Efficient Triggering with the LHCb Detector for Precise CP Measurements

1
Efficient Triggering with the LHCb Detector for
Precise CP Measurements
8th International Conference on Advanced
Technology and Particle Physics 6 October
2003 Como, Italy

• LHCb detector
• Changes in geometry since Technical Proposal
  (98)
• Technical Design Report Sep 2003
• Trigger
• Technical Design Report Sep 2003
• Physics performance

Niels Tuning (CERN) on behalf of the LHCb
collaboration
2
LHCb A Large Hadron Collider Beauty Experiment
for Precision Measurements of CP-Violation and
Rare Decays

• Measure B-decays
• CP violation in Standard Model
• New particles in loop diagrams?
• Additional CP violation!
• Branching fraction of rare decays

• Colliding beams
• 7 TeV x 7 TeV pp (every 25 ns)
• L 2.1032 cm-2 s-1
• ?(visible) 68 mb
• ?(pp?b?bX) 0.5 mb
• ? 1012 b?b / year
• BR(interesting ch.) 10-4 10-9

3
The LHCb detector
Trigger Tracker p for trigger
Tracking Stations p of charged particles
Calorimeters PID e,?, ?0 Trigger on hadr.
RICH PID K,? separation
VELO primary vertex impact parameter displaced
vertex
Muon System
4
Detectors in the Trigger
VELO

• Vertex Locator
• 220 ?m n-on-n Si
• Pitch 40-100 ?m
• R-? geometry
• 170k channels
• Pileup System
• 2 VELO disks

16 mm
84 mm
21 stations, 100cm
? sensor stereo angle 10o,-20o
R sensor 4 ? sectors

• Trigger Tracker
• Full Si tracker
• 4 layers (x,u 30 cm gap v,x)
• Wide pitch 200 ?m
• 180k channels
• Placed in front of magnet

5
Trigger Overview
40 MHz
L0 (4 ?s)

• L0 high PT
• CalorimeterMuon
• Fully synchronous on custom boards
• L1 high PT impact parameter
• VELOTT
• Max. latency 52.4 ms
• (L1 buffer size 58254 events)
• Software trigger
• HLT high PT displaced vertex B-mass
• Full detector information available

1 MHz
L1 (1 ms)
40 kHz
HLT (14 ms)
6
L0 pileup system

• Calculate vertex for all combinations of 2 points
  a and b.
• Find highest peak ( prim.vtx)
• Remove the hits and find 2nd peak
• Veto if peakgtthreshold
• ?(Zvtx) ? 2.8 mm, ?(beam) ? 53 mm

7
L0

• High-pT ?, e, ? and hadrons with Calorimeter and
  Muon system

Muons
Fraction of events
8
L1 1 MHz ? 40 kHz
45o slice

• 2d tracks in VELO
• 80 / event
• Vertex
• ?z 60 ?m
• High imp.par 3d tracks
• pT information
• L0 muons
• TT dp/p 30

J/?(??-)
9
L1 HLT

• pT information from TT
• dp/p 30
• 2 high-IP tracks with highest pT

• pT information from T
• dp/p 0.6
• Confirm L1 decision
• down to 20kHz
• 95 efficiency
• In only 4 ms
• 14 ms for the rest

• L1HLT implemented on same CPU farm
• 1000 CPUs for L1, 800 for HLTreconstruction
• HLT runs in the background to limit deadtime.

10
Trigger performance

• Good efficiencies for useful events
• L0 50 90
• L1 50 70
• Timing is OK 2007
• L0 3.5 ?s (4 ?s)
• L1 8 ms (1 ms, max. 50 ms)

11
What do we do with the triggered events?
12
CP violation

• Mixing
• Small in B0 system, 1-p/q10-3
• BH0 pB0gtq?B0gt
• LHCb B0s?Ds-?, B0?D-?.
• Decay
• Interference between diagrams with same final
  states (e.g. tree, penguin)
• e.g. (B?f)-(B-?f -) (NB no mixing)
• Interference between (B0?f) and (B0??B0 ?f)
• ffCP LHCb B0?J/?KS, B0s?J/??, B0???.
• f?fCP LHCb B0s?DSK , B0?D?, B0?D0K.

• Present status
• sin(2?)0.731 ? 0.055 (B?J/?KS from ee-)
• sin(2?)0.695 ? 0.055 (from ?md and Vub)
• ? 64.5o ?7o (combining all measurements)

• Measuring CKM angle ? in LHCb
• B0s?D/-sK-/
• Only tree diagrams theoretically clean.
• B0??-?, B0s?K-K
• Penguin contributions solved with SU(3) symm.
• B0?D0K0,?D0K0
• Sensitive to new physics in D0,?D0 mixing

13
Rare decays

• Branching ratios of rare decays might be enhanced
  by the presence of new particles in the loop
• BR 10-5 (104 selected events/year)
• B0?K0?
• B0???
• BR 10-6 (103 sel. events/year)
• B0???- K0
• BR 10-9 (101 sel. events/year)
• B0s???-

14
Event selection
. B0s?D-sK
. B0s?D-s?

• Variables
• pT, impact parameter, PID.
• Decay length, vertex, mass constraints.
• B-mass, pointing.

15
Yields

• Efficiencies
• Acceptance x Reconstruction x Selection x Trigger
• 10 x 80 x 20 x
  35 0.5
• Branching ratios 10-5
• Yields 1012 bb x 0.005 x 10-5 50k

Typically
16
CP measurement

• Extract CP parameters from fast simulation
• Given the resolutions, yields and background from
  full simulation

• Examples
• ACP(B0?J/?KS)
• ACP( B0s?DsK-)

?f
17
LHCb physics reach in 1 year

• Excellent ? sensitivity
• Twice current BABARBELLE sensitivity
• Various ? measurements to disentangle new physics

• Rare decay
• ?(B0?K0?) 2 higher than SM?
• ? 3? significance

18
Conclusions

• The LHCb trigger
• reduces the rate from 40 MHz to 200 Hz (5.10-6
  !),
• with high efficiencies (20-70),
• and within the tight time budgets.
• Precise measurements of CKM parameters
• with many different approaches,
• to disentangle new physics.
• Precise measurements of branching ratios
• where new physics could show up.