Search of axions from a nuclear power reactor with a high-purity - PowerPoint PPT Presentation

Search of axions from a nuclear power reactor with a high-purity germanium detector Hsi-Ming Chang Department of Physics, National Taiwan University Institute of Physics, Academia Sinica TEXONO Collaboration TAUP 2007 Sep. 11, 2007 @ Sendai 1 / 14

Outline Introduction to Axions Outline ■ Axion Production & Detection ■ Data analysis ■ Physics Results ■ This work is published in PRD 75, 052004 (2007), a by-product of Taiwan EXperiment On NeutrinO. 2 / 14

Introduction to Axion Strong CP Problem: Introduction to ■ Axion Neutron EDM < 10 − 25 e cm, Why QCD does not seem to break the CP-symmetry? PQWW Axion ( m a � 100 keV): ■ ◆ A hypothetical particle to solve stong CP problem. ◆ Excluded after extensive searches. Invisible Axion: ■ ◆ Evade previous experimental searches. Mass window 10 − 6 � m a � 10 − 2 (eV), ◆ from cosmological and astrophysical arguments. ◆ Popular models: DFSZ, KSVZ. 3 / 14

Reactor as Source ■ Axion Production & Axions could be emitted via magnetic transition. Detection ■ Inspired by F. T. Avignone III et al. , PRD37, 618 (1988). Reactor as Source ⇒ Radioactive 65 Zn source & HPGe detector. Branching Ratio Γ a / Γ γ ■ Reactor is the most powerful radioactive source we can control! Complications Reactor Building ◆ Slow neuton capture: n + ( Z, A ) → ( Z, A + 1) + γ ( or axion ) . Detector & Shielding Nuclear de-excitation: ( Z, A ) ∗ → ( Z, A ) + γ ( or axion ) . ◆ Axion Detection Event Rate Formula ■ The photon fluxes φ γ at detector: Energy Mode φ γ ( 10 10 cm − 1 s − 1 ) (keV) np → d γ 2230 Isovector M1 22.1 7 Li ∗ 478 M1 24.7 91 Y ∗ 555 M4 2.10 97 Nb ∗ 743 M4 4.81 135 Xe ∗ 526 M4 0.85 137 Ba ∗ 662 M4 0.37 Γ a ■ Axion flux is φ a = φ γ Γ γ . eV ) 2 cm − 2 sec − 1 , with average energy ∼ 4 keV. Solar axion flux ∼ 10 12 ( m a ■ 4 / 14

Reactor as Source ■ Axion Production & Axions could be emitted via magnetic transition. Detection ■ Inspired by F. T. Avignone III et al. , PRD37, 618 (1988). Reactor as Source ⇒ Radioactive 65 Zn source & HPGe detector. Branching Ratio Γ a / Γ γ ■ Reactor is the most powerful radioactive source we can control! Complications Reactor Building ◆ Slow neuton capture: n + ( Z, A ) → ( Z, A + 1) + γ ( or axion ) . Detector & Shielding Nuclear de-excitation: ( Z, A ) ∗ → ( Z, A ) + γ ( or axion ) . ◆ Axion Detection Event Rate Formula ■ The photon fluxes φ γ at detector: Energy Mode φ γ Kinematics Constraint! ( 10 10 cm − 1 s − 1 ) (keV) np → d γ 2230 Isovector M1 22.1 7 Li ∗ 478 M1 24.7 91 Y ∗ 555 M4 2.10 97 Nb ∗ 743 M4 4.81 135 Xe ∗ 526 M4 0.85 137 Ba ∗ 662 M4 0.37 Γ a ■ Axion flux is φ a = φ γ Γ γ . eV ) 2 cm − 2 sec − 1 , with average energy ∼ 4 keV. Solar axion flux ∼ 10 12 ( m a ■ 4 / 14

Branching Ratio Γ a / Γ γ Complications The axion-to-photon branching ratio for M1 transition is: Axion Production & Detection Reactor as Source « 2 g 0 aNN β + g 1 „ Γ a 1 1 1 + δ 2 ( p a Branching Ratio ǫ a ) 3 aNN Γ γ = . Γ a / Γ γ ( µ 0 − 1 2 πα 2 ) β + ( µ 1 − η ) Complications Reactor Building δ : E2/M1 mixing ratio ≈ 0 . Detector & Shielding µ 0 ( µ 1 ): Isoscalar (isovector) magnetic moment = 0 . 88 (4 . 71) . Axion Detection Event Rate Formula η, β : Matrix elements from nuclear physics. ■ Numerical calculations of η and β are needed. Even if η and β are known, two free parameters g 0 aNN and g 1 ■ aNN still remain. How to circumvent the complications? ■ It happens that np → d γ is an isovetor M1 transition: ǫ a ) 3 ( g 1 „ Γ a « ≡ Γ a 1 2 πα ( p a aNN ) 2 . ) 2 ∝ ( g 1 aNN Γ γ ( np → dγ ) ≈ Γ γ µ 1 np ■ In analysis, g aNN can be parametrized as a function of m a with axion models. 5 / 14

Reactor Building Axion Production & Detection Reactor as Source Branching Ratio Γ a / Γ γ Complications Reactor Building Detector & Shielding Axion Detection Event Rate Formula Power: 2.9 GW. Data Size: ■ ■ ν e flux: ■ ON: 459.0 days. • 6 × 10 12 cm − 2 · s − 1 . OFF: 96.3 days. • 30 mwe overburden. ■ in two ON/OFF periods. 6 / 14

Detector & Shielding Outer Shielding: Axion Production & Detection Reactor as Source 1. Plastic scintillator: cosmic-ray Branching Ratio veto. Γ a / Γ γ Complications 2. Lead: block γ ’s from outside. Reactor Building 3. Stainless steel: support the Detector & Shielding structure. Axion Detection Event Rate Formula 4. B-loaded polyethylene: neutron capturer. 5. OFHC copper: reduce the γ ’s from lead or polyethylene. HPGe detector: Mass: 1 kg. ■ Threshold: 5 keV. ■ CsI and NaI: anti-Compton ■ system. 28m from reactor core. ■ 7 / 14

Axion Detection Axion Production & g a ΓΓ � 1 GeV � 1 Detection γ Reactor as Source 2 g aee � 1 Branching Ratio Γ a / Γ γ 2 � Σ � 10 � 22 cm 1.5 Complications Ge a Reactor Building Detector & Shielding 1 Compton Axion Detection Primakoff conversion ( g aγγ ) Primakoff � � 10 4 � Event Rate Formula 0.5 500 1000 1500 2000 m a � keV � γ γ σ Pri = g 2 aγγ · f ( m a , ǫ a ) ■ + a ⇒ sensitive at low m a a e e σ Com = g 2 aee · f ( m a , ǫ a ) ■ Compton conversion ( g aee ) ⇒ sensitive at high m a (Here ǫ a = 2230 keV) 8 / 14

Event Rate Formula The event rate in unit of day − 1 kg − 1 is Axion Production & Detection Reactor as Source Branching Ratio Γ a � � Γ a / Γ γ R = σ φ γ · P decay · P matter Nǫ , Complications Γ γ Reactor Building Detector & Shielding P decay : Survival probability without decay. Axion Detection Event Rate Formula P matter : Survival probability without interaction. N : # of Ge atoms in kilogram target. ǫ : Efficiency of full-energy deposition at detector. R = R ( m a , g aγγ/aee , g aNN ) . Invoking the widely-used DFSZ model ( g aNN ∝ m a ) to reduce free parameter: R ∝ g 2 aγγ/aee m 2 a . 9 / 14

Energy Spectra Data Analysis Energy Spectra ON-OFF Residual 40 K counts/day-kg-keV Results 214 Pb 208 Tl 226 Ra 228 Ac ON 10 208 Tl 1 -1 10 -2 10 0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000 (a) keV counts/day-kg-keV OFF 10 1 -1 10 -2 10 0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000 (b) keV 10 / 14

ON-OFF Residual —: overlaid best-fit Gaussians Data Analysis 0.6 0.6 0.6 Energy Spectra Events / (day-kg-keV) ON-OFF Residual 0.4 0.4 0.4 Results 0.2 0.2 0.2 0 0 0 -0.2 -0.2 -0.2 -0.4 -0.4 -0.4 -0.6 -0.6 -0.6 460 480 500 520 540 540 560 Energy (keV) Energy (keV) Energy (keV) 0.6 0.6 0.08 Events / (day-kg-keV) 0.06 0.4 0.4 0.04 0.2 0.2 0.02 0 0 0 -0.02 -0.2 -0.2 -0.04 -0.4 -0.4 -0.06 -0.6 -0.6 -0.08 640 660 680 720 740 760 2200 2250 Energy (keV) Energy (keV) Energy (keV) 11 / 14

Results Statistical results: Data Analysis 1 Energy Spectra ON-OFF Residual Results Energy Period A Period B (day − 1 kg − 1 ) (day − 1 kg − 1 ) (keV) 0.5 478 -0.88 ± 0.75 0.14 ± 0.41 counts � day � 1 � kg � 1 526 0.26 ± 0.67 0.38 ± 0.16 555 -0.47 ± 0.67 -0.33 ± 0.15 662 -0.46 ± 0.62 -0.02 ± 0.50 0 743 0.14 ± 0.55 0.22 ± 0.37 2230 -0.10 ± 0.17 -0.03 ± 0.03 -0.5 Energy P-A&P-B Combined Upper Bound (day − 1 kg − 1 ) (day − 1 kg − 1 ) (keV) 478 -0.09 ± 0.36 0.49 526 0.37 ± 0.15 0.62 555 -0.34 ± 0.15 0.05 -1 662 -0.19 ± 0.39 0.46 np � d Γ 7 Li 91 Y 97 Nb 135 Xe 137 Ba 743 0.19 ± 0.31 0.69 2230 -0.04 ± 0.03 0.02 P � A & P � B combined Systematics Uncertainty: < 20%, dominated by evaluation of φ γ from np → d γ . 12 / 14

m a − g a Space Physics Results m a − g a Space 10 0 10 0 10 2 10 2 R Summary Int Int Beam PQWW Dump 10 0 10 0 Decay TEXONO 10 � 2 10 � 2 Positronium Zn Macro � PQWW Laser scopic Decay Zn Decay TEXONO 10 � 2 10 � 2 Force Experiments 10 � 4 10 � 4 Beam 10 � 4 10 � 4 Dump Kine 10 � 6 10 � 6 g a ΓΓ � GeV � 1 � g a ΓΓ � GeV � 1 � 10 � 6 10 � 6 R g aee g aee Kine Solar � Germanium 10 � 8 10 � 8 10 � 8 10 � 8 HW HW CAST HB Stars 10 � 10 10 � 10 10 � 10 10 � 10 Microwave Telescope Cavity KSVZ 10 � 12 10 � 12 10 � 12 10 � 12 Red Giant DFSZ 10 � 14 10 � 14 10 � 14 10 � 14 DFSZ 10 � 16 10 � 16 10 � 8 10 � 6 10 � 4 10 � 2 10 � 8 10 � 6 10 � 4 10 � 2 10 0 10 0 10 2 10 2 10 4 10 4 10 6 10 6 10 8 10 8 10 � 8 10 � 8 10 � 6 10 � 6 10 � 4 10 � 4 10 � 2 10 � 2 10 0 10 0 10 2 10 2 10 4 10 4 10 6 10 6 10 8 10 8 m a � eV � m a � eV � m a � eV � m a � eV � 13 / 14