The Past and Future of CP Violation

Transcription

1 The Past and Future of CP Violation Michael Hunter Cochran Stony Brook University September 14, 2015 Michael Hunter Cochran (Stony Brook University) CP Violation September 14, / 14

2 Overview 1 CP Symmetry 2 Cronin and Fitch Overview 3 Cronin and Fitch The Math of the Violation Experimental Setup Aftermath 4 Unitarity Triangle 5 B Factories Overview Results 6 The Future of CP Violation Michael Hunter Cochran (Stony Brook University) CP Violation September 14, / 14

3 What is CP Symmetry? C is charge conjugation. It transforms a particle into its antiparticle. P is parity. It transforms the spatial coordinates of a particle into their opposites. For example: (x, y, z) ( x, y, z). Thus, if we had a CP mirror, CP symmetry would require the image to behave like the pre-image. Michael Hunter Cochran (Stony Brook University) CP Violation September 14, / 14

4 Cronin and Fitch: Overview Cronin/Fitch used KS 0 and K L 0, which are superpositions of neutral kaons K 0 and K 0 with identical mass but different half-lifes and decay modes. KS 0 decays into two pions with half-life s, whereas KL 0 three pions with half-life 10 8 s. decays into They sent a beam of these kaons down a 17.4 meter tube so that any trace of KS 0 would effectively be gone, leaving only K L 0 decay products. However, they found that 1/500 decay products were characteristic of KS 0, implying that some KL 0 had oscillated into K S 0 and thereby broke CP symmetry! Michael Hunter Cochran (Stony Brook University) CP Violation September 14, / 14

5 Cronin and Fitch: The Math of the Violation CP(K 0 ) = K 0 K S = 1 2 (K 0 K 0 ) CP(K S ) = 1 2 ( K 0 + K 0 ) = K S eigen is +1 K L = 1 2 (K 0 + K 0 ) CP(K L ) = 1 2 ( K 0 K 0 ) = K L eigen is 1 Therefore, K S/L and its decay products must have the same CP eigenvalue. However, the K L were decaying into two pions (CP eigenvalue 1) and consequently violated CP symmetry! Michael Hunter Cochran (Stony Brook University) CP Violation September 14, / 14

6 Cronin and Fitch: Experimental Setup [figure taken from quantum diaries survivor/answers physics questions] Michael Hunter Cochran (Stony Brook University) CP Violation September 14, / 14

7 Cronin and Fitch: Aftermath In 1973, Kobayashi and Maskawa proposed a third family of quarks to explain CP violation, developing also the CKM matrix which is used to form the constraints of the unitarity triangle. Cronin/Fitch demonstrated that CP symmetry was violated in the meson sector. However, kaons are very difficult objects to model in theory...b mesons provide the ideal environment for measurements of CP violation. [Sciolla] In 1999, after nearly 4 decades of performing (and perfecting) the CP violation experiment with kaons, the Stanford Linear Accelerator Center (SLAC) and the KEK laboratory built asymmetric colliders to study CP violation in B mesons. Michael Hunter Cochran (Stony Brook University) CP Violation September 14, / 14

8 Unitarity Triangle [Figure taken from: sites/default/files/legacy/pdfs/200512/deconstruction unitarity triangle.pdf] Michael Hunter Cochran (Stony Brook University) CP Violation September 14, / 14

9 B Factories: Overview Although B mesons pose less of a theoretical challenge than kaons, a lot more is required of the experiment. The B factories must produce hundreds of millions of B mesons with asymmetric momenta in an incredibly clean environment to extract meaningful data about CP violation. By 2006, each lab was able to collect over 10 6 B mesons per day! [Sciolla] Michael Hunter Cochran (Stony Brook University) CP Violation September 14, / 14

10 B Factories: Results The experiments at SLAC/KEK were a huge success: 1 They verified CP violation in B mesons and showed strong agreement with the Kobayashi/Maskawa theory. 2 They measured various lengths/angles of the unitarity triangle (β within 1.2 uncertainty) 3 They measured β in so-called penguin modes and found that it differs by 2.7 standard deviations. Michael Hunter Cochran (Stony Brook University) CP Violation September 14, / 14

11 The Future of CP Violation Although current research affirms the Kobayashi/Maskawa theory, each angle and side-length of the unitarity matrix can be measured more accurately (and with different methodology). CP violation in the quark sector has now been well documented, but it does not account for the matter/antimatter imbalance we see in the universe. Researchers are not looking to the lepton sector (particularly at neutrinos) for additional sources of CP violation. (T2K) Tokai to Tamioka Michael Hunter Cochran (Stony Brook University) CP Violation September 14, / 14

12 References (1) 1 U. Nierste, Z. Ligeti, A. S. Kronfeld (2001). B Physics at the Tevatron: Run II and Beyond. FERMILAB-Pub-01/197 hep-ph/ G. L. Fogli, E. Lisi, A. Marrone, et al. (2012) Global analysis of neutrino masses, mixings, and phases: Entering the era of leptonic CP violation searches. PHYSICAL REVIEW D 86, T. Yamanaka. (2014). CP Violation in Kaon Decays (II). 4 M. Rohrken. (2014). CPT, T, and CP Violation in B Mixing. 5 G. Sciolla. (2006). The Mystery of CP Violation. MIT Physics Annual 6 P. Harrison. (2014) CP Violation: Past, Present, and Future. CERN Courier 7 W. Herr and B. Muratori. Concept of Luminosity. CERN. Michael Hunter Cochran (Stony Brook University) CP Violation September 14, / 14

13 References (2) 1 M. Mazur. (2006) Deconstruction: Unitarity Triangle. Symmetry Vol. 02, 10 2 Cronin and Fitch Experiment with Kaons: 3 I. Senderovich. (2007) Observation of CP Violation in Kaon Decays. senderovich/perm/cpviolation(oralexam) 4 (Cronin/Fitch picture): quantum diaries survivor/answers physics questions Michael Hunter Cochran (Stony Brook University) CP Violation September 14, / 14

14 The End Michael Hunter Cochran (Stony Brook University) CP Violation September 14, / 14