Pakhlov Pavel ITEP Moscow University of Lausanne 11122001

Pakhlov Pavel (ITEP, Moscow) University of Lausanne 11/12/2001 • Why B physics is still interesting • Belle detector • Measurement of sin 2 • Rare B decays • Future plans

B-physics • Test of the Standard Model (SM) mechanisms • hadronic models, CKM, etc… • Measurement of the fundamental parameters of SM • exact values can be a hint for new phenomenology • Search for physics beyond SM • large b-quark mass • SM decays suppression (Vcb<<1) • large contribution from loop and box diagrams Pakhlov Pavel (ITEP, Moscow) 2

Why CP is important • Test CKM mechanism as a single source of CP violation: • During 35 years CP violation measured only in K system. CKM theory single (free) parameter; Experiment single measurement . • Measurement of CKM matrix elements: • sin 2 : constrain on CKM matrix elements without QCD uncertainties. • sin 2 from B DK, xd/xs, B : free of model uncertainties, but requires much more statistics. • New physics: • Need overfull constrain on CKM parameters (better if without QCD uncertainties) to test the SM • … or to observe very large discrepancy Pakhlov Pavel (ITEP, Moscow) 3

CPV in B mesons at e+e- colliders • B 0 are produced and remain in coherent p-state until one of them decays. • If the first B decays to flavor specific mode, the state of the other B is orthogonal at this time. • Then the second B propagates (oscillating). • If it decays to a CP-final state: two contributions from B and B interfere. • If the first B decays to the CP final state and the second to a specific flavor state – the interference results into opposite sign of CP asymmetry. The time integrated asymmetry vanishes! Pakhlov Pavel (ITEP, Moscow) 4

Mixing-induced CP asymmetry Pakhlov Pavel (ITEP, Moscow) 5

The Belle collaboration ~300 authors from 50 institutions (13 countries) Group from the University of Lausanne joined Belle recently Pakhlov Pavel (ITEP, Moscow) 6

KEKB asymmetric e+e- collider • Two separate rings • e+ : 3. 5 Ge. V • e- : 8. 0 Ge. V • Ecm : 10. 58 Ge. V • c 200 m • Luminosity: • • design: 1034 cm-2 s-1 achieved: 5. 46 x 1033 cm-2 s-1 • Crossing angle 22 mrad • Beam size: • x=100 m • y=3 m Pakhlov Pavel (ITEP, Moscow) 7

KEKB/Belle luminosity summary May 1999 - December 2001: accumulated: 44. 3 /fb analyzed: 32. 8 /fb KEKB records on the luminosity peak: 5. 466 × 1033 /cm 2/sec (World record) per day: 282. 5 /pb (> whole ARGUS statistics) per month: 6120. /pb Pakhlov Pavel (ITEP, Moscow) 8

The Belle detector Pakhlov Pavel (ITEP, Moscow) 9

B-meson reconstruction • Reconstruct all low background (cc)K 0 CP-final states: Pakhlov Pavel (ITEP, Moscow) 10

B 0 J/ KS J/ + - 10 Me. V/c 2 KS + 4 Me. V/c 2 J/ e+e- 11 Me. V/c 2 Pakhlov Pavel (ITEP, Moscow) 11

B 0 J/ KS Energy difference: E=EJ/ KS-Ecm/2 Beam-constrained mass: Mbc= (Ecm/2)2 - p. J/ KS 2 457 events ~3% bkgd Pakhlov Pavel (ITEP, Moscow) 12

All full reconstructed modes Decay mode: signal bkgd J/ KS, KS + - 457 11. 9 J/ KS, KS 0 0 76 9. 4 (2 S)KS, (2 S) l+l- 39 1. 2 (2 S)KS, (2 S) J/ + - 46 2. 1 c 1 KS, c 1 J/ 24 2. 4 c KS, c KSK 23 11. 3 c KS, c K+K- 0 41 13. 6 747 58 41 6. 7 All CP=-1 modes J/ K*0, K*0 KS 0 Pakhlov Pavel (ITEP, Moscow) 13

B 0 J/ KL • KL momentum is not measured, only direction is known • Reconstruct J/ l+l • Assume M(J/ KL)=MB to calculate P(KL) • Remove full reconstructed J/ K, J/ K*. • Cut on B-candidate likelihood based on kinematics and event shape. • Look at P(J/ KL) Pakhlov Pavel (ITEP, Moscow) 14

B 0 J/ KL • Main background from B J/ X (quasy two-body) – well understood: use MC. • Some backgrounds are CP-finale states: special care when CP-fit. • Special case: J/ K*0, K*0 KL 0 - mixture =-1 and =+1: from angular analysis B J/ K* 569 events= 346 signal+ 223 bkgd Pakhlov Pavel (ITEP, Moscow) 15

Flavor tagging • Use tracks from the accompanying B specific flavor • Inclusive leptons • High momentum leptons b c l- • Intermediate momentum leptons s l+ • Inclusive hadrons • High momentum pions B 0 D*- + (X), D- + (X) • Intermediate momentum kaons K+ X • Low momentum pions D 0 • Take into account correlations Pakhlov Pavel (ITEP, Moscow) 16

Multi-dimensional tagging likelihood • Each class of tagging / each specific tagging particle have different tagging purity. If sum all events with different purity loose accuracy. • Divide all events into several categories depending on tagging purities, then average over independent measurements: • Calculate probability for each track to belong to one of the flavor tagging class. • Combine information about all tracks into likelihood for event to be B 0 or B 0. • Divide the whole likelihood range into 6 bins of different purities. • Extract dilution factor for each bin from the data. Use specific flavor channels: B 0 D(*)- + , B 0 D(*)-l+ Pakhlov Pavel (ITEP, Moscow) 17

Determination of wrong tag fraction • A( t)measured~(1 -2 )sin( md t); =Nwrong/N. • For sin(2 ) we need to know ! • Get from B 0 B 0 mixing amplitude ~(1 -2 )cos( md t); • Fit to the data with free (r). Efficiency >99% effective=27. 0 1. 2% Pakhlov Pavel (ITEP, Moscow) 18

Vertex reconstruction • CP-side vertexing: • use prompt tracks from J/ , (2 S), c • Reject poorly fit vertices • z 75 m • Tagging B vertexing: • Use well fit tracks • Iterative procedure: fit discard worst track • z 140 m • Efficiency: 87%, • t 1. 5 ps • not-Gaussian tails 3%, Pakhlov Pavel (ITEP, Moscow) 1137 events are used for CP fit 19

Check vertex resolution function B D(*)-l+ B =1. 55 0. 02 ps B+ =1. 64 0. 03 ps 0 Pakhlov Pavel (ITEP, Moscow) 20

CP-fit • Each event has individual sensitivity to sin 2 (depending on signal purity, tagging dilution, z and vertex fit accuracy, etc…) • For each event calculate its likelihood as a function of sin 2 : Resolution function signal fraction wrong tag fraction PDG free parameter • Calculate sin 2 which maximize the total likelihood Li Pakhlov Pavel (ITEP, Moscow) 21

sin 2 results sin 2 =0. 99 0. 14 0. 06 Pakhlov Pavel (ITEP, Moscow) 22

Cross-checks Check asymmetries in Non. CP sample. “sin 2 ”=0. 05 0. 04 Pakhlov Pavel (ITEP, Moscow) Mode dependencies: 23

Compare with other experiments Pakhlov Pavel (ITEP, Moscow) 24

Rare B-decays • New level of sensitivity to the rare Bdecays: • • Cabibbo-suppressed decays: B D(*)K+, D*+D(*)Color-suppressed decays: B 0 D(*)0 X 0 Hadronic penguin decays: B+ K+K+K-, K+ + Electro-weak penguin decays: B Kl+l- • To be used in future for CP violation study Pakhlov Pavel (ITEP, Moscow) 25

Cabibbo-suppressed decays • B D(*)K+ (10. 4 /fb): • Large background from Cabibbo-allowed is suppressed by PID • Remaining background disentangled by E • Branching ratios: Br(DK -)/BR(D -)~0. 068 -0. 079 • B- D(*)0 K- (D 0 CP) to be used in future for measuring angle Pakhlov Pavel (ITEP, Moscow) 26

Color-suppressed Decays D 0 0 Pakhlov Pavel D*0 0 (ITEP, Moscow) B D(*)0 X 0 have been observed for the first time: Mode Br (X 10 -4) D 0 0 3. 1 0. 4 0. 5 D*0 0 2. 7 0. 8 0. 6 D 0 0 1. 4 0. 5 0. 3 D*0 0 2. 0 0. 9 0. 4 D 0 0 1. 8 0. 5 0. 4 D*0 0 3. 1 1. 3 0. 8 27

Electroweak penguin decays • FCNC are forbidden at tree level, but loop or box induced. • Sensitive to the New Physics. • B K + - observed for the first time Pakhlov Pavel (ITEP, Moscow) 28

Future plans • Nearest Belle upgrade – summer 2002: reduce beampipe 2 cm 1. 5 cm; new 4 layers silicon detector: • Better vertex resolution • Higher efficiency for slow track reconstruction • e+e- machines competitive with LHCB and BTe. V if L~1035. Super. KEKB is under investigation Pakhlov Pavel (ITEP, Moscow) 29

Summary • Belle observed large CP-violation in B decays. sin 2 =0. 99 0. 14 0. 06 • Many new rare B decays observed for the first time. • KEKB/Belle continue successful operation. • Many new interesting results are expected in future. • KEKB/Belle plan to compete with LHC in Bphysics after LHC starts. Pakhlov Pavel (ITEP, Moscow) 30