1. SLAC 12-4-2003Niels van Bakel 1 I.Physics potential –CKM status –LHCb requirements II.The LHCb detector III.Vertex detector (VELO) –Read-out chip (Beetle) –Silicon sensors –Radiation –System tests –Wakefields IV.VELO performance –Vertex detection –Tracking –B s →D s -  + V. Summary Vertex detection in LHCb

2. SLAC 12-4-2003Niels van Bakel 2 I. Quark mixing and CP violation Stringent test of the Standard Model –Probes weak, electromagnetic and strong interactions at short and long distance scales Involves most of the free parameters of SM –Quark masses and CKM parameters Test quantum structure of the theory –Large class of processes solely occur as loops Investigate nature of CP, T and CPT

3. SLAC 12-4-2003Niels van Bakel 3 I. The CKM matrix With 3 families, the CKM matrix is a 3  3 complex unitary matrix. Requires 4 independent parameters to describe it; 3 real numbers & 1 complex non-trivial phase. Complex phase  = arg (V td )  = arg (V ub )  +  +  =  | V ub / V cb | | V td / V cb |

4. SLAC 12-4-2003Niels van Bakel 4 I. The CKM matrix V tb V ub * + V ts V us * +V td V ud * =0 With 3 families, the CKM matrix is a 3  3 complex unitary matrix. Requires 4 independent parameters to describe it; 3 real numbers & 1 complex non-trivial phase. Complex phase -A 2 +A 4 (1/2-  -i  )

5. SLAC 12-4-2003Niels van Bakel 5 oDirect Measurement of angles:   (sin(2  )) ≈ 0.03 from J/  K s in B factories  Other angles not precisely known oKnowledge of the sides of unitary triangle (Dominated by theoretical uncertainties):   (|V cb |) ≈ few % error   (|V ub |) ≈ 5-10 % error   (|V td |/|V ts |) ≈ 5-10% error (assuming  m s observed) oParameter inputs to CKM fit:  Experimental CKM elements  CP violating and mixing observables  SM predictions from real data  SM predictions from theory I. Current status of CKM

6. SLAC 12-4-2003Niels van Bakel 6 I. Large Hadron Collider A dedicated B-physics experiment at the LHC: LHCb Precision tests of the consistency of the CKM picture requires ~10 12 B mesons/year Access to B s, B c and b-baryon decays √s14 TeV (10.5 GeV) L10 34 cm -2 s -1 (few 10 33 ) bbbb 500  b (1 nb)  inel /  bb 160 (4)

7. SLAC 12-4-2003Niels van Bakel 7 I. B production at LHC bb production: (forward!) bb bb LHCb is a Forward Spectrometer and needs: Efficient trigger for many B decay final states Good tracking and Particle ID performance Excellent momentum and vertex resolution Adequate flavor tagging  Many tracks available for primary vertex  Large B flight distance, better proper time resolution  Triggering is an issue  Many particles not associated to b hadrons  b hadrons are not coherent: mixing dilutes tagging BsBs KK KK  ,K   DsDs B Decay eg.: B s ->D s h At LHC, B mesons are mainly produced forward

8. SLAC 12-4-2003Niels van Bakel 8 I. B events in LHCb B0 +-B0 +- Primary vertex Typical ~ 10 mm B 0   - D *+  D 0  + For CP physics: reconstruct B’s proper time tag flavour ( B or B )  Essential: vertexing and PID  total = 100 mb  visible = 65 mb  bb /  visible = 0.8% Bunch crossings in LHCb Size of luminous region Simultaneous pp interactions (“pileup”): number of visible interactions n (in events with at least one) distributed according to L = 2  10 32 cm -2 s -1, = 30 MHz, 100 kHz event rate  x =  y = 70  m,  z = 5 cm At least two tracks reconstructable in whole spectrometer bb event = 1.42

9. SLAC 12-4-2003Niels van Bakel 9 II. The LHCb detector VELO: primary vertex impact parameter displaced vertex Trigger Tracker: p for L1 trigger Tracking Stations: p of charged particles Calorimeters: PID: e, ,  0 Trigger on hadr. Muon System L0 RICH: PID: K,  separation RICH: Different radiators: aerogel, C 4 F 10, CF 4 Hybrid photon detectors; granularity 2.5 * 2.5 mm 2 Mirror support out of acceptance Iron B field shielding box (RICH1) 450k readout channels  3 stations with 4 double layers  5 mm straws tubes  Fast drift gas (signal within 50 ns)  50k readout channels. Outer Tracker ~6  5 m 2

10. 10 ~1.4  1.2 m 2  3 stations 4 layers each  320 μm thin silicon  198 μm readout pitch.  130k readout channels. Inner Tracker Trigger Tracker: 180k readout, 410  m thick  66 layers 2mm Pb + 4mm scintillator)  Transverse granularity 4,6,12 cm cells  ~6000 channels, 25 X o  Energy resolution: σ/E ~ 10%/sqrt(E)Ecal 70% modules produced II. The LHCb detector Trigger Tracker: p for L1 trigger Calorimeters: PID: e, ,  0 Trigger on hadr. Muon System L0  chambers: MWPCs Hcal ( 15% modules produced )  16 mm Fe + 4 mm scintillator tiles  1468 cells,, 5.6 I  σ/E ~ 75% / sqrt(E)

11. SLAC 12-4-2003 11 II. TriggerL1  ln p T  ln IP/  IP Signal Min. Bias B->  Bs->DsK Level-1: Displaced vertex Impact parameter Rough p T ~ 20% 40 kHz Vertex Locator Trigger Tracker Level 0 objects 200 Hz output HLT: Final state reconstruction Full detector information 1 MHz Calorimeter Muon system Pile-up system Level-0: p T of , e, h,  40 MHz L0 <100 MB/s

12. SLAC 12-4-2003Niels van Bakel 12 II. The VELO in LHCb Pile-up VETO detector: Veto bunch crossings with more than one interaction (L0). VErtex LOcator: Find primary vertex (L1) Reconstruct tracks with large impact parameter (L1) Precision vertexing (HLT) Good decay distance and proper time resolution (HLT)  Sensors close as possible to the PV  Little material in between  In LHC vacuum  Close to beam and high rates give a few design constraints:  High Radiation  Fast readout  Cooling of the detectors  Wakefields

13. SLAC 12-4-2003Niels van Bakel 13 -20 80 [cm] 0 Z opposite halves staggered to allow overlap II. VELO Sensors Hybrid Beetles Silicon Beetles 84 mm Diodes Routing lines Silicon comes to 7 mm from beam axis R  220  m thick Silicon single-side n-on-n, S/N=14 42 VELO modules: –R and  measuring planes –Varying pitch: ~ 40…120  m –Beetle front-end chip –170 k channels, analogue –Used in trigger L1, which makes explicit use of axial symmetry (2D r-z tracks) –Sensor resolution  4  m –Temperature -10 ºC –Second metal layer 21 + 2 1 meter Pile - Up stations

14. SLAC 12-4-2003Niels van Bakel 14 III. The Vertex detector Detector on X-Y tables Silicon stations in vacuum Retractable detector halves for beam injection R detector Phi detector Beam 281k readout channels

15. SLAC 12-4-2003Niels van Bakel 15 III. The VELO in LHCb Close to beam and high rates give a few design constraints:  Fast readout  High Radiation  Cooling of the detectors  Wakefields

16. SLAC 12-4-2003Niels van Bakel 16 Beetle was selected in January 2003 Used in Vertex Detector and Silicon Trackers IBM 0.25  m CMOS technology Analogue and digital output Digital output used in level-0 Analogue output used in level-1 III. Read-out chip; Beetle Pipeline cells Front-ends Beetle: 128 frontend channels 186 deep pipeline (4  s latency) 6.1×5.5 mm 2 Input pitch 41.2  m 2.5 V supply Analogue output ~ 50 mV/MIP

17. SLAC 12-4-2003Niels van Bakel 17 III. Read-out chip; Beetle Beetle specifications: 40 MHz clock frequency 1 MHz read-out Signal / Noise > 14 Rise time < 25 ns Spill over < 30 % Power < 6 mW / channel 90% 10% Rise time Spill over 25 ns

18. SLAC 12-4-2003Niels van Bakel 18 III. Beetle architecture preampshaper Pipeline 128  186 pipeline readout multiplexer 32  4 test channel 128 channels dummy channel

19. SLAC 12-4-2003Niels van Bakel 19 III. The VELO in LHCb Close to beam and high rates give a few design constrains:  Fast readout  High Radiation  Cooling of the detectors  Wakefields

20. SLAC 12-4-2003Niels van Bakel 20 Radiation hardness Replace detectors every few years: Maximum irradiation per station 5 x 10 12 to 1.3 x 10 14 n eq /cm 2 /year Middle station Far station III. Radiation Detector could have undepleted layer after irradiation – Resolution of p on n detector degrades fast, undepleted layer insulates strips from bulk. – n on n ~100% efficient for only 60% depletion depth

21. SLAC 12-4-2003Niels van Bakel 21 III. Radiation hard design Tolerable irradiation dose > 100 kGy in 5 years Field oxide Leakage current Gate oxide Obtain radiation hardness with: Technology: T ox < 10 nm : tunneling of trapped ions Layout:  Enclosed nMOS  Guardrings around nMOS Single event upset (SEU) : triggered by single particles Protect Control logic with triple redun- dant flip-flops with majority encoding Polysilicon Aluminum

22. SLAC 12-4-2003Niels van Bakel 22 Beetle1.1 showed full functionality up to 300 kGy (15 LHCb years): full trigger / readout functionality full slow control functionality performance degradations are small III. Radiation tests (TID) Test with X-ray facility at CERN Total ionizing dose results in gate bias voltage shifts V out [V] time [ns]

23. SLAC 12-4-2003Niels van Bakel 23  noise Baseline Signal 3 ns Goal –Optimize performance –Check chip behavior 16 chips on 1 hybrid Test beam environment Under LHCb operation Took 10 million events III. System Tests Peak Spill over point Convolution of Landau and Gaussian

24. SLAC 12-4-2003 24 ENC behaviour of the Beetle front- end (measured on a test chip): 449 e - + 46.8 e - /pF The channel thermal noise dominates the noise for an input transistor with a large area: 45.3 e - /pF (calculated) 1 MIP in the detector generates 22,000 electrons III. ENC measurements Average capacitance: 10 pF Signal/Noise= 17.4  0.2 Spill over = 36.1 %  1 Rise time = 23.5 ns  0.5 ENC= 500 + 50 e-/pF Power = ~ 3 mW/channel Detector capacitance : 6 - 14 pF Resulting S/N range:18.0 - 21.5

25. SLAC 12-4-2003Niels van Bakel 25 III. CO 2 Cooling Silicon CO 2 cooling capillaries Operate Si at about –10 o C to reduce radiation damage effects Diameter 1 mm, walls 0.15 mm, 15 mbar 50 W per capillary Radiation damage; 1/r 2 dependence Increase of leakage currents Avoid thermal run-away 1 MeV neutron equivalent

26. SLAC 12-4-2003Niels van Bakel 26 III. The VELO in LHCb 0 400 800 1200 1600 2000 Frequency (MHz) 10 6 10 4 10 2 Shunt resistance R s (  ) Close to beam and high rates give a few design constrains:  Fast readout  High Radiation  Cooling of the detectors  Wakefields

27. SLAC 12-4-2003Niels van Bakel 27 High LHC vacuum: excessive outgassing of sensors + hybrids + cables Wake field effects: adequate geometry and materials to avoid coupling to beams III. Final shielding solution The design takes into account: –Dynamic vacuum phenomena –Multi pacting –Material traversed by particles; low mass, no surface parallel to tracks –Sensors in opposite halves must overlap  We need a clean, light, bakeable, coatable, corrugated, vacuum tight foil –Complex shape –250  m thick –Rigidity (1.2 m long)

28. SLAC 12-4-2003Niels van Bakel 28 Track finding challenges in LHCb High density of hits and tracks. Track pattern recognition must be fast. High track efficiency important. o MC Pythia 6.2 tuned on CDF and UA5 data o Multiple pp interactions and spill-over effects included o Complete description of material from TDRs o Individual detector responses tuned on test beam results o Complete pattern recognition in reconstruction IV. Simulation and reconstruction

29. SLAC 12-4-2003Niels van Bakel 29 IV. L1 vertexing 91 cm 3.4 cm Tracks in one 45 o sector Primary Vertex x,y  (core) ~ 8  m Low occupancy ~0.5%, “easy” tracking Use r-sensors only (~70 r-z tracks/evt) to get primary vertex per event Tracks with 0.2 < d/mm < 3 (~8/evt) are reconstructed in 3D using  - sensors (d = impact parameter to primary vertex) PV found in 98% of b events Primary Vertex z  (core) ~ 45  m

30. SLAC 12-4-2003Niels van Bakel 30 IV. Track finding strategy VELO seeds Long track (forward) Long track (matched) T seeds Upstream track Downstream track T track VELO track T tracks  useful for RICH2 pattern recognition Long tracks  highest quality for physics (good IP & p resolution) Downstream tracks  needed for efficient K S finding (good p resolution) Upstream tracks  lower p, worse p resolution, but useful for RICH1 pattern recognition VELO tracks  useful for primary vertex reconstruction (good IP resolution)

31. SLAC 12-4-2003Niels van Bakel 31 IV. Resolution  p/p = 0.35% – 0.55% p spectrum B tracks  IP = 14  + 35  /p T 1/p T spectrum B tracks Momentum resolution parameter resolution Impact parameter resolution

32. SLAC 12-4-2003Niels van Bakel 32 Selected events (untagged) as function of proper time  =mL/p  Detector acceptance Trigger on high p t displaced tracks –In level-1 trigger (1 MHz) –Standalone track reconstruction –Use stray field to select high p t Selection –IP of D s,  to Primary Vertex –B s -D s vertex separation –B s vertex between PV and D s vertex –IP of B s vertex to PV –Angle between rec. B s momentum and PV-B s line –Reconstructed B s and D s mass Identify B s oscillations –Vertex resolution: 14  m + 35  m/p t  44 fs (D s  After Tagging; 36,000 D s  events in one year IV. B s → D s  effective efficiency :  eff =  tag (1-2  tag ) 2 Combining tags  tag [%]  tag [%]  eff [%] B s  D s  55309

33. SLAC 12-4-2003Niels van Bakel 33 –Needed for the observation of CP asymmetries with B s decays (  m s,  tag ) –Use B s  D s    –If  m s = 25 ps  1 –Can observe >5  oscillation signal if well beyond SM prediction IV. B s oscillation frequency:  m s  (  m s ) = 0.013 ps  1  m s < 68 ps  1 Expected unmixed B s  D s    sample in one year of data taking.

34. SLAC 12-4-2003Niels van Bakel 34 V. LHCb Physics potential Direct Measurement of angles after one year data taking:   (sin(2  )) ≈ 0.02 from J/  K s   ≈ 7 ° from several decays   < 5 ° (  +  ) from B→ , B→    m s  ps -1 (at 25 ps -1 ) from B s →D s  (limited by QCD)   (  ) ≈ 2 ° from J/   In case new physics is present in mixing, independent measurement of  can reveal it… Interesting topics: –Unitarity –CKM elements –CP asymmetries –Rare decays –…….

35. SLAC 12-4-2003Niels van Bakel 35 V. Summary LHCb will perform a precision study of CP violation. A probe for physics beyond the SM. Redundancy of measurements in many channels. Good particle ID, vertexing, and efficient & flexible trigger are essential. Detector construction has started and progressing well. LHCb will be ready for data-taking at LHC startup in 2007.