First Results from BaBar

Transcription

1 First Results from BaBar Marco Serra University of Rome La Sapienza & I.N.F.N. Roma1 for the BaBar Collaboration Les Rencontres de Physique de la Vallee d Aoste 1 March 2000, La Thuile, Aosta Valley, Italy

2 The BABAR Collaboration USA [34/349] California Institute of Technology UC, Irvine UC, Los Angeles UC, San Diego UC, Santa Barbara UC, Santa Cruz U of Cincinnati U of Colorado Colorado State Florida A&M U of Iowa Iowa State U LBNL LLNL U of Louisville U of Maryland U of Massachusetts, Amherst MIT U of Mississippi Mount Holyoke College Northern Kentucky U U of Notre Dame ORNL/Y-12 U of Pennsylvania Prairie View A&M Princeton Rutgers SLAC U of South Carolina Stanford U U of Tennessee U of Texas at Dallas Vanderbilt U of Wisconsin 9 Countries 71 Institutions 652 Collaborators Canada [5/17] U of British Columbia McGill U U de Montréal TRIUMF U of Victoria China [1/6] Inst. of High Energy Physics, Beijing France [5/71] LAPP, Annecy LAL Orsay LPNHE des Universités Paris 6/7 Ecole Polytechnique CEA, DAPNIA, CE-Saclay Germany [2/21] Ruhr U Bochum Technische U Dresden Italy [12/92] INFN, Bari INFN, Ferrara Lab. Nazionali di Frascati dell' INFN INFN, Genova INFN, Milano INFN, Napoli INFN, Padova INFN, Pavia INFN, Pisa INFN, Roma and U "La Sapienza" INFN, Torino INFN, Trieste Norway [1/4] U of Bergen Russia [1/15] Budker Institute, Novosibirsk May, 1999 United Kingdom [10/77] 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

3 Introduction The main goal of BaBar is CP in B Rare B decays, precise measurement of V ub, V cb & τ physics are other important topics of BaBar Today is too early for physics results (next summer) Now we are understanding and improving the performance of the detector and the reconstruction software The validation of the tools for the sin(2β) measurement is proceeding using standard B physics analyses Will show the key points for sin(2β) measurement

4 Unitary Triangle B d D*π, Κπ

5 Sin(2β) a f CP Γ( B = Γ ( B ( t) High luminosity z measurement (asymmetric collider) Excellent tracking and vertexing PID (e, µ, K, π) Neutral reconstruction (γ, π 0, K 0 L ) 0 0 ( t) f f CP CP ) Γ( B ) + Γ ( B 0 0 ( t) ( t) f f CP CP ) ) Reconstruction of the CP eigenstate βγ=0.56 Golden mode B J/Ψ K 0 S Y(4s) Y(4S) B_tag B_cp J/Ψ l + l - B_cp K 0 S Measurement of z 250 µm π Tag of the other B B_tag π +

6 PEPII 9GeVe GeV e + Asymmetric collider (βγ ~ ϒ(4S) First collisions on 26 th May 1999 Achieved* Design Luminosity 1.45x10 33 cm -2 s x10 33 cm 2 s -1 # of Bunches e+ Current (3.1GeV) 1700 ma 2140 ma e- Current (9.0 GeV) 920 ma 750 ma Lumi Lifetime ~ 120 min ~ 120 min Sigma y Sigma x * not all at the same time ~ 6.5 microns ~ 215 microns 6.65 microns 222 microns

7 Resonance scan ϒ(4S) scanning on June to find working point Analysis of 3 pb -1 : m ϒ(4S) = ± GeV (PEP-II scale) Γ ϒ(4S) = 11.1 ± 3.4 MeV

8 performance Luminosity record: 1.45 x cm -2 /s First data set recorded with incomplete coverage (DIRC / IFR) BaBar operating full coverage since Oct 1999 L 60 pb -1 in one day DIRC bar-boxes machine fix & improvement days

9 Data Sample More than 2.8 fb -1 recorded (0.335 off peak)

10 Interaction region Permanent magnets inside the support tube

11 Beam related background PEPII and BaBar are coping well with backgrounds from beam-gas and synchrotron X-rays No important reconstruction problems from background The radiation dose received by BaBar (mainly SVT) is well below the budget (~200 krad/year)

12 BaBar EMC DIRC quartz bars DCH DIRC Stand-off box e GeV e GeV SVT IFR Superconducting coil

13 SVT: Silicon Vertex Tracker 5 double sided layers (φ,z) Radiation hard 143K channels Acceptance 20 <θ lab <150 Vertexing & z Stand alone tracking for p t <100 MeV (µm) (µm) SVT Hit Resolution vs. Incident Track Angle Layer 1 - Z View B ABAR Data - Run 7925 Monte Carlo - SP Layer 1 - φ View B ABAR Data - Run 7925 Monte Carlo - SP (deg) (deg) Design resolution 90 ) achieved (MC perfect alignment) 144mm 32mm

14 SVT BaBar Silicon Vertex Tracker Kevlar/carbon-fiber support rib Carbon-fiber endpiece z=0 Si detectors Carbon-fiber support cone Beam pipe 30 cm 30 o e- e+ 350 mr 20 cm Cooling ring Upilex fanouts Hybrid/readout ICs 40 cm

15 DCH: Drift Chamber Inclusive track selection 7104 hexagonal cells 80%He - 20%C 4 H 10 good tracking capability & de/dx PID information Average resolution as expected (140 µm design)

16 Tracking (SVT+DCH) Single track from Hadronic events

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

18 DIRC Cherenkov ring D 0 K - π + p * (D 0 ) > 1.5 GeV/c 0.5 < p(k) < 4.0 GeV/c K efficiency within DIRC acceptance ~80% bkg reduced by more than a factor ~5

19 Towards tagging DIRC: θc (mrad) Kinematically Identified Kaons from D* Decays 0.84 e µ 0.78 >3σ π/k separation DCH up to 0.5 GeV DIRC from 0.5 GeV π K 0.7 DCH: p 0.68 Resolution ~ 7.5 % (design 7%) Momentum 3 2 (GeV/c ) * Kinematically Identified Pions from D Decays θc (mrad) 80% truncated mean (arbitrary units) de/dx vs momentum 10 4 p d 0.84 e µ BABAR 0.78 K π 10 3 e π K 0.7 µ p Track momentum (GeV/c) Momentum 3 2 (GeV/c )

20 EMC: Electromagnetic Calorimeter 6580 CsI (Tl doped) crystals Material in front: X 0 Readout by 2 large area photodiodes Expected π 0 resolution: ~ 6.5 MeV γ down to 20 MeV (background!) π 0 up to 4 GeV e-id down to 500 MeV

21 IFR: Instrumented Flux Return 19(18) layers RPC 2 inner cylindrical layers inside the coil 2000 m 2 RPCs µ and K 0 L detection Fraction of the IFR was off for summer run Now complete coverage µ-id eff. from γγ events fake from τ/ K 0 S events

22 Trigger L1 L1 (hardware) 800 Hz (12 µs latency / <1% dead time) track trigger from DCH energy trigger from EMC global trigger: match spatial and angular info from DCH & EMC Designed to generate L1 accept at no more than design luminosity

23 Trigger L3 L3 (software) 60 Hz Level 3 process all the L1 accepted events, all detector info available beam bkg rejection scale high rate processes select physics The rate is reduced to less than 100 Hz Physics 6 Hz + bhabha(prescaled) ~ 15 Hz

24 BaBar computing C++ code since the first day OO management of data/mc (Objectivity) 100s physicists all accessing the same multi-terabyte db 3 Mb/sec of data all day, every day. Performance improving but still work to do: Objectivity more complex than expected Now BaBar is testing an alternative to Objectivity for analysis: ROOT (Micro DST 5Kb/event) OO design flexible fast development Prompt Reco

25 Testing Tracking + Vertexing Only kinematic cuts, No PID D 0 K - π + σ m = 8.0 ± 0.2 Mev/c D *+ D 0 π +, D 0 K - π + σ 1 (m(kππ)-m(kπ))= 252 kev (59%)

26 D reconstruction D 0 proper decay time distribution shows the expected lifetime

27 Semi-leptonic B-decay B 0 D* - e + ν D 0 π - K - π + Select electrons with P * > 1GeV/c kinematical constraint with missing ν : P * (B) Θ * (B,D*e) P * (ν) P * (D * e) cosθ * (B,D*e) < 1 (equivalent to missing mass cut)

28 Semi-leptonic B-decay L ~ 400 pb -1 Nice control sample for tagging studies

29 Inclusive K 0 S reconstruction K 0 s π + π <flight length> ~ 4cm in BB events Tight K 0 S kinematic selection (high purity): oppositely charged tracks from common vertex pointing to the beam spot σ 1 = 2.8 MeV ( ~70%) σ 2 = 11 MeV ( ~30%)

30 Inclusive J/ψ reconstruction B J/ψ X ( ~ 1%) J/ψ l + l - ( ~ 12%) Candidates / 10 MeV/c J/ψ e + e - BABAR 20 Very loose lepton-id L ~ 540 pb m(e + e - ) GeV/c 2 J/ψ candidate: oppositely charged tracks identified as leptons from common vtx Candidates / 10 MeV/c J/ψ µ + µ - BABAR 25 L ~ 380 pb m(µ + µ - ) GeV/c 2

31 B 0 decay into charmonium B 0 J/ψ K 0 S L ~ 600 pb -1 N ev /2.5MeV BABAR Fit with constraints: PDG values for m(j/ψ,k 0 S ) Common vertex Beam energy E(GeV) B 0 mass(gev) B A B AR M b (GeV)

32 B 0 J/ψ K 0 S

33 B decay into charmonium N ev /2.5MeV BABAR B + J/ψ K + L ~ 600 pb Control samples for sin(2β) analysis B ch mass(gev) B 0 J/ψ K * 0 (K * 0 K + π - ) L ~ 1 fb -1

34 Tagged event

35 z First look at z MC distribution in agreement with Data J/ψ K + + J/ψ K * 0 (K * 0 K + π - ) Signal Sidebands Data/MC Comparison MC L ~ 1fb -1

36 Conclusions PEPII is working very well and routinely delivers luminosity > cm -2 s -1 Design luminosity expected by the end of this run (August) BaBar has already accumulated more than 2.8 fb -1 (more than 1 fb -1 since January pb -1 off p.) Detector understanding continues using validation studies Plan to perform first measurement of sin(2β) in the channel B 0 J/ψ K 0 S from 10 fb-1 for the end of this run

37 BaBar data load Characteristic Size No. of Detector Subsystems 7 No. of Electronic Channels ~250,000 Raw Event Size ~32kBytes DAQ to Level 3 Trigger 2000Hz 50MByte/sec Level 3 to Reconstruction 100Hz 2.5MByte/sec Reconstruction 100Hz 7.5MByte/sec Event Rate 10 9 events/year Storage Requirements (real ~300TByte/year & simulated data)

38 typical shift seconds

39 background for DIRC control sample