1. July 22, 2002Brainstorming Meeting, F.Teubert L1/L2 Trigger Algorithms L1-DAQ Trigger Farms, July 22, 2002 F.Teubert on behalf of the Trigger Software group Introduction L1 Algorithm L2 algorithm Summary

2. July 22, 2002Brainstorming Meeting, F.Teubert Introduction Minimum bias vs B-events: L0 Pileup Veto (VELO) (VELO) Track,  s properties L0 High Pt tracks,  s (CAL0/MUON) (CAL0/MUON) L1 Impact parameter and high Pt tracks. (VELO + TT1 + L0) Event properties L2 Secondary vertex Lifetime (VELO) (time consuming) Mass (VELO+STs) (precision) 10 MHz 1 MHz 40 kHz 5 kHz 0.2 kHz

3. July 22, 2002Brainstorming Meeting, F.Teubert L1 Algorithm The L1 algorithm under development is based on: m 2D VELO tracks + Primary vertex reconstruction (~4 ms) m About 10 3D-tracks (~2 ms) to be extrapolated to TT1 and/or matched to L0 objects (~0.5 ms) matched to L0 objects (~0.5 ms) m Assign b-event probability based on Impact parameter and Pt. Input Data:

4. July 22, 2002Brainstorming Meeting, F.Teubert L1 Algorithm Performance Pt from TT1  Pt/Pt ~ 25 % Pt from L0+VELO  Pt/Pt ~ 3 %

5. July 22, 2002Brainstorming Meeting, F.Teubert L1 Algorithm Performance blue: minimum bias red: signal in acceptance define a trigger variable L1 = L1(PT1, PT2, IPS1, IPS2) where tracks are required to have impact parameter between 0.1 and 3 mm, and are ordered according to their pt. If a L0  /e remove cut on impact parameter significance.

6. July 22, 2002Brainstorming Meeting, F.Teubert L1 Algorithm Performance Pt from TT1 Pt from L0

7. July 22, 2002Brainstorming Meeting, F.Teubert L1 Algorithm Limitations L1 limitations. 1) Pileup events left over from the L0 pileup, affect L1 at low output rates (<20 kHz). Need to work on an optimized algorithm to deal with these events at L1. 2) Momentum resolution not good enough to use mass information in an effective way. What L2 can do? 1) Downstream tracking of few selected candidates to ST1-ST3. 2) Confirm L1 decision. 3) Use mass information and displaced vertex to form a b-event probability. Channel dependent cuts left to L3.

8. July 22, 2002Brainstorming Meeting, F.Teubert L2 Algorithm Input # offline clusters in TT1 + IT # offline clusters in OT # offline clusters in VELO B 0 d   -  + after L0 Db v248r2 Noise+spillover+pileup+…

9. July 22, 2002Brainstorming Meeting, F.Teubert L2 algorithm feasibility study Simple/fast downstream tracking:  Pt/Pt

10. July 22, 2002Brainstorming Meeting, F.Teubert L2 algorithm feasibility study B.Hommels, M.Merck LHCb week (29/05/02) Efficient for P > 5 GeV 1.7 ms/track  ~20 ms/event

11. July 22, 2002Brainstorming Meeting, F.Teubert L2 algorithm feasibility study Confirm L1 decision: log(ip1/  1) + log(ip2/  2) log(Pt1) + log(Pt2) Example: 40 kHz  25 kHz  (B 0 s  D - s K + ) 93%  ( B 0 d   -  + ) 95% If  Pt/Pt ~ 2% available at L1, the output rate can be reduced by a factor 2 for the same signal efficiency. + use of sec. Vertices and use of sec. Vertices and invariant mass invariant mass

12. July 22, 2002Brainstorming Meeting, F.Teubert L1 output rate optimization  B 0 d   +  -  B 0 s  D - s K + No L2 10 kHz 5 kHz First attempt to use secondary vertices and invariant mass at L2 (LHCb week 29/05/02)

13. July 22, 2002Brainstorming Meeting, F.Teubert Summary L1 Algorithm: INPUT: VELO+TT1+L0 summary, total ~1500 digital clusters ALGORITHM: select few VELO tracks (~10)/event to assign Pt. Compute b-event probability using the two highest Pt tracks. PERFORMANCE: typically 80-90% signal efficiency for events finally “analyzed”, at 20-40 kHz output rate.Takes per event in a 1GHz CPU today. L2 Algorithm: INPUT: VELO+TT1+ST1-3, total ~3200 offline clusters. ALGORITHM: Confirm L1 decision with  Pt/Pt ~ 2%. Select few VELO+ST1-3 tracks to form a secondary vertex, and compute invariant mass. PERFORMANCE: expect typically 80-90% signal efficiency for events finally “analyzed”, at 5-10 kHz output rate. Expect per event, but we don’t really have a measurement today.