BABAR Status & Physics Reach in Coming Years

Transcription

1 BABAR Status & Physics Reach in Coming Years Gautier Hamel de Monchenault CEA-Saclay DAPNIA/SPP on behalf of the BABAR Collaboration CERN, 14 February 2006

2 Status of PEP-2 and BABAR

3 PEP-2 and BABAR at SLAC PEP-2 Asymmetric B Factory Started construction in 1994 Completed in 1999 Reached design luminosity in Luminosity records PEP-2 / BABAR at SLAC design peak: cm 2 s 1 best peak: cm 2 s 1 total recorded: 319 fb 1 best month: 16 fb 1 ~230 million BB pairs used for most analyses 9 GeV e on 3.1 GeV e + SLAC Accelerator Complex shut down from October 2004 to April 2005 as a consequence of a severe electrical accident PEP-2/BABAR resumed operation in April 2005 (additional ~76 fb -1 recorded since then)

4 The BABAR Experiment EMC DIRC DCH SVT

5 Projections to Summer 2008 Today Toward 2008 Summer 2006 : Added integrated luminosities of BABAR and Belle ~1000 fb -1 = 1 ab -1 (1 inverse attobarn) PEP-2/BABAR are set to run between 2006 and 2008 with the goal of reaching a data set of order 1 ab -1 Of order 1 ab -1 for BABAR by 2008

6 Flavor Physics & CP Violation

7 The Kobayashi-Maskawa Model 1972, M. Kobayashi & T. Maskawa : introduction of CP violation in electroweak theory Origin of CP violation : the CKM matrix ( «quark flavor mixing matrix» ) 3 families A single CP-violating parameter transitions between quarkflavor and mass eigenstates Elements of the CKM matrix: «couplings» between Down-type quarks and Up-type quarks

8 d s b u V = c t magnitudes d s b phases d s b u c t u c t

9 The Unitarity Triangle V is a complex unitary matrix: determined by 4 real parameters sine of Cabibbo angle λ 0.22 b c transition (in units of λ 2 ) A coordinates of the apex of the Unitarity Triangle ~24 o Unitarity Triangle ~62 o

10 Ways to Look for New Physics measure γ measure α Im (,0) Ru γ ( ρ,η) α UT Rt β 0 ( 1,0 ) improve UT side measurements Re measure sin2β in decay modes sensitive to different short-distance physics

11 Physics at the Y(4S)

12 The Y(4S) Region The cleanest way to produce B mesons collisions around production of pairs with a cross section of ~1nb over a continuum of ~3 nb & proper time difference Quantum coherence antisymmetric wave function : one and one flavor tagging required for CP measurements measurement of : boost the CoM frame asymmetric-energy beams

13 Kinematics at the Y(4S) Reconstruction of a B candidate (from tracks and clusters in the event) Lab frame Boost CoM frame The beam-energy substituted mass with The energy difference (half-com energy) MeV two largely independent analysis variables signal region sidebands GeV/c 2 dominated by beam energy spread dominated by energy resolution

14 Time-Dependent Analyses

15 Differential Event Rates final state f interference parameter (observable) define C and S coefficients: and (usual phase convention) mixing disintegration differential event rate 2 special cases f is a CP eigenstate: f is flavor specific: and and

16 Foundations of Time Measurements event-by-event vertex errors t resolution function shape from signal MC, parameters from data efficiency ~ 97% tagging effective efficiency 30% measured on data ~1.5 ps ( t meas - t true )/σ( t) σ( z) [cm] Flavor control sample: events CP sample for sin2β: events flavor sample m ES [GeV/c 2 ] B 0 tag B 0 tag

17 Flavor Oscillations mixed asymmetry mixed/unmixed unmixed unmixed maximum mixing ½period ~ 6 ps ~ 4 B-meson lifetimes

18 Mixing Measurements LEP Tevatron B-Factories B-meson lifetime and flavor-oscillation frequency TD techniques developed at LEP & Tevatron average dominated by B-factories measurements B-Meson lifetimes (average 05) B 0 : ps B + : ps ratio :

19 Measurement of β Im (,0) Ru γ ( ρ,η) α UT Rt β 0 ( 1,0 ) Re and friends

20 A Precision Measurement PRL 94, (2005), (hep-ex/ )

21 latest evolution of the measurement non-sm solution disfavored: sensitive to cos2β (BABAR 04: angular analysis + study of S/P-wave interference) 227M 386M direct extraction of 2β (Belle 05: β [-30,62 95% C.L.)

22 sin2β at High Luminosity Current analyses Clean modes, Lepton tags Current analyses Clean modes, Lepton tags Integrated L (fb 1 ) Statistical error Systematic error Total error today

23 Measurements of Angle α Im (,0) Ru γ ( ρ,η) α UT Rt β 0 ( 1,0 ) Re

24 Charmless 2-Body B ππ : historically (perhaps ultimately?) the best way to measure sin2 α if Tree amplitudes dominate if Gluonic Penguin amplitude contributes need to estimate e.g. isospin analysis (Gronau-London) B ππ B Kπ

25 Penguins at Work (likelihood projections) Observation of Direct CP Violation entries / 10 MeV 467±33 ππ 1606±51 Kπ 1606= Spectacular manifestation of tree-penguin interference One can not ignore penguin amplitudes in B ππ and (a 4.2 sigma effect)

26 CP results in ππ evolution size of samples indicated in million BB pairs Belle and BABAR in marginal agreement (2.3σ) Belle observes significant direct CP violation in this mode while BABAR result is consistent with no CP violation

27 Worst Case Scenario for α? Observation of B π 0 π 0 (5 sigma significance) π 0 π 0 rate much too large to obtain a useful Grossman-Quinn limit 35 o (90% C.L) much too small for a precise direct-cp measurement New hope for α : combination of B ρ + ρ and B ρπ modes! poor constraints on angle α from full isospin analysis 2005 projection 2 ab 1 Issues to be resolved with more data direct CP Violation in π + π? π 0 π 0 : factor ~2 discrepancy with Belle?

28 Why is ρρ so Promising for α? the final state is a mixture of CP-even and CP-odd in principle this complicates the isospin analysis BUT the data show that CP-even (longitudinal polarization) dominates small rate of B ρ 0 ρ 0 indicates much smaller penguin pollution while π 0 π 0 is of order 30% of π + π ρ 0 ρ 0 is smaller than 4% of ρ + ρ (at 90%CL) BABAR, PRL 94, (2005) with reasonable theoretical assumptions this mode provides the present best constraints on α α=100 ±13 Br( B ρ 0 ρ 0 ) < 1.1x10-6 (90% CL) 79 < α 90% CL PRL 95, (2005)

29 The B 3π Analysis The three-pion final state is dominated by the transitions through a ρ meson Dalitz plot interfering contributions from ρ + π, π + ρ (and ρ 0 π 0 ) full time-dependent Dalitz analysis (Snyder-Quinn method) ρ from W A 3.4σ effect of direct CPV which is not expected (e.g. from QCD factorization) BW phase variations break degeneracy in solutions Already interesting constraints on angle α and an evidence for direct CPV α = ( 113 ± + 27 o 17 6) ρ from spectator quark

30 The α Program is just Starting! Constraints from, and CKM Constraints BABAR & Belle combined With more statistics: observe B ρ 0 ρ 0 improve S and C in B ρρ confirm that mirror solution in B ρρ is disfavored by Dalitz analysis in B ρπ investigate direct CPV effect in B ρπ projection 2 ab 1 3 scenarios for ρ 0 ρ 0 central +1σ 1σ

31 Constraints on α in the ( ρ, η ) Plane

32 Measurements of Angle γ Im (,0) Ru γ ( ρ,η) α UT Rt β 0 ( 1,0 ) Re

33 Methods to Measure Angle γ Basic Idea use interference between tree decays Cabibbo-suppressed (b c ) B + anti-d 0 K + and CKM- and color-suppressed (b u ) B + D 0 K +, where the D 0 and the anti-d 0 decay to a common final state only tree diagrams: no issue with new physics in loops interference parameter color factor GWL (Gronau-Wyler-London) ADS (Atwood-Dunietz-Soni) GGSZ (Giri-Grossman-Soffer-Zupan) is a CP eigensate is doubly-cabibbo suppressed (interference in Dalitz plot)

34 GWL & ADS, First Analyses Gronau-Wyler-London (GWL) Method B D CP K small interference sensitivity to γ no sensitivity to r B CP + + K K + π π 75 ± ± 7 CP K π 0 76 ± 13 S R Atwood-Dunietz-Soni (ADS) Method larger interference unknown D relative strong phase sensitivity to r B Br( D Br( D [K [K π π ]K ]K + c.c.) + c.c.) ( )0 + ( ) ( )2 K π = ~ r ( )0 + B no observation yet set limits r 2 B < 0.23 (90 % C.L) r 2 B < 0.21 (90 % C.L) from D lim it 0 + [K π ] K on from D lim it on ] K 0 + [K π

35 Analysis of B D ( )0 0 + [ K S π π ] K Giri-Grossman-Soffer-Zupan (GGSZ) method exploit interference pattern in Dalitz plot in principle sensitivity to both γ and r B a two-fold ambiguity remains in the extraction of γ D 0 K 261 ±19 schematic view of the interference 2 m m 2 m ± 2 A m 2 = i( γ± δ) + rb e 2 m ± 2 m m

36 Dalitz Amplitudes from the D Sample m 2 (GeV 2 ) CA K*(892) m + 2 (GeV 2 ) m + 2 (GeV 2 ) ρ (770) DCS K*(892) m 2 (GeV 2 ) m 0 2 (GeV 2 )

37 Dalitz Plots and Projections m 2 (GeV 2 ) + 0 B "D " K + m + 2 m 2 sensitivity on γ across the Dalitz Plot m + 2 (GeV 2 ) m+ 2 (GeV 2 ) 0 B "D " K m 2 m + 2 DCS K*(892) Large statistics is needed for this method! m 2 (GeV 2 )

38 γ from B DK (all methods) Direct constraints from all modes Indirect CKM constraints

39 Prospects on γ importance of the value of r B on the error on gamma, illustrated here for the GGSZ method in BABAR: error on γ (deg) GGSZ GGSZ + GLW GGSZ + GLW + ADS r B =0.1 error as a function of r B projected systematic error luminosity (ab -1 ) error as a function of integrated luminosity for r B =0.1

40 Measurements of UT Sides Im (,0) Ru γ ( ρ,η) α UT Rt β 0 ( 1,0 ) Re

41 Measurement of V ub V ub : a key CKM constraint (only Trees, no NP) dependence on theory predictions for kinematical extrapolations inclusive : extract m b and QCD parameters from B Xc l ν and B Xs γ spectra (error on m b ~ 4.5%) lepton spectrum end-point recoil analysis hadronic tags 167 ±21 l purity ~26% with p > 1GeV l m ES

42 Vub Results & Prospects inclusive Inclusive most methods with uncertainties around 10% with mode data, uncertainty on inclusive V ub can be pushed down to ~6% Exclusive: πlν at high q 2 + lattice QCD Exclusive still limited by statistics expect errors from πlν on the lattice down to below ~8% by end of decade Goal for 2008: precision of ~5% on V ub

43 Summary of Constraints on the UT Apex Position

44 All measurements

45 Angle measurements only

46 Measurements of sin2β in Decay Modes Sensitive to Different Short-Distance Physics Im (,0) Ru γ ( ρ,η) α UT Rt β 0 ( 1,0 ) Re

47 CP Violation in s-penguin Modes Reference mode: Tree dominance 0 B b d W c c s d J/ ψ s d d s 0 K t,c,u 0 K B b u,d W internal penguin g s s s u,d Penguin dominance φ K B b g t,c,u W s s s u,d u, d flavor-singlet penguin φ K

48 T-D Analyses in η Ks and KsKsKs 804±40 signal events take advantage of the small beam size in the transverse plane 88±10 signal events

49 Compilation of s-penguin Results Naïve average of s-penguin S coefficients 2.4σ away from reference value of sin2β (cc) (significance of deviation decreased due to recent updated value of sin2β by Belle) ~2.4σ from s-penguin to sin2β New physics may affect different modes in different ways: use the pattern of deviations to go beyond the naïve average

50 Deviations from Standard Model Projected errors as a function of time 0.40 K*γ 0.35 f 0 K S 0.30 K S π φ K S 0.20 η K S 0.15 KKK S Error on sine amplitude Jan-03 Jul-03 Theory errors Jan-04 Jul-04 Jan-05 Jul-05 Jan-06 Jul-06 Jan-07 Jul-07 Jan-08 Jul-08 Jan-09 Jul-09 Significance of deviation from Standard Model expectation as a function of luminosity (assuming fluctuations around present central values) Number of standard deviations BABAR+Belle in 2008 average η K S φ K S integrated luminosity (/fb)

51 Discriminating Among NP Models Exploit the pattern of deviations S in the various modes to discriminate among different models Wilson coefficients: Three NP models, six scenarios: NP only in the Z 0 -penguin coupling NP in Kaluza-Klein gluon excitations NP in chromo-magnetic operator Full analysis: for each model constraints in the plane of the two NP parameters (modulus and phase) Buchalla, Hiller, Nir, Raz (hep-ph/ ) S SM Six NP scenarios Exclusion vs luminosity

52 Selected Measurements Sensitive to New Physics

53 New Physics Issues KM mechanism: one single source of CP violation New sources of flavor or CP violation can induce large deviations from SM predictions Where can one expect deviations? For instance, in MSSM 124 independent parameters 44 are CP violating Flavor Mixing large deviations in Bd system are unlikely but SUSY can affect mixing in the Bs system distinguish measurements involving flavor mixing or not Flavor Changing Neutral Currents helicity-changing helicity-conserving Very rare decays (e.g. leptonic) gluonic penguin diagrams with intermediate squarks and gluinos SUSY

54 FCNC: b s γ b s γ The transition has been heavily studied by CLEO then by BABAR and Belle in a variety of ways fully inclusive exclusive (B K*γ) semi-inclusive So far all measurements are consistent with SM predictions (typical errors: 10%) photon energy (semi-inclusive analysis) this mainly constrains LR mass insertions expect improvements towards 5% error by 2008

55 Leptonic B decays Br ( B l ν ) Recoil technique (semileptonic and hadronic) Look for 1 and 3 prong tau decays = G 2 F V 8π 2 ub f 2 B τ B m B m 2 l m 1 m ( B + + τ ν ) < 2.6 CL Br 4 τ 2 l 2 B (decay constant from LQCD) 2 plot the energy in addition to the signal candidate limit reaching a factor of ~2 of SM expectation : soon a constraining measurement no signal found Extra Energy (GeV)

56

57 B τν: Sensitivity to NP Models Two examples of constraints on the parameter space for specific NP models Limits on m(h + ) in the MSSM from Br( B τ ν) H + 90% Upper Limit on BR( B τν) B τ ν Luminosity (fb 1 ) Limits on the m(h + )-tanβ plane in 2HDM (of type II) from Br( B τ ν) and Br( b s γ )

58 Conclusions B-Factories will perform important SM measurements some of which cannot be improved elsewhere Four major CKM measurements will improve by 2008 sin2 β -- with expected error of order ±0.025 angle α -- with charmless two-, three- and four-body decays angle γ -- with DK modes, to better than 9, depending on r B V ub -- with m b and QCD parameters extracted from the data and progress on exclusive measurements Overconstraining the Unitarity Triangle strongly bounds New Physics The flavor sector is a key ingredient to NP model building B-Factory physics goes beyond CKM metrology! sensitivity to New Physics through radiative corrections, e.g. b sg (complementary to direct observation of NP particles at the LHC) sensitivity to very rare B, D, D s and τ decays

59 Possible Situation in 2008? σ ( V ub ) = 7% σ ( m s ) = 5% σ (sin 2 β ) = o o σα ( ) = 6 σγ ( ) = 10

60 BABAR Status & Physics Reach Gautier Hamel de Monchenault CEA-Saclay DAPNIA/SPP on behalf of the BABAR Collaboration CERN, 14 February 2006