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Title: Peter Kri


1
Evidence for D0 mixing at Belle
  • Peter Križan
  • University of Ljubljana and J. Stefan Institute
  • (for the Belle Collaboration)

2
Belle _at_ KEK-B in Tsukuba
Tsukuba-san
Belle
KEKB
diameter 1 km
Peak luminosity 1.7 x 1034 cm-2s-1
3
Belle spectrometer at KEK-B
? and KL detection system (14/15 layers
RPCFe)
Aerogel Cherenkov Counter
(n1.015-1.030)
3.5 GeV e
Silicon Vertex Detector (4 layers DSSD)
Electromag. Cal.(CsI crystals, 16X0)
8 GeV e-
Central Drift Chamber (small cells, He/C2H6)
ToF counter
1.5T SC solenoid
Data sample gt750M BB-pairs, gt850M cc pairs
4
Contents
Motivation ?M. Sokoloffs talk Belle_at_KEK-B Se
arch for D0 mixing in D0?Kp- and semileptonic
decays D0?KK-, pp- apparent lifetime of a CP
eigenstate D0?KS0pp- time-dependent Dalitz plot
analysis CP violation searches in D
mixing Summary and prospects
5
D0 - D0 mixing
_
  • An arbitrary linear combination of the neutral
    D-meson flavor eigenstates

is governed by a time-dependent Schroedinger
equation
M and G are 2x2 Hermitian matrices.
The light D1 and heavy D2 mass eigenstates are
6
Time evolution in the B system
_
  • Time evolution is governed by the parameters x,
    y, G

A D0 at t0 evolves as
_
Decay time distribution of different final states
of D0, D0, and DCP sensitive to different
combinations of mixing parameters.
7
D0 - D0 mixing
_
Mixing in the neutral D system highly suppressed
due to GIM mechanism (msmd). ? A place to
search for new physics (in principle). Mixing in
SM completely dominated by long-range
contributions. New physics xgtgty, CPV ?
E. Golowich et al., arXiv0705.3650
x (SM)
x(NP)
y (SM)
A. Petrov, hep-ph/0311371
8
Experimental methods in D0 mixing searches
The method investigate D decays in the decay
sequence D? D0p, D0?specific final
states Used for tagging the initial flavour and
for background reduction
D0 or D0 at decay time
K- p
D ? D0 p
_
pcms(D) gt 2.5 GeV/c eliminates D meson
production from b ? c
9
Experimental methods
Performance of the apparatus -PID performance
-vertex resolution
e(K) 85 e(p?K) ? 10 for p lt 3.5 GeV/c
D0?
ltstgt/t(D0) 1/2
t(D0)/3
st/t(D0)
10
D0 mixing in D0?Kp and Ken decays
  • The method search for D mixing in the decay
    sequence D? D0p, D0?flavour specific final
    state.
  • Semileptonic decay
  • K- e n no mixing (RS, Right Sign)
  • K e- n mixing (WS, Wrong Sign)
  • measure WS rate
  • Hadronic decay
  • K- p no mixing
  • K p- mixing or doubly Cabbibo suppressed
    (DCSD)
  • measure WS time evolution

11
D0 mixing in D0?Kp decays
D0?Kp time evolution
for x,y ltlt 1
dN/dt a RD RD1/2 y t (x2 y2) t2/4
e-t DCS interference
mixing
  • x x cos d y sin d
  • y y cos d - x sin d
  • x DM/G y DG/2G
  • strong phase difference

12
D0 mixing in D0?Kp decays
PRL 96, 151801 (2006), 400fb-1
Signal extraction
3s Q interval
3s M interval
WS
Qm(psKp)-m(Kp)-m(p)
Mm(Kp)
Wrong sign combinations D0?K p-
13
D0 mixing in D0?Kp decays
Results
PRL 96, 151801 (2006), 400fb-1
Wrong sign time evolution
95 C.L. (x2, y) contour
(x2, y) (0,0) C.L. 3.9
RD (3.64 0.17 ) 10-3 x2 (0.18 0.210.23)
10-3 y (0.6 4.03.9) 10-3
BaBar result consistent ? previous talk
BaBar PRL 98, 211803 (2007), 384fb-1
14
D0 mixing in D0?Ken decays
PRD72, 071101 (2005), 253 fb-1
  • Wrong charge combination ? mixing (no DCS decays)
  • Again tag with D charge D? D0p, D0? K-en
  • Selection criteria
  • c.m.s. momentum of the Ke system gt 2 GeV (rejects
    bb, combinatorial background)
  • Inv. mass of e-e (e?p) gt 0.15GeV (rejects g
    conversions)
  • Cut on decay time (signal t2 e-t)
  • Neutrino reconstruction hermiticity,
    kinematic constraints.
  • Signal yield Dmm(psKen)-m(Ken)

NRS (229.45 0.69) 103
15
D0 mixing in D0?Ken decays
PRD72, 071101 (2005), 253 fb-1
RM x10-3
Decay time reduce bkg., increase
sensitivity ltt gt(bkg., RS) lt ltt gt(mix.
signal) 6 bins in 1 lt t lt 10
Result
allowed
RM (0.20 0.47 0.14) 10-3 RM lt 1.2 10-3
95 C.L.
Update this summer with 4x statistics
16
D0 mixing in KK-, pp-
PRL 98, 211803 (2007), 540fb-1
D0 ? KK- / pp-
CP even final state in the limit of no CPV
CPD1gt D1gt ? measure 1/G1
side band
S. Bergman et al., PLB486, 418 (2000)

AM, f CPV in mixing and interference
Signal D0 ? KK- / pp- from D
M, Q, st selection optimized in MC
KK- K-p pp-
Nsig 111x103 1.22x106 49x103
purity 98 99 92

17
D0 mixing in KK-, pp-
PRL 98, 211803 (2007), 540fb-1
Decay time distributions for KK, pp, Kp

Difference of lifetimes visually observable in
the ratio of the distributions ?
18
D0 mixing in KK-, pp-
PRL 98, 211803 (2007), 540fb-1
Fit
simultaneous binned likelihood fit to KK-
/K-p/pp- decay-t ? yCP
(M sideband)
R ideally each si Gaussian resol. term with
fraction fi
event-by-event st
each si ? 3 Gauss
(trec-tgen)/st described by 3 Gaussians ?
MC
parameters of R depend slightly on data taking
conditions
t 408.70.6 fs
19
D0 mixing in KK-, pp-
PRL 98, 211803 (2007), 540fb-1
  • Expected statistical precision in t(KK-/pp-)
    0.3
  • ?Cross-checks
  • MC yCP(out) - yCP(input) lt 0.04 for a large
    range of input values
  • yCP independent of resolution function
    parameterization R(t) single
    Gaussian ? Dt 3.9, but DyCP 0.01
  • Exchanging data side band with signal window
    background from tuned MC DyCP -0.04
  • Measure yCP with subsamples (run periods,
    KK-/pp-, separate free offset t0) ? all
    consistent
  • ?Systematic error conservative estimates equal
    t0 0.14, acceptance 0.12, selection variation
    0.11, signal band/sideband background
    differences 0.09, background distribution B(t)
    0.07, M window position 0.04 ? 0.25

20
D0 mixing in KK-, pp-
PRL 98, 211803 (2007), 540fb-1
Result
simultaneous binned likelihood fit to KK-
/K-p/pp- decay-t ?
negligible CPV, yCPy
yCP (1.31 0.32 0.25)
3.2 s from zero (4.1 s stat. only)
evidence for D0 mixing (regardless of
possible CPV)
21
D0 mixing in KS pp-
arXiv 0704.1000, 540 fb-1 submitted to PRL
time-dependent Dalitz plot analysis different
decays identified through Dalitz plot analysis
CF D0 ? K-p DCS D0 ? Kp- CP D0
? r0 KS
time-dependence
m2m2(KS p) Dalitz variables
lt f D0 gt
l1,2 m1,2 -iG1,2/2 f(x,y)
Rate terms with cos(xGt) exp(-Gt), sin(xGt)
exp(-Gt), exp(-(1-y)Gt) ? sensitive to x and y
(n.b. for Kp- x2, y)
22
D0 mixing in KS pp-
arXiv 0704.1000v2, 540 fb-1 submitted to PRL
t
Fit assume no CPV
fit M(m-2,m2,t) to data distribution ? x, y
Signal
M(KS pp- ) and Q M(KS pp-ps)- M(KS pp-)-
M(p) 3 s signal region in M, Q
Nsig (534.40.8)x103 P ? 95
Dalitz model
18 resonant BW terms non-resonant contribution
23
D0 mixing in KS pp-
arXiv 0704.1000v2, 540 fb-1
KX(1400)
Dalitz projection of fit
K(892)
r/w
K(892)-
Results (fit fractions, phases) in agreement with
(measurement of f3(g))
PRD73, 112009 (2006)
24
D0 mixing in KSpp-
arXiv 0704.1000v2, 540 fb-1 submitted to PRL
Decay-t projection of fit
x (0.80 0.29 0.090.07 0.100.14) y
(0.33 0.24 0.080.12 0.060.08)
stat. exp.syst. decay model syst.
?most sensitive meas. of x
comb. bkg.
Cleo, PRD72, 012001 (2005)
x 1.8 3.4 0.6 y -1.4 2.5 0.9
t 409.90.9 fs
tPDG410.11.5 fs
  • (x,y)(0,0) has C.L. 2.6 (2.2 s)
  • xgt0 2.4 s significance

25
D0 mixing results from KSpp- and KK-/pp-
PRL 98, 211803 (2007), 540fb-1
arXiv 0704.1000v2, 540 fb-1 submitted to PRL
  • KK- / pp- y0 has
  • C.L. 6x10-4
  • KS pp- (x,y)(0,0) has
  • C.L. 2.6

26
D0 mixing Belle Babar D0?Kp results combined
y
y
x2
x2
x2 (0.001 0.020) y (0.55 0.280.37)
27
D0 mixing all results combined
y
Assuming no CPV
x (0.87 0.300.34) y (0.66 0.210.20) d
0.33 0.260.29
x
(x,y)(0,0) excluded by gt5s
28
Search for CP violation
CPV in D0 system
Relevant CKM elements of the 2x2 submatrix
phase CPV in D0
very small, ? 10-3 parameterization
D0 ? Kp-,KK- / pp- ,KS pp- t evolution
depends also on CPV parameters - x, y at upper
limit of SM expectation ? search for CPV - at
current level of sensitivity positive signal
clear indication of NP
29
Search for CP violation
CPV in D0 ? Kp-
PRL96, 151801 (2006), 400 fb-1
CPV allowed fit separate D0 and D0
tags (x2,y,RD) ? (x2, y,RD)
CPV allowed
AD (23 47) 10-3 AM (670 1200) 10-3
direct CPV indirect CPV
PRL 98, 211803 (2007), 540fb-1
CPV in D0 ? KK- / pp-
AG (0.01 0.30 0.15)
indirect CPV
30
Search for CP violation - continued
CPV in D0 ? KS pp-
arXiv 0704.1000v2, 540 fb-1 submitted to PRL
  • 95 C.L. contours for (x, y)
  • CPV allowed dash-dotted statistical, dashed
    statistical and systematic
  • (No CPV assumed dotted and solid)

_
  • Dalitz plot fit separately for D0 and D0
  • Fit parameters consistent for both samples ? no
    direct CPV
  • Parameters q/p and farg(q/p) consistent with
    CP conservation

Fit assuming no direct CPV ? Parameters of CPV in
mixing and interf. in mixing and decay
q/p 0.95 0.220.20 f arg(q/p) (-21011)0
31
Prospects near future
B-factories near future 1 ab-1 Contours
for combined KSpp- and KK/pp- (assuming
present mean)
CLEO and BESIII new measurements of the
phase d ? needed to interpret the measurements
of x and y in terms of x and y in the Kp-
decays
32
Prospects
Super-B factory rough expectations at 5 ab-1
combination of results from Kp, KK/pp, KSpp s(x)
s(y) 0.10 ?mixing s(q/p)
0.09, s(f) 0.1 ?CPV
possible CPV - New Physics would be tested with
O(5) better sensitivity at 50 ab-1 (several
extensions of SM predict CPV O(1))
Y. Grossman et al., hep-ph/0609178
33
Summary
  • Belle and BaBar presented evidence for D0 mixing
  • Combined result of all measurements
  • y (0.66 0.21-0.20 ) ? clearly established
  • x (0.87 0.30-0.34 ) ? still marginal
  • Values of mixing parameters at the upper end
  • of SM expectations.
  • New measurements to further constrain y and
  • clearly establish x -
  • - and hope for more accurate predictions.
  • Search for CPV NP search
  • Super-B factory would allow for sensitive
    searches
  • in reasonable extensions of SM

34
Belle Upgrade for Super-B
6
35
Backup slides
36
D0 mixing all results combined
x (0.87 0.300.34) y (0.66 0.210.20) d
0.33 0.260.29
x
d
y
37
Search for CP violation D0 system
CPV in D0 very small, ? 10-3 ? full
parameterization
Af decay amplitude to a given final state d
phase difference between Af and Af f phase
difference between the ratio of decay amplitudes
and the mixing matrix
_
38
D0 - D0 Phenomenology
x and y in SM 2nd order perturb.
short distance
x O(10-5)
G. Burdman, I. Shipsey, Ann.Rev.Nucl.Sci. 53,
431 (2003)
DCS SU(3) breaking
absorptive part (real interm. states) ?
y dispersive part (off-shell interm. states) ? x
long distance
x, y O(10-2)
I.I. Bigi, N. Uraltsev, Nucl. Phys. B592, 92
(2001) A.F. Falk et al., PRD69, 114021 (2004)
39
D0 mixing in KSpp-
arXiv 0704.1000v2, 540 fb-1 submitted to PRL
x (0.80 0.29 0.090.07 0.100.14) y
(0.33 0.24 0.080.12 0.060.08)
stat. exp.syst. decay model syst.
  • Systematic error due to our choice of the D0
    decay model is evaluated
  • vary the masses and widths of the intermediate
    resonances by their known uncertainties
  • try fits with Blatt-Weisskopf form factors set to
    1 and with no q2 dependence in the Breit-Wigner
    widths.
  • perform a series of fits successively excluding
    intermediate resonances that give small
    contributions, and we also exclude the NR
    contribution.
  • account for uncertainty in modeling of the S-wave
    pp component by using K-matrix formalism
  • include an uncertainty due to the effect of
    around 10-20 bias in the amplitudes for the
    K(1410), K0 (1430) and K2(1430)
    intermediate states (observed in MC studies).
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