SearchesforNewPhysicsattheLargeHadronCollider

Jeffrey D. Richman Department of Physics

University of California, Santa Barbara

Scottish Universities Summer School in Physics, St. Andrews, 19 August – 1 September 2012

Lecture 3: odd things

Outline

•  SUSYsignatureswithleptons;direct(EW)producBonofneutralinos&charginos– Charginoshidinginplainsight?

•  HidingSUSY(“exoBcmodels”)– LonglivedparBcles(e.g.,long‐livedgluinosinsplitSUSY)

– R‐parityviolaBngSUSYsearches•  Largeextradimensions(monojets...)

•  Blackholes•  Conclusions

ExoBca‐fromareviewtalkatICHEPSteve Worm – Searches for Physics Beyond the Standard Model, ICHEP

Several key topics covered in other talks at this school (e.g., SM physics): dijet mass & angular distrib, Z’ l+l-, ttbar

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σ pb( )

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σ pb( ) As we push up the allowed mass range for the strongly interacting SUSY particles (gluinos & squarks), searches for potentially lower mass EW SUSY particles become competitive.

Thefamousneutralinodileptoncascade

p

p

χ20

χ1±

χ10

χ10

±

ν

ν

Opposite-sign, same flavor leptons

The can be produced in any process, not just direct EW production.

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ThefamousSUSYtrileptonsignature

p

p

χ20

χ1±

χ10

χ10

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ν

The can be produced in any process, not just direct EW production. Extensive searches for trilepton signatures, including tau leptons.

χ20

Foramusement...http://arxiv.org/abs/1206.6888

ATLAS:σ(pb) CMS:σ(pb)

Measuredcrosssec.

53.4±2.1±4.5±2.1 52.4±2.0±4.5±1.2

Theorycrosssec.NLO

45.1±2.8 47.0±2.0

ppW+W‐kinemaBcdistribuBonshttp://cdsweb.cern.ch/record/1430734/files/ATLAS-CONF-2012-025.pdf

Main selection requirements •  Opposite-sign dileptons (ee, emu, mumu), leading lepton pT>25 GeV •  No additional leptons •  Exclude Z mass window (±15 GeV) for same flavor leptons •  No jets with pT > 25 GeV (suppresses ttbar); no b-jets pT>20 GeV •  ETmiss_Rel > 25 -55 GeV

EWKSUSYcancontributea“background”toppW+W‐

m( χ1

± ) ≈ 112 GeV

m( χ1

0 ) ≈ 15 GeV

tanβ = 10

σ (pp→ χ1

+ χ1− ) = 2.8 pb

parameters used for plots

ExcessintheW+W‐crosssecBon?http://arxiv.org/abs/1206.6888

Whatdoesitmean?

Ihavenoidea.Firstofall,itisamodesteffectrelaBvetotheuncertainBes.LotsofreasonsthiscouldhavenothingwhatsoevertodowithanaddiBonalphysicsprocessinthedata.ButitdoesshowthatwehavetobeverycarefulaboutSUSY...itmightappearinplacesthatwearenotexpecBng.Wealsohavetobecarefulaboutourcontrolsamples.

Directgauginosearches(ATLAS,7TeV)

•  CombinaBonof2‐leptonand3‐leptonsearchesforleptonsproducedincascadesstarBngfrom,,producBon.

+

− χ1+ χ2

0 χ1+ χ1

−

Dilepton search χ1+ χ1

−

https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/SUSY-2011-23/

χ1+ χ2

0Trilepton search

https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/SUSY-2012-13/

Opposite‐signdileptons+jets+MET

EventselecBon•  2opp‐signleptons•  ee,μμ,eμ(control)•  eτ,μτ(sepcuts)•  ≥2jets,pT>30GeV•  pT(lep1)>20GeV•  pT(lep2)>10GeV•  HT>100GeV,MET>50GeV

•  Zvetoregion• 

CMS SUS-11-011 http://arxiv.org/abs/arXiv:1206.3949

Thefamousneutralinodileptoncascade

p

p

χ20

χ1±

χ10

χ10

±

ν

ν

Opposite-sign, same flavor leptons

The dominant background (ttbar) produces different flavor leptons as well use eµ control sample!

Opposite‐signdileptons:m(l+l‐)

Fitsignalandcontrolregionsjointlytoshapesdescribingnbar+DY+signal(smearedtriangle).

eµ control region: ttbar (+WW)

signal region

Signal contrib. from fit (2.1 σ) local signif.

Signal shape reflects kinematics of sequential two-body decay (mmax=280 GeV)

Opposite‐signdileptons:METpredicBon

HT > 300 GeV

In SM events, can use lepton spectrum to predict the MET spectrum! In general need suitable corrections for W polarization in W+jets and ttbar, as well as resolution and threshold effects.

UsingtheleptonspectrumtopredictMETinsingle‐leptonevents

•  InnbarandW+jetsevents,thelepton&neutrinoareproducedtogetherinWdecay.

•  InmanySUSYmodelstheleptonandMETaredecoupled.decoupled.

CMS-PAS-SUS-12-010 http://cdsweb.cern.ch/record/1445275

UsingtheleptonspectrumtopredictMETinsingle‐leptonevents

•  The MET distribution for SM events is dominated by ttbar and W+jets. •  The MET is dominated by the neutrino. •  The neutrino spectrum can be predicted from the lepton spectrum, taking into account W polarization in both cases! MET resolution also included.

CMS-PAS-SUS-12-010 http://cdsweb.cern.ch/record/1445275

Searchforlong‐lived,stoppingparBcles

•  ImagineaparBclethatliveslongenoughthatitdoesnotdecayduringthebeamcrossingintervalwhenitwasproduced,butstopsinthedetector!

•  Itdecays(asynchronouslytobeamX‐ing.)

•  SuchparBclesarepredictedinseveralmodels.

•  Doweeventriggeroneventslikethis?•  “Ifitdidn’ttrigger,itdidn’thappen.”

–  oritmightaswellnothavehappened...

Searchforlong‐lived,stoppingparBcles

Somereferences•  M.J.StrasslerandK.M.Zurek,“Echoesofahiddenvalleyat

hadroncolliders”,Phys.Len.B651(2007)374,arXiv:hep‐ph/0604261.

•  N.Arkani‐HamedandS.Dimopoulos,“SupersymmetricunificaBonwithoutlowenergysupersymmetryandsignaturesforfine‐tuningattheLHC”,JHEP06(2005)073,arXiv:hep‐th/0405159.

•  P.Gambino,G.F.Giudice,andP.Slavich,“Gluinodecaysinsplitsupersymmetry”,Nucl.Phys.B726(2005)35,arXiv:hep‐ph/0506214.

•  R.MackeprangandA.Rizzi,“InteracBonsofcolouredheavystableparBclesinmaner”,Eur.Phys.J.C50(2007)353,arXiv:hep‐ph/0612161.

Examplescenario:splitSUSY

SUSY scalar particles (including squarks) are at extremely high mass scale

gluino neutralino LSP

LHC energy scale g→ g χ1

0 (via loops)

g→ qq χ1

0

huge gap in Split SUSY

Compare with lifetime of free neutron!

Whathappenstoalong‐livedgluino?

•  HadronizaBonturnsgluino/stopinto“R‐hadron”

•  TheR‐hadroninteractswiththematerialofthedetector.SomefracBonwillstop,typicallyinthedensestregonsinthedetector.Probtostop∼0.07.

•  Eventuallythegluinodecays.

gg gqq gqqq ...

M ( g), M (t )

tq tqq ...

Gluinodecayinhadroniccalorimeter(MC)Trigger = CALO cluster + no incoming p bunches + no muon segments

Trigger: Calo jet ET>50 GeV + veto on signals from Beam Position and Timing Monitors (BPTX) 175 m on either side of CMS. Don’t want either proton bunch present (beam gas events can be produced with just one p bunch). Also veto on beam halo forward muon trigger.

CMS simulation

EventselecBonforstoppingparBcles

•  During2011run,numberbunches/beamvariedfrom228to1380.

•  SelectBmeintervalsforanalysisbetweenbunchcrossings.

•  VetoanyeventwithintwoLHCclockcycles(BX=25ns)ofeitherpbunchpassingthroughCMS.

•  Get85%oforbitBmefor228bunchfills;16%oforbitfor1380bunchfillsforthesearch249hoursliveBme.LHCorbitperiodis89μs.

•  Cutstorejectbeamhalomuons,cosmics,HCALnoise.Finalrate:(1.5±2.5)×10‐6Hz.

Stoppedgluinosearch:Background&observedyields

Estimate of background contributions over total live time.

Estimate of background contributions for live-time intervals chosen for each lifetime hypothesis.

For lifetimes shorter than one LHC revolution time, search in an time window of 1.3τ after beam xing.

CrosssecBonexclusionfromstoppedgluinosearch

Hypothetical lifetime

Masslimitsonstoppingand g t

Hypothetical lifetime

Massexclusionfromstoppedgluinosearch

Monophotonsearch:interpretaBoninLargeExtraDimensionsmodels

MPl2 ≈ MD

n+2Rn

•  Try to explain difference between Planck and EW scales. •  n extra compact spatial dimensions, characteristic scale R •  Gravity propagates in the (4+n) dimensional bulk of space-time; SM fields are confined to four dimensions. Graviton production seen as missing momentum. qq → γG qq → gG gg→ gG

R‐parityviolaBngSUSY

•  WhatifSUSYviolatesR‐parity?

•  Mainissue:canhaveverylinleMET.SomeexisBngSUSYsearcheswith“strong”signaturescanworkwithlooseMETrequirements(e.g.,same‐signdileptons).

CMS multilepton analysis: http://arxiv.org/abs/1204.5341 CMS three-jet search: https://twiki.cern.ch/twiki/bin/view/CMSPublic/PhysicsResultsEXO11060

(GeV)jjjM0 200 400 600 800 1000

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12

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Data300 GeV gluino450 GeV gluino

= 7 TeVs

(b)

-1CMS, 5.0 fb

3 jet search

Excludes gluino masses below ~460 GeV.

Searchfor“microscopic”blackholes

•  Signatureoflow‐scalequantumgravity.

•  Butmanydifferentscenarios–smallindustryofsimulaBons/models.

•  PhysicsofblackholeformaBonandevaporaBonhasseveralsubtleBes.(E.g.,whatfracBonoftheiniBalpartonenergyistrappedintheeventhorizon,rotaBngvs.non‐rotaBng,etc.)

CMS black hole search: http://arxiv.org/abs/1202.6396

•  ObjectselecBonissimple– Leptons(e,mu):pT>50GeV

– Photons(e,mu):pT>50GeV–  Jets:pT>50GeV– NonoverlappinginconeΔR=0.3.

•  Computetotalscalarsumoftransversemomentaintheevent.

•  StudySTasafuncBonofobjectmulBplicity,whichdoesnotincludeMET.

Searchformicroscopicblackholes

ST = pTj

j= jets, leptons, photons, MET∑

Blackholes:backgroundesBmaBonCMS black hole search: http://arxiv.org/abs/1202.6396

•  Background shape is obtained from fit to low-multiplicity (N) events and restricting ST to range 1200 < ST < 2800 GeV. •  Shapes in N=2 and N=3 samples are very similar. •  Dedicated search for new physics in N=2 sample shows no signal.

Searchformicroscopicblackholes

750 MC samples for the signal scenarios considered... Excluding black hole masses below 4-6 TeV.

Cross sections vs. black hole mass Example of high-multiplicity sample

Blackholesearch:highSTevent

Conclusions

•  ThisisauniqueperiodinthehistoryofparBclephysics.

•  Wedon’tknowwhatwewilldiscover–thatisthefundamentalnatureofscience.

•  Therearenoguarantees,butthepotenBalforbreakthroughshasneverbeengreater.

•  YourworkandleadershiparecriBcaltothefutureofhighenergyphysics.

•  Manythankstoalltheorganizers,staff,postdocs,andstudents!

SearchforZ’e+e‐,μ+μ‐

SearchforZ’e+e‐,μ+μ‐

DatawithsimulatedADDsignal