CP Violation in Particle Physics 违反 CP Violation in Particle Physics

Summary of Lecture 4 K0 and K0 mesons are not mass eigenstates; KS and KL are mass eigenstates KL mesons discovered at Brookhaven Laboratory a K0 will oscillate into a K0 and vice versa neutral K mesons produced in f decay are ~100% “quantum correlated” KS mesons are “regenerated” when a KL passes through matter _ _

My plan for week 2 Done Week 2: Monday: The neutral K meson system: the KS and KL mass eigenstates and K0-K0 mixing. Wednesday: CP violation in KL decays; measurements of CPV parameters; Friday: Superweak or not superweak? Search for direct CP violation in KL decay.

the search for CP violation

Properties of the Mass Matrix -- slide from lecture 4 -- I ignore K0 life-time terms (for now) CPT symmetry requires: CP symmetry says: Let’s not use this condition & assume CP is violated Schrodinger’s equation for energy eigenstates;

Hamiltonian operator with decays 2 H=M - -- G - -- now we will include decays -- Hermitian Mass matrix Decay matrix CPT symmetry: no assumptions about CP Hermiticity:

Schrodinger’s Equation -- allowing for CP violation and including decays -- to conform to the standard notation: Schrodinger’s equation for energy eigenstates;

Solutions for Y(t) eigenvalue equation: eigenvalues eigenstates in terms of the CP eigenstates:

Decay of the KL CP odd CP even CP even CP odd OK OK CP even CP odd If CP is violated: KL contains a CP -even K1 component

Discovery of KL decays to p+p-

“Hint” for KLp+p- ?? a Bubble chamber in a neutral beam at Brookhaven saw some p+p- events neutrons & KL’s KLp+p-events or KLKS via regeneration

proposal

AGS Brookhaven’s 2nd HE accelerator -- world’s first strong focusing accelerator, still running, more than 50 years later -- “Inner Mongolia”

BEPC—AGS see the differences?

AGS combined function magnets

Quadrupoles & dipoles dipole Quadrupole

the “inner Mongolia” beam line shielding blocks sweeping magnet AGS accelerator magnets Internal target

The Fitch-Cronin experiment Helium gas all KS have decayed

Spark chamber

Data-taking and analysis

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p+ cosq p+p- “invariant mass” M(p+p-)<M(KL) M(p+p-)=M(KL) 5211 KL  π+ + π- candidates remeasured on a commercial bubble chamber measuring machine p+p- “invariant mass” M(p+p-)<M(KL) M(p+p-)=M(KL) p+ | q=1o p+p-)>M(KL) cosq

Results

CP is violated!! James Cronin Val Fitch 1980 Nobel Prize for Physics No prizes for Christenson or Turlay

25 year anniversary reunion

Let’s look at e: what we know about p & q definition of e: rewrite e in terms that we know:

Some comments CP is only violated if the off- diagonal terms are different Hermiticity: M21=M12 & G12=G21 CPV only driven by imaginary terms * * Latest numbers: CPV is very small, ~10-3GF2, far from the maximum that is possible (unlike P and C violations)

virtual & on-shell K0--K0 couplings _ 2nd-order quark-level virtual |DS|=2 process “short-distance processes” On-shell pion-induced |DS|=2 process “long-distance processes”

Phase of e (h+-)

K0 -- K0 basis states with CPV _ Solve for K0 and K0 _ Please check this for HW

The CPLEAR experiment

Strangeness-tagging at CPLEAR _ _

Time-dependence of K0(K0)p+p- _ KL(xh+-)

Phase of (h+-) from CPLEAR

Exploit KLKS regeneration Need to know regeneration phase p- p+ p- p+

DM and f(h+-) measured via regeneration

K0 K0 oscillations (mixing);no CPVCPV _ eigenstates start at t=0 with a K0: then, at a later time t: These are the K0 and K0 rates we measure I0 = beam intensity (particles/s) _

K0 K0 in a neutral K beam no CPVCPV _ _ e=2.23 start with ≈75% K0 and ≈25% K0 (fe=400±40) 2Ree= 3.4±0.2x10-3

Neutral Kaon spectrometer @ CERN expanded view of target region

Measurements of 2Ree (circa 1974)

Recent values of K-meson CPV parameters

Summary of Lecture 5 Discovery of KLp+p- decays proved that CP symmetry is violated Measurements consistent with KL=K2+eK1; e= 2.2x10-3 Phase of e consistent with CPV originating from short-distance Mass-Matrix terms Many beautiful, high-statistics measurements of CPV interference effects reported