Progress on H/Abb -> 4b

1
Progress on H/Abb -gt 4bschannel for the FTK
physics case 4jets trigger w/ and w/o FTK

• Kohei Yorita
• 
  Young-Kee Kim
• 
  University of Chicago
• _at_ the FTK Meeting on June 6th ,
  2006

2
Signal Process
If MA gt 150 GeV, A and H masses are degenerated
and experimentally undistinguishable.
Consider H/Abb -gt 4 bs process.
gt bb decay 85-90 if tan? gt20
Coupling to up-type is enhanced at low tan?, so
decay into tt becomes large.
Samples generated with Atlfast, 500K events each
at tan?30
MA(GeV) 150 200 250 300 350 400 500 600 700 800 900
XsecBR pb 610 212 87.9 42.1 39.9 21.9 12.1 4.30 4.18 1.74 0.81 0.82 0.40 0.21 0.21
is the number in TDR
3
TDR expectation (w/o FTK)
This channel
All channels with 300fb-1
How much can we lower tan? with FTK ? How
well/better can we see H/A mass distribution
with FTK ? (If it exists).
?? channel seems promising. But hard to
reconstruct the mass. -gt Still need this 4b
channel !
4
Strategy
Current 4J Menu w/o btag
w/ FTK (btag _at_ LVL2)

LVL1 Max


Essentially anything can be done _at_ EF (sec), but
still there are many unknown factors here. So
this study has been done where LVL2 output rate
is kept as TDR(100Hz)
LVL1 Current 200Hz

5
Trigger Rate _at_ 2x1033
Background Sherpa 2to2 2to3 process, ytgt25 GeV
4jets w/o btag
LVL1 Out 1KHz
LVL2 Out 100Hz
EF out 10Hz If nobtag, It is 110GeV
6
Setting up Working Points
LVL1 LVL2
w/o FTK Jet Pt Rate - 40GeV 1KHz (No btag) 70GeV 100Hz
w/ FTK Jet Pt Rate - 40GeV 1KHz btag 40GeV 100Hz

• In order to reduce rates by
• a factor of 10 _at_LVL2, while keeping
• Jet Pt threshold to 40 GeV,
• FTK rejection factor has to be
• (1) Ru gt 8 (eff. lt 12.5) with 1btag
• (2) Ru gt 3 (eff. lt 33.3) with 2btag
• (here, btagging eff. is 50.)
• Is this feasible ? Need realistic estimate.

(2) 2tag
(1) 1tag
7
Figure of Merit _at_ Trigger Level
_at_ MA 150 GeV gt1btag (left) x3 higher
acceptance while keeping trigger rate. gt2btag
(right) x1.5-2 times higher acceptance while
keeping trigger rate.
8
After Optimization
Btagging bjet 50 cjet 10 Ru
100 (expected offline quality)
5?
Jet Pt cut optimization has been done for each
mass sample separately. Cut values are summarized
in next page. Generally requiring 4btag gives
better or the same sensitivity than 3btag.
9
Optimized Cut Values
MA w/ FTK (4btag) w/o FTK (4btag)
150 (40,40,40,40) (70,70,70,70)
200 (60,40,40,40) (70,70,70,70)
250 (70,40,40,40) (70,70,70,70)
300 (80,60,40,40) (70,70,70,70)
350 (100,60,40,40) (70,70,70,70)
400 (120,80,40,40) (100,70,70,70)
500 (160,90,40,40) (140,90,70,70)
600 (200,100,40,40) (160,90,70,70)
700 (230,130,40,40) (210,120,70,70)
800 (280,150,40,40) (230,120,70,70)
900 (300,200,40,40) (280,170,70,70)
w/ FTK starts from (40,40,40,40) w/o FTK starts
from (70,70,70,70)
10
5? Discovery with 30fb-1
gt Systematic uncertainty is not included. gt Great
improvement using FTK !!!
11
Dijet Mass Distribution (1)
Comparison of signal dijet mass btw w/ FTK and
w/o FTK _at_ Optimized cut
MA 150GeV
MA 200GeV
Much better shape w/ FTK due to lower Pt
threshold for jets. Peak position input
mass.
MA 250GeV
MA 300GeV
12
Dijet Mass Distribution (2)
Comparison of signal dijet mass btw w/ FTK and
w/o FTK _at_ Optimized cut
MA 350GeV
MA 400GeV
Difference becomes smaller as mass gets larger
since higher mass sample tends to have more
energetic jets. -gt lowering threshold does not
help much. Peak position does not
correspond to input mass. Is this because
correction factor (ATLFASTB) for b-jet is
tuned by using SM Higgs VH-gtVbb where H is 150
GeV.
MA 500GeV
MA 600GeV
13
Dijet Mass Distribution (3)
Comparison of signal Background dijet mass _at_
Optimized cut Normalization Expected Number of
Events with L30fb-1.
MA 150GeV
w/ FTK
MA 250GeV
w/o FTK
w/ FTK
w/o FTK
MA 200GeV
w/ FTK
w/o FTK
MA 300GeV
w/ FTK
w/o FTK
It will be very hard to measure the mass w/o FTK,
even w/FTK, high mass measurement seems very
tough. (may need to optimize the analysis not
by the significance but for this dijet mass
measurement .. But not in this study.)
14
Summary and Plan

• w/ FTK we observed a significant improvement in
  this channel by lowering LVL1/LVL2 Pt threshold.
• w/o FTK, it will be really hard to measure the
  Higgs(H/A) mass (if it exists..) (even w/ FTK,
  very hard in high mass)
• Things to do
• - Use Sherpa with bb in ME sample and redo
  all of them.
• - Multi-Threshold Need careful study on
• trigger rate at very low threshold.
• - Is ytgt25 (parton level cut) low
  enough ?
• - LVL1 Param uses jets with Pt gt 10
  GeV.
• Documentation
• gt Sections I (plan to) take
• - 4Jet Trigger Rate with multi-threshold
  discussion
• - H/Abb physics case.

15
Sherpa 2to3 ytgt10 GeV
ytgt10 only has 1M events. Still under
investigation.
16
Btagging DAQ-Conf-2005-007(Online btagging
selection for the ATLAS experiment at the LHC)
Andreas Kootz et al.
17
Sherpa with bb
Sherpa with bb in ME sample has only 1M events
(others here are roughly10M events.) Need more
statistics, though essentially do not expect to
see big difference.
0tag
1tag
2tag
Sherpa with bb, ytgt25 would be a default for a
final study.
3tag
4tag