Monte Carlo Reweighting: an Alternative to 10TeV Production? Claire Gwenlan, UCL Recently investigated reweighting existing FullSim samples to 10 TeV My.

Monte Carlo Reweighting: Monte Carlo Reweighting: an Alternative to 10TeV Production?an Alternative to 10TeV Production?

Claire Gwenlan, UCLClaire Gwenlan, UCL

Recently investigated reweighting existing FullSim samples to 10 TeV Recently investigated reweighting existing FullSim samples to 10 TeV My motivation was to look at the potential for SUSY discovery with small amounts My motivation was to look at the potential for SUSY discovery with small amounts

of 10 TeV, BUT given the decisions currently being made on which samples to of 10 TeV, BUT given the decisions currently being made on which samples to produce at 10 TeV, perhaps method is relevant and/or interesting to this audience?produce at 10 TeV, perhaps method is relevant and/or interesting to this audience?

Just a couple of slides shown here, taken from a recent talk I gave in the Just a couple of slides shown here, taken from a recent talk I gave in the ATLAS-UK SUSY meeting (full talk appended in Backups)ATLAS-UK SUSY meeting (full talk appended in Backups)

If no 10 TeV Monte Carlo … can If no 10 TeV Monte Carlo … can re-weightre-weight existing 14 TeV samples existing 14 TeV samples hadronic cross section given by:hadronic cross section given by:

For a particular set of MC events – with particular incoming parton momenta (pFor a particular set of MC events – with particular incoming parton momenta (p 11, p, p22) –) –the hard cross section is *fixed*. To change to a different beam energy, need to the hard cross section is *fixed*. To change to a different beam energy, need to adjust the *probability* that partons of those momenta were found in the proton in the adjust the *probability* that partons of those momenta were found in the proton in the

first place (i.e the PDFs)first place (i.e the PDFs) just a PDF re-weight just a PDF re-weight

1

0

ˆ 2 2 2 21 2 1 1 2 2 1 2 s

flav

= dx dx PDF(x ,Q ,flav ) × PDF(x ,Q ,flav ) × σ p ,p ,α (Q ),Q

proton PDFs

' 2 ' 21, 2

2 21 2

PDF x Q ,flav1 ×PDF x ,Q ,flav2Weight=

PDF x ,Q ,flav1 ×PDF x ,Q ,flav2

' 2 ' 21, 2

2 21 2

PDF x Q ,flav1 ×PDF x ,Q ,flav2Weight=

PDF x ,Q ,flav1 ×PDF x ,Q ,flav2

xi : x of parton i at 14 TeV; x i’: x of parton i at 10 TeV

Re-weight 14 TeV MC to 10 TeV using:Re-weight 14 TeV MC to 10 TeV using:

22

hard sub-process cross section

What you need to know:What you need to know:incoming parton momenta for:incoming parton momenta for:

x = |px = |pzz|/E|/Ebeambeam

(different for different beam (different for different beam energies)energies)

QQ22, the fact. scale of the process , the fact. scale of the process (same for both beam energies)(same for both beam energies)

incoming parton flavoursincoming parton flavours

Reweighting : 14 TeV Reweighting : 14 TeV 10 TeV 10 TeV

Check of Reweight MethodCheck of Reweight Method

Good agreement between reweighted and 10 TeV samplesGood agreement between reweighted and 10 TeV samples

EG:EG: 50000 SU3 SUSY events generated in ATLFAST 50000 SU3 SUSY events generated in ATLFAST

pTJet,1,2 >150,100

GeV

Meff = pTJet,1 + pT

Jet,2 + MET

Effective Mass

example weights (all < 1)example weights (all < 1)

33

PDF weight

Other example checksOther example checks a few other example checks a few other example checks (currently low statistics, except for J8MET)(currently low statistics, except for J8MET) good good agreementagreement

CSCID: 008270CSCID: 008270CSCID: 008190CSCID: 008190

CSCID: 005985CSCID: 005985CSCID: 008094CSCID: 008094

Results: SU3 SUSY vs. BkgResults: SU3 SUSY vs. Bkg

Integrated L = 100 pbIntegrated L = 100 pb-1-1

BEFOREBEFORE reweighting reweighting

AFTERAFTER reweighting reweighting

14 TeV 14 TeV 10 TeV: 10 TeV: SU3 signal reduced by ~ 2.9SU3 signal reduced by ~ 2.9

SM bkg reduced by ~ 2.3SM bkg reduced by ~ 2.3

55

Example: CSC5 0Example: CSC5 0lepton lepton + MET dijet analysis+ MET dijet analysis

SummarySummaryThe PDF re-weight method The PDF re-weight method seemsseems to work to work

Note some caveats however Note some caveats however method is not adjusting the amount of method is not adjusting the amount of energy left in the beam remnant, so the underlying event treatment is energy left in the beam remnant, so the underlying event treatment is not quite rightnot quite right

however, all checks done so far indicate this isn’t a big effect however, all checks done so far indicate this isn’t a big effect

Could this method be useful, given the large amount of 10 TeV Could this method be useful, given the large amount of 10 TeV simulation we are about to set going? simulation we are about to set going?

At the very least, it could be used by individuals whose favourite At the very least, it could be used by individuals whose favourite samples are not planned to be produced at 10 TeV samples are not planned to be produced at 10 TeV

But perhaps it could even be more helpful than this? But perhaps it could even be more helpful than this? i.e. an alternative to some 10 TeV production, saving lots of time, CPU, … ?i.e. an alternative to some 10 TeV production, saving lots of time, CPU, … ?

Presumably this would all have to be verified and validated Presumably this would all have to be verified and validated

66

BackUps - (Full Talk)BackUps - (Full Talk)

SUSY Discovery at 10 TeV ?SUSY Discovery at 10 TeV ?

ATLAS-UK SUSY/Exotics MeetingATLAS-UK SUSY/Exotics Meeting

88thth May 2008 May 2008

Claire GwenlanClaire Gwenlan

IntroductionIntroduction

10TeV run coming soon (2-3 months? 100 pb10TeV run coming soon (2-3 months? 100 pb-1-1 possible?) possible?)

Studies show that, if SUSY is relatively light, it could be discovered Studies show that, if SUSY is relatively light, it could be discovered very early at the LHC (based on 14TeV Monte Carlo)very early at the LHC (based on 14TeV Monte Carlo)

– – so what about at 10TeV – could we hope to see something?so what about at 10TeV – could we hope to see something?

99

“Commissioning to 10 TeV should be fast, no quench being anticipated, giving us confidence that the experiments will be recording data at record high energies by the summer.

In 1989, it was only a matter of weeks before LEP produced its first profound result – a measurement of the number of light neutrino families. In this respect at least, history will not be repeating itself. The LHC is a discovery machine, and the discoveries it is chasing will require a little more patience.”

Robert Aymar, on the 10TeV run

1

0

ˆ 2 21 2 1 1 2 2

flav

= dx dx PDF(x ,Q ,flav ) × PDF(x ,Q ,flav ) ×

PDFs PDFs from 14TeV from 14TeV 10TeV 10TeV

Currently no MC… BUT can re-weight existing 14TeV samplesCurrently no MC… BUT can re-weight existing 14TeV samples hadronic cross section given by:hadronic cross section given by:

For a particular kinematic configuration For a particular kinematic configuration

with s, t, u, should just need to change the with s, t, u, should just need to change the

probability that incoming partons *had* probability that incoming partons *had*

that configuration i.e. just a PDF re-weightthat configuration i.e. just a PDF re-weight

proton PDFs

' 2 ' 21, 2

2 21 2

PDF x Q ,flav1 ×PDF x ,Q ,flav2Weight=

PDF x ,Q ,flav1 ×PDF x ,Q ,flav2

' 2 ' 21, 2

2 21 2

PDF x Q ,flav1 ×PDF x ,Q ,flav2Weight=

PDF x ,Q ,flav1 ×PDF x ,Q ,flav2

Plot from James Stirling: DIS08

^ ^ ^ ^ ^̂

xi : x of parton i at 14TeV; x i’: x of parton i at 10TeV

Re-weight MC to 10TeV using:Re-weight MC to 10TeV using:

1010

Check of Reweight MethodCheck of Reweight Method

Good agreement between reweighted and 10TeV samples (bkgs also checked)Good agreement between reweighted and 10TeV samples (bkgs also checked)

EG:EG: SU3 SUSY events generated in ATLFAST SU3 SUSY events generated in ATLFAST

pTJet,1,2 >150,100

GeV

Meff = pTJet,1 + pT

Jet,2 + MET

Effective Mass

example weights (all < 1)example weights (all < 1)

1111

PDF weight

EG: CSC5-style, inclusive 2- and 3-Jet analyses (full details in note)EG: CSC5-style, inclusive 2- and 3-Jet analyses (full details in note) results shown in main part of talk are for the 2-Jet case (3-Jet results in backups)results shown in main part of talk are for the 2-Jet case (3-Jet results in backups)

Cut No.Cut No. 2-Jet Analysis Cuts2-Jet Analysis Cuts

00 J70_XE70 triggerJ70_XE70 trigger

11 ppTTJet,1Jet,1 > 150 GeV > 150 GeV

22 ppTTJet,2Jet,2 > 100 GeV > 100 GeV

33 MET > max(100,0.3*MMET > max(100,0.3*Meffeff))

44 |phi(Jet1,2)-phi(MET)| > 0.2|phi(Jet1,2)-phi(MET)| > 0.2

55 no isolated leptonno isolated lepton

SUSY analysisSUSY analysis

“Generic search for R-parity conserving SUSY in 2-Jet + MET+0-lepton channel”

Effective Mass: Meff = ∑ pTJet,i + MET [sum runs over two highest-pT jets]

1212

Results: SU3 vs. SM bkgResults: SU3 vs. SM bkg

Integrated L = 100 pbIntegrated L = 100 pb-1-1

BEFOREBEFORE reweighting reweighting

EG: CSC5 2EG: CSC5 2Jet + MET + Jet + MET + 00lepton SUSY analysis:lepton SUSY analysis:

1313

Results: SU3 vs. SM bkgResults: SU3 vs. SM bkg

Integrated L = 100 pbIntegrated L = 100 pb-1-1

BEFOREBEFORE reweighting reweighting

AFTERAFTER reweighting reweighting

14 TeV 14 TeV 10 TeV: 10 TeV: SU3 signal reduced by ~ 2.9SU3 signal reduced by ~ 2.9

SM bkg reduced by ~ 2.3SM bkg reduced by ~ 2.3

1414

EG: CSC5 2EG: CSC5 2Jet + MET + Jet + MET + 00lepton SUSY analysis:lepton SUSY analysis:

Integrated L = 100 pbIntegrated L = 100 pb-1-1

Comparison of some Comparison of some other SUSY benchmark other SUSY benchmark points (SUX)points (SUX)

all are mSUGRA, but cover all are mSUGRA, but cover quite a wide range of quite a wide range of phenomenologies phenomenologies

SU1SU1 coannihilation regioncoannihilation region

SU2SU2 focus point regionfocus point region

SU3SU3 bulk regionbulk region

SU4SU4 low mass pointlow mass point

SU6SU6 funnel regionfunnel region

SU8.1SU8.1 coannihilation regioncoannihilation region

Results: Results: other mSUGRA pointsother mSUGRA points

1515

EG: CSC5 2EG: CSC5 2Jet + MET + Jet + MET + 00lepton SUSY analysis:lepton SUSY analysis:

Statistical Significance (S/√B)Statistical Significance (S/√B)

14TeV14TeV 10TeV10TeV

SU1SU1 2323 1212

SU2SU2 < 1< 1 < 1< 1

SU3SU3 3939 2222

SU4SU4 106106 6767

SU6SU6 1616 88

SU8SU8 2424 1212

Statistical SignificancesStatistical Significances

100 pb100 pb-1-1

Numbers are maximum Numbers are maximum significances (taken above significances (taken above some Msome Meffeff threshold) threshold)

(don’t take too much notice of the (don’t take too much notice of the actual values – it’s just to get a actual values – it’s just to get a rough feeling)rough feeling)

1616

Discovery SignificancesDiscovery Significances

100 pb100 pb-1-1

Discovery Significance (ZDiscovery Significance (Znn) *) *

14TeV14TeV 10TeV10TeV

SU1SU1 9.19.1 5.95.9

SU2SU2 <1<1 <1<1

SU3SU3 11.211.2 8.38.3

SU4SU4 12.512.5 12.512.5

SU6SU6 7.57.5 4.84.8

SU8SU8 9.79.7 6.26.2

* Zn is a measure of the significance (as used in CSC5) which tries to take into account systematic

uncertainties on the bkg measurements. The numbers in the table above are calculated assuming

50% uncertainty on QCD and 20% on all other bkgs – these are not necessarily the “right”

numbers – dedicated bkg studies needed for those! 1717

Numbers are maximum Numbers are maximum significances (taken above significances (taken above some Msome Meffeff threshold) threshold)

(don’t take too much notice of the (don’t take too much notice of the actual values – it’s just to get a actual values – it’s just to get a rough feeling)rough feeling)

SummarySummary

Is there potential for discovery with small amounts of 10 TeV data?Is there potential for discovery with small amounts of 10 TeV data?

YES – there does seem to be potential!YES – there does seem to be potential!

A 5x increase in centre-of-mass energy compared to previous A 5x increase in centre-of-mass energy compared to previous experiments is still a lot!!! – and the discovery of light SUSY may experiments is still a lot!!! – and the discovery of light SUSY may not need much data (it doesn’t take much to give large S/not need much data (it doesn’t take much to give large S/B values B values for the models considered here)for the models considered here)

BUT that data still needs to be understoodBUT that data still needs to be understood

This was really just a quick look for fun – to see if anything is even This was really just a quick look for fun – to see if anything is even potentially feasible! It looks like it could be, but the limiting factor potentially feasible! It looks like it could be, but the limiting factor will of course be how well we can will of course be how well we can determine and understanddetermine and understand the the backgrounds with the small amount of data we expect.backgrounds with the small amount of data we expect.

1818

BackUpsBackUps

Integrated L = 100 pbIntegrated L = 100 pb-1-1

Results: Results: other mSUGRA pointsother mSUGRA points

2020

Cut Cut 3-Jet Analysis Cuts3-Jet Analysis Cuts

00 J70_XE70 triggerJ70_XE70 trigger

11 ppTTJet,1Jet,1 > 150 GeV > 150 GeV

22 ppTTJet,3Jet,3 > 100 GeV > 100 GeV

33 MET>max(100,0.25*MMET>max(100,0.25*Meffeff))

44 |phi(Jet1,2,3)-phi(MET)| > |phi(Jet1,2,3)-phi(MET)| > 0.20.2

55 no isolated leptonno isolated lepton

EG: CSC5 3EG: CSC5 3Jet + MET + Jet + MET + 00lepton SUSY analysis:lepton SUSY analysis:

mSUGRA PointsmSUGRA Points

m0m0 m1/2m1/2 A0A0 tantan RegionRegion

SU1SU1 7070 350350 00 1010 > 0> 0 CoannihilationCoannihilation

SU2SU2 35503550 300300 00 1010 > 0> 0 Focus pointFocus point

SU3SU3 100100 300300 -300-300 66 > 0> 0 BulkBulk

SU4SU4 200200 160160 -400-400 1010 > 0> 0 Low massLow mass

SU6SU6 320320 375375 00 5050 > 0> 0 FunnelFunnel

SU8.1SU8.1 210210 360360 00 4040 > 0> 0 CoannihilationCoannihilation

More details on the mSUGRA points consideredMore details on the mSUGRA points considered

2121

MC Bkg SamplesMC Bkg SamplesSampleSample CSC IDCSC ID (pb)(pb) NN

T1T1 005200005200 450450 600 K600 K

TTbarTTbar 005204005204 383383 100 K100 K

J4METJ4MET 008090008090 916.40916.40 70K70K

J5METJ5MET 008091008091 655.655. 85K85K

J6METJ6MET 008092008092 67.4267.42 35K35K

J7METJ7MET 008093008093 5.35.3 4K4K

J8METJ8MET 008094008094 2.21x102.21x10-2-2 4K4K

WWWW 005985005985 24.524.5 50K50K

WZWZ 005986005986 2.12.1 50K50K

ZZZZ 005987005987 7.87.8 50K50K

ZeeZee 008194008194 46.246.2 5K5K

ZmumuZmumu 008195008195 9.609.60 5K5K

ZtautauZtautau 008191008191 4.504.50 5K5K

ZnunuZnunu 008190008190 41.3341.33 35K35K

WenuWenu 008270008270 49.0549.05 50K50K

WmunuWmunu 008271008271 28.6428.64 50K50K

WtaunuWtaunu 008272008272 55.9155.91 50K50K2222

Sensitivity to choice of QSensitivity to choice of Q22

2 2 2F LSP LSP2 2 2

2F 2 2 2

2F

2st'u'• default : ; t' = t-m , u'=u-m

s +t' +u'2stu

(1): s +t +u

(2): s

s, t, u are the usual Mandelstam variables

Reweighting technique is not very sensitive to choice of factorisation scale