1. Hidden Valley Processes
Feb 21, 2007
Erik Brubaker
FTK meeting

2. Aside: FTK training production
After last meeting, Francesco managed to turn off unneeded calorimeter sim, digi, reco.
Jobs are faster (factor of ~3-4) and output smaller (factor of ??)!
UC tier3 cluster had dCache problems for ~1 wk, putting a big dent in production progress.
Right now I estimate almost 30M events done—time to ship them off to Pisa and check patterns!
February 21, 2007
FTK Meeting

3. Hidden Valley models
Matt Strassler (U Washington) explores “Hidden Valley” model space—regions having light particles, but so far inaccessible experimentally for some reason.
One class of HV models has light scalar Higgs decaying into new long-lived (3 ps-3 ns) particles. (hep-ph/ )
If those new particles decay to jets, the event signature is 2 pairs of jets, each pair sharing a displaced vertex.
February 21, 2007
FTK Meeting

4. HV process features Using mH = 100 GeV, mS = 40 GeV, tS  30 ps.
All partons (4/ev)
Lowest pT
Highest h
Very low!
February 21, 2007
FTK Meeting

5. Truth tagging information
HV events have nearby vertices at large distance from the beamline…
Decay vs Prod Vertex
February 21, 2007
FTK Meeting

6. Event Selection for “offline” analysis
Require ≥ 2 jets w/ |h| < 2.5, pT > 15 GeV.
Find ≥ 1 pair of jets matched to vertices w/ Dx < 2 cm, avg(r) > 4 cm.
Vertices used are B _production_ vertices.
Selection is 60% efficient for this benchmark sample.
Becomes 96-98% efficient after LVL1 trigger cuts.
February 21, 2007
FTK Meeting

7. Benchmark signal rates
Model
LVL1 trigger eff.
LVL1
Ev/yr (10^7 s)
mH=100; Br(HSS)=1-100%; mS=40; tS=30 ps
4j40:
[6e-6,6e-4]
4j25:
[2e-5,2e-3]
mH=130; Br(HSS)=1-100%; mS=40; tS=30 ps
4j40:
4j25:
[2e-5,1e-3]
mH=170; Br(HSS)=0.1-1%; mS=40; tS=30 ps
4j40:
[7e-7,7e-6]
7-70
4j25:
[2e-6,2e-5]
20-200
No FTK
FTK
No FTK
FTK
No FTK
FTK
LVL1 is the bottleneck, so these numbers tell most of the story
February 21, 2007
FTK Meeting

8. Background to HV process
No background processes with the same signature, including shared displaced vertex.
BG contributions at some level from
KS, L decays in flight + accidentals?
Misreconstructed primary vertex?
Overlapping jets from different primary vertices?
All _should_ be manageable with time and effort, but hard to get an estimate for this study!
Existing SHERPA jet samples lack B hadron info in ntuple.
Have to regenerate samples—move operation to UC tier3 etc.
Make b-enriched.
February 21, 2007
FTK Meeting

9. Next steps Background study for Hidden Valley:
Generate b-enriched sample.
Check rate to pass cuts using B _decay_ vertex, which is still an overestimate.
Perform multi-threshold study a la Kohei.
Looks like maybe not needed for HV?
LVL1 rates shared with H->hh->4b.
February 21, 2007
FTK Meeting

10. Additional Materials

11. Different benchmark point
Using mH = 130 GeV, mS = 40 GeV, tS  30 ps.
Slightly harder than mH = 100 GeV, but not much…
February 21, 2007
FTK Meeting

12. BOLD = I have a 100k-event sample…
HV benchmark models
Production Process
Higgs mass
Br(h ==> SS)
Mass of S
Lifetime of S
S decay channels
Comments
All standard model Higgs production
gg ==> h, qq==>qqh, qq==>Wh, Zh
80 GeV; 100 GeV; 130 GeV
100%; 10 %; 1%
20 GeV; 40 GeV
3 ns;
300 ps;
30 ps;
3 ps
bb;
tau tau
 An 80 GeV higgs decaying to SS with lifetime less than 300 ps may well be ruled out; LEP has not published limits
170 GeV
1%; 0.1 %
20 GeV; 40 GeV; 65 GeV
 3 ns;
A Higgs that can decay to WW, ZZ cannot easily have a large Br to SS
BOLD = I have a 100k-event sample…
February 21, 2007
FTK Meeting

13. Signal rates Production cross section is gg->H, depends on mH
H->SS is 0.1%--1% for high mass, 1%--100% for low mass Higgs
Analyze with our full machinery to get LVL1 trigger efficiency for (ATLAS default) and (with FTK)
LVL2 efficiency depends on S lifetime, but e.g. a single tag requirement should be highly efficient
Assume 10^33—low LHC luminosity…
February 21, 2007
FTK Meeting