exotics at the lhc sam harper (ral, stfc) uk hep forum 08/09/11

Exotics at the LHC

Sam Harper (RAL, STFC)

UK HEP Forum 08/09/11

08/09/11 Sam Harper - Exotics - HEP Forum UK 1/37

EXO Searches at LHC

• from Ian’s EXO HEP Forum UK talk last year:

• Huge number of Exotic results out– ATLAS: 15 papers – CMS: 20 papers

• will only focus on results with 2011 data– some interesting results missed sadly– 7 ATLAS, 18 CMS results with 2011 data

08/09/11 Sam Harper - Exotics - HEP Forum UK

correct! (and thanks for inviting me to give this talk Ian )

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Exo 2011 Searches• New Gauge Bosons– di-lepton, di-jet, ttbar, di-lepton+di-jet final states,

lepton+MET, WZ

• Extra Dimensions– di-fermion, di-photon, jet+MET, photon + MET

• Long Lived– displaced muons/electrons– stopped gluinos

• 4th Generation fermions– t’, b’, T

• The Truly Exotic….– blackholes, heavy stable charged particles, W+dijet


see recent “Implications of LHC results for TeV-scale physics”

https://indico.cern.ch/conferenceOtherViews.py?view=standard&confId=141983

for a more detailed set of talks

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New Gauge Bosons


Z’->ee / µµ• classic discovery channel:

– inclusive search: mass of 2 leptons |η|<2.5, no cuts on MET / other activity in event

– no OS required eles / OS required muons

• excitement earily on this year but sadly died away

• no significant excess:– highest in CMS: 970 GeV, local: 2.1sigma

• with LEE effect, 0.2 sigma

– ATLAS doesn’t quote highest excess, its either ~570 GeV or ~950 GeV with similar significance to CMS


acc (ele) res (ele) acc (mu) res (mu)

CMS 64% 1.7% 80% 7%

ATLAS 65%* ~1% 40%* 15%*ATLAS accxeff quoted at 1.5 TeV but should be similar at 1 TeV

UK effort both ATLAS + CMS!

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Z’->ee / µµ


acc (ele) res (ele) acc (mu) res (mu)

CMS 64% 1.7% 80% 7%

ATLAS 65%* ~1% 40%* 15%*ATLAS accxeff quoted at 1.5 TeV but should be similar at 1 TeV

• classic discovery channel:– inclusive search: mass of 2 leptons |η|<2.5,

no cuts on MET / other activity in event– no OS required eles / OS required muons

• excitement earily on this year but sadly died away

• no significant excess:– highest in CMS: 970 GeV, local: 2.1sigma

• with LEE effect, 0.2 sigma

– ATLAS doesn’t quote highest excess, its either ~570 GeV or ~950 GeV with similar significance to CMS

6/37

Z’->ee / µµ: Limits

• limits:– ATLAS/CMS about the same ele– CMS does much better muons

• note: CMS missed the cu –cd

from this update due to lack of time but will happen for next update

Model Mass Limit (GeV)ee μμ ee+μμ

CMS 1730 1780 1940

ATLAS 1700 1610 1830


Z’ SSM limits

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35pb-1 to 1.1fb-1

• Z’->ee/µµ exclusion from 0.05pb to 0.002pb• large jump in sensitivity– thanks LHC!


Z’/W’->di-jet

• search di-jet resonance – CMS |η|<2.5, |Δη|<1.3, ATLAS, |η|<2.8 |y*|<0.6

• good agreement with data to fit parameterisation– no evidence of any significant excess


Z’/W’->di-jet• limits are final state dependent

– FSR reduces resolution– gg final states: more FSR, worse

resolution, worse limits

• ATLAS better jet resolution means they are slightly ahead


mass limit (TeV)expt obs

ATLAS 2.81 2.99

CMS 2.68 2.49

excited quark limits

CMS also quotes W’ limit of: 1-1.55 TeV10/37

Z’/W’->dijet: Wide Jets


• inspired by recent jet grooming algos

• aim is to improve FSR recovery and therefore resolution– previously used Anti-kT 0.7 jets

• wide jet algo starts with anti-kT 0.5 jets – identifies two leading jets– for each of these jets, sums in all

surrounding jets in ΔR cone of 1.1

• gg states have more FSR– wide jet algo improves resolution – reduces differences between qq, qg

and gg limits

combine into single ‘wide jet’

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Z’->ttbar• top particle can be special

in BSM theories• new physics can

preferentially couple to it– important channel to

study• current analyses:– semi-leptonic– di-lepton modes– fully hadronic (boosted)


UK effort on ATLAS here!

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Z’->ttbar• top particle can be special

in BSM theories• new physics can

preferentially couple to it– important channel to

study• current analyses:– di-lepton modes– semi-leptonic– fully hadronic (boosted)


• non-resonant signature due to MET– look for excess in high end tail

• similar to Z’ analysis, just replace 1 lepton with MET– efficiency: ~80% in both channels– CMS uses particle flow based MET

• excellent agreement between SM + data– no hint of any excess in 1fb-1

– see what 2011 dataset offers

• set limits using Bayesian cut and count above MT threshold optimized on signal samples

W’->eν / μν


W’->eν / μν


• σ.Br limits both very similar– ATLAS slightly better expected, CMS better obs

• ATLAS:– ~8fb

at 1 TeV to ~10fb at 2.5 TeV

• CMS:– ~7fb at 1.4 TeV to ~9fb at 2.5 TeV

expt obsATLAS 2.23 TeV 2.15 TeVCMS 2.18 TeV 2.27 TeV

W’ mass limits

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W’->WZ->3lν, l=e,μ• event selection:

– 2 same flavour opposite charge leptons with 60<Mll < 120

– 1 more high pT lepton + MET > 30 GeV

– HT cut, optimised for each W’ mass

• analysis motivated by technicolor• limits set by Bayesian cut and count

techniqueHT Cut for 600

GeV W’


WR + Heavy Neutrino

• searches for WR to heavy ν predicted by L-R SM extension

– require 1 lepton > 60 GeV• accxeff: 50% ele, 60% muons


Extra Dimensions


TeVPlanck

Bulk (y)

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Di-Photon• favoured channel for ED– factor 2 high BR to photons

over eles/muons

• requires two photons with ET > 70 GeV, |η|<1.44– data driven background

estimates of jet background– di-photon background from

pythia reweighted by mass dependent NLO k-factor from DIPHOX+GAMMA2MC

• searches for both warped (resonant) and ADD (non-resonant) scenarios


k/Mpl γγ ee + μμ

0.01 0.77 -0.05 1.41 1.450.10 1.74 1.78

RS Graviton Mass Limits (TeV)

UK effort on ATLAS here!

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Mono Jet

• searches for jet + MET – benchmark model: ADD extra dim

• main background: Z->νν + jets– estimate from Z->μμ + jet events

• limits are cut and count above optimised jet/ MET thresholds


δ MD limit

ATLAS CMS

2 3.2 3.7

4 2.3 2.6

6 2.0 2.2

UK effort on ATLAS + CMS!

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Mono Photon


• searches for γ + MET – pho ET > 95 GeV, |η|<1.44 + MET> 80 GeV– benchmark model: ADD extra dim

• main background: Z->νν+γ– estimate direct from MC– estimate jet backgrounds from data

δ MD limit

photon jet

2 1.2 3.7

4 1.2 2.6

6 1.3 2.222/37

fourth family


t’->bW• search for t’t’ ->bWbW

– ie ttbar search but with higher mass

• done in lepton+jets, di-lepton channels

• uses mass techniques used in top mass methods


t’->bW

• limits set using CLS method on measured mass spectra

• t’ mass limit: – dilepton: 422 GeV – lepton + jet: 450 GeV


T->tZ• search for vector like charge

2/3 quark decaying to tZ– can appear in UED, composite

Higgs models, Little Higgs

• signature:– Z->ee/μμ + 1e/μ + 2 jets

• eles > 20 GeV, jets > 25 GeV, muons > 15 GeV

• search variable:– ST = Σ jet + lep pT

– cut ST > 80 GeV

• total acc: – 14-35% from 250 to 550 GeV


b’->tW• signature:– 2 same sign leptons + 2 jets (1 b-tag)– 3 lepton (2 opp sign) + 1 b-tag jet

• looks for excess in ST distribution


Long Lived


Displaced leptons• search for neutral objects decaying to

ele/mu pairs– eg H0-> 2X, X->l+l-

• look for tracks with large transverse impact parameter


cosmic data

from MC

data / MC difference leads to 20% uncertainty on disaplace track eff

UK effort on CMS here!

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Displaced Leptons

• signal selection:– high transverse impact cut

significance– pT > 38 GeV (ele), 25 GeV (mu)– have dedicated trackless triggers

• muons: expect 0, obs 0• electrons: some bkg around Z08/09/11 Sam Harper - Exotics - HEP Forum UK

estimate backgrounds from extrapolation of decay length significance

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Stopped SUSY• looks for long lived particles

stopping in CMS– specifically the central region of

HCAL– 40-50% gluinos, 30-20% stops stop

• trigger on 50 GeV jets when there is no beam– main bkgs: beam halo, comics,

detector noise – cuts reduce event rate to O(10-5

Hz)– 12-13% efficient for stopped

particles

• probes lifetimes from 75ns to ~2 weeks


UK effort on CMS here!

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Exotic Exotics


Same Sign Muon Pairs

• a catch all exo search– same sign di-lepton

signatures come from variety of models

– main motivation is double charged Higgs

• searches for two SS muons, pT > 20/10 GeV, |η|<2.5

• sets model independent limits total cross-section above mass M


W+2jets

• follow up on the CDF bump using cuts as close as possible to CDF– no excess observed


Blackholes• searches for high ST events

– ST: ΣpT of all objects > 50 GeV in event (including MET)

• low multiplicity (N=2,3) control region – ST shape of QCD bkg independent of

number of final state objects– fit to this region to get bkg shape

• search for new physics in high multiplicity region (N>3)


9 jet candidate with ST =2.6 TeV

UK effort on ATLAS here! CMS UK also starting out

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Blackholes

• no evidence of any signal• set limits on various black hole

types


Summary• CMS + ATLAS have produced many many exotic

searches for new physics– huge phase space explored where new physics could

have been lurking• no significant deviation seen in any channel– slightly concerning – but on other hand shows we understand our

detectors very well• but good news: the LHC is delivering lots of lumi,

our detectors are working perfectly– all we need now is nature to be kind to us

(and to make sure we trigger on it…)08/09/11 Sam Harper - Exotics - HEP Forum UK 37/37

References

• for much more information please see:– https://

twiki.cern.ch/twiki/bin/view/AtlasPublic/ExoticsPublicResults

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


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



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

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

Backups


Z’->ττ

• actively being worked for 2011– stay tuned…

• low backgrounds but complicated final state– acceptance: of order ~15% at 1 TeV

over all channels• MET in final state means Z’ is wide,

signal will not be as clear cut as in light leptons

• Bayesian binned likelihood for limits


EXO-10-022

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• non-resonant signature due to MET– look for excess in high end tail

• similar to Z’ analysis, just replace 1 lepton with MET– 0.4 < pT / ET

miss <1.5 , Δϕ > 2.5– acceptance: 80% in both channels

• excellent agreement between SM + data– no hint of any excess in 1fb-1

– see what 2011 dataset offers

• set limits using Bayesian cut and count– exclusion W’ up to 2.27 TeV

W’->eν / μν

channel σ.Br limit at 1.4 TeV (pb)

σ.Br limit at 2.5 TeV (pb)

eν 0.011 0.012

μν 0.006 0.008

combined 0.0042 0.0055


W’/Z’ Summary

channel σxbr 95% CL limit (pb)

0.5 TeV 1 TeV 2 TeV 3 TeV

Z’->ee,µµ 0.008 0.005 0.002 0.002

Z’->ttbar (had) n/a 4 0.5 0.1

Z’->ttbar (μ+jet) n/a 3 0.2 0.1

Z’->ττ (35pb-1) 3 1 n/a n/a

Z’/W’->di-jet (qq)

n/a 1 0.1 0.02

W’->enu/munu n/a n/a 0.0045 n/a

W’->WZ->3l 1nu 0.02 ~0.008* n/a n/a


*limit at 0.9 TeV42/37

e*/μ*

• searches for excited states of composite fermions with scale Δ– pp->ll*->llγ

• update in progress for 2011


arXiv:1107.1773

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Leptoquarks

• search for pair production of lepto quarks– not yet updated to 2011 data

• search in following channels:– eejj , μμjj, eνjj

• no excess is found


exotics at the lhc sam harper (ral, stfc) uk hep forum 08/09/11

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