMTA (MeV) 4 Liquid DS US DS US DS US 2000 Water N C %-WbLS Q C + Q s Q s Water %-WbLS N s N s Uncertainties: ±% for > 2PE, ±20% otherwise. Q C = N C (1 P a ) and Q s = N s + N C P a P r where P a absorption prob. and P r re-emission probability. Illustrative only, neglects λ-dependence of production, absorption, re-emission, transmission and detection efficiency. Complications: MeV is not below proton Č threshold (Doh!) 2. δ ray production 3. Non-zero reflectivity 4 Deposited energies: 37 and 26.3 MeV for 475 and 2000 MeV, resp. 14 / 16

15 NSRL13A interpretation of results 1. A full Geant4-based simulation has been developed and applied for the NSRL13A data. 2. Combining results and taking into account the calculated energy loss in the liquid, the scintillator light yield is 113(±%) optical photons per MeV deposited. 3. To first order, P a = 1 NWbLS DS N WbLS US NDS Water 46%, in other words, approximately half of the photons in Čerenkov ring will be eliminated in the 1% WbLS. Comparison of simulation(hist) and data(points) for 475 MeV protons in 1%-WbLS Normalized Counts Charge Collected (Number of Photoelectrons) 15 / 16

16 Next steps 1. Unified analysis of NSRL12C and NSRL13A data with full Geant4-based simulation. 2. Measurement of decay-time distributions in NSRL12C, NSRL13A data 3. Measurement and simulation of WbLS attenuation length in 2 meter system 4. Re-examination of p K + ν sensitivity 5. Deployment of 1-ton-prototype, a 995 mm ID, 1250 mm internal height, 25.4 mm thick UVT acrylic vessel, for measurements with cosmics 2 1 B B A A 16 / 16