Jim s early days: Brookhaven, Princeton, and the CP Discovery. September 30, 2016 Stewart Smithx

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1 Jim s early days: Brookhaven, Princeton, and the CP Discovery September 30, 2016 Stewart Smithx

2 Partial Chronology Sep 29,1931 Born in Chicago (Father was UC GS) Marion, Alabama Dallas, Texas Undergraduate, Southern Methodist Graduate student, U. Chicago Postdoctoral scientist, Brookhaven Lab Faculty member, Princeton Univ CP Violation!! Distinguished Professor, U. Chicago 1980 Nobel Prize in Physics Distinguished Professor Emeritus Jim Cronin Memorial 2

3 Jim s work at Brookhaven: Married and with a new baby, in 1955 Jim accepted an assistant scientist position at Brookhaven National Laboratory to work in a group led by Rod Cool and Oreste Piccioni. At the Cosmotron, a new 3 GeV proton accelerator, they measured absorption and diffractive cross sections of pions on nuclei. Jim used the optical model to find that a Fermi distribution with reasonable radius and skin width fit the data extremely well. In 1957 Jim had just built an innovative K meson detector in anticipation of measuring more total cross sections. However, at this time parity violation was discovered. So Jim and Cool used it instead to search for parity-violating asymmetries in decays of Σ + and Σ - hyperons. Had to use the Berkeley Bevatron because t the Cosmotron was out of action. Their measurements were suggestive but not conclusive; e.g. for Σ + π 0 p they found αp = 0.7± 0.3. The experience at Berkeley inspired Jim to do it right when he got back to Brookhaven but fate intervened. Jim Cronin Memorial 3

4 Life at BNL Brookhaven was arguably the center of the particle physics universe. A satirical restaurant guide rated the BNL cafeteria as the worst, with the comment we just don t understand why people come from all over the world to eat here. With their new baby Cathryn, Jim and Annette greatly enjoyed the Brookhaven experience, including the beaches. Jim Cronin Memorial 4

5 From BNL to Princeton Val Fitch got to know Jim at the Cosmotron, as a neighbor and as a bridge companion. Even though Jim s list of publications was a bit thin (through no fault of his own), Val knew a gem when he saw one, and brought Jim to Princeton in (Hank Martin, New Yorker ) Jim Cronin Memorial 5

6 From Counters to Spark Chambers A brief stint with a bubble chamber experiment showed Jim the power of visual tracking. In 1959 the discharge chamber work of Fukui and Miyamoto caused the light bulb to go off. Jim quickly tested and improved this technology, called it the spark chamber, and immediately designed experiments around it. Counters and fast logic selected interesting events, and then a thyratron quickly applied a multi-kilovolt pulse across the gaps filled with a neon mixture. Jim Cronin Memorial 6

7 Jim s famous 18-plate chamber ( ) In his first SC experiment, and with his first graduate student Gene Engels, Jim measured spin correlations in p p scattering. Jim Cronin Memorial 7

8 Replica of the 18-plate chamber on display in Princeton, and the Liberty Science Museum Jim Cronin Memorial 8

9 Spark chambers go viral! Spark chambers enabled a new class of sensitive, precise experiments! Comparable spatial resolution to bubble chambers Much better time resolution: 1 μsec vs 1 msec Highly-selective triggers via scintillators, Cerenkovs, fast logic allowed efficient detection of rare processes. People quickly learned to make them cheaply and quickly, first with thin foils, later with wires and electronic readout to avoid taking pictures. In a review talk in 1963, Jim listed 20 experiments that had already used spark chambers. Jim and his students carried out three of them, one a year! Schwartz, Lederman and Steinberger, after consulting with Jim in Princeton, built huge spark chambers for their Nobel prize experiment that discovered electron and muon neutrinos. Jim Cronin Memorial 9

10 Cronin s second spark ch expt. Scintillators were used to select events having Ʌ 0 π-p decays within the fiducial region of spark chambers. The asymmetry of proton scatters in carbon plates was used to measure the parity-violating polarization. Jim Cronin Memorial 10

11 Jim builds a pair spectrometer -a fateful move! For his next experiment, in 1961 Jim designed a high-resolution pair spectrometer for an experiment at the Cosmotron, to study the production cross section and line shape of the recently discovered ρ 0 meson, via its decay ρ 0 π + π -. In spring 1963, Val Fitch proposed moving Jim s spectrometer to a neutral beam at the new AGS, to study interesting phenomena in decays of the longlived neutral K meson. Jim Cronin Memorial 11

12 An excellent detector applied to a less than excellent experiment September 30, 2016 Jim Cronin Memorial 12

13 a. A sketch of the spectrometer as reconfigured for the neutral kaon beam (from Jim s notebook). September 30, 2016 Jim Cronin Memorial 13

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15 Regeneration of short-lived K mesons θ 0 ~θ 1 +θ 2 θ 2 ~ θ 0 + θ 0 θ 1 s reappear September 30, 2016 Jim Cronin Memorial 15

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17 Proposal for the CP Experiment September 30, 2016 Jim Cronin Memorial 17

18 The CP Violation Detector September 30, 2016 Jim Cronin Memorial 18

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21 Angle of π + π - pair with the K 0 2 beam cos θ September 30, 2016 Jim Cronin Memorial 21

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24 T T Wu and C N Yang PRL (1964) By 1965 η +- measured to be (2.04 ± 0.14) x 10-3 and coherence established If ε >> ε then η 00 = 2 η +- If ε /ε small then η 00 η +- = 1-3 ε ε If superweak ε = 0 September 30, 2016 Jim Cronin Memorial 24

25 Jim s pursuit of K 20 π 0 π 0 and direct CPV. September 30, 2016 Jim Cronin Memorial 25

26 Princeton University

27 Jim s pursuit of K 20 π 0 π 0 and direct CPV. September 30, 2016 Jim Cronin Memorial 27

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29 Jim s Princeton Students Eugene Engels Richard Roth Alan Clark James Christenson Paul Kunz Paul Wheeler James Pilcher John Liu Mel Shochet Bruce Knapp September 30, 2016 Jim Cronin Memorial 29

30 25 years later September 30, 2016 Jim Cronin 30 Memor

31 Status of CKM (2015) All is well with the CKM picture at O(10%) level: α + β + γ = (175.2 ± 9.3) o Direct ( ) o ( ) o ( ) o +4.5 α = β = γ = β s = ± 0.07 CKM fit ( ) o 2.9 ( ) o 1.57 ( ) o Sin2β tension (driven by B τν) eased sin2β = ± 0.019(meas) ( fit) (< 2.3σ ) 31# 31

32 Jadwin Hall of Fame September 30, 2016 Jim Cronin Memorial 32

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34 CP Violation vs Standard Model Kobayashi-Maskawa Mechanism (1973) CP violation originates from the scalar sector of Stan Interactions of quarks with Higgs & with gauge boson A complex matrix, in general For 3 generations of quarks, parametrised by 3 angles and a single complex phase as the sole source of CPV in SM

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37 π + - proton separation by time of flight September 30, 2016 Jim Cronin Memorial 37

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