Matter-Antimatter asymmetry in the B-meson system

Fred BlancUniversity of Colorado

EPFL, Lausanne, April 11th, 2005

Outline

Introduction on CP violation The angles of the Unitarity Triangle

(B, , ) (BDK, Bs) (BJ/KS, KS , KS etc...)

An interesting case study: B0 KS and related decays in BABAR

bsg

The CP (a)symmetry

The CP operation is the combination of charge conjugation C operator (inversion of charge) parity P operator (x) (-x)

CP is conserved if P (AB+C) = P (CP[AB+C])

Example: CP violation in K0 decay

Neutral kaon system:produced K0 and K0 have different lifetimes

P(K0 +-,t) P(K0 +-,t) CPLEAR measured these rates (Phys. Lett. B458 (1999) 545)

Thomas Schietinger 3 December 2003Role of the b quark in particle physics 17

PS 1

95

Since then measured with high precision: (for instance CPLEAR) Angelopoulos et al., Phys. Lett. B 458, 545 (1999)

K0 !"#$#%

K0 !"#$#%

decays

decay time [&S]

Nb decays

Decay time [s]

How to generate CP violation

CP violation is seen when a process occurs through 2 (or more) paths 2 amplitudes have different weak AND strong phases

A = A1ei + A2ei A = A1e-i + A2ei

(0 and 0 ) |A|2 |A|2

weak phase strong phasedifference difference

Direct CP violation

11/14/03 Owen Long, UCSB 6

+!

+!

-!

-!" "

B!f

B!f

B!f

B!f

A

A

A A

Weak phase difference: !

Strong phase difference: "No strong phase difference

Non-zero strong phase difference

|A|=|A|

|A|#|A|!

Interfering amplitudes

11/14/03 Owen Long, UCSB 6

+!

+!

-!

-!" "

B!f

B!f

B!f

B!f

A

A

A A

Weak phase difference: !

Strong phase difference: "No strong phase difference

Non-zero strong phase difference

|A|=|A|

|A|#|A|!

Interfering amplitudes

11/14/03 Owen Long, UCSB 6

+!

+!

-!

-!" "

B!f

B!f

B!f

B!f

A

A

A A

Weak phase difference: !

Strong phase difference: "No strong phase difference

Non-zero strong phase difference

|A|=|A|

|A|#|A|!

Interfering amplitudes

=0

|A| = |A|

0

|A| |A|

Direct CP in B0K+- 1999: Direct CP violation first observed in K0 decays

=> very small effect (~10-6)

2004: Direct CP violation seen in B0 K+- ACP = -0.109 0.019 (5.7)

!"#$%&'(')&*$+,''--'./(0$1*

B0 K +-

! Observation of direct CP in B0K! " decays

NBB

NK!

ACP

signif.

BABAR 227M 160651 -0.1330.0300.009 4.2"Belle 275M 214053 -0.1010.0250.005 3.9"

B0K+! -B0K-! +B0K+! -

B0K-!+

Significantasymmetry insignal region

!"#$%&'(')&*$+,''--'./(0$1*

B0 K +-

! Observation of direct CP in B0K! " decays

NBB

NK!

ACP

signif.

BABAR 227M 160651 -0.1330.0300.009 4.2"Belle 275M 214053 -0.1010.0250.005 3.9"

B0K+! -B0K-! +B0K+! -

B0K-!+

Significantasymmetry insignal region

Phases in the standard model

Strong phase from final state interactions (FSI) doesnt change sign under CP

Weak phase from weak processes in quark sector qu W+ qd (+c.c) charged currents between all up-type and down-type quarks

(not only within each family)

3 x 3 = 9 possible currents(ud, us, ub, cd, cs, cb, td, ts,tb)

u c t

d s b

The CKM matrix

Amplitude of current qi qj : Vij (Vij) => Cabibbo-Kobayashi-Maskawa (CKM) matrix

Constraints (unitarity, unphysical phases) => 4 parameters 3 angles + 1 irreducible complex phase

Vud Vus Vub

Vcd Vcs Vcb

Vtd Vts Vtb( )

Sole source of CP violationin the standard model

Wolfenstein parametrisation

= 0.22 (=> 2 0.05, 3 0.01) A, and 1 Unitarity => VijV*kj = 0 and VijV*ik = 0

=> 6 triangles in the complex plane!

4 triangles are squashed (different powers of ) 2 triangles have all sides of similar size (3)

1.4 Violation in the Standard Model 21

!

" #

$

A%

(b) 7204A57921

VtdVtb&

|VcdVcb|&

VudVub&

|VcdVcb|&

VudVub&

VtdVtb&

VcdVcb&

$

#

"

0

0

(a)

Figure 1-2. The rescaled Unitarity Triangle, all sides divided by .

The rescaled Unitarity Triangle (Fig. 1-2) is derived from (1.82) by (a) choosing a phase convention

such that is real, and (b) dividing the lengths of all sides by ; (a) aligns one side

of the triangle with the real axis, and (b) makes the length of this side 1. The form of the triangle

is unchanged. Two vertices of the rescaled Unitarity Triangle are thus fixed at (0,0) and (1,0). The

coordinates of the remaining vertex are denoted by . It is customary these days to express the

CKM-matrix in terms of four Wolfenstein parameters with playing

the role of an expansion parameter and representing the -violating phase [27]:

(1.83)

is small, and for each element in , the expansion parameter is actually . Hence it is sufficient

to keep only the first few terms in this expansion. The relation between the parameters of (1.78)

and (1.83) is given by

(1.84)

This specifies the higher order terms in (1.83).

REPORT OF THE BABAR PHYSICS WORKSHOP

Vtd V*td

Vub V*ub

The Unitarity Triangle (UT)

1st and 3rd columns => V*ubVud+ V*cbVcd+ V*tbVtd=0 3 sides of order 3 => large angles phases from V*ub () and Vtd ()

1.4 Violation in the Standard Model 21

!

" #

$

A%

(b) 7204A57921

VtdVtb&

|VcdVcb|&

VudVub&

|VcdVcb|&

VudVub&

VtdVtb&

VcdVcb&

$

#

"

0

0

(a)

Figure 1-2. The rescaled Unitarity Triangle, all sides divided by .

The rescaled Unitarity Triangle (Fig. 1-2) is derived from (1.82) by (a) choosing a phase convention

such that is real, and (b) dividing the lengths of all sides by ; (a) aligns one side

of the triangle with the real axis, and (b) makes the length of this side 1. The form of the triangle

is unchanged. Two vertices of the rescaled Unitarity Triangle are thus fixed at (0,0) and (1,0). The

coordinates of the remaining vertex are denoted by . It is customary these days to express the

CKM-matrix in terms of four Wolfenstein parameters with playing

the role of an expansion parameter and representing the -violating phase [27]:

(1.83)

is small, and for each element in , the expansion parameter is actually . Hence it is sufficient

to keep only the first few terms in this expansion. The relation between the parameters of (1.78)

and (1.83) is given by

(1.84)

This specifies the higher order terms in (1.83).

REPORT OF THE BABAR PHYSICS WORKSHOP

B physics: strategy

Measure the UT sides and angles with as many independent measurements as possible=> constrain the UT... and hopefully see inconsistency

Review here current status of the measurements of the angles , and

Measuring the UT angles in B decays

Phases in B (Bd, Bu) physics bu (CKM suppressed) => phase mixing => phase no phase from dominant bc transitions

Methods for measuring the angles B0 mixing + bc => B0 mixing + bu => - - = B decays with bu transition =>

Current Experimental Status

Review measurements of the UT angles(in an unusual order...)

(2) (3) (1)

14

CKM angle

is measured by modes that involve mixing (=> B0) and bu (tree) transition B B B

B0 +- B0 +-

B0 mixing => Vtd => phase decay tree => Vub => phase => + = - => measure of

Unfortunately, +- can also occur through a loop transition=> no phase => measured asymmetry eff (penguin pollution)

Solution: Determine penguin contribution with an isospin analysis (B0,+ +- , +0 , 00 and c.c.)FNAL - March 11, 2005 J. Olsen 17

!"#$%&'()*!"'(*+*! %%,

W#W$

b

d b

d

!B

b

d

t

td

u

u

d%$&'$

!B

"#$%&'#$% tmACP (() !

%#&'#

-(."&/"&"(0"*+".1""(*2"#,'()*#(,*

(3(42"#,'()*."&5$*1'.6*,'//"&"(.*

$.&3()*#(,*1"#7*86#$"$

9%+42"#,'()*:8"()%'(; #582'.%,"

W

b

d

d

u

u

d

g

tcu ((

"'#$%&)

"#$%&

*++

' !

*

ff

f

CS

C

#)

+

!"#$%&'()&*#, +, -#./012

ACP = sin2 sin(mt)

B Isospin analysis Gronau-London (PRL 65 (1990), 3391)

decays relatedby SU(2) symmetry:

I=0 and I=2 states penguins I=0 only +0 is a pure I=2 state => no penguin => |A+0| = |A-0|

Measure all three decay modes (+c.c) => If too small => Grossman-Quinn limit

But 00 is large (larger than expected)=> poor limit ...but hopes for using GL method!

6.1 Theoretical Background: The Role of Penguins and -Extraction 333

6.1.2.1

In the absence of penguin contributions, the asymmetry in measures . However,

penguins can contribute to this decay. Indeed, as was argued above, it appears that such penguin

contributions are sizeable. Since the weak phase of the penguin diagram is different from that

of the tree diagram, penguin pollution can affect the clean extraction of from this process. An

isospin analysis can be used to eliminate the penguin pollution in this case [4].

The isospin decomposition of the amplitudes ,

and is shown in Table 6-1. Note that because of Bose statistics the

two-pion state produced in decay has no contribution. Thus the three two-pion decay

amplitudes depend only on two isospin amplitudes, hence there is one relationship,

(6.19)

between them. Thus they form a triangle, as drawn in Fig. 6-1.

The amplitudes for the -conjugate processes , and are

obtained from the amplitudes by simply changing the sign of the CKM phases; the strong phases

remain the same. These amplitudes also form a triangle:

(6.20)

The measurements of the total rates for and yield and ,

respectively. The measurement of the time-dependent decay rates for and

!""

698

8418A3

A(B "")~

A(B "")A(B "+"

)

~

A(B "") = A(B

+ "

+")

~

1

2

A(B "+"

)

1

2

Figure 6-1. Isospin analysis of decays.

REPORT OF THE BABAR PHYSICS WORKSHOP

= 2(eff-)

from B Large 00 => | eff - | < 35o

=> 67o < < 113o

Poor limit from modes alone

HFAG plotsMoriond 2005

http://www.slac.stanford.edu/xorg/hfag/

Comparison BABAR / Belle

Until 2004, BABAR and Belle numbers diagreed Since 2005, the agreement seems acceptable (2.2)

-1

-0.5

0

-1 -0.5 0

88122

227

85

152 275

Belle

BABAR

S!!

C !!

-1

-0.5

0

-1 -0.5 0

Belle

2.2!

BABAR

S""

C ""

B & B B

time-dependent Dalitz analysis = ( 113 +27-17 6 )o => better than

B Vector-Vector decay

=> longitudinal (CP even) & transverse (mixed CP) polarizations

Analysis shows ~100% longitudinally polarized => CP even B 00 very small => good limit on | eff - | < 11o

=> even better than

: summary HFAG (CKM Fit): = ( 101 +16-9 )o

CKM angle

Phase of Vub Measuring it at the Bd factories:

B DK: difficult... but Dalitz analysis => =(701010)o (average of Belle+BABAR)

B K+ - : ACP0 is direct evidence for 0 !...but large uncertainty on the strong phase :-(

Domain of BS decays => LHCb

CKM angle from charmonium

Charmonium modes B(cc)KS (e.g. J/ KS) decay dominated by one bc amplitude (no phase)

=> only phase from mixing (2)

theoretically clean(negligible uncertainty)

experimentally accessible

=> sin2 = 0.7260.037 (HFAG)

Wouter Verkerke, NIKHEF

Combined golden modes result for sin2b

sin2 = 0.722 0.040 (stat) 0.023 (sys)No evidence for additional CPV in decay |?|=0.9500.031(stat.)0.013

J/? KL (CP even) mode(cc) KS (CP odd) modes

(2002 measurement: sin(2) = 0.7410.0670.034)

he p- e x/ 0408127

hep-ex/0408127

CKM angle from bs gluon bsg modes

penguin loop: Vtb & Vts => no phase

...but Vub from bu treemay be non-negligible

KS: no u-quark in final state => clean (0.05th) KS, 0KS, KS, KSKSKS, etc...

may get contribution from tree diagram => sin2eff theoretical estimates for th for each mode (difficult)

a

g b

Fred Blanc 4DPF'04

SM expectations for h'KS and p0K

S

! DS = sin2bcharmonium

sin2beff

= 0

! B0 ! h'K

S

" DS bound from SU(3) analysis:using B0 decays to pairs of light

pseudoscalar mesons

|DS| < ~0.1 [Grosman et al., PRD68, 015004 (2003)] [Chiang et al., PRD68, 074012 (2003)]

" Specific model calculations: DS ~0.01[Beneke et al., NuclPhys B675, 333 (2003)]

! B0 ! p0K

S (b ! sdd is dominant)

" SU(3): DS ~0.2 [Gronau et al., PLB579, 331 (2004)]

" model-dependent QCD: DS ~0.1[Buras et al., Ciuchini et al, Charles et al.]

?

mixing

penguin (dominant)

Physics beyond the SM

may enter the loop

(sensitivity to high virtual mass)

tree (CKM + color-supressed)

phase g

from bs gluon: results

Estimated theoretical uncertainty for each mode

3.7 apart!(naive average of bsg modes)

BABAR+Belleaverages

: summary

Accurate measurement of sin2 from (cc)KS modes => sin2 = 0.7260.037 (5% uncertainty)

sin2 from bsg systematically low Question 1: is this effect significant?

=> need more measurements and better theoretical understanding

Question 2: what is the cause of this shift? => standard model? e.g. if tree contamination is poorly understood => new physics? e.g. heavy non-SM particle entering the penguin loop! ATTRACTIVE ALTERNATIVE!!!

=> Need more measurements...

SM describes wellmost measurements

amazing consistency betweenindependent measurements

...but hints of disagreement!=> need to understand better the SM predictions for bsg asymmetries=> need more accurate measurements

study case: BKS (BABAR analysis)

CKM: Summary

B K decays

K first seen by CLEO BF 70x10-6 Expect sin2 if pure

penguin decay

tree polution => sin2eff need to estimate tree contribution use BF of related B ()X decays

a

g b

Fred Blanc 4DPF'04

SM expectations for h'KS and p0K

S

! DS = sin2bcharmonium

sin2beff

= 0

! B0 ! h'K

S

" DS bound from SU(3) analysis:using B0 decays to pairs of light

pseudoscalar mesons

|DS| < ~0.1 [Grosman et al., PRD68, 015004 (2003)] [Chiang et al., PRD68, 074012 (2003)]

" Specific model calculations: DS ~0.01[Beneke et al., NuclPhys B675, 333 (2003)]

! B0 ! p0K

S (b ! sdd is dominant)

" SU(3): DS ~0.2 [Gronau et al., PLB579, 331 (2004)]

" model-dependent QCD: DS ~0.1[Buras et al., Ciuchini et al, Charles et al.]

?

mixing

penguin (dominant)

Physics beyond the SM

may enter the loop

(sensitivity to high virtual mass)

tree (CKM + color-supressed)

phase g

Measuring sin2 in B decays

B0 and B0 produced coherently Proper time difference between BKs and other B

(Btag) : t = tKs - ttag

Decay time distribution:

Standard model => S sin2 C 0 Corrections:

B mistag t resolution

3F. Blanc DPF/APS '03 Philadelphia, PA

CP-violation in B!h'K0

Only phase from interference between mixing and decay

If penguin amplitude dominates sin2b

If tree amplitude not negligible sin2beff

Proper time difference between Bh'K

and the other B (Btag

)

Dt = th'K

- ttag

Decay time distribution (F+ if Btag B0, F- if Btag B

0):

Standard model ! S sin2b & C 0

Correction for B0/B0 mistag

Dt detector resolution (Dt) convolute F(Dt) with (Dt)

PEP-II Factory at SLAC

PEP-II asymmetry e+e- B factory at SLAC 3.1 GeV e+ / 9.0 GeV e- => = 0.56 Peak luminosity: 9.2x1033 cm-2 s-1 Lint = 244 fb-1

The BABAR detector

a

g b

Fred Blanc 5DPF'04

PEP-II and the BABAR detector

e- (9GeV

)

e+ (3.1G

eV)

Silicon Vertex Tracker5 double-sided layers

Instrumented Flux Return

1.5T Solenoid(superconducting)

Electro-Magnetic Calorimeter6580 CsI(Tl) crystals

DIRC (PID)

144 quartz bars

Drift Chamber40 layers

PEP-II

BABAR Lpeak

= 9.2 x 1033cm-2s-1

Lint

= 221fb-1 (on-peak)

(23fb-1 off-peak)

These results based on

Lint

= 205fb-1

=> 227x106 BB pairs

Analysis technique: overview

Event selection: +- (44%) 0 (30%) with (39%) reject continuum background loose cuts => keep sidebands for background fitting

Extract S & C (and BF) from unbinned extended maximum likelihood fit

Discriminating variables

Kinematic variables E = EB - Ebeam mES = (E2beam - p2B) resonance masses

Event shape variables angle between B and rest-of-event thrust axes energy distribution about B thrust axis

=> variables combined into Fisher discriminant (1 separation)

Time difference t

!"#$%&'&(%)#*+&&,,&-.'/#0)

mES

!E

mES

resolution

2-3MeV/c2 !E resolution 20-50MeV

Analysis techniques (I)! Experimental challenge: isolate tiny signal in very large

background (100s M events)

! Variables used to identify the signal:

" B kinematics (exploit the known total energy of the B candidate)B mass: Energy:

mES

(BABAR) = mbc

(Belle)

" secondary resonance mass(es), etc...

!"#$%&'&(%)#*+&&,,&-.'/#0)

Analysis techniques (II)! Backgrounds:

" combinatoric e+e- qq (q=u,d,s,c) (dominant background) # event shape variables

" other B decays

! Signal extracted with ML fit on discriminating variables

t and flavor tagginga

g b

Fred Blanc 8DPF'04

Dt variable and flavor tagging

Determine Dt from Dz:Dz !"bgct

B ! 260 mm

(sDz ! 180 mm)

Partially reconstructed B decay (Btag

)

# B flavor (lepton charge, kaon strangeness, etc...)

# decay vertex$ ~2/3 of the events are tagged$ Effective tagging efficiency Q ! 28.8%

Reconstructed exclusive

B decay (Brec

)

1.

2.3.

Btag

Brec

Dz

e- e+%(4S)

Results: K Branching fractions ML fit => 804 40 K0S events [hep-ex/0502017]

~2/3 are tagged => used in CP fit

BF(B K+) = (69 2)x10-6 BF(B K0) = (68 3)x10-6

K+

K0S

5.25 5.26 5.27 5.28 5.29

Even

ts /

2 M

eV

0

100

200

300

400

5.25 5.26 5.27 5.28 5.29

Even

ts /

2 M

eV

0

100

200

300

400

-0.2 -0.1 0 0.1 0.2

Even

ts /

20 M

eV

0

200

400

-0.2 -0.1 0 0.1 0.2

Even

ts /

20 M

eV

0

200

400

(GeV) ESm5.25 5.26 5.27 5.28 5.290

50

100

150

(GeV) ESm5.25 5.26 5.27 5.28 5.290

50

100

150

E (GeV)!-0.2 -0.1 0 0.1 0.20

50

100

150

200

E (GeV)!-0.2 -0.1 0 0.1 0.20

50

100

150

200

(a) (b)

(c) (d)

Results: S & C

S(K0S) = 0.30 0.14 C(K0S) = -0.21 0.10 Systematics: 0.02 expected S 0.7!

~3 discrepancy

t (ps)!-10 -5 0 5 10

Asym

met

ry

-0.5

0

0.5(c)

t (ps)!-10 -5 0 5 10

Asym

met

ry

-0.5

0

0.5

0

50

100(b)

0

50

100

Even

ts /

( 1 p

s )

0

50

100(a)

Even

ts /

( 1 p

s )

0

50

100

a

g b

Fred Blanc 14DPF'04

B0 h'K

S results: S & C

PRELIMINARY

B0 tag

B0 tag

Asymmetry

S(h'KS) = +0.27 0.14

stat 0.03

syst

C(h'KS) = -0.21 0.10

stat 0.03

syst

! Systematics dominated by MC statistics

and signal modeling 0.02! Single most accurate measurement from

non-charmonium mode!

sin2b value from BABAR charmonium decays[BABAR-CONF-04/38]

3.0s

[hep-ex/0408090]

sin2 from charmonium

Interpretation

Difference between K0S and charmoniumSexp = S - sin2 = -0.300.12

Estimate of the tree contribution is necessary in the interpretation of the results

Flavor SU(3) is used to set bounds on S Sth < | Ks |

Ks function of branching fractions of related modes

Setting bound on S

Ks is function of flavor SU(3) related decay modes B , , , 0, 0, 00

[Grossman et al. , PRD68 (2003) 015014][Gronau et al. PLB 596 (2004) 107]

Need to measure BF for all these modes All modes with small BF (10-6 or smaller) Use ML fit technique to extract yields

bound most sensitive on these modes

Experimental issue: fit biases

Sources of fit biases fitter bias [tested with toy MC samples generated from PDFs] BB bkg [tested with fit on embedded BB events passing the selection] correlations between fit variables

[tested with samples containing fully simulated signal events]

small sample biasML fit is unbiased for large samplesFor small (clean) samples, we observe a bias towards negative yieldsCorrection for this bias as determined from toy MC studies

Limits on most modes(only B000 has been observed)

=> Sth < ~0.1[compare to Sexp 0.3]

Sexp>>0.1 => new physics! Need more accurate measurements...

Current bound on S

!"#$%&'(')&*$+,''--'./(0$1*

B decays to pairs of light isoscalar mesons

! !Sth

= S("'KS) - sin2# < |$

"' Ks|

! $"'Ks

function of the BF for flavor SU(3)

related decay modes B0" '" '," '" ,"" ," '%0," '%0,etc...[Grossman et.al., PRD68 (2003) 015014][Gronau et.al., PLB596 (2004) 107]

! Current limit: !Sth

> 0.1 => signature for new physics

! !Sth

will improve with better BF measurements

a

g b

Fred Blanc 15DPF'04

Comparison to SU(3) limits on DSh'Ks

! Correlated limits on S & C for B0 ! h'KS

based on SU(3)

[Gronau et al., PLB 596, 107 (2004)]

! Uses experimental results

on B decays to pairs of

light mesons

limits on S & C

! See talk by A. Lazarro(session VII, Tuesday)

SM

SU(3) bounds

old h 'KS result

(BABAR + Belle)

new h 'KS

preliminary result

[Gronau et al., PLB 596, 107 (2004)]

Summary / Conclusion

The B factories have obtainedan accurate measurement of sin2

sin2 also quite accurate (thanks to )

Discrepancy between sin2 from charmonium and bs penguin is probably the most intriguing result

Is it a sign for new physics?Need more measurements!

Exciting time for all (and for LHCb in particular...)