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
Physics performance
Niels Tuning (CERN)
on behalf of the
LHCb collaboration
6 Oct 2003
8th ICATPP Conference, Como, N.Tuning

2. 8th ICATPP Conference, Como, N.Tuning
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 = cm-2 s-1
(visible) = 68 mb
(ppbbX) = 0.5 mb
 ~1012 bb / year
BR(interesting ch.) ~10-4 – 10-9
cern
LHCb p
6 Oct 2003
8th ICATPP Conference, Como, N.Tuning

3. 8th ICATPP Conference, Como, N.Tuning
The LHCb detector
RICH:
PID: K, separation
Trigger Tracker:
p for trigger
Tracking Stations:
p of charged particles
Calorimeters:
PID: e,, 0
Trigger on hadr.
VELO:
primary vertex
impact parameter
displaced vertex
Muon System
6 Oct 2003
8th ICATPP Conference, Como, N.Tuning

4. Detectors in the Trigger
Vertex Locator:
220 m n-on-n Si
Pitch: m
R- geometry
170k channels
Pileup System
2 VELO disks
VELO
16 mm
84 mm
21 stations, 100cm
 sensor:
stereo angle +10o,-20o
R sensor:
4  sectors
Trigger Tracker (TT)
20 ladders, 140cm
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
6 Oct 2003
8th ICATPP Conference, Como, N.Tuning

5. 8th ICATPP Conference, Como, N.Tuning
Trigger Overview
Bunch crossing rate
40 MHz
Non empty bunch x-rate
30 MHz
Visible interaction rate
~12 MHz
Output of L0
1 MHz
40 MHz
L0 (4 s)
L0: high PT
Calorimeter+Muon
Fully synchronous on custom boards
L1: high PT + impact parameter
VELO+TT
Max. latency 52.4 ms
(L1 buffer size: events)
Software trigger
HLT: high PT + displaced vertex + B-mass
Full detector information available
1 MHz
L1 (~1 ms)
40 kHz
HLT (~14 ms)
200 Hz
6 Oct 2003
8th ICATPP Conference, Como, N.Tuning

6. 8th ICATPP Conference, Como, N.Tuning
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 peak>threshold
(Zvtx)  2.8 mm, (beam)  53 mm
6 Oct 2003
8th ICATPP Conference, Como, N.Tuning

7. 8th ICATPP Conference, Como, N.TuningL0
High-pT , e,  and hadrons with Calorimeter and Muon system
Muons:
Hadrons:
Efficiency
Fraction of events
6 Oct 2003
8th ICATPP Conference, Como, N.Tuning

8. 8th ICATPP Conference, Como, N.Tuning
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/(+-)
6 Oct 2003
8th ICATPP Conference, Como, N.Tuning

9. 8th ICATPP Conference, Como, N.Tuning
L 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
ln pT
ln IP/IP
L1+HLT implemented on same CPU farm:
~1000 CPUs for L1, ~800 for HLT+reconstruction
HLT runs in the background to limit deadtime.
6 Oct 2003
8th ICATPP Conference, Como, N.Tuning

10. 8th ICATPP Conference, Como, N.Tuning
Trigger performance
Good efficiencies for useful events:
L0: 50 – 90%
L1: 50 – 70%
Timing is OK: :
L0: 3.5 s (4 s)
L1: 8 ms (1 ms, max. 50 ms)
8 ms (1 GHz PIII)
6 Oct 2003
8th ICATPP Conference, Como, N.Tuning

11. What do we do with the triggered events?
6 Oct 2003
8th ICATPP Conference, Como, N.Tuning

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CP violation
Mixing
Small in B0 system, 1-|p/q|~10-3
BH0~ p|B0>+q|B0>
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)
f=fCP: LHCb: B0J/KS, B0sJ/, B0.
ffCP: LHCb: B0sDSK , B0D*, B0D0K*.
Present status:
sin(2)=0.731  (BJ/KS from e+e-)
sin(2)=0.695  (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D0K*0,D0K*0
Sensitive to new physics in D0,D0 mixing
6 Oct 2003
8th ICATPP Conference, Como, N.Tuning

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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K*0
B0
BR ~10-6: (~103 sel. events/year)
B0+- K*0
BR ~10-9: (~101 sel. events/year)
B0s+-
bs penguin
6 Oct 2003
8th ICATPP Conference, Como, N.Tuning

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Event selection
. B0sD-sK+
. B0sD-s+
Variables:
pT, impact parameter, PID.
Decay length, vertex, mass constraints.
B-mass, pointing.
6 Oct 2003
8th ICATPP Conference, Como, N.Tuning

15. 8th ICATPP Conference, Como, N.Tuning
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 x ~ 50k
“Typically”
6 Oct 2003
8th ICATPP Conference, Como, N.Tuning

16. 8th ICATPP Conference, Como, N.Tuning
CP measurement
(B0 -B0)/(B0+B0)
(1 year of B0J/KS)
sinmdt
sin2
Extract CP parameters from fast simulation
Given the resolutions, yields and background from full simulation
Examples:
ACP(B0J/KS) =
ACP( B0sD+sK-) =
(B0s -B0s)/(B0s+B0s)
B proper lifetime (ps) 
(5 years of B0sD-sK+)
f =
6 Oct 2003
8th ICATPP Conference, Como, N.Tuning

17. LHCb physics reach in 1 year
Excellent  sensitivity
Twice current BABAR+BELLE sensitivity
Various  measurements to disentangle new physics
Rare decay
(B0K*0) 2% higher than SM?
 3 significance
6 Oct 2003
8th ICATPP Conference, Como, N.Tuning

18. 8th ICATPP Conference, Como, N.Tuning
Conclusions
The LHCb trigger:
reduces the rate from 40 MHz to 200 Hz ( !),
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.
6 Oct 2003
8th ICATPP Conference, Como, N.Tuning