Status of the LHCb Experiment 高原宁 清华大学高能物理研究中心 Introduction & physics motivations Status of the detector construction Topics on physics potentials Conclusions 高能物理学会第七界学术年会 2006 年 10 月 29 日 桂林

LHCb is a dedicated B physics experiment at the LHC

Forward spectrometer (running in pp collider mode) Great potential for B physics! Pythia 100μb 230μb η of B-hadron P T of B-hadron

Physics motivations The Standard model CP violation is described by the single complex phase in the CKM matrix, two unitarity triangles relevant to B physics at LHCb stat.

Current SM fit of the Unitarity Triangles (including CDF result on m s )  = 94.6° ± 4.6°  = 23.9° ± 1.0°  = 61.3° ± 4.5°  s = 2.1° ± 0.2°

— high statistics B d and B s samples are essential — robust and efficient trigger, even for non-leptonic decays — good decay vertex resolution; good tracking; good particle identification

Many final states need to be reconstructed … HIGH STATISTICS

News from the experiment

r- and  measuring sensors rather than x,y  fast and easy impact parameters for use in the trigger VErtex LOcator “VELO” 21 stations (pile-up veto detector) RF foil beam-spot  z =5.3cm  -measuring sensor r-measuring sensor  - sensor: radial strips (inner and outer) 2048 strips stereo angle (-20 , +10  ) 37–98 µm pitch r-sensor: concentric strips 2048 strips 4 sectors (45  )  m pitch harsh radiation environment:  n-n sensors: keep good resolution if undepleted  sensor cooling to -5°C with CO 2 cooling system

good impact parameters  detectors as close as 8mm to LHC beam  sensors placed in secondary vacuum (10 -9 mbar) separated from beam-vacuum just by an 300  m Al “RF-foil” move sensors out during filling (3cm) re-positioning accuracy: <10  m Vertex Locator Mechanics RF-foils vacuum vessel installed and surveyed (0.2mm accuracy)

VELO Modules Production and Commissioning Test real life detector modules real “LHCb visualisation tool” Testbeam: Alignment and Commissioning challenge using (almost) final HARD and LHCb SOFTware successfully operated: important experience for commissioning online/offline software lots of test-beam data to be analysed now 9 out of 42 final detector modules are ready  awaiting “burn-in”

Expected VELO Performance  IP = 14  m + 35  m / p T core  z = 44  m core  x =  y = 8  m impact parameter use all tracks that include VELO: bb vertex resolution: _ average B flight path = ~1cm !! average:40  m dominated by material before 1 st measurement

Other Tracking Detectors TT-station silicon strips: P T info for the trigger Outer Tracker: straw tubes Inner Tracker: silicon strips 1.3% of the station surface 20% of accepted tracks magnet:

TT-Station 4 layers: (2 with ±5º stereo angle) silicon strips: 143k channels, 7.9m 2 up to 39cm readout strips inner sectors connected via Kapton interconnect cables operation at ~5°C, liquid C 6 F 14 cooling ~ 60% of modules finished lower hybrid upper hybrid Station assembly for testing in the lab Good quality modules with low leakage currents

Inner Tracker silicon strips: 129k channels, 4.3m modules 11 and 22cm long modules/strips 4 individual boxes per station 4 layers per station:(2 stereo layers) operation at ~5°C, liquid C 6 F 14 cooling ~ 60% of modules produced and tested

Inner Tracker Installation First Inner Tracker box has been assembled and partially tested support frames have been brought to the pit will be cabled soon

Outer Tracker pitch 5.25 mm 5mm cells Track e-e- e-e- e-e- Straw tube tracker: ArC0 2 drift gas resolution: 200  m 4 layers / station 2 stereo layers ±5º Module production finished December 2005 ! HV > 1520 V –ε  98% –σ  200 µm

Outer Tracker Installation Support bridge… … installed …with modules 1/4 of the stations are already equipped with modules now: testing, cabling, survey

selection of specific B-decay channels for CP measurements without particle ID, the bkg-dilutes/overwhelms the signal RICH – Particle ID B s  D s    B s  D s  K 

2 RICH Detectors with 3 Cherenkov Radiators RICH1: 5cm silica aerogel (2-10GeV/c) 85cm C 4 F 10 gas (<50GeV/c) spherical (CF) and planar (glass) mirrors RICH2: 170cm CF 4 gas (<100GeV/c) spherical and planar glass mirrors before and behind the magnet  c (mrad) Expected photons detected Aerogel 7 C 4 F CF 4 23

RICH – Photon Detector Hybrid Photon Detectors (HPDs): photo tubes with silicon pixel chip 2.5x2.5mm2 resolution for single photons low noise  excellent single photon detection efficiency (200nm–600nm) 85% detection efficiency (after photon conversion ~25%) about 50% of HPDs are produced and tested  only 3% failures number of pixel hits/event data simulation 10GeV pions, 1.1m N 2

RICH Installation RICH2 cabling ongoing RICH1 magnetic shield, gas enclosure and seal to VELO RICH2: installed end spherical mirrors aligned to σ θ ~ 50 μrad

Calorimeter System SPD/PS/ECAL/HCAL they all use similar cost efficient technology: scintillating tiles in between lead/steel absorbers read out via wavelength shifting fibres SPD: scintillating pads/tiles  distinguish e ± and  PS: PreShower after 2.5cm of lead identifies electromagnetic particles ECAL: shashlik type  measure energy of electromagnetic shower HCAL: iron interleaved with scintillating tiles  energy of hadrons SPD-scintillating pad

ECAL/HCAL Performance  E E EE  (0.83  0.02)%   ((145  13) MeV)/E (9.4  0.2)% E beam GeV  E E ECAL HCAL

Calorimeter Installation ECAL in place since June 2005 Activity now focuses on cabling / commissioning using calibration LEDs HCAL in place since Sept SPD/PS modules have been installed this summer

Muon Multi-Wire-Proportional-Chambers (MWPC) & GEMs (at center at 1 st station) 4ns time resolution  use in the trigger (20% P T resolution) muon filters are in place 1380 MWP-Chambers production completed 24 GEM production is ongoing MWPCsTriple GEMsMWPC supportmuon filter testbeam:anode efficiency Efficiency [%] HV (kV)

Two Trigger Levels:  e,  ,K L0: hardware trigger 10MHz (interaction rate)  1MHz calorimeter: (SPD multiplicity, # E T clusters) muon: (two high p T muons) pile-up system (indentify multiple interactions) L0 Decision Unit Latency: 4  s HLT: software trigger 1MHz  2kHz all sub-detectors readings L0 confirmation dedicated physics channel triggers depending on type of L0 trigger trigger on impact parameters Many different custom electronics, all close to final production Trigger commissioning will start 2007 L0 efficiencies: for channels with muons: ~90% leptons: ~70% hadrons: ~50% HLT efficiencies:.. no final numbers: still in transitions from former L1+HLT scheme (it was 50-80%)

Online Event Filter Farm Readout Network Front-end Electronics TFC System Storage System PC ~1800 computer nodes FE Switch VELO TT IT OT RICH CALO MUON L0 1 MHz 2 kHz Full detector info available for HLT LHCb common readout board (TELL1) commercial network switch

Magnet Magnet has long been installed ∫Bdl : 4 Tm, warm coils 4.2MWatt, 15 tons fully operational magnetic field map to precision: 3x10 -4, symmetry w.r.t. polarity:  B / ~ 3x10 -4 stray B stray field between VELO and TT  fast P T info in Trigger - calculation o measurement VELO TT Magnet z [cm] B y [T]

Beam Pipe support wires 25mrad Be section + Velo exit window 1 st and 2 nd 10 mrad Be section stainless steel section All beam-pipe pieces are at hand, 1 st section installed and sealed to the VELO vessel

Selected topics on physics potentials 1. Measurement of the angle  from B s  D s  K +  CP asymmetry arises from interference between two tree diagrams via B s mixing: B s  D s + K  and B s  D s  K + Measures   extract   is determined using B s  J/   decay,  (sin 2  ) ~ 0.06 for one year)

Background from Bs  D s  is suppressed using PID information from RICH1 & RICH2  remaining contamination ~ 10% Reconstruct using D s   K  K    5400 signal events/year The strong phase difference of the two diagrams can be resolved by fit two time-dependent asymmetries: Phase of D s + K  asymmetry is  (   Phase of  D s  K  asymmetry is  (   can extract both  and  (   (  ) ~ 14  in one year Asymmetries for 5 years of simulated data Theoretically clean; insensitive to new physics

Selected topics on physics potentials 2. Measurement of the angle  from B 0   +  –, B s  K + K – b  u processes with possible large b  d(s) penguin contributions Measure time-dependent CP asymmetries for B 0      and B s      A CP (t) = A dir cos(  m t) + A mix sin(  m t)  extract four asymmetries A dir (B 0      ) = f 1 (d, ,  ) de i  = ratio of penguin and tree A mix (B 0      ) = f 2 (d, ,  ) amplitudes in B 0      A dir (B s      ) = f 3 (d’,  ’,  ) d’e i  ’ = ratio of penguin and tree A mix (B s      ) = f 4 (d’,  ’,  ) amplitudes in B s     

Assume U-spin flavour symmetry (under interchange of d and s quarks) d = d’ and  =  ’ [R. Fleischer, PLB 459 (1999) 306] Taking  and  from other channels  can solve for  blue bands from B s  K  K  (95% CL) red bands from B       (95% CL) ellipses are 68% and 95% CL regions (  input = 65  ) d-  plot “fake” solution Theoretical uncertainty from U-spin assumption (can be tested); Sensitive to new physics in the penguin loops  (  ) ~ 5  in one year

Selected topics on physics potentials 3. Measurement of the angle  from B 0  D 0 K *0, D 0 K *0 – CP asymmetry arises from interference between two tree diagrams via D 0 -mixing

Measure six rates ( following 3 + CP-conjugates )  can be extracted from triangles [Gronau and Wyler, PLB 265 (1991) 172, Dunietz, PLB 270(1991) 75] 3.4K, 0.5K and 0.6K events respectively for one year data taking  (  ) ~ 7-8  in one year No theoretical uncertainties; sensitive to new physics in D CP

Selected topics on physics potentials 4. Charm physics at LHCb –

Selected topics on physics potentials 5. Bc Studies at Tsinghua – BcGen (BcVGPY) is now LHCb standard Physics + Manual > LHCb note

Bc mass & lifetime Refinements due to Trigger change > LHCb note soon

Selected topics on physics potential Outlook A possible scenario after the LHCb measurement of  new physics? Many other interesting topics not covered by this talk  TDR, LHCb notes, …

Conclusions LHCb is dedicated to the study of B physics, with a devoted trigger, excellent vertex and momentum resolution, and particle identification Construction of the experiment is progressing well It will be ready for first LHC collisions in 2007 (TELL1s from Tsinghua group are delivered to the experiment) LHCb will give unprecedented statistics for B decays, including access to the B s meson, unavailable to the B factories Our Beauty is also Charming Physics preparations for Bc physics from Tsinghua group is well underway.