Calibration and Databases

1
Search for Large Extra Dimensions at the Tevatron
Bob Olivier LPNHE - Paris
XXXVIème Rencontre de Moriond 17 - 24 Mars 2001
On behalf of the CDF and D0 collaborations
2
Signatures for Large Extra Dimensions at the
Tevatron
Real Gravitons

• Single Energetic jet
• Missing Energy from the graviton

• Single Vector Boson
• Missing Energy from the graviton

• ? CDF and D0 analysis on going...

Virtual Gravitons

• Fermion or Vector Boson pairs

• ? New Results from D0 !

3
Effects of Virtual Graviton Exchange at the
Tevatron

• In models with Large Extra Dimensions,
  Kaluza-Klein gravitons can modify
  difermion/diphoton production in
  collisions

? interference between SM and gravity
contribution (e.g., ll- production)

• difermion/diphoton production angle
• M difermion/diphoton mass

• n number of large extra dimensions
• MS cut-off scale for KK-diagrams

? search for deviations in distributions for
and M
4
Search Strategy at DØ

• Based on Cheung/Landsberg PRD 62, 035004 (2000)
• DØ detector does not have a central magnetic
  field, hence cannot measure electric charge of
  electrons
• ? use cos?
• Dimuon mass resolution at high mass is poor
• ? use dielectrons, do not use dimuons
• EM objects not separated into electrons and
  photons
• Low background expected at high mass use loose
  EM-ID cuts
• ? maximize EM efficiencies
• use EM cluster direction to pick vertex
• ? better and M resolutions

5
Data Selection and Efficiency

• Use entire Run I luminosity, low-threshold,
• di-EM triggers ?Ldt 127 ? 6 pb-1
• Offline criteria
• Exactly 2 EM clusters, ET gt5 GeV,
• passing basic EM ID criteria
• No other kinematic restrictions in the
• analysis, since (M, ) define the
• process completely
• Resulting data sample contains 1250 events
• Overall Signal efficiency 79 ? 2

of events
Criterion
87,542
Starting sample
82,947
Quality criteria
82.927
?2 EM
82,425
2 EM
36,409
ET gt 25 GeV
30,585
Acceptance
10,711
EM ID
1,250
ET gt 45 GeV
6
Backgrounds

• SM backgrounds in the MC
• Drell-Yan (e-pairs)
• qq ? gg (gg ? gg is negligible
• ? not included)
• Wj/ g ,WW, Top, Z negligible

At high mass, SM background dominated by qq ? gg
s, fb/bin
Total SM background
qq ? gg
Landsberg Matchev, PRD 62, 035004 (2000)
gg ? gg
M(di-EM), GeV

• Instrumental background
• QCD induced jj/jg ? gg
• (jet fake a g)

7
MC Description of Data and Systematics

• Kinematic distributions are well described by the
  sum of SM and instrumental backgrounds
• Following systematic uncertainties on
  differential cross sections were taken into
  account

Uncertaint
Source
10
K-factor
5
Choice of PDF
4
?Ldt
3
Efficiency
12
Overall
Instrumental background (uncertain to 25)
8

• Observe good agreement in

9
Mass and Angular Distributions
Instrumental background
10
Monte Carlo for Signal and Background
11
DØ Results in Di-EM Channels

• High mass and small cosq are characteristic
  signatures of LED
• 2-dimensional analysis resolves LED from
  high-mass and large cosq tail from QCD
  diphotons
• No excess seen at high mass, where LED signal is
  expected

signal
background
12
DØ Limits on Large Extra Dimensions

• No evidence for SM deviations in D0 data
• Measured fitted with parametrized
  contributions from large extra dimensions
• Fit result consistent with 0, extracts limits at
  95 C.L.
• Complementary to those from LEP2
• (0.7 - 1.0 TeV), probing different range of
  energies
• CDF pursues similar dilepton and diphoton
  analyses
• (similar sensibility expected)
• Combined Tevatron limits are expected to be the
  most restrictive to date

PRL 86, 1156 (2001)

• Sensitivity is limited by statistics reach in
  terms of MS will double in Run-2a (2 fb-1) and
  triple in Run-2b (20 fb-1)

13
Highest-Mass Candidate
M(gg) 574 GeV cosq 0.86
Event with highest mass observed in Run I
2 photons with Et 81 GeV Met 15 GeV

• Parameters of the candidate event
  of highest mass

14
Monojet Signatures
n 2, MS 1 TeV, ?s 1.8 TeV CDF sensitivity
study in progress
Typical process

• Single jet
• Missing energy
• from the
• graviton

15
Real Graviton Signature (CDF)

• Sensitivity on transverse
• mass (jet, Etmiss) for
• different values of n
• CDF analysis on going

16
Summary

• DO has searched for contributions from virtual
  graviton exchange in the context of large
  extra spatial dimensions. On the basis of the
  production of massive e-pairs and di-photons,
  such a scale, must be higher than 1 TeV
• More studies are being pursued at both DO and
  CDF, both on virtual-graviton exchange as well as
  real graviton (mono-jet) production. Expected
  spring 2001.
• Run I limits are most stringent up to date
• Run II will be sensitive to scales of 3-4 TeV
• The LHC will be able to access effective Planck
  scales of 10 TeV

17
Run II !

• Tevatron Run II has started
• March 1 2001
• One of the first Run II
• events in D0
• A lot of missing energy
• ? new physics ???