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Giampiero MancinelliUniversity of Cincinnati

CHARM 2007 – Cornell, USA

Experimental Prospects for Experimental Prospects for CP and T Violation CP and T Violation Studies in CharmStudies in Charm

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OutlineTHE RESEARCH

CP Violation in the Charm Sector

Direct CP Violation

Experimental Techniques

CP/T Violation Searches

Charged D decaysNeutral D decays

CP states3-Body

CP Violation at the (3770)T-odd Correlations

Summary: Current Status

Future Prospects

Conclusions

THE PLAYERS

CLEO-c BESIII

E-791

SUPER-KEK

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Charming CP Violation

Sakharov conditions for baryogenesis (1967): Baryon number violationCP violation Non-equilibrium

SM CP Violation in kaon and beauty systems too smallNeed other sources

Three types of CP ViolationCPV in mixing matrix (tiny)

CPV in decay amplitudes

CPV in interference between mixing and direct decay, for a subset of final states (mixing suppressed, hence very small)

fDAfDA

12

2

1212

1212

2

2

iM

iM

q

pRm

f

fim

f

ff A

AeR

A

A

p

q

See previous sessionfor CPV in mixing

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Direct CP Violation in Decay

Two amplitudes with different strong & weak phases needed to observe CPV (in SM from tree and penguins)

THE DECAYS

Cabibbo Favored (CF)

Singly Cabibbo Suppressed (SCS)

Doubly Cabibbo Suppressed (DCS)

c sdu

c dduc ssu

c dsu

1 32 2 *

1 2 1 2 1

2 21

2

*2Im ( )( ) ( )10

( ) ( ) 2Re ( )CP

sinf fA

f f A A A A co

A A

s

strong phase difference

c

s

uW+

uW+

c

s

ss

e.g. SCS D0 → K+K-

K+

K-

K-

K+

uD0

D0

2 weak amplitudes

with phase difference

u

u

u

s

Only SCS decays probe penguins

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CP Violation in the Standard Model

Standard Model charm physics is “CP conserving”

2x2 Cabibbo quark mixing matrix is real (no CPV at tree level)CPV in penguins and loops (by virtual b quarks)

Diluted weak phases in SCS decaysIn mixing, CPV enters at O(VcbVub/VcsVus)In decay, penguin CPV enters at O(VcbVub/VcsVuss/)

No weak phases in CF and DCS decays …except D+ K0+ - SM ~0.003 (CPV in K0 decay)

Note: in general we can separate direct and indirect CP Violation by:

Combine measured ACP with time-dependent CPV measurements (both for CP eigenstates)Just using time-integrated measurements (assuming negligible new CPV in CF or DCS decays):

The time-integrated CP asymmetry for CF decay to a CP eigenstate gives indirect ACP

e.g: ACP_DIRECT(P+P−) = ACP(P+P−) − ACP(KS00) , P =

K, Light readings:New physics and CP violation in singly Cabibbo suppressed D decays. Y. Grossman, A. L. Kagan, Y. Nir, Phys.Rev.D75:036008,2007. “I Know She Invented Fire, But What Has She Done Recently?" - On The Future Of Charm Physics, I.I. Bigi, Int.J.Mod.Phys.A21:5404-5415,2006. Mixing and CP-violation in charm. A. A. Petrov, Nucl.Phys.Proc.Suppl.142:333-339,2005. A Cicerone for the Physics of Charm, S. Bianco, F. L. Fabbri, D. Benson, I. Bigi, Riv. Nuovo Cim. 26N7 (2003) 1.

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CP Violation and New Physics (NP)

Extensions of the Standard Model (ex: SUSY) contain CP violating couplings that should show up at some level (1%?) in flavor physics

Precision measurements and theory are required to detect the NP

BSM Physics: charm is unique probe of the up type quark sector, especially models in which CKM mixing is generated in the up sector

top quarks: do not hadronize No T0-T0 oscillationsHadronization helps observability of CP Violation

up quarks : 0, η and η′ do not decay weaklyNo 0-0 oscillations possible CP asymmetries mostly excluded by CPT theorem)

(relatively) Large statistics

Flavor models where the CKM mixing is “generated” in the up sector predict large D − D mixing and sizable CPV in D, but smaller effects in the B sector

SCS D decays are now more sensitive to gluonic penguin amplitudes than are charmless B decaysCF and DCS decays:

Direct CPV in charm would mean NPSCS decays:

SM ~ 10-3 from CKM matrix

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Experimental Approaches for DCPV

Measure asymmetry in time integrated partial widths

Measure asymmetries in final state distributions on Dalitz plots

Exploit quantum coherence of DD produced in (3770) decays

Study T-violation in 4-body decays of D mesons (assuming CPT) with triple product correlations (T-odd)

All analyses (except CLEO-c) share many common featuresMany D0s produced in colliders,

Easy to determine the flavor of the D0 (by unbiased tag: D*

D0)Common backgrounds (e.g. K)

Random combining with a real D0K+-

Multibody D0 decay from D*D0 Random Kcombinatoral background

Signal and Background yields taken from mKvs M(D*-D0)Signal shape/resolution functions/efficiency calibrations taken from CF modesp(D*) cut to suppress from BD*D decaysOften normalize asymmetries to CF (or other) modes

Keep many systematics to a minimum

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BABARK−K++ K+K--

+ -

K*0K+ K*0K-

K−K++ K+K--

~42500 events80fb-1

D+ → K−K++, -++

~55000 events80pb-1

193 pb-1

D+ → K−K++ D+ → -++

CDFII

Large statistics gives access to detailed features in Dalitz plots

http://www-cdf.fnal.gov/physics/new/bottom/040422.dplus/

Phys. Rev. D71, 091101 (2005)m(-++)

m2(-+)m

2(

- +)

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D0KYield: 180K

123 pb-1

D0 KK, - I

SM CPV~10-3 in single Cabibbo suppressed modes (KK,), but null in Cabibbo allowed (K)

BR(D0->KK) >> BR(D0->) (R~2.8) – Large FSI and/or penguin contributions

NP CP asymmetriesStandard Model (Buccella et al, 1995) KK: (0.01 ± 0.08)%,

: (0.002 ± 0.001)%CDF II

Use D0K as normalization mode D0KKYield: 16220 200

D0Yield: 7334 97

Issues:Tracking charge asymmetrypartially reconstructed D background for KK modePhys. Rev. Lett. 94, 122001 (2005)

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BABARAnalysis Difficulties:

Precise quantification of asymmetry in D0 flavor taggingForward-backward asymmetries in cc production (novel issue)

Interference in e−e+ -> cc as mediated by either a virtual photon or a virtual Z0.

Higher-order QED box- and Bremsstrahlung-diagram interference effects

Can produce asymmetries due to boost of the CMS relative to the lab at asymmetric BABAR

Data corrected for charge-dependent detection efficiencies By tagging with an independent sample of D0 decays

Systematics:All corrections used for data will be calculated from data.

Goal: reduce systematics in these measurements to the 0.1% level

Soft-Pion Tagging efficiency corrections calculated from the CF decay (K)

With 400 fb-1 we expect:

KK (ACP)= ~ 0.3 10-2 (stat.) (ACP )= ~ 0.5 10-2 (stat.)

Both results expected to be statistically dominated

D0 KK, - II

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CLEO-c’s MeasurementsNew!

281 pb-1At the (3770)

Pure DD final state, no additional particles Low particle multiplicity(DD) = 6.4 nb ((4S)BB ~ 1 nb)Single tag sample

Mostly CF modesHigh efficiencies

SCS

Uncertainties ~1% most casesCharged Kaon tracking largest syst. ~0.7%

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Why Dalitz Plot Analyses?

In case of indirect CPV and final CP eigenstates the time integrated and time dependent CP asymmetries are:

Universal

Equal to each other

In contrast, for direct CPV:

The time-integrated asymmetries are not expected to be universal

Parts of phase-space might have different asymmetries

They may even cancel each other out when integrated over the whole phase-space

New Physics might not show up in the decay rates asymmetries

It could show up simply in the phase difference between amplitudes!

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3-Body Dalitz Plot Analyses - I

3-Body decays permit the measurement of phase differences

The Dalitz plot technique allows:

Increased sensitivity to CP asymmetry

Probes the decay amplitude rather than the decay rate.

Access to both CP eigenstates (e.g. D00, f00, 00, …) and non eigenstates (e.g. D0+--+, K*+-K-+, …) with relatively high statistics in the modes D0-+0, D0K-K+0, …

As measurements are normalized to the whole phase space, the flavor dependence of s tagging efficiency is null and the effect of mistagging is very small.

CLEO

D0-+0 - Difference in the integrated coherent sum of all amplitudes across the Dalitz Plot between D0 and D0 events

D0KS-+ - Full Dalitz analysis (see next slide)

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3-Body Dalitz Plot Analyses - II

BABAR (expect results this Fall)

D0-+0, D0K-K+0

MODEL DEPENDENT approach: fit D0 and D0 Dalitz plots separately, with a resonance (isobar) model (higher systematic uncertainties)

Parameterize the amplitude coefficients explicitly in the form: A eiδ = a ei(α + β) (1 + b/a) (for D0) A' eiδ' = a ei(α - β) (1 - b/a)

(for D0) Calculate |b| / |a|, values,

asymmetries in the fit fractions for each isobar.

Follows CLEO’s KS analysis technique, (Phys.Rev.D70:091101,2004).

MODEL INDEPENDENT approach: use moments of the cosine of the helicity angle for each of the three channels ( h-h+, h-0, h+ 0); plot vs invariant mass.

Measure asymmetry in these moments.

The phase/interference information is (mostly) contained in the odd moments

Decay rate asymmetry is contained in the even moments.

D0→ρ0π0 b=-0.05 = -5o

D0→ρ0π0 b=0 =0

D0-+0

MC

MC

m2(-+)

m2(-+)m

2(

- +)

m2(

- +)

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(3770): Quantum Correlation Analysis - I

Pure JPC = 1-- initial state CP+

If a D0 (tag) decays to a CP eigenstate f1, CP conservation requires the recoiling state f2 to have a definite CP as well, which must be of opposite sign:

e+e- (3770) D0D0

e+ e

0D

0D

+

K+

Quantum Correlation Analysis (TQCA): Due to quantum correlation between D0 and D0, not all final states allowed.

CP(f1 f2) = CP(f1) CP(f2) (-1)l = CP+

- - (since l = 1)

e.g. K+K- DCP ’’(3770) DCP Ks0 (-1) l

+ - - = CP+

At the (3770) (CLEO-c)22% double tagging efficiency (~0.1% @ (4S))

Same number of DD fully reconstructed as BB @ (4S)

Unique CPV search strategyComplementary to other experiments

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K-+ vs K-+

K-+ vs K+-

CP+ vs CP+

CP- vs CP-

K vs CP+

K vs CP-

CP+ vs CP-

(3770): Quantum Correlation Analysis - II

Reconstruct both D mesons (double tag)

Maximal constructive interference

Forbidden by CP

Conservation

Data favors QC interpretation: constructive and destructive interference and no D mixing

CP+ CP+

CP- CP-

CP+ CP-

K K

K K

K CP±

CP± K

X Kl

Interference of Cabibbo Favored with

Doubly Cabibbo SuppressedUnaffected

Forbidden (Bose Symm., if no D

mixing

<KD0>/<KD0> = rei

New!

Data consistent with no C+ initial state,(~1.5%, stat dominated) “hence” no CPV

Improved technique + KL CP+ modes

Interference: Two paths to K-+ vs K+-

281 pb-1

cos = 1.06 0.19 0.06

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T Violation: T-odd Correlations

Some references:E. Golowich and G. Valencia, Phys. Rev. D 40, 112 (1989)I.I. Bigi, Proceedings of KAON2001, 417 (2001)(*) I.I. Bigi, A.I. Sanda,‘CP Violation’, Cambridge University Press 2000

We can build T-odd asymmetries as:

And the T-Violation asymmetry as:

tests T-Violation even with strong phases

0 00 0

0 0 0 0T TT T

T TT T T T

C CC CA A

C C C C

1

2T Viol T TA A A

Method searches for Triple Product Asymmetries in (e.g.) D0 → K−K+−+

T-odd correlations can be formed using the momenta of the decay products (and assuming validity of the CPT theorem):

Under time reversal T, CT →−CT .

CT<>0 does not necessarily established T-Violation, because FSI can “fake” this asymmetry(*)

Consider D0 → K+K-+-

where we can compute:

Finding:

establishes T violation.

T KC p p p

T KC p p p

T TC C

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T-Violation Measurements

FOCUSFOCUSYield: 828

370 fb-1Yield: ~32000

BABAR

Preliminary

D0 → KS0K+−+D0 → K−K+−+

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Direct CP/T Violation Results – D0 Decays

Experiment (year)

Decay mode ACP (%) Comments

CDF (2005) D0 K+ K- 2.0 1.2 0.6

CLEO (2002) D0 K+ K- 0.0 2.2 0.8

FOCUS (2000) D0 K+ K- - 0.1 2.2 1.5

CDF (2005) D0 + - 1.0 1.3 0.6

CLEO (2002) D0 + - 1.9 3.2 0.8

FOCUS (2000) D0 + - 4.8 3.9 2.5

CLEO (2001) D0 K0S K0

S - 23 19

CLEO (2001) D0 0 0 0.1 4.8

CLEO (2001) D0 K0S

0 0.1 1.3

CLEO (1995) D0 K0S

2.8 9.4

CLEO (2005) D0 + - 0 1 (+9-7) 5 Dalitz plot – integr.

CLEO (2004) D0 K0S

+ - - 0.9 2.1 (+1.6-5.7) Dalitz plot analysis

BELLE (2005) D0 K+ + - - - 1.8 4.4 A of ratios DCS/CF

FOCUS (2005) D0 K+ K- + - - 8.2 5.6 4.7

CLEO (2007) D0 K- + - 0.4 0.5 0.9

CLEO (2007) D0 K- + 0 0.2 0.4 0.8

CLEO (2007) D0 K- + + + 0.7 0.5 0.9

BELLE (2005) D0 K+ - 0 - 0.6 5.3 A of ratios DCS/CF

BABAR (2007) D0 K+ - - 2.1 5.2 1.5 A of ratios DCS/CF

BELLE (2007) D0 K+ - 2.3 4.7 A of ratios DCS/CF

FOCUS (2005) D0 K+ K- + - 1.0 5.7 3.7 T violation - TPCor

Partiallist

New!

Ne

w!

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Direct CP/T Violation Results – D+ Decays

Experiment (year)

Decay mode ACP (%) Comments

BABAR (2005) D+ K- K+ + 1.4 1.0 0.8 A of ratios SCS/CF

BABAR (2005) “ D+ + 0.2 1.5 0.6 Resonant substructureof D+ K- K+ +

BABAR (2005) “ D+ K*0 K+ 0.9 1.7 0.7

CLEO (2007) D+ K- K+ + - 0.1 1.5 0.8

FOCUS (2000) D+ K- K+ + 0.6 1.1 0.5 A of ratios SCS/CF

E791 (1997) D+ K- K+ + - 1.4 2.9 A of ratios SCS/CF

E791 (1997) “ D+ + - 2.8 3.6 Resonant substructureof D+ K- K+ +

E791 (1997) “ D+ K*0 K+ - 1.0 5.0

FOCUS (2002) D+ K0S + - 1.6 1.5

0.9

CLEO (2007) D+ K0S + - 0.6 1.0

0.3

CLEO (2007) D+ K0S + 0 0.3 0.9 0.3

CLEO (2007) D+ K0S + + - 0.1 1.1 0.6

CLEO (2007) D+ K- + + - 0.5 0.4

0.9

CLEO (2007) D+ K- + + 0 1.0 0.9 0.9

CLEO (2007) DS+ K+ - 20 18

CLEO (2007) DS+ K+ ’ - 17 37

CLEO (2007) DS+ K0

S 27 11

CLEO (2007) DS+ K+ 2 29

E791 (1997) D+ + - + - 1.7 4.2 A of ratios SCS/CF

FOCUS (2005) D+ K0S K+ + - 2.3 6.2 2.2 T violation through

triple product correlationsFOCUS (2005) DS

+ K0S K+ + - - 3.6 6.7

2.3

New! Partial

list

New!

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Average Result, by Mode

Decay mode ACP (%)

D0 K+ K + 1.4 ± 1.2

D0 KS0 KS

0 2.3 ± 1.9

D0 + + 1.3 ± 1.3

D0 0 0 + 0.1 ± 4.8

D0 + 0 + 1 ± 9

D0 KS 0 + 0.1 ±

1.3

D0 K + - 0.4 ± 1.0

D0 K + 0 + 0.2 ± 0.9

D0 K + + - + 0.7 ± 1.0

D0 K+ 0.8 0.8 ± 3.1

D0 K+ 0 0.1 ± 5.2

D0 KS + 0.9 ± 4.2

D0 K+ + 1.8 ± 4.4

D0 K+ K + 8.2 ± 7.3

D+ KS + 0.9 ± 0.9

D+ KS + 0 ++ 0.3 ±

0.9

D+ KS + + - + 0.1 1.3

Decay mode ACP (%)

D+ K- + + - 0.5 1.0

D+ K- + + 0 + 1.0

1.3

D+ KS K+ + 7.1 ±

6.2

D+ K+ K + + 0.6 ± 0.8

D+ + + 1.7 ± 4.2

D+ KS K+ + 4.2 ± 6.8

AT

SCS modes

For most references http://hal9000.mib.infn.it/~pedrini/hfag/charm_asymcp.htmlSee the HFAG pages http://hal9000.mib.infn.it/~pedrini/hfag/charm_todd_asym.html

Partiallist

HFAG +

my averages

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Future Prospects – Current Efforts - I

D0KK,

CDF yield prospects2M D* tagged D0K per 1 fb-1 ACP) ~ 10-3 is achievable with full Tevatron run (4-9 fb-1)

- at SM limitIssue will be if trigger can cope with Luminosity increase

BABAR: 1 ab-1 KK (A)~0.2% (stat) (A)~0.3% (stat)

D+ K+K-

BABAR – now (A)~0.45 (systematically dominated – (syst~0.8)) 1 ab-1 (A)~0.28% (stat) Dalitz Analysis: fit fractions and phase differences ~ 1%

and 1o precisions

D0+-0 Dalitz Analysis

BABAR 200,000 signal events @ 1 ab-1 in 1 mass region. (A) (stat) ~ 0.25 % (integrated)If the asymmetry is larger, but confined to only a part of

the phase-space or only to certain specific decay(s), or both (constructively) in amplitude phases and magnitudes, our observation potential might be higher (or lower if destructively)

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Future Prospects – Current Efforts - II

T-Odd Correlations

BABAR (KK)

now ~ 0.9-0.6% level (if systematics under control)1 ab-1 0.55-0.35%

Relevant datasets I am aware of (larger backgrounds than KK):

CLEO: D0+-+- 7,300 - D0+-00 2,700 – D++-+0 5,700 BABAR: D0+-+- - current ~140,000 – 1 ab-1 ~320,000 + many large CF decays datasets from all 3 experiments

NOTE: Expect similar yields/results from BELLE

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Future Prospects – Future Efforts

BEPCII/BESIII

Data taking beginning of 2008 - 3 yrs @ 3770 = 30M DD/yr = 90M DD = ~20 times full CLEO-c dataset

Super-B (D, …)

10 ab-1/yr at (4S)With option to lower energy to ~4 GeV (~1ab-1/yr)

LHCb

Will implement a dedicated D* trigger stream selecting huge and clean samples of hadronic D modesIn one year of running at nominal lumi (2·1032 cm-2s-1):

Expect 250 - 500 M D* D0 decays with D0K channel = 100 times CDF !

K-K+

A < 0.08 (CLEO-c), < 0.004 (BESIII)(A) ~1 x 10-4 (stat.) LHCb/yr (A) ~6 x 10-5 (stat.) Super-B/yr

(3770) Quantum Correlation Analysis

A < 0.025 (CLEO-c) (A) ~0.01 (just KK, ) (BESIII)(A) ~7x 10-4 (stat.) Super-B/yr

KS-+ Dalitz analysis

Super-B (5 years = 50 ab-1) A < 5 10-4

BESIII – SUPER-D-too Factory (KEK and/or Frascati) – LHCb

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Conclusions

Charm physics provides unique opportunities for indirect search of NP

Theoretical calculation of x, y have large uncertainties Physics BSM hard to rule out from D0 mixing measurements alone

Observation of (large) CPV robust NP signal

SCS D decays now more sensitive to gluonic penguin amplitudes than charmless B decaysExciting new results (CLEO, Belle, BABAR): Total errors ~1% level BUT far from observation Now entering the interesting domain

Promising future: Current experiment ~0.1-0.3% in the “best” modes Future efforts (Super-Bs, LHCb, BESIII) ~ 0.001-0.01%