B Physics and CP Ise-Shima, Japan February 19, 2001 Summary of - PowerPoint PPT Presentation

Stewart Smith Princeton University for the BABAR Collaboration B Physics and CP Ise-Shima, Japan February 19, 2001

� Summary of PEP-II/BaBar performance � Basics of measuring CP violation at an asymmetric B Factory � Details of the data sample and analysis � Extracting sin 2 β � Cross-checks and error analysis � Looking to the future � Conclusion February 19, 2001 BCP4 Ise-Shima, Japan 2

Running began Jan 2000 � ~24 fb -1 total by Oct 31 � ~21 fb - 1 Υ Υ (4S); Υ Υ ~3 fb -1 continuum � Shutdown Nov1 – Feb1 � � PEPII improvements � BaBar repair/maintenance � Computing development for 5 x 10 33 2001 Run is underway � � Began 3 Feb � 1.5 10 33 As of 15 Feb � Expect ~40 fb -1 in CY ‘01 February 19, 2001 BCP4 Ise-Shima, Japan 3

Extremely fast PEP-II Turnon (fb -1 ) 18 12 CESR/CLEO (from CESR Web page) PEPII/B A B AR 6 ‘80 ‘90 ‘00 February 19, 2001 BCP4 Ise-Shima, Japan 4

… � By end of 2000 run, peak & average luminosity were above design and climbing: DESIGN : 3.0 nb -1 /s 135 pb -1 /d ~ 0.80 fb -1 /w ~ 3.3 fb -1 /m ACHIEVED: 3.28 184 1.03 3.8 � BaBar performed just fine at 3.2 × × 10 33 × × Preliminary � This year we expect to reach 5 × × × × 10 33 (~2% uncertainty) � Luminosity profile - next few (calendar)years: 2000 2001 2002 2003 2004 2005 180 fb -1 25 43 80 110 130 � Ldt > > > 500 fb -1 by end of 2005 > � � � � We’re going to need it – life is hard. February 19, 2001 BCP4 Ise-Shima, Japan 5

A AR February 19, 2001 BCP4 Ise-Shima, Japan 6

B 0- B 0 CP � Neutral B and B mix into mass eigenstates, oscillating at a frequency determined by ∆ m B Concezio Bozzi talks on BaBar mixing results at 0900 Thur. * q V V φ = = 2 i tb td e M * p V V q A tb td λ = � We define , where = 0 | | A f H B p A � � = 0 | | A f H B � � φ � For a single decay amplitude with weak phase D Im λ λ = sin 2( φ φ M - φ φ D ) λ λ φ φ φ φ Leads to CP -violating asymmetries interpretable by � the Standard model February 19, 2001 BCP4 Ise-Shima, Japan 7

CP * V V V td tb * V V * V td V V ud ub B 0d →ππ →ππ →ππ →ππ cd cb ub * V V cd cb B 0d → → → J/ ψ → ψ ψ K 0S ψ s →ϕ →ϕ K 0 →ϕ →ϕ B 0 S (0,0) + + = V V * * * 0 V V V V V V cd cb ud ub cd cb td tb CP -violating Asymmetries in B decays directly measure phases α α α , β α β β , and γ β γ γ via– “no” hadronic uncertainties γ February 19, 2001 BCP4 Ise-Shima, Japan 8

ϒ (4S) ϒ ϒ ϒ CP � The ϒ (4S) decays into a P -wave B 0 B 0 state that evolves coherently till one of the B ’s decays. The B ’s are almost motionless in the ϒ (4S) rest frame. � We measure the interference between direct and mixed decays to a CP eigenstate 0 B A f β ∆ ∆ e 2 i sin / 2 m d t i CP ( ) = J ψ 0 0 f / B K CP S ∆ m d ∆ cos / 2 t A f 0 B CP February 19, 2001 BCP4 Ise-Shima, Japan 9

Decay-time Distributions For a tag B 0 (B 0 ) at time t TAG , the time distribution of the B 0 → → → f CP ( f + ) → other meson into a B 0 → → → f CP (f - ) → CP eigenstate at time ∆ t = t CP - t TAG is given by f + f - February 19, 2001 BCP4 Ise-Shima, Japan 10

� For b → → ( C C ) S → → | λ λ |=1 and λ λ I m λ λ λ λ = - η η f sin2 β η η β β β β β β = arg [ V cd V cb */ V td V tb * ] β � We reconstruct the “gold / silver”CP eigenstates : J/ ψ ψ K 0S , ψ ψ ψ ψ (2s)K 0S ( η ψ ψ η η η f = -1) J/ ψ ψ K 0L ( η ψ ψ η η η f = +1 ) � t-dependent asymmetries: � A CP dt = 0 � � Asymmetric B Factory! � � February 19, 2001 BCP4 Ise-Shima, Japan 11

∆ ∆ ∆ ∆ � E - = 9.0 GeV; E + = 3.1 GeV Lorentz Boost � βγ βγ βγ βγ = 0.56 ∆ t ≈ ∆ ∆ ∆ z / β β γ γ c ∆ ∆ ∆ ∆ β β γ γ e + σ CP ≈ ≈ 70 µ ≈ ≈ µ µ m µ e — ψ J/ σ tag ≈ ≈ 180 µ ≈ ≈ µ µ µ m 0 B CP π + ϒ (4S) 0 K ( ) π — S 0 B 0 B ( ) ( ) ( ) tags + − µ + − + − , , e K ∆ z February 19, 2001 BCP4 Ise-Shima, Japan 12

Fully reconstruct exclusive B decays to eigenstates of CP or flavour, and tag flavour of the other B in the event. � Select B CP candidates ( B 0 → J/ ψ K s , etc.) and B flav candidates ( B 0 → D* +, etc.) � S elect B tag events using, primarily, leptons and K ’s from B hadronic decays, and determine the B flavour . � Measure the mistag fractions w i and determine the D i =1 – 2w i dilutions � Measure ∆ Z between B CP and B tag to determine the signed time difference ∆ t between the decays � Determine the resolution function for ∆ ∆ ∆ ∆ t February 19, 2001 BCP4 Ise-Shima, Japan 13

Crucial Elements in A( ∆ ∆ ∆ ∆ t ) measurement : I. Vertex Resolution Even at PEP- II, B ’s don’t go very far! ( ≈ 250 µ µ µ µ m) � 5 Layer Silicon Vertex Tracker σ σ σ σ z ≈ 70 µ µ µ µ m: reco’d B 180 µ µ µ m: tagging B µ (rms for 99% of events) February 19, 2001 BCP4 Ise-Shima, Japan 14

Crucial Elements in A ( ∆ ∆ ∆ ∆ t ) measurement : II. Particle ID and Tagging � J/ ψ ψ ψ ’s are detected by their ee and µµ ψ µµ µµ modes µµ � K L modes are an important contributor to CP sample. K L ‘s are detected by their strong interaction debris in EMC and IFR � The flavour of the tagging B decay is determined from its lepton and kaon content, and from slow pions from D* ’s February 19, 2001 BCP4 Ise-Shima, Japan 15

Particle ID: • Track matching in the EMC • 0.89 < E/P < 1.2 • EM shower shape requirements • DCH d E /d x consistent with electron hypothesis • Efficiency and π π misID π π probabilities determined from the data (Control Samples) • Typical Tight Electron selection: ~92% efficiency above 500 MeV, with 0.1% π π π π misID February 19, 2001 BCP4 Ise-Shima, Japan 16

Particle ID: Muons • Cut on # interaction lengths and • consistent with a MIP in the EMC difference from that expected for • Typical Tight Muon selection: ~75% a µ µ µ µ track efficiency above 1.5 GeV , with ~3% • IFR hit pattern rejects hadron pion mis ID showers 1 0.1 Muon efficiency Pion misidentification B A B AR B A B AR 0.8 0.08 0.6 0.06 0.4 0.04 0.02 0.2 0 0 0 1 2 3 4 0 1 2 3 4 5 p lab (GeV/c) p lab (GeV/c) February 19, 2001 BCP4 Ise-Shima, Japan 17

Kaon efficiency Pion misidentification y 1 • dE/dx from 0.8 DCH and SVT 0.6 B A B AR 0.4 • θ θ C from DIRC θ θ 0.2 0 0 1 2 3 4 Better than 3 σ σ σ σ K/ π p lab (GeV/c) p lab (GeV/c) p lab (GeV/c) π π π separation for p K > 250 MeV/c February 19, 2001 BCP4 Ise-Shima, Japan 18

B K - l - → B 0 tag ) s � Leptons ( l l l • � Electron P cm >1.0 GeV/c e - , µ - � Muon P cm >1.1 GeV/c c � Kaons • � Σ Kaon Charge ≠ ≠ 0 ≠ ≠ b � NT1,NT2 (neural net) � slow pions (from D *) � Isolated unidentified leptons February 19, 2001 BCP4 Ise-Shima, Japan 19

A candidate in the Golden Mode + − → ψ → π π 0 0 0 / , B J K K CP S S + − ψ → µ µ / J with: • A negative kaon is found in the decay products of the other B meson, which is 0 B therefore tagged as a • ∆ ∆ z is measured precisely, ∆ ∆ thanks to the Silicon Vertex Detector February 19, 2001 BCP4 Ise-Shima, Japan 20

Reconstructed Hadronic B events for mixing and fitting ( B flav Sample) Events/0.002 GeV/c 2 2000 B A B AR D ( * ) - π π + , D ( * ) - ρ ρ + , D ( * ) - a 1 1500 π π ρ ρ + J/ ψ ψ ψ K *0 (K *0 → ψ → → → K + π - ) 1000 ~ 6700 events 500 0 5.2 5.22 5.24 5.26 5.28 5.3 Energy Substituted Mass (GeV/c 2 ) February 19, 2001 BCP4 Ise-Shima, Japan 21

B 0 → → J/ ψ ψ (K s → → π π + π π - ) → → ψ ψ → → π π π π 2 50 Events / 2.5 MeV/c B A B AR 40 ( ) B 0 → J/ ψ K S 2 100 B A B AR K S → π + π – 30 Events / 2.5 MeV/c J/ ψ → e + e – 20 ( ) B 0 → J/ ψ K S 80 10 K S → π + π – 0 60 5200 5210 5220 5230 5240 5250 5260 5270 5280 5290 5300 2 2 Beam-Energy Substituted Mass (MeV/c ) Events / 2.5 MeV/c B A B AR 50 40 ( ) B 0 → J/ ψ K S 40 K S → π + π – J/ ψ → µ + µ – 20 30 20 0 5200 5210 5220 5230 5240 5250 5260 5270 5280 5290 5300 10 2 Beam-Energy Substituted Mass (MeV/c ) 0 5200 5210 5220 5230 5240 5250 5260 5270 5280 5290 5300 2 Beam-Energy Substituted Mass (MeV/c ) February 19, 2001 BCP4 Ise-Shima, Japan 22