Progress on H/Abb -> 4b’schannel for the FTK physics case~ 4jets trigger w/ and w/o FTK ~

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

Signal Process

MA(GeV)

150 200 250 300 350 400 500 600 700 800 900

Xsec*BR

[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

Samples generated with Atlfast, 500K events each at tan=30

If MA > 150 GeV, A and H masses are degenerated and experimentally undistinguishable. Consider H/Abb -> 4 b’s process.

Coupling to up-typeis enhanced at low tan, so decay into ttbecomes large.

> bb decay : ~85-90% if tan >20

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.-> Still need this 4b channel !

Current 4J Menu w/o btag

w/ FTK (btag @ LVL2)

Essentially anything can be done@ EF (~sec), but still there are manyunknown factors here. So this study has been done where LVL2output rate is kept as TDR(~100Hz)

Strategy

LVL1 Max

LVL1 Current ~200Hz

Trigger Rate @ 2x10^33Background : Sherpa 2to2 + 2to3 process, yt>25 GeV

4jets w/o btag

LVL1 Out1KHz

LVL2 Out100Hz

EF out10Hz

If nobtag,It is ~110GeV

Setting up Working PointsLVL1 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 bya factor of 10 @LVL2, while keepingJet Pt threshold to 40 GeV,FTK rejection factor has to be: (1) Ru > ~8 (eff. < 12.5%) with 1btag (2) Ru > ~3 (eff. < 33.3%) with 2btag(here, btagging eff. is 50%.)

Is this feasible ? Need realistic estimate.(2) 2tag (1) 1tag

Figure of Merit @ Trigger Level

@ MA = 150 GeV :>1btag (left) : x3 higher acceptance while keeping trigger rate.>2btag (right) : x1.5-2 times higher acceptance while keeping trigger rate.

LVL1 outLVL2 outw/o FTK

LVL2 outw/ FTK

LVL1 outLVL2 outw/o FTK

LVL2 outw/ FTK

LVL1 outLVL2 outw/o FTK

LVL2 outw/ FTK

After Optimization

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.

5

Btagging :bjet = 50%cjet = 10%Ru = 100(expected offline quality)

Optimized Cut ValuesMA 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)

5 Discovery with 30fb-1

> Systematic uncertainty is not included.> Great improvement using FTK !!!

Dijet Mass Distribution (1)Comparison of signal dijet mass btw w/ FTK and w/o FTK @ Optimized cut

MA= 150GeV MA= 200GeV

MA= 250GeV MA= 300GeV

Much better shape w/ FTK due to lower Pt threshold for jets.

Peak position ~ input mass.

Dijet Mass Distribution (2)Comparison of signal dijet mass btw w/ FTK and w/o FTK @ Optimized cut

MA= 350GeV MA= 400GeV

MA= 500GeV MA= 600GeV

Difference becomes smaller as mass gets larger since higher mass sample tends to have more energetic jets.-> lowering threshold does not help much.

Peak position does not correspond to input mass.Is this because correction factor(ATLFASTB) for b-jet is tunedby using SM Higgs VH->Vbbwhere H is ~ 150 GeV.

Dijet Mass Distribution (3)Comparison of signal & Background dijet mass @ Optimized cutNormalization : Expected Number of Events with L=30fb-1.

MA= 150GeV

MA= 200GeV

w/ FTK

w/ FTK

w/o FTK

w/o FTK

MA= 250GeV

MA= 300GeV

w/ FTK

w/ FTK

w/o 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 bythe significance but for this dijet mass measurement ….. But not in this study.)

Summary and Plan• w/ FTK we observed a significant improvement in this chann

el by lowering LVL1/LVL2 Pt threshold.• w/o FTK, it will be really hard to measure the Higgs(H/A) ma

ss (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 yt>25 (parton level cut) low enough ? - LVL1 Param uses jets with Pt > 10 GeV. • Documentation > Sections I (plan to) take: - 4Jet Trigger Rate with multi-threshold discussion - H/Abb physics case.

Sherpa 2to3: yt>10 GeV

yt>10 only has 1M events. Still under investigation.

Btagging : DAQ-Conf-2005-007(Online btagging selection for the ATLAS experiment at the LHC)

Andreas Kootz et al.

Sherpa with bb

0tag

1tag 2tag

3tag 4tag

Sherpa with bb in ME samplehas only 1M events (others hereare roughly10M events.)Need more statistics, though essentiallydo not expect to see big difference.

Sherpa with bb, yt>25 wouldbe a default for a final study.