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Small Extra Dimension Graviton Detection at ATLAS. Looking at the Graviton as it decays through G*->Z 0 Z 0 ->e - e + e - e + Audrey Todhunter Case Western Reserve University Dominik Dannheim Columbia University. The Graviton.

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Small extra dimension graviton detection at atlas l.jpg

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 l.jpg
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


Slide3 l.jpg

This analysis:

ppG*Z0Z0e+e-e+e-

against a Standard Model background

qqZ0Z0e+e-e+e-

The 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 l.jpg
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



Particle selection l.jpg
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)


Slide7 l.jpg
Invariant Z0 mass from a 300GeV signal: from electron pairs closest to Z0 mass within each interaction


Graviton reconstruction l.jpg
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


Slide9 l.jpg
Signal at 500GeV with a Gaussian fitsigma parameter used to look at events within a mass window of ±3


Signal and background added and fit with p0 e x p1 2 2 p2 2 p3 e p4 x p5 l.jpg
Signal and background added and fit with[p0]e(-(x-[p1])2/2[p2] 2+ [p3]e([p4]x+[p5])


Potential discovery of resonances from g z 0 z 0 e e e e at atlas l.jpg
Potential discovery of resonances fromG*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 n sig 5 n bg or n sig 10 l.jpg
Luminosity needed for Nsig>5√ (NBG) or Nsig >10

L=100fb-1: one year running at design luminosity


Conclusions l.jpg
Conclusions

-for the processG*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


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