Search for Extra-Dimensions at D0

1
Search for Extra-Dimensions at D0
M. Jaffré LAL Orsay for the D0 Collaboration

• Tevatron and D0 status
• Extra Dimensions
• Large ED
• Tev-1 ED
• Randall Sundrum Model

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Tevatron RunII Status

• New Main Injector 150 GeV
• New Recycler
• Higher Energy (1.96TeV)
• Higher luminosity ( 36x36 bunches)
• Design Run IIa 0.8x1032 cm-2s-1
• Run IIb 2-4x1032 cm-2s-1
• Upgrades to come
• Slip stacking end 04
• Electron cooling end 05 ?
• Stacktail upgrade end 06 ?
• New helix beam separation end 06 ?
• Projected Integrated lumi. / expt
• 2006 2fb-1
• 2009 8fb-1

1.02 1032 cm-2 s-1
Run I record
2002
2003
2004
3
DØ Run II

• Solenoid (2T)
• 4-layer Silicon Vertex (barrels and disks)
• 16-layer Fiber Trackers
• Muon forward chamber (?lt2 ), shielding
• New preshower, upgrade Calorimeter electronics
• Upgrade to Trigger and DAQ system

• For Run IIb (Fall 05)
• Silicon layer 0
• Trigger upgrade

4
Half A Femtobarn of Data!
D0 analysis
Integrated Luminosity more than doubled in the
last 12 months Efficiency gt80
5
Why ED ?

• String theory is the only currently known way to
  incorporate gravity in Quantun Mechanics.
• ED come  naturally  with string theory (n6 or
  7)
• In short, models with ED try to address the
  problem of the huge hierarchy between EW and
  Planck scales.
• .
• These ideas can be tested at existing and nearly
  existing colliders

6
Models of Extra Dimensions

• ADD Model
• Arkani-Hamed,Dimopoulos,Dvali Phys Lett B429 (98)
• SM particles and gauge bosons are confined in
  D3-brane
• Only gravity propagates in n spatial ED
• Gauss law
• MPl (apparent 4D Planck Scale)
• MD (fundamental Planck Scale)
• Size of EDs (n2-7) between 100 mm and 1 fm

• TeV-1 Scenario
• Dienes,Dudas,Gherghetta Nucl Phys B537 (99)
• Lowers GUT scale by changing the running of the
  couplings
• Only gauge bosons (g/g/W/Z) propagate in a single
  ED gravity is not in the picture
• Size of the ED 1 TeV-1 or 10-19 m

• RS Model
• Randall,Sundrum Phys Rev Lett 83 (99)
• A rigorous solution to the hierarchy problem via
  localization of gravity
• Gravitons (and possibly other particles)
  propagate in a single ED, w/ special metric
• Size of this ED as small as 1/MPl or 10-35 m

M2Pl ? MDn2 x Rcn
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Kaluza-Klein Spectrum

• ADD Model
• KK excitations with energy spacing 1/r, i.e. 1
  meV 100 MeV
• Cant resolve these modes they appear as
  continuous spectrum

• TeV-1 Scenario
• KK excitations with nearly equal energy spacing
  1/r, i.e. TeV
• Can excite individual modes at colliders or look
  for indirect effects

• RS Model
• Coupling of graviton to SM fields is k/MPl
  0.01-0.1
• Light modes might be accessible at colliders
• Model characterized by M1 and k/MPl

E
MGUT
E
MPl


Mi
Mi
M0
M1
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Collider Signatures Large Extra Dimensions

• Kaluza-Klein gravitons couple to the
  energy-momentum tensor, and therefore contribute
  to most of the SM processes
• For Feynman rules for GKK see
• Han, Lykken, Zhang, PRD 59, 105006 (1999)
• Giudice, Rattazzi, Wells, NP B544, 3 (1999)
• Since graviton can propagate in the bulk, energy
  and momentum are not conserved in the GKK
  emission from the point of view of our 31
  space-time
• Depending on whether the GKK leaves our world or
  remains virtual, the collider signatures include
  single photons/Z/jets with missing ET or
  fermion/vector boson pair production
• Graviton emission direct sensitivity to the
  fundamental Planck scale MD
• Virtual effects sensitive to the ultraviolet
  cutoff MS, expected to be MD (and likely lt MD)
• The two processes are complementary

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Search for Monojets

• Very challenging because of instrumental
  background from MET mismeasurement, cosmics.
• Irreducible Physics background from Z(??)
  jet(s).
• Special trigger for Physics with jets and MET
  since spring 03 MHT ? pT(jets) gt 30 GeV/c
• ? 85 pb-1 (april-august 2003)
• Calorimeter Data Quality is very important for
  JetMet analyses, since most calorimeter problems
  (hot cells, noise...) will increase the MET tail
  distribution
• Offline to fight mixvertexing and cosmics
• jets have associated tracks originating from
  primary vertex

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Search for Monojets

• Final Selection
• Leading jet pT gt 150 GeV(??1)
• Isolated electron and muon veto
• MET gt 150 GeV
• No extra jet with pT gt 50 GeV
• MET separated from any jet by ? 30?
• Signal simulation Pythia Lykken-Matchev code
• ( 5 signal
  efficiency)
• Largest uncertainty is from JES and have already
  been much improved
• With 85 pb-1 better than D0 Run I
• still below CDF Run I

QCD bckg
N6 MD 0.7 TeV
before MET cut
Mostly Z(??)jets
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Search for effects in high mass dilepton,
diphoton events

• ED processes predict high mass di-lepton and/or
  di-photon events
• Study High Pt di-electron, di-muon, and di-photon
  mass spectra
• Main backgrounds Drell Yan and QCD jet events
  where jets fake leptons and photons
• Drell-Yan shape vs mass known from theory
• QCD get shape from events that (just) fail
  particle ID cuts.
• Normalize DY and QCD to low mass events
  (typically about 50 GeV to 120 GeV) includes Z.

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LED Virtual Graviton Effects

• In the case of pair production via virtual
  graviton, gravity effects interfere with the SM
  (e.g., ll- at hadron colliders)
• Therefore, production Xsection has three terms
  SM, interference direct gravity effects
• where ?G F/MS4
• Hewett F 2l/p with l 1
• GRW F 1
• HLZ F log(MS2/s) for n 2
  F 2/(n-2) for n gt 2

• The sum in KK states is divergent in the
  effective theory, so in order to calculate the
  cross sections, an explicit cut-off is required
• An expected value of the cut-off MS ? MD,as this
  is the scale at which the effective theory needs
  to be used to calculate production.
• There are three major conventions on how to write
  the effective Lagrangian
• Hewett PRL 82, 4765 (1999)
• Giudice, Rattazzi, Wells NP B544, 3 (1999)
  revised version, hep-ph/9811291
• Han, Lykken, Zhang PRD 59, 105006 (1999)
  revised version, hep-ph/9811350
• Fortunately all three conventions turned out to
  be equivalent and only the definitions of MS are
  different

cos?? cosine of scattering angle in c.o.m
frame
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diEM Selection

• DiEM ee ??
• 2 EM objects ET gt 25 GeV
• Track isolation
• CC ??1.1 EC 1.5lt??2.4
• Overall ID efficiency 85?1 / EM

200 pb-1
Signal ?G0.6 TeV-4
min. Mass Data Bckg
300 350 400 450 480 14 8 5 1 0 17.3 8.1 4.4 2.6 1.9
DY Direct ?? QCD
QCD
Source of systematics Uncertainty
K-factor Choice of p.d.f. Luminosity x efficiency ET dependence of efficiency 10 5 2 5
Total 12
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Search for LED in diEM channel

• Combine diphotons and dielectrons into di-EM
  objects to maximize efficiency
• Sensitivity is dominated by the diphoton channel
  (spin 2 graviton ? 1 1)

• Data agree well with the SM predictions proceed
  with setting limits on large ED alone or in
  combination with published Run I result PRL 86,
  1156 (2001)
• ?G95 0.292 TeV-4
• Translated into the following mass limits
• RunII result
• Combined RunI RunII result
• These are the most stringent constraints on large
  ED for n gt 2 to date, among all the experiments

See these 2 evts in next slide
200 pb-1
Hewett Hewett GRW HLZ (TeV, _at_95 CL) HLZ (TeV, _at_95 CL) HLZ (TeV, _at_95 CL) HLZ (TeV, _at_95 CL) HLZ (TeV, _at_95 CL) HLZ (TeV, _at_95 CL)
l 1 l -1 GRW n 2 n 3 n 4 n 5 n 6 n 7
1.22 1.10 1.36 1.56 1.61 1.36 1.23 1.14 1.08
1.28 1.16 1.43 1.67 1.70 1.43 1.29 1.20 1.14
170 mm 1.5 nm 5.7 pm 0.2 pm 21 fm 4.2 fm
rmax
MS 1 TeVn6
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Interesting Candidate Events
Mee 475 GeV, cos? 0.01
Mgg 436 GeV, cos? 0.03
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Search for LED in diMuon channel

• 2 ?s with pT gt 15 GeV
• isolated, ?lt2.0
• for M?? gt 300 GeV Nexp 6.4?0.8
  and Nobs 5
• Systematics 13

Fit the 2D distributions as for diEM ?G95
0.72 TeV-4 (Bayesian)
250pb-1
Hewett Hewett GRW HLZ (TeV, _at_95 CL) HLZ (TeV, _at_95 CL) HLZ (TeV, _at_95 CL) HLZ (TeV, _at_95 CL) HLZ (TeV, _at_95 CL) HLZ (TeV, _at_95 CL)
l 1 l -1 GRW n2 n 3 n4 n 5 n6 n7
0.97 0.95 1.09 1.00 1.29 1.09 0.98 0.91 0.86
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Search for TeV-1 ED

• Apply the same 2D-technique as for LED search.
• Z/? KK states effects parameterized by
• ?C?2/3MC2
• Data agree with the SM predictions, which
  resulted in the following limit on their size
• MC gt 1.12 TeV _at_ 95 CL
• r lt 1.75 x 10-19 m
• Well below indirect contraints from EW
  measurement (?6 TeV)

• Di-electron channel ?200 pb-1
• QCD fake bckg much reduced compare to diEM

CC-CC
signal for ?C 5 TeV-2
Note the negative interference
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DØ Search for RS Gravitons

• Analysis based on 200 pb-1 of ee- and ?? data
  the same data set as used for searches for LED
• Search window size has been optimized to yield
  maximum signal significance
• G(1) is narrow compare to the mass resolution

300 GeV RS signal
QCD
DYdirect ?? QCD
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DØ Limits in the eegg Channel
The tightest limits on RS gravitonsto date
Assume fixed K-factor of 1.3 for the signal
Masses up to 785 GeV are excluded for k/MPl 0.1
DØ Run II Preliminary, 200 pb-1
Already better limits than the sensitivity for
Run II, as predicted by theorists!
DØ Run II Preliminary, 200 pb-1
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Conclusion - Outlook

• The data agree well with the Standard Model
• New limits from D0 on Extra Dimensions
• Twice the statistics is available,
• more will come soon
• Expect to increase the mass limits for LED models
  up to 2TeV before the LHC startup

Topic Prelim. Results
LED ee ?? ?? MS gt1.43 TeV (GRW Run 12) MS gt 1.09 GeV
TeV-1 longitudinal ED ee Mc gt 1.12 TeV
RS ee ?? M(G(1)) gt 785 GeV for k/MPl0.1