1. LoF Rejection for Your Analyses & Preliminary Report on Multijet Background
May 3, 2011
Steve Alkire

2. Contents LoF Rejection Multijet Background
Summary of 2 cuts to remove Line of Fire
2-segment triangle cut
Calo-only cut designed for EF implementation
Rates and overlap of cuts
Rejecting LoF in your analyses
Multijet Background
General Strategy
Preliminary results
Conclusions

3. LoF Rejection 2 cuts 2 triangle cut: Tile cell timing cut:
Removes Moore segments in the MS endcaps which point in the z-direction and are phi-matched to a jet
Requires one such segment on the A and C sides of the detector.
Tile cell timing cut:
Requires 4 or more cells which:
are phi-matched to the jet
are > .3 dR from a jet axis
are > 3 ns early
are +/- .5 ns from ideal beam halo timing
> 240 MeV energy

4. Rates and Overlap
Reduction in rates from collision and MC in Cal Ratio Trigger:
2 triangle
Tile Cell
Combined
Collision
32%
31%
36% MC
<0.1%
How much LoF is not being captured by either cut?
Can naively estimate around 5/36 of 4% or ~0.5% of total signal rate assuming the cuts are entirely independent.
This question can also be answered with unpaired bunches, however statistics are low right now:
Only ~3-5 events passing our triggers/run

5. Using LoF Cuts 2 Triangle: Tile Cell Timing:
bool <Your Analysis>::passes_double_triangle_cut(double phi, double dz, double dphi)
Recommended usage: passes_double_triangle_cut(<phi of jet>, 0.98, 0.4)
Returns true if the event IS a Line of Fire event.
Tile Cell Timing:
bool <Your Analysis>::passes_early_halo_time_had_cell_jet_exclusion(double t_halo, double t_early, double eta, double phi, double dphi, double dr, int n_cell, double energy_cut)
Recommended usage: passes_early_halo_time_had_cell_jet_exclusion( 5.0, 3.0, <jet eta>, <jet phi>, 0.2, 0.3, 4, 240.0)

6. Using LoF Cuts
Both cuts will be available for use in your offline analyses:
There will be a working analysis example in svn: /Physics/Exotic/Analysis/LongLived/HVHeavyFermionPair s/HVNtuple/trunk/macros ?
Also instructions will be on the twiki soon: alleyLongLived

7. Multijet Background General Strategy: Tag and Probe Dijets
First goal: find the probability that a single jet from a Dijet event passes our triggers:
Extrapolate to the case of 2,3,4,5 jet events using relative rates of multijet events from this paper: ATL- COM-PHYS
Use entire 2010 data because jet prescales are much worse in 2011.

8. Tag and Probe Criteria Tag: Probe:
L2_jXX where XX is 15,30,60, 90 etc..
These are highly prescaled, however if we use more complicated triggers or just the whole L2 or offline containers we bias the study.
Match to Offline jet: < .1 dR
Require good jet criteria
Soon: require x tracks of Pt > 1 GeV
Soon: (pt1-pt2)/(pt1+pt2) < .2
Probe:
|phi_tag – phi_probe| > 2.6
Offline Et:
>35 GeV for Cal Ratio
>17.5 GeV for Trackless
None for Muon RoI

9. Rates (r15986) QCD: Regular Tag and Probe criteria described previous
Cal. Ratio, Trackless, Muon RoI
(Pass) - Probe jet from QCD criteria also passes HV trigger.
(Total) – Total number of events passing HV trigger for which the L2_jXX trigger was turned on.
L2 Trig.
QCD
Cal. Ratio
Trackless
Muon
RoI
Pass
Total
L2_j15
62929 2 46 1
L2_j30
155402 7
223 5
L2_j60
18911
112
L2_j90
3882 70

10. Conclusions:
Tag and Probe suffers from highly prescaled single jet triggers.
With complete 2010 data we expect ~100 Cal. Ratio, ~60 Trackless, and ~30 Muon RoI events.
This is much better than we have from MC.
Further criteria to strengthen the Tag jet are coming soon.
Rates from QCD should be quotable with 10-30% uncertainty from poisson.