FTK Studies: Hhhbbbb

FTK Physics Case Meeting

11/03/05

Erik Brubaker

University of Chicago

Nov 3, 2005 FTK Physics Case Meeting 2

Organization• Web page here: http

://hep.uchicago.edu/~brubaker/ftk/– Links to previous meetings– Mailing list– Information about tools, e.g. L1 response

parameterizations– Analysis code snippets, e.g. jet trigger combinatorics– Collect useful plots, results

Nov 3, 2005 FTK Physics Case Meeting 3

Topics• Hhhbbbb process, signal sample

• SHERPA multijet background sample

• Some event rates

• Next steps

Nov 3, 2005 FTK Physics Case Meeting 4

Reminder: Strategy• Making the physics case for FTK means studying

signal and background trigger rates for several processes.

• For now, quantify improvements as a function of increase in L1 rate.– In parallel, studies of FTK speed and efficiency will tell

us the magnitude of that increase.

• Use fully simulated events to parameterize the L1 jet and tau trigger response vs ATLFAST jet pT. Then various processes for physics studies can be studied using ATLFAST.

Nov 3, 2005 FTK Physics Case Meeting 5

Response parameterization• Functional form:

tried & true double Gaussian.– No pathological

behaviors– Second Gaussian

can take care of high tails (?)

• Can be modified & improved as needed.

Nov 3, 2005 FTK Physics Case Meeting 6

Double Higgs—Process• Resonant production of

lightest MSSM neutral scalar Higgs h0 through the heavier H0.

• Previous study (ATL-PHYS-97-104)– For MH=300 GeV and tan(=3, S/sqrt(B) of 5.7 can

be reached using 300 fb-1; this requires 4 jets with ET>40 GeV and ||<2.5.

– For lower integrated luminosity, more tricks are needed and jets down to 20 GeV are preferred.

– They concluded trigger rates probably prohibitive.

Nov 3, 2005 FTK Physics Case Meeting 7

Signal Sample• Contrary to last time’s claim, one can use Pythia

for resonant Hhh production.– mH = 300 GeV

– mh = 130 GeV

– Pythia reports = 2 fb• Not sure I’m working in a consistent MSSM world.

• Earlier studies used low tan (so lower mh), and ≈ 2 pb.

• Generated 10M events, so far only fast simulation.

• Should check sensitivity to mH, mh.

Nov 3, 2005 FTK Physics Case Meeting 8

Signal sample• Quite low jet pT,

especially for j4.

• Probably want multiple trigger thresholds.

Nov 3, 2005 FTK Physics Case Meeting 9

SHERPA event generator• Many of our processes have backgrounds with

four jets in the final state.– Want accurate ME description of kinematics.

• SHERPA: developed by Dresden group.– http://www.physik.tu-dresden.de/~krauss/hep/

• Generator of generators, like CompHEP etc.• Handles consistently boundary between matrix

element and parton shower emissions.• Produces unweighted events.• Not widely used, tested in ATLAS.

Nov 3, 2005 FTK Physics Case Meeting 10

SHERPA multijet sample• Unexpected distributions

of njet, jet pT.

• Expected higher <njet> for higher-order ME—opposite is true.

• PS/ME boundary is set to 50 GeV.

Nov 3, 2005 FTK Physics Case Meeting 11

SHERPA multijet sample• No obvious “turn-on” of add’l jets from ME.

Nov 3, 2005 FTK Physics Case Meeting 12

Signal & Background L1 rates• Use fast simulated signal & SHERPA samples.

– Want Pythia dijets too, but these are more complicated.

• Require at least 4 ATLFAST jets inside ||<2.8.• Find the probability for the event to have four jets

passing a 40 (60, 80, 100) GeV trigger.– Want multiple trigger thresholds as well, but that is more

complicated.

Nov 3, 2005 FTK Physics Case Meeting 13

Beginnings of an L1 rate tableSample Signal Pyth dijet SHERPA

x-section 2 pb 24.6 ub

N Events 110k 10k

Eff,#/fb-1

40 5.8%,116 0.17%, 42M

60 1.7%, 34 0.049%, 12M

80 0.64%, 13 0.022%, 5.4M

100 0.29%, 6 0.012%, 3M

Nov 3, 2005 FTK Physics Case Meeting 14

Next steps• Get full simulation of Hhh4b.

– Check that L1 response param. matches observed rate– Work out analysis more thoroughly—need to

determine improvement from FTK relative to some “state of the art”.

• Generate large SHERPA multijet sample.

• What other background samples are needed?

• Revisit L1 response—improve as needed.