cp violation studies in b decays - max planck society · 2003. 5. 23. · the road map for...
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CP Violation Studies in B Decays
Vivek SharmaUniversity of California San Diego
Ringberg Phenomenology Workshop on Heavy Flavors : Rottach-Egern, Germany
2003
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Special Thanks !
Gautier Hamel de MonchenaultGabriella Sciolla
Shahram RahatlouH. Sagawa
I have drawn heavily from their recent talk(s) at FPCP’02, APS’03, Moriond’03, CKM’03…
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The Road Map For Understanding CP Violation in B Decays
( )0,0 ( )0,1
( )η,ρ
Re
Im
α
βγ
uR tR
cR
Reminder : Promising ways to look for New Physics in B Decays
measure sin2β in several decays sensitive to different
short-distance physics
On the road to γA dream for now
(See Fleischer’s talk) (Discussed this yesterday)
UT
measure/constrain the other 2 angles
improve UT side measurements
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+e-e
B0 → J/ψ Ks
B0 → π+ π-
B0 → ΦK0
........etc.
B0 → J/ψ Ks
B0 → π+ π-
B0 → ΦK0
........etc.
CP Asymmetry Measurements at Asymmetric B Factory : in Picture
z
∆z∆t βγ c≈< >
Brec
Btag( )4sΥ
βγΥ(4S) = 0.55
z∆-π
0sK
+π
+µ-µ
Coherent BB pair
B0
B0
µ−
Κ−
Distinguish
B0 and B0
« Flavor Tag »
Distinguish
B0 and B0
« Flavor Tag »
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CP Asymmetry in B0 Decays : Notation
)sin()cos())(())(())(())(()( 00
00
mtSmtCftBNftBNftBNftBNtA
ff
CPCP
CPCPCP
∆+∆=→+→→−→
=
2
2
1
1f
f
f
Cλ
λ
−=
+2
2 Im
1f
f
f
Sλ
λ
−=
+
ff f
f
Aqλ ηp A
= ⋅
Scenario 1 :Only one amplitude contributes:
ACP(t) = - (Im λ) sin(∆mt)
Im λ=sin2β, sin2α, etc
Scenario 2 :More than one amplitude contributes
both sin and cos terms present- Sf: depends on Imλ
sensitive to UT angles- Cf: depends on |λ|, direct CP
(ηf)
β− i2e~
0B
0B
CPf
mixing
decay
0=t t
CPfA
CPfA
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Data Samples For Sin2β Studies: Babar
before tagging and vertexing cutsSamples of B decays to flavor-specific
final states
Samples of B decays to CP-eigenstateswith charmonium
Note: charge conjugate
decays are implied, unless
specified
angular analysis(not shown)mixed CP
energy-substituted mass
energy difference
Nov 1999- June 2002 data82 fb−1 on-peak – 88 million BB pairs
CP = +1
(not shown)
CP = −1
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220 lepton-tagged events
Textbook Example of CP Violation in the B System
Select events with a B candidate reconstructed into a CP-eigenstatecontaining a Charmonium meson and a K-short
Require the presence of a fast lepton (e or µ) in the rest of the event
Split the event sample according to the charge of the lepton (call B0-tag the sample with positively-charged leptons, and B0bar-tag the other sample)
Plot the proper time difference ∆tbetween the two decays (deduced from the distance between the two vertices along the boost axis)
Interpret the observed time-dependent asymmetry in terms of CP Violation amplitude sin2β
although ~90 million Y(4S) decays needed !
e.g.
CP Violation in the B system is not a small effect!
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CP Fits to the Proper time difference Spectrum (all flavourTags)
CP=+1CP=-1
sin(2β) = 0.741 ± 0.067stat ± 0.034syst
Unbinned maximum likelihood fit to ∆t distribution
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sin2φ1 = 0.719 ± 0.074(stat) ± 0.035(syst)sin2φ1 = 0.719 ± 0.074(stat) ± 0.035(syst)
Belle: CP Violation in b → ccs Transition
B0 → fCP
B0 → fCP
BB
BB
N NN N
−+ vs. ∆t
@ 78 fb−1
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Measurement of sin2β
This measurement is statistics limitedat least 1 inverse attobarn needed to reach the level
of systematic errors
systematics include possible subtle effects due to QM interference in the decays of the two B mesons
Some (excellent) assumptions are usually made in such analyses
main systematic errors: knowledge of mis-tagging probabilities and time resolution function
Note: 1 inverse attobarn ≈10 times present statistics
the two neutral B mass eigenstates have same lifetimeindirect CP violation in BB mixing can be neglectedCPT is an exact symmetry
direct CP violation in J/ψ KS-like decays is negligibleJ/ψ KS and J/ψ KL measure the same angle β
Experimental Focus now: start testing these assumptions(I will be very brief about this nothing unusual found)
Phys. Rev. Lett. 89 (2002) 201802
Babar
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Search for Direct CPV in B J/ψ K-
20.7 fb−1
~1300 candidates Phys. Rev. D-RC 65 (2001)
b
d
d
−W cc
s
0B ψ/J0K
0K0Bb
d−W
s
d
cc
g
u,c,t
ψ/J
Dominant diagram: color-suppressed tree Gluonic penguin diagam
In SM: expect very little direct CP violation
No fundamental wayto distinguish between direct CPV and indirect CPV in mixingfrom the measurement of | λCP |
Study CPV for isopsin-related charged mode
Experimentally
To be updated with more statistics
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Could (sin2β)J/ψKs and (sin2β)J/ψKL Differ ?
?d
cc
s 00 K,K ∗
ψ/Jb
d0B
Grossman, Kagan & LigetiPhys. Lett. B538 (2002) 327
b
d
d
−W cc
s
0B ψ/J
u,c,t0K 0Ksds
d
mixing…In the absence of
and…no possible interference between
How good is the relation
new preliminary result
indirect CPV in K0 mixing: negligible
only possible effect: wrong-flavor decays
no suchthing in SM!
From time-dependent rates, measure:
no sizable deviation from 0 (SM expectation)
860856
purity 96%?
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“Sin2β” in other modes: Β → φK
Pure penguin decay, therefore potentially a place to look for New Physics
φ helicity
KK mass
beam energy-substitutedmass
~50 events~175 events
Branching fractions and ACP
new results with 89 million BB pairs
Bb
d,u
−Wsss
gφ
Kd,u
b−W
s
ss
g
u,c,t
φ
Kd,u d,u
B
internal penguin
flavor-singlet penguin
would be enhanced in case of large FS rescattering
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Time-Dependent CP Asymmetry: B → φKS0
new results (supercede ICHEP2002)
(expect zero) 84 million BB pairs
In SM, expect
Goodness-of-fit: 23%
Correlation: 7%
Sample
Results
Assuming no direct CPV
Fit on control sample (charged decays)
C=0
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Time-Dependent CP Asymmetry B → η′KS0
If non-sss contribution negligible,expect
Results
compatible with isospin-symmetry
prelim. results with 89 million BB pairs
to be submitted to PRL
mostly?
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Time-Dependent CP Asymmetry B → J/ψ π0
b
d
d
−W cc
d
0B ψ/J0π
0Bb
d−W
d
d
cc
g
u,c,t
ψ/J
0π
penguin: competing weak phase? tree: color- and
Cabibbo-suppressed
If penguin contribution negligible
Sample
Results
prelim. result with 89 million BB pairssubmitted to PRL
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bd d
−Wccd −∗)(D
+∗)(D0B
B → D∗+D−
0Bt,c,ub
dd
−W
d
+∗)(D
cc
g−∗)(D
Cabibbo-suppressed tree b → d penguin
If penguins are negligible
Sample
time-integrated asymmetryResults
(Note: non-CP modes)
new result with 89 million BB pairs submitted to PRL
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B → D∗+D∗−
Sample(before flavor-tagging)
Vector-Vector decay (L=0,1,2)possible mix of CP = +1 and CP = −1
Transversity analysismostly CP-even
Results
If penguin contribution negligible
define CP-even parameter
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Warning : Prospects for Ambulance chasing ahead !
Theorist !
Putting it all together
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Summary of “sin2β” Results from BaBar
“reference” sin2β
pure penguin
mostly penguin?
color- & CKM-suppr’d treecompeting penguin
CKM-suppressed treesmall penguin pollution
All alternate BABAR measurements “agree” with the reference sin2β
within two standard deviations, or betterbut… consistently on the low side
“sin2β”C 0.7
41
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Average of Measurements of “sin2β” From Belle & BaBar
Golden mode 7% measurement
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B → ππ/Kπ & Quest for α
Simultaneous ππ/Kπ analysis
DIRC
bd d
−Wuud −− ρπ ,
0B ++ ρπ ,0B
t,c,ub
dd
−W
dcc
g
++ ρπ ,
−− ρπ ,
penguins cannot be neglected final results with 89 million BB pairs
Phys. Rev. Lett. 89 (2002) 281802
Note: signal-enriched plots after optimized cut on likelihood ratio, with
projection of fitted likelihood superimposed
0
10
20
30
5.2 5.225 5.25 5.275 5.3
mESGeV/c2
Eve
nts
per
2 M
eV/c
2
mESmES
(a)
0
5
10
15
20
-0.1 0 0.1
∆E GeV
Eve
nts
per
10 M
eV
∆E∆E
(b)
0
50
100
150
5.2 5.225 5.25 5.275 5.3
mESGeV/c2
Eve
nts
per
2 M
eV/c
2
mESmES
(c)
0
20
40
60
80
-0.1 0 0.1
∆E GeV
Eve
nts
per
10 M
eV
∆E∆E
(d)
continuum continuum
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CP Asymmetry in Β0 π+π−
Significant contribution from both diagrams: – P/T ~ 1/3 from Br(B Kπ)/Br(B ππ)
– Sππ sin2αeff related to angle α through isospin analysis– Cππ direct CP violation
)sin()cos())(())(())(())(()( 00
00
mtSmtCftBNftBNftBNftBNtACPCP
CPCPCP ∆+∆=
→+→→−→
= ππππ
b uu
dW
ubVb d
u
u
W
T = Tree P = Penguin
gtbV
*tdV
eff: α α 51 @ 90% C.L.Grossman Quinn− − <
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Babar: Time-Dependent CP Asymmetry: B → π+ π−
BABARNo CP asymmetry seen in B π+π−04.025.030.0
05.034.002.0±±−=
±±=
ππ
ππ
CS
(a)B0 tags
(b)B0 tags
Eve
nts
/ 1 p
s
∆t (ps)
0.5
-0.5
(c)A
ππ /
2 p
s
0
20
0
20
-5 -2.5 0 2.5 5
Nππ=157 ± 20
)sin()cos())(())(())(())(()( 00
00
mtSmtCftBNftBNftBNftBNtACPCP
CPCPCP ∆+∆=
→+→→−→
= ππππ
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Belle: B 0 → π+π−Reconstruction
Mass
Energy differencefrom expected value
(0 GeV if signal)
760 B 0 → π+π− candidates in signal region
Number of expected signal is 2324163+−
B→Kπ
B→ππB→ππ+Kπ
Higuchi @ JPS’03
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K. Abe et al. [Belle Collaboration], submitted to Phys. Rev. D, arXiv:hep-ex/0301032.
Belle: CP Asymmetry in B 0 → π+π− Decays
0.080.071.23 0.41
0.77 0.27 0.08C
+−=− ±
=− = + ± ±
S
A
When fixed S = 0 and A = 0,the probability to observesuch large CP violation
is less than 0.1%.
0B π π+ −→
0B π π+ −→
@ 78 fb−1
278 152 @ 95% C.L.φ≤ ≤
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Belle Asymmetry Fits for C & S : B 0 → π+π−
aaaaa
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Belle : Confidence Region
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Constraints on φ2 : Βelle
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Constraints on φ2 : Βelle (Sagawa, KEK03)
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BaBar: B0 ρ±π∓ and B0 ρ±Κ∓
• Related to the angle α • Compared to B ππ:
– Higer BF: B(B ρπ) ~ 4 x B(B ππ)– “Smaller penguins expected”
• … but challenging analysis – Not a CP eigenstate – 4 configurations: B0 ρ±π∓, B0 ρ±π∓
– 3π final state killer combinatorial backgrounds• Analysis strategy
– Pseudo two-body analysis• avoid interference regions of Dalitz plot
– Continuum background suppressed by NN– Simultaneous fit for ρ+π− and ρ+Κ−
α
b uud
W
d d
ρ−,π−
π+,ρ+
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B0 ρ±π∓ and B0 ρ±Κ∓
Combined Maximum Likelihood fit measures:
– BF(B0 ρπ)= (22.6±1.8±2.2) 10-6
– BF(B0 ρΚ)= (7.3±1.3±1.3) 10-6
– and 6 other parameters related to CP: ρπρπρπρπρρπ SCSCAA KCPCP ∆∆ ,, ,, ,
Indication for small penguins
N(ρπ) = 428 ± 34 N(ρΚ) = 120 ± 20
BaBar Preliminary
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Time-(in)dependent CP Asymmetry : B0 ρ±π∓ (Κ∓)
• Time integrated direct CP:
• Time dependent CP:
• Asymmetry between rates:
08.017.028.0 ±±=KCPAρ
03.008.018.0 ±±−=ρπCPA
04.018.036.0 ±±=ρπC
03.024.019.0 ±±=ρπS
03.00.250.15 ±±=∆ ρπS
04.00.28 0.180.19- ±=∆ +
ρπC
-- B backg.-- all backg.
First step towards a measurement of α in B ρπ decays.
Full Dalitz analysis with more data
BaBar Preliminary
BaBar Preliminary
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Prospects for γ & sin2β+γ Μeasurements
Difficult now because either CP asymmetry is very small or largedata sample or theoretical prejudice is required
Β± → D0CP K±
• Theoretically clean (Gronau & Wyler, Dunietz 1991 saga)• Interference between b u (cs) and b c (us)• Small accessible Branching Fractions ~ 10-7
– B0 → D(*) + π−, ρ−, a1• Theoretically clean measurement of 2β+γ• Interference between b u (cd) and b c (ud) • Tiny, tiny CP asymmetries (in progress)
– B0 →D(*)0 K(*)0 : observation of large rate by Belle– B → ππ, Kπ
• Interference between penguin and tree diagrams• Take ratios of Br’s to eliminate dependence on strong phases • Model dependent - relies on assumptions of factorization, SU(3)
– Leave it to theorists to dissect this
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2DD
:seigenstate CP are Dwhere00
CP
0CP
D±=±
2γ
D K )0 --A(B
-
=D K )0 +A(B+
D K )0 -A(B-
2 A(B D K )+0 ++
D K )0 +A(B+ 2 A(B D K )+0 - )(2 0 −− → KDBA CP
)(2 0 ++ → KDBA CP
• Isospin analysis
• Measurements:
Progress in B± D0CPK± γ
)%20.035.031.8()()(
0
0
±±=→→
= −−
−−
πDBBFKDBBFR
)%5.06.18.8()()(
)()(00
00
±±=→+→→+→
= ++−−
++−−
ππ CPCP
CPCPCP DBBFDBBF
KDBBFKDBBFR
06.017.006.0)()()()(
00
00
±±=→+→→−→
= ++−−
++−−
KDBBFKDBBFKDBBFKDBBFA
CPCP
CPCPCPBa
Bar
Prel
imin
ary
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Summary of CPV Studies
• CP Violation in B Decays established • Sin2β in “golden mode” is a ~7% measurement • Disagreement (>2σ) between Belle & Babar on CPV in B->pi pi• Some tantalizing results (B ΦΚ) !
– All CPV searches are statistics limited • Hope to get 500 fb-1 each by 2006