Results from the B-factories - Particle Physicspprc.qmul.ac.uk/~bevan/helmholtz/lecture1.pdf ·...

August 2008 Adrian Bevan 1

Results from the B-factories(Lecture 1)

Adrian Bevan

Helmholz International Summer SchoolHEAVY QUARK PHYSICS

Bogoliubov Laboratory of Theoretical Physics,Dubna, Russia, August 11-21, 2008


OutlineThese lectures will cover:

• Introduction– The B factories– CKM, mixing, and measuring CP asymmetries

• Unitarity triangle physics– CP violation measurements

• The angles: (α, β, γ) = (φ1, φ2, φ3)• Direct CP violation• Searching for new physics

– Side measurements• Vub and Vcb

• Measurements of b→dγ processes (related to |Vtd| / |Vts|)

• Tests of CPT• B →VV decays

– Testing SM calculations and searching for new physics

• Bostjan Golob will discuss charm physics, mixing, spectroscopy and other new physics searches from the B-factories.


Notes• The B factories have produced many excellent results.

– Rather than show the results for both experiments for each measurement, I have selected results from either BaBar or Belle.

– Where possible I show world average results based on the latest measurements.

– I choose to use the α, β, γ convention for the Unitarity triangle angle measurements, and the S, C convention for time-dependent CP asymmetry measurements.

– Experimental references are listed at the end of each lecture.


The B factories• 1964:

– Christensen, Cronin, Fitch and Turlay discover CP violation.

• 1967:– A. Sakharov: 3 conditions required to generate a baryon asymmetry:

• Period of departure from thermal equilibrium in the early universe.• Baryon number violation.• C and CP violation.

• 1981:– I. Bigi and A. Sanda propose measuring CP violation in B→ J/ψK0 decays.

• 1987:– P. Oddone realizes how to measure CP violation: convert the PEP ring into an

asymmetric energy e+e- collider.

• 1999:– BaBar and Belle start to take data. By 2001 CP violation has been established

(and confirmed) by measuring sin2β ≠0 in B→ J/ψK0 decays.BaBar Collaboration, PRL 87, 091801 (2001);Belle Collaboration, PRL 87, 091802 (2001).

Detector Considerations P. Oddone (LBL, Berkeley) . 1987In the Proceedings of Workshop on Conceptual Design of a Test Linear Collider: Possibilities for a B Anti-B Factory, Los Angeles, California, 26-30 Jan 1987, pp 423-446.

I. Bigi and A. Sanda Nucl.Phys.B193 p85 (1981)


How do we make B mesons?• Collide electrons and positrons

at √s=10.58 GeV/c2

many types of interaction occur.

• We’re interested in (for B physics).

• Where

9.44 9.46

Mass (GeV/c2)

0

5

10

15

20

25

σ (e

+e- →

Had

rons

)(nb

) ϒ(1S)

10.00 10.020

5

10

15

20

25

ϒ(2S)

10.34 10.370

5

10

15

20

25

ϒ(3S)

10.54 10.58 10.620

5

10

15

20

25

ϒ(4S)

Υ(4S)off-peak


PEP-II and KEKB

PEP-II• 9GeV e- on 3.1GeV e+

• Υ(4S) boost: βγ=0.56

KEKB• 8GeV e- on 3.5GeV e+

• Υ(4S) boost: βγ=0.425


BABAR and Belle

BABAR

The differences between the two detectors are small. Both have:

• Asymmetric design.• Central tracking system• Particle Identification System• Electromagnetic Calorimeter• Solenoid Magnet• Muon/K0

L Detection System• High operation efficiency

DCH

DIRC

EMCIFR

SOLENOID

e−

e+

SVT


What does an event look like?

π0

π0

0 0 0 eventB π π→


Data

• Many Interactions produce B meson pairs:

0 0 and producedin equal quantitiesB B B B+ − Both experiments have recorded data while scanning

through the region above the Y(4S)


The CKM matrix• Quarks change type in weak interactions:

• We parameterise the couplings Vij in the CKM matrix:

• At the B factories we want to measure:

32

2 2

23

4

(1 / 2 )

(1 1)1 / 2 ( )

A i

iV A

AAO

λ ρ η

λ

λ

λρλ λ

η

λλ λ

⎛ ⎞−⎜ ⎟

= − − +⎜ ⎟⎜ ⎟−⎝ ⎠

−

− −

~ 0.22~ 0.8~ 0.2 0.27~ 0.28 0.37

Aλ

ρη

−−

V =, ,iq u c t=

, ,jq d s b=

W +

ijV

2 2(1 / 2), (1 / 2)ρ ρ λ η η λ≈ − ≈ −


Mixing• Neutral B mesons oscillate between B0 and B0, The Hamiltonian is

• We study the mass eigenstates:– If CPT is conserved z=0– p and q are mixing parameters:

– Physics depends on mass eigenstate differences in m and Γ:

– Δ Γ / Γ = -0.003 (usually set ΔΓ = 0).

= + Long Distance TermsW− W+

u, c, t

u, c, t


Time-dependent CP asymmetries• Ingredients of a time-dependent CP asymmetry measurement:

– Isolate interesting signal B decay: BREC.– Identify the flavour of the non-signal B meson (BTAG) at the time it

decays.– Measure the spatial separation between the decay vertices of both B

mesons: convert to a proper time difference Δt = Δz / βγc; fit for S and C.• The time evolution of BTAG = B0(B0) is

• S is related to CP violation in the interference between mixing and decay.

• C is related to direct CP violation.

• ηf is the CP eigenvalue of BREC.

Note that Belle use a convention where C is replaced by ACP = −C


Time-dependent CP asymmetries• Ingredients of a time-dependent CP asymmetry measurement:

– Isolate interesting signal B decay: BREC.– Identify the flavour of the non-signal B meson (BTAG) at the time it

decays.– Measure the spatial separation between the decay vertices of both B

mesons: convert to a proper time difference Δt = Δz / βγc; fit for S and C.• The time evolution of BTAG = B0(B0) is Note that Belle use a convention

where C is replaced by ACP = −C


Time-dependent CP asymmetries• Construct an asymmetry as a function of Δt:

Δt (ps)Δt (ps)

f+(Δt)f-(Δt)

Experimental effects we need to include:• Detector resolution on Δt.• Dilution from flavor tagging (see later).

With detector resolution With detector resolution and dilution


Time integrated CP asymmetries• Charged B mesons do not oscillate.• Measure a direct CP asymmetry by comparing amplitudes of decay:

• Event counting exercise! • With two (or more) amplitudes

see that we need different weak and strong phases to generate.

• ACP is largest when a1 = a2.

• Need to measure δ!

• We can use this technique when studying neutral B mesons decaying to a self tagging final state.


Isolating signal events• Beam energy is known very well at an e+e− collider

– use an energy difference and effective mass to select events:

MES σ ~ 3 MeV

B background

signal

σ(ΔE)~ 15-80 MeV (mode dependent)


More background suppression• Use the shape of an event to distinguish between Υ(4S)→BB and

e+e− → qq.• √s=10.58 GeV: compare mBB = 10.56 GeV/c2 with

– muu, mdd, mss ~ few to 100 MeV/c2

– mcc ~ 1.25 GeV/c2

B-pair events decay isotropically continuum (ee→qq) eventsare ‘jetty’

Analyses combine several event shape variables in a single discriminating variable: either Fisher or artificial Neural Network.

This allows for some discrimination between B and continuum events

Signal

u,d,s,cbackground

Fisher Discriminant:

Arb

itrar

y U

nits

i ii

F xα= ∑


Measuring Δt

Asymmetric energiesproduce boosted Υ(4S), decaying into coherent BB pair

e- e+

B0

B0

Fully reconstruct decay to state or admixture under study (BREC)

π+

π−


Measuring Δt


e- e+

B0

B0

Determine time between decays from vertices

Δz=(βγc)Δt


π+

π−

• βγ = 0.56 (BaBar)= 0.425 (Belle)

• t = t1 corresponds to the time that BTAG decays.

• t2-t1= Δtt=t1t=t2


Measuring Δt

• Then fit the Δt distribution to determine the amplitude of sine and cosine terms.


Determine flavor and vertex position of other B decay (BTAG)

l-

K-

e- e+

B0

B0

Determine time between decays from vertices

Δz=(βγc)Δt


π+

π−

• βγ = 0.56 (BaBar)= 0.425 (Belle)

• t = t1 corresponds to the time that BTAG decays.

• t2-t1= Δtt=t1t=t2


Flavor tagging

0B0B

• Decay products of BTAG are used to determine its flavor.

• At Δt=0, the flavor of BREC is opposite to that of other BTAG.

• BREC continues to mix until it decays.

• Different BTAG final states have different purities and different mis-tag probabilities.

• Can (right) split information by physical category or (below) use a continuous variable to distinguish particle and anti-particle.

Lepton

Kaon 1

Kaon 2 Kaon-Pion

Pion Other

BaBar’s flavor tagging algorithm splits events into mutually exclusive categories ranked by signal purity and mis-tag probability. Belle opt to use a continuous variable output. These plots are for the 316fb-1 h+h- data sample.


Flavor tagging• Don’t always identify BTAG flavor correctly: asymmetry diluted by

• ω is probability for assigning the wrong flavor (mistag probability).• Effect is slightly different for B0 and B0 tags: Δω• Define an effective tagging efficiency:

• Use a modified f±(Δt):


Flavor tagging• Don’t always identify BTAG flavor correctly: asymmetry diluted by

• ω is probability for assigning the wrong flavor (mistag probability).• Effect is slightly different for B0 and B0 tags: Δω• Define an effective tagging efficiency:

• Use a modified f±(Δt):

Example: The BaBar tagging algorithm:


Fitting for CP asymmetries• Perform an extended un-binned ML fit in several dimensions (2 to 8).

– P ji is the probability density functions for the ith event and jth component

(type) of event.– nj is the event yield of the jth component.– N is the total number of events.– Usually replicate the likelihood for each tagging category (BaBar) or

include a variable in the fit that incorporates flavor tagging information (Belle).

• In practice we minimize –lnL in order to obtain the most probable value of our experimental observables with a 68.3% confidence level (1σ error) using MINUIT.

• S and C (or ACP) are observables that are allowed to vary when we fit the data.


Angles of the Unitarity triangle


0 0

0 0

0 0

0 01

0 0

0 *0

/

/

(2 )

/

L

S

S

c S

c S

b ccsB J K

B J K

B S K

B K

B K

B J K

ψ

ψ

ψ

χ

η

ψ

→

→

→

→

→

→

→

0

(*) (*)

0

0

0

0 0

(*)0

0

0 0

/

(980)

B JB D DB KB KB KB KB KB KKKB f K

ψπ

η

ρ

ω

π

φ

+ −

→

→

′→

→

→

→

→

→

→

Theoretically clean (SM uncertainties ~10-2 to 10-3) tree dominated decays to Charmonium + K0 final states.


CP violation: β• Need to determine many parameters before we can extract S and C

(and the angles of the triangle):– ω, Δω, εTAG, ΔεTAG for signal and for background.– Use a sample of fully reconstructed B decays to flavor specific final

states to determine these parameters (Bflav).– Sample includes:

0 (*)

0 (*)

0 (*)1

0 *0 *0/ , Background

B DB DB D a

B J K K K

π

ρ

ψ π

− +

− +

− +

+ −

→

→

→

→ →

D−

π+

π−π+π−

BREC=BFLAV

BTAG

Lepton, pion or kaon

νThis method to validate the tagging performance is used for all time-dependent CP asymmetry measurements.

BaBar sin2β analysis


CP violation: β• Measure S and C in several modes.

• Theoretically clean: Tree level process dominates:

• Gluonic loop (penguin) is small:

• Calculations suggest C<10-3.

• Data driven methods constrain C<0.012.

b ccs→

1fη = +

1fη = −

~ 0.5efffη

This mode is a CP admixture with CP even and odd parts that need to be distinguished using an angular analysis.

b

d

d

−W cc

s

0B ψ/J0K

0K0Bb

d−W

s

d

cc

g

u,c,t

ψ/J



CP violation: β• CP violating asymmetry is well established in these decays!

1fη = +

1fη = −

BaBar Collaboration, SLAC-PUB-13317, PRL 99, 171803 (2007)


1998

2000

2000

2001

2008

sin 2 0.671 0.024β = ±


CP violation: β

0 0

0 0

0 0

0 01

0 0

0 *0

/

/

(2 )

/

L

S

S

c S

c S

B J K

B J K

B S K

B K

B K

B J K

ψ

ψ

ψ

χ

η

ψ

→

→

→

→

→

→

• Theoretically clean CP violation measurements consistent with the Standard Model for:

• Established technique for extracting S and C that can be used for other final sates.

• Measured S=sin2 β provides a reference point to search for New Physics (NP).

• Four solutions exist in the ρ-η plane as we compute arcsin(2β).

• Additional measurements provide cos(2β) and help to resolve ambiguities.


b uudBBB

ππρπρρ

→→→→

1

1

1

1

1 1

B aB aB bB bB a a

πρπρ

→→→→→

b→uud transitions with possible loop contributions. Extract α using• SU(2) Isospin relations.• SU(3) flavour related processes.


CP violation: α• Interference between box and tree results in an asymmetry that is

sensitive to α in B→hh decays: h=π, ρ, …• Loop corrections are not negligible for α.

• Measure S ∝αeff.• Need to determine δα=αeff-α [ P/T is different for each final state ]

:tdV β

* :tdV β

:ubV γ

+Loops (penguins)

0sin(2 )

hh

hh

CS α

=

=

2eff

sin( )

1 sin(2 )hh

hh hh

P T

C

S C

δ

αδ δ δ

∝

= −

= −

• This scenario is equivalent to the measurement of sin2β in Charmonium decays … but nature is more complicated than this!


CP violation: α• Interference between box and tree results in an asymmetry that is

sensitive to α in B→hh decays: h=π, ρ, …• Loop corrections are not negligible for α.

• Measure Shh ∝αeff.• Need to determine δα=αeff-α [ P/T is different for each final state ]

:tdV β

* :tdV β

:ubV γ

+Loops (penguins)

0sin(2 )

hh

hh

CS α

=

=

2eff

sin( )

1 sin(2 )hh

hh hh

P T

C

S C

δ

αδ δ δ

∝

= −

= −


Bounding penguins• Several recipes describe how to bound penguins and measure

alpha.– These are based on SU(2) or SU(3) symmetry.

SU(2)(Isospin analysis)

π+π− and ρ+ρ−

Gronau-LondonIsospin Triangles

π+ / − ρ− / +

Lipkin (et al.)Isospin Pentagons

• Use charged and neutral B decays to the hh final state to constrain the penguin contribution and measure alpha.

• Use charged and neutral B decays to the ρπ final state to constrain the penguin contribution and measure alpha. Remove any overlapping regions in the Dalitz plot.

π+ / − π − / + π0

Snider-Quinn (et al.)Fit Dalitz plot and extract parameters related to α

• Regions of the Dalitz plot with intersecting ρ bands are included in this analysis; this helps resolve ambiguities.


Bounding penguins• Several recipes describe how to bound penguins and measure

alpha.– These are based on SU(2) or SU(3) symmetry.

SU(3)flavor analysis

Fit for T and P amplitudes, as well as phase differences

δTP in related decays

• Theoretical uncertainties tend to result in weaker constraints than the SU(2) analyses.

• No choice for decays like B→a1π.

• Exception exists for B→ρ+ρ−: Use K*0ρ+ to constrain penguin contribution in ρ+ρ− and measure α with better precision than SU(2).


Isospin analysis• Consider the simplest case: B→ππ / ρρ decays.

• There are SU(2) violating corrections to consider, for example electroweak penguins, but these are much smaller than current experimental accuracy and can be incorporated into the Isospin analysis.

δα

δα = αeff-α

0

0 0 0

0

( ) . .( ) . .( ) . .

h h

B h h C CB h h C CB h h C C

S + −

+ −

+ +

→ +

→ +

→ +

BBB

For ππ & ρρ require:

00 0

00 0

12

12

A A A

A A A

+− +

+− +

+ =

+ =

Measuring S in h0h0

provides an additional constraint on this angle.


Belle π0π0 0 taggedB

0 taggedB

B→ππ• Easy to isolate signal for π+π− and π+π0 as these modes are

relatively clean and have large B ~ O(5 ×10−6).

• Much harder to isolate π0π0: B ~ 1.5×10−6

– No tracks in the final state to provide vertex information.– Have to reconstruct B0→π0π0→ γγγγ, which has a large ΔE resolution.

• Possible to separate flavor tags tomeasure C00. This information completes the set of informationrequired for an Isospin analysis.

Belle π+π−

Belle π+π−

0 taggedB0 taggedB

0.65 0.07

0.38 0.06

S

Cπ π

π π

+ −

+ −

= − ±

= − ±


B→ππ• Inputs from:

How do I read plots like this?

• 1-CL = 1: central value reported from measurements, before considering uncertainties.

• 1-CL = 0: Region excluded by experiment.

• If we think in terms of Gaussian errors, then 1-CL = 0.317, 0.046, 0.003 correspond to regions allowed at 1σ, 2σ and 3σ.

Gronau-London Isospin analysis0

0

0 0 0

BBB

π π

π π

π π

+ −

+ +

→

→

→


B→ππ

How do I read plots like this?

• At 68.3% CL = 1σ for Gaussian errors we have the following allowed regions for α:

7.582.5 103.1118.0 152.4

166.7

α

α

α

α

°

°

°

°

<

< <

< <

>

Gronau-London Isospin analysis


B→ππ• If we have measured CP violation in B→π+π−, does this tell us

something about α?

• Yes!• CP violation measured as a non-

zero value of S is related to α via:

Cππ ≠ 0 gives a scale factor.

Sππ ≠ 0 means there is CP violation in this decay and sin(2αeff) ≠0.

If α=0, then the unitaritytriangle would be flat, so if S≠0 we must have α≠0.

Can use constraints on P from Bs→K+K− to remove the solutions near α=0° and 180°.

Excluded usingAdditionalinformation.


B→ρρ• This is a decay of a B meson to two vector mesons.• Requires a (simplified) angular analysis (will come back to this in Lecture 2).• Inputs from:

• fL ~ 1 for B→ρρ decays: this helps simplify extracting α.• Can measure S00 as well as C00 to help resolve ambiguities.• Finite width of the ρ is ignored in the α determination (see Falk et al.)

• We define the fraction of longitudinally polarised events as:

0

0

0 0 0

BBB

ρ ρ

ρ ρ

ρ ρ

+ −

+ +

→

→

→


B→ρρ• Obtain a more stringent constraint on α than from B→ππ decays.

BaBar ρ0ρ0 paper

• Not including S00 and C00.• Include C00, but not S00.• Using all constraints.

Some features of this result:

• Two of the solutions overlap near 90°and 180°.

• Using S00 and C00 we see that the solution at 80° is very slightly preferred over the other solutions.

• There are two regions for α that are excluded:

45130

α

α

≠

≠


Using SU(3)• Can relate the penguin contribution in K*+ρ0 to that in ρ+ρ−:

0.9 0.6F = ±

• If we assume that |δTP| < 90°:

• Relaxing this assumption:

• Most precise determination of α!

|δTP| > 90°|δTP| < 90°

BaBar ρ+ρ− paper


B→ρπ (π+π−π0 Dalitz Plot)• Analyse a transformed Dalitz Plot to extract parameters related to α.• Use the Snyder-Quinn method.

• Fit the time-dependence of the amplitudes in the Dalitz plot:

• 26 parameters: Bi-linear form factor coefficients: U’s and I’s.

ρ+ π−

ρ 0π 0

ρ−π+

(m0=mπ+π-)

(θ0=

π+ π-he

licity

)


B→ρπ (π+π−π0 Dalitz Plot)• The amplitudes are written in terms of Us and Is:

• Which are related to CP conserving and CP violating observables:

CP conservingobservables

CP violatingobservables

Some features of this result:

• No region is excluded at 3σ significance.

• A high statistics measurement will help resolve ambiguities in the measured value of α.

• Results from the Dalitz analysis, and the pentagon analysis (solid) are more stringent than using the Dalitz analysis alone.

Belle ρ+π− paper


CP violation: α• No single mode dominates our knowledge of α.

– Three comparable inputs from ππ, ρρ, ρπ using SU(2).– SU(3) can be used to provide a more stringent constraint for α from

ρ+ρ−.• Many modes are required

to try and measure αprecisely. Any deviation in measured values of could indicate new physics.

0 0 0

0 0 0

0

1

1

, ,, ,

...

BBBB aB a

π π π π π π

ρ ρ ρ ρ ρ ρ

π π ππρ

+ − +

+ − +

+ −

→

→

→→→

Show

n he

re

Not shown: Need more data than currently available, and use SU(3) to extract α from final states with axial-vector mesons. These are related to hh modes above.

6.2 7.0(2) 5.3 (3) 6.497.5 89.8SU SUα α+ +

− −= =


(*) (*)

0

0 (*)

0 (*)

0

interfering with b c b uB D KBB DB D

charml s

D K

es

π

ρ

π− +

→

→+

→ →

→

→

Extract γ using B→D(*)K(*) final states using:• GLW: Use CP eigen-states of D0.• ADS: Interference between doubly suppressed decays.• GGSZ: Use the Dalitz structure of D→Ksh+h− decays.

Measurements using neutral D mesons ignore D mixing.


γ: GLW Method• GLW Method: Study and• X+ is a strangeness one meson e.g. a K+ or K*+.• is a CP eigenstate (use these to extract γ):

• The precision on γ is strongly dependent on the value of rB.– rB~0.1 as this is a ratio of Cabibbo suppressed to Cabibbo allowed

decays and also includes a color suppression factor for B+→D(*)K(*) b→udecays.

• Measurement has an 8-fold ambiguity on γ.

Gronau, London, Wyler, PLB253 p483 (1991).

0CPB D X+ +→ ( )0 0. . B D X C C D K π+ + + −→ + →

0CPD

01

0 0 0 0 01

,

, ,CP

CP S S S

D K K

D K K K

π π

π ω φ

+ − − +=+

=−

=

=0 0

20 0

( ) ( )2 1 2 cos cos( ) ( )

CP CPCP B B B

B D K B D KR r rB D K B D K

γ δ− − + +

± ±± − − + +

Γ → + Γ →= = + ±

Γ → + Γ →0 0

0 0

( ) ( ) 2 sin sin( ) ( )

CP CP B BCP

CP

B D K B D K rAB D K B D K R

δγ− − + +± ±

± − − + +±

Γ → − Γ →= = ±

Γ → + Γ →

• 4 observables• 3 unknowns:

rB, γ and δ

cos cos0.23 0.97sin sin 0.23 0.23

cs c

cd c

VV

θθ

∝ = =∝ = =

Cabbibo allowed

Cabbibo suppressed


γ: GLW Method• Insufficient data to constrain γ:

• x± is related to RCP± and ACP±.

BaBar GLW paper

149±16

90±13

106±14

129±15

• We can perform similar measurements using D*CPK:

• Again: insufficient statistics to perform a precision measurement of γ.


γ: GLW Method21 2 cos cosCP B B BR r r γ δ± = + ±2 sin sinB B

CPCP

rAR

γ δ±

±

= ±

• All measured ACP and RCP values are compatible with 0 and 1, respectively.


γ: ADS Method• ADS Method: Study• Reconstruct doubly suppressed decays with common final states

and extract γ through interference between these amplitudes:

• γ extracted using ratios of rates:

,0 *0 *B D K± ±→

Attwood, Dunietz, Soni, PRL 78 3257 (1997)

Vcb

VusVub

Vcs

(*)0 (*)B D K− −→ (*)0 (*)B D K− −→CKM and Color SuppressedCKM Favoured

(*) (*)2 2 (*) (*)2 cos cosB D B DR r r r r γ δ= + +(*)0(*)

(*)0

0

0

( )( )

( )( )

B

D

A B D KrA B D K

A D KrA D K

ππ

− −

− −

+ −

− +

→=

→

→=

→

• δ(*) = δ(*)B + δD

• δ(*) is the sum of strong phase differences between the two B and D decay amplitudes.

• rD and rB are measured in B and charm factories.

• δD is measured by CLEO-c

u

d(*)0D K π+ −→CKM FavouredD(*)0 K+

π−

W−

c s

u u

Vcs

Vud

(*)0D K π+ −→Doubly CKM Suppressed D(*)0 π−

K+

W+

c d

u u

s

u

Vus

Vcd


γ: ADS Method(*) (*)2 2 (*) (*)2 cos cosB D B DR r r r r γ δ= + +

• Insufficient precision to extract γusing the ADS method alone.

• Measurement of RADS can be used to constrain rB.

Help when extracting γ using other methods.

• Full statistics from the B factories will not improve the situation significantly.


γ: GGSZ Method• GGSZ (“Dalitz”) Method: Study D(*)0K(*) using the D(*)0→Ksh+h− Dalitz

structure to constrain γ. (h = π, K)– Self tagging: use charge for B± decays or K(*) flavour for B0 mesons.

where

– Need a detailed model of the amplitudes in the D meson Dalitz plot.

Giri, Grossman, Soffer, Zupan, PRD 68, 054018 (2003)

( )0 2 2 2 2( , ) ,( ( )( ) ) BS D

iBf mA B K h h mK em f m r δ γ±

+±+

−−

− +±→ ∝ +

0SK h

m m ±± =

• Use a control sample (CLEO-c data or D*+→D0π+) to measure the Dalitz plot.

π+π− K+K−

Control sample plots from BaBar GGSZ paper

* 0D D π+ −→

0 0SD K h h+ −→


γ: GGSZ Method

Belle GGSZ paper

• Note: axes swapped between Figures (a) and (b).

• Differences between the two plots contain information on γ.

• Method has a 2-fold ambiguity on γ.

B DK+ +→ B DK− −→

( )( )

1213 stat syst model

2324 stat syst model

76 4 9

76 5 5

Belle

BaBar

γ

γ

+−

+−

= ± ±

= ± ±

• rB ~0.16 (Belle), and ~0.09 (BaBar)

• The Belle measurement has a larger value for rB, hence a smaller uncertainty on γ.

BaBar GGSZ paper


CP violation: γ• As with α, no single channel dominates the determination of γ.

– Several methods available. Best results come from the GGSZ Dalitz method.– LHCb will produce more precise analyses of these decay modes, and will also be

able to use U-spin related rare charmless decays to try and measure γ more precisely.

• The B factories have started to measure γ! • With β measured to ~1°, and α measured to ~7°, we can use γ measurements to over-constrain the Unitarity triangle and test the integrity of the CKM mechanism.

• The CKM mechanism works at this level:

• New experiments are needed to test the CKM to a higher accuracy: LHCb, SuperB, and SuperKEKB.

( )180 10 21α β γ+ + − = ±


Next Lecture• Direct CP Violation.

• CP violation: Searching for new physics.

• Summary of CP violation signals found.

• Side measurements.

• B→VV decays.


Experimental References• Experiments Averages

• β

• α

• γ

ππ ρρ

ρπ

b ccs→

GGSZ ADS

GLW

Results from the B-factories - Particle Physicspprc.qmul.ac.uk/~bevan/helmholtz/lecture1.pdf ·...

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