Michael D. Sokoloff 1 Time-Dependent Particle-Antiparticle Asymmetries in the Neutral B-Meson System Michael D. Sokoloff University of Cincinnati The story

1Michael D. Sokoloff

Time-Dependent Particle-Antiparticle Asymmetries in the Neutral B-Meson System

Michael D. SokoloffUniversity of Cincinnati

The story of CP Violation has changed qualitatively in the past two years.

Babar and BELLE have observed time-dependent CP violation in neutral B-mesons, in accord with the Standard Model.

The ensemble of these and other results appear to validate the Kobayashi-Maskawa mechanism as the source of CP violation in the electroweak sector.

New Physics may yet be manifest in CP violation measurements to come.

B0B 0fCP

B0

B 0 fCP


The Nature of Particle Physics

• Particle physicists study the fundamental constituents of matter and their interactions.

• Our understanding of these issues is built upon certain fundmental principles– The laws of physics are the same everywhere– The laws of physics are the same at all times– The laws of physics are the same in all inertial reference

systems (the special theory of relativity)– The laws of physics should describe how the wave function

of a system evolves in time (quantum mechanics)

• These principles do not tell us what types of fundamental particles exist, or how they interact, but they restrict the types of theories that are allowed by Nature.

• In the past 30 years we have developed a Standard Model of particle phyiscs to describe the electromagnetic, weak nuclear, and strong nuclear interactions of constituents in terms of quantum field theories.


Special Relativity• Energy and Momentum

– Energy and momentum form a four-vector (E,px,py,pz). The Lorentz invariant quantity defined by energy and momentum is mass:

– For the special case when an object is at rest so that its momentum is zero

• When a particle decays in the laboratory, we can measure the energy and momenta of it decay products (its daughter particles), albeit imperfectly.

• The energy of the parent is exactly the sum of the energies of its daughters. Similarly, each component of the parent’s momentum is the sum of the corresponding components of the daughters’ momenta.

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

From the reconstructedenergy and momentum of thecandidate parent, we cancalculate its invariant mass.


Classical Field Theory (E&M)


Fields and Quanta

• Electromagnetic fields transfer energy and momentum from one charged particle to another.

• Electromagnetic energy/momentum is quantized:– E = hp = hc

• These quanta are called photons: • In relativistic quantum field theory: A • To calculate cross-sections and decay rates we use

perturbation theory based on Feynman Diagrams:


Strong Nuclear Interactions of Quarks and Gluons

Each quark carries one of three strong charges, and each antiquark carries an anticharge. For convenience, we call these colors:

Just as photons are the quanta of EM fields, gluons are the quanta of strong nuclear fields; however, while photons are electrically neutral, gluons carry color-anticolor quantum numbers.

The Nobel Prize in Physics 2004

Gross Politzer Wilczek


Baryons and Mesons

• Quarks are never observed as free particles.– Baryons consist of three quarks, each with a

different color (strong nuclear) charge proton = neutron =– Mesons consist of quark-antiquark pairs with

canceling color-anticolor charges

• Baryons and meson (collectively known as hadrons) have net color charge zero.

• A Van der Waals-types of strong interaction creates an attractive force which extends a short distance (~ 1 fm) to bind nucleii together.


Weak Charged Current Interactions

neutrino scattering charm decay

As a first approximation, the weak charged current interaction couples fermions of the same generation. The Standard Model explain couplings between quark generations in terms of the Cabibbo-Kobayashi-Maskawa (CKM) matirx.

f

f


Weak Phases in the Standard Model


• A second order weak charged current process, a box diagram amplitude, provides a mechanism by which particles oscillate into antiparticles.

• Particles decay exponentially with characteristic times

• Neutral B-mesons mix sinusoidally with characteristic times

• Experimentally

which makes mixing observation relatively easy.

Particle-Antiparticle Mixing


Time-Dependent CP Violation

• Both particles and antiparticles can decay to common final states which are CP eigenstates. As an example,

• The final state is invariant under charge and parity conjugation; that is, it remains .

• The Standard Model predicts that the CKM phase will produce a time dependent asymmetry in the decays of and to this final state, and that the asymmetry will vary sinusoidally.

B0B 0

fCPB0

B 0 fCP


Elements of Macroscopic CP Violation

B0B 0

fCP


Some Relevant Feynman Diagrams


Elements of Macroscopic CP Violation

B0B 0

fCP


The PEP-II Storage Ring at SLAC

• PEP-II is SLAC’s ee

B factory running at the (4S) c.m. energy

• The (4S) resonance decays to charged and neutral B-anti-B pairs

Total: 244 fb-1 (Jul 31st 04)

16

BaBar Detector

SVT: 97% efficiency, 15 m z hit resolution (inner layers, transverse tracks)

SVT+DCH: (pT)/pT = 0.13 % pT + 0.45 %

DIRC: K- separation 4.2 @ 3.0 GeV/c 2.5 @ 4.0 GeV/c

EMC: E/E = 2.3 %E-1/4 1.9 %

All subsystems crucial for CP analysis

17

/ KL detection 14/15 lyr. RPC+Fe

Tracking + dE/dx small cell + He/C2H5

CsI(Tl) 16X0

Aerogel Cherenkov cnt. n=1.015~1.030

Si vtx. det. 3 lyr. DSSD

TOF counter

SC solenoid1.5T

Belle DetectorBelle Detector

8GeV e

3.5GeV e


+e-e

Boost: = 0.55

Start the Clock

Coherent L=1 state

B0

B0

Experimental Technique at the (4S) Resonance

4S

e+e- (4S) B B

Exclusive B meson and vertex reconstruction

Exclusive B meson and vertex reconstruction

zΔ

€

Δt ≈Δzβγ c

Btag

Brec

K-

Flavor tag and vertex

reconstruction

Flavor tag and vertex

reconstruction

Stop the Clock

KS


Identifying Fully Reconstructed B’s

For fits, both Belle and Babar characterize signals and backgrounds with PDF’s which utilize M

bc, ΔE, tagging category, etc.

( )


Tagging Errors and Finite Δt Resolution

€

Btag= B0

perfect tagging & time

resolution

€

Btag= B 0

(f-)(f+)

B0 D(*)-+/ +/ a1+

Ntagged=23618Purity=84%

€

fUnmixedMixed

(Δt) =e−Δt /τ

B

4τ B

1± (1− 2w) cos(ΔmdΔt)[ ]

⎧

⎨ ⎪

⎩ ⎪

⎫

⎬ ⎪

⎭ ⎪⊗R

typical mistagging & finite

time resolution


Effective Tagging Efficiency QQ=(1-2w)2

Babar Tagging Performance

Category

w Q (%)

Lepton 9.0.

3.3 0.6

7.9 0.3

Kaon I 16.7 0.2 9.9 0.7

10.7 0.4

Kaon II 19.8 0.3 20.9 0.8

6.7 0.4

Inclusive

20.0 0.3 31.6 0.9

2.7 0.3

Total 65.6 0.5 28.1 0.7

r = estimated tagging dilution

6

hep-ex/020825 v1Summer 2002


sin2 Golden Sample: (cc)KS and (cc)KL

85 x 106 BB evts

2938 events used to

measure sin21Summer

2002


|f| = 0.948 0.051 (stat) 0.017 (sys) Scss = sin(2

1 ) = 0.759 0.074 (stat) 0.032

(sys)

sin(21 ) = 0.719 0.074 (stat) 0.035 (sys)

asumming |f| = 1 (hep-ex/020825, v1)

CP odd: sin 21 = 0.716 0.083

CP even: sin 21 = 0.78 0.17

sin(2) Fit Results

Summer 2002


sin2 = 0.723 0.158 sin2 = 0.755 0.074

sin(2) Fit Results

f =-1 f =+1

sin2 = 0.741 0.067 (stat) 0.034 (sys) with

Summer 2002

|f| = 1

|f| = 0.948 0.051 (stat) 0.017 (syst) Sf = 0.759 0.074 (stat) 0.032 (syst)

}f =-1


The best of the best!

Ntagged = 220Purity = 98%Mistag fraction

3.3%

Δt 20% better than other tag categories

sin2 = 0.79 0.11

Golden modes with a lepton tag

Consistent results across mode, data sample, tagging category

background

Summer 2002


Standard Model Comparison

One solution for is in excellent

agreement with measurements of unitarity triangle

apex

Method as in Höcker et al, Eur. Phys.J.C21:225-259,2001

= (1-2/2)

= (1-2/2)

Nir@ICHEP2002: Im(K) = 0.734 0.054

sin2 = 0.741 0.067 (stat) 0.034 (sys)sin21= 0.719 0.074 (stat) 0.035 (sys)

sin2 = 0.722 0.040 (stat) 0.023 (sys)

sin21= 0.728 0.056 (stat) 0.023 (sys)

HFAG@ICHEP2004: Im(K) = 0.725 0.037


2.7 from s-penguin to sin2 (cc)

2.4 from s-penguin to sin2 (cc)

sin2 from the Penguin Decay b sss


B to Measure sin2eff

mixing

*

*

ubud

ubud

VV

VV= *

*

tdtb

tdtb

VV

VV

decay

No Penguins (Tree only):

€

=e i

C = 0S = (sin )

With Penguins (P):

€

=e i + P /T eiδ ei

+ P /T eiδ e−i

C ∝ (sin δ )

S = −C (sin eff )


B CP Asymmetry Results


B CP Asymmetry Results

PRL 93, 021601 (2004)

152M BB pairs


Time-Dependent CP Violation in B-DecaysA January 2005 Summary

Babar and BELLE have observed time-dependent CP violation in neutral B-mesons, in accord with the Standard Model.

HFAG@ICHEP2004: Im(K) = 0.725

0.037

The ensemble of these and other results appear to validate the Kobayashi-Maskawa mechanism as the source of CP violation in the electroweak sector.

New Physics may yet be manifest in CP violation measurements to come. Lots of experimental work is being done. Several “> 2.5””” effects are stimulating theoretical work.

Documents

Michael D. Sokoloff 1 Time-Dependent Particle-Antiparticle Asymmetries in the Neutral B-Meson System Michael D. Sokoloff University of Cincinnati The story