Measurements of the CKM angle g in tree-dominated decays at LHCb
Stefania Ricciardi(STFC Rutherford Appleton Laboratory)
on behalf of the LHCb Collaboration
Hadron Collider Physics Symposium, Kyoto, November 12-16, 2012
Stefania Ricciardi 2
OutlineA very productive year for g at LHCb!
Results from time-integrated methods B+ D(KK,pp,Kp)K+ [PLB 712(2012),213] B+ D(Kppp)K+ [LHCB-CONF-2012-030] B+ D(KSpp,KSKK)K+ [PLB 718(2012) 43]
First g average from LHCb [LHCB-CONF-2012-032] First measurements with neutral B decays
B0 D(KK,Kp)K*0 [LHCB-CONF-2012-024]
First time-dependent measurements B0
sDS K± [LHCB-CONF-2012-029]
Other promising multibody decays first observation B0
sDS K ± p+p-
[LHCB-PAPER-2012-033]
All results based on 1 fb-1 (2011 data-set)
14/11/2012
Stefania Ricciardi 3
Precision on , g a path to NP discovery
CKM fits: overall a triumph for SM! However, a few tensions exist More precision needed to unravel subtle
NP effects
g at tree-level largely unaffected by NP, essentially no theoretical uncertainties
g still least-well measured angle of the UT
14/11/2012
66 ± 12 CKMFITTER72 ± 9 UTFIT
g from tree-level decays: theoretically very clean, but experimentally very challenging![Zupan, arXiv:1101.0134]
Post-ICHEP 2012 average using BaBar, Belle, CDF and first LHCB results
fD H
D0H
D0H
B
g from trees: time-integrated methods
14/11/2012 Stefania Ricciardi 4
Sensitivity to g through interference of b → c and b → u tree-level amplitudes Interference requires D0 and D0 decay to common final state fD
D0 GLW -CP eigenstates: KK, pp [Gronau-London-Wyler]PLB 253,483(1991), PLB 265,172 1991)
ADS- Quasi-flavour-specific: Kp, Kppp [Atwood-Dunietz-Soni] PRL 78,257(1997), PRD 63,036005 (2001)
GGSZ - Self-conjugate 3-body : KSpp, KSKK [Giri-Grossman-Soffer-Zupan] PRD 68,054018(2003)Bondar,PRD 70,072003 (2004)
Vcb
Favoured
B-
Suppressed
B-
Vub
)( BiBer
DiDer
D0
H-
H-
u u
u u
D0
H Expected rB
K 0.1 p 0.005Naïve assumptions , charged B decays only
Hadronic unknowns: rB, dB
rD , dD All from data No hadronic uncertaintiesMethod to extract them depends on D decay
Stefania Ricciardi 5
Experimental challenges
14/11/2012
Large data samplededicated triggerEfficient retention of fully hadronic B decays while limiting the overall output <5KHz
Precision @VERTEXLHCB Vertex detector and trackingExcellent invariant mass resolution Excellent vertex resolution
Mass resolution and displaced vertices for separation from low-mass background and rejection of combinatorial background
PID : 2 RICH detectors @LHCb K-p separation over 2—100GeV/c
Effectively separate B→DK from10x more abundant B→Dp
KS reconstruction(specific to GGSZ mode)About 2/3 of KS decay downstream of vertex detector
Stefania Ricciardi 6
GLW with B+→D(hh)K+
14/11/2012
coscos21
sinsin2
)()(
)()(2
BBB
BB
CPCP
CPCPCP rr
r
KDBKDB
KDBKDBA
ACP+ (KK)= (-14.8 ± 3.7 ± 1.0)% ACP+ (pp)= (-13.5 ± 6.6 ± 1.0)%
DCP H
D0H
D0H
B
B±DK± : clear asymmetryB± Dp± : no significant asymmetry
Evidence of non-zero ACP+ in B±DK± with 4.5 s significance (KK+pp)
coscos21)()(
)()(2 2
00 BBBCPCP
CP rrKDBKDB
KDBKDBR
B±DK±
B± Dp±
[PLB 712(2012),213]
Stefania Ricciardi 7
ADS with B+→D(Kp)K+
14/11/2012
Large asymmetry in BDK : AADS = (-52 ± 15 ± 2)% [4 ]s
Hint of asymmetry in BDp: AADS = (14.3 ± 6.2 ± 1.1)% [2.4s]
First observation of rare ADS OS B+ D(K-p+)K +
(Opposite Sign kaons) [10s]
(K-p+) H+
D0H
D0H
B+
CF DCS
DKADSDBDB
DD
DDDKADS
DBDBDBDD
DDDKADS
RrrKKKK
KKKKA
rrrrKKKK
KKKKR
/)sin(sin2)]([)]([
)]([)]([
)cos(cos2)]([)]([
)]([)]([ 22
Stefania Ricciardi 8
GLW and ADS with B+→D(Kp)K+
14/11/2012
GLW ADS
LHCb results on ADS and GLW observables more precise than B-factories and Tevatron results
Stefania Ricciardi 9
ADS with B+→D(K3p)K+
14/11/2012
First observation of rare ADS mode in BDK [5.1s] and BDp [>10s]
ADS
KDBK
KDB
ADS R
Rrr
KKDBKKDB
KKDBKKDBA
sin)sin(2
))3(())3((
))3(())3(( 33
3
CLEO-cPRD 0031105(2009)
Hint of asymmetry in BDK: AADS = (-42 ± 22 )%
BDp: AADS = (13 ± 10 )%
Same rB and dB, but different D decay parametersComplementary information to B D(Kp)K not just additional statistics
RADS (K) = (1.24 ± 0.27 )% RADS (p) = (0.369 ± 0.036 )%
[LHCB-CONF-2012-030]
Stefania Ricciardi 10
GGSZ: g from B+→D(KSh+h-)K+
14/11/2012
Exploits interference pattern in the D→KSh+h- Dalitz plots (different for B+ and B-)
Extraction of g requires information on the D→KShh decay amplitude variation over Dalitz plot: both magnitude and phase dD
1. model of decay amplitude or2. external measurements (model independent approach)
Rich resonance structure powerful method (dominates precision on g from B-factories)
DKSp+p-
690 signal events
DKSK+K-
110 signal events
B+ B-
B+ B-
m± = m(KSh ±)
m+ (G
eV2 /
c4 )m
+ (G
eV2 /
c4 )
[PLB 718(2012) 43]
Stefania Ricciardi 11
GGSZ: binned approach
14/11/2012
}{2)()( 22iiiiiii sycxKKKyxKBN
Use discrete measurements of dD in Dalitz plot bins from CLEO-c: ci,si [PRD82(2010)112006]
Ki = i |AD(m+ 2,m-
2)|2 dm+2dm-
2
from flavour specific D decaysiDic cos iDis sin
x±,y± extracted from a simultaneous fit to the signal yields in each Dalitz-plot bin
Chosen binning optimise g sensitivity
KSKK sample adds just 2 bins
DKSp+p- DKSK+K-
)sin(
)cos(
BB
BB
ry
rx
Stefania Ricciardi 12
GGSZ results
14/11/2012
Likelihood scan (statistical error only)
x+ = (-10.3 ± 4.4 ± 1.8 ± 1.4) x 10-2
y+ = (-0.9 ± 3.7 ± 0.8 ± 3.0) x 10-2 x- = (0.0 ± 4.3 ± 1.5 ± 0.6) x 10-2
y- = (2.7 ± 5.2 ± 0.8 ± 2.3) x 10-2
Uncertainties: 1. Statistical2. Experimental systematic3. CLEO-c inputs
Leading source of experimental systematic uncertainty: assumption of no CPV in BD pused to determine efficiency
Results on x,y have similar precision to those from BaBar and Belle
Lower rB implies larger uncertainty on g compared to B-factories from this mode
g = (44 +43 -38) ⁰
rB = 0.07 ± 0.04(0,0)rB
rB2g
[PLB 718(2012) 43]
Stefania Ricciardi 13
Combination of B+→DK+ results
14/11/2012
Precision achieved by combination of GLW, ADS and GGSZ measurements Frequentist method adopted using LHCb only results + constraints on D parameters from CLEO-c
< > = 71.1 g +16.1-15.2
()
<rB > = 0.092 ± 0.008
<dB> = 112.0 +12.6-15.5 ()
[43.9 – 98.8] @ 95%C.L.
[LHCB-CONF-2012-032]
Comparable precision to g averagesfrom BaBar and Belle
BaBar : < > = 69 g +17 -16
() Belle : < > = 68 g +15
-14
()
Stefania Ricciardi 14
Including B+Dp+ in the g average
14/11/2012
g, rBp and dB
p from combination of B+Dp+ GLW and ADS results only
B+→DK+ and B+→Dp+
[43.8 – 101.5] @ 95%C.L.
< > g [61.8-67.8] [77.9-92.4] @ 68%C.L.
Non-Gaussian behaviour Impact on best-fit value: 71 85 (<1s) 95% confidence level essentially unchanged
g
rB( )p
dB(p)
Stefania Ricciardi 15
GLW with B0 →D(KK)K*0
14/11/2012
Self-tagged mode time-integrated methods similar to B+ D(hh)K+
Interfering diagrams both colour suppressed: Larger rB (3x) larger interference Low yields
B0
Bs
B
Bs
D0D0 b u
sd
c
d
b c
sd
u
d K(*)0 K(*)0B0 B0
Vcb Vub
Hint of large asymmetry in B0DK0* : AdCP+ = (-47 ± 25 ± 2)%
No significant asymmetry in BsDK*0 : AsCP+ = (4 ± 17 ± 1)%
[LHCB-CONF-2012-024]
Stefania Ricciardi 16
Bs→Ds
K: time-dependent method
14/11/2012
Two final states: Ds
+K- and Ds-K+
Both accessible to Bs and Bs
CPV in decay w & w/out mixing sensitive to -2g bs
Time-dependent analysis and flavour tagging requiredUnique to LHCb
CP sensitivity in Stagged events only
CP sensitivity in Dthanks to DGs 0 untagged&tagged events
b→c b→u
)]sin()cos()2
sinh()2
[cosh()(
)]sin()cos()2
sinh()2
[cosh()(
tmStmCt
Dt
edt
td
tmStmCt
Dt
edt
td
sfss
fstfB
sfss
fstfB
ss
ss
2
2
1
1
KD
KD
s
s
r
rC
21
))2(cos(2
KD
sDsKf
sr
rD
rDsK ~0.4
relative magnitude of the CKM-suppressed to CKM-favoured amplitudes
21
))2(sin(2
KD
sDsKf
sr
rS
+ other2 equations for f
ff
ff
DD
SS
C
,
,
:sObservable 5
Stefania Ricciardi 17
Bs→Ds
K : analysis ingredients
14/11/2012
Tagging:OS only used in this first analysis, eD2=1.9%
Proper time acceptance:a,b,n,b from fit to BsDs p data
Precision tracking and PID: for background suppressionB mass fit: statistical separation of signal from remaining background
Signal yield = 1390±98
Bs DsKDs KK p / /ppp Kpp
<st>~50 fs
Proper time resolution:from MC corrected for data/MC differences
psttbat
tan
2.0)1()(1(
11)(
Stefania Ricciardi 18
Bs→Ds
K : time-dependent analysis results
14/11/2012
First measurement of the CP parameters in Bs→Ds K
Extraction of g sensitive to correlations: work in progress to determine systematic error covariance matrix Includes both tagged (40%) and untagged (60%) events
Main systematic uncertainties:fixed parameters (Gs, DGs, Dms, acceptance); tagging calibration
[LHCB-CONF-2012-029]
Stefania Ricciardi 19
More under way: Bs→Ds
K p+p-
14/11/2012
Bs→Ds
K p+p-
can also be used to measure -2g bs
with TD analysis (similar to Bs→Ds
K )Bs and B0
→DsKpp (first observation)
First step: measurement of the branching fractions
Selected Ds decays only: Ds K*K and DsfpExpect yield 40% of Bs→Ds
K
when other Ds modes added and selection tuned for CP analysis
ArXiv:1211.1541 NEW
Stefania Ricciardi 20
Conclusions First results on g from GLW/ADS/GGSZ measurements at LHCb
No single method dominates sensitivity
Combined measurement from B+ →DK+ decays (1/fb, 2011 data sample)
similar precision to Belle and Babar
First results from other sensitive modes
B0 →D(KK)K*0 first observation
B+→D (hh)K+p+p- first observation
Bs→Ds
K
Bs→Ds
K p+p- first observation
will provide additional measurements of g with 2011+2012 data sample
Additional g-sensitive B+,B0, Bs, Lb decays under study
Excellent prospects for big improvements on g precision from tree-dominated decays!
14/11/2012
< >g = 71.1 +16.1-15.2 ()
Stefania Ricciardi 2114/11/2012
Thank You
Kyoto, HCP2012 < >g = 71.1 +16.1
-15.2 ()from tree decays [B+ →DK+ only]
…and Thanks to Nature for these beautiful trees!
Stefania Ricciardi 22
GLW-like with B+→D K+p+p-
14/11/2012
First observation of B+DK+p+p-
with D CP eigenstates and first measurement of CP observables (GLW)
Larger data-samples needed to perform ADS analysis andconstrain g from these decays
[LHCB-CONF-2012-021]
Stefania Ricciardi 23
GGSZ
14/11/2012
Sum of B+ and B- yieldsDifference of B+ and B- yields