Dijet Mass Dijet Mass Sherpa vs PythiaSherpa vs PythiaMulti-ThresholdMulti-Threshold

e.t.c.e.t.c.for H/Abb->4b’sfor H/Abb->4b’s

Kohei YoritaKohei YoritaUniversity of ChicagoUniversity of Chicago

FTK MeetingFTK Meeting12/19/200612/19/2006

4J Trigger Rate4J Trigger Rate@2x10@2x103333

NEV Xsection (pb) Yt(pt) cut

SHERPA 2->3 10M 3.19e7 Yt>25

SHERPA 2->2+3

10M 3.39e8+3.18e7

Yt>25

Pythia dijet 4M 3.58e8 Pt>25

SHERPA 2->3 10M 1.51e9

Yt>10

SHERPA 2->2+3

10M 8.29e9+1.50e9

Yt>10

Pythia dijet 5M 9.46e9 Pt>10Based 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 : higherBut not considered here.)

w/ FTK

w/o FTK

Pythia vs Sherpa: Why so different ?Pythia vs Sherpa: Why so different ?11stst jet jet 22ndnd jet jet 33rdrd jet jet 44thth jet jet

Sherpa: 2->3Sherpa: 2->3 MEME MEME MEME PS*/UE*PS*/UE*

Sherpa: 2->2+3Sherpa: 2->2+3MEME MEME MEME PS*/UE’*PS*/UE’*

MEME MEME PS*/UE*PS*/UE* PS*/UE*PS*/UE*

PythiaPythia MEME MEME PS/UEPS/UE PS/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 eventIf Pythia PS/UE = Sherpa PS/UE -> A=B=C in 4jet event

Lowest Pt jet spectraLowest Pt jet spectra==2jet ==3jet

>=4jet > Upper-left : == 2jet bin : > 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 :> Upper-right : == 3jet bin : - Almost consistent in pt > 25 GeV.- Almost consistent in pt > 25 GeV. -> Pythia PS has ~ same energy as 3-> Pythia PS has ~ same energy as 3rdrd ME ME parton in SHERPA !parton in SHERPA !> Lower-Left : >= 4 jet bin :> 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 !So PS/UE activity : Pythia >> Sherpa !

SHERPA 2->3 yt>25SHERPA 2->3 yt>25SHERPA 2->2+3 yt>25SHERPA 2->2+3 yt>25PYTHIA 2->2 pt>25PYTHIA 2->2 pt>25

yt/pt cut effectyt/pt cut effect==2jet ==3jet

>=4jet

SHERPA 2->3 yt>25SHERPA 2->3 yt>25SHERPA 2->3 yt>10SHERPA 2->3 yt>10PYTHIA 2->2 pt>25PYTHIA 2->2 pt>25PYTHIA 2->2 pt>10PYTHIA 2->2 pt>10

> Upper-left : == 2jet bin : > 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 :> 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 :> 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 !And again, PS/UE activity : Pythia >> Sherpa !

> 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.)

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 ReachH/Abb->4b’s Discovery Reach

A set of ThresholdsA set of Thresholds@ Optimized Point @ Optimized Point

(significance)(significance)MA 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)

1.1. Dijet Mass SpectrumDijet Mass Spectrum for Higgs Mass Measurement for Higgs Mass Measurement

2.2. Multi-threshold Multi-threshold - MC issue.- MC issue. - Results with Atlfast Pt.- Results with Atlfast Pt.

Signal Signal ShapeShape

Mean RMS

MAw/FTK w/oFTK w/FTK w/oFTK

150 225 305 122 152

300 332 380 124 144

400 416 419 118 135

500 480 487 98 117

> 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=150 M=300

M=400 M=500

Background : in >=4jet ev Background : in >=4jet ev Within SHERPAWithin SHERPA

Normalized to each other(equal area)

Absolute normalization atL=30fb-1.

> Shapes are the same and absolute difference should be within 30% systematics.

Background : in ==3jet ev Background : in ==3jet ev Within SHERPAWithin SHERPA

Normalized to each other(equal area)

Absolute normalization atL=30fb-1.

> For 3jet events, dijet mass shapes are the same as well.> Some normalization difference.

Dijet Mass in >=4jet evDijet Mass in >=4jet evSHERPA vs PYTHIASHERPA vs PYTHIA

Normalized to each other(equal area)

Absolute normalization atL=30fb-1.

> Here we do see softer shape in Pythia. Partially due to lack of 2->3 ME, but larger PS/UE activity.

Leading Jet Pt shapeLeading 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.

Signal vs Background (Sherpa)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)

Signal Dijet Mass @ Signal Dijet Mass @ TriggerTrigger

Just maximizing statistical significance seems not goodenough 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=150 M=300

M=400 M=500

Dijet mass at Trigger level.w FTK : Pt>30 GeVw/o FTK : Pt>50 GeV

Multi-Threshold StudyMulti-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 ?

4J Trigger Rate 4J Trigger Rate (Single Threshold)(Single Threshold)

Pt>30

How much we can lower4th jet Pt ?

10 GeV ? 20 GeV ?

jet Pt in >=4 jet events

1st

3rd

2nd

4th

Ratio Ratio (bin-by-bin w.r.t. sherpa 2->3 yt>25)(bin-by-bin w.r.t. sherpa 2->3 yt>25)

for 1for 1stst,2,2ndnd,3,3rdrd,4,4thth jet Pt spectrum jet Pt spectrum (Atlfast Pt>10 GeV)(Atlfast Pt>10 GeV)

10 GeV is dangerous to use. -> Statistics limited. -> 10 GeV jet not so reliable.

Pt>20 GeV seems goodBut does 4th Pt > 20 GeVkill difference in 1st, 2nd

3rd jet Pt ?

-> next page.

Ratio Ratio (bin-by-bin w.r.t. sherpa 2->3 yt>25)(bin-by-bin w.r.t. sherpa 2->3 yt>25)

for 1for 1stst,2,2ndnd,3,3rdrd,4,4thth jet Pt spectrum jet Pt spectrum (Atlfast Pt>20 GeV)(Atlfast Pt>20 GeV)

4th jet Pt > 20 GeVcancels any differencein 1st,2nd,3rd 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 default2->3 yt>25 SHERPAsample.

Comparison to PYTHIA Comparison to PYTHIA (Atlfast Pt>20 GeV in 4jet event)(Atlfast Pt>20 GeV in 4jet event)

> Again, we do see big difference. - hard to conclude

-> Anyway, our defaultis Sherpa ->3 yt>25.Then check with Pythia.

Extracting Thresholds giving 1KHExtracting Thresholds giving 1KHSingle threshold (30,30,30,30) gives 1KHz.Let’s get (x,y,z,20) giving the same rate as (30,30,30,30).

Case Category Cuts Rate(2x1033

)PYTHIA

Case1: j1>j2>j3>j4 :

80 60 30 20 993Hz 80 60 30 20 : 1012Hz

Case2: j1>j2>j3=j4 :

80 70 20 20 971Hz 90 60 20 20 : 947Hz

Case3: j1>j2=j3>j4 :

60 40 40 20 1047Hz 80 40 40 20 : 962Hz

Case4: j1=j2>j3>j4 :

50 50 40 20 989Hz 60 60 40 20 : 936Hz

Case5: j1>j2=j3=j4 :

100 20 20 20

1072Hz 100 20 20 20 : 937Hz

Case6: j1=j2=j3>j4 :

40 40 40 20 1137Hz 50 50 50 20 : 731Hz

Case7: j1=j2>j3=j4 :

70 70 20 20 1016Hz 70 70 20 20 : 949Hz

w/o FTK single 50 50 50 50 ~200Hz 50 50 50 50 : ~250Hz

w/ FTK single 30 30 30 30 ~1000Hz 30 30 30 30: ~1500Hz

* j1=j2=j3=j4 : 20 20 20 20 4650Hz 20 20 20 20: 9289Hz

Signal Gain with Multi-ThresholdSignal Gain with Multi-Threshold

SummarySummary• Final study : Multi-Threshold with L1 param. - before doing this, wanted to make sure everythin

g 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.)