Giampiero Mancinelli

1
Experimental Prospects for CP and T Violation
Studies in Charm

• Giampiero Mancinelli
• University of Cincinnati
• CHARM 2007 Cornell, USA

2
Outline
THE RESEARCH CP Violation in the Charm
Sector Direct CP Violation Experimental
Techniques CP/T Violation Searches Charged D
decays Neutral D decays CP states 3-Body CP
Violation at the ?(3770) T-odd Correlations Summa
ry Current Status Future Prospects Conclusions
THE PLAYERS
3
Charming CP Violation

• Sakharov conditions for baryogenesis (1967)
• Baryon number violation
• CP violation
• Non-equilibrium
• SM CP Violation in kaon and beauty systems too
  small
• Need other sources
• Three types of CP Violation
• CPV in mixing matrix (tiny)
• CPV in decay amplitudes

See previous session for CPV in mixing
4
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)

2 weak amplitudes with phase difference
strong phase difference
e.g. SCS D0 ? KK-
u
W
K
c
D0
s
K-
u
W
K
c
s
D0
s
Only SCS decays probe penguins
K-
5
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 decays
• In mixing, CPV enters at O(VcbVub/VcsVus)
• In decay, penguin CPV enters at
  O(VcbVub/VcsVusas/p)
• No weak phases in CF and DCS decays
• except D g K0p - 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(PP-)
  ACP(PP-) - ACP(KS0p0) , P K, p

Light readings New physics and CP violation in
singly Cabibbo suppressed D decays. Y. Grossman,
A. L. Kagan, Y. Nir, Phys.Rev.D75036008,2007.
I Know She Invented Fire, But What Has She Done
Recently?" - On The Future Of Charm Physics, I.I.
Bigi, Int.J.Mod.Phys.A215404-5415,2006. Mixing
and CP-violation in charm. A. A. Petrov,
Nucl.Phys.Proc.Suppl.142333-339,2005. A
Cicerone for the Physics of Charm, S. Bianco, F.
L. Fabbri, D. Benson, I. Bigi, Riv. Nuovo Cim.
26N7 (2003) 1.
6
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 oscillations
• Hadronization helps observability of CP Violation
• up quarks p0, ? and ?' do not decay weakly
• No p0-p0 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 decays

CF and DCS decays Direct CPV in charm would
mean NP SCS decays SM 10-3 from CKM matrix
7
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
  y(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
  features
• Many D0s produced in colliders,
• Easy to determine the flavor of the D0 (by
  unbiased tag D? g D0??)
• Common backgrounds (e.g. Kp)
• Random ? combining with a real D0gK?-
• Multibody D0 decay from D?gD0??
• Random K???combinatoral background
• Signal and Background yields taken from mK??vs
  DM(D-D0)
• Signal shape/resolution functions/efficiency
  calibrations taken from CF modes
• p(D) cut to suppress from BgDgD decays

8
D ? K-Kp, p-pp
D ? K-Kp
D ? p-pp
CDFII
193 pb-1
42500 events 80fb-1
m(p-pp)
Phys. Rev. D71, 091101 (2005)
m2(p-p)
Large statistics gives access to detailed
features in Dalitz plots
m2(p-p)
http//www-cdf.fnal.gov/physics/new/bottom/040422.
dplus/
9
D0 g KK, pp - I

• SM CPV10-3 in single Cabibbo suppressed modes
  (KK,pp), but null in Cabibbo allowed (Kp)
• BR(D0-gtKK) gtgt BR(D0-gtpp) (R2.8) Large FSI
  and/or penguin contributions
• NP CP asymmetries
• Standard Model (Buccella et al, 1995) g KK (0.01
  0.08), pp (0.002 0.001)
• CDF II
• Use D0?Kp as normalization mode

D0?KK Yield 16220 ?200
D0?pp Yield 7334 ?97
Issues Tracking charge asymmetry partially
reconstructed D background for KK mode
Phys. Rev. Lett. 94, 122001 (2005)
10
D0 g KK, pp - II

• BABAR
• Analysis Difficulties
• Precise quantification of asymmetry in D0 flavor
  tagging
• Forward-backward asymmetries in cc production
  (novel issue)
• Interference in e-e -gt 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 (Kp)
• With 400 fb-1 we expect

11
CLEO-cs Measurements
New!

At the ?(3770) Pure DD final state, no
additional particles Low particle
multiplicity (DD) 6.4 nb (U(4S)gBB 1
nb) Single tag sample Mostly CF modes High
efficiencies
281 pb-1
Uncertainties 1 most cases Charged Kaon
tracking largest syst. 0.7
SCS
12
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!

13
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. D0???0, f0?0,
  ?0?0, ) and non eigenstates (e.g. D0??-?-,
  K-K-, ) with relatively high statistics in
  the modes D0??-??0, D0?K-K?0,
• As measurements are normalized to the whole phase
  space, the flavor dependence of ps 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
• D0gKS?-? - Full Dalitz analysis (see next slide)

14
3-Body Dalitz Plot Analyses - II

• BABAR (expect results this Fall)
• D0??-??0, D0?K-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 eid
  a ei(a ß) (1 b/a) (for D0)
  
  
• A' eid' a ei(a - ß) (1 - b/a)
  (for D0)
• Calculate b / a, ? values, asymmetries in
  the fit fractions for each isobar.
• Follows CLEOs KSpp analysis technique,
  (Phys.Rev.D70091101,2004).
• MODEL INDEPENDENT approach use moments of the
  cosine of the helicity angle for each of the
  three channels ( h-h, h-p0, h p0) 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??-??0
D0??0p0 b0 b 0
m2(p-p)
MC
m2(p-p)
m2(p-p)
D0??0p0 b-0.05 b -5o
MC
m2(p-p)
15
?(3770) Quantum Correlation Analysis - I

• At the ?(3770) (CLEO-c)
• 22 double tagging efficiency (0.1 _at_ U(4S))
• Same number of DD fully reconstructed as BB _at_
  U(4S)
• Unique CPV search strategy
• Complementary to other experiments

Pure JPC 1-- initial state g CP
Quantum Correlation Analysis (TQCA) Due to
quantum correlation between D0 and D0, not all
final states allowed.
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
16
?(3770) Quantum Correlation Analysis - II
New!
Improved technique KL CP modes
Reconstruct both D mesons (double tag)
CP CP
CP- CP-
CP CP-
K-p K-p
K-p K-p
K-p CP
CP K-p
X Kl-n
Forbidden by CP Conservation
281 pb-1
CP vs CP
CP- vs CP-
Maximal constructive interference
Forbidden (Bose Symm., if no D mixing
CP vs CP-
Interference Two paths to K-? vs K?-
K-? vs K-?
Interference of Cabibbo Favored with Doubly
Cabibbo Suppressed
K-? vs K?-
Unaffected
K? vs CP
K? vs CP-
Data favors QC interpretation constructive and
destructive interference and no D mixing
Data consistent with no C initial
state, (s1.5, stat dominated) hence no CPV
cosd 1.06 ? 0.19 ? 0.06
17
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
18
T-Violation Measurements
D0 ? KS0Kp-p
D0 ? K-Kp-p
Yield 828
FOCUS
FOCUS
19
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 ? p p- 1.0 ? 1.3 ? 0.6
CLEO (2002) D0 ? p p- 1.9 ? 3.2 ? 0.8
FOCUS (2000) D0 ? p p- 4.8 ? 3.9 ? 2.5
CLEO (2001) D0 ? K0S K0S - 23 ? 19
CLEO (2001) D0 ? p0 p0 0.1 ? 4.8
CLEO (2001) D0 ? K0S p0 0.1 ? 1.3
CLEO (1995) D0 ? K0S f 2.8 ? 9.4
CLEO (2005) D0 ? p p- p0 1 (9-7) ? 5 Dalitz plot integr.
CLEO (2004) D0 ? K0S p p- - 0.9 ? 2.1 (1.6-5.7) Dalitz plot analysis
BELLE (2005) D0 ? K p p- p- - 1.8 ? 4.4 A of ratios DCS/CF
FOCUS (2005) D0 ? K K- p p- - 8.2 ? 5.6 ? 4.7
CLEO (2007) D0 ? K- p - 0.4 ? 0.5 ? 0.9
CLEO (2007) D0 ? K- p p0 0.2 ? 0.4 ? 0.8
CLEO (2007) D0 ? K- p p p 0.7 ? 0.5 ? 0.9
BELLE (2005) D0 ? K p- p0 - 0.6 ? 5.3 A of ratios DCS/CF
BABAR (2007) D0 ? K p- - 2.1 ? 5.2 ? 1.5 A of ratios DCS/CF
BELLE (2007) D0 ? K p- 2.3 ? 4.7 A of ratios DCS/CF
FOCUS (2005) D0 ? K K- p p- 1.0 ? 5.7 ? 3.7 T violation - TPCor
Partial list
New!
New!
20
Direct CP/T Violation Results D Decays
Experiment (year) Decay mode ACP () Comments
BABAR (2005) D ? K- K p 1.4 ? 1.0 ? 0.8 A of ratios SCS/CF
BABAR (2005) D ? f p 0.2 ? 1.5 ? 0.6 Resonant substructure of D ? K- K p
BABAR (2005) D ? K0 K 0.9 ? 1.7 ? 0.7 Resonant substructure of D ? K- K p
CLEO (2007) D ? K- K p - 0.1 ? 1.5 ? 0.8
FOCUS (2000) D ? K- K p 0.6 ? 1.1 ? 0.5 A of ratios SCS/CF
E791 (1997) D ? K- K p - 1.4 ? 2.9 A of ratios SCS/CF
E791 (1997) D ? f p - 2.8 ? 3.6 Resonant substructure of D ? K- K p
E791 (1997) D ? K0 K - 1.0 ? 5.0 Resonant substructure of D ? K- K p
FOCUS (2002) D ? K0S p - 1.6 ? 1.5 ? 0.9
CLEO (2007) D ? K0S p - 0.6 ? 1.0 ? 0.3
CLEO (2007) D ? K0S p p0 0.3 ? 0.9 ? 0.3
CLEO (2007) D ? K0S p p p- 0.1 ? 1.1 ? 0.6
CLEO (2007) D ? K- p p - 0.5 ? 0.4 ? 0.9
CLEO (2007) D ? K- p p p0 1.0 ? 0.9 ? 0.9
CLEO (2007) DS ? K h - 20 ? 18
CLEO (2007) DS ? K h - 17 ? 37
CLEO (2007) DS ? K0S p 27 ? 11
CLEO (2007) DS ? K p0 2 ? 29
E791 (1997) D ? p p- p - 1.7 ? 4.2 A of ratios SCS/CF
FOCUS (2005) D ? K0S K p p- 2.3 ? 6.2 ? 2.2 T violation through triple product correlations
FOCUS (2005) DS ? K0S K p p- - 3.6 ? 6.7 ? 2.3 T violation through triple product correlations
New!
New!
Partial list
21
Average Result, by Mode
Decay mode ACP ()
D0 ? K K? 1.4 1.2
D0 ? KS0 KS0 ? 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 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? p p0 0.3 0.9
D ? KS? p p p- 0.1 ? 1.3
Decay mode ACP ()
D ? K- p p - 0.5 ? 1.0
D ? K- p p p0 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
HFAG my averages
Partial list
AT
For most references
http//hal9000.mib.infn.it/pedrini/hfag/charm_asy
mcp.html See the HFAG pages
http//hal9000.mib.infn.it/pedrini/hfag/charm_tod
d_asym.html
22
Future Prospects Current Efforts - I

• D0gKK, pp
• CDF yield prospects
• 2M D tagged D0?Kp per 1 fb-1
• s(ACP) 10-3 is achievable with full Tevatron
  run (4-9 fb-1) - at SM limit
• Issue will be if trigger can cope with Luminosity
  increase
• BABAR 1 ab-1
• KK s(A)0.2 (stat)
• pp s(A)0.3 (stat)
• D g KK-p
• BABAR now s(A)0.45 (systematically dominated
  (syst0.8))
• 1 ab-1 s(A)0.28 (stat)
• Dalitz Analysis fit fractions and phase
  differences 1 and 1o precisions
• D0gpp-p0 Dalitz Analysis

23
Future Prospects Current Efforts - II

• T-Odd Correlations
• BABAR (KKpp)
• 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 KKpp)
• CLEO D0gpp-pp- 7,300 - D0gpp-p0p0 2,700
  Dgpp-pp0 5,700
• BABAR D0gpp-pp- - current 140,000 1 ab-1
  320,000
• many large CF decays datasets from all 3
  experiments
• NOTE Expect similar yields/results from BELLE

24
Future Prospects Future Efforts

• BEPCII/BESIII
• Data taking beginning of 2008 - 3 yrs _at_ 3770
  30M DD/yr 90M DD 20 times full CLEO-c
  dataset
• Super-B (D, t)
• 10 ab-1/yr at U(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
  modes
• In one year of running at nominal lumi (21032
  cm-2s-1)
• Expect 250 - 500 M D ? D0p decays with D0?Kp
  channel 100 times CDF !

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

• K-K
• A lt 0.08 (CLEO-c), lt 0.004 (BESIII)
• s(A) 1 x 10-4 (stat.) LHCb/yr
• s(A) 6 x 10-5 (stat.) Super-B/yr
• y(3770) Quantum Correlation Analysis
• A lt 0.025 (CLEO-c)
• s(A) 0.01 (just KK, pp) (BESIII)
• s(A) 7x 10-4 (stat.) Super-B/yr
• KSp-p Dalitz analysis
• Super-B (5 years 50 ab-1) A lt 5 10-4

25
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 g robust NP signal
• SCS D decays now more sensitive to gluonic
  penguin amplitudes than charmless B decays

Exciting 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