1. Dijet Mass Sherpa vs Pythia Multi-Threshold e.t.c. for H/Abb->4b’s Kohei Yorita University of Chicago FTK Meeting 12/19/2006

2. 4J Trigger Rate @2x10 33 NEVXsection (pb)Yt(pt) cut SHERPA 2->310M 3.19e7Yt>25 SHERPA 2->2+310M3.39e8+3.18e7Yt>25 Pythia dijet4M3.58e8Pt>25 SHERPA 2->310M 1.51e9Yt>10 SHERPA 2->2+310M8.29e9+1.50e9Yt>10 Pythia dijet5M9.46e9Pt>10 Based on default Sherpa (2->3 yt>25), at LVL1, - W/o FTK (100-200Hz) Atlfast Pt > 50 GeV - W/ FTK (1KHz) Atlfast Pt > 30 GeV Based on Pythia (v6.2), - W/o FTK (100-200Hz) Atlfast Pt > 55 GeV - W/ FTK (1KHz) Atlfast Pt > 35 GeV (*v6.3 Pythia : higher But not considered here.) w/ FTK w/o FTK

3. Pythia vs Sherpa: Why so different ? 1 st jet 2 nd jet 3 rd jet 4 th jet Sherpa: 2->3 MEMEMEPS*/UE* Sherpa: 2->2+3 MEMEMEPS*/UE’* MEMEPS*/UE*PS*/UE* PythiaMEMEPS/UEPS/UE In 4jet events, A: Default sherpa 2->3 : 3ME+1PS. B: Sherpa 2->2+3 : (2ME+2PS) + (3ME+1PS). C: Pythia : 2ME+2PS. So expect to see : -> B=C in 2jet event (B>C ?) -> A=B in 3jet event If Pythia PS is good for +1p -> A=B=C in 3jet event If Pythia PS/UE = Sherpa PS/UE -> A=B=C in 4jet event

4. Lowest Pt jet spectra ==2jet==3jet >=4jet > Upper-left : == 2jet bin : - Missing 2->2 process in 2->3 sherpa. - Missing 2->2 process in 2->3 sherpa. - 2->3 contribution in 2->2+3 sherpa. - 2->3 contribution in 2->2+3 sherpa. > Upper-right : == 3jet bin : - Almost consistent in pt > 25 GeV. - Almost consistent in pt > 25 GeV. -> Pythia PS has ~ same energy as 3 rd ME -> Pythia PS has ~ same energy as 3 rd ME parton in SHERPA ! parton in SHERPA ! > Lower-Left : >= 4 jet bin : - In Pythia, Large contribution from PS/UE. - In Pythia, Large contribution from PS/UE. So PS/UE activity : Pythia >> Sherpa ! SHERPA 2->3 yt>25 SHERPA 2->2+3 yt>25 PYTHIA 2->2 pt>25

5. yt/pt cut effect ==2jet==3jet >=4jet SHERPA 2->3 yt>25 SHERPA 2->3 yt>10 PYTHIA 2->2 pt>25 PYTHIA 2->2 pt>10 > Upper-left : == 2jet bin : - If pt>25, pythia is consistent btw 10&25. - If pt>25, pythia is consistent btw 10&25. - 2->3 sherpa are meaningless. - 2->3 sherpa are meaningless. > Upper-right : == 3jet bin : - If pt>25, 4 of them are consistent. - If pt>25, 4 of them are consistent. - Pythia(10) sample covers low pt phase space. - Pythia(10) sample covers low pt phase space. > Lower-Left : >= 4 jet bin : - Pythia PS/UE : (pt:10) >> (pt:25). - Pythia PS/UE : (pt:10) >> (pt:25). And again, PS/UE activity : Pythia >> Sherpa !

6. > So conclusion (w.r.t. Pythia issue) is … -> Pythia should be good for up to 3jet events. But not so reliable for 4jet events. -> Use Sherpa 2->3 + PS/UE (should be closer to 2->4 configuration than Pythia.) > Still PS/UE model uncertainty remains. -> Pythia > Sherpa --- But who knows ? > Take systematics within sherpa. (30%) Pythia difference can be discussed in document. > Again, working point is: (Note Atlfast Pt>25 is safe.) Atlfast Pt > 30 GeV with FTK Atlfast Pt > 50 GeV without FTK (extracted from 2->3 yt>25 Sherpa.)

7. Even if background rate is much higher due to high lum or wrong MC tuning (in this case x3), FTK can provide almost same sensitivity ! -> without FTK, very weak against higher background (compare dotted line.) H/Abb->4b’s Discovery Reach

8. A set of Thresholds @ Optimized Point (significance) MAMA w/ FTK (+4btag)w/o FTK (+4btag) 150(30,30,30,30)(50,50,50,50) 200(60,60,60,30)(60,60,50,50) 250(60,60,60,30)(80,50,50,50) 300(110,50,50,30)(110,100,50,50) 350(110,100,50,30)(110,100,70,50) 400(160,100,50,30)(110,100,70,50) 500(190,120,40,30)(170,120,70,50) 600(230,120,40,30)(200,120,70,50) 700(260,120,40,30)(200,140,70,50) 800(250,190,40,30)(250,120,70,50) 900(290,190,30,30)(250,120,70,50)

9. 1. Dijet Mass Spectrum for Higgs Mass Measurement 2. Multi-threshold - MC issue. - MC issue. - Results with Atlfast Pt. - Results with Atlfast Pt.

10. Signal Shape MeanRMS MAMA w/FTKw/oFTKw/FTKw/oFTK 150225305122152 300332380124144 400416419118135 50048048798117 > Showing dijet mass distributions for 150, 300 400, 500 GeV Higgs mass with FTK and without FTK > Mean gets back closer to input Higgs mass with FTK. > Dijet mass resolution becomes better w/ FTK. - Especially it is significant in low Higgs mass. -> 10~20% improvement Dijet Mass dist. at optimized points M=150M=300 M=400 M=500

11. Background : in >=4jet ev Within SHERPA Normalized to each other (equal area) Absolute normalization at L=30fb-1. > Shapes are the same and absolute difference should be within 30% systematics.

12. Background : in ==3jet ev Within SHERPA Normalized to each other (equal area) Absolute normalization at L=30fb-1. > For 3jet events, dijet mass shapes are the same as well. > Some normalization difference.

13. Dijet Mass in >=4jet ev SHERPA vs PYTHIA Normalized to each other (equal area) Absolute normalization at L=30fb-1. > Here we do see softer shape in Pythia. Partially due to lack of 2->3 ME, but larger PS/UE activity.

14. Leading Jet Pt shape ==2jet==3jet >=4jet > ==2jet event : Sherpa 2->2+3 >~ Pythia > ==3jet & >=4jet event : Pythia has more phase space in lower region due to more active PS/UE. -> Actually this makes low energetic event go into higher jet bin. > High tail looks consistent.

15. Signal vs Background (Sherpa) Each of them are normalized to expected NEV at optimized point. -> each histogram uses different threshold. (60,60,60,30) (30,30,30,30) (50,50,50,50) (60,60,50,50)

16. Signal Dijet Mass @ Trigger Just maximizing statistical significance seems not good enough for Higgs Mass Measurement. -> need some optimization for this purpose. > The most important thing is to keep better resolution and closer mean to its input mass “at Trigger Level”, -> Further improvement can be potentially done in offline. M=150M=300 M=400 M=500 Dijet mass at Trigger level. w FTK : Pt>30 GeV w/o FTK : Pt>50 GeV

17. Multi-Threshold Study > How much we can lower 4th jet Pt ? - Is generator yt(pt) cut low enough ? - What about correlation btw jets ? > How much is signal gain ?

18. 4J Trigger Rate (Single Threshold) Pt>30 How much we can lower 4 th jet Pt ? 10 GeV ? 20 GeV ? jet Pt in >=4 jet events 1 st 3 rd 2 nd 4 th

19. Ratio (bin-by-bin w.r.t. sherpa 2->3 yt>25) for 1 st,2 nd,3 rd,4 th jet Pt spectrum (Atlfast Pt>10 GeV) 10 GeV is dangerous to use. -> Statistics limited. -> 10 GeV jet not so reliable. Pt>20 GeV seems good But does 4 th Pt > 20 GeV kill difference in 1 st, 2 nd 3 rd jet Pt ? -> next page.

20. Ratio (bin-by-bin w.r.t. sherpa 2->3 yt>25) for 1 st,2 nd,3 rd,4 th jet Pt spectrum (Atlfast Pt>20 GeV) 4 th jet Pt > 20 GeV cancels any difference in 1 st,2 nd,3 rd jet. These four samples (2->2+3 (10),2->3(10) 2->2+3 (25),2->3(25)) are quite consistent. So we can use default 2->3 yt>25 SHERPA sample.

21. Comparison to PYTHIA (Atlfast Pt>20 GeV in 4jet event) > Again, we do see big difference. - hard to conclude -> Anyway, our default is Sherpa ->3 yt>25. Then check with Pythia.

22. Extracting Thresholds giving 1KH Single threshold (30,30,30,30) gives 1KHz. Let’s get (x,y,z,20) giving the same rate as (30,30,30,30). Case CategoryCutsRate(2x10 33 )PYTHIA Case1: j1>j2>j3>j4 :80 60 30 20993Hz 80 60 30 20 : 1012Hz Case2: j1>j2>j3=j4 :80 70 20 20971Hz 90 60 20 20 : 947Hz Case3: j1>j2=j3>j4 :60 40 40 201047Hz 80 40 40 20 : 962Hz Case4: j1=j2>j3>j4 :50 50 40 20989Hz 60 60 40 20 : 936Hz Case5: j1>j2=j3=j4 : 100 20 20 201072Hz 100 20 20 20 : 937Hz Case6: j1=j2=j3>j4 : 40 40 40 201137Hz 50 50 50 20 : 731Hz Case7: j1=j2>j3=j4 : 70 70 20 201016Hz 70 70 20 20 : 949Hz w/o FTK single50 50 ~200Hz 50 50 50 50 : ~250Hz w/ FTK single30 30 ~1000Hz 30 30 30 30: ~1500Hz * j1=j2=j3=j4 :20 20 4650Hz 20 20 20 20: 9289Hz

23. Signal Gain with Multi-Threshold

24. Summary Final study : Multi-Threshold with L1 param. - before doing this, wanted to make sure everything is reasonable and understandable with Atlfast Pt. (because L1 param. is based on Atlfast Pt (as input).) - Now I think everything is well validated with some remaining/unknown issues. -> I believe it is time to finish up this study ! > Writing up Document. (hopefully by January) > Move to FTKSim (rawhit e.t.c.)