0 mixing D 0 D mixing in D 0 meson system considerably smaller than - PowerPoint PPT Presentation

BELLE SEARCH FOR CP VIOLATION IN D 0 Ñ KK , ππ , K π AND D 0 Ñ π 0 π 0 Tara Nanut on behalf of the Belle Collaboration 7th International Workshop on Charm Physics May 2015 1 { 17 Search for CP violation in D 0 Ñ KK , ππ , K π and D 0 Ñ π 0 π 0 Tara Nanut 1/17

0 mixing D 0 ´ D ‚ mixing in D 0 meson system considerably smaller than in K 0 , B 0 0 y | D 0 1,2 y “ p | D 0 y ˘ q | D ‚ mixing parameters x “ ∆ m { Γ , y “ ∆Γ { 2 Γ ‚ if p ‰ q Ñ | D 0 1,2 y not CP eigenstates Ñ CPV 2 { 17 Search for CP violation in D 0 Ñ KK , ππ , K π and D 0 Ñ π 0 π 0 Tara Nanut 2/17

From mixing to CPV From mixing arises a difference in effective lifetime of CP eigenstates (KK, ππ ) and flavour eigenstates (K π ): y CP “ τ p D 0 Ñ K ´ π ` q τ p D 0 Ñ K ` K ´ q ´ 1 “ “ y cos p φ q ´ 1 no CPV 2 A M x sin p φ q “ y (1) no CPV φ “ arg p p { q q “ 0 no CPV A M “ | q { p | ´ | p { q | “ 0 0 gives a Difference in effective lifetimes of CP eigenstates of D 0 , D non-zero asymmetry: 0 Ñ K ´ K ` q ´ τ p D 0 Ñ K ` K ´ q A Γ “ τ p D “ 0 Ñ K ´ K ` q ` τ p D 0 Ñ K ` K ´ q τ p D “ 1 no CPV 2 A M y cos p φ q ´ x sin p φ q “ 0 (2) SM CPV in charm O p 10 ´ 3 q Ñ anything larger indicates NP. 3 { 17 Search for CP violation in D 0 Ñ KK , ππ , K π and D 0 Ñ π 0 π 0 Tara Nanut 3/17

D 0 Ñ KK , ππ , K π update of PRL 98, 211803 (2007) TIME-DEPENDENT ANALYSIS ‚ measure only indirect CPV - common to all D 0 decay modes ‚ get y CP , A Γ from measurements of proper decay time Updated analysis: ‚ twice as large data sample: 976 fb ´ 1 ( Υ (4S), Υ (1S), Υ (2S), Υ (3S), Υ (5S)) ‚ improved analysis method - take into account ˝ two different configurations of SVD ˝ polar angle dependence ‚ final results are shown here 4 { 17 Search for CP violation in D 0 Ñ KK , ππ , K π and D 0 Ñ π 0 π 0 Tara Nanut 4/17

D 0 Ñ KK , ππ , K π Selection D ˚` Ñ D 0 π ` Flavour tag S p value ą 10 ´ 3 vertex fit p CMS (D ˚` ) ą 2.5 GeV (3.1 GeV for Υ (5S)) window in m(D 0 q 2.25 σ M p σ M « 6 ´ 8 MeV) window in q 0.66 MeV (SVD1), 0.82 MeV (SVD2) σ t ă 440 fs (SVD1), 370 fs (SVD2) Table: Selection criteria. Optimisation: minimal statistical error on y CP . Events per 0.45 MeV/c 2 Events per 0.45 MeV/c 2 Events per 0.45 MeV/c 2 8000 (a) D 0 → K + K - (b) D 0 → π + π - (c) D 0 → K - π + 70000 2500 60000 6000 2000 50000 1500 40000 4000 sideband sideband sideband sideband sideband sideband 30000 1000 20000 2000 500 10000 0 0 0 1.82 1.84 1.86 1.88 1.9 1.82 1.84 1.86 1.88 1.9 1.82 1.84 1.86 1.88 1.9 M (GeV/c 2 ) M (GeV/c 2 ) M (GeV/c 2 ) Signal yield: 242 ˆ 10 3 Signal yield: 114 ˆ 10 3 Signal yield: 2.61 ˆ 10 6 5 { 17 Search for CP violation in D 0 Ñ KK , ππ , K π and D 0 Ñ π 0 π 0 Tara Nanut 5/17

D 0 Ñ KK , ππ , K π Lifetime fit ‚ Proper decay time t distribution: F p t q “ N ż e ´ t 1 { τ R p t ´ t 1 q dt 1 ` B p t q τ ‚ Perform simultaneous binned maximum likelihood fit to all 3 channels (KK, ππ , K π ), separately for SVD1,2. ‚ cos p θ ˚ q dependence Ñ perform fit in bins of cos p θ ˚ q . ‚ Combine results from all bins with least squares fit to constant to obtain the final result. ‚ Fit tested on MC, linearity tests show no bias. 6 { 17 Search for CP violation in D 0 Ñ KK , ππ , K π and D 0 Ñ π 0 π 0 Tara Nanut 6/17

D 0 Ñ KK , ππ , K π Lifetime fit 10 4 Events per 41 fs Events per 41 fs (a) D 0 → K + K - (c) D 0 → π + π - 10 3 10 3 10 2 10 2 10 10 Events per 41 fs (e) D 0 → K - π + + cc 10 5 1 1 pull 4 pull 4 10 4 2 2 0 0 -2 -2 -4 -4 10 3 -2000 -1000 0 1000 2000 3000 4000 -2000 -1000 0 1000 2000 3000 4000 t (fs) t (fs) 10 2 10 4 Events per 41 fs Events per 41 fs  0 → K + K -  0 → π + π - (b) D (d) D 10 3 10 10 3 pull 4 2 0 10 2 -2 10 2 -4 -2000 -1000 0 1000 2000 3000 4000 t (fs) 10 10 1 1 pull 4 pull 4 2 2 0 0 -2 -2 -4 -4 -2000 -1000 0 1000 2000 3000 4000 -2000 -1000 0 1000 2000 3000 4000 t (fs) t (fs) 7 { 17 Search for CP violation in D 0 Ñ KK , ππ , K π and D 0 Ñ π 0 π 0 Tara Nanut 7/17

D 0 Ñ KK , ππ , K π Systematics and result Source ∆ y CP (%) ∆ A γ (%) SVD misalignment 0.060 0.041 Mass window position 0.007 0.009 Background 0.059 0.050 Resolution function 0.030 0.002 Binning 0.021 0.066 Total 0.092 0.066 Table: Systematic uncertainties. FINAL RESULT: A Γ “ r´ 0.03 ˘ 0.20 p stat . q ˘ 0.07 p syst . qs % consistent with no CPV y CP “ r 1.11 ˘ 0.22 p stat . q ˘ 0.09 p syst . qs % 4.7 σ significance 8 { 17 Search for CP violation in D 0 Ñ KK , ππ , K π and D 0 Ñ π 0 π 0 Tara Nanut 8/17

D 0 Ñ KK , ππ TIME-INTEGRATED ANALYSIS ‚ measure direct + indirect CPV ‚ asymmetry due to a difference in time-integrated decay rates of 0 Ñ f : D 0 Ñ f , D 0 Ñ f q A CP “ Γ p D 0 Ñ f q ´ Γ p D 0 Ñ f q Γ p D 0 Ñ f q ` Γ p D Experimentally measured quantity: 0 Ñ f q A raw “ N p D 0 Ñ f q ´ N p D “ 0 Ñ f q N p D 0 Ñ f q ` N p D “ A CP ` A FB ` A π ` S ‚ get A CP from extracted signal yields and corrections for detector-induced asymmetries and asymmetries in production 9 { 17 Search for CP violation in D 0 Ñ KK , ππ , K π and D 0 Ñ π 0 π 0 Tara Nanut 9/17

D 0 Ñ KK , ππ Detector-induced and production asymmetries DETECTOR-INDUCED ASYMMETRY ‚ due to different reconstruction efficiencies for π ` S , π ´ S ‚ determined from tagged and untagged D 0 Ñ K π decays ‚ evaluated in bins of p π S , θ π S PRODUCTION ASYMMETRY ‚ forward-backward asymmetry in production of D ˚` and and D ˚´ ( γ ´ Z 0 interference and higher order QED effects in e ` e ´ Ñ cc ) ‚ assumed same for all charm mesons ‚ odd function of θ ˚ , correct for using: A CP “ 1 2 r A corr rec p cos θ ˚ q ` A corr rec p´ cos θ ˚ qs and A FB “ 1 2 r A corr rec p cos θ ˚ q ´ A corr rec p´ cos θ ˚ qs where A corr rec is after A π ` S correction 10 { 17 Search for CP violation in D 0 Ñ KK , ππ , K π and D 0 Ñ π 0 π 0 Tara Nanut 10/17

D 0 Ñ KK , ππ Selection and A CP extraction all KK K π ππ D ˚` Ñ D 0 π ` Flavour tag S p value ą 10 ´ 3 vertex fit p CMS (D ˚` ) [GeV] ą 2.5 (3.1 for Υ (5S)) window in m(D 0 q [MeV] 17.8 17.8 17.2 window in q [MeV] 1.00 1.85 0.90 Table: Selection criteria. Optimisation: minimal error on asymmetry ( σ A ). ‚ Extract signal yield from signal window via background subtraction. ‚ Determine background from 2 sidebands ˘ 20 MeV from m p D 0 nom ). ‚ Limit to |cos θ ˚ | ă 0.8 to decrease A π S -related systematics. ‚ A CP extracted via fit to constant. 11 { 17 Search for CP violation in D 0 Ñ KK , ππ , K π and D 0 Ñ π 0 π 0 Tara Nanut 11/17

D 0 Ñ KK , ππ A CP fit D 0 → K + K - D 0 →π + π - 0.04 0.04 A CP A CP 4.058 / 3 6.537 / 3 P1 -0.3249E-02 0.2088E-02 P1 0.5470E-02 0.3575E-02 0.03 0.03 a) b) 0.02 0.02 0.01 0.01 0 0 -0.01 -0.01 -0.02 -0.02 -0.03 -0.03 -0.04 -0.04 0 0.2 0.4 0.6 0.8 0 0.2 0.4 0.6 0.8 |cos θ * | |cos θ * | 0.02 0.02 A FB A FB c) d) 0.01 0.01 -0 -0 -0.01 -0.01 -0.02 -0.02 -0.03 -0.03 -0.04 -0.04 -0.05 -0.05 0 0.2 0.4 0.6 0.8 0 0.2 0.4 0.6 0.8 |cos θ * | |cos θ * | 12 { 17 Search for CP violation in D 0 Ñ KK , ππ , K π and D 0 Ñ π 0 π 0 Tara Nanut 12/17

D 0 Ñ KK , ππ Systematics and result A KK CP p % q A ππ CP p % q ∆ A CP (%) Signal counting method 0.055 0.023 0.037 π S correction 0.065 0.067 0.014 A CP extraction method 0.06 0.050 0.051 Total 0.085 0.087 0.064 Table: Systematic uncertainties. FINAL RESULT: A KK CP “ r´ 0.32 ˘ 0.21 p stat . q ˘ 0.09 p syst . qs % A ππ CP “ r 0.55 ˘ 0.36 p stat . q ˘ 0.09 p syst . qs % ∆ A CP “ r´ 0.87 ˘ 0.41 p stat . q ˘ 0.06 p syst . qs % Results consistent with no CPV. 13 { 17 Search for CP violation in D 0 Ñ KK , ππ , K π and D 0 Ñ π 0 π 0 Tara Nanut 13/17

D 0 Ñ π 0 π 0 PRL 112, 211601 (2014) TIME-INTEGRATED ANALYSIS D ˚` Ñ D 0 π ` Flavour tag S p CMS (D ˚` ) ą 2.5 GeV (3.1 GeV for Υ (5S)) mass window m(D 0 q (1.758, 1.930) GeV mass window ∆ m (0.14, 0.16) GeV Table: Selection criteria. Optimisation: minimal error on A rec . 0 . ‚ Fit ∆ m “ m p D ˚` q ´ m p D 0 q simultaneously for D 0 , D ‚ Perform fit in bins of (cos p θ ˚ q , p π S T , cos p θ π S qq . ‚ Obtain average via a χ 2 fit on values in bins of cos p θ ˚ q . ‚ Procedure tested and confirmed on MC. 14 { 17 Search for CP violation in D 0 Ñ KK , ππ , K π and D 0 Ñ π 0 π 0 Tara Nanut 14/17

D 0 Ñ π 0 π 0 ∆ m fit and asymmetries fit 0 D 0 ∆ D 3 × 10 3 × 10 ) 2 ) Events/(0.2 MeV/c 2 Events/(0.2 MeV/c 2.5 2.5 2 2 1.5 1.5 1 1 0.5 0.5 0 0 0.145 0.15 0.155 0.16 0.145 0.15 0.155 0.16 2 ∆ M (GeV/c ) 2 M (GeV/c ) ∆ Signal yield: 34460 ˘ 273 | θ | 0.04 0.06 0.04 0.02 0.02 0 CP FB 0 A A -0.02 -0.02 -0.04 -0.04 -0.06 ∆ -0.06 0 0.2 0.4 0.6 0.8 1 0 0.2 0.4 0.6 0.8 1 * * |cos θ | |cos | θ 15 { 17 0.04 Search for CP violation in D 0 Ñ KK , ππ , K π and D 0 Ñ π 0 π 0 Tara Nanut 15/17 θ