Progress on H/Abb -> 4b’s channel for the FTK physics case ~ 4jets trigger w/ and w/o FTK ~ Kohei Yorita Young-Kee Kim University of the FTK.
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Progress on H/Abb -> 4b’s channel 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 6 th, 2006
Signal Process M A (GeV ) 150200250300350400500600700800900 Xsec*BR [pb] 61021287.942.1 *39.9 21.912.14.30 *4.18 1.740.81 *0.82 0.400.21 *0.21 * is the number in TDR Samples generated with Atlfast, 500K events each at tan =30 If M A > 150 GeV, A and H masses are degenerated and experimentally undistinguishable. Consider H/Abb -> 4 b’s process. Coupling to up-type is enhanced at low tan , so decay into tt becomes large. > bb decay : ~85-90% if tan >20
TDR expectation (w/o FTK) This channelAll 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 many unknown factors here. So this study has been done where LVL2 output rate is kept as TDR(~100Hz) Strategy LVL1 Max LVL1 Current ~200Hz
Trigger Rate @ 2x10^33 Background : Sherpa 2to2 + 2to3 process, yt>25 GeV 4jets w/o btag LVL1 Out 1KHz LVL2 Out 100Hz EF out 10Hz If nobtag, It is ~110GeV
Setting up Working Points LVL1LVL2 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 @LVL2, while keeping Jet Pt threshold to 40 GeV, FTK rejection factor has to be: (1) R u > ~8 (eff. < 12.5%) with 1btag (2) R u > ~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 @ M A = 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 out w/o FTK LVL2 out w/ FTK LVL1 outLVL2 out w/o FTK LVL2 out w/ FTK LVL1 outLVL2 out w/o FTK LVL2 out w/ 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. 55 Btagging : bjet = 50% cjet = 10% Ru = 100 (expected offline quality)
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 M A = 150GeVM A = 200GeV M A = 250GeVM A = 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 M A = 350GeVM A = 400GeV M A = 500GeVM A = 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 tuned by using SM Higgs VH->Vbb where H is ~ 150 GeV.
Dijet Mass Distribution (3) Comparison of signal & Background dijet mass @ Optimized cut Normalization : Expected Number of Events with L=30fb-1. M A = 150GeV M A = 200GeV w/ FTK w/o FTK M A = 250GeV M A = 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.)
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 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 1tag2tag 3tag4tag 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. Sherpa with bb, yt>25 would be a default for a final study.