1. Erik Brubaker U of Chicago
LVL1 rates & Hhh4b
Erik Brubaker
U of Chicago

2. Outline Almost-final word on LVL1 jet rates.
Understanding cross-section for Hhh4b process.
Talk descoped due to UC Tier2 going down last night…
September 7, 2006
FTK Meeting

3. Jet rates from Sherpa
Sample
LVL1 4jet(40) [Hz]
LVL2 4tag [10-3 Hz] 10
38.5 ± 4.4
0.2 ± 0.2 25
47.5 ± 1.0
3.0 ± 2.9 50
50.7 ± 0.3
0.8 ± 0.4 10
42.0 ± 22.7
0.0 ± 0.0 25
65.9 ± 3.8 50
56.2 ± 0.6
0.4 ± 0.2 10
58.4 ± 2.3
0.1 ± 0.1 25
58.7 ± 0.4
0.3 ± 0.0 50
66.7 ± 0.2
0.8 ± 0.1 10
75.2 ± 32.5 25
82.8 ± 4.0
18.7 ± 18.6 50
73.7 ± 0.6
2.3 ± 1.3
Check different ME combinations, kT,cut values to balance stats/resources, and to estimate systematics.
LVL1 rates scatter in Hz.
“LVL2” rates require 4 tags, have units of mHz! Not too interesting as is.
September 7, 2006
FTK Meeting

4. Cross-check: jet rates from Alpgen
Samples from Ambreesh/SUSY group.
ALPGEN light jet samples only.
LVL1 rates slightly underestimated
Total rate lower than, but on the order of, Sherpa results.
Caveat: 4- and 5-jet samples ntupled with 0.7-cone jets—inconsistent with parametrizations…
Sample
LVL1 4jet(40) [Hz]
3 jet
8.79 ± 0.03
4 jet
15.71 ± 0.01
5 jet (incl)
9.64 ± 0.02
Total
34.14 ± 0.04
September 7, 2006
FTK Meeting

5. Cross-check: jet rates from Pythia
Check against Pythia dijets
Generic QCD incl heavy flavor
Caveat: Default Pythia settings for UE etc. have been unstable…
Sample
LVL1 4jet(40) [Hz]
pT > 50 GeV
95.0 ± 11.9
So…
1. Consistency among models?
2. All are consistently lower than TDR rate: 200 Hz for GeV, where 90~=60 in our calibration…
September 7, 2006
FTK Meeting

6. Systematics on LVL1 jet rates
Variations in ycut, ME configurations in Sherpa
RMS of the 12 sample results, weighted by reported stat unc.: 12%
Differences among generators
Alpgen lower, Pythia higher with caveats: 30% for now
Additional possible factors—need to check explicitly?
PDFs
UE/MPI
Parametrizations
RMS=13.1
RMS=7.5
September 7, 2006
FTK Meeting

7. LVL1 rates conclusion
Need to finish checking effect of UE/MPI in Sherpa, also different pythia settings (MWT2 died on me last night).
Run this by ATLAS trigger gurus.
Any similar recent studies?
Difference w.r.t. TDR understood?
Recommendation for FTK studies:
Use Sherpa sample with best combination of statistics, ME configuration, and kT,cut for your proposed thresholds. (Best to try more than one.)
Use my machinery to calculate rates for a range of thresholds.
Assign 35% uncertainty on absolute rate.
September 7, 2006
FTK Meeting

8. Example LVL1 rate scan
Require 4 jets: 1st & 2nd at cut on x-axis; 3rd & 4th at cut in legend.
4th jet cut drives rate— not surprising
September 7, 2006
FTK Meeting

9. Hhhbbbb sigma*BR
I had a problem with low s*BR (2 fb) reported by pythia for Hhhbbbb w/ mh=130, mH=300.
What MSSM model was pythia assuming?
Turns out Hhh is large only for lowish tanb, and for 2mh<mH<2mt.
To find operating points:
Use mhmax scenario to stay away from LEP direct search limits.
For a given tanb, scan mA to maximize s(ggH) x BR(Hhh) x BR(hbb) x BR(hbb).
tanb
2.5
2.75
3.0
3.25
3.5
4.0
4.5
5.0 mA
360
260
230
240
250
s*BR [fb]
233
1019
1060
818
637
398
168
September 7, 2006
FTK Meeting

10. Additional slides

11. Physics Case (Details)
Statement #1
FTK vs TDR menus, i.e. no tracking at LVL2—ignore timing.
Statement #2
FTK vs nominal LVL2, incl. tracking.
Need:
FTK allows b-jet (t) ID w/ eb, ec, eq, et.
Correlation w/ offline?
Depends on environment
LVL1 trigger rate, driven by multijet evts, estimated using modern generator + parametrization of full ATLAS LVL1 simulation.
Fix LVL2 output rate.
Limit LVL1 output rate to sth reasonable.
Optimize LVL1 cuts & LVL2 tagging reqs, maximizing signal acceptance/ significance.
Same as stmt #1, but add trigger timing into the eqs.
Hard to estimate, large uncertainties.
But more realistic, stronger case.
September 7, 2006
FTK Meeting

12. CKKW vs MLM CKKW: 2 parts MLM: matching prescription ALPGEN SHERPA
Reweight ME to reproduce PS behavior for soft emissions.
Reject showers that overlap higher-order ME.
Boundary is kT,cut or ycut  kT,cut2/s.
MLM: matching prescription
Cluster partons after shower, compare to ME partons.
Require each ME parton to match a unique “jet”, else reject event.
ALPGEN
SHERPA
4p ME
3p ME
CKKW
MLM
September 7, 2006
FTK Meeting