New Era of Particle Physics In past two decades or so, many new - PowerPoint PPT Presentation

H ADRONIC D M ESON D ECAYS Cheng-Wei Chiang National Central University Academia Sinica National Center for Theoretical Sciences

New Era of Particle Physics • In past two decades or so, many new physics (NP) models have been proposed to addresses such issues as: s m c m e i s n e l y b o l h b o s i t p o r s n a p a r r c r p e m e fi g t i t y n t n t a h o a i u n p n m c u d r i r r a t o n - t k u r e v a r e e a n a r i g n d h fl fi • Most of them are believed to leave detectable imprints in various low-energy flavor physics. • Lots of high-precision data have been obtained and more to come. Have we really seen any of it? Cheng-Wei Chiang for FPCP 2013 2

New Era of Particle Physics • In past two decades or so, many new physics (NP) models have been proposed to addresses such issues as: s m c m e i s n e l y b o l h b o s i t p o r s n a p a r r c r p e m e fi g t i t y n t n t a h o a i u n p n m c u d r i r r a t o n - t k u r e v a r e e a n a r i g n d h fl fi • Most of them are believed to leave detectable imprints in various low-energy flavor physics. • Lots of high-precision data have been obtained and more to come. Have we really seen any of it? • Probing NP in flavor physics = waiting for Godot? Cheng-Wei Chiang for FPCP 2013 2

Energy Frontiers • LHC experiments have been probing particle physics at unprecedented energy frontier. • Up to now, no BSM particle from direct searches yet. • Found a SM Higgs-like resonance at ~125 GeV instead. ➠ completing the SM Cheng-Wei Chiang for FPCP 2013 3

Precision Frontiers • Flavor physics experiments have been probing particle physics at precision frontier. • Many FCNC processes of B physics are used to impose stringent constraints on new physics models. • disappearing low-energy anomalies such as B s meson mixing and FBA in B → K*µµ • reduced tension between B → τν and sin2 β about |V ub |. • stronger constraints / bounds from BR(B s,d → µ + µ − ). • some lingering problems such as K π puzzle and like-sign dimuon asymmetry. • In general, current data point to contrived NP models if it has to show up at the TeV scale. Cheng-Wei Chiang for FPCP 2013 4

What About Charm System? • Being studied for about 4 decades, a lot of charm data (D meson mixing, decay BR’s, A CP ’s) have been collected and analyzed (from BABAR, Belle, CLEO-c, BES-III, and LHCb). ➠ Consistent with SM expectations? ➠ A good place to observe NP? • Recent direct CPA difference in hadronic D decays ➠ indicating NP beyond the SM? ➠ demanding new understanding of SM? Cheng-Wei Chiang for FPCP 2013 5

Peculiarities of Charm Quark • Resides at an awkward place in mass spectrum ➠ no suitable effective theory to work with, particularly for hadronic decays • Too light to grant reliable heavy-quark expansions Λ QCD /m c ∼ 0 . 3 Λ QCD /m b ∼ 0 . 1 vs • Too heavy to use chiral perturbation theory • Strong QCD coupling regime ➠ perturbative QCD calculations expected to fail • Many resonances around ➠ nonperturbative rescattering effects kick in • Flavor SU(3) symmetry for decays to light mesons • Good realm to test various approaches Cheng-Wei Chiang for FPCP 2013 6

Dominant Charm Decays • D mesons decay dominantly (~84%) into hadronic final states, 3/4 of which are two-body modes. ➠ unlike B mesons Mode BR ∼ 10% PP V P ∼ 28% P: pseudoscalar meson ∼ 10% V V V: vector meson ∼ 4 . 2% SP A: axial vector meson ∼ 10% AP T: tensor meson ∼ 0 . 3% TP 2-body ∼ 63% hadronic ∼ 84% semileptonic ∼ 16% Cheng-Wei Chiang for FPCP 2013 7

Two-Body Hadronic Charm Decays • Cabibbo-favored (CF): involving V ud* V cs ~ 1 −λ 2 ~ 0.95 • Singly Cabibbo-suppressed (SCS): involving V us* V cs / V ud* V cd ~ λ ~ 0.22 • Doubly Cabibbo-suppressed (DCS): involving V us* V cd ~ λ 2 ~ 0.05 Cheng-Wei Chiang for FPCP 2013 8

Two-Body Hadronic Charm Decays • Cabibbo-favored (CF): involving V ud* V cs ~ 1 −λ 2 ~ 0.95 • Singly Cabibbo-suppressed (SCS): involving V us* V cs / V ud* V cd ~ λ ~ 0.22 • Doubly Cabibbo-suppressed (DCS): involving V us* V cd ~ λ 2 ~ 0.05 • Only SCS decays can possibly involve diagrams with different CKM phases and thus possibly have CPA’s: Amp = V ∗ cd V ud (trees + penguins) + V ∗ cs V us (trees + penguins) Cheng-Wei Chiang for FPCP 2013 8

CP Violation in SCS Decays • CPA’s in SCS decay modes are expected only at 10 − 4 to 10 − 3 level � � � � � � CP = 2Im( V ∗ us ) cd V ud V cs V ∗ A 2 V ∗ cb V ub A 2 a dir � � � � � � � sin δ = 2 � sin γ � sin δ � � � � � � cd V ud | 2 | V ∗ A 1 V ∗ cd V ud A 1 � � � � � A 2 ∼ 10 − 3 � � � sin δ ( δ = relative strong phase) � � A 1 � ➠ new physics, if measured to be sizable Cheng-Wei Chiang for FPCP 2013 9

Flavor Diagrams Zeppenfeld 1981 • Diagrams for 2-body hadronic D Chau and Cheng 1986, 1987, 1991 meson decays can be classified Savage and Wise 1989 Grinstein and Lebed 1996 according to flavor topology into Gronau et. al. 1994, 1995, 1995 the tree- and loop-types: Cheng and Oh 2011 Tree-type Loop-type Cheng-Wei Chiang for FPCP 2013 10

CF D → PP Decays • η - η ’ mixing (with ϕ = 40.4°): KLOE 2009 satisfactory fit ✓ ◆ ✓ ◆ ✓ ◆  � 1 η cos φ − sin φ η q u + d ¯ � � u ¯ d , η s = s ¯ s = η q = η 0 sin φ cos φ η s √ 2 Cheng-Wei Chiang for FPCP 2013 11

Extracted Amplitudes CWC, Luo, Rosner 2002, 2003 • The amplitudes extracted from Wu, Zhong, Zhou 2004 Cabibbo-favored modes in units Bhattacharya and Rosner 2008, 2010 Cheng and CWC 2010 of 10 − 6 GeV are ( Χ 2 /dof = 0.65): C = (2 . 61 ± 0 . 08) e − i (152 ± 1) � , T = 3 . 14 ± 0 . 06 , − 0 . 08 ) e i (122 ± 2) � , � 33 ) � . − 0 . 09 ) e i (31 +20 E = (1 . 53 +0 . 07 A = (0 . 39 +0 . 13 [CKM factors extracted] E A T C • Results are used to predict SCS and DCS decays utilizing the flavor SU(3) symmetry. Cheng-Wei Chiang for FPCP 2013 12

Implications Cheng and CWC 2010 • T and C are almost opposite in phase, and C and E are quite sizable ( cf . B decays) ➠ large final-state interaction effects ➠ result of rescattering via abundant resonances around D mesons ➠ failure of perturbative approaches T → E T → C E A T C Cheng-Wei Chiang for FPCP 2013 13

SCS D → PP Decays -- SU(3) Limit Cheng-Wei Chiang for FPCP 2013 14

DCS D → PP Decays -- SU(3) Limit • Predictions and measured data agree well. Cheng and CWC 2010 to be checked against future data Cheng-Wei Chiang for FPCP 2013

Problems With K + K − and π + π − Modes • These two modes are closely related and identical under SU(3) limit: A π + π − = 1 2( λ d − λ s )( T + E + ∆ P ) ππ − 1 2 λ b ( T + E + Σ P ) ππ → λ d ( T + E ) − λ b Σ P [SU(3) limit] A K + K − = 1 2( λ s − λ d )( T + E − ∆ P ) KK − 1 2 λ b ( T + E + Σ P ) KK → λ s ( T + E ) − λ b Σ P [SU(3) limit] Σ P = ( P + PE + PA ) d + ( P + PE + PA ) s ∆ P = ( P + PE + PA ) d − ( P + PE + PA ) s λ q = V ∗ cq V uq quark involved in penguin loop Cheng-Wei Chiang for FPCP 2013 16

A Long-Standing Puzzle • D → π + π − , K + K − modes are known to deviate from naive expectations for a long time. • Empirically, the ratio of their decay rates Γ ( K + K − ) Γ ( π + π − ) ' 2 . 8 is noticeably larger than 1 for the SU(3) limit, not to mention that K + K − has less phase space than π + π − . • SU(3) breaking in factorizable part F DK ( m 2 T ( K + K − ) K ) T ( π + π − ) ' f K ' 1 . 22 or f K + π ) ' 1 . 38 F D π f π f π + ( m 2 is insufficient to account for data. Cheng-Wei Chiang for FPCP 2013 17

Direct CP Asymmetry Difference • Time-integrated asymmetry to first order in the average decay time <t>: A CP ( f ) ⌘ Γ ( D 0 ! f ) � Γ ( ¯ D 0 ! ¯ f ) Γ ( D 0 ! f ) + Γ ( ¯ D 0 ! ¯ f ) CP ( f ) + h t i ' a dir a ind CP τ D • Consider ∆ A CP ⌘ A CP ( K + K − ) � A CP ( π + π − ) CP ( π + π − ) + ∆ h t i ' a dir CP ( K + K − ) � a dir a ind CP τ D (1) common systematic factors cancel out; (2) insensitive to indirect CPV; (3) SM and most NP models predict opposite signs. Cheng-Wei Chiang for FPCP 2013 18

Δ A CP for K + K − and π + π − circa 2012 HFAG ICHEP 2012 • Combination of the LHCb, CDF , BaBar and Belle measurements yields a CPind = − (0.027±0.163)%, ∆ a CPdir = − (0.678±0.147)%. 4.6 σ from no CPV A CP ( K + K − )(%) A CP ( π + π − )(%) Experiment ∆ A CP (%) BaBar 0 . 00 ± 0 . 34 ± 0 . 13 − 0 . 24 ± 0 . 52 ± 0 . 22 LHCb − 0 . 82 ± 0 . 21 ± 0 . 11 CDF − 0 . 24 ± 0 . 22 ± 0 . 09 0 . 22 ± 0 . 24 ± 0 . 11 − 0 . 62 ± 0 . 21 ± 0 . 10 Belle − 0 . 32 ± 0 . 21 ± 0 . 09 0 . 55 ± 0 . 36 ± 0 . 09 − 0 . 87 ± 0 . 41 ± 0 . 06 ➠ ~30 theory papers followed Cheng-Wei Chiang for FPCP 2013 19