Violazione diret t a di CP e decadiment i rari del mesone B a BaBar Gianluca Cavoto Univ.Roma La Sapienza INFN Roma 1 Seminario fisica dei campi e delle particelle Sezione INFN Roma 8 ottobre 24
The CKM Unit arit y Triangle Flavour Physics Cabibbo-Kobayashi-Maskawa matrix matrix elements 2
Out line Selection of charmless hadronic B decays First observation of direct CP violation in B physics Charge asymmetry in B K New non-leptonic B decays B K S K S, K S K Experimental measurement of CKM angle Time-dependent CP asymmetries B B B Understand hadronic physics physics in in weak weak decays decays Dalitz New New powerful constraint on on CKM CKM UT UT ((,, )) 3 Many results not covered here, you will hear about them in few weeks
Where we st art ed f rom www.utfit.org. hep-ph/4879 Inputs from kaon Physics, B physics, Lattice QCD,HQET =.348 ±.28 =.172 ±.47 CP CP violation in in B physics 4 The challenge is is to to constrain the the triangle with angle measurements only with angle measurements only
B A 2 2 f B A f Direct CP violation has been observed in Kaon system We had not yet observed direct CP violation in B meson system arising from decay amplitude A CP A A f f 2 2 A f Direct 2 2 A f CPV It took more than 3 years to establish DCPV in Kaon system! PRL 83, 22 (1999) Re / 28 1 4 5 Experimentally: look for charge asymmetries (in rare decays though ) A CP Br B f Br B f Br B f Br B f
BaBar at PEP- I I Rare decays, need a B-factory! PEP-II Records Peak luminosity Best shift (8 hours) Best day Best week Best 3 days BABAR logged.921x1 34 cm -2 s -1 246.3 pb -1 71.5 pb -1 4.2 fb -1 16.5 fb -1 243.7 fb -1 6
Analysis t echniques High reconstruction efficiency m ES E *2 beam p *2 B E * * E B E beam Cerenkov angle No charge confusion. separation / at high momentum 7 e e Reject qq events topological variables in Neural Network or Fisher discriminant
Ext ract ing rare decays Small BF (1-5 1-6 ) Need high efficiency analysis Detailed parametrization of discriminant variables Global maximum likelihood fit 8 Count how many K + and how many K -
224M BB pairs First Observat ion of Direct CPV in B decay n K A K 166 51.133.3.9 n B n B K K 91 696 B K + BABAR B K + 4.2, syst. included BABAR background subtracted signal enhanced 9
A K : syst emat ics and cross- checks CPV due to mixing ruled out PRL 89, 28182 (22) Asymmetries consistent in different Kaon momentum ranges Asymmetries consistent when including decay time information Asymmetries consistent in different running period Asymmetries consistent with SM predictions Running period:.1 Source Error Signal fisher PDF c PDF.1 Potential MC bias.3 Potential Charge bias Total Background charge asymmetry free in the fit: b A K Systematics:.8.9.1.8 1
Branching f ract ion measurement s 224M BB pairs 11
B KK 224M BB pairs First evidence for K K Hint of a signal for K + K 12 How can we translate all this into CKM phases?
Hadronic int eract ions hassles M.Pierini talk at ICHEP4 Color suppressed B 13 Perturbative calculation of hadronic contributions too naïve. QCD/mb Non-perturbative terms
A working phenomenological model M.Pierini talk at ICHEP4 Weak Amplitudes Complex parameters (strong phases!) E 1 ~ 1 Evaluated with Factorization technique P I (c) ~ QCD /m b 14 Parametrize QCD /m b terms Global fit to BF and ACP, statistical test for consistency of theory with experiment Two terms with different CKM elements: interference! sensitivity to
B KK syst em M.Pierini talk at ICHEP4 Different CKM matrix element as Different amplitudes (different quark contents) Pure penguin, sensitive to new physics effect!!! Given the small yields, application for a super B-factory? 15
Const raining t he big pict ure M.Pierini talk at ICHEP4 Input from HFAG averages Good agreement data/theory A(K + ) predicted! A posteriori PDF Evidence of non-perturbative effects Hints of discrepancy?? A posteriori PDF UTfit value (, ) free input 16 P I (c) (normalized to E 1 ) Charmless 2body decays still still within SM SM framework
Decay- mixing int erf erence Decay+mixing B B No oscillation Net oscillation Decay+mixing phys No oscillation Net oscillation B ( t) f CP B B f CP f CP f CP A f CP t phys CP phys CP B t f B t f phys CP phys CP B t f B t f A C cos( mt) S sin( mt) CP parameter f f f CP CP CP q A p A e 2i Amplitude ratio f f CP CP C S f f CP CP 1 CP 1 f f 2Im CP 1 f CP f 2 2 CP 2 For single amplitude Im f CP B ( t) f phys CP C f CP implies Direct CP Violation 17
b f rom mixing- decay int ef erence B mixing d b uu d transition B decay: tree B decay: penguin d b * q / p VtbV td VtbV td A V V * ub ud A V V 3 * 3 td tb In fact: = - ( + ) hh q A p A e 2i 1 1 P T P T e e i i e i 2 eff 18 q p e 2i i i A e T e P, i i A e T e P
Current predict ions Pierini s formulas You fit for sin(2 eff ) Time dependent CP asymmetries You d like to extract Isospin analyses Eventually you want (, ) constraints. P I (c) ~ QCD /m b Sin(2 ) = -.16.26 UT fit prediction 19
Time- dependent analysis t e Y.55 (4 S ) z (4S) 1 c t is a signed quant it y B Asymmetric B-factory t e ~ 1 ps 17 m ~ 1.6 ps 25 m B rec B tag z Exclusive B meson reconstruction flavour or CP eigenstate K l - Inclusive reconstruction B-flavour tagging Tagging per f or mance: Q = 3.5% 2
B + - sample Likelihood ratio ratio cuts cuts 3body Background negligible 21 224 M BB pairs N 467 33
B + - t ime- dependent CP asymmet ry B 224 M BB pairs B all S.3.17.3 bkg C.9.15.4 No No evidence of of CP violation 22
Belle versus BaBar Belle claims 3.2 observation of direct CP Based on Feldman-Cousins analysis (ensemble of toymc experiments) 3.2 Physical bound C 2 +A 2 =1 5.2 Belle evidence for Direct CP violation not supported by BABAR measurements S 23
Trapping t he penguins Isospin analysis 1 (B ) (B ) (B ) 2 A A A S sin (2 ) 1 C 2 1 2 A 1 2 A A A Need to measure C too! (and still do not solve ambiguities!) Bound the penguins: 2 BR( B ) sin ( eff ) Grossman-Quinn BR( B ) A A 24 But pure SU(2) could not be be the end of of the story!!
B - / K - 25
B Fisher discriminant (topology + flavour tagging) Large continuum background 3body contamination 26 Fit qq bkg d + B signal BF (1. 17.32. 1) 1 C. 12.56.6 First measurement 6 GQ bound (WA) o eff 21 at 68% CL
Our experiment al knowledge f rom BaBar dark yellow: 68% light yellow:95% (selecting one solution) Relatively large penguin BF( ) large loose (, ) constraints 27
A clean mode? : B What about a small BF(B )? BF( ) (3 4stat 5 syst )1 6 BF B 6 ( / B ) 1.1 1 @ 9% CL 28 BF B 6 ( ) (26.4 6.4) 1 ( HFAG) Penguins are are smaller!!! eff eff < 11 (68% CL)
Angular analysis VV mode S,P,D wave components, need angular analysis to determine CP contents.4 f long.99.3(stat) syst.3 ( ) 29 Pure CP CP eigenstate!
A t ough job B rec e (4S) e B tag z Self-cross-feed effects (39% longitudinal signal events) Possible dilutions effect, careful studies reveals few percents effect (accounted for) K l - 3
Syst emat ics b Detailed description of B-background 2 exclusive channels studied u decays (small) b c decays (large!) m ES a 1 E Sensitivity to other wave? m ES Largest systematics on S and C come from unknown CP properties of BB background. Systematic error interference of signal with a 1, :.2 for both S and C E 31
t ime- dependent asymmet ry B 121M BB pairs Maximum likelihood fit to m ES, E, NN,cos, mass B S C long long.19.33.11 stat.23.24.14 stat syst syst Likelihood projections 32
Bounding BaBar 121M BB pairs dark yellow: 68% light yellow:95% (selecting one solution) Neglect I=1 component of amplitude Validity Validity of of isospin isospin analysis analysis approach under under scrutiny scrutiny though though 33 Internal crosscheck of SU(2) assumption in UT fit
Const raint s f rom and Indirect UT fit constraints: dark yellow: 68% light yellow:95% These measurements: 34 But there is is more
B wit h Dalit z analysis Idea: Extract and strong phases using interference between amplitudes. Form factors + Rel. Breit-Wigner Dalitz variables: Time dependance: Contain CP violating phase Coefficients are function of (26 parameters) 35 No quasi-2 body approximation, interference effects in!
Dalit z dist ribut ion Isobar model dominated by vectors [ Scalar contribution assumed to be negligible Small signal, 26 16 parameters Reparametrize Dalitz distribution (better handling of background) : helicity angle - + 36 + -
dat a sample 37
Time dependent f it result s 213M BB pairs Direct CP asymmetry 2.9 C( + - )and C( - + ) (including interference effect) 38
f rom Assuming SU(2) 213M BB pairs Dalitz model systematics Ambiguities removed! A promising channel 39
Conclusions 4 In 224M BB pairs BaBar has observed direct CP violation in B K + - A K.133.3.9 Indications for direct CP in Non-leptonic charmless 2-body B-decays Well explained by phenomenolgical models within SM New state observed (K K ), good for future? extraction was never straightforward. Need full isospin analysis for first measurement of C ) in smaller penguins First time-dependent Dalitz analysis in ( BaBar: known to 1 No big surprise, SM seems rock solid!
Many more!!! New physics could hide in some of them!!! 41
PEP I I Luminosit y Proj ect ions 12 3 1 Yearly Integrated Luminosity [fb-1] Cumulative Integrated Luminosity [fb-1] Peak Luminosity [1**33] 25 Integrated Luminosity ( fb-1) 8 6 4 2 15 1 Peak Luminosity [1**33]. 5 ab - 1 2 5 1999 2 21 22 23 24 25 26 27 28 29 Yearly Integrated Luminosity [fb-1] 3 23 41 39 62.6 66.1 12.1 151 16.1 217 216 Cumulative Integrated Luminosity [fb-1] 3 26 67 16 168.6 234.7 354.8 55.8 665.9 882.9 198.9 Peak Luminosity [1**33] 1 2 4.4 5 7.5 1 13 16 2 22 25 Year 42 24 26 1. 6 x 1 34
Out look Next future will see experiments at hadron colliders take over B-physics (larger cross sections, B s physics) Nevertheless e + e - environment is unique Final states with many neutrals, high flavour tagging efficiency, ultra-pure samples (recoil), coherent state Measurement of at 1 possible only at e + e - And many other accurate B d physics measurements to spot New Physics A super B-factory? 1 ab -1 /year Detector and machine challenging 43 LHC measures NP masses, super B-factory couplings and phases?
Angles only, as promised (, ) plane from measurements of sin(2 ), sin(2 ), and only as of today 44 Many thanks to M.Bona and M.Pierini for UT fit support
Backup slides 45
B + - quasi- t wobody f B h ( t) (1 A CP ( h)) e t / (1 ( S h S h )sin( m t) ( C h C h )cos( m t) f B h ( t) (1 A CP ( h)) e t / (1 ( S h S h )sin( m t) ( C h C h )cos( m t) S C.13.18.4.35.13.5 B 113 fb - 1 S C.33.18.3.2.13.5 B A CP = -.114.62.27 Significance for direct CPV: 2.5 46 More promising: perform full Dalitz plot analysis;
Dalit z analysis paramet ers 47
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