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Home , Maurice Goldhaber

Measuring the Helicity of the

Lee Grodzins June 14, 2010

Dedicated to Maurice Goldhaber Born April 18, 1911 Still Active • Start with a small table. • Place on it a NaI detector, surrounded by Sm152. • Eu152 Put a Pb cone on top of the detector. magnet • Place an electromagnet on top of the Pb cone. Pb cone • Place a Eu152m source on the magnet. Sm152 • Measure the gamma NaI on PMT spectra as B field Table Top flips. Outline

1. Preludes

2. Measuring the lifetime of a nuclear state by making use of the recoil from a ν.

– Conservation of momentum and energy

3. Measuring the helicity of the ν.

– and the conservation of spin 1930’s • 1930’s: Wen Yu Zhang comes to the to obtain his PhD under Ernest Rutherford. • Maurice Goldhaber has also come to Cavendish. – He suggests that the the deuteron can be disintegrated by MeV γs. confirms the suggestion and Maurice is a star. • Rutherford dies in 1937. Zhang becomes the student of James Chadwick. • Goldhaber becomes Zhang’s de facto supervisor. Early 1950’s

• Goldhaber leaves U of Illinois to become a group leader at Brookhaven.

• Zhang joins the physics faculty of Purdue University.

• I do my thesis with Zhang, who recommends that I postdoc with Goldhaber. 1954-55

• I Arrive at BNL in 1955.

• Knowing nothing about nuclear spectroscopy. Goldhaber suggests that I study the

spectroscopy of nuclear states in

isotopes that have a mass of 152. 152 63Eu 0- 9 hr 3- 13 yr 152 e- capture Eu β- decay

1- 963 2+ 930 + 6+ 707 β+ decay 4 755 + 0 615

4+ 366 + 2 344 2+ 122 + 0+ 0 0 0 152 152 62 Sm90 64 Gd88 The 88-90 Region 66

65 64 63 62 61 60 Rotational Vibrational

4+ 2+ 6+ 7 0+ 2

4+ 3.3 2+ 1 2+ 1 0+ 0 0+ 0 88 : Vibrational Spectra 90 Neutrons: Rotational Spectra 3.2 3.1 Sm Gd 3 Nd Dy 2.9 Ce 2.8 90 neutrons Er 2.7 2.6 2.5 2.4

E(4+): E(2+) E(4+): 88 neutrons 2.3 Nd Yb 2.2 Sm Er Dy 2.1 Gd 2 146 148 150 152 154 156 158 160 Atomic Weight Eu152m - 0 9 hr

~ 940 keV

1- 963 keV t < 10-13 s, expected

2+ 122 0+ 0 Sm152 Andrew Sunyar

• Student of Goldhaber who brings him to BNL

• Taught me the trade.

• I had a ball. 152 63Eu 0- 9 hr 3- 13 yr 152 e- capture Eu β- decay

1- 963

β+ decay

4+ 366 + 2 344 2+ 122 + 0+ 0 0 0 152 152 62 Sm90 64 Gd88 τ , θ puzzle

• Lee and Yang suggest that τ and θ are the same particle (K) and that parity is violated in weak interaction.

• Preprints proposing their tests circulate.

• Sergio DeBenedetti of Carnegie Mellon proposes a test of parity violation not considered by Lee and Yang. Parity Test

• Measure a pseudoscalar quantity. p . σ

• Reverse all coordinates.

• See if the result changes. Circular polarization of γ correlated with the momentum of β Na24 . 5+ pβ σγ β- 1.39 MeV

4+ 4.2 MeV β- γ

2+ 1.4 MeV

0+ Mg24 Spin Dependence of Compton Scattering

Spin Dependence Effect per mfp of Iron

Measurement of Helicity. L Grodzins, Progress in Nuclear Physics, Vol 7, 1959 Sergio DeBenedetti S. DeBenedetti, L. Grodzins, R. Madey & A. Sunyar We observed a small effect. Too small to be a credible test. On the plus side: • Andy and I know how to measure circular polarization of γs.

• And we have a magnet. 1957 • C.S. Wu, E. Ambler et al measure the anisotropy of the beta decay from polarized Co60.

– Parity is totally not conserved in β decay.

• R. Garwin, et al, show that parity is totally not conserved in muon decay.

• Parity is not conserved in weak interactions.

• Lee and Yang win Nobel Prize Goldhaber: bremsstrahlung from β- should be polarized Experiment

Sr90

β− Converter Bremsstrahlung x-rays

Iron Electromagnet

Reversing Switch γ detector M. Goldhaber, L. Grodzins & A. Sunyar, Phys. Rev. 106, 826, 1957 Part II: Back to Europium • The 1- level in Sm152 at 963 keV.

• Part of the rotational band?

• If so, the lifetime should be very fast.

• And most important of all,

• fun to measure by Resonance. Eu152m 0-

Gamow-Teller β-decay

1- Simple Dipole Transition 6+ 4+ 2+ 0+ Sm152 Resonance Fluorescence

Γ 963keV Γ 963keV

• Problem: The line width, Γ, is narrow. • The energy lost to nuclear recoils at emission and absorption is > 100 Γ. • The recoil from the neutrino emission, and temperature broadening makes it happen. PART II. Line width of the 1- state

• Expected meanlife to be < 10-14 secs.

 10−15 eV − sec Γ = ≅ ≅ 0.01eV 2τ 10−13 sec Energy lost to Recoil

Sm152* → Sm152 (0) + 963 γ ← → γ p(γ ) E(γ ) v (Sm152 ) = = M152 M152c 2 152 1 2 1  E (γ )  E(Sm ) = M152 v =  2  ≅ 3 eV 2 2  M152c  Recoil Energy is Lost Twice

963 keV

Sm152 Sm152

Must make up for 6 eV of Energy Loss Temperature (Doppler) Broadening Mv2 kT = 2

v 2kT .5 = ( 2 ) c Mc 0 0 2kT .5 ∆E = E v / c = E 2 γ γ γ (Mc )

∆Eγ ≅ 0.5 eV The effective width of both the emitted and absorbed states. Γ ~ 0. 5 eV Γ ~ 0. 5 eV

~ 6 eV • At 300oC, we still need to make up ~ 5.5 eV.

• The Doppler shift from the recoiling neutrino emission makes the fluorescence possible. • Does Sm152* decay in flight in solids?

5 • vSm = Eν / (MSmc) ≈ 2 10 cm/s

• Time to travel 2 Å ≈ 10-13 sec

The lifetime of the 963 keV state should be short enough. Maybe. ν is monoenergetic

9 hr 63Eu + eK

62Sm*(963) + ν(940) Eu152m S - 0 9 hr 940 Gamow-Teller b-decay

1- 963 1-

Dipole

2+ 0+ 0+ Sm152 Recoil from ν Doppler Shifts γ E p (Sm152* ) = p[ν ] = υ c

152* v (Sm ) Eν = 2 c M152 c

E E ∆ = 963 υ θ Eγ (963) 2 cos M152 c Energy Balance Loss 963keV Recoil from γ emission & absorption 2 Eγ 2 3 eV + 3 eV ≈ 6 eV 2 Mc2 Gain

EγEν Recoil from ν recoil = ≈ 5.6 eV Mc2 Temp Broadening: .5 eV 2 + EγEν/Mc from ν emission

2 2 - Eγ /2Mc from in- flight Sm152 recoil

2 2 - Eγ /2Mc from target Sm152 recoil L.Grodzins, Phys. Rev.109, 1014, 1958 Helicity: H = (σ . p)/│σ.p│

Maurice added the conservation of spin and the experiment is still celebrated. Eu152m S - 0 9 hr

Gamow-Teller β-decay

1- 1-

Dipole

2+ 0+ 0+ Sm152 Eu152m S - 0 9 hr

Gamow-Teller b-decay

1- 1-

Dipole

2+ 0+ 0+ Sm152 The Helicity Experiment Set-Up Helicity of ν Transferred to Recoiling Sm152* l =0 152m - 152 93Eu + e (Κ) = ν + 92Sm *

σ 0− + 1/2 = 1/2 + 1− p ν Helicity Transferred to Recoiling Sm152* Helicity of Recoil is Transferred to the Helicity of the 963 γ

152* γ Sm = Sm152 + s 1− = 0 + 1(dipole) p Helicity of the Recoiling Sm152* is Transferred to Helicity of γ-ray 963 γ Traverses Magnet and Fluoresces the 963 State in Sm152

152 152* 963 γ + Sm = Sm (963 keV)

σ 1 + 0 = 1− p 963 keV γ Traverses Magnet and fluoresces Sm152 Fluorescence The excited 963 keV state decays in 10-13 s, emitting a 963keV or an 838 keV, and 122 keV cascade

Sm152* (964 kev) = Sm152 + 963/838 keV

1- = 0+/2+ + dipoles Sm152* deexcites

The Helicity of the 963 γ-ray is Negative M. Goldhaber, L. Grodzins, A. Sunyar, Phys. Rev. 109, 1015, 1958. • The 963 keV γ-ray has negative H.

• The recoiling Sm152* has negative H.

• The neutrino has negative H.

• Beta decay proceeds via Vector and Axial Vector currents. Science and Jazz in the NY Daily News Sunday September 21, 1958

Eu152m - 0 9 hr

~ 940 keV

1- Γ ~ 0.5 eV 963 keV

0+ 0 Sm152 Sm152 152m 0- Eu S E = ? 9 hr 13.5 yr ~ 940 keV

1- 963 keV : < 10-13 s, expected

2+ 122 0+ 0 Sm152 • Goldhaber has a new parity violation method.

• Grodzins and Sunyar take the magnet out of storage. Bremsstrahlung Bremsstrahlung

σ = −1/2

σ = 1 s =1/2 New title here

The Fluorescence Requirement 963keV

Line Width: ~ .05 eV

Recoil Loss ~ 3 eV ~ 3 eV = ~ 6 eV

Temp Broadening: ~ 1 eV Gain From Neutrino Recoil : ~ 5.4 eV

New title here Place a radioactive source on a magnet, that sits on a Pb cone, that is on top of a PMT, that is surrounded by a separated isotope. Put them on a table. Measure. Eu152 • Choose a radioactive nucleus that decays by K- magnet capture to a γ emitting excited state whose lifetime Pb cone is so short that the γ is emitted as the nucleus recoils. Sm152 • Measure the momentum of NaI on PMT the recoiling nucleus and the helicity of the γ-ray. • The helicity of the γ-ray Table Top measures the helicity of the ν. The τ/θ Puzzle • Two elementary particles that decayed via a weak interaction, had all the same properties (mass, lifetime, etc) but opposite parity. • Lee and Yang showed that parity had never been tested in weak interactions • They proposed that it should be tested in beta decay. • Need to measure a quantity that changes when the coordinate system changes sign. Measure a Pseudoscalar

Find a physical quantity that will change when you reverse all the signs that establish the coordinate system that defines the quantity. X,Y,Z = - (-X,-Y,-Z) We seek a scalar quantity that changes sign when we flip the coordinate system We seek a pseudoscalor: A . (BxC). p . σ “Weak” Forces

n decay: n p + e- + ν

+ 22 22* + e decay: 11Na 10Ne + e + ν

22 - 22 EC decay: 11Na + e 10Ne + ν

π µ + ν µ e + ν + ν e+ Emission vs Capture

22 22* + 11Na 10Ne + e + ν

3-body final state. ν has a continuum of energies

22 - 22* 11Na + e 10Ne + ν

2-body final state. ν is monoenergetic Parity • It is “obvious” that the laws of nature should not depend +Z on the coordinate system used to describe them. +Y +X • Right- handed.

+Y • Left-handed system. +X

+Z • In 1920’s atomic physics studies showed that classifying states as odd or even was useful for understanding atomic spectra and transitions. (LaPorte)

• In 1927, proved that Maxwell’s equations demanded that nature should be left-right symmetric. (Nobel Prize) Pseudoscalars • We measure scalars.

• Independent of the coordinate system.

• Pseudoscalars: A . (B x C) reverses sign when the r → - r • The physical quantity that is the vector dot product of a linear momentum and an angular momentum was always assumed to be taboo. eK captured, ν emitted γ emitted opposite ν direction Fluoresce the 963 keV State The 963 keV State Decays The 88-90 Neutron Region 66

65 64 63 62 61 60 The Effective Width of the 963 keV State

• Natural width of a 10-13 second state:

 10−15 eV − sec Γ = ≅ ≅ 0.01eV 2τ 10−13 sec

• At 300o K, line broadens to ~ 0.5 eV

• Which turns out to be essential. Energy of γ lost to recoiling nucleus

Sm152 963 keV – E (Sm152)

p (Sm152) = p (γ) K electron capture

9hr 63Eu + eK

62Sm*(963 keV) + ν Compton Scattering is Spin Dependent γ e-