ckm physics and flavor anomaliessimi/didattica/1-ckm-and...ckm is a unitary 3x3 matrix it can be...
Post on 06-Aug-2021
9 Views
Preview:
TRANSCRIPT
CKM Physics and Flavor anomaliesLecture1: Motivation and CKM Physics intro
Gabriele SimiUniversitá di Padova and INFN
2018 Lectures for the PhD program in Physics at University of Padova
April 2018 G. Simi - Flavour Phys. and Anomalies 2
Motivation for studying flavour physics
April 2018 G. Simi - Flavour Phys. and Anomalies 3
Outline
● Motivation for studying flavor physics
● CP violation and CKM physics
● How to observe CP violation: general considerations
● Bfactories
● Unitarity triangle determination
● Rare Decays
● Universality
● Dark Matter at colliders
April 2018 G. Simi - Flavour Phys. and Anomalies 4
Motivation for studying flavor physics
● The study of flavor physics has contributed to many advances in particle physics
– Discovery of CP violation (Christenson, Cronin, Fitch and Turlay - 1964)
– The smallness of KL → μ+ μ– predicts charm quark
– GIM mechanism forbids FCNC at tree level
– KM theory describing CP violation predicts third quark generation
● CP violation cannot be obtained with only two generations
– ΔmK = m(KL) – m(KS ) predicts charm quark mass range
– Frequency of B0 B0 mixing predicts a heavy top quark
– Measurements overconstraining the Cabibbo-Kobayashi-Maskawa matrix confirm the CKM theory
– Search of new sources of flavor and CP violating terms is used as tool to search for new physics with sensitivity extending to high very energy scales
April 2018 G. Simi - Flavour Phys. and Anomalies 5
Motivation for studying flavor physics
● In the Standard model the Yukawa couplings of the Higgs boson to the fermions determine the quark mixing matrix
● 10 out of 19 of the free parameters of the model are the masses and the mixing parameters of the quarks. Their study gives us fundamental informations. But there are also some fundamental open questions
● Why are there 3 generations?
April 2018 G. Simi - Flavour Phys. and Anomalies 6
Motivation for studying flavor physics
● In the Standard model the Yukawa couplings of the Higgs boson to the fermions determine the quark mixing matrix
● 10 out of 19 of the free parameters of the model are the masses and the mixing parameters of the quarks. Their study gives us fundamental informations. But there are also some open fundamental questions
● Why there is a striking hierarchy in the quark masses? Why the Higgs mass is at the EW scale?
April 2018 G. Simi - Flavour Phys. and Anomalies 7
Motivation for studying flavor physics
● In the Standard model the Yukawa couplings of the Higgs boson to the fermions determine the quark mixing matrix
● 10 out of 19 of the free parameters of the model are the masses and the mixing parameters of the quarks. Their study gives us fundamental informations. But there are also some open fundamental questions
● Why is there a striking hierarchy in the quark mixing parameters
April 2018 G. Simi - Flavour Phys. and Anomalies 8
Motivation for studying flavor physics
● In the Standard model the Yukawa couplings of the Higgs boson to the fermions determine the quark mixing matrix
● 10 out of 19 of the free parameters of the model are the masses and the mixing parameters of the quarks. Their study gives us fundamental informations. But there are also some open fundamental questions
● Why is there a large matter anti matter asymmetry in the universe?
April 2018 G. Simi - Flavour Phys. and Anomalies 9
CP violation and CKM Physics
April 2018 G. Simi - Flavour Phys. and Anomalies 10
Matter dominance and CP violation
● CP is the combination of C=charge conjugation and P=parity (spatial inversion)
● Why is matter dominance related to CP symmetry?
– Anti-matter is composed of anti-particles
– Anti-particles have opposite charge (and opposite baryon and lepton quantum numbers) with respect to matter
● It is not sufficient to change the charge of a particle to transform it into its own antiparticle because the spin is a pseudovector and does not change sign under parity
● Es. take the pion decay: RH neutrino does not exist
π+
νμ
μ+
spin
π−
νμ
μ−
CP
P
π−
νμ
μ−
C
April 2018 G. Simi - Flavour Phys. and Anomalies 11
Matter dominance: Sakharov conditions
● Conditions propose by A. Sakharov in 1967 to explain the formation of a baryon asymmetry from the evolution of an initial symmetric state
– (1) baryon number violation
– (2) C & CP violation
– (3) thermal inequilibrium
● An example [from T. Gershon, Univ. Warwick]:
– Suppose initial equal amounts of matter (X) and anti matter (X)
– X decays to:
● A (baryon number NA ) with probability p
● B (baryon number NB ) with probability (1-p)
– X
● A (baryon number -NA) with probability p
● B (baryon number -NB ) with probability (1-p)
– Generated baryon asymmetry:
● ΔNTOT=NAp+NB(1-p)-NAp-NB(1-p)=(p-p)(NA-NB)
● ΔNTOT≠0 requires p≠p (CP violation) and NA ≠ NB (baryon number violation)
April 2018 G. Simi - Flavour Phys. and Anomalies 12
CP Violation: a bit of history
● First measured in K decays in 1964
April 2018 G. Simi - Flavour Phys. and Anomalies 13
● Christenson, Cronin, Fitch and Turlay - 1964
April 2018 G. Simi - Flavour Phys. and Anomalies 14
CP Violation: a bit of history
● First measured in K decays in 1964
● Kobayashi and Maskawa, based on the Cabibbo theory, propose in 1973 a mechanism to include it in the Standard Model, however it needed at least a third generation
● ARGUS measured B anti-B mixing in 1973 => the CP violation effect could be large in B decays (Bigi, Sanda)
● Measured in 2001 by the two dedicated experiments BaBar and BELLE
April 2018 G. Simi - Flavour Phys. and Anomalies 15
CKM● In the Standard model Lagrangian the Yukawa couplings of the Higgs boson to the fermions
determine the quark mixing matrix
– H is the Higgs Field <H>=(0,v/√2), YU,D are 3x3 complex matrices, i,j are generation labels
– Physical states obtained by redefinition of the quark states
–
– After diagonalization the interaction term becomes
U L, R→U L , RUL , R , DL, R→ DL , R DL , R
April 2018 G. Simi - Flavour Phys. and Anomalies 16
How many parameters does CKM have
● VCKM is a unitary 3x3 matrix
● It can be parameterized by 3 mixing angles (corresponding to real rotation matrices) and 6 complex phases [blackboard]
● However some phases (6) can be re-absorbed by phase rotations of the up and down quarks. An overall phase rotation of all quark phases does not affect the CKM matrix => only 5 phases can be re-absorbed
● => CKM matrix can be parameterizes by 3 mixing angles and one complex phase
April 2018 G. Simi - Flavour Phys. and Anomalies 17
CKM Parameterizations
April 2018 G. Simi - Flavour Phys. and Anomalies 18
The Unitarity triangle
● The unitarity of the matrix can be represented as a triangle relation between its elements
● Measuring angles and sides of the triangle and over-constrains the model => consistency checks
April 2018 G. Simi - Flavour Phys. and Anomalies 19
CP Violation
● In the standard model CP violation is described in by a single weak phase in the quark mixing (CKM) matrix
● The relative magnitude of the CKM elements has a very intriguing pattern, with no a-priori reason and very different from the neutrino sector
● Since the CP symmetry corresponds to the complex conjugate operation the phase in the CKM matrix gives rise to CP symmetry violation.
ie
ie
April 2018 G. Simi - Flavour Phys. and Anomalies 20
The Unitarity triangle
● The CKM mechanism is extremely successful in describing the observed pattern of decays, mixing and CP violation
● In the SM the phase in the CKM matrix is the sole origin of CP violation therefore all measurements must agree on the apex of the unitarity triangle
April 2018 G. Simi - Flavour Phys. and Anomalies 21
The Unitarity triangle
● The CKM mechanism is extremely successful in describing the observed pattern of decays, mixing and CP violation
CP conserving CP violating
looptree
April 2018 G. Simi - Flavour Phys. and Anomalies 22
However...
● Baryon asymmetry requires large CP violation: why is that?
● We can estimate the baryon asymmetry of the Universe cause the CKM mechanism [PRL 55 (1985) 1039]
ΔnBobserved
n
= 10−9
ΔnBCKM
n
=10−17
April 2018 G. Simi - Flavour Phys. and Anomalies 23
How to observe CP violation?
April 2018 G. Simi - Flavour Phys. and Anomalies 24
CP violation observable
April 2018 G. Simi - Flavour Phys. and Anomalies 25
B Mesons
● B Mesons have a long lifetime ~1.5ps
April 2018 G. Simi - Flavour Phys. and Anomalies 26
B Mesons
● B Mesons have a long lifetime ~1.5ps
● Can be produced in pairs in the decay of bb in a coherent L=1 state
OffOn
)MeV(ME )S4(CM
PEP-II BABAR
April 2018 G. Simi - Flavour Phys. and Anomalies 27
B Mesons
● B Mesons have a long lifetime ~1.5ps
● Can be produced in pairs in the decay of bb in a coherent L=1 state
● B Mesons Mix
– Y(4S)→BB→B1B2
● B1→D1*-μ1ν1
● B2 D→ 2*-μ2ν2
ARGUS, PL B 192, 245 (1987)
April 2018 G. Simi - Flavour Phys. and Anomalies 28
How can CP violation be observed
● Three types of CP violation
– trough the interference of decay amplitudes
April 2018 G. Simi - Flavour Phys. and Anomalies 29
How can CP violation be observed
– Trough the interference of mixing diagrams
– Trough the interference between mixing and decay amplitudes
● Directly related to CKM angles for single amplitude
● Golden channel B0→J/psi KS,L
● Tree level diagram
● Higher order contributions have
the same weak phase
– => theoretically clean
measurement of CKM phase
beta
● Clear experimental signature
– A pair of high momentum leptons and a pair of low momentum pions
● Relatively large branching fractions
0Bfi
CPA eCPf
0B
12
2 Mi
M
ie fi
CPA e
April 2018 G. Simi - Flavour Phys. and Anomalies 30
Time evolution of the B system
[from P. Krizan, Univ. Lubljana]
April 2018 G. Simi - Flavour Phys. and Anomalies 31
Time evolution of the B system
April 2018 G. Simi - Flavour Phys. and Anomalies 32
Time evolution of the B system
April 2018 G. Simi - Flavour Phys. and Anomalies 33
Time evolution of the B system
April 2018 G. Simi - Flavour Phys. and Anomalies 34
Time evolution of the B system
April 2018 G. Simi - Flavour Phys. and Anomalies 35
Time evolution of the B system
April 2018 G. Simi - Flavour Phys. and Anomalies 36
Time evolution of the B system
April 2018 G. Simi - Flavour Phys. and Anomalies 37
Time evolution of the B system
April 2018 G. Simi - Flavour Phys. and Anomalies 38
April 2018 G. Simi - Flavour Phys. and Anomalies 39
April 2018 G. Simi - Flavour Phys. and Anomalies 40
April 2018 G. Simi - Flavour Phys. and Anomalies 41
April 2018 G. Simi - Flavour Phys. and Anomalies 42
April 2018 G. Simi - Flavour Phys. and Anomalies 43
top related