Search for New Phenomena at Colliders

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Search for New Phenomena at Colliders

• E. Nagy (CPPM)
• for the
• CDF, D0 (Tevatron)
• and
• H1, ZEUS (HERA)
• Collaborations

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In spite of the great success of the SM we still
miss an ultimate theory (TOE) which would provide
unification of all the 4 known forces (gravity!)
into a finite (renormalizable) theory. Therefore,
new, BSM physics is expected at some energy
scale MX. The questions are what is the TOE and
what is MX? Today only elements of such a theory
are proposed for experimental tests. In the
present talk some arbitrary choice of topics
addressed by two active colliders Tevatron and
HERA.
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• Extra Dimensions
• Super Symmetry
• Z, Lepto-Quarks, Beyond SM Higgses
• Substructure (Contact Interactions, Excited
  Leptons)
• Anomalies

Frequently, the same event topology (e.g. high
mass di-leptons) allows to test several
theoretical models
For MX the natural value is MPl to unify
gravity. However this leads to  unnatural  fine
tuning of scalar masses (problem of
hierarchy). Some of the above topics present
solution to this problem.
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Tevatron
gt3 times more luminosity than in Run I soon L is
1032cm-2s-1 and counted in fb-1

• 200 pb-1 and only most recent results from Run
  II reported here

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HERA
HERA I Luminosity
HERA II will deliver 10 times more luminosity
(at present 70 pb-1) longitudinal
polarisation of e-beam

• Results mainly from HERA I

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Extra Dimensions (ED)

• EDs provide framework for unification with
  gravity (Th. Klauza, 1919)
• EDs are compact since not seen (O. Klein, 1926)
• Compact EDs generate replica of particles
  (KK-tower) propagating in them
• In string theories, EDs restore QM
  probabilities in the range 0,1.
• EDs can be large (LED RgtgtTeV-1) if only
  gravity can propagate in them
• LED can explain why gravity is weak
  1/GM2PlMsn2 Rn and can solve the hierarchy
  problem MsMW
• LED can be tested by gravity experiments (nlt3)
  but also at colliders through virtual effects or
  direct emission of KK gravitons (ngt2).
• Smaller EDs (R TeV-1) can also be tested at
  colliders (interference of KK states)
• Randall-Sundrum model (1 small ED of size
  R1/MGUT with a metric damped by e-kRf ) predicts
  graviton resonances (S2) of k1.

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Determination of Ms of LED
Look for effects of virtual gravitons in high
mass lepton (photon) pairs
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• Select
• 2 (and only 2) high pT em objects pTgt25 GeV
• Precisely determined vertex
• Compare
• SM and instrumental (mis-ID) background
• Extract limit

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Limit on MS from HERA ??/MS4
CDF ee limit
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Determination of Md from KK graviton emisson
Signature is Monojet MET

• Selection
• Leading jet pTgt150 GeV
• 2nd jet pT lt 50 GeV
• METgt150 GeV
• Lepton (e,µ) veto

Main Background Z(-gt??)nj W(-gtl?)nj
Main uncertainty Jet energy scale
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Determination of MC of TeV-1-size (Longitudinal)
ED

• Fermions are confined in the ordinary 3d world.
• Gauge bosons can propagate in 3d brane of d
  compact ED.
• Look for effects of KK replica of gauge bosons in
  high mass lepton pairs and determine the scale
  MC of ED.

• Same selection as above trackmatch of at least
  1 em object
• Data is compatible with SM
• Mc gt 1.12 TeV _at_ 95

Interference of KK states
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Search for Randall-Sundrum resonancesin high
mass di-lepton states
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SUper SYmmetry
Symmetry of Nature for Bosonlt-gtFermion
interchange Basic ingredient for unification
with gravity (SuperString/M-theory) The only
nontrivial extension of the Lorentz-Poincaré
group Provides elegant solution for the
hierarchy problem Minimal extension of the SM
MSSM every SM particle has ?S ?1/2 partner
R (-1)3B2LS 1 (SM) -1 (SUSY) 2nd
Higgs doublet is needed
If SUSY were exact only 1 additional parameter
(µ) needed
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SUSY is a broken symmetry since nobody has seen
the partners many more parameters describe
breaking with additional hypotheses they are
reduced in the 2 models treated here
gravitation mediated (mSUGRA) model to 5 (m0,
m1/2, tanß, sgnµ, A0) gauge mediated (GMSB)
model to 6 (?, Mm, N5, tanß, sgnµ, Cgrav)
parameters. R-parity is approximately
conserved severe limits on B- and L-violating
processes SUSY partners are pair produced
LSP is stable (neutral and weakly
interacting) Basic signature is MET (LSP),
multiple jets and leptons from cascade
decays Main bg is t tb and gauge boson pair
production Small violation of R-parity is not
excluded allows single resonant formation of
SUSY particles many more jets/leptons in final
state additional couplings (48) At Tevatron
both RPC and RPV can be studied HERA is
competitive only for RPV processes
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The golden signature chargino (?1) and
neutralino (?20) pair production
The signatures exploited by D0 MET from ?10 and
? 3 leptons (e,µ,l/e,e,l) or 2 leptons (µ, µ)
of same sign
D0 has searched beyond the stringent mSUGRA LEP
limit and has chosen the following parameter
region
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e µ l
Jet veto mTmin gt15 GeV 15ltmeµlt100
GeV METsignifgt25 GeV½ pT3gt 3 GeV 0 data
0.540.25 bg
High quality, isolated electron pTgt12 GeV muon
pTgt8 GeV charged track
eel
Jet veto mTe gt15 GeV meelt60 GeV ?feelt2.8 METgt20
GeV pT3xMETgt 250 GeV2 1 data 0.270.42 bg
High quality, isolated electrons pTgt8,12 GeV
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µ µ
High quality, isolated like-sign muons pT1gt11
GeV, pT2gt5 GeV METgt15 GeV mµµlt80 GeV ?fµµlt2.7 (if
pT2lt11 GeV) ?fMETµmingt0.5 (if pT2lt11
GeV) ?fMETµmaxlt2.4 (if pT2lt11 GeV) ?fMET,jlt2.4 1
data 0.130.06 bg
Bg is mainly heavy flavour Estimated from OS pairs
Combined 3lMET
Great improvement wrt Run I Sensitivity very near
to mSUGRA prediction
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At least 2 jets pT1gt60 GeV lepton
veto ?fMETjmingt30o ?fMETjmaxlt165o METgt175
GeV HTSpTjgt275 GeV 4 data 2.670.95 bg Bg
mainly Z-gtvvnj
mSUGRA
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GMSB
Select 2 photons pT gt 20 GeV
Expected signal vs M2? messenger mass scale
Signal is at high MET MET gt 40 GeV Data 1 Bg
2.50.5
Best limit on ? gt 78.8 TeV m?0 gt 105 GeV, m? gt
192 GeV
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R-parity violation
Introduces 48 new L and B violating Yukawa
couplings
with more leptons, jets in the final state
Single sparticle production and decay depends on
coupling ?
Decay of the LSP (?10) if fast, does not depend
on coupling ?
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Look for signal in multiple event topology (H1).
Below an exemple of the lepton-jet(s) inv mass
spectrum No deviation from the SM -gt Limits on
?1j1 and m0, msq, tanß
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R-parity violation in GMSB (H1)
Signature METgt25 GeV, and an isolated ? (pTgt25
GeV) 1 event found, 2.551.30 expected Limits on
?1j1, mNLSP, msel
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CDF agreement of the high mass di-lepton spectra
with the SM is transformed into limits on ? and
msnu
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Z
Z is predicted in several extensions of the
SM E6 and little Higgs models are considered here
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Limits for ee- (in GeV)

• SM Couplings
• CDF 750
• DØ 780
• E6 ZI Z? Z? Z?
• CDF 570 610 625 650
• DØ 575 640 650 680

Similar, somewhat smaller limits for µµ-
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Little Higgs
Proposes new fermions and bosons to solve the
hierarchy problem. Contrary to SUSY, here the
quadratically divergent diagrams are cancelled by
the same type of particle (fermion-loops by
fermion-loops, etc.) ZH is one of the new bosons
to cancel divergent boson loop. Its coupling is
parametrized by T. CDF establishes limits on the
mass of ZH and T in both of ee and µµ final
states.
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Lepto-Quarks
Hypothetical bosons (scalars or vectors) carrying
both L and B. Proposed in several extension of SM
based on Q-L symmetry. HERA is an ideal machine
to produce 1st generation LQs. No deviation is
found wrt SM -gt Limits on MLQ and coupling ?
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ZEUS has also searched for taus in the final
state Lepton Flavour Violation
No events have been found limits on ?eq1 ?tqj
vs MLQ
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1st generation Lepto-Quarks at Tevatron
Dominantly produced in pairs of the same
generation (avoid topology of FCNC or
LFV) Production is independent of ? Final state
is characterized by 2j2l lepton can be charged
or neutral with BR ß -gt possible final states
2j2l, 2jlMET, 2jMET
2j2e channel 2j ETgt20 GeV 2e ETgt25
GeV Z-veto STSETjSEtegt450GeV 0 data, 0.40.1 bg
2jev channel 2j ETgt25 GeV 1e ETgt25 GeV METgt30
GeV W-veto mTgt130 GeV STgt330GeV 2 data, 4.70.9
bg
D0 MLQ1 limits in GeV
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Similar analyses of CDF - also in the jjMET
channel
METJets channel gt2j (j1,2 central w/4
tracks) Jets and MET shouldnt be
aligned e/µ-veto METgt60 GeV 80lt?F(j1,j2)lt165o 124
data, 11813 bg 78ltMLQlt117 GeV excluded
CDF MLQ1 limits in GeV
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2nd generation Lepto-Quarks at Tevatron
jjµµ channel 2µ pTgt25 GeV 2j ET1,2gt30, 15
GeV Z-veto Topological cuts (see Fig.) 2 data,
3.21.2 bg MLQlt240 GeV excluded
MLQlt186 GeV excluded (L104 pb-1)
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Beyond SM Higgses
On the way to discover HSM one may find BSM
Higgses

• H-gt??
• H-gtWW
• Neutral SUSY/2-Doublets h,H,A
• H/--

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• In some extensions of the SM BR(H-gt??) can be 1
• (e.g. Fermiophobic or Topcolor Higgs)

Select 2 isolated photons pT1,2gt25 GeV pT??gt35
GeV Estimate background Instrumental, DY,
?? Determine limit on BR sliding window technique
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H-gtWW-gt2lMET
ee (OS) channel pT1,2gt12,8 GeV METgt20
GeV METsiggt15 GeV1/2 SpTMETgt100 GeV 12lt Mee lt
80 GeV Jet-veto ?feelt1.5 2 data, 2.70.4 bg
eµ (OS) channel pTe,µgt12,8 GeV METgt20
GeV METsiggt15 GeV1/2 SpTMETgt90 GeV MTmin lt 20
GeV Jet-veto ?feµlt2.0 2 data, 3.10.3 bg
µµ (OS) channel pT1,2gt20,10 GeV METgt30
GeV METgt100.75pT1 GeV Jet-veto Z-veto ?fµµlt2.0 2
data, 3.10.3 bg
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• H,h,A (f)

sftan2ß
Select gt2j ET1gt20 GeV, ET2,3gt 15 GeV with well
defined vertex (gt3 tracks) Apply b-tag with SVT
algorithm etag0.75, ebtag0.51, ectag 1/4ebtag,
fake0.02
Background Multijet fakes (estimated from
data) HF fakes (estimated from data and MC) Bg
is normalized to data outside the signal Limits
for mAmh(lt135) or mAmH(gt135GeV) and for tanß
are calculated
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• H/--

Predicted in L-R symmetric, Triple Higgs, Little
Higgs, etc. models
Signature is multilepton (SS) events
At HERA one searched for multi-e events (in
general) H1 finds 6 multi-e events with M12gt100
GeV (0.540.6 expected) No excess for ZEUS 2
found (1.20.1 expected)
However only 1 event of H1 agrees with H/--
topolgy Limit on coupling hee vs MH
TEVATRON
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D0 selected events in the 2µ channel At least 2
isolated muons, pTgt15 GeV of same charge with
?Flt0.8 (anti-Z) Bg mainly HF and Z (wrong charge
id) 3 events observed, 1.50.4 expected
CDF selected events in the ee, eµ and µµ channels
Predicted background
0 events observed
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Substructure of quarks and leptons

• A possible substructure manifests itself by
• Excited states of quarks and leptons
• Finite size of quarks and leptons
• Contact interaction of qs / ls of scale
  ?gtgtsqrt(s)

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Excited Leptons at the Tevatron (CDF)
Gauge mediated interaction
Contact interaction
Select ee? events ETe1,ETe2,ET?gt25 GeV Z-veto 3
events observed
Expected background events
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Excited Leptons at the Tevatron (CDF)
? - compositness scale f relative coupling
strength to SU2L gauge boson
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Contact Interactions
Deviation from the SM of inclusive ep-gteX is
parametrized as
No deviation (ZEUS, H1) is transformed to limits
on ?
and also to limits on q-radius Rqlt1.0 10-18 m
(H1) Rqlt0.85 10-18 m (ZEUS)
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General search for deviations from the
SMpioneered by D0, here carried out by H1
Select events with at least 2 isolated objects
e, µ, j , ?, ? with PT gt 20 GeV to look for
large deviation from SM in Mall and ?pT
HERA I
HERA II
Largest deviation in µ-j-?
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• Excess of isolated leptons at HERA

5 H1 events are compatible with FCNC single top
production s(ep-gtetX) 0.290.15
pb Alternatively, upper limit on ktu? lt0.27 _at_
95CL ZEUS is compatible with SM limit on vtuZ
vs ktu?
Is the tau excess of ZEUS a sign of stop decay at
large tanß?
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Conclusions
The performances of both Tevatron and HERA
improve steadily allowing to test experimentally
many new ideas in the search for an ultimate
theory Although some anomalies observed
already, no conclusive sign of new, BSM physics
yet
More results are expected soon
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Acknowledgments for help in preparing this
materialto colleagues of the D0, CDF, H1 and
ZEUS collaborationsand especially to Elisabetta
Gallo (ZEUS) andJianming Qian (D0)
Apologies for subjects I havent had time to
present here
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Backup slides
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The CDF upgraded detector
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The D0 upgraded detector
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The H1 detector
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The ZEUS detector
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Extra Dimensions
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Highest DiEm Masses
Mee 475 GeV cosT0.01
M?? 435 GeV cosT0.02
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Analogous study for stop (H1) assuming
mstgtmsbDoesnt explain isolated lepton events -gt
Limits on ?131 and mst
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Z-gtµµ
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Excited Leptons
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Excited Leptons at the Tevatron (CDF)
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• Multi-e events at HERA II