D0D0bar Mixing and CP Violation at BESIII

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D0D0bar Mixing and CP Violation at BESIII

• Kanglin He
• June 2006, Beijing

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OutLine

• D0D0bar Mixing
• CKM ?/?3 measurements
• CP violation
• Dalitz Plot analysis
• Time-Independent measurements using The Quantum
  Correlation Analysis (TQCA)
• Summary

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D0D0bar Mixing

• Flavor eigenstate mass eigenstate
• Expected to be very small in Standard Model
• Sensitive to New Physics
• x, y 0 in the SU(3) limit
• Experiments are beginning to probe interesting
  region of mixing parameter space (x, y 10-3)

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Mixing in the Standard Model and Beyond
Common hadronic final states
Standard Model
(real, on-shell)
(virtual, off-shell)
New Physics
Loops provide sensitivity new physics via x FSI
may enhance both x and y in SM
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Mixing Parameters
Mixing rate
Strong phase difference of CF decay and DCS
decay, important to measure
CP eigenstate lifetime difference
CP violation phase
CPV in mixing
CP violation in mixing/decay interference
If CP is conserved, ?0, ?0, yCPy
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Theoretical Predictions
x, y in range of 10-7-10-2
Standard Model
New Physics
From A. Petrov Charm Physics Theoretical
Review hep-ph/0311371
Theoretical predictions are very variable
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Mixing in High Energy Experimentflavor tag by
D?pD0fitting the time distribution
Wrong-sign semileptonic decays(K()ev), measure
Rmix
(E791, FOCUS, BELLE, BaBar, etc)
Decay to CP eigenstates(KK), measure yCP
(E791, FOCUS, BELLE, BaBar, CLEO, etc)
Wrong-sign Kp decays, measure x 2 and y
(CLEO, FOCUS, Belle, BaBar, etc)
Dalitz plot analysis
(CLEO, Belle, BaBar, etc)
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Experimental Situation
yCP measurements
PDG06
(Close to confirm)
No evidence of mixing has been reported in the
charm sector Hopefully to be found in near future
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D0D0bar Mixing at BESIII

• Charm events at threshold are very clean
• Ratio of signal to background is optimum
• Lots of systematic uncertainties cancellation
  while applying double tag method
• Mixing at threshold
• Bad news no time-dependent information
• Good news Quantum coherence, CP tags
• The coherence of two initial D allows simple
  methods to measure DDbar mixing, strong phase and
  CP violation
• Sophisticated methods combining semileptoinc, CP
  and hadronic modes provide additional sensitivity

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D0D0bar Mixing (Kp)

D0 decays as D0bar Key Point Separate Mixing
from DCSD
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Separate Mixing from DCSD
Two path to D0?D0bar decay final state 1.
D0?Kp- (DCSD) 2. D0?D0bar-gtKp- (MIX)
In the case of no mixing, (Kp- )(Kp - ) is
forbidden by Bose-Einstein statistics D0?Kp and
D0bar?Kp require L even, but for ?(3770) decay, L
1
mixing
D0
DCSD
D0
Kp-
CF
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Challenge to PID

• BESIII PID system
• dE/dx, resolution (6-7)
• Two layer barrel TOF, time resolution 100ps,
  83 solid angle coverage
• 1 layer endcap TOF, 110ps
• Selection efficiency is gt20 with a K/p double
  mis-identification rate at lt 10-4 level

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Mixing in double semi-leptonic decays (Kev
channel) at BESIII

• Two missing neutrinos in events
• Electron PID can suppress background
• The selection efficiency is similar as the Kp
  channel
• Background level is also negligible while running
  a small MC data sample (1 of 20fb-1). More
  detail study is needed.

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Rmix sensitivity at BESIII

• With 20fb-1(4-5 years running) ?(3770) data
  sample, we may get
• 20,000 right sign Kp events
• 20,000 right sign Kev events
• If more electronic channels and muonic channels
  are applied (need further MC studies), more right
  sign events will be obtained
• BESIII will probe

Rmix lt10-4
(At least)
in combined Kp and semileptonic channels
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CP eigenstate Tags

• CP
• KK- (3.89X10-3 )
• pp- (1.38X10-3 )
• Ks p0p0
• p0p0 (8.4X10-4)
• KSKS (7.1X10-4)
• ?0 p0 (3.2x10-3)

• CP
• KSp0(0.012)
• Ks? (3.9X10-3)
• KS ? (0.0094)
• KS?0 (0.0078)
• Ks? (0.012)
• KSf (4.7X10-3)

Dalitz Analysis
KL modes can also be applied partially
In 20fb-1 ?(3770) data, we can get gt 4.5x105 CP
tags and gt 3.6x105 CP- tags
With large sample of CP tags, we may improve the
measurements of strong phase, probe the direct
CP, and other mixing parameters
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CKM?/?3 measurement
Unitarity Triangle
Extract ?/?3 from B?DK decays, where D decays to

• D to CP eigenstates (GLW) improved constraints
  on charm mixing amplitude
• D to flavor eigenstates Kp (ADS) measurement of
  relative rate and strong phase
• D to Kspp(Dalitz plot analysis) studies of charm
  Dalitz plots tagged by flavor or CP eigenstates

Need help from charm sector
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Strong Phase (I)
CP eigenstate
Asymmetry
CP eigenstate
If CPV0 Mixing is small
Ratio of DSCD/CF
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Strong Phase (II)
In 20fb-1 ?(3770) data, we can get gt 10,000 CP
vs Kp double tags gt 10,000 CP- vs Kp double tags
The precision of cosd lt 0.06 level is expected at
BESIII, Be helpful to improve the precision of
?/?3 measurement
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CP Violation
1. Direct CP Violation (in decay)
2. Indirect CP Violation (in mixing)
3. CP violation in the interference between
decays with/without mixing
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CP violation in Charm decays

• In SM, no Direct CP asymmetry in CF and DCS
  modes. New physics
• Buccella et al. predict CP asymmetries in decay
  in the range of 0.002?0.14, may up to 10-3
  level
• Indirect CPV due to mixing is a possibility for
  D0 decays
• CP studies in charm transitions represent an
  almost 0-background search for New Physics (Bigi
  and Sanda)
• If New Physics intervenes through DCSD, then it
  would have the cleanest impact on D?KS,Lp (Bigi
  and Sanda)

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Direct CP Violation

• Need two paths (CKM?weak FSI?strong) from
  initial D to final state f

Singly Cabbibo Suppressed decays (SCSD) should be
the good choice to measure a sizeable asymmertry
Not too diff.
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Experimental search CP Violation in Charm decays

• A Cabbibo allowed reference states is needed to
  calibrate the known production/detection
  asymmetries

Define
Where ? is the ratio of N (searched) / N
(referenced)
D0 K-K, p-p, Ksp0, etc D K-Kp, Ksp, KsK,
etc Ds KsK, Ksp, etc
D0 K-p, D K-pp, Ds K-Kp
DCSD mode D?Kpp- D0?Kp-p-p
Probe New Physics
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CP asymmetry measurement
1 level reached for some decay modes, no
evidence of CP Violation
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CP Violation at BESIII

• Quantum Coherence
• Psi(3770) --? D(CP)D(CP), D(CP-)D(CP-)
• CP asymmetry in D and Ds decays
• Lots of modes, include DCSD
• CP asymmetry in D0 decays
• Have to pay price for tag
• Flavor tag with semileptonic mode at ?(3770)
• Flavor tag with D-?Kp-p- modes above DD
  threshold (4.03GeV / 4.17 GeV)
• Indirect CP asymmetry is too hard to BESIII

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Quantum Coherence
Suppose Both D0 decay to CP eigenstate f1 and f2
.
Thus if a final state such as (KK)(pp) observed,
we immediately have evidence of CP violation
In 20 fb-1 ?(3770) data, gt 1000 double CP and
CP- tags can be obtained. if 100CPV, it lead to
ACP10-3 level
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CP Violation in Charm decays (I)
In 20fb-1 data, BESIII can obtain the precision
of CP asymmetry in decays of charmed mesons
for the DCSD modes, BESIII can probe New
Physics at ACP (10-2 ? 10-4) level
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CP Violation in Charm decays (II)

• If 20fb-1 data taking at
• 4.03GeV, 9,000 D0 CP tags
• 4.17GeV, 5,000 D0 CP tags

Flavor tagged by D-?Kp-p-
Expected to be obtained
The precision of CP asymmetry will be
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CPV interference with Mixing
Two interesting case with semileptonic tag CP
tags
CPV in Mixing is small, ?0

• In 20fb-1 psi(3770) data,
• 10,000 SLCP() tags
• 10,000 SLCP(-) tags

?yCP and ?AG 1 level
Applying the inclusive semileptonic tag Can
improve the measurements
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Dalitz Plot Analysis

• Developed by CLEO, BaBar, Belle, etc
• Modes Kspp-, K-pp0, K-Kp, p-pp0, etc
• Time-dependent Mixing measurements
• DCSD branching ratio measurement (including
  phase)
• CP Violation studies
• Measurements of ?/?3 in B?D()K()
• Strong phase measurement

The powerful tool will be applied in BESIII

• What will we do next?
• Understanding the pp or Kp S-wave scattering
  (learn from BESII J/Psi analysis and other
  experiments, such as applying K-matrix formulism
  etc)
• Currently, we have a piece of FORTRAN code.
  Develop a OO version PWA package for charm decays
  in future

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CPV in Dalitz Analysis
Strong phase, do not change sign under CP
conjugation
CPV phase, change sign under CP conjugation
Phase difference hints that CP is violated
CP asymmetry across Dalitz plots

• Advantage of using Dalitz plot Analysis
• Measure CP asymmetries
• Direct access to the phase

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Dalitz Analysis at BESIIIInteresting topic (I)

• K-pp0, Kspp- vs CP tags, measure strong phase
  of K?, Kp
• K-pp0, Kspp- vs flavor tags, measure Br of DCSD
• Kspp-, p-pp0 vs CP tags, search for CP
  Violation (via same sign CP Tags)
• CP asymmetries across Dalitz Plots
• Kspp-, p-pp0 vs flavor tags
• D ? K-K p

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Dalitz Analysis at BESIIIInteresting topic (II)

• Simultaneously fit two Dalitz plots of K-pp0 vs
  K-pp0 and Kspp- vs Kspp- , search for Mixing
  in K?, Kp modes
• PWA analysis to D?VV vs CP Tags, search for CP
  violation and measure the strong phase
• more and more,

Lots of interesting modes can be applied, to
improve the measurements of Mixing parameters and
search for CP violations in charm decays
Key point Quantum Coherence
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Time-independent Quantum Coherence

• The Quantum Coherence Analysis (TQCA)
• ?(3770)?D0D0bar C-1
• ?(4040)/?(4160)?(m?)(np0)D0D0bar C(-1)m1
• measure RM, r, cosdKp, y and xsindKp (at ?(4040)
  or ?(4160))
• Suggested by D. Asner and Sun etc, part of CLEO-c
  physics program
• Will be applied at BES III

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TQCA at psi(3770)
RM (x2y2)/2 r Amp DCS/Amp CF
See PRD 73 034024 (2006) hep-ph/0507238 by
Asner and Sun
DT
ST
Measure RM, r, cosdKp and decay fractions
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TQCA (C1)
DT
ST
Have a chance to measure y and xsindKp
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Estimated uncertainties (stat.) of Mixing
parameters using TQCA
Scale to BESIII
From PRD 73 034024 (2006) by Asner and Sun
Have to identify C1 of ?D0D0bar and ?D0D0barp0
from DDbar and DDbar decays
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Summary

• Mixing parameters
• Rmix lt 10-4 in Kp and Kev channels
• ?cosdKp lt 0.05
• Probe y yCP 10-4, ?yCP 1, Probe x
  4.03/4.17 GeV
• Possible to probe CPV phase ? if x is sizeable
• CP Violation
• ?ACP10-3 in D decays,
• Probe new physics at ACPlt10-2 level in DCSD
• Probe ACPlt10-3 level with DT CP tags
• Dalitz Plot Analysis are expected to improve the
  measurements
• TQCA method can improve the measurements
• A lot of work need to do in future

Excited results can be produced at BESIII in
Mixing and CP Violation in Charm sector!!!
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Thank You !
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