the central jet veto in vector boson fusion analysis markus schumacher lhc-d higgs workshop,...
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The Central Jet VetoThe Central Jet Vetoin Vector Boson Fusion Analysisin Vector Boson Fusion Analysis
Markus Schumacher
LHC-D Higgs Workshop, Freiburg October 8/9th 2007
Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007 2
Outline
The importance of the VBF production mode
Characteristics and Challenges of the VBF topology
Issues for the Central Jet Veto (CJV)
Overview of CJV Applications at LHC
Track Veto versus Calorimeter Jets
Comparison of MC Generators
Ideas about Efficiency Determination from Data
Conclusions and Outlook
Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007 3
Production of a SM Higgs Boson at LHC
dominant process: gluon fusion
factor 10 suppressed: Vector Boson Fusion (VBF)
but: additional signature in the detector
Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007 4
ATLAS: Hl had 3 + ll 4
HWW lqq and ll
Entdeckungspotenzial im Standardmodell
VBF dominates discovery potential at LO in ATLAS
VBF provides the only channel to see H
CMS: Hl had 3
HWW lqq and llnew
Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007 5
Properties of the Higgs Boson
CP Quantum NumbersRatio of Partial Width
dominated by VBF channels
(only assumed 30fb-1)
HWW used as reference
as measured most precisely
ATLAS
Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007 6
MSSM: VBF, esp. Hdominates discovery potential at LO
invisible Higgs: VBF cleary most sensitive channel
Discovery Potential in Extensions of the SM
30 fb-1
MSSM
30 fb-1
ATLAS
ATLAS preliminary
Invisible Higgs
Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007 7
ATLASprel.
300 fb-1
SM or Extended Higgs Sector e.g. Minimal SUSY ?
Discrimination via VBF
R =BR(h WW) BR(h )
assume: Mh precisely known no sys. uncerainties
Compare expected measurement
of R in MSSM with SM prediction
for same MH
=|RMSSM-RSM|exp
similar study by M. Dührssen et al. incl. 13 channels VBF dominates
Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007 8
VBF: Event Topology
Signature: 2 tagging jets at large rapidities
challenge: jet reconstruction no color flow between jets, rapidity gap
challenge: central jet veto Higgs decay products in central region
challenge: mass reconstruction
for H and HWWlqq
dominated by ETmiss resolution
ATLAS
=-ln tan(/2)
Tagging Jets
Higgs-Zerfall
W/Z
W/Z
degree 1 2 15 90 15 2 1
Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007 9
„low lumi“ 10 to20 fb-1/year „high lumi“ 100 fb-1/year
An Event at the LHC
+ ~23 overlapping pp-interactions per bunch crossing at high lumi.
~109 proton proton collisions / second ~1600 charged particles in detector per event
+ effects from „pile up“: readout time > t btw. bunch
hard collision
+ ISR,FSR
+ „underlying
event“
Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007 10
Jet Reconstruction
pT>20GeV
Reconstruction efficiency
- approximately confirmed by new
preliminary ATLAS studies
- optimisation w.r.t jet algo ongoing
ATLAS
90 15 2 1o
ATLAS CMS
both experiments: fake rate ~ 2% for ET>20 GeV
fake rate = probability to find jet from pileup in central part of detector
low lumi
low lumi
Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007 11
Basic selection cuts
ATLAS
(a) 2 tagging jets: ET(1,2)>x(y) up to |max| with 1x2<0
(b) rapidity difference (c) invariant dijet mass
CMS CMS CMS ATLAS ATLAS ATLAS ATLAS
WWll WWlqq lhad WWll WWlqq ll lhad
max 4.5 4.5 4.5 4.9 4.9 4.9 4.9
ET(GeV) 50/30 45/35 40/40 40/20 60/60 50/30 40/20
4.2 4.2 4.2 3.8 5.0 4.4 4.4
Mjj 600 1000 1000 550 1200 700 700
CMS
Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007 12
Central Jet Veto (CJV)
EW: color singlet exchange
QCD: color octet exchange
different radiation
pattern expected
EW QCD
born level distribution for Z + 3 jets
D. Zeppenfeld et al., Phys.Rev.D54:6680-6689,1996
Challenge: calculation of CJV efficiencies
- „matching“ of Z+2j and Z+3j calculations
- correct QCD scales
- validity of approx. for phase space region
Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007 13
Central Jet veto
PhD thesis D. Rainwater, hep-ph 9908378
CJV survival probabilities : no jet with ET>20GeV btw. tagging jets
two approaches: - truncated shower approximation (dotted and dashed dotted)
- exponentiation model (solid and dashed)
(for details see, e.g.:
Phys.Rev.D54:6680-6689,1996
and PhD thesis by D. Rainwater)
or talks by Terrance Figy and
Christoph Hackstein this afternoon
Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007 14
Issues for the Central Jet Veto
Towards Discovery
- optimise CJV for significance
- robust against pileup, underlying event
detector noise, MC modelling, …
- if modelling wrong: kill (partially) our signal
need more data for observation
- knowledge of CJV efficiency not needed
Investigation of properties
couplings: (pollution from gluon fusion)
NOBS – NBG = (effVBF VBF + eff.GGFVBF GGF) x lumi
need knowledge of CJV eff. for VBF and GGF
HVV coupling structure from jj
need efficiencies and correlation with
observable for VBF, GGF (and background)
Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007 15
VBF: H
He
ATLAS
30 fb-1
comparable sensitivity in
lep had channel
caveat: different x-sections,
MC generators,
BG uncertainty, stat. tool
Zjj dominant background
QCD to EW ~ 3:1
Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007 16
CMS: CJV in Hlep had
No jet with: ETraw>10 GeV in min+0.5 < 3 < max-0.5
and 3= ptrack /ETraw>0.1
(sum over tracks in cone of 0.5 around jet axis)
motivation: distiniguish „signal“ from „pileup“ jets
CMS
CMS
Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007 17
Comparison of CJV: CMS and ATLAS
dependence of CJV efficiency
on ET of MC jet (10,15,20,..,45GeV)
10 GeV raw ~ 20 GeV MC Jet
Eff. of CJV(%) Higgs EW Zjj QCD Zjj W+jets tt
CMS lep had 81 71 40 29 24
ATLAS lep had 88 96 64 57 14
ATLAS lep lep 72 95 45 77 13
Rainwater 89 80 28 - 29
ATLAS: lep lep: no jet with ET>20 GeV ||<3.2
lep had: ‘‘ btw. tagging jets
10 GeV
45 GeVCMS
Comparison of CJV survival probabilities
Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007 18
HWWATLAS: HWWe CMS: HWWlqq
Comparison of significance:
ll: ATLAS more powerful
lq: CMS more powerful
But: different x-sections,
MC generators, etc.
Now: investigation of differences
Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007 19
Central Jet Veto in HWWllCMS: PT-Balance: <40 GeV
CJV: no jet with ET>20 GeV in |3* |< 2.0
CMS Higgs tt+j WWjj (EW) WWjj(QCD)
Eff. PTBAL.(%) 65 39 52 40
Eff. CJV(%) 68 27 62 48
Higgs tt+Wt WW+js (EW) WW+js (QCD) Z+j EW Z+j QCD
Eff. PTBAL (%) 85 24 76 66 77 67
Eff. CJV (%) 86 31 89 75 100 63
ATLAS: PT-Balance: <30 GeV
CJV: no jet with ET>20 in |3|<3.2
Higgs tt+ttj(j) WW+j (EW) WW+j (QCD) Z+j EW Z+j QCD
Eff. CJV (%) 89 46/29 75 29 - -
Rainwater no jet with ET>20 GeV btw. tagging jets
Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007 20
Summary of Current „Officical“ Experimental Status
no coherent picture of CJV performance (my feeling)
- different applications in channels and both collaborations
is the optimal that different for different channels?
- different MC generators
which gives most correct description?
how do they compare with the theo. calculations (TSA, Exp Mod.)?
is the use of current MC generators meaningful at all?
- disentangle effects from underlying event, pileup, noise, … ?
does the inclusion of track information really help?
- different basic VBF cuts (correlation not studied in great detail)
what is correlation with method and threshold of CJV?
better understanding by cooperation from theory+CMS+ATLAS
maybe good candidate for Analyis Group in Helmholtz Alliance
Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007 21
Track Jet Veto versus Calorimeter Jet Veto in HWWll
S. Horvat, S. Kaiser, O.Kortner MPI Munich
Idea:
disentangle jets from pileup pp collision and signal pp collision via tracks
for now: signal vertex = vertex with largest ptsum of tracks
jet finding via cone of 0.4 on tracks and calorimeter objects
Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007 22
Multiplicities without and with pile-up
Calo jets: increased multiplicity at low ET and large eta
Track jets: multiplicity distribution stable
Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007 23
Multiplicities above Threshold without and with pile-up
Calo Jets
Track Jets
||<2.5 tracking detector acceptance
Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007 24
Survival Probabilities
pT of track jets ~ 0.5 of calo jets
compare jet veto for
- track jets above 10 GeV
- calo jets above 20 GeV
both within || < 2.5
jet veto survival probabilities
track jet veto seems more robust ongoing study and optimisation
Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007 25
idea:count charged particles in rapidity gap: Jmin+0.5<trk<Jmax-0.5
Track Veto versus Central Jet veto (S. Nikitenko)
without
underlying event
with
underlying event
hadron level study with PYTHIA
Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007 26
Eff. veto cut Higgs Z+jets
CJV ETJ3>20 GeV 0.83 (0.81) 0.44 (0.46)
TV Ntrk > 9 0.80 0.55
* Numbers in parenthesis from CMS PTDR with full simulation
Track veto vs CJV: Survival probabilities for Hl had
Jet veto Track veto
Next steps:- check with full simulation
- compare results without and with pileup
Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007 27
Rapidity of non tagging jets with PT>20 GeV
Cuts applied: pt1(2) >50(30)GeV, |1,2|<4.9, 1x2< 0, mj1j2 > 700 GeV, j1j2> 4.4, j1j2 < 2.2
Comparison of MC Event Generators (M. Röder, BN)
Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007 28
Comparison of Different MC Generators
Survival probability depending on pt of 3rd jet in ||<3.2
significant dependence on event generator
mainly caused by different parton shower, not by underlying event
Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007 29
Determination of CJV Efficiency from Data
needed for investigation of Higgs boson properties
useful for optimising selection w.r.t. discovery
general interest to understand radiation pattern
goal: find and select samples with similar topology as VBF signal
with reasonable rate and signal-to-background ratio determine radiation pattern transfer to Higgs signal process (directly or via MC) tune MC generators to reproduce data
two candidates:
„the obvious“: jjZee+competing QCD and EW contribution
„the obscure“: single top (t-channel) purely EW process
Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007 30
The obvious jjZee(D. Zeppenfeld et al. Phys.Rev.D54:6680-6689,1996)
problem: QCD rate large compared to EW rate, still factor 7 after above cuts
EW QCD
Z
disentangle jjZ EW from QCD by VBF like selection
Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007 31
The obvious jjZee
good S/B only
- with hard cuts
on Mjj and jl
- at (too) small rate
small S/B
discrimination om
statisticsl basis
in fb
QCD
EW
Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007 32
The obvious jjZee
CJV: no jet with ETr>10GeV in min+0.7 < 3 < max-0.7
average vetos per event n calculated in exponentiation model
CJV thresholds
> 10 GeV
> 20 GeV
> 40 GeV
> 80 GeV
-
negligible correlation between veto prbabilty and jl (for <2.2)
maybe unfolding in jl may be usful
detailed experimental study needed
Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007 33
The obscure: single top (t-channel) production (MS, Si)
q q
b t
W
q q
q q
W
W
H
(NLO)~50 pb (incl. BR tbWbl)
Efficiency: ~ 0.5% 250 evts/fb
Signal-to-BG(tt): 2 to 3
(LO,120GeV)~0.4 pb
Efficiency: ~0.4%
similar colour structure similar radiation pattern after selection?
is it possible to prepare sample with similar topology? what is influence of differences? - initial b from gluon splitting
- different polarisations of Ws
- tbW decay
W
b
e,
Single top: qbqt VBF H
Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007 34
The obscure: single top (t-channel) production
samples produced with: Herwig+Jimmy+ ATLAS fast detector simulation
select tagging jets in opposite hemispheres
for single top: require b-tag (|b|<2.5 due to tracker acceptance)
invariant tag jet mass rapidity difference of tag jets
Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007 35
Characteristics of the third jet
with small statistics no definite conclusion possible!
at 1st glance: no significant discrepancy btw. single top and VBF
next steps: - use ME calculations for 3rd jets
- determine amount of tt background after „VBF“ selection
- use TSA or Exponentiation Model to get CJV efficiencies
transverse momentum 3*=3 - ½(1+2)
Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007 36
Conclusions and Outlook
None yet. This is supposed to be a workshop !
Hope for lively and interesting
discussions during this meeting.
Hope for close, good and fruitful cooperation
between theory, CMS and ATLAS people
here and in the future.