Small Extra Dimension Graviton
Detection at ATLAS
Looking at the Graviton as it decays
through G*->Z0 Z0 ->e-e+e-e+
Audrey Todhunter
Case Western Reserve University
Dominik Dannheim
Columbia University
The Graviton
Massive graviton resonances are predicted by
models using extra dimensions
-resonances could be well separated in mass
The graviton couples universally (ee,,,,Z0Z0,
etc…)
-Products could be detected at ATLAS
Analysis used the Randall-Sundrum model, which
predicts the mass of the first resonance by:
mn =xn(k/MPl)
We chose k/MPl=0.01 to give resonances on the TeV
scale
This analysis:
ppG*Z0Z0e+e-e+eagainst a Standard Model background
qqZ0Z0e+e-e+eThe branching ratio Br for Z0Z0e+e-e+e- is
only 3.4%*3.4% = 11.56% for this decay
process
Signal and Background Simulation
-Pythia event generator
-mass points at 300GeV, 500GeV, 700GeV,
1TeV, and 1.5TeV, as well background
processes around each point
-want to know how well these signals can be
detected at ATLAS Geant4 used in a full
simulation of the ATLAS reconstruction
Process
Inv. mass of G*
resonance (GeV)
G*Z0Z0e+e-e+e-
300
4.807
1480
500
0.7347
1918
700
0.0972
1677
1000
0.0167
1999
1500
0.001938
1899
200
9.068
1480
400
1.527
1000
500
0.7347
1986
800
0.167
1678
1200
0.03684
1876
qqZ0Z0e+e-e+e-
(·Br) (fb)
Nev events
generated
Properties of simulated signal and background
Particle Selection
We can identify electrons by their characteristics
detected in the EM calorimeter and the central
tracker
• Transverse energy eT > 20 GeV
• Likelihood > 0.9 being electron rather than pion
• 2e+e- pairs in each entry
- best combination of particles decided by comparing
reconstructed Z0 mass to known Z0 mass
(91.1GeV)
Invariant Z0 mass from a 300GeV signal: from
electron pairs closest to Z0 mass within each
interaction
Graviton Reconstruction
-electrons chosen for Z0 mass used to
reconstruct invariant G* mass
-signal scaled for 100 fb-1 luminosity (1 year
running at design luminosity)
NEv = (·Br) · L
imposing a weight factor on the number of
simulated events
Signal at 500GeV with a Gaussian fit
sigma parameter used to look at events within a mass
window of ±3
Signal and background added and fit with
[p0]e(-(x-[p1]) /2[p2] + [p3]e([p4]x+[p5])
2
2
Potential discovery of resonances
from G*Z0Z0e+e-e+e- at
ATLAS
- count number of signal and background
events within the ±3 window
- need to have Nsig>5√ (NBG) or Nsig > 10 for a
statistically significant signal
- number of events can be increased by
raising luminosity
Luminosity needed for Nsig>5√ (NBG) or Nsig > 10
L=100fb-1: one year running
at design luminosity
Conclusions
-for the process G*Z0Z0e+e-e+e- the upper
mass limit is slightly below 700GeV
-higher discovery potential at increased
luminosity
-other decay channels are possible for the
graviton which may have higher upper
limits for detection