“Higgs” at high mass
 Overview of
experimental results (~1 fb-1 published, 5 fb-1 under review)
theory: (Yellow Report 1, done!)
Yellow Report 2 in preparation (differential distributions)
 What’s next?
As seen in previous days, issues are many and still under discussion
this is my partial (imprecise?) summary !
S.Bolognesi (Johns Hopkins University)
Workshop on Implications of LHC results for TeV-scale physics (WG1)
Paris, 23 November 2011
Sources
CMS AN-2010-35: Angular Analysis of Resonances pp → X → ZZ
JHU seminar: Path-Integral Jets by David Krohn (Harvard)
§
¤
www.pha.jhu.edu/groups/particle -theory/seminars/talks/F11/talk.khron.pdf
First LHC to Terascale Workshop (Sept 2011):
LCH at LHC by J.R. Espinoza
☼
Boson Boson scattering analysis by A.Ballestrero (INFN Torino)
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‡
S.Bolognesi (Johns Hopkins University)
Outline
 Status: CMS and ATLAS results in a nutshell
→ what are the limiting factors?
 Next: move to larger mass
improve sensitivity to lower xsec
→ which experimental and theoretical issues?
 The final arbiter: VV scattering
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S.Bolognesi (Johns Hopkins University)
Current status
“high” mass: > 200 GeV (i.e. H→WW, ZZ)
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S.Bolognesi (Johns Hopkins University)
From HPC summary talk about Higgs
Several
channels
BR→sensitivity: almost
reversed order ! 
6
Limiting factors
 WW→lnqq, ZZ→llqq limited by huge V+jets background, taken from
simu/data with large theoretical/statistical error
 WW→lnln at high mass limited by signal << WW background (Df not effective)
 ZZ→llnn: • 200-400 GeV limited by non-Z background (top, W+jets, WW)
• >400 GeV limited by Z+jets tail at high MET: not large but not well
known (controlled with g+jets → statistical error+met uncertainty)
drives the UL for mH>350
 ZZ→4l limited by statistics (only ZZ background: small and well known)
drives the UL for mH 200-300
Future improvements ?
 Combination of >5 different channels (ele, mu, btag, …) Robust!
 Very optimized analyses, some space for further improvement. With higher lumi:
• use shape analyses (where not yet done)
• extract signal with multidimensional fit (now only mZZ fit)
• extract background (norm and shape) from data with lower uncertainty
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S.Bolognesi (Johns Hopkins University)
What’s next ?
higher mass
lower xsec
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S.Bolognesi (Johns Hopkins University)
1 TeV masses: not anymore “the” Higgs
→ General search for X→VV→4f: exotic models (eg, Technicolor,
ExtraDimension, …)
RS Graviton vs SM Higgs:
xsec larger than Higgs
at high mass still very low
number of events per fb -1
→ importance of
semileptonic final states
§
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S.Bolognesi (Johns Hopkins University)
Available results: ZZ
 CDF search for G→ZZ: same features discussed for high mass Higgs @ LHC
ZZ→4l
ZZ→llnn MET control V+jets
low
statistics
ZZ→lljj: large V+jets
arXiv:1111.3432v1
CDF “bump”
Available results:
W+2jets
ATLAS & D0
xchecks
Control of
V+jets
 Example of number of
events per fb -1:
§
• Z+2j ~ 103 ZZ → 4l
• Z+2j ~ 102 ZZ → 2l2j
ATLAS-CONF-2011-060
CMS PAS EWK-10-011
 Control region (eg, Z→jj
sidebands) has very low
stat for M(lljj)~1 TeV
 Improving theoretical tool
(Blackhat, Madgraph, …)
• test them where
we have statistics
• extrapolation at higher
energy/multiplicity
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S.Bolognesi (Johns Hopkins University)
High mass: what’s new ?
 Can we simply keep the same Higgs analysis strategy? Not at very high
masses!
 New experimental issues at very high mass (1 TeV and above)
X → boosted VV → jet merging (and nearby leptons)
 Unknown signal and very small background → no point in pushed optimization!
Keep model independent approach as much as possible
 How to disentangle the various models?
• peak → mass and width, xsec and BR
•spin! → angular analysis
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S.Bolognesi (Johns Hopkins University)
>1 TeV M(ZZ)→4f : jet merging (1)
 Jet merging: DR 
qq
1
MZ
T
z (1  z ) pZ
( z | pq | / | pZ |)
approx
DR 0.8 (CA) → MX>600 GeV
DR 0.5 (Akt) → MX>900 GeV
To distinguish wrt to jets from QCD (eg, X→ZZ→2l2j VS Z+jets)
 jet mass
CMS JME-10-013
ttbar → WW→ln (jj)
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CMS EXO-11-006
S.Bolognesi (Johns Hopkins University)
Jet merging (2)
 jet radiation:
no singularity, just decay!
soft/collinear singularity in QCD
number of subjets
CMS JME-10-013
¤
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S.Bolognesi (Johns Hopkins University)
Jet pruning
 Remove all parts of the jet which are
soft and wide angle
¤
 QCD jets mass substantially
decreased -> lower backgrounds
arXiv:0912.0033v1
Boosted objects mass
reconstruction improved
Typically used for boosted top or
boosted H→bb …
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S.Bolognesi (Johns Hopkins University)
Example in X→ZZ→2l2j
First look at Z boosted (no numbers yet) …
preliminary, A.Bonato, R.Covarelli
• RS Graviton
• MG 1500 GeV
• CA 0.8
signal
Z+jets
before jet pruning
before jet pruning
after jet pruning
after jet pruning
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S.Bolognesi (Johns Hopkins University)
Angular analysis (1)
 X→ZZ→4f decay kinematic fully defined by 5 angles
signal (MX 250):
Z decays
X→ZZ
MC from Johns Hopkins
0+ , 0-
1+ , 1-
2+m , 2+L , 2-
§
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S.Bolognesi (Johns Hopkins University)
CMS PAS -11- 017
Angular analysis (2)
 Can be clearly used to disentangle different
signals… but what about background?
 Already used in H→ZZ→2l2q: cut on likelihood
• signal: ideal × uncorr. accept
• Z+jets from MC: no correlations,
(background from jj sidebands)
 To optimize further (multidimensional fit), need full theoretical description of
background:
 qq → ZZ:
§
 gg also available → can be used to disentangle qq-gg!!
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S.Bolognesi (Johns Hopkins University)
What’s next ?
higher mass
lower xsec
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S.Bolognesi (Johns Hopkins University)
Improve UL
 WHY? Models with lower xsec
Ex of (light) composite higgs
just an example
for mH [80,200]
☼
 HOW?
 Factor 10 in luminosity wrt to present results
 Improve theoretical control of
• signal/background interference
(YR2)
• signal: → NNLO&NNLL effects, precise mass shape prediction
• background: → precise prediction ZZ, WW ewk continuum
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S.Bolognesi (Johns Hopkins University)
Mass shape
From Passarino talk at last LHC to Terascale WS
 Present approx:
• xsec for on-shell Higgs
production and decay in
zero width approx
• acceptance from MC with
ad-hoc BW distribution
10-30% uncertainty on xsec
for mH 400–600 GeV
Study with QFT-consistent Higgs
propagator in the YR2
Higgs qT
 HqT: qT > mH NNLO
qT << mH NNLL
(resumming ln(mH2/qT2))
Uncertainties: • factor/renorm scale
• non perturb. effects
• PDF
(smearing with NP form factor)
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• large mt approximation
S.Bolognesi (Johns Hopkins University)
Reweight to HqT
 HqT used to reweight full event generators (POWHEG at NLO)
H pT
mH 500 GeV
mH 120 GeV
Powheg
Powheg reweighted to
Hqt
(to be redone
before PS)
HNNLO
Hy
mH 120 GeV
mH 500 GeV
 Very small effect on acceptance in 4l: 1-2% (larger if jet veto!)
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S.Bolognesi (Johns Hopkins University)
Signal: jet counting
 Analysis in exclusive jet bins • if background depends on Njets
(ex, WW+0,1,2 jets)
• for VBF
→ theoretical uncert in jet bins to
be combined with correlations
different treatments of
the uncontrolled higherorder O(α3s) terms
 varying renormalization and
factorization scales in the fixedorder predictions for each
exclusive jet cross section σN
(results as 100% correlated)
i.e., different NNLO
expansions
 inclusive xsec (σ≥Njets), as source
of perturbative uncertainties
σN = σ≥N − σ≥N+1
with error propagation
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S.Bolognesi (Johns Hopkins University)
Signal: jet veto
 Resummation of jet-veto logarithms ( ln(pcut/mH) ), induced by jet cut parameter p cut
Presently doable only on beam thrust variable
(~raw approx of p cut)
and used to reweight MC@NLO
from inclusive to
exclusive prediction
direct exclusive
prediction
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S.Bolognesi (Johns Hopkins University)
Signal-background interference
 Recent results for WW, but focused on low mass
( arXiv:1107.5569v1 )
Effect on gg→H→WW at LO
mT < mH
non-resonant diagrams can
be large for mT > mH
also shape effects!
 Worth to investigate further at high mass?
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S.Bolognesi (Johns Hopkins University)
Background: ZZ
prediction
Single resonant contribution
 ZZ fully from MC, well under control
Interference in the final state
with identical leptons
qq→ZZ NLO + gg→ZZ
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S.Bolognesi (Johns Hopkins University)
qq
gg
scale
S.Bolognesi (Johns Hopkins University)
PDF+a s
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gg
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ZZ uncertainties
qq
WW uncertainties
 WW taken from MC for large mH
→ gg+qq NLO available (MCFM)
PDF+a s and scale uncertainty dominates
 in jet bins using uncert on s(>=N) + modeling: MC@NLO vs ALPGEN
 WW from control region for mh<200 GeV (mll, Dfll)
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S.Bolognesi (Johns Hopkins University)
VBF and VV scattering
 VV scattering tell us that something must be there
→ fundamental to test nature of Higgs boson or to find
alternative EWSB mechanism
LSB<1TeV
SB sector
weakly
coupled
LSB>1TeV
Strongly interacting light Higgs
SB sector
strongly
coupled
‡
SM No
higgs
‡
 Increasing in lumi → look into
 resonance in VBF
 measurement of VV scattering spectrum
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S.Bolognesi (Johns Hopkins University)
Higgs-like resonance in VBF
 RE-DO all the analyses in VBF mode (eg, fermiophobic)
 Today only WW→lnln. Expectations for next year:
• lumi > 10 fb-1
• s(vbf) ~ 0.1×s(gg)
• 0.5 effic. VBF cuts
VBF signal yields in 2012 ~ 0.5 gg signal yields used
in present results
 ZZ→4l will be still limited by statistics
 WW→lnln will improve S/B (signal/10, WW/a s2)
 semileptonic final states will have reasonable signal yields +
much lower background than inclusive analysis
eg, ZZ→lljj :
• signal yields for mh300-500 ~ 15 – 5 events
• V+(N+1)jets/V+N jets ~ 0.15 → asking 2 jets
reduce to 2% the background!
• S/B may increase of more than factor 2 (eff 0.5 × s 0.1 / 0.02)
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S.Bolognesi (Johns Hopkins University)
Measurement of VV scattering spectrum
 Increasing of xsec at high VV is suppressed by PDF and for unpolarized V
→ small difference btw SM and violation of unitarity (no Higgs)
SILH
W ±W ±
scattering
‡
→ with proper cut (which increase VLVL scattering contribution, eg Dh jets)
can be enhanced
→ see next talk
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S.Bolognesi (Johns Hopkins University)
Summary
 Higher mass:
 theoretical issue: control of V+jets
 experimentally new strategies needed (eg, jet pruning)
 Lower xsec:
 several theoretical uncertainties:
• mass shape (should be solved)
• exclusive jet counting
→ PDF+a s
 If something observed → angular analysis
 If not, → VBF search, measurement of VV scattering spectrum
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S.Bolognesi (Johns Hopkins University)