cp violation studies in b decays - max planck society · 2003. 5. 23. · the road map for...
Post on 24-Feb-2021
1 Views
Preview:
TRANSCRIPT
CP Violation Studies in B Decays
Vivek SharmaUniversity of California San Diego
vsharma@ucsd.edu
Ringberg Phenomenology Workshop on Heavy Flavors : Rottach-Egern, Germany
2003
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…
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
+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 »
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
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
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!
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
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
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
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
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%?
“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
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
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?
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
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
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
Warning : Prospects for Ambulance chasing ahead !
Theorist !
Putting it all together
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
Average of Measurements of “sin2β” From Belle & BaBar
Golden mode 7% measurement
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
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− − <
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
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
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≤ ≤
Belle Asymmetry Fits for C & S : B 0 → π+π−
aaaaa
Belle : Confidence Region
Constraints on φ2 : Βelle
Constraints on φ2 : Βelle (Sagawa, KEK03)
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+
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
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
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
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
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
top related