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Experimental Prospects for CP and T Violation Studies in Charm

Experimental Prospects for CP and T Violation Studies in Charm. Giampiero Mancinelli University of Cincinnati CHARM 2007 – Cornell, USA. Outline. BESIII. CLEO-c. E-791. SUPER-KEK. THE RESEARCH CP Violation in the Charm Sector Direct CP Violation Experimental Techniques

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Experimental Prospects for CP and T Violation Studies in Charm

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  1. Experimental Prospects for CP and T Violation Studies in Charm Giampiero Mancinelli University of Cincinnati CHARM 2007 – Cornell, USA

  2. Outline BESIII CLEO-c E-791 SUPER-KEK • 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 • Summary: 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 • CPV in interference between mixing and direct decay, for a subset of final states (mixing suppressed, hence very small) See previous session for CPV in mixing

  4. Direct CP Violation in Decay u u u u s s • 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 → K+K- 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(P+P−) = ACP(P+P−) − 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.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.

  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 isunique 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, η and η′ 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 Ddecays are now more sensitive to gluonic penguin amplitudes than are charmless Bdecays 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 BgD*gD decays • Often normalize asymmetries to CF (or other) modes • Keep many systematics to a minimum

  8. D+ → K−K+p+, p-p+p+ K−K+p+ K+K-p- BABAR fp+ fp- ~55000 events 80pb-1 K*0K+ K*0K- K−K+p+ K+K-p- D+ → K−K+p+ D+ → p-p+p+ CDFII 193 pb-1 ~42500 events 80fb-1 m(p-p+p+) 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. D0g KK, pp - I D0Kp Yield: 180K 123 pb-1 • SM CPV~10-3 in single Cabibbo suppressed modes (KK,pp), but null in Cabibbo allowed (Kp) • BR(D0->KK) >> BR(D0->pp) (R~2.8) – 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. D0g 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+ -> 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: • KK gs(ACP)= ~ 0.3 10-2 (stat.) • ppgs(ACP )= ~ 0.5 10-2 (stat.) • Both results expected to be statistically dominated

  11. CLEO-c’s 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 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 KSpp 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-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→ρ0π0 b=0 b =0 m2(p-p+) MC m2(p-p+) m2(p-p+) D0→ρ0π0 b=-0.05 b = -5o MC m2(p-p+)

  15. (3770): Quantum Correlation Analysis - I e+e-  (3770)  D0D0 K+ CP(f1 f2) = CP(f1) CP(f2) (-1)l = CP+ K- - - (since l = 1) e- e+ e.g. K+K- DCPy’’(3770)  DCP Ksp0 (-1) l p- + - - = CP+ p+ • At the (3770) (CLEO-c) • 22% double tagging efficiency (~0.1% @ U(4S)) • Same number of DD fully reconstructed as BB @ 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 <K-p+|D0>/<K-p+|D0> = -re-id New! Improved technique + KL CP+ modes Reconstruct both D mesons (double tag) 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, (s~1.5%, stat dominated) “hence” no CPV cosd = 1.06  0.19  0.06

  17. T Violation: T-odd Correlations Method searches for Triple Product Asymmetries in (e.g.) D0 → K−K+p−p+ 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-p+p- where we can compute: Finding: establishes T violation. We can build T-odd asymmetries as: And the T-Violation asymmetry as: tests T-Violation even with strong phases 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 370 fb-1 Yield: ~32000 BABAR Preliminary D0 → K−K+p−p+ D0 → KS0K+p−p+ Yield: 828 FOCUS FOCUS

  19. Direct CP/T Violation Results – D0 Decays Partial list New! New!

  20. Direct CP/T Violation Results – D+ Decays New! New! Partial list

  21. Average Result, by Mode SCS modes HFAG + my averages Partial list AT For most references http://hal9000.mib.infn.it/~pedrini/hfag/charm_asymcp.html See the HFAG pages http://hal9000.mib.infn.it/~pedrini/hfag/charm_todd_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) • pps(A)~0.3% (stat) • D+g K+K-p+ • BABAR – now s(A)~0.45 (systematically dominated – (syst~0.8)) • 1 ab-1s(A)~0.28% (stat) • Dalitz Analysis: fit fractions and phase differences ~ 1% and 1o precisions • D0gp+p-p0 Dalitz Analysis • BABAR 200,000 signal events @ 1 ab-1 in 1 mass region. • s(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)

  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: D0gp+p-p+p- 7,300 - D0gp+p-p0p0 2,700 – D+gp+p-p+p0 5,700 • BABAR: D0gp+p-p+p- - 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 @ 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 (2·1032 cm-2s-1): • Expect 250 - 500 M D*  D0pdecays with D0Kp channel = 100 times CDF ! BESIII – SUPER-D-too Factory (KEK and/or Frascati) – LHCb K-K+ A < 0.08 (CLEO-c), < 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 < 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 < 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 grobust NP signal • SCS D decays now more sensitive to gluonic penguin amplitudes than charmless Bdecays • 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%

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