Searches for Heavy Resonances

at the LHC

Tetiana Berger-Hryn’ova(LAPP, CNRS-IN2P3)

For the ATLAS and CMS collaborations

Moriond QCD 2014

Higgs Discovery & Searches• Following the discovery of a scalar boson Standard

Model (SM) is complete (but for an axion) and self-consistent

• A lot of questions still need answers:– Why is Higgs light?– What is dark matter? – How to accommodate gravity?– Why are there three generations? – …– Is there a theory which answers all our questions?

• We are looking for something – we do not know what – neither where to look – nor if there is any chance of finding it…

Does it remind you of something?2T. Berger-Hryn'ova Moriond QCD 2014

How do we search

Approach 1• Pick a Theory• Pick a model• Look at various production/decay modesof new states! (model-independently)

Approach 2Pick a final state & look(model-independently)

Get lucky!It sounds like a quest

Go there- I don’t know where,

Bring that – I don’t know what

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Look for Signatures!Interesting Models:• Extended Gauge Groups• Compositeness• Wraped Extra Dimentions• Technicoloretc …

Interesting Signatures:• Dibosons• /W/Z+jet(s)• Di/Tri-jet• Dileptons (ll, )etc…

Look for bumps on smooth SMbackgrounds!

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• Focus on selection of results• Apologies if your favourite is left out• All limits are quoted at either 95% Confidence Level or Credibility Level (CL)

Today’s menu• Searches in +jet

final state• Dilepton searches• Diboson searches• Tri-jet resonant

searches• XHHbbbbT. Berger-Hryn'ova Moriond QCD 2014 5

Searches in +jet final stateSelection CMS(ATLAS): pT

j/>175(125) GeV + iso;

||<1.44(1.37), |j|<3.0(2.8) |,j|<2.0(1.6)No significant excess seen.Exclude m(q*)<3.5 TeV @ 95% CL

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Background fit function:

ATLAS: PLB 728, 562 (2013)

+jet limits• Limit behaviour quite similar

for various models: • (QBH/q*)~83-72/85-80%• What happens at high mass?

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QuantumBlackHole

(QBH)

q*

Effect on limits from Signal Shapes

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• Increased fraction of the off-shell production for the signal events (“parton-luminosity tail”) as the kinematic production limit is approached • size increases with the resonance width. • Noticeable impact of this tail on cross-section limit values when >5-10% of events in the tail

This affects most of the limits (q*, Z’ etc)!

Usual signalBreit-Wigner

shape

Parton distribution functions

Parton-luminosity tail

Effect on limits from Signal Shapes

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• For thresholds or resonances with suppressed low-mass contributions (Z*) “parton-luminosity tail” effect is not present

• It is also not present it the resonance shape is input “by hand”, e.g. assuming a Gaussian or Breit-Wigner of certain width, instead of using shape from simulation

QBH Productionis a threshold!

MD=MTH Mass

MD=fundamental scaleof quantum gravity

MTH=threshold for black hole production

+jet limits:width effects

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Width assumptions matter at low masses: smaller width = better limits

Also parton luminosity tail is larger for wider resonances, which leads to worse limits

Dilepton Resonant Searches

Data consistent with SM predictions

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CMS signal shape assumption: Breit-Wigner with Z’ width

(/M=0.5%) convolutedwith Gaussian of signal resolution

ATLAS signal shape assumption:Monte-Carlo based

Z’SSM shape (with width /M~3%)

Dilepton Resonant Search Results

Limits @ 95% CL are: M(Z’SSM) > 2.96 TeV (CMS) & 2.8 TeV (ATLAS)

M(Z’)>2.60 TeV (CMS) & 2.38 TeV (ATLAS)

Those assumptions affect the final results, making limits not comparable directly: effects of parton luminosity tail visible

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VV & Vq (V=W/Z) Resonant Search

Jets Cambridge-Aachen R=0.8, W/Z-tag jet, isolated leptons, kinematic cutsNo excess over SM backgrounds is seenxBR(XWW)>70 (3) fb @ 0.8(2.5) TeV; m(G*ZZ)>710 GeV for k/MPl=0.5

Different channels to enhance sensitivityT. Berger-Hryn'ova Moriond QCD 2014 13

See also ATLAS-CONF-2012-150 (ZZlljj) & ATLAS-CONF-2013-015 (WWlll)

k/MPl=0.1

k/MPl=0.1

Search for XHH(bb)(bb)

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2 back-to-back boosted doubly btagged di-jet systems

4 b-jets (MV1, eff 70%) anti-kt 0.4 pT>40 GeV, R(2b)<1.5, pT

jj>200 GeVHadronic ttbar veto

Background: multijet (90%); ttbar (<10%); Z+jets

No evidence of signal is foundExclude @95% CL for k/MPl=1.0

590<M(G*RS)<710 GeV

<1.6

XX(3j)(3j) Resonant Search

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No excess over SM backgrounds is seen.Limits on m(gluino) of 650GeV at 95% CL is set for light flavour jets 835GeV at 95% CL for 2 light and 1 b-jets

See also ATLAS-CONF-2013-091, dijet: CMS PAS EXO 059, ATLAS-CONF-2012-148

We should notgive up!

Perspectives/Conclusions• Resonant searches are very powerful

– Many final states have been explored

• But no new physics seen in 8 TeV data yet…

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LHC Run 2 will provide us with more luminosity to explore lower couplings & LHC energy increase to higher masses.

We should notgive up!

Perspectives/Conclusions• Resonant searches are very powerful

– Many final states have been explored

• But no new physics seen in 8 TeV data yet…

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LHC Run 2 will provide us with more luminosity to explore lower couplings & LHC energy increase to higher masses.

Stay tuned to new exciting results in 2015!

Documentation

• https://twiki.cern.ch/twiki/bin/view/CMSPublic/PhysicsResultsEXO

• https://twiki.cern.ch/twiki/bin/view/AtlasPublic/ExoticsPublicResults

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Backup slides

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Dijet Search

T. Berger-Hryn'ova Moriond QCD 2014 22CMS PAS EXO 059, ATLAS-CONF-2012-148

Z’ hadronic search

Z’hadhad(~42% of the BF)

No excess over SM backgrounds seen.Excluded M(Z’SSM)<1.89TeV @ 95%CL

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