Risultati recenti dellesperimento BABAR Matteo Rama Ba Bar

Risultati recenti dell’esperimento BABAR Matteo Rama Ba. Bar Collaboration Università/INFN Pisa INFN – Commissione Scientifica Nazionale 1 5 -6 Aprile 2004, Roma 1

Outline Ba. Bar has shown a lot of new results at the Winter conferences 2004 o measurements finalized and sent for publications o new preliminary results - introduction - results related to the measurements of the UT angles , , - measurements sensitive to new physics - |Vcb| - properties of recently discovered particles and rare decays 5 Aprile 2004 Matteo Rama 2

Ba. Bar and PEP-II Run 4 Run 3 Run 2 Run 1 Future expectations Lpeak Lint Iher Iler 12. 5 18. 2 23 30 260 395 580 880 1600 1800 2000 2200 2700 3600 4500 (1033) 2004 2005 2006 2007 5 Aprile 2004 fb-1 (m. A) Matteo Rama 3

Il rivelatore Ba. Bar 1. 5 T solenoid Čerenkov Detector (DIRC) 144 quartz bars 11000 PMTs Electro. Magnetic Calorimeter 6580 Cs. I(Tl) crystals e+ (3. 1 Ge. V) e- (9 Ge. V) Drift CHamber 40 stereo layers Silicon Vertex Tracker 5 layers, double sided strips Instrumented Flux Return iron/RPCs (muon/neutral hadrons) SVT: 97% efficiency, 15 mm z hit resolution (inner layers, tracks) SVT+DCH: (p. T)/p. T = 0. 13 % p. T + 0. 45 % DIRC: K- separation 4. 2 @ 3. 0 Ge. V/c >3. 0 @ 4. 0 Ge. V/c EMC: E/E = 2. 3 % E-1/4 1. 9 % 5 Aprile 2004 Matteo Rama 4

B Meson Reconstruction at U(4 S) Kinematic signature for B decays: Typical resolutions: m. ES (m. ES) 2. 5 Me. V ( E) 15 - 30 Me. V (*) measured in U(4 S) rest frame E*B E*beam Improve resolution signal region B signal: E=0, m. ES= m. B E • Define 2 regions in E, m. ES plane: Signal region Sideband region sidebands m. ES (Ge. V) 5 Aprile 2004 Matteo Rama 5

B decay time separation in Ba. Bar Asymmetric B factories optimized for measurements of time-dependent CP violating asymmetries Inclusive tag (lepton, K, …): tag(1 -2 w)2 28% (Exclusive tag: tag 0. 1 0. 2%) z(tag) z(CP) < z > 260 m z (RMS) 190 m rec 15 40% OK also for other measurements (rare B decays, …) Open trigger! No B physics losses at trigger level High efficiencies, small bkgd Unique tool at B factories: exclusive B tagging with fully rec. B (“single B beam”) Luminosity is a key factor 5 Aprile 2004 Matteo Rama 6

CP asymmetry: Time Dependence CPV in mixing-decay interference direct CPV d. N exp(–|Dt|/t. B) ( 1 ± D (S sin(Dm. Dt) - C cos(Dm. Dt)) ) R Flavour tag Amplitude ratio B 0 fcp/B 0 fcp CP eigenvalue B mixing D mis-tag dilution R time resolution function 5 Aprile 2004 Measured from data (Flavour sample)! Matteo Rama 7

Constraints on the angles of the Unitarity Triangle f. Ks, ’Ks, Ksp 0… new results on these B decays: 5 Aprile 2004 Matteo Rama 8

sin 2 a from B 0 - ( - +) decays • Proceeds mainly through b uud tree diagram, but penguin contributions introduce additional phases. Tree Penguin extra weak and strong phases + |P/T| modify a by k: sin 2 aeff=2 a+k • How to relate the angle a with aeff? Two methods: o Grossmann-Quinn bound: o isospin analysis Need flavor tagged rates for + -, 0, 0 0 2 aeff=2 a+k 5 Aprile 2004 Matteo Rama 9

B 0 + -: time-dependent CP asymmetry • ML fit on m. ES, E, NN(evt. shape), t, M( ), hel. angles Moriond EW 04 B 0 tag background • on 89 106 BB pairs: f. L=longitudinal polarization fraction B 0 tag CP-even final state • on 114 106 Acp(t) BB pairs: preliminary 5 Aprile 2004 Matteo Rama 10

B 0 + - : constraints on a • From the time-dependent asymmetry we measure sin(2 aeff). • Using the Grossmann-Quinn bound to set a limit on the penguin contamination on a : f. L=longitudinal pol. fraction (see Phys. Rev. D 69: 011502, 2004 for discussion on the applicability to B ) • …and using the exp. measurements of Br(B ): o o (the solution closest to the CKM fit result was chosen) The limiting factor on a is the penguin contamination. Can be reduced with more precise measurement of Br(B 0 0) 5 Aprile 2004 Matteo Rama 11

Measurement of a: status of B 0 time dependent asymmetry in B 0 + - (winter 2004) (Ba. Bar) PRL 91, 241801 (2003) Br(B 0 0 0)/Br(B+ + 0) too large to constrain with G-Q bound statistics is too low to constrain with isospin analysis 5 Aprile 2004 Matteo Rama 12

How to extract g from B DK decays • g is the phase between b u and b c amplitudes • most straightforward tool: B DK decays color suppressed • exploits the interference between B- D 0 K- and B- D 0 K- when D 0/D 0 bar decays to a common final state f B- D 0 K- vs. B- D 0 K- f f • theoretically clean extraction of g but generally with discrete ambiguities (number of ambiguities depends on the D final state f) 5 Aprile 2004 Matteo Rama 13

B- [K+ -]DK-: ADS method • Atwood-Duniets-Sony: equalize the interference amplitudes favored suppressed favored • relate the observable RADS and AADS with the unknown rb, d and g unknowns • for most methods based on B DK, the larger rb, the better precision on g 5 Aprile 2004 Matteo Rama 14

B- D 0[K+ -]K-: results • selection of B- D 0[K+ -]K-: AADS not measured, limit on RADS hep-ex/0402024 Sub. to PRL 5 Aprile 2004 RADS • first experimental limit on rb Matteo Rama 15

Measurement of g: perspectives • the measurement of g is now one of the main goal of Babar and Belle • a number of decay modes give information on g: B D(*)K(*), D 0 CP eigenstate o B D(*)K(*), D 0 Double Cabibbo Suppressed (previous slides) o B D(*)K(*), D 0 3 -body (require Dalitz analysis) o B 0 D* (time dependent analysis, measures sin(2 b+g)) o others o • the methods based on B D(*)K(*) provide a New method. Quite promising, first results for Summer. Preliminary result from Belle theoretically clean measurement of g, but require very large B samples large effort to provide the first Babar measurement of ( ( )~15 -20 o) this Summer 5 Aprile 2004 Matteo Rama 16

Measurement of b: status & perspectives • CP violation in B decays has been observed and sin 2 b is measured with good precision sin 2 b=0. 741 0. 067 0. 034 (Ba. Bar, 89 M BB) theory error on sin 2 b with J/YK 0 s <1% still room for improvement with larger data samples www. utfit. org • New time-dependent asymmetry measurement with B 0 J/Y K*0(Ks 0) • P VV: angular analysis required • cos 2 b 0 89%CL preliminary • other B decays are sensitive to sin 2 b: K 0 s , K 0 s 0, etc. . . mostly useful to search NP (see later slides) plan to update the sin 2 measurement on >200 M BB this Summer 5 Aprile 2004 Matteo Rama 17

Probe for new physics sensitive to NP in sin 2 eff EM penguin EW penguin radiative decays (semi-inclusive) 5 Aprile 2004 Matteo Rama 18

B 0 K 0: time-dependent CP asymmetry • Decay dominated by pure b sss gluonic penguins • In SM: comparison of CP-violating observable with SM expectation probes new physics (new heavy particles in penguin loops, new CP-violating phases) • Reconstruct B 0 K 0 s and B 0 K 0 L K+KB 0 K 0 s 5 Aprile 2004 B 0 K 0 L Matteo Rama 19

B 0 K 0: time-dependent CP asymmetry • Combined (B 0 K 0 s+B 0 K 0 L) result from Ba. Bar hep-ex/0403026 B 0 tag SM prediction: S K=sin 2 b=0. 74 Sf. K consistent at 1 level with SM prediction • Result from Belle (B 0 K 0 s only) based on 152 106 BB pairs Ks background Acp(t) B 0 tag KL B 0 tag 3. 5 deviation from SM expectation!! 2. 3 deviation from Ba. Bar result 5 Aprile 2004 Matteo Rama Acp(t) 20

B 0 K+K-K 0 s: time-dependent CP asymmetry • same final states as B 0 K 0 , but without going through the resonance measure time-dependent CP-violation and compare with expectation from SM • K+K- are vetoed • need to determine CP-even fraction from: o o Moriond EW 04 helicity angle dist. of K+Kfcp-even= [fcp-even=0. 98+/-0. 15+/-0. 04] • fit of Acp(t) on data: SM expectation: sig. evts. S, C consistent with SM prediction 5 Aprile 2004 Matteo Rama 21

B 0 f 0(980)K 0 s: time-dependent CP asymmetry • decay probably dominated by pure b sss gluonic penguins (also b uus , but suppressed) Moriond EW 04 f 0 is scalar f 0 K 0 s is CP-even S -sin 2 b in time-dependent CPV total bkg continuum bkg • f 0 reconstructed in + -. The signal is extracted through a fit on m. ES, E, m( + -) and quantities sensible to event shape • fit of Acp(t) on data: preliminary sig. evts. SM expectation: S -sin 2 b = - 0. 74; C 0 S, C consistent with SM prediction 5 Aprile 2004 Matteo Rama 22

B K*0( K 0 s 0)g: time-dependent CP asymmetry • In the limit of massless s quark, the photons in final states are completely polarized with opposite helicities for B and Bbar. In SM: • A time-dependent measurement with this B decay is experimentally challenging: the B decay vertex cannot be reconstructed directly • The Bcp decay position is reconstructed thanks to: Moriond EW 04 o the SVT information for tracks from K 0 s • From time fit on data: preliminary 5 Aprile 2004 compatible with SM Matteo Rama asymmetry B 0 bar B 0 o the beam-spot position t 23 (ps)

B K 0 s 0: time-dependent CP asymmetry • in SM decay dominated by penguin b sqq diagram. If other contributions are ignored, S=sin 2 b • B decay position determined with a beam constrained vertexing. Same technique as used for B K*0( K 0 s 0)g hep-ex/0403001 sub. to PRL B 0 bar B 0 signal enhanced m. ES distribution asymmetry Acp(t) fit result: S, C consistent with SM prediction 5 Aprile 2004 Matteo Rama t (ps) 24

Status of the S (sin 2 beff) measurements Belle as of Moriond EW 5 Aprile 2004 Matteo Rama 25

Radiative decays • The Standard Model forbids flavour changing neutral currents at the tree level • additional contributions may come from exotic particles and modify the SM previsions: • The measurements of BR and CP (isospin) asymmetry are compared with theoretical predictions of SM. New particles in the loop may modify these observables in some super-symmetric scenarios 5 Aprile 2004 Matteo Rama 26

B Xsg: semi-inclusive selection • Xs is fully reconstructed in 12 exclusive self-tagging channels: o Kaon+n (n<4, at most 2 0) o 0. 6 Ge. V<m(Xs)<2. 3 Ge. V: 48% of the total rate • Signal and background are extracted with a fit of m. ES Whole sample High-purity sample: one high-momentum lepton in rest of event Whole sample SM prediction: hep-ex/0403035 5 Aprile 2004 Matteo Rama Acp up to 10% with contributions to the loop beyond SM 27

B K*g: CP and isospin asymmetry • Reconstruct B 0 K*0 g [K*0 K+ -, K 0 s 0] and B+ K*+g [K*+ K+ 0, K 0 s +] • Extract signal yield through a fit on m. ES, E, and measure CP and isospin asymmetries • SM predictions for the asymmetries: • Measured asymmetries: consistent with SM prediction 5 Aprile 2004 Matteo Rama 28

B X s l +l • The process is allowed in SM via electroweak penguin and Wbox diagrams non-SM physics in these loops would contribute at the same order as the SM • Xs = 1 kaon + at most 2 , no more than one 0 • SM predictions for branching fraction: • Measured branching fraction: 5 Aprile 2004 Matteo Rama 29

Measurement of |Vcb| (leptonic moments) (hadronic moments) Vcb (Vub) (u) ( , …) 5 Aprile 2004 Matteo Rama 30

Measurement of |Vcb| from semileptonic B decays • semileptonic B decays provide best method for determination of |Vcb| and |Vub| ØTransition matrix element factorizes: o o leptonic current (W l ) (easy) hadronic current (b W c) (QCD, hadronic uncertainties) • Theoretical framework: Heavy Quark Expansions (HQEs) relate Br(B Xcl ) with |Vcb| and 6 parameters (mb(m), mc(m) and 4 non-perturbative parameters). determine Br(B Xcl ), |Vcb| and the parameters from a fit to the moments of the hadronic-mass and electron-energy distributions: • Select B Xe decays for meas. of electron-energy moments hep-ex/0403031 sub. to PRD • Select B Xl decays for meas. of hadronic-mass moments hep-ex/0403030 sub. to PRD 5 Aprile 2004 Matteo Rama 31

Combined fit to El and MX moments preliminary fit of the moments 5 Aprile 2004 Matteo Rama Moriond EW 04 32

Study of new particles and measurement of rare decays B charmless isoscalar pairs B (‘)K*, (‘) 0, 0 B a 0(K, K 0, ) 5 Aprile 2004 Matteo Rama 33

B- J/YK- + -, B- X(3872)KMoriond EW 04 • Confirmed the observation of X(3872) J/Y + - by Belle and CDF Br(B- J/YK-p+p-)= (11. 6 0. 7 0. 9) 10 -4 M(J/Ypp) m. X= 3873. 4 1. 4 Me. V/c 2 Br(B- X(3872)K-) Br(X J/Yp+p-) = (1. 28 0. 41) 10 -5 hc Y(2 S) X(3872) In addition, limits set on hc J/Y + - and on B- J/YD 0 -: Br(B- hc. K-) Br(hc J/Y + -) = (1. 28 0. 41) 10 -5 Br(B- J/YD 0 -)< 5. 2 10 -5 5 Aprile 2004 90% CL Matteo Rama 34

Discovery of Ds. J • During 2003 Ba. Bar discovered a new narrow Ds+ 0 resonance near 2. 32 Ge. V/c 2 and observed a second new Ds*+ 0 resonance near 2. 46 Ge. V/c 2. observed in decays: • most likely spin-parity assignement are: Further investigate the properties of Ds. J by studying the B D(*)Ds. J decays 5 Aprile 2004 Matteo Rama 35

Study of B Ds. JD(*) • Production analyzed both in neutral Moriond EW 04 and in charged B decays: where • angular analysis of Ds. J(2458) Dsg qh=angle between Ds and B momentum in Ds. J rest frame E (Ge. V) m(Ds. J) (Ge. V/c 2) J=2 J=1 c 2 fit of cosqh dist. favors J=1 wrt J=2 (J=0 is ruled out by P and ang. mom. conservation) preliminary 5 Aprile 2004 cosqh Matteo Rama cosqh 36

B (‘)K*, (‘) 0, 0 hep-ex/0403025 sub to PRD PRL 91, 161801 2003 PRL 92, 061801 2004 New 5 Aprile 2004 Matteo Rama 37

Search for B 0 decays to charmless isoscalar meson pairs hep-ex/0403046 sub. to PRL CLEO 5 Aprile 2004 Matteo Rama 38

B to final states with scalar a 0, mesons PRELIMINARY B is Br(B a 0 X) B(a 0 p) • • Unbinned ML fits (89 M BB events); a 0 p, gg 3 p Only previous search from BABAR (20 fb-1, Lep. Pho 2001) o Found 3. 7 evidence for B 0 a 0(980)- o Do not confirm that with substantially improved sensitivity n Studies indicate the previous result was a statistical fluctuation o No evidence for signals in the other 5 charge states 5 Aprile 2004 Matteo Rama 39

Contribution from italian institutions BA: 3 -body D, D 0, Ds. J*(2317)+, Ds. J(2460)+ decays (Dalitz) FE: Vub (recoil), dilepton mixing LNF: B Ds. Ds*, Ds , ISR, B D*D* GE: B (ccbar)( hadrons), B (ccbar)( c g)K, t mg MI: B K/ , Ks, ’K/ , sin(2 b), B ’Ks, ’KL, B ’ , B , , , ’ ’, ’ NA: Vcb (B 0 D*l ), B J/ K, J/ , B t , semilep. B decays PD: Vcb (B 0 D*l ), Vub, B lifetime/mixing, sin(2 a), B K , , t mg PG: B Ds. Ds*, Ds , CPV(tag side), t mg PI: sin 2 b/CP/CPT, t lifetime, b sg(inclusive), B D 0(CP)K, D 0(CP)K 0 , B D*l (T), B D(dalitz)K RM 1: sin(2 b+g), B Ds /K, DKs, Vub, B K 0, sin(2 a), B (0), pp, b sg(recoil), dilepton mix, B D(dalitz)K, B K*g (t. d. ), X(3872), B K 0, , t mg TO: B Ks 0, Ks. K, B 0 , 0 0, 0 K, K 0 K 0, Vub (recoil) TS: B D*D*, Vcb (B 0 D*l ), B D(*)Ds. J 5 Aprile 2004 Matteo Rama 40

Conclusions • The physics program of the B factories covers a very wide spectrum of heavy flavors measurements • In this presentation a selection of Ba. Bar results were presented, a lot of them have been shown for the first time at the recent Winter conferences. The Ba. Bar physics program is much richer (also includes charm and tau physics) • The increase in integrated luminosity is significantly extending the physics reach of the B factories, both for precision measurement of the Unitarity Triangle and for search of new physics in rare decays Looking forward to Summer 2004 (more than 200 million BB expected) 5 Aprile 2004 Matteo Rama 41

BACKUP 5 Aprile 2004 Matteo Rama 42

B 0 + -: physics interest • Same scenario as B 0 : proceeds mainly through b uud tree diagram + penguin contributions. asymmetry sensitive to sin 2 aeff • P VV decay: 3 helicity states. From angular analysis: longitudinal polarization is dominant CP-even final state • Branching fraction relatively high ( 30 10 -6 [Br(B 0 ) 5 10 -6]) • Penguin contamination expected to be small (can be bound experimentally) Good candidate for the measurement of sin 2 a 5 Aprile 2004 Matteo Rama 43

5 Aprile 2004 Matteo Rama 44

B K*0( K 0 s 0)g: time-dependent CP asymmetry • Final state K 0 s 0 g accessible to both B 0 and B 0 look for CP asymmetry in the interference between decay and mixing • In the limit of massless s quark, the photons in final states are completely polarized with opposite helicities for B and Bbar. In the SM one expects: the measurement of S and C may give hints of new physics 5 Aprile 2004 Matteo Rama 45

Measurement of |Vcb| from semileptonic B decays • semileptonic B decays provide best method for determination of |Vcb| and |Vub| ØTransition matrix element factorizes: leptonic current (W l ) (easy) o hadronic current (b W c) (QCD, hadronic uncertainties) o • Theoretical framework: Heavy Quark Expansions (HQEs) relate the semileptonic inclusive decay width with |Vcb|. Such relation: contains b- and c- quark masses: mb(m), mc(m) 2 2 3 3 o 4 non-perturbative parameters: m , mg , D , LS o • problem: large uncertainties in mb(m), mc(m), m 2, mg 2, D 3, LS 3 • solution: determine Br(B Xcl ), |Vcb| and the parameters (mb(m), mc(m), m 2, mg 2, D 3, LS 3) from a fit to the moments of the hadronicmass and electron-energy distributions: lepton energy spectrum 5 Aprile 2004 mass of hadronic system Matteo Rama 46

Measurement of the moments • Selecting B Xe decays for meas. of electron-energy moments: identify Bbbar events by observing a high energy electron: p*>1. 4 Ge. V/c o look for oppositely charged electron from other B (signal electron) o remove electron pairs back-to-back (most likely to come from same B); veto electrons from J/Y e+eo • Selecting B Xl decays for meas. of hadronic-mass moments: fully reconstruct hadronic B decay o look for semileptonic decay of the other B (require the presence of an electron or muon) 2 o MX determined from kinematic fit requiring: p =0, 4 -momentum conservation, m. B (MX) 350 Me. V/c o 5 Aprile 2004 Matteo Rama 47

Combined fit to El and MX moments • |Vcb|: • Br(B Xce , El>E 0): • ith central El moment for El>E 0: • ith MX momend and for El>E 0: fit of the moments 5 Aprile 2004 Matteo Rama hep-ex/0403031 48

Measurement of b: status & perspectives • CP violation in B decays has been observed and sin 2 b is measured with good precision using the decays: o J/Y K 0 s o Y(2 S)K 0 s o cc 1 K 0 s o c K 0 s o J/YK*0(K*0 K 0 s 0) o J/YK 0 L sin 2 b=0. 741 0. 067 0. 034 (Ba. Bar, 89 M BB) www. utfit. org theory error on sin 2 b with J/YK 0 s <1% still room for improvement with higher data samples • other B decays are sensitive to sin 2 b: K 0 s , K 0 s 0, etc. . . mostly useful to search NP (see later slides) plan to update the sin 2 measurement on >200 M BB this Summer 5 Aprile 2004 Matteo Rama 49