d 0 - d 0 mixing at b a b ar
DESCRIPTION
D 0 - D 0 Mixing at B A B AR. Amir Rahimi The Ohio State University For B A B AR Collaboration. Outline. Introduction to mixing Motivation for using this mode Mixing formalism in a multibody decay Lifetime fit and mixing results. D 0 -D 0 Mixing with. Introduction. - PowerPoint PPT PresentationTRANSCRIPT
D0-D0 Mixing at BABAR
Amir RahimiThe Ohio State University
For BABAR Collaboration
A. Rahimi Charm2006 2
Outline
– Introduction to mixing – Motivation for using this mode – Mixing formalism in a multibody decay– Lifetime fit and mixing results
D0-D0 Mixing with 0 0D K
A. Rahimi Charm2006 3
Introduction
• The mass eigenstates and have different masses and lifetimes
• Signs of new physics:– Observation of CP violation
–
Time integrated mixing rate:
1D 2D
2 2
2M
x yR
x y
001,2
2 1 2 1
2 1 2 1
2 ,
D p D q D
m mx y
A. Rahimi Charm2006 4
Decay Mode
• Obtain a pure sample by reconstructing:
• In cc-bar events – Obtain the flavor of D0/D0bar from charge of slow
– Right-sign Cabibo-favored (CF) D0K-+0 used for normalization
– Wrong-sign D0K+-0 has contributions from doubly Cabibo-suppressed (DCS) decays and CF mixed decays
– Separate signal from background by fitting to m(K0) and
M = m(K0s) – m(K0)
* 0 0 0,sD D D K
0 0D K
A. Rahimi Charm2006 5
Branching Ratio
• In non-leptonic search for D mixing, DCS obscure the signs of mixing:– Consider
– Belle
– BABAR
– Compare to the standard decay D0K+-
0 0
0 0
( )
( )
D KR
D K
0.0130.009(0.229 0.015( ) ( ))%R stat syst
0
0
( )(0.362 0.029)%
( )
D K
D K
(0.214 0.008( ) 0.008( ))%R stat syst preliminary
hep-ex/0507071
0 0D K
A. Rahimi Charm2006 6
Resonance Contributions
• The resonance amplitudes are different for DCS and CF- there is more sensitivity to mixing– In D0 K-+0 the main
resonance is K- +
– In D0 K+-0 the main resonance is K*+ -
u
u
u
uu
u
s
d
+, +
-, -
s
c
c
d
ss
W +
W +
CF
DCS
A. Rahimi Charm2006 7
Event-level tagging
• To do a Dalitz analysis need to reduce the large peaking background in DCS– Real D0’s with uncorrelated
slow pions
• Use an event-level tag• Require a second tag in the
opposite event hemisphere– Use K+, ±
s, e±, and ±, in the other side of the event
– Provides consistency check on
tagK+
tag
0
+tag
D0
D0-tag
interaction point
beamspot
-tag
e-tag
K-
A. Rahimi Charm2006 8
Event-Level Tagging
• Using an event-level tag significantly reduces background – Use K+, ±
s, e±, and ±, in the other side of the event
– Never done before in this type of analysis
A. Rahimi Charm2006 9
Event-Level Tagging
• With this second tag, we can now look at the resonance contributions
A. Rahimi Charm2006 10
Resonance Contributions
• Event-level tagged• Prominent K* peak in DCS Mode
D0 K- + 0 D0 K+ - 0
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Resonance Contributions
• Event-level tagged• Prominent peak in CF Mode
D0 K- + 0 D0 K+ - 0
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Selection of Phase-Space Regions
• Based on inspection of the Dalitz plots, we exclude events in the regions:– 850 < m(K) < 950 MeV/c2
– 850 < m) < 950 MeV/c2
WS (3.8 ± 0.36) x 102 (3.79 ±0.36) x 102
RS (2.518 ±0.006) x 105 (2.512 ±0.006) x 105
WS (7.5 ± 0.5) x 102 (8.1 ±0.5) x 102
RS (3.648 ± 0.007) x 105 (3.646 ± 0.006) x 105
(a)
(b)
D0 Cand. D0 Cand.
(a) entire allowed phase-space region
(b) selected phase-space region for mixing analysis
Preliminary
A. Rahimi Charm2006 13
2 22( )
( ) ( )( ) 4
0 1
WSD D
RS
t x yR y R t t
t
Decay Time with Mixing
• At any particular point in phase space (Dalitz Plot):
• Integrating over an arbitrary region of phase space:
2 22( )
( ) ( )( ) 4
WSD D
RS
t x yR y R t t
t
is the suppression factor) cos sin
cos sin
y y x
x y x
2 2 2 2x y x y
cos sin
cos sin
y y x
x y x
A. Rahimi Charm2006 14
1
1
2 2 2 2
0 0 0 0
0 0 0 0
( cos sin )
( ) ( )
( ) ( ) / ( )
( ) ( ) / ( )
py y x
q
px y x y
q
for D K D K
for D K D K
Consider CP Violation
• We account for possible CP violation by fitting D0
and D0 separately and making the substitutions:
( and are the suppression factors)
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PDF Fit to Decay Times
• Data after a statistical background subtraction
Decay times in a signal region
A. Rahimi Charm2006 16
Preliminary Mixing Results
CP Conserved0.0180.014
0.0260.022
(0.023 0.004)%
(0.164 0.012)%
M
D
R
R
0.0060.0080.012 0.002y
• RM < 0.054% upper limit at 95% confidence level (determined using logL )
• Consistent with no mixing at 4.5% confidence level (determined using a frequentist method)
Contours determined using logL levels
hep-ex/0605046
A. Rahimi Charm2006 17
Preliminary Mixing Results
CP Violation Allowed
0.0060.007
0.0020.005
cos 0.012
sin 0.003
y
x
1.91.02.2p q
• Contours determined using logL levels
0.0220.007(0.010 )%MR
A. Rahimi Charm2006 18
Summary and Outlook
• Performed the first analysis of D0 K-+0
• Uncovered the DCS Dalitz plot• Time-dependent Dalitz plot analysis of this mode is
underway• Additional BABAR mixing results coming up soon:
– Semi-leptonic mixing using doubly-tag analysis– D0 K-
– D0 K-
• An observation of D mixing may be on the horizon
A. Rahimi Charm2006 19
Charm Mixing in The Standard Model
• Box Diagram SM Charm Mixing is expected to be very low
• Long distance SM predictions accommodate higher rates
d, s, bV*ci Vui
Vuj V*cj
D0 D0
c
u
W
d, s, b
W
c
u
SM Mixing: box diagram
SM Mixing: a long-range contribution
D0
D0
c
u
c
u
u
W+
d
d
u
u
d
d
u
W-
(Plot courtesy of A. Petrov, hep/ph 0311271)
: x=M/: y=/2
mix
ing
rate
= |a
mpl
itude
|2
SM Mixing Predictions
A. Rahimi Charm2006 20
Fit to the CF Events
• ML Fit and data projected in signal regions
0.145 < M < 0.146 GeV/c2 1.85 < m(Kpp0)< 1.88 GeV/c2
A. Rahimi Charm2006 21
Upper Limit on RM
• We use logL to set an upper limit– Behavior near zero
consistent with a frequentist method
– Straight forward to compare with other experiments