1. New Physics on Rare and Doubly Cabibbo-Suppressed D Decays
Chuan-Hung Chen
Department of Physics,
National Cheng-Kung U.,
Tainan, Taiwan
In collaboration with C-Q Geng & S-H Nam
Evidence for D0D0bar mixing & the implications
New physics on D0   K+
New physics on lifetime difference
in mixing
Summary

2. New Physics on Rare and DCS D
PPbar oscillations are important
In the SM, FCNC induced from loop effects, box diagrams
-- GIM mechanism to KKbar mixing, mK
-- Heavy top-quark mass enhancement
to BBbar mixing, mBq
-- Except DDbar mixing, K  Kbar, Bq Bqbar are observed
Due to these effects induced from loops, they are sensitive to
the new physics, e.g.
-- New CP violating phase on
-- New Physics on
New Physics on Rare and DCS D

3. Strong GIM cancellation, no heavy quark enhancement,
How is D0D0bar mixing ?
Strong GIM cancellation, no heavy quark enhancement,
short-distance effects are negligible; long-distance effects are dominant
CPV is negligible
With SU(3)F limit, it vanishes
Non-zero contributions are associated with SU(3) breaking, i.e. ( ms )n
Heavy-quark effective theory with OPE
Georgi (‘92),
Bigi & Uraltsev (’01),
Exclusive approach,
Donoghue, Golowich, Holstein, Trampetic (’86); Petrov (’97);
Falk, Grossman, Ligeti, Petrov (’02)
with large uncertainity

4. Evidence for D-Dbar mixing observed by
Babar, arXive: hep-ex/ , PRL98, (’07)
& Belle, arXive: hep-ex/ , PRL98, (’07)
With doubly Cabibbo-suppressed (DCS) decays D0 K+ 
Interference
mixing

5. No signal for CP violation

6. New Physics on Rare and DCS D
With singly Cabibbo-suppressed decays D0 K+ K
No signal for CP violation
New Physics on Rare and DCS D

7. New Physics on Rare and DCS D
New physics on doubly Cabibbo-Suppressed (DCS) D0   K+
In the SM
The definition of RD
With SU(3) limit,
New Physics on Rare and DCS D

8. New Physics on Rare and DCS D
Factorization assumption & SU(3) breaking
& Data for
Factorization assumption
Semileptonic decays P FP  K
[ Gao, PLB645, 59 (‘07) ]
Babar’s result in hep-ex/
Indication of new physics
New Physics on Rare and DCS D

9. New Physics on Rare and DCS D
Left-right model on DCS D decay
Left-right Model: SU(2)L  SU(2)R  U(1)X
-- Two charged gauge bosons WL and WR
-- Both will mix to be
W1  WL
-- Besides CKM matrix for left-handed quark, now
we have similar flavor mixing effects for right-handed quark
-- LR symmetric model, gL=gR, V(L)=V(R) , the contributions
will be much smaller than those in the SM
New Physics on Rare and DCS D

10. New Physics on Rare and DCS D
Non-manifest LR model,
Langacker & Sankar, PRD40,’89
London & Wyler, PLB232, ‘89
The relative size between SM and LR models
all the hadronic effects are the same,
if destructive interference happens
New Physics on Rare and DCS D

11. New Physics on Rare and DCS D
New physics (NP) on lifetime difference in DDbar mxing
Golowich, Pakvasa, Petrov proposed that the lifetime difference could
be sensitive to new physics. The idea is as follows:
New Physics on Rare and DCS D

12. effective interactions with Operator product expansion (OPE)
The leading term in the OPE is given

13. New Physics on Rare and DCS D
In the SM, only O1 and O2 have the contributions
SM result from short-distance is
-- proportional to x3s, vanished in SU(3)F limit
-- result of x3s displays the strong cancellation
from GIM mechanism
-- y(LO) ~ 108
New Physics on Rare and DCS D

14. New Physics on Rare and DCS D
Non-manifest Left-right model on lifetime difference in D0
V(L)cs =O(1)
V(R)us =O(1)
New Physics on Rare and DCS D

15. New Physics on Rare and DCS D
With leading OPE, the result of LR mixing effect
With the values of parameters as:
World average,
A. Schwartz in FPCP
New Physics on Rare and DCS D

16. New Physics on Rare and DCS D
Summary
Evidence of D-Dbar mixing implies
y  O( 102 )
If CP violation in D-Dbar mixing is non-zero,
it should be small
Improved measurement on RD is necessary for new physics
Left-right model has important effects on RD and
lifetime difference in DDbar mixing
New Physics on Rare and DCS D