# Presentation: 672679

## L1 and L2 Triggers for MSP’s and    ‘s

- Yu. Gershtein
- Brown U
- DøPAM, Sep/30/99

##   Outline

- Introduction
-  why trigger with tracker
- What makes it difficult
- Changes to L1 terms
-  track isolation
-  estimate of number of interactions at L1
-    (total occupancy)
-  local occupancy
- New features of L2CTT
- Summary

- Yu. Gershtein

- 9/30/99

## Why Tracker?

- Sometimes it is all we have
-  Massive Stable Particles
-  can be too slow or decay before the muon system
- More efficient
-   leptons
-  recover low Et (⋲10 GeV) taus which often do not give a triggerable jet
- Just because
-  Stiff isolated track is always interesting!!
-  flavor blind lepton trigger
-  physics we don’t know about

- Yu. Gershtein

- 9/30/99

## Why Is It Difficult?

- Only 8 axial fiber layers in L1 track finder -> fakes!!!

- Yu. Gershtein

- 9/30/99

##   Fake L1 Tracks

-  Tracks with pt > 11 GeV/c

-  huge rate at high Nint comes from fake tracks
-    check occupancy near high pt track
-    suppress high Nint events

***≤******4 int***
***≤******2 int***

- Yu. Gershtein

- 9/30/99

## Track Isolation

-  L1 track is isolated if it is the only track in the home and both adjacent sectors (3 sectors out of 80)

- 2 tracks, one isolated, Nint≤4

- Yu. Gershtein

- 9/30/99

##    Total Occupancy

-  count hits in each of 80 FE and set bit if the number of hits is over a threshold (29 =12%)
-  OBC counts sectors with set bits and reports the number to FBC.
-  00, 10, 21, 32, 43, 54, 65, 76, 87, 97, 107
-  FBC adds 8 OBC reports and sets “high number of interactions” bit if the sum is greater than 15

-  Occupancy in CFT is determined by the number of soft (untriggerable) tracks and strongly correlated with number of interactions

- Yu. Gershtein

- 9/30/99

##    Total Occupancy

- Note, that this is signal efficiency.
- The background rejection can be
- Much higher.
- No way to simulate at the moment 

- Yu. Gershtein

- 9/30/99

##   Local Occupancy

- One step further: (D.Cutts)
-  probability to have a fake track is a very steep function of occupancy in the home sector
-  Cut on it!
- Note: Inefficient for tau decays...

- Yu. Gershtein

- 9/30/99

##   L1  Strategy

- If not for the fake tracks one could trigger, for example,  just on a pair of tracks with pt>5 GeV
- Most of the fake tracks come from low ET events with high number of interactions ->
- Suppress very high Ninteractions
- Suppress very low ET events

- Require L1 jet seeds of
- 3 GeV,
- 5 GeV,
- 6 GeV

**TTK(2,5)TIS(5)**

- Yu. Gershtein

- 9/30/99

##    L1/L2 Strategy

**     ****Level 2**
- Confirmation of tracks in the silicon should kill most of the fakes
- Many other handles
-  dE/dx in silicon
-  dE/dx in CPS
-  calorimeter tau tool
-  ...
-  **more sophisticated isolation in CFT**

**Level 1**

- Yu. Gershtein

- 9/30/99

##    Isolation at L2

- At L2 one can examine the event topology in more detail
- Things we look for have a common feature: they are narrow isolated objects
- One prong
-  track with pT>5 GeV and in <0.5 there is no more than one track with pT<2 GeV and no tracks with pT> 2 GeV
- Three prong
-  as one prong, but allow up to two additional tracks in <0.1 around the track

- Yu. Gershtein

- 9/30/99

##     Isolation at L2

- Can have more elaborate isolation at L2
-    * One-prong:
-         -> no tracks over P0 GeV in ±0.5 rad
-         -> one or no tracks below P0 GeV

- TTK(2,5)*TIS(5)
- P0 = 3 GeV
- P0 = 2 GeV
- P0 = 0 GeV

-   * Three-prong:
-        -> allow one or two tracks within ±0.1
-  -> less pure object but still factor of 5

- Yu. Gershtein

- 9/30/99

##     L2CTT

- Receives a list of tracks from L1FT or L2STT
- Recalculates pT
- Sorts tracks in pT
- Has some spare time for low track multiplicity events

- Yu. Gershtein

- 9/30/99

##    Algorithm

- Only one pass trough the track list
- As the tracks are uploaded from the input buffers they are
-  tagged as a one/three prong candidate if pT>5 GeV
-  two 160-bit bitmaps are filled for tracks with pT>P0 and for pT<P0, making a “histogram” of track azimuth angle
-  for all one/three prong candidates (usually a very short list) bit sums are performed, giving a track count “almost” in wedges <0.5 and <0.1
- The L2CTT output words format has enough spares to accommodate two bits for one and three prong tags

- Yu. Gershtein

- 9/30/99

##   L2CTT  Timing

- Run optimized code on d02ka for 20-40 GeV QCD and for ttbar + 2 minbias

- Time, s

- Before
- After
- Increase

- Yu. Gershtein

- 9/30/99

##    The Efficiency

- Study efficiency on Z->tau+tau-
-  select events with two taus ||<1.5  pT>10
-  Require TTK(2,5)·TIS(5) at L1
-  L2 loose means P0=2 GeV, tight -> P0=0

- Eff(L1)=72%
-     85%/tau
- Eff(L1·L2)=40-60%
- NOTE that THT efficiency of 85-90% is not included

- Yu. Gershtein

- 9/30/99

##    Summary

- The improvements
-    of the tracking
-    system in Run II
-    gives new opportunities
- New L1 terms are included in the design
- Modifications to L2CTT  algorithms are coded and timed
- New items in the trigger menu

- Yu. Gershtein

- 9/30/99