- Email: [email protected]
The Daya Bay Experiment to measure Θ13
Progress in Particle and Nuclear Physics 64 (2010) 342–345
Contents lists available at ScienceDirect
Progress in Particle and Nuclear Physics journal homepage: www.elsevier.com/locate/ppnp
Review
The Daya Bay Experiment to measure Θ13 Herbert Steiner 1 Lawrence Berkeley National Laboratory, United States
article Keywords: Neutrinos Neutrino mixing
info
abstract I present here a brief description of the goals, method and status of the Daya Bay antineutrino oscillation experiment to measure the mixing angle Θ13 . © 2010 Elsevier B.V. All rights reserved.
Other speakers at this meeting2 have discussed the importance of the mixing angle θ13 and some of the experiments to measure it. Here I will describe the Daya Bay Experiment that has as its design goal a measurement of sin2 2θ13 with a sensitivity of 0.008 after three years of data taking. A plot of the expected sensitivity as a function of time is shown in Fig. 1. The Daya Bay Collaboration consists of 233 scientists and engineers, mostly from China and the United States, who will initially use four reactors producing 11.6 GW of nuclear power at Daya Bay in China as the source of the antineutrinos. An additional two reactors that will raise the total power to 17.4 GW are expected to come on line in 2010. The principle of the experiment is shown in Fig. 2. Its key feature is to make relative measurements of the number of antineutrino interactions at two near sites and one far site using eight identical detectors. Two of the detectors will be in each of the near sites and four in the far site. The overall layout of the experiment is shown in Fig. 3, and the method is outlined in Fig. 4. The fractional difference in the measured rates in the near and far detectors is proportional to sin2 2θ13 . Based on existing experiments we know that this quantity is very small, perhaps even < 0.01, so it will be crucially important to understand and minimize all sources of systematic error. The reactor antineutrino flux and spectrum will largely cancel out in the kind of relative measurement to be described here. On the other hand the number of target protons in each of the eight detectors, the detection efficiency, the energy resolution and calibration, the cosmogenic and other backgrounds, and the response of the electronics have to be known, at least in a relative sense, at the level of 0.1%. The main sources of uncertainty and background are listed in Tables 1 and 2. The expected antineutrino interaction rates are 840 and 740 per day per module in the two near halls, and 90 events per day in each of the four far detector modules. The antineutrino detection scheme is based on the reaction ν¯ e + p → e+ + n, and is summarized in Fig. 5. The event signature is a prompt pulse proportional to the total energy of the positron, followed by an 8 MeV delayed pulse (30 µs) due to neutron capture in Gd. A schematic diagram of one of the antineutrino detectors is shown in Fig. 6. It is a cylinder having an outer diameter of 5 m and a height of 5 m. Inside the stainless steel outer vessel are two nested acrylic cylinders, with diameters of 4 m and 3 m respectively. Twenty tons of Gd-loaded Linear Alkyl Benzene (LAB) liquid scintillator is the target material inside the inner acrylic vessel, and another twenty tons of unloaded LAB is the gamma catcher in the outer acrylic vessel. Forty tons of mineral oil fills the outermost region of the detector. Its main purpose is to shield the inner regions from background. One-hundred-ninety-two 8-inch-diameter Hamamatsu R5912 photomultiplier tubes √ near the outer wall of each detector are used to record the light pulses. The energy resolution is expected to be 0.12/ E (MeV). Cherenkov light produced by energetic muons in a water filled pool surrounding the detector modules is used to veto the bulk of the cosmogenically induced background. The top of the pool is covered with Resistive Plate Chambers (RPC) to
E-mail address: [email protected]. 1 Presented on behalf of the Daya Bay Collaboration. 2 See for example the talks by S.-B. Kim, M. Lindner, and R. McKeown at this Conference. 0146-6410/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.ppnp.2009.12.044
H. Steiner / Progress in Particle and Nuclear Physics 64 (2010) 342–345
343
Sensitivity of Daya Bay Sensitivity in sin22θ13 (90%CL)
0.05 0.04 0.38% relative detector systematics. 0.03
uncertaintyΔm231 = 2.5 × 10-3 eV2
0.02 0.01 0
Fig. 1. Sensitivity as a function of time.
Disappearance probability
0.8
0.6
0.4
0.2
0
-0.2 0.1
1
10
100
Baseline (km) Fig. 2. Principle of sin2 2θ13 experiment.
Ling Ao Near site ~500 m from Ling Ao Overburden: 112 m
900
Far site 1615 m from Ling Ao 1985 m from Daya Overburden: 350 m
m
4 x 20 tons target mass at far site
465 m
810 m
Water hall
Filling hall entrance 295 m
Ling Ao-ll NPP (under construction) 2×2.9 GW in 2010
Construction tunnel Ling Ao NPP, 2×2.9 GW
Daya Bay Near site 363 m from Daya Bay Overburden: 98 m
Daya Bay NPP, 2×2.9 GW
Fig. 3. Layout of the Daya Bay Experiment.
further improve the detection efficiency. In this way more than 99.7% of the muons passing through the liquid scintillator will be tagged. A schematic diagram of the muon detecting system is shown in Fig. 7. A key element of the experiment is the calibration system. It is shown in Fig. 8. Radioactive sources and light-emitting diodes can be lowered under computer control into the active regions of the detectors, and thereby calibrate energy response and monitor detector performance.
344
H. Steiner / Progress in Particle and Nuclear Physics 64 (2010) 342–345
Method
Measured ratio of Rates
Proton Number Ratio
Filling Gd-LS and Mass measurement
Detector Efficiency Ratio
sin22θ13
Calibration Systems
Fig. 4. Method of extracting sin2 2θ13 .
Fig. 5. Daya Bay detection scheme.
Fig. 6. Daya Bay detector module.
Finally let me briefly discuss the status of the experiment. The excavation of access tunnels and experimental halls is nearing completion. The first two stainless steel vessels have arrived at Daya Bay, as have the first of the acrylic vessels. Mounting and in situ testing of the photomultiplier tubes has started. The liquid scintillator filling hall will be ready for beneficial occupancy in November 2009. The present schedule calls for data taking in the so-called Daya Bay Near Hall to commence in the summer of 2010, and operation of all eight detectors to start in the summer of 2011. Thus it is quite possible that by the next Erice School of Neutrino Physics we will know the value of sin2 2θ13 , and perhaps, if it is large enough it will be possible to go on to investigate CP violation in the neutrino sector.
H. Steiner / Progress in Particle and Nuclear Physics 64 (2010) 342–345
345
Table 1 Sources of uncertainty. Detector uncertainty source
Baseline (%)
Goal (%)
Chooz experience (%)
Number of protons
0.3
0.1
0.8
0.2 0.1 0.1 0.05 0.01 <0.01
0.1 0.1 0.03 0.05 0.01 <0.01
0.8 1.0 0.4 0.5 0.01 <0.01
Detection efficiency
Energy cuts H/Gd ratio Time cut Neutron mult Trigger Live time
Total uncertainty
0.38 0.18 Two detector relative efficiency
1.7 One detector absolute uncertainty
Table 2 Backgrounds.
Radioactivity (Hz) Muonrate/AD (Hz) v¯ e -signal (events/day) Accidental B/S (%) Fast neutron B/S (%) 9 He + 9 Li B/S (%)
Daya Bay near
Ling Ao near
Far hall
<50
<50
<50
36 840 <0.2 0.1 0.3
22 740 <0.2 0.1 0.3
1.2 90 <0.1 0.1 0.2
Fig. 7. Muon tagging system.
Fig. 8. The Daya Bay calibration system.
Contents lists available at ScienceDirect
Progress in Particle and Nuclear Physics journal homepage: www.elsevier.com/locate/ppnp
Review
The Daya Bay Experiment to measure Θ13 Herbert Steiner 1 Lawrence Berkeley National Laboratory, United States
article Keywords: Neutrinos Neutrino mixing
info
abstract I present here a brief description of the goals, method and status of the Daya Bay antineutrino oscillation experiment to measure the mixing angle Θ13 . © 2010 Elsevier B.V. All rights reserved.
Other speakers at this meeting2 have discussed the importance of the mixing angle θ13 and some of the experiments to measure it. Here I will describe the Daya Bay Experiment that has as its design goal a measurement of sin2 2θ13 with a sensitivity of 0.008 after three years of data taking. A plot of the expected sensitivity as a function of time is shown in Fig. 1. The Daya Bay Collaboration consists of 233 scientists and engineers, mostly from China and the United States, who will initially use four reactors producing 11.6 GW of nuclear power at Daya Bay in China as the source of the antineutrinos. An additional two reactors that will raise the total power to 17.4 GW are expected to come on line in 2010. The principle of the experiment is shown in Fig. 2. Its key feature is to make relative measurements of the number of antineutrino interactions at two near sites and one far site using eight identical detectors. Two of the detectors will be in each of the near sites and four in the far site. The overall layout of the experiment is shown in Fig. 3, and the method is outlined in Fig. 4. The fractional difference in the measured rates in the near and far detectors is proportional to sin2 2θ13 . Based on existing experiments we know that this quantity is very small, perhaps even < 0.01, so it will be crucially important to understand and minimize all sources of systematic error. The reactor antineutrino flux and spectrum will largely cancel out in the kind of relative measurement to be described here. On the other hand the number of target protons in each of the eight detectors, the detection efficiency, the energy resolution and calibration, the cosmogenic and other backgrounds, and the response of the electronics have to be known, at least in a relative sense, at the level of 0.1%. The main sources of uncertainty and background are listed in Tables 1 and 2. The expected antineutrino interaction rates are 840 and 740 per day per module in the two near halls, and 90 events per day in each of the four far detector modules. The antineutrino detection scheme is based on the reaction ν¯ e + p → e+ + n, and is summarized in Fig. 5. The event signature is a prompt pulse proportional to the total energy of the positron, followed by an 8 MeV delayed pulse (30 µs) due to neutron capture in Gd. A schematic diagram of one of the antineutrino detectors is shown in Fig. 6. It is a cylinder having an outer diameter of 5 m and a height of 5 m. Inside the stainless steel outer vessel are two nested acrylic cylinders, with diameters of 4 m and 3 m respectively. Twenty tons of Gd-loaded Linear Alkyl Benzene (LAB) liquid scintillator is the target material inside the inner acrylic vessel, and another twenty tons of unloaded LAB is the gamma catcher in the outer acrylic vessel. Forty tons of mineral oil fills the outermost region of the detector. Its main purpose is to shield the inner regions from background. One-hundred-ninety-two 8-inch-diameter Hamamatsu R5912 photomultiplier tubes √ near the outer wall of each detector are used to record the light pulses. The energy resolution is expected to be 0.12/ E (MeV). Cherenkov light produced by energetic muons in a water filled pool surrounding the detector modules is used to veto the bulk of the cosmogenically induced background. The top of the pool is covered with Resistive Plate Chambers (RPC) to
E-mail address: [email protected]. 1 Presented on behalf of the Daya Bay Collaboration. 2 See for example the talks by S.-B. Kim, M. Lindner, and R. McKeown at this Conference. 0146-6410/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.ppnp.2009.12.044
H. Steiner / Progress in Particle and Nuclear Physics 64 (2010) 342–345
343
Sensitivity of Daya Bay Sensitivity in sin22θ13 (90%CL)
0.05 0.04 0.38% relative detector systematics. 0.03
uncertaintyΔm231 = 2.5 × 10-3 eV2
0.02 0.01 0
Fig. 1. Sensitivity as a function of time.
Disappearance probability
0.8
0.6
0.4
0.2
0
-0.2 0.1
1
10
100
Baseline (km) Fig. 2. Principle of sin2 2θ13 experiment.
Ling Ao Near site ~500 m from Ling Ao Overburden: 112 m
900
Far site 1615 m from Ling Ao 1985 m from Daya Overburden: 350 m
m
4 x 20 tons target mass at far site
465 m
810 m
Water hall
Filling hall entrance 295 m
Ling Ao-ll NPP (under construction) 2×2.9 GW in 2010
Construction tunnel Ling Ao NPP, 2×2.9 GW
Daya Bay Near site 363 m from Daya Bay Overburden: 98 m
Daya Bay NPP, 2×2.9 GW
Fig. 3. Layout of the Daya Bay Experiment.
further improve the detection efficiency. In this way more than 99.7% of the muons passing through the liquid scintillator will be tagged. A schematic diagram of the muon detecting system is shown in Fig. 7. A key element of the experiment is the calibration system. It is shown in Fig. 8. Radioactive sources and light-emitting diodes can be lowered under computer control into the active regions of the detectors, and thereby calibrate energy response and monitor detector performance.
344
H. Steiner / Progress in Particle and Nuclear Physics 64 (2010) 342–345
Method
Measured ratio of Rates
Proton Number Ratio
Filling Gd-LS and Mass measurement
Detector Efficiency Ratio
sin22θ13
Calibration Systems
Fig. 4. Method of extracting sin2 2θ13 .
Fig. 5. Daya Bay detection scheme.
Fig. 6. Daya Bay detector module.
Finally let me briefly discuss the status of the experiment. The excavation of access tunnels and experimental halls is nearing completion. The first two stainless steel vessels have arrived at Daya Bay, as have the first of the acrylic vessels. Mounting and in situ testing of the photomultiplier tubes has started. The liquid scintillator filling hall will be ready for beneficial occupancy in November 2009. The present schedule calls for data taking in the so-called Daya Bay Near Hall to commence in the summer of 2010, and operation of all eight detectors to start in the summer of 2011. Thus it is quite possible that by the next Erice School of Neutrino Physics we will know the value of sin2 2θ13 , and perhaps, if it is large enough it will be possible to go on to investigate CP violation in the neutrino sector.
H. Steiner / Progress in Particle and Nuclear Physics 64 (2010) 342–345
345
Table 1 Sources of uncertainty. Detector uncertainty source
Baseline (%)
Goal (%)
Chooz experience (%)
Number of protons
0.3
0.1
0.8
0.2 0.1 0.1 0.05 0.01 <0.01
0.1 0.1 0.03 0.05 0.01 <0.01
0.8 1.0 0.4 0.5 0.01 <0.01
Detection efficiency
Energy cuts H/Gd ratio Time cut Neutron mult Trigger Live time
Total uncertainty
0.38 0.18 Two detector relative efficiency
1.7 One detector absolute uncertainty
Table 2 Backgrounds.
Radioactivity (Hz) Muonrate/AD (Hz) v¯ e -signal (events/day) Accidental B/S (%) Fast neutron B/S (%) 9 He + 9 Li B/S (%)
Daya Bay near
Ling Ao near
Far hall
<50
<50
<50
36 840 <0.2 0.1 0.3
22 740 <0.2 0.1 0.3
1.2 90 <0.1 0.1 0.2
Fig. 7. Muon tagging system.
Fig. 8. The Daya Bay calibration system.