[Paper Review] Searches for Large Extra Dimensions at the Tevatron

V. Krutelyov|ArXiv.org|Jul 3, 2008

Particle physics theoretical and experimental studies10 references4 citations

TL;DR

This paper presents a comprehensive search for large extra dimensions (LED) at the Tevatron collider using proton-antiproton collisions at √s = 1.96 TeV. It analyzes signatures of direct graviton production (via missing transverse energy with photons or jets) and virtual graviton exchange (via dilepton, diphoton, and diboson final states), finding no evidence for LED and setting new lower limits on the fundamental Planck scale $M_D$ up to 1400 GeV/c² for $n=6$ extra dimensions, comparable or superior to LEP constraints.

ABSTRACT

The presence of extra dimensions can be probed in high energy collisions via the production or exchange of gravitons. The former corresponds to signatures with missing energy while the latter corresponds to modifications of the final state spectra. Here I review results of analyses performed by the CDF and D0 Collaborations on ppbar collisions at 1.96 TeV in signatures sensitive to large extra dimensions. These include analyses of photon+(missing transverse energy) and jet+(missing transverse energy) as signatures of graviton production as well as analyses of dilepton and diboson final states sensitive to graviton exchange.

Motivation & Objective

• To test the viability of large extra dimensions (LED) as a solution to the hierarchy problem in the Standard Model.
• To probe the existence of graviton production and exchange in high-energy $p\overline{p}$ collisions at the Tevatron.
• To set experimental limits on the fundamental scale $M_D$ in LED models using data from CDF and DØ.
• To improve sensitivity by combining multiple final states and leveraging high-precision kinematic reconstruction.

Proposed method

• Searches for direct graviton production via final states with missing transverse energy ($E\!\!\!/_T$) and a high-$E_T$ photon or jet, requiring exclusive signatures with no additional jets or leptons.
• Utilized data-driven background estimation techniques, including $Z\to\ell\ell$ and $W\to\ell\nu$ control samples to estimate $Z\to\nu\nu$ and $W\to\ell\nu$ backgrounds with lost leptons.
• Employed photon timing (CDF) and photon pointing (DØ) to suppress cosmic-ray muon misidentification as photons.
• Analyzed virtual graviton exchange in dilepton, diphoton, and $ZZ$ final states by reconstructing invariant masses and angular distributions to probe spin-2 exchange effects.
• Combined results from $\gamma+{E\!\!\!/_T}$ and $\mathrm{jet}+{E\!\!\!/_T}$ channels at CDF to improve sensitivity.
• Used simulation and data-driven methods to estimate contributions from jet-to-photon misidentification and cosmic ray backgrounds.

Experimental results

Research questions

• RQ1 What are the limits on the fundamental scale $M_D$ for large extra dimensions based on direct graviton production in $p\overline{p}$ collisions at the Tevatron?
• RQ2 How does the sensitivity of $\gamma+{E\!\!\!/_T}$ and $\mathrm{jet}+{E\!\!\!/_T}$ signatures compare in probing LED?
• RQ3 What constraints can be placed on virtual graviton exchange in dilepton and diboson final states?
• RQ4 How do the Tevatron results compare to previous limits from LEP experiments?
• RQ5 Can the combination of multiple final states improve sensitivity to LED beyond individual channels?

Key findings

• No significant excess over the Standard Model background was observed in any of the $\gamma+{E\!\!\!/_T}$, $\mathrm{jet}+{E\!\! olimits/_T}$, dilepton, diphoton, or $ZZ$ final states.
• The combined CDF analysis of $\gamma+{E\!\!\!/_T}$ and $\mathrm{jet}+{E\!\!\!/_T}$ channels set the most stringent limits, with $M_D > 1400$ GeV/c² at 95% confidence level for $n=6$ extra dimensions.
• For $n=2$, the lower limit on $M_D$ reached 1600 GeV/c² from the $\gamma+{E\!\!\!/_T}$ channel at CDF, comparable to LEP constraints.
• Constraints on virtual graviton exchange via dilepton and diphoton final states yielded $\Lambda$ values between 1 and 2 TeV, depending on theoretical parameters.
• The $ZZ$ final state analysis showed consistency with the Standard Model, and based on theoretical estimates, $\Lambda$ is expected to be constrained to 1.5–2.5 TeV.
• The sensitivity of the Tevatron searches for LED is comparable to or better than that of LEP experiments, particularly in the $\gamma+{E\!\!\!/_T}$ and $\mathrm{jet}+{E\!\!\!/_T}$ channels.