prospects for vv scattering : latest news
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Prospects for VV scattering: latest news
S.Bolognesi (Johns Hopkins University)on behalf of CMS and ATLAS
Implications of LHC results for TeV-Scale physics – CERN, March 2012
Same behavior for all VV amplitudes
without Higgs, W+LW-
L->W+LW-
L would break unitarity
V
V V
V
VV -> VV
V
VV scattering is the smoking gun of the EWSB !
2Implication of LHC results for TeV-Scale physics S.Bolognesi (JHU)€
1v 2 −s − t +
s2
s −mH2 +
t 2
t −mH2
⎛ ⎝ ⎜
⎞ ⎠ ⎟
LLLL WWWWA
2
2
2
2
2
1
HHLLLL mt
tmssts
vWWWWA
S channel T channel QGC
W,Z mass (-> longitudinal degrees of freedom) arise from the Higgs mechanism:
VV scattering: unitarity violation
LSB<1TeVSB sector weakly coupled
SB sector strongly coupled
eg, strongly interacting light Higgs
SM No-HiggsLSB>1TeVUnitarity violation
other scenarios possible:
VV scattering spectrum s(VV->VV) vs M(VV) is the fundamental probe to test nature of Higgs boson or to find alternative EWSB mechanism
VV scattering as probe for EWSB
3Implication of LHC results for TeV-Scale physics S.Bolognesi (JHU)
talk at First LHC to Terascale Workshop (Sept 2011):Personal adaptation from “Boson Boson scattering analysis” by A.Ballestrero (INFN Torino)
Experimental signature
Typical signature: forward-backward “spectator” jets with very high energy
JHEP 0704 (2007) 052
ggH + 2jets ggH + 2jets
4Implication of LHC results for TeV-Scale physics S.Bolognesi (JHU)
VV scattering in real life (1) In no Higgs case: increasing of xsec at high VV is suppressed by
→ small difference btw SM and violation of unitarity (no Higgs)
→ with proper cut (eg Dh jets) can be enhanced -> selection of the longitudinal W
• PDF• offshell bosons• unpolarized bosons
SILH
5Implication of LHC results for TeV-Scale physics S.Bolognesi (JHU)
W±W± W±W±
PHANTOM MC PHANTOM MC
talk
at F
irst L
HC to
Tera
scal
e W
orks
hop
(Sep
t 201
1):
Pers
onal
ada
ptati
on fr
om “
Boso
n Bo
son
scatt
erin
g an
alys
is” b
y A.
Balle
stre
ro (I
NFN
Torin
o)
Longitudinal vs Transversal
mH 500 GeVnoHiggs (unitarity violation)
WW tail (TT): neutrino WW tail (TT): lepton
Higgs peak (LL): neutrino Higgs peak (LL): lepton
Transverse distributionLongitudinal distribution
Angular analysis can boost LL-TT separation (new!):
partonic study in the center of mass of W
6Implication of LHC results for TeV-Scale physics S.Bolognesi (JHU)
VV scattering in real life (2)
WW approximated without interference
JHEP 0603 (2006) 093
WW signal with “a posteriori” cuts
...2signal
irreducible background (aEW6)
7Implication of LHC results for TeV-Scale physics S.Bolognesi (JHU)
hep-ph/0505225v1
Outline Review of theoretical tools
Experimental status: no new results but similar issues under study in other analyses
(short!) historical review and comparison with recent results for similar final states: graviton and higgs searches at high mass
• fully leptonic• semi-leptonic: V+jets control
jet merging for high pt V->jj
tag jets and central jet veto• VBF Higgs search• Z VBF analysis• first (QCD) measurements of FWD jets and jet veto
8Implication of LHC results for TeV-Scale physics S.Bolognesi (JHU)
Theoretical toolsVarious complementary MC
• PHANTOM qq->6f @ aEW6 + aEW
4 × aS2
LO, full description of irreducible background with correct interference
• VBF@NLO
QCD+EW NLO for VBF Higgs production
• HAWK
• POWHEG
• LO ME MC + PS (Madgraph, Pythia, Herwig)
9Implication of LHC results for TeV-Scale physics S.Bolognesi (JHU)
QCD NLO for VV scattering
QCD+EW NLO for VBF+HiggsStralung Higgs production
QCD NLO for VBF+HiggsStralung + PS matching
ratio btw scales
hep-ph/0701105v2
Any news from experiments?
higher mass
higher sensitivity
BSM search for VV resonance @ 1 TeV(DY production)
VBF dedicated search
No dedicated analysis yet (low lumi) -> but arriving to VV scattering in 2 ways
-> studying same final states as VV scattering
10Implication of LHC results for TeV-Scale physics S.Bolognesi (JHU)
-> characterization of tag jets signature
HIG-12-008
low statistics
MET control V+jetsZZ→4l ZZ→llnn Search for G→ZZ: same features discussed for high mass Higgs
ZZ→lljj: large V+jets
Graviton->ZZ search
11Implication of LHC results for TeV-Scale physics S.Bolognesi (JHU)
CMS is working on
ZZ->2l2j (angular analysis)
ZZ->2l 1j (jet merging)
ZZ→4l ZZ→lljj
hep-
ex a
rXiv
:120
3.07
18Ph
ys. R
ev. D
83, 1
1200
8 (2
011)
VV scattering: fully leptonicOnly background VV+jets, very low xsec
B~ 80S~ 200
Latest results:B~ 6S~ 10
Number of events for 20 fb-1 (fully MC based, no systematics, 14 TeV)
500 GeV
>1 TeV
2.2
0.1
1.9
0.2
CMS ZZ->4e, 4m
6.4 3.0
ATLAS ZZ->2l2n
>1 TeV 0.9 0.8
CMS ZW->mmmv 500 GeV 8 5
ATLAS ZW->lllv
1.1 TeV 1.4 0.4
• reso m(ll) as expected• improved reco-id efficiencies(eg ele ID: TDR time 85-90% -> today 95%)
12Implication of LHC results for TeV-Scale physics S.Bolognesi (JHU)
N sign. N back.
14 TeV, 30 fb-1
500 GeV
N sign. N back.
N sign. N back.
N sign. N back.
Example: ggF Higgs 300 GeV
CERN-OPEN-2008-020
hep-ex arXiv:1202.1415
CMS
AN 2
007-
005
CERN
-OPE
N-2
008-
020
VV scattering: semileptonicSemileptonic is most promising: reasonable signal yield
Number of events for 20 fb-1 (fully MC based, no systematics, 14 TeV)
• more sophisticated analysis developed(btag categories, angular analyses, m(jj)=mZ kinematic fit)
• data driven background
Improved JES: mjj reso from 20-25% to 10-15% !
WV -> lnjjZV -> lljj
ATLAS
500 GeV
800 GeV
1.1 TeV
6.2
13
4.8
16
17
9.2
CMS
500 GeV
>1 TeV
337
45
20759
3281
Implication of LHC results for TeV-Scale physics S.Bolognesi (JHU)
N sign. N back. N sign. N back. CMS
500 GeV
>1 TeV
62
5
3415
348
N sign. N back.
For recent inclusive Higgs search: Z->jj mass forH->ZZ->2l2q
13
HIG-11-027
CERN
-OPE
N-2
008-
020
CMS
AN 2
007-
005
V+jets
Improving theoretical tools (Blackhat, Madgraph, …)
Control region (eg, Z→jj sidebands) has very low stat for M(lljj)~1 TeV
• rely on them to extrapolate at higher energy• test them where we have statistics
-> Angular analysis to boost sensitivity -> angular correlations in Z+jets !!
Implication of LHC results for TeV-Scale physics S.Bolognesi (JHU) 14
PRL
106,
1718
01 (2
011)
V+jets measurements QCD measurement (jet pT>20-30 GeV):
syst. dominated by jet scale + PileUp removal, but good status at LHC
→ Tevatron: angular variables
D0 novel measurement: angular correlations have much lower systematics
-> LHC: very high statistics even at high multiplicity -> differential distributions
Implication of LHC results for TeV-Scale physics 15
hep-
ex a
rXiv
:120
1.12
76
X->ZZ->2l2q signal
Z+jets
Jet merging
DR 0.8 (CA) → MX>600 GeVDR 0.5 (Akt) → MX>900 GeV
approx
1(1 )
Zqq T
Z
MRpz z
D
( | | / | |)q Zz p p
Issue under study for EXO searches (boosted top, gravitons) WW scattering
(1.1 TeV resonance) @14 TeV
AkT 0.6
jet mass
jet radiation (sub-jet structure) -> pruning
Handles to distinguish V->j wrt to jets from QCD (Z+jets):
Implication of LHC results for TeV-Scale physics S.Bolognesi (JHU) 16
ww
w.p
ha.jh
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u/gr
oups
/par
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ory/
sem
inar
s/ta
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talk
.khr
on.p
df
Any news from experiments?
higher mass
higher sensitivity
BSM search for VV resonance @ 1 TeV(DY production)
VBF dedicated search
No dedicated analysis yet (low lumi) -> but arriving to VV scattering in 2 ways
-> studying same final states as VV scattering
17Implication of LHC results for TeV-Scale physics S.Bolognesi (JHU)
-> characterization of tag jets signature
HIG-12-008
WHY? Ex of (light) composite higgs:
Fermiophobic-like
“State of the art”
• NO dedicated VBF analysis yet for ZZ !!
• gg at low mass, WW at high mass
Implication of LHC results for TeV-Scale physics S.Bolognesi (JHU) 18
Firs
t LHC
to Te
rasc
ale
Wor
ksho
p (S
ept 2
011)
LCH
at L
HC b
y J.R
. Esp
inoz
a
HIG-12-008 HIG-12-008
First look at tag jets
control of VV background in jet-multiplicity bins
Z prodution in VBF: a candle for jet tagging and jet veto efficiency?
MC tools to describe FWD jets and gap events -> related with description of UE, MPI and QCD at wide angle
Starting to face issues related with tag jets topology and jet vetoing -> very relevant for VV scattering:
-> theoretical systematics (no control regions for ZZ, WW at high mass)
-> (after feasibility) real data analysis ongoing
-> many useful measurements can be done NOW to constraint FWD jets modeling
Implication of LHC results for TeV-Scale physics S.Bolognesi (JHU)
-> TO BE REVIEWED THIS YEAR WITH MUCH HIGHER PU
FWD jet
FWD jet
no color flow -> jet veto
19
WW backgr. in jet multiplicity bins
Uncertainty from MC@NLO scale variation (2nd jet from PS) + ALPGEN comparison
Exclusive computation have huge errors due to higher pertubative orders different treatments of
the uncontrolled higher-order O(α3
s) terms
i.e., different NNLO expansions
ex for H signal:
Inclusive xsec (σ≥Njets), as source of perturbative uncertainties-> uncert. on σN = σ≥N − σ≥N+1
with error propagation
Acceptance evaluated in each exclusive jet bin (uncert~5%) + PDF uncertainty (~2%)
Implication of LHC results for TeV-Scale physics S.Bolognesi (JHU) 20
Higg
s xse
c W
G: h
ep-e
x ar
Xiv:
1201
.308
4
Z in VBF as a candle? VBF Z production as reference: feasibility study at parton-level @ 10 TeV
Z+qq (4 pb) :
signal (~5%) isolated “a posteriori” with partonic cuts
-> 2700 events @ 15 fb-1
irreducible background
-> 45% eff for VBF-specific cuts
S/B improved of a factor 100: 600/78k events @ 15 fb-1 (S/sqrt(B)~ 2)
• Observation feasible but to use as reference need high lumi and to know Z+jets with high precision• Central jet veto suppress only 10% of Z+jets (~useless!)
Implication of LHC results for TeV-Scale physics S.Bolognesi (JHU)
-> 23% tighter cuts against Z+jets QCD (2700 pb)
21
hep-
ex a
rXiv
:100
1.43
57
Jet veto 3rd jet not well modeled by PS, central veto De btw Pythia and Herwig ~ 40%
-> POWHEG NLO: remaining uncertainty ~%
Check with dijet events + rapidity gap (in low PU)(at large pTjet/pTveto or Dy -> fixed order fails)• NP effects<2% (pTveto > LQCD)• HEJ all-order resummation for wide-angle emissions of similar pT-> fails for pT jet>>pTveto
• POWHEG+Pythia good agreement with data-> differences btw Herwig and Pythia
Implication of LHC results for TeV-Scale physics S.Bolognesi (JHU) 22
Similar study in ttbar events !
Higgs xsec WG: hep-ex arXiv:1201.3084
hep-ex arXiv:1107.1641
hep-ex arXiv:1203.5015
FWD jets modeling
useful also to commission our detector -> especially in view of PU
FWD jet spectrum (|h|3.2-4.7) with low PU events
NLO+NP and Powheg+Pythiacatch the dependence, not the xsec
Herwig does a better job than pythiaPythia Z2 tuned to LHC UE
Non-perturbative effects:• energy lost from jets due to hadronisation • energy added to jets from UE
23Implication of LHC results for TeV-Scale physics S.Bolognesi (JHU)
central + forward jet
hep-
ex a
rXiv
:120
2.07
04
Summary
Start studying VV-scattering related issues in different frameworks:
• high mass general X->VV search (Higgs SM or BSM, eg graviton)
• tag jets and jet veto
improve V+jets control
understanding VV in jet multiplicites
studying jet merging
exercising the reconstruction and identification of same final states
testing FWD jets modeling and jet vetoing in data
24Implication of LHC results for TeV-Scale physics S.Bolognesi (JHU)
BACK-UP:
prospects for VV scattering: latest news
S.Bolognesi (Johns Hopkins University)on behalf of CMS and ATLAS
Implications of LHC results for TeV-Scale physics – CERN, March 2012
Di-boson backgroundqq→ZZ NLO + gg→ZZ
PDF+as
scale
Signal: jet counting Analysis in exclusive jet bins
(ex, WW+0,1,2 jets)
• if background depends on Njets• for VBF
→ theoretical uncert in jet bins to be combined with correlations
varying renormalization and factorization scales in the fixed-order predictions for each exclusive jet cross section σN
(results as 100% correlated)
different treatments of the uncontrolled higher-order O(α3s) terms
i.e., different NNLO expansions
inclusive xsec (σ≥Njets), as source of perturbative uncertainties
σN = σ≥N − σ≥N+1with error propagation
LHC To Terascale Physics WS S.Bolognesi (Johns Hopkins University)41
WW same sign
10 TeV 60 fb-1
Final state with largest effects from unitarity violation
Implication of LHC results for TeV-Scale physics S.Bolognesi (JHU)
10 TeV 60 fb-1
15
Eur.P
hys.
J.C71
:151
4,20
11.
Higgs-like resonance in VBF
Today only WW→lnln. Expectations for next year:
• lumi > 10 fb-1• s(vbf) ~ 0.1×s(gg)• 0.5 effic. VBF cuts
VBF yields in 2012 ~ 0.5 gg yields of 2011 summer results,
ZZ→4l will be still limited by statistics
WW→lnln will improve S/B (signal/10, WW*as2)
semileptonic final states will have reasonable signal yields + much lower background than inclusive analysis
RE-DO all the analyses in VBF mode
with much less background:
summer2011
Implication of LHC results for TeV-Scale physics S.Bolognesi (JHU) 24
HIG-11-011
Looking forward to VV scattering
V+jets control
fully leptonics: much lower stat, much cleaner
Same issues (as Higgs search and) as expected in VV scattering search
semileptonic: larger yields, huge background
high VV mass -> boosted V -> jet merging
uncertainty on VV+2j production
3Implication of LHC results for TeV-Scale physics S.Bolognesi (JHU)
first look at fully hadronic final state ongoing
SUSY-like discriminators (eg, Razor)
14 TeV, 60 fb-1qqmmmm
14 TeV, 60 fb-1qqqqmm
Historical references
CMS model independent-approach
13Implication of LHC results for TeV-Scale physics S.Bolognesi (JHU)
Higgs resonance @ 500 GeV
ATLAS Chiral Lagrangian with Pade’ unitarization
-> higher xsec with resonance peak
14 TeV !!!!
CMS AN 2007-005
CERN-OPEN-2008-020
most conservative scenario: SM with no Higgs (mH->inf)
xsec ~ 100 fb
Implication of LHC results for TeV-Scale physics S.Bolognesi (JHU)
VBF H->WW->lnjj(electron channel)
H->ZZ->lljj
VBF 14 TeV vs recent inclusive results
Comparing to recent
results
14 TeV, 60 fb-1
B~ 2000S~ 300
14 TeV, 60 fb-1(muon channel)
B~ 5000S~ 80
ggF (2btag)B~ 20S~ 8
B~ 20S~ 2
14
HIG-11-027
ATLAS-CONF-2012-018
Jet pruning Remove all parts of the jet which are soft and wide angle
Boosted objects mass reconstruction improved
QCD jets mass substantially decreased -> lower backgrounds
• MG 1500 GeV
• RS Graviton
• CA 0.8
X->ZZ->2l2q signal Z+jets
Implication of LHC results for TeV-Scale physics S.Bolognesi (JHU) 18
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