A preliminary study of the -...
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A preliminary study of the Vector Boson Fusion Process with FAMOS PRS/Higgs meeting 06/08/05 Sara Bolognesi (TORINO)
Transcript of A preliminary study of the -...
A preliminary study of the Vector Boson Fusion Process with
FAMOS
PRS/Higgs meeting 06/08/05Sara Bolognesi (TORINO)
Signal and background definition
PRS/Higgs meeting 06/08/05Sara Bolognesi (TORINO)
Vector Boson Fusion in PHASE
pp qq qqVLWL qqVLWL qqqqµν
V= Z\W qqW µν
xsec = | fusion diagrams + irreducible background |2pp->qqqqµν O(αEW
6)PHASE
exact calculation of all the processes
Reference for PHASE
• only boson fusion diagrams
huge interference effects
PYTHIA
• EVBA approximation
MadEvent
production and decay approximation(i.e. only diagrams with on shell bosons outgoing)
The signal is pp qq qqVW qqVW qqqqµν where
• only longitudinal bosons
pp qq qqVW qqqqµν
PREVIOUS EXISTING MC
NEW MC DEVELOPED BY TURIN GROUP (Accomando, Ballestrero, Maina)
hep-ph/0404236C.Mariotti talk (12/08/04) at PRS session of CMS WeekE. Maina talk (05/14/05) at LesHouches Workshop
Signal definition: cutBecause of the presence of the irreducible background, we need a definition for signal “a posteriori” (i.e. after events generation)
Cut against the top contribution*
Ask for two bosons in the final state*
Cut against three bosons in the final state*
160 < M(bqq’,bµν) < 190 (GeV)
[ 70 < M(µν) < 90 (GeV) ] &&
for the other 2 quarks
[ 80 < M(qq) < 100 (GeV) || 70 < M(qq’) < 90 (GeV) ]
[ 80 < M(qq) < 100 (GeV) || 70 < M(qq’) < 90 (GeV) ]
b t b
WW
V
q q’
* the right quarks flavours are always requested
Signal definition: xsec
signal 0.247 pb 0.184 pb 0.169 pb 0.158 pbtop (EW) 0.495 pb 0.494 pb 0.493 pb 0.495 pbother irr. backg. 0.052 pb 0.040 pb 0.037 pb 0.036 pb
M(H) (GeV) 300 500 700 no Higgs
TOP (EW)• big contribution (at low invariant mass VV)
• little contribution (~ constant over all the spectrum) • Higgs mass dependence (because of the Higgsstrahlung diagrams)
OTHER IRREDUCIBLE BACKGROUND:
- NON RESONANT - THREE BOSONS OUTGOING
total 0.794 pb 0.718 pb 0.699 pb 0.689 pb
2 central q + µν ~ 2 outgoing bosons
p
pqq
µ
ν
q’
q
W
V
V
V
q tag
q tag
2 q tag: high η and big ∆η, very high energy
2 q from boson decay: central, little ∆η, high pT
2 central bosons with high pT
high METcentral muonwith high pT
Signal kinematicsNo Higgs sample
Backgrounds
2. Background with the same final state of the signal but at a different perturbative order
3. Background with lower multiplicity of quarks in the final state (e.g.: Wqq, Wqqq, single W)
We are waiting for the new AlpGen version: it will generate W + n jets without multiple counting
single and double top (pure EW),
1. Irreducible background (i.e. background with the same final state of the signal and at the same perturbative order αEW
6 )
pp t t 1µ+X αS2 αEW
4 622 pb PYTHIA
pp qqWW qqqqµν αS2 αEW
4 9.1 pb MadEvent
pp qqqqW qqqqµν αS4 αEW
2 359 pb AlpGen
q = u,d,c,s,g
not considered to avoid multiple counting due to initial/final state gluon radiation during the parton shower evolutionWqq Wqqqq
q
qg
g
g
q
qW
non resonant diagrams,events with three bosons outgoing
(xsec in a previous slide: ~ 0.5 pb)
pp qqZW qqqqµν still missing (but xsec ~ 3 fb)
Reco with FAMOS_1_2_0 GlobalMuons
We try to reconstruct jets with different algorithms
Combined Btagging Algo
We try to reconstruct MET with different algorithms
Iterative Cone Algo
JetRecom = 1
ConeCut =0.5ConeSeedEtCut = 0.5
EcalPlusHcalTowerEt = 0.5
JetInput = EcalPlusHcalTower
JetCalibration = GammaJet
MidPointConeRadius= 1MidPointConeSeedThreshold = 0.5
MidPoint Cone Algo
KtJet RParameter Algo
KtJetAngle = 2
RParameter = 1
KtJet DCut Algo DCut = 400
KtJet NJet Algo NJet = 4
Primary Vertex FinderIterative Cone Algo for jets (with the previous parameters)
TowerEtCut = 0.5
FamosMETfromCaloTower
FamosMETfromJet
Tower Correction = true
JetUnclusterTower = trueJetUnclusterCorrection = true
JetCorrection = true
NO PILE-UP !!
“MC” resolution
resolution (%) =reconstructed value – generated value
generated value
absolute resolution = reconstructed value – generated value
(No Higgs sample used as reference in the following)
PRS/Higgs meeting 06/08/05Sara Bolognesi (TORINO)
Resolution: µ and νWe choose the closest muon to the generated one (only if ∆R<0.2)
In order to reconstruct pzν we ask for (pµ + pν)2 = mW
2
• resolution < 10% in 86% of the events• transverse momentum underestimated
Total generated MET ~ pT of signal ν
• MET underestimated
absolute resolution:FWHM ~ 43 GeVpeak at ~ -3 GeV
absolute resolution: FWHM ~ 1.6 GeVpeak at ~ -0.3 GeV
• resolution < 10% in 19 % of the events
resolution peaked at -1.3 %
resolution peaked at -15 %
• METfromJets more precise
Resolution: leptonic Wmuon pT and neutrino pT underestimated (previous slide)
W pT underestimated
W pseudorapidity overestimated (absval)
• absolute resolution (gaussian fit):std. deviation ~ 24 GeVmean ~ -7 GeV
• resolution peaked at -12.5 %
resolution with asymmetric shape
Resolution: jets hadronic W/Z
Calibration only for ICA !!!
Resolution calculated for selected events with only 4 jets: each of them has been matched with the closest generated quark (∆R < 1)
JETS RESOLUTION
HADRONIC BOSON MASS RESOLUTION
• mV resolution peaked at +10% (ICA)• mV absolute resolution (gaussian fit):
std. deviation ~ 18 GeVmean at ~ 10 GeV
Data analysis
Work in progress
PRS/Higgs meeting 06/08/05Sara Bolognesi (TORINO)
Considered Higgs masses: 300 GeV, 500 GeV, 700 GeV, no Higgs case
Cuts (1)Signal reconstruction
• hadronic V
|ηj1|, |ηj2| <3
50 < M(j1,j2) <125 (GeV)|ηj1-ηj2| < 2
(if more then one, the most central has been chosen)
52 %
signal (NoHiggs)
background
36 %
• ask for other 2 tag jets = 2 most energetic remaining jets
• leptonic Wmuon with maximum pT ( > 20 GeV)pT
ν = MET ( > 20 GeV)
pzν (pµ+pν)2 =mW
2
(considered only jets with pT > 30 GeV)
74 % 50 %
44 % 25 %
(no cut on mW!)
Cuts (2)Background rejection
100 < M(W,q), M(V,q) < 300 (GeV)
100 < M(W,b), M(V,b) < 300 (GeV)for any jet with |η| > 3 (out of B-tag algo acceptance)
b = jet with maximum probability of b-tagging (only if P(b)>1)
• cut against top
M(jtag1,jtag2) > 600 GeV|ηjtag1-ηjtag2| > 1.5ηjtag1*ηjtag2 < -1
pTjtag1,pT
jtag2 > 50 GeV
|ηW| < 2M(V,W,jtag1, jtag2) > 1 TeV(Njet with |ηj|<2) < 12
• cuts on tag jets
• some other cuts
backgroundsignal (NoHiggs)
14 %
38 % 14 %
1.1 %
12 % 0.8 %
(considered only jets with pT > 30 GeV)
considered also jets with pT < 30 GeV
Analysis resolution • resolution on the signal after the previous analysis cuts• resolution on the signal using the MC truth
(histos normalized to 1)
Comparison between
With the previous cuts we keep a resolution roughly equal to the “MC” resolution…
… but …
Efficiency and significance
We would like to be more efficient at high M(VW)
(too many fluctuation: we need more statistic)
The biggest background at high M(VW)after our analysis cuts is Wjjjj
… the bad reconstruction resolution affects our efficiency on the signalremember: we loose 50% of the signal only by asking pT
µ, pT
ν > 20 GeV and the presence of an hadronic boson !!!
No
Hig
gs -
100
fb-1
different backgrounds already summ
ed
100 fb-1100 fb-1
Events
100 fb-1
signal events
background events
significance
1893 1023 473 26
437297 243833 124172 10932
2.9 2.1 1.3 0.2
500 fb-1
signal events
background events
significance
9463 5113 2364 128
6.4 4.6 3.0 0.5
With this resolution some years are necessary to discover a heavy Higgs boson
2.186×106 620858 54662
Number of events and significance at the Higgs peak ± 30 % ( = our analysis resolution)
300 ± 90 500 ± 150 700 ± 210 NoH (> 1 TeV)M(H) ± 30% (GeV)
300 ± 90 500 ± 150 700 ± 210 NoH (> 1 TeV)M(H) ± 30% (GeV)
1.219×106
ProblemsGenerate W + n jets without double counting with the future AlpGen versionBad resolution (also when we use the MC truth) first of all for the jets
Not a FAMOS problem (I think)
Is it a software problem? (i.e. we have to wait for a more realistic resolution because the software is still in development?)
Or maybe is it a detector problem? Is this the best that we can do with our detector?
Is it a problem related with our reconstruction program (e.g. ConeSeedEtCut too low)?
We are investigating on…
Plans: to apply the same analysis cuts to the MC truth to “quantify” the resolution problem on the signal efficiency
our hint !we have to check, more deeply, different values for the parameter
something similar for top and W mass in ORCA / R.Chierici talk (03/14/05) at PRS Session of CMS Week
Good news
We have for the first time a MC (PHASE) able to generate the signal in an exact way (without any approximation) and the irreducible background
An analysis with FAMOS is not only possible but also reliable and VERY fast
• An ENOURMOUS help from developers always available at [email protected]
For a comparison of the different MC see R.Bellan talk (03/15/05) at PRS Session of CMS Week
• In 1 day we have processed 500.000 events of signal (via LSF)
The background and signal samples we are producing in Turin, are being submitted to the official productionThe production status is reported at http://www.to.infn.it/~bellan/works/status_produzione.html
Next-to-next step = to perform the same analysis in ORCA to compare the results
Backup slides
MV, M(VW) distributions
pzν reconstruction
Generated statistic
Events and significance integrated over all the spectrum
Detailed efficiency of the cuts
xsec and generated events
M(H) = 300 GeV 0.794 pb 500.000
signal and irreducible background
M(H) = 500 GeV 0.718 pb 500.000
M(H)= 700 GeV 0.699 pb 500.000
no Higgs 0.689 pb 500.000
pp t t 1µ+X 622 pb 200.000
pp qqWW qqqqµν 9.1 pb 253736
pp qqqqW qqqqµν 359 pb 180006
other backgrounds
pp qqW+W- qqqqµν 9.04 pb 249231
pp qqW+W+ qqqqµν 0.05 pb 1996
pp qqW-W- qqqqµν 0.02 pb 2509
M(V), M(VW) distributionsimpossible to distinguish W and Z peaks
100 fb-1
100 fb-1 background histrograms superimposed (not stacked)
Neutrino reconstruction
pTν = MET (METFromJets algorithm)
second degree equation with two solutions
we chose the biggest solution and we take the real part if the discriminant is negative
pzν calculated with (pµ + pν)2 = mW
2
( 30 % of the events )
Detailed efficiency of the cutshadronic V 2 tag jetsleptonic W cut top cuts on
tag jetssome other cuts
300 GeV
500 GeV
700 GeV
no Higgs
pp t t 1µ+X 43 % 34 % 24 % 9 % 0.4 % 0.3 %
pp qqWW qqqqµν 56 % 34 % 15 % 13 % 0.6 % 0.4 %
pp qqqqW qqqqµν 62 % 40 % 26 % 23 % 2.2 % 1.6 %
signal 75 % 56 % 46 % 39 % 13 % 12 %irred. backg. 72 % 57 % 37 % 17 % 1 % 0.8 %signal 75 % 55 % 46 % 40 % 14 % 12 %irred. backg. 71 % 57 % 38 % 17 % 1 % 0.8 %signal 74 % 53 % 45 % 39 % 14 % 12 %irred. backg. 72 % 57 % 38 % 17 % 1 % 0.7 %signal 73 % 52 % 44 % 38 % 14 % 12 %irred. backg. 72 % 57 % 38 % 17 % 1 % 0.8 %
For a description of the cuts see slides “Cuts(1)” and “Cuts(2)”
Events
M(H) = 300 GeV M(H) = 500 GeV M(H)=700 GeV No Higgs100 fb-1
signal events
background events
significance
2860 2303 2064 1898
771689 771633 771596 771594
3.2 2.6 2.3 2.2
M(H) = 300 GeV M(H) = 500 GeV M(H)=700 GeV No Higgs500 fb-1
signal events
background events
significance
14289 11510 10320 9493
7.3 5.9 5.2 4.8
~ 3.858 × 106
With this resolution some years are necessary to discover a heavy Higgs boson
irreducible background depends on the Higgs mass
Events and significance integrated over all the M(VW) spectrum
