University of Kentucky UKnowledge Theses and Dissertations--Physics and Astronomy Physics and Astronomy 2017 NEUTRON-ANTINEUTRON TRANSITIONS: EXPLORING B – L VIOLATION WITH QUARKS Xinshuai Yan University of Kentucky, [email protected] Digital Object Identifier: https://doi.org/10.13023/ETD.2017.308 Right click to open a feedback form in a new tab to let us know how this document benefits ou.y Recommended Citation Yan, Xinshuai, "NEUTRON-ANTINEUTRON TRANSITIONS: EXPLORING B – L VIOLATION WITH QUARKS" (2017). Theses and Dissertations--Physics and Astronomy. 46. https://uknowledge.uky.edu/physastron_etds/46 This Doctoral Dissertation is brought to you for free and open access by the Physics and Astronomy at UKnowledge. It has been accepted for inclusion in Theses and Dissertations--Physics and Astronomy by an authorized administrator of UKnowledge. For more information, please contact [email protected]. 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Xinshuai Yan, Student Dr. Susan Gardner, Major Professor Dr. Christopher Crawford, Director of Graduate Studies NEUTRON-ANTINEUTRON TRANSITIONS: EXPLORING B − L VIOLATION WITH QUARKS DISSERTATION A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the College of Arts and Sciences at the University of Kentucky By Xinshuai Yan Lexington, Kentucky Director: Dr. Susan Gardner, Professor of Physics Lexington, Kentucky 2017 Copyright c Xinshuai Yan 2017 ABSTRACT OF DISSERTATION NEUTRON-ANTINEUTRON TRANSITIONS: EXPLORING B − L VIOLATION WITH QUARKS In the Standard Model (SM), the quantity baryon number (B) − lepton number (L), B − L, is perfectly conserved. Therefore, the observation of B − L violation would reveal the existence of physics beyond the SM. Traditionally, given the severe experimental constraints on j∆Bj = 1 processes, B − L violation with baryons is probed via neutron-antineutron (n − n¯) oscillations, although this process suffers from quenching in the presence of external fields or matter. In this dissertation, we discuss another possibility, n − n¯ conversion, in which the j∆Bj = 2 process appears with an external source. We start with the Lorentz invariant B − L violating operators of lowest mass dimension and show how the appearance of constraints on the \arbitrary" phases in the discrete symmetry trans- formations help restrict the possible low energy n − n¯ transformation operators. To explain the appearance of CPT odd n−n¯ transition operators (although they eventu- ally vanish due to the fermion anticommutation relations), we connect it to theories of self-conjugate isofermions and show that the appearance of n − n¯ oscillations cannot occur in pure Quantum Chromodynamics (QCD) in the chiral limit. We then show how n − n¯ conversion can be free from quenching and demonstrate one way how it can be connected to n − n¯ oscillations since the quarks carry electromagnetic charge. Effective field theory is utilized to find the quark-level conversion operators and to determine the coupling parameter associated with the nuclear-level conversion oper- ators. Finally, we argue how n − n¯ conversion can provide a complementary probe to oscillation experiments. We discuss possible n−n¯ conversion proposals and explicitly show how n − n¯ conversion experiments can set limits on the scale of B − L violation. KEYWORDS: n − n¯ oscillation, discrete symmetries, n − n¯ conversion, CP violation Author's signature: Xinshuai Yan Date: July 28, 2017 NEUTRON-ANTINEUTRON TRANSITIONS: EXPLORING B − L VIOLATION WITH QUARKS By Xinshuai Yan Director of Dissertation: Dr. Susan Gardner Director of Graduate Studies: Dr. Christopher Crawford Date: July 28, 2017 ACKNOWLEDGMENTS First of all, I would like to express my great gratitude to my advisor Dr. Susan Gardner. She is an amazing physicist and a wonderful mentor. Her broad research interest leads me to work on different research projects and inspires my interest in various topics of physics. Her continuous encouragement in attending various summer schools and in giving presentations not only helps to broaden my research horizon but also to improve my social skills. Working under her guidance has been a great experience that I will always cherish. Besides my advisor, I would like to thank the rest of my committee members: Dr. Sumit Das, Dr. Keh-Fei Liu, and Dr. Peter Perry for their kind guidance. I also really appreciate the help I received from Dr. Brad Plaster and Dr. Michael Eides. Last but not least, I am very grateful to my parents and my younger brother and sister for their unconditional love and support. iii TABLE OF CONTENTS Acknowledgments . iii Table of Contents . iv List of Figures . vi List of Tables . viii Chapter 1 Introduction . 1 Chapter 2 Phenomenology of n − n¯ oscillations . 7 2.1 n − n¯ oscillations in the 2 × 2 framework . 7 2.1.1 n − n¯ oscillations in vacuum . 9 2.1.2 n − n¯ oscillations in a static magnetic field B . 10 2.1.3 n − n¯ oscillations in matter . 11 2.2 Quantum damping of n − n¯ oscillations . 13 2.3 Dinucleon decay . 14 2.4 Motivation for n − n¯ conversion . 16 Chapter 3 Phase constraints on discrete-symmetry transformations of fermions in B − L violating theories . 18 3.1 Discrete-symmetry transformations of fermion fields . 20 3.2 Discrete-symmetry phase constraints on Majorana fields . 21 3.3 Discrete-symmetry phase constraints on Dirac fields in B −L violating theories . 24 3.4 Lorentz invariant B − L violating operators and their CPT transfor- mation properties . 25 3.5 CPT -odd \problem" . 27 3.5.1 CPT -odd operators with Majorana fields . 27 3.5.2 CPT -odd operators with Dirac fields . 28 3.6 CPT -even n − n¯ transition operators . 29 Chapter 4 B − L violation and theories of self-conjugate fermions . 31 Chapter 5 n − n¯ oscillations and matrix elements in the MIT bag model . 33 5.1 Quark-level n − n¯ oscillation operators . 33 5.2 The MIT bag model . 35 5.2.1 Proper bag model wave functions . 35 5.2.2 Quark fields in the MIT bag model . 38 iv 5.3 Matrix elements in the MIT bag model . 39 5.4 n − n¯ oscillation matrix elements in lattice QCD . 40 Chapter 6 Phenomenology of nn¯ conversion . 44 6.1 Spin-flip and n − n¯ conversion . 44 6.1.1 nn¯ oscillation in 4 × 4 framework . 44 6.1.2 n − n¯ conversion operator . 46 6.2 Effective theories of nn¯ conversion . 47 6.2.1 Dimensional analysis of n − n¯ conversion operators . 47 6.2.2 Quark-level n − n¯ conversion operators . 48 6.3 Matrix elements of nn¯ conversion operators in the MIT bag model . 53 6.4 n − n¯ conversion coupling parameter . 57 Chapter 7 Applications of n − n¯ conversion . 59 7.1 n−n¯ conversion cross section at low energies, mediated by electromag- netically charged particle scattering . 59 7.2 Some experimental proposals . 61 7.3 n − n¯ conversion limits on δ ....................... 63 7.4 n − n¯ conversion limits on η ....................... 66 7.5 Conclusion and discussion . 69 Chapter 8 CP violation and Neutron-antineutron oscillation . 70 8.1 Introduction of CP violation . 70 8.2 CP violation for neutral flavored mesons mixing . 73 8.2.1 Charged- and neutral-hadron decays . 73 8.2.2 Neutral meson mixing . 73 8.2.3 Classification of CP violation . 75 8.3 CP violation in the B system . 76 8.3.1 Time evolution of the B states and time-dependent observables 76 8.3.2 The golden modes . 79 8.3.3 Time reversal violation in B physics . 81 8.3.4 Generalized T violation method to trap penguin . 84 8.4 CP violation in nn¯ oscillations . 88 8.4.1 Indeterminate CP transformation phase . 89 8.4.2 CP violation in n − n¯ oscillations through on-shell decays . 89 Chapter 9 Summary . 91 Appendices . 93 Chapter A Phase restrictions for two-component fields . 94 Bibliography . 97 Vita . 109 v LIST OF FIGURES 1.1 Diagrams responsible for (a) proton decay; (b) neutron decay; and (c) n−n¯ oscillations. Note that we have revised these diagrams from Ref. [33] to make them more transparent. The blue circle denotes the vertex asso- ciated with the dimension 6 operator, and the red polygon is the vertex associated with the dimension 9 operator. It is easy to check that pro- cesses (b) and (c) break the B − L, while (a) does not though both B and L are violated.