Weak boson fusion at the Large Hadron Colliderpartsem/fy13/jaeger-bnl2012.pdf · the first hadron...
Transcript of Weak boson fusion at the Large Hadron Colliderpartsem/fy13/jaeger-bnl2012.pdf · the first hadron...
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Weak boson fusionat the Large Hadron Collider
Barbara J ager
Johannes-Gutenberg University Mainz
Particle Physics Seminar
Brookhaven NationalLaboratory
October 2012
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what’s on the menu today?
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
weak vector boson fusion (VBF)
the appetizer: Higgs production
· signal topology
· backgrounds
· quantum corrections
main course: weak boson scattering
· precision calculations
· phenomenological results
· signatures of new physics
dessert:
· VBF and parton showers
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the standard model of elementary particles
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
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the standard model of elementary particles
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
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experimental bounds on the Higgs mass
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
information on the Higgsboson is obtained via
✦ indirect searches:Higgs boson affects variousobservables indirectly via
quantum corrections
✦ direct searches for explicitHiggs production in· e+e− collisions
· hadronic collisions
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indirect searches
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
Higgs boson affects electroweak precision data(e.g. gauge boson mass determination)
via quantum corrections
+
corrections proportional to lnM2
H
M2
Z
☞ constrain MH by precision data fromvarious experiments (LEP, SLC, CDF, D0):
MH . 161 GeV @ 95% CL[LEP EWWG, July 2011]
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Higgs couplings
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
gauge boson V fermion f self interaction
∝ MV∝ mf ∝ M2
H
coupling of the Higgs boson to any particleproportional to its mass
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direct search in electron-positron collisions
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
e−
e+
Z
Z
H
direct Higgs production
at the CERN-LEP e+e− collider
(c.m.s. energy√S . 209 GeV):
mainly via Higgs-strahlung
MH & 114 GeV
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the first hadron collider at the terascale
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
the Tevatron at Fermilab:
high energy synchrotron
with proton–anti-proton collisions
at c.m.s. energy√S ≃ 2 TeV
two major experiments:
CDF
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the Higgs at Tevatron?
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
combination of CDF & D0 searcheswith up to 10 fb−1 of data
(July 2, 2012):
excess with 2.9 σ inH → bb channels
b
b
ℓ+
ℓ−
H
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the world’s largest hadron collider . . .
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
. . . and its four major experiments . . .
CMS•
ATLAS•
ALICE•
LHCb •
Compact MuonSolenoid
A Large Ion ColliderExperiment
A Toroidal LHC Apparatus
LHC-beauty
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Spiegel Online, July 4, 2012
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status as of July 4, 2012
the ATLAS experiment reports theobservation of an excess of events
at a mass of 126.5 GeVwith local significance of 5.0 σ
the CMS experiment reports theobservation of a new boson
with a mass of125.3 ± 0.6 GeV
at 4.9 σ significance
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Higgs production @ LHC
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
[GeV] HM100 200 300 400 500 1000
H+
X)
[pb]
→(p
p σ
-210
-110
1
10= 7 TeVs
LH
C H
IGG
S X
S W
G 2
010
H (NNLO+NNLL QCD + NLO EW)
→pp
qqH (NNLO QCD + NLO EW)
→pp
WH (NNLO QCD + NLO EW)
→pp
ZH (NNLO QCD +NLO EW)
→pp
ttH (NLO QCD)
→pp
Higgs cross section working group
gluon fusion (GF)
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Higgs production @ LHC
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
[GeV] HM100 200 300 400 500 1000
H+
X)
[pb]
→(p
p σ
-210
-110
1
10= 7 TeVs
LH
C H
IGG
S X
S W
G 2
010
H (NNLO+NNLL QCD + NLO EW)
→pp
qqH (NNLO QCD + NLO EW)
→pp
WH (NNLO QCD + NLO EW)
→pp
ZH (NNLO QCD +NLO EW)
→pp
ttH (NLO QCD)
→pp
Higgs cross section working group
gluon fusion (GF)
ttH production
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Higgs production @ LHC
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
[GeV] HM100 200 300 400 500 1000
H+
X)
[pb]
→(p
p σ
-210
-110
1
10= 7 TeVs
LH
C H
IGG
S X
S W
G 2
010
H (NNLO+NNLL QCD + NLO EW)
→pp
qqH (NNLO QCD + NLO EW)
→pp
WH (NNLO QCD + NLO EW)
→pp
ZH (NNLO QCD +NLO EW)
→pp
ttH (NLO QCD)
→pp
Higgs cross section working group
gluon fusion (GF)
ttH production
vector boson fusion (VBF)
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Higgs production @ LHC
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
[GeV] HM100 200 300 400 500 1000
H+
X)
[pb]
→(p
p σ
-210
-110
1
10= 7 TeVs
LH
C H
IGG
S X
S W
G 2
010
H (NNLO+NNLL QCD + NLO EW)
→pp
qqH (NNLO QCD + NLO EW)
→pp
WH (NNLO QCD + NLO EW)
→pp
ZH (NNLO QCD +NLO EW)
→pp
ttH (NLO QCD)
→pp
Higgs cross section working group
gluon fusion (GF)
ttH production
W,Z bremsstrahlung
vector boson fusion (VBF)
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Higgs production @ LHC
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
[GeV] HM80 100 200 300 400 1000
H+
X)
[pb]
→(p
p σ
-210
-110
1
10
210= 8 TeVs
LH
C H
IGG
S X
S W
G 2
012
H (NNLO+NNLL QCD + NLO EW)
→pp
qqH (NNLO QCD + NLO EW)
→pp
WH (NNLO QCD + NLO EW)
→pp
ZH (NNLO QCD +NLO EW)
→pp
ttH (NLO QCD)
→pp
Higgs cross section working group
gluon fusion (GF)
ttH production
W,Z bremsstrahlung
vector boson fusion (VBF)
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Higgs production @ LHC
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
[GeV] HM100 200 300 400 500 1000
H+
X)
[pb]
→(p
p σ
-110
1
10
210= 14 TeVs
LH
C H
IGG
S X
S W
G 2
010
H (NNLO+NNLL QCD + NLO EW)
→pp
qqH (NNLO QCD + NLO EW)
→pp
WH (NNLO QCD + NLO EW)
→pp
ZH (NNLO QCD +NLO EW)
→pp
ttH (NLO QCD)
→pp
Higgs cross section working group
gluon fusion (GF)
ttH production
W,Z bremsstrahlung
vector boson fusion (VBF)
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weak vector boson fusion (VBF)
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
✦ important Higgs search channelover entire mass range
✦ sensitive to Higgs couplingsand CP properties
☞ accurate predictions andflexible tools essentialfor signal and backgrounds!
CMS & ATLAS:VBF selection included inH → γγ, H → WW ,
H → ττ
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VBF event topology
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
p
p
HZ,W
Z,W
jet
jet
suppressed color exchange between quark lines gives rise to
✦ little jet activity in central rapidity region
✦ scattered quarks → two forward tagging jets(energetic; large rapidity)
✦ Higgs decay products typically between tagging jets
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Higgs production in VBF @ NLO QCD
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
NLO QCD:inclusive cross section:Han, Valencia, Willenbrock (1992)
distributions:Figy, Oleari, Zeppenfeld (2003)
Berger, Campbell (2004)
NLO QCD correctionsmoderate
and well under control(order 10% or less)
publicly availableparton-level Monte Carlos:
vbfnloMCFM
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Higgs production in VBF @ NLO EW
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
QCDEW
EW+QCD
MH = 200GeV
pp → Hjj + X
pj1,T [GeV]
dσ
dσLO− 1 [%]
400350300250200150100500
10
5
0
−5
−10
−15
−20
−25
−30
−35
−40
publicly availableparton-level Monte Carlo
program: HAWK
Ciccolini, Denner, Dittmaier, Muck:
NLO EW corrections to inclusive cross sections and distributions
☞ NLO EW corrections non-negligible, modify K factors anddistort distributions by up to 10%
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SUSY QCD+EW corrections to VBF
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
0.001
0.01
0.1
1
1000 600 400 200 100
SPS1b LEP χ1±
m1/2 [GeV]
-∆σ/σ [%]
total (µ fixed)total (µ var)
Ο(αs) (µ fixed)
Hollik, Plehn, Rauch, Rzehak & Figy, Palmer, Weiglein (2008-2010):
SUSY QCD & EW corrections . 1%
for inclusive cross sections
in typical regions of the MSSM parameter space
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vbfnlo
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
vbfnlo is a fully flexible parton level Monte Carlo for processeswith electroweak bosons at NLO-QCD in the SM and beyond
it can simulate:
✦ various weak vector boson fusion processes
✦ double and triple weak boson production processes
✦ double weak boson production processesin association with a hard jet
✦ Higgs production via gluon fusionin association with two jets
http://www-itp.particle.uni-karlsruhe.de/∼vbfnloweb
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vbfnlo: features
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
✦ cross sections and distributions at NLO-QCD accuracy
✦ NLO-EW corrections to VBF Hjj production
✦ arbitrary selection cuts
✦ various choices for factorization and renormalization scales
✦ LO predictions for all processes with one extra jet
✦ interface to LHAPDF → any currently available PDF set
✦ LO: event files in Les Houches Accord (LHA) format
✦ MSSM: SUSY parameters input via standard SLHA file
✦ various BSM features:anomalous couplings, Kaluza-Klein models, . . .
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higher orders of QCD in VBF
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
Harlander, Vollinga, Weber (2007):
gauge invariant, finite sub-class of virtual
two-loop QCD corrections to pp → Hjj via VBF
gg → qqH, qq → ggH,qg → qgH, qg → qgH
important due to largegluon luminosity at LHC?
minimal set of cuts: σ2−loopgluon ∼ 2 % of σLO
VBF
VBF cuts: relative suppression by additional order of magnitude
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higher orders of QCD in VBF
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
Bolzoni, Maltoni, Moch, Zaro (2010,2011):
subset of the NNLO QCD contributionsto the total cross section for pp → Hjj via VBF
in the structure function approach1
V ∗
2
V ∗
1
P1
P2
X1
X2
q1
q2
µ
ρ
σ ∼∫
dPS1
2s
1(
Q21 + M2
V1
)2
1(
Q22 + M2
V2
)2
× Wµν
(
x1, Q21
)
AµρA∗νσWρσ
(
x2, Q22
)
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higher orders of QCD in VBF
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
σ (pb) at LHC√s = 7 TeV
scale choice:Q/4 ≤ µR,µF ≤ 4Q
LONLONNLO
10-1
1
10-1
1
σ(µR,µF)/σNNLO(Q)
0.70.80.9
11.11.21.31.4
100 150 200 250 300 350 400 450 500
mH(GeV)
✦ NNLO predictions arein full agreementwith NLO results
✦ residual scale uncertaintiesare reduced
from ∼4% to 2%
✦ NNLO PDF uncertaintiesare at the 2% level
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PDF uncertainties in VBF
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
CTEQ:
difference between setsσ6.1/σ6.6 . 4%
PDF uncertainty∆PDF . 3.5 %
for 100 GeV ≤ MH ≤ 800 GeV
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pp → Hjj via gluon fusion
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
VBF can be faked by double real corrections
to gg → H (“gluon fusion”)
✦ complete LO calculation (including pentagons) in the SMDel Duca, Kilgore, Oleari, Schmidt, Zeppenfeld (2001)
✦ and in a generic two-Higgs doublet model:Campanario, Kubocz, Zeppenfeld (2011)
✦ complementary: NLO QCD calculation in mt → ∞ limit:Campbell, Ellis, Zanderighi (2006)
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pp → Hjj via VBF×GF at tree level
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
can VBF×GF interference pollute the clean VBF signature?
Georg (2005) & Andersen, Smillie (2006):
tree-level interference possible only for
· neutral current graphs (no charged current interference)
· identical quark contributions with t ↔ u crossing(kinematically suppressed)
☞ completely negligible
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pp → Hjj via VBF×GF beyond tree level
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
additional gluon → VBF×GF interference for qq′ → qq′H ✔
Andersen et al. (2007)
Bredenstein, Hagiwara, B. J. (2008)
strong cancelation effects betweencontributions of different flavor
interaction cross section tiny → no effect on VBF signal
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VBF event topology
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
φθ1θ2
J1J2
ℓ
ℓ
p p
distinct event topology
of the Higgs signal in
pp → Hjj via VBF with
H → W+W− → e±µ∓/pT
☞ important for suppression of backgrounds
✦ tt + 0, 1, 2 jets production(note: tt → W+W−bb)
✦ QCD W+W−jj production
✦ EW W+W−jj production
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tt + jets backgrounds
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
b
b
t
tW−
W+
✦ large top productioncross section at the LHC
✦ t → Wb branching ratio ∼ 100%
✦ b quarks may be identifiedas tagging jets
✦ exploit kinematic featuresfor background suppression
NLO-QCD predictions available:Denner et al.; Bevilaqua et al. (2011-2012)
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EW V V jj production
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
irreducible background toVBF-induced Higgs production,
followed by decay into W bosons
pp → Hjj → W+W−jj
NLO-QCD predictions availableOleari, Zeppenfeld, B.J. (2006)
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angular distribution of charged leptons
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
Rainwater, Zeppenfeld (1999)
EW W+W−jj
QCD W+W−jj
Hjj via VBF, H→WW
tt+ jets
in H → W+W−: spins anti-correlated
leptons emitted preferentially in samedirection
no such correlation, if W bosonsdo not stem from the Higgs
Dittmar, Dreiner (1996)
distribution for EW W+W− productionsignificantly
different from Higgs signal
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QCD-induced V V jj production
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
QCD-induced W+W−jj productionconstitutes irreducible background to
pp → Hjj → W+W−jj
NLO-QCD predictions availableMelia, Melnikov, Rontsch, Zanderighi (2011);
Greiner et al. (2012)
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tagging jets: properties
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
rapidity separation of the tagging jets
jjη∆1 2 3 4 5 6 7
jjη∆/dσ
dσ1/
0
10
20
30
40
50
60
70
80
90
-310×
gluon fusionVBF
+Jetstt
QCD-WW
Klamke, Zeppenfeld (2007)
jets more central in QCD- than in EW-inducedproduction processes
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VBF signal / background analysis
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
☞ selection of signal and background rates
for MH = 160 GeV (in [fb])
in the H → e+µ−/pT decay mode at the LHC :
cuts Hjj tt+jets QCD WWjj EW WWjj . . . S / B
forward tagging 17.1 1080 4.4 3.0 . . . 1/65
+b veto 64 . . . 1/5.1
+angular cuts 11.4 5.1 0.50 0.45 . . . 1.7/1
+central jet veto 10.1 1.48 0.15 0.34 . . . 4.6/1
all cuts 7.5 1.09 0.11 0.25 . . . 4.6/1
Rainwater, Zeppenfeld (1999)
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central jet veto
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
central jet veto (CJV):
remove events with extra jet(s) in central-rapidity regionpvetoT
> 20 GeV, ηminjet
< ηvetojet
< ηmaxjet
cuts Hjj tt+jets QCD WWjj EW WWjj . . . S / B
forward tagging 17.1 1080 4.4 3.0 . . . 1/65
+b veto 64 . . . 1/5.1
+angular cuts 11.4 5.1 0.50 0.45 . . . 1.7/1
+central jet veto 10.1 1.48 0.15 0.34 . . . 4.6/1
all cuts 7.5 1.09 0.11 0.25 . . . 4.6/1
Rainwater, Zeppenfeld (1999)
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central jet veto
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
central jet veto (CJV):
remove events with extra jet(s) in central-rapidity region
pvetoT
> 20 GeV, ηminjet
< ηvetojet
< ηmaxjet
☞ precise knowledge of extra jet activity essential,requiring
✦ pp → Hjj interfaced to parton shower programs
✦ pp → Hjjj at NLO-QCD accuracy
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pp → Hjjj via VBF
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
Figy, Hankele, Zeppenfeld (2007)
✦ dominant NLO-QCD corrections modest
✦ scale uncertainties of CJV observables significantly reduced
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pp → Hjj via VBF and parton showers
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
for realistic description ofscattering processes at hadron
colliders:
✦ combine matrix elements forhard scattering
with programs for simulation of
underlying event, partonshower, and hadronization
(Pythia, Herwig, Sherpa,...)
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pp → Hjj via VBF & parton showers @ LO
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
rapidity separation of the third jet: y⋆ = y3 − 1
2(y1 + y2)
Hackstein et al. (2008)leading order:
no third jet from matrixelement for hard partonic
scattering
Pythia/ Herwig:
very different patterns infilling of rapidity gap by
parton shower
☞ better understanding andmodeling needed
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NLO-QCD vs. shower Monte Carlo
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
NLO QCD:
✔ accurate shapes at high pT
✔ normalization accurate at NLO
✔ reduced scale dependence
✘ wrong shapes at low pT
✘ description only at parton level
LO SMC:
✘ bad description at high pT
✘ normalization accurate only at LO
✔ Sudakow suppression at low pT
✔ events at hadron level
☞ merge the two approaches, keeping the advantages of both:
· MC@NLO [Frixione, Webber]
· POWHEG [Nason et al.]
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parton showers & NLO-QCD: the POWHEG method
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
general prescription for matching parton-level NLO-QCDcalculations with parton shower programs
[Frixione, Nason, Oleari]
✦ applicable to any pT -ordered parton shower program
✦ no double counting of real-emission contributions
✦ produces events with positive weights
✦ tools for “do-it-yourself” implementationpublicly available (the POWHEG-BOX)
[Alioli, Nason, Oleari, Re]
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parton showers & NLO-QCD: the POWHEG-BOX
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
✘ user has to supply process-specific quantities:
✦ lists of flavor structures for Born and real emission processes
✦ Born phase space
✦ Born amplitudes squared, color-and spin-correlated amplitudes
✦ real-emission amplitudes squared
✦ finite part of the virtual corrections
✦ Born color structure in the limit of a large number of colors
✔ all general, process-independent aspects of the matchingare provided by the POWHEG-BOX
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parton showers & NLO-QCD: the POWHEG-BOX
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
up-to-date info on the POWHEG-BOXand code download:
http://powhegbox.mib.infn.it/
VBF processes in the POWHEG-BOX:
✦ Higgs production via VBF [Oleari, Nason (2009)]
✦ Z-boson production via VBF [Schneider, Zanderighi, B.J. (2012)]
✦ W+W+ production via VBF [Zanderighi, B.J. (2011)]
. . . and various background processes
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pp → Hjj via VBF in the POWHEG-BOX
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
Nason, Oleari (2009)
✦ good agreement between parton-level NLO calculation andPOWHEG matched with HERWIG or PYTHIA for many observables
✦ for high multiplicites, HERWIG produces harder jets than PYTHIA
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Higgs signal in VBF
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
pp → Hjj via VBF under excellent control:
✦ QCD & EW NLO corrections at 10% level
✦ dominant NNLO QCD corrections small
✦ interference with GF Hjj production negligible
✦ SUSY corrections small within the MSSM
✦ small PDF uncertainties . 4%
✦ NLO-QCD matched with parton shower available
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what else is VBF good for?
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
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the versatility of VBF processes
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
vector boson fusion (VBF)
Standard Model:
important production modefor the Higgs boson
sensitive to Higgs couplingsand CP properties
beyond the Standard Model:
sensitive to the mechanism ofelectroweak symmetry breaking
lstrongly interacting weak sector,
new resonances, . . . ?
![Page 54: Weak boson fusion at the Large Hadron Colliderpartsem/fy13/jaeger-bnl2012.pdf · the first hadron collider at the terascale Barbara Jager, October 2012¨ JGU Mainz weak boson fusion](https://reader034.fdocuments.net/reader034/viewer/2022050111/5f492382e626683991269b0b/html5/thumbnails/54.jpg)
gauge boson scattering
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
reminder: pp → Hjj via VBF with H → V V
important production mode for SM-type Higgs boson
(used in official ATLAS and CMS analyses)
important irreducible background: EW V V jj production
interesting per se: contains VLVL → VLVL scatteringsensitive to origin of electroweak symmetry breaking
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EW V V jj production
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
need stable, fast & flexible Monte Carlo program allowing for
✦ computation of various jet observables for
W+W−jj, ZZjj, W±Zjj , and W±W±jj
production via VBF at NLO-QCD accuracy
(leptonic decay correlations being fully taken into account)
✦ straightforward implementation of cuts
C. Oleari, D. Zeppenfeld, B. J. (2006, 2009)
G. Bozzi, C. Oleari, D. Zeppenfeld, B. J. (2007)
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ingredients of the calculation
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
need to compute numerical value for . . .
|MB|2 = + + + . . .2
. . . Born amplitude squared in 4 dim
|MR|2 = + + + . . .2
. . . real-emission amplitude squared in 4 dim andcounter-terms for infrared-divergent configurations
almost 3000 diagrams → essential: organize calculation economically!
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virtual contributions
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
MV = + + + . . .
= MB F (Q)
[
− 2
ε2− 3
ε
]
+ MfiniteV
determined numerically[c. f. Denner, Dittmaier (2002,2005)]
combination of real emission, virtuals,and subtraction terms:
poles canceled analytically → finite results
phase-space integration can be performed numerically (Vegas)
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precision tools
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
Monte Carlo program for cross sections and distributionswhich allows for the implementation of
realistic experimental selection cuts
☞ embedded in more general frameworkfor various VBF-type processes
vbfnlo
publicly available from
http://www-itp.physik.uni-karlsruhe.de/∼vbfnloweb/
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pp → V V jj @ LHC: settings
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
use design energy of 14 TeV, apply kT jet algorithm,
CTEQ6 parton distributions, and typical VBF cuts:
tagging jets
charged leptons
pTj ≥ 20 GeV, |yj| ≤ 4.5,
∆yjj = |yj1 − yj2| > 4,
Mjj > 600 GeV
jets located in opposite hemispheres
pTℓ ≥ 20 GeV, |ηℓ| ≤ 2.5,
∆Rjℓ ≥ 0.4,
yj,min < ηℓ < yj,max
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scale uncertainty: pp → W+W+jj
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
LO, ξF = ξ
NLO, ξF = ξ, ξR = 1
NLO, ξF = 1, ξR = ξ
NLO, ξF = ξ, ξR = ξ
Oleari, Zeppenfeld, B. J. (2009)
choose default scale µ0 = mW or µ0 = Qset µR = ξRµ0 and µF = ξFµ0, with variable ξ
LO: no control on scaleNLO QCD: scale dependence strongly reduced
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W+W+jj distributions: invariant mass of tagging jets
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
Oleari, Zeppenfeld, B. J. (2009)
µ = ξ µ0
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pp → W+W+jj: energy dependence
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
B. J. (2009)
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pp → W+W+jj in the POWHEG-BOX
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
QCD-induced productionMelia, Melnikov, Rontsch, Zanderighi (2010);
Melia, Nason, Rontsch, Zanderighi (2011)
EW productionOleari, Zeppenfeld, B.J. (2009);
Zanderighi, B.J. (2011)
NLO-QCD results with basic jet cuts only (ptagT
> 20 GeV):
σincQCD = 2.12 fb σinc
EW = 1.097 fb
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pp → W+W+jj: QCD versus EW production
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
Zanderighi, B.J. (2011)
10-7
10-6
10-5
10-4
10-3
10-2
0 500 1000 1500 2000 2500 3000
dσ/d
Mj 1
j 2 [f
b/G
eV]
Mj1j2 [GeV]
QCDEW
00.05
0.10.15
0.20.25
0.30.35
0.40.45
-4 -3 -2 -1 0 1 2 3 4
dσ/d
∆ y j
1j2 [f
b]
∆yj1j2
QCDEW
· √s = 7 TeV
· basic jet cuts only
· NLO-QCD accuracy
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pp → W+W+jj in the POWHEG-BOX
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
QCD-induced productionMelia, Melnikov, Rontsch, Zanderighi (2010);
Melia, Nason, Rontsch, Zanderighi (2011)
EW productionOleari, Zeppenfeld, B.J. (2009);
Zanderighi, B.J. (2011)
NLO results with basic jet cuts only (ptagT
> 20 GeV):
σincQCD = 2.12 fb σinc
EW = 1.097 fb
NLO results with VBF cuts:
σcutsQCD = 0.0074 fb σcuts
EW = 0.201 fb
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pp → W+W+jj in the POWHEG-BOX
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
Zanderighi, B.J. (2011)
0.02
0.04
0.06
0.08
dσ/
dyj1
[fb]
POWHEG+PYTHIANLO
0.81.01.2
-3 -2 -1 0 1 2 3(Pw
g+P
yt)/
NLO
yj1
10-6
10-5
10-4
10-3
dσ/
dpT
, j1
[fb/G
eV]
POWHEG+PYTHIANLO
0.81.01.2
100 200 300 400 500 600 700(Pw
g+P
yt)/
NLO
pT, j1 [GeV]
good agreement between parton-level NLO calculation andPOWHEG matched with PYTHIA for many observables
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pp → W+W+jj in the POWHEG-BOX
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
Zanderighi, B.J. (2011)
4
8
12
dσ/
dyj3
[10-3
fb]
POWHEG+PYTHIANLO
0.51.01.5
-4 -3 -2 -1 0 1 2 3 4(Pw
g+P
yt)/
NLO
yj3
10-6
10-5
10-4
10-3
10-2
dσ/
dpT
, j3
[fb/G
eV]
POWHEG+PYTHIANLO
0.81.01.2
40 60 80 100 120 140(Pw
g+P
yt)/
NLO
pT, j3 [GeV]
typical for VBF processes: little jet activity at central rapidities→ exploited by central-jet veto techniques
note: parton-shower effects slightly enchance central jet activity
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parton showers and NLO-QCD
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
✦ for precise and realistic predictions NLO-QCD calculationsmatched to parton shower programs are important
✦ codes for several VBF processesare publicly available in the POWHEG-BOX from
http://powhegbox.mib.infn.it/
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new interactions in the gauge boson sector
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
VBF processes are extremelysensitive to new interactions in the
gauge boson sector
can we spot signatures ofnon-standard scenarios for
electroweak symmetry breaking?
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framework: signal
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
consider two “prototype” scenarios for the VBF signal:
✦ SM with heavy Higgs boson (MH = 1 TeV, ΓH = 0.5 TeV)
naive estimate of strongly coupled sector withscalar, iso-scalar resonance at the TeV scale
✦ Warped Higgsless model withextra vector resonances (“Kaluza-Klein excitations”)
( mW2= 700 GeV , Γ = 13.7 GeV ,
mZ2= 695 GeV , Γ = 18.7 GeV ,
mZ3= 718 GeV , Γ = 6.4 GeV )
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LO results: scalar / vector resonances
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
Englert, Worek, Zeppenfeld, B.J. (2008)
ZZjj → 4ℓjj W+Zjj
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impact of NLO-QCD corrections
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
Englert, Zeppenfeld, B.J. (2008)
W+ZjjµR = µF = Q
NLO-QCD corrections always in the few-percent rangefor V V jj production in Warped Higgsless model
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summary
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
VBF crucial for understandingmechanism of
electroweak symmetry breaking
important pre-requisites:
✦ explicit calculations revealed that VBF reactionsare perturbatively well-behaved
(moderate NLO QCD and EW corrections,negligible higher order and interference effects)
✦ backgrounds are well under control
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conclusions
JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC
for understanding and interpreting physicsat the LHC (and beyond . . . ) it is vital to provide:
✦ precise predictions for signals and backgrounds, including
· NLO QCD corrections· NLO EW corrections· and more: interference effects, resummations,
well-constrained PDFs, . . .
✦ realistic predictions, allowing for
· calculation of distributions within experimental selection cuts· matching to parton-shower Monte Carlos
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JGU MainzBarbara Jager, October 2012 weak boson fusion at the LHC