MatterAntimatter asymmetry in the Bmeson system ...
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MatterAntimatter asymmetry in the Bmeson 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 = A1ei + A2ei
(0 and 0 ) A2 A2
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
Nonzero 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
Nonzero 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
Nonzero 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 (~106)
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 uptype and downtype 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) => CabibboKobayashiMaskawa (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 12. The rescaled Unitarity Triangle, all sides divided by .
The rescaled Unitarity Triangle (Fig. 12) 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
CKMmatrix 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 12. The rescaled Unitarity Triangle, all sides divided by .
The rescaled Unitarity Triangle (Fig. 12) 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
CKMmatrix 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 GronauLondon (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 = A0
Measure all three decay modes (+c.c) => If too small => GrossmanQuinn 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 61. Note that because of Bose statistics the
twopion state produced in decay has no contribution. Thus the three twopion 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. 61.
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 timedependent decay rates for and
!""
698
8418A3
A(B "")~
A(B "")A(B "+"
)
~
A(B "") = A(B
+ "
+")
~
1
2
A(B "+"
)
1
2
Figure 61. 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
timedependent Dalitz analysis = ( 113 +2717 6 )o => better than
B VectorVector 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 +169 )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
hepex/0408127

CKM angle from bs gluon bsg modes
penguin loop: Vtb & Vts => no phase
...but Vub from bu treemay be nonnegligible
KS: no uquark 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)]
" modeldependent 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 + colorsupressed)
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 nonSM 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 70x106 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)]
" modeldependent 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 + colorsupressed)
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
CPviolation 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)

PEPII Factory at SLAC
PEPII asymmetry e+e B factory at SLAC 3.1 GeV e+ / 9.0 GeV e => = 0.56 Peak luminosity: 9.2x1033 cm2 s1 Lint = 244 fb1

The BABAR detector
a
g b
Fred Blanc 5DPF'04
PEPII and the BABAR detector
e (9GeV
)
e+ (3.1G
eV)
Silicon Vertex Tracker5 doublesided layers
Instrumented Flux Return
1.5T Solenoid(superconducting)
ElectroMagnetic Calorimeter6580 CsI(Tl) crystals
DIRC (PID)
144 quartz bars
Drift Chamber40 layers
PEPII
BABAR Lpeak
= 9.2 x 1033cm2s1
Lint
= 221fb1 (onpeak)
(23fb1 offpeak)
These results based on
Lint
= 205fb1
=> 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 restofevent thrust axes energy distribution about B thrust axis
=> variables combined into Fisher discriminant (1 separation)
Time difference t
!"#$%&'&(%)#*+&&,,&.'/#0)
mES
!E
mES
resolution
23MeV/c2 !E resolution 2050MeV
Analysis techniques (I)! Experimental challenge: isolate tiny signal in very large
background (100s M events)
! Variables used to identify the signal:
" B kinematics (exploit the known total energy of the B candidate)B mass: Energy:
mES
(BABAR) = mbc
(Belle)
" secondary resonance mass(es), etc...
!"#$%&'&(%)#*+&&,,&.'/#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 [hepex/0502017]
~2/3 are tagged => used in CP fit
BF(B K+) = (69 2)x106 BF(B K0) = (68 3)x106
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
noncharmonium mode!
sin2b value from BABAR charmonium decays[BABARCONF04/38]
3.0s
[hepex/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 (106 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...)