BaBar: Risultati recenti e prospettive Fernando Ferroni Universita’ di Roma “La Sapienza” & I.N.F.N. Roma1

BABAR Collaboration China [1/5] Inst. of High Energy Physics, Beijing Germany [3/23] Ruhr U Bochum TU Dresden U Rostock France[5/51] LAPP, Annecy LAL Orsay LPNHE des Universités Paris 6/7 Ecole Polytechnique CEA, DAPNIA, CE-Saclay United Kingdom [10/71] U of Birmingham U of Bristol Brunel University U of Edinburgh U of Liverpool Imperial College Queen Mary & Westfield College Royal Holloway, University of London U of Manchester Rutherford Appleton Laboratory Italy [12/89] INFN Bari INFN Ferrara INFN Frascati INFN Genova INFN Milano INFN Napoli Canada [4/15] U of British Columbia McGill U U de Montréal U of Victoria INFN Padova INFN Pavia INFN Pisa INFN Roma INFN Torino INFN Trieste Norway [1/2] U of Bergen Russia [1/7] Budker Inst., Novosibirsk USA [36/253] Caltech, Pasadena UC, Irvine UC, Los Angeles UC, San Diego UC, Santa Barbara UC, Santa Cruz U of Cincinnati U of Colorado Colorado State Elon College Florida A&M U of Iowa Iowa State U LBNL LLNL U of Louisville U of Maryland U of Massachusets MIT U of Mississippi Mount Holyoke College Northern Kentucky U U of Notre Dame ORNL/Y-12 U of Oregon U of Pennsylvania Prairie View A&M Princeton SLAC U of South Carolina Stanford U U of Tennessee U of Texas at Dallas Vanderbilt U of Wisconsin Yale U

PEPII

BaBar SVT: z resolution ~70 microns Tracking:  (p T )/p T = 0.13%  p T  0.45% DIRC: K-  separation > 3.4  for P<3.5GeV EMC:  E /E = 1.33%  E -1/4  2.1%

PEPII & BaBar Physics Motivation: CP in B Results: Mixing & Lifetimes sin 2b Rare decays Perspectives Outline

Origin of masses Remote energy scale (Gravity) CP Violation and our universe Particle physics in new millennium

Needed for matter-antimatter asymmetry Standard Model CP-Violation (CKM) thought to be insufficient to explain universe asymmetry 37 years of intense experimental and theoretical effort of background Why CP violation ?

CP Violation in SM SM with three generation accommodates CP violation through phase in CKM matrix SM predicts a variety of CP violating asymmetries in the B-system, some of which can be cleanly interpreted in terms of CKM matrix elements

The Triangle B d  D*  CP

The Unitarity Triangle The sides are determined by measurements of the magnitudes of CKM elements CP asymmetries to f CP measures angles of triangle, in some cases with little or no theoretical ambiguities Goal of the B-physics program is to overconstrain triangle, critically test CKM structure of SM

CP measurement Reconstruct a CP eigenstate Flavour tag with other B Measure  z --->  t = t CP - t tag Fit time evolution

B decay topology  c  /2  c  250   =0.56 Y(4S) Measurement of  z Reconstruction of the CP eigenstate Tag of the other B B0 Lifetime, Mixing, CP

Smearing of an asimmetry

PEPII-BaBar Operations Design : 3.0 nb -1 /s 135 pb -1 /d ~0.80 fb -1 /w ~ 3.3 fb -1 /m Achieved : Data from run 20.7 fb -1 on-resonance N(  (4S)) = ±0.36 million 2.6 fb -1 off-resonance

PEPII-BaBar Operations

Interaction region Permanent magnets inside the support tube

J/  Ks Event at BaBar B 0  J/  K s J/  ->     K s ->    

DIRC: Detection of Internally Reflected Cherenkov light 144 quartz bars (1.7 cm thick) PMT in 6 m 3 of purified water Total space: 8 cm (0.14 X 0 ) e-e- e+e+ New design for a Cherenkov detector

K/  separation Pion-Kaon separation at high momenta

Mixing and sin2  Common wrong tag fractions and resolution function parameters can be determined by a large B flav sample

B flav sample B 0  D (*) -  , D (*) -  , D (*) - a 1 +, J/  K* 0 B   D (*)0  , J/  K -,  S  K -  E=E* B -  s /2  ~15 MeV m ES =  (s/4 - p* B 2 )  ~3MeV

B reconstruction Y(4S) -> BB  m ES signal m ES sideband energy difference  E sideband energy substituted (constrained) mass one more pion...

B flav sample 6368 evts Purity ~ 84% 7645 evts Purity ~ 86%

Run I Data Set 23M BB pairs recorded 3 fb -1 of continuum

CP sample (K s modes) J/  K s (  +  - ) 259 (purity 98%) J/  K s (  0  0 ) 50 (84%)  (2s)K s (  +  - ) 55 (97%) J/   l l  (2S)  l l  J/ 

Final CP sample of K 0 s modes

CP sample (K L modes) Reconstructed with EMC Reconstructed with IFR 92 signal Purity =40% 108 signal Purity =51% Neutral clusters not consistent with noise,  or  0 are considered as K L candidates B mass constraint is imposed

Tagging

Vertexing Use per event error and parametrize the resolution function with scaling factors  t  z/

Lifetimes  B 0 =   ps  B + =   ps  B + /  B 0 =   PDG 1.55± ± ±0.03

Mixing adronico/leptonico

Mixing : compilation

Fitting procedure Mixing and sin2b measurements are done with the same strategy: do a global fit to all the events that can carry information Mixing : tagged flavour eigenstates sin2  : tagged flavour and CP eigenstates Extract as many parameters as possible from data Biggest correlation with sin2  7.6%

Log Likelihood vs sin 2  KLKL KSKS Total  sin 2  = 0.34  0.20(stat)  0.05(sys)

Systematics

Asymmetries J/  K L J/  K S sin2  0.25  0.22 (stat) sin2  0.87  0.51 (stat)

Asymmetries Total CP tagged sample : 529 events 164 of background mainly in J/  K L

sin2  by decay mode

sin2  by tagging category (K s only)

Compilation of all known results

Comparison to predictions of non-CP  K  |Vub/Vcb|,  M d,  M s sin 2 

New fuel for sin2  B  D  D  ) The Standard Model predicts time-dependent CP-violating asymmetries in the decays B 0  D  D  proportional to sin2  D  Reconstruction D   D 0  , D   0 D 0  K   , K     0, K       , K S     D   K     , K S  , K  K   

New fuel for sin2  Beware of this one (non flying birds !)

B  D  D , Signal Nsignal = 31.8 Events NBkg = 6.2 Events Estimated from sideband in  E and M ES Br (B 0  D  D  ) = (8.0 ± 1.6 (stat) ± 1.2 (syst))  (But angular analysis to do CP)

Charmless two-body B decays Direct CP search Time-dependent CP asymmetry      sin(2  ),  0  sin(2  ) Theoretical model validation b d d u d,s b d u u d V ub V ud,s V td,s V tb  +, K + -- -- t W W B0B0 Cabibbo-suppressed tree diagrams penguin diagrams B0B0 u

Charmless decays             (h + h - )         (   h + )         (   h + )             K 0 as K S to  +  -   K + K - K* +  K +  0,K S  + Fully reconstructed decays Efficiency (with daughter BF)  0  0,h +  0,h +  0,h + h: 10-45%    ,    3-20%

Composite particles K S mass  4.3 MeV   mass  8.5 MeV ~ 3 GeV  mass

Background suppression Jet-like topology cos  S signal background cos(  S ) cosine of angle between sphericity axes of B and rest of the event Background dominated by continuum qqbar production (u,d,s,c) 

Background suppression Fisher discriminant signal h  h   E sideband ( dots ) continuum h  h  MC ( his ) ( dots ) B -  D 0   ( his )  h  h  MC background Linear combination of event-shape variables (cones)

Likelihood analysis Use an extended global likelihood fit to extract different signal yields (N S ) in each topology m ES,  E, Fisher(cos  Th ), (  mass),  C Independent control sample to study Probability Density Function for both BKG and SIG Gaussian   2.6 MeV B -  D o  - ARGUS function h+h-  E sideband

More PDFs  E with pion hypothesis             signal MC GeV Background udsc

More PDFs (Cherenkov)  C –  C  Control sample: D* +  D 0       

Results

Systematics Variation in % Vary PDF parameters alternative PDF

Results Likelihood visualization onto m ES

Predicting  or disproving models B.Beneke et al. input  SM  CLEO/Belle/BaBar (my) average: /- 0.06

Radiative decays (B  K  0  CKM matrix elements V td, V ts No considerable CP asymmetry expected in Standard Model (< 1%) Sensitive to New Physics (SUSY,W   H  

B 0  K  0 , Signal and Backgrounds B0 K0B0 K0 e  e   qq  e  e   qq  X  0

B  K  0 , Signal Estimation Yield: N signal = ± 13.1 events Br (B 0  K  0  ± 0.41 (stat) ± 0.27(syst))  M ES Distribution -200 MeV <  E < 100 MeV A CP =  (stat)  (syst)

The near future Expect to have 40fb -1 more by the end of the run II

The near future: recoil physics In 20 fb-1 (present stat ~ 5 times more by end of 2002): 12 K fully reconstructed hadronic B mesons 40 K semi-exclusive B (maybe one/two missing particles) 20 K semi-leptonic B (one missing) Will be able to reconstruct single B in modes with BF ~

The immediate future The usual painful start-up however better than last year

while the competitor….. Belle is doing very well

The near future for sin2  BaBar will collect ~0.5 ab -1 We will know sin2 at the ~0.02 level by 2005

The far future It could be a new machine at slightly higher energy [Y(5S)] and asymmetry and considerably higher luminosity (10 36 cm -2 s -1 ) You’re all invited !