REVIEW
Search for High-Mass Resonances Decaying to e-mu in ppbar Collisions at sqrt(s)=1.96 TeV
High Energy Physics - Experiment · Submitted 3 Mar 2006 · 29 references
Pith's verdict: Secure null result in e-mu; exclusion limits rest on unpublished theory curves and deserve referee scrutiny.
T0 · AI review
Why Pith says this
Highlight any text to comment on it.
Referee report
The paper
The paper claims
The CDF experiment finds no high-mass electron-muon resonance in 344 pb^-1 of Tevatron data and sets 95% confidence limits on sneutrino and Z' masses for lepton-flavor-violating couplings.
The reading
What carries the argument
The search target is the opposite-sign electron-muon pair, a final state with almost no Standard Model background. The analysis has three parts: acceptance $\alpha\times\epsilon$ for signal and backgrounds from PYTHIA Monte Carlo and GEANT detector simulation with CTEQ5L parton distribution functions, corrected by trigger and identification efficiencies; a background model built from $Z/\gamma^*\to\tau\tau$, $t\bar t$, diboson, and fake-lepton contributions with NLO or NNLO cross sections; and a Bayesian 95% CL limit calculation that scans the mass spectrum in 10 GeV/c$^2$ steps and weights data and background events by the simulated mass resolution. For the model interpretations, the key external inputs are NLO $\sigma\times BR$ curves for $d\bar d\to\tilde\nu_\tau\to e\mu$ under the single-coupling-dominance hypothesis with $\lambda'_{311}$ and $\lambda_{132}$ nonzero, and for E6-inspired $Z'$ production extended with an off-diagonal LFV coupling $Q^l_{12}$.
Extended reading notes
Core claim
Using 344 pb$^{-1}$ of CDF II data, the paper finds that the electron-muon invariant mass spectrum between 50 and 800 GeV/c$^2$ is consistent with Standard Model background predictions: 5 events observed versus $7.7\pm0.8$ expected for $M_{e\mu}>100$ GeV/c$^2$, a $\chi^2/N_{\rm dof}$ of $14.0/11$ ($p\approx23\%$), and no events above 159 GeV/c$^2$. Interpreting the non-observation as a null result, the paper sets 95% CL upper limits on the production cross section times branching ratio for $d\bar d\to\tilde\nu_\tau\to e\mu$ and for $p\bar p\to Z'\to e\mu$, translating them into exclusion regions: the RPV sneutrino mass limit reaches about 530 GeV/c$^2$ for $\lambda'_{311}=0.10$ and $\lambda_{132}=0.05$, a gain of roughly 170 GeV/c$^2$ over the Run I search, and the LFV $Z'$ coupling $Q^l_{12}$ is bounded above by roughly 0.01 to 0.1 for masses between 200 and 700 GeV/c$^2$ depending on the E6-inspired model.
Load-bearing premise
The mass and coupling exclusions rest on NLO cross-section curves for sneutrino and $Z'$ production that came from private communications (references [24] and [27]) and are not independently sourced in the paper; if those curves are wrong, the derived limits move, although the central null result does not depend on them.
Editorial extensions
If this is right
- For the RPV sneutrino model, the paper excludes at 95% CL a $\tilde\nu_\tau$ with $\lambda'_{311}=0.10$ and $\lambda_{132}=0.05$ below about 530 GeV/c$^2$, improving on the Run I limit by roughly 170 GeV/c$^2$.
- For a 300 GeV/c$^2$ sneutrino and $\lambda_{132}\gtrsim0.02$, $\lambda'_{311}$ values above about 0.01 are excluded.
- For E6-inspired $Z'$ models with LFV couplings, the paper excludes $Q^l_{12}$ above about 0.01 to 0.1 for $Z'$ masses between 200 and 700 GeV/c$^2$, depending on the model.
- The background model is validated by the data: the measured electron-muon spectrum agrees with Standard Model predictions with $\chi^2/N_{\rm dof}=14.0/11$ and $p\approx23\%$, supporting the model-independent statement that no excess exists in the explored mass range.
Reading between the lines
- The same validated background model could be reinterpreted to constrain non-resonant lepton-flavor-violating contact interactions in the electron-muon channel, not just narrow resonances, without requiring new data.
- A higher-luminosity future run at the Tevatron or at the LHC could either confirm the null result by sharpening these exclusions or populate the region just below the plotted curves, since the current limits define where any new signal would have to appear.
- Because the $Z'$ limits rely on extending E6 models by hand with the off-diagonal coupling $Q^l_{12}$, a fully consistent ultraviolet model with different initial-state couplings could change the production cross section and therefore shift the derived exclusions.
- The single-coupling-dominance assumption, which sets all RPV couplings except $\lambda'_{311}$ and $\lambda_{132}$ to zero, means the sneutrino interpretation is not directly applicable if additional RPV couplings contribute to the same final state.
Original abstract
We describe a general search for resonances decaying to a neutral e-mu final state in ppbar collisions at a center-of-mass energy of 1.96 TeV. Using a data sample representing 344 pb^-1 of integrated luminosity recorded by the CDF-II experiment, we compare Standard Model predictions with the number of observed events for invariant masses between 50 and 800 GeV/c^2. Finding no significant excess (5 events observed vs. 7.7 +/- 0.8 expected for e-mu invariant masses > 100 GeV/c^2), we set limits on sneutrino and Z' masses as functions of lepton family number violating couplings.
The compiled record
The paper's own sentences, arranged, kept beside the review and separate from it. Each label is drawn from a closed vocabulary; the number beside it is the probability the classifier gave that label. Numbers in the tables are the authors', checked by code. No sentence in this record was written by a model.
The abstract, sentence by sentence
We describe a general search for resonances decaying to a neutral e-mu final state in ppbar collisions at a center-of-mass energy of 1.96 TeV. Using a data sample representing 344 pb^-1 of integrated luminosity recorded by the CDF-II experiment, we compare Standard Model predictions with the number of observed events for invariant masses between 50 and 800 GeV/c^2. Finding no significant excess (5 events observed vs. 7.7 +/- 0.8 expected for e-mu invariant masses > 100 GeV/c^2), we set limits on sneutrino and Z' masses as functions of lepton family number violating couplings.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | We describe a general search for resonances decaying to a neutral e-mu final state in ppbar collisions at a center-of-mass energy of 1.96 TeV. | contribution 1.00 | 0.85 | 0.03 | asserted 0.80 |
| s1 | Using a data sample representing 344 pb^-1 of integrated luminosity recorded by the CDF-II experiment, we compare Standard Model predictions with the number of observed events for invariant masses between 50 and 800 GeV/c^2. | method 1.00 | 0.93 | 0.03 | asserted 0.97 |
| s2 | Finding no significant excess (5 events observed vs. 7.7 +/- 0.8 expected for e-mu invariant masses > 100 GeV/c^2), we set limits on sneutrino and Z' masses as functions of lepton family number violating couplings. | result 0.99 | 0.97 | 0.92 | asserted 1.00 |
What was examined, and what was not
- arXiv listing abstract v2
- full text
- figures and tables
- references and citing sentences
- relations to other papers
- P abstract
- S sections
- T body sentences
- C citations
- R cross-paper relations
Figures
Showing 2 of the paper's 4 figures. See all figures in the PDF ↗ Figures reproduced from arXiv:hep-ex/0603006 by the authors.
References
How the literature uses it
5 arXiv papers cite this in 6 sentences
Papers citing it · 5 sentences without a confident label
Cites it as background 1 paper
-
CDF and D0 reported on their search for $eμ$ final states from $s$-channel heavy resonance decays in Refs. [ref] .
A Case Study of the Sensitivity to LFV Operators with Precision Measurements and the LHC · LHC Search · 0.83
Discussion
Disagree with the review, or know something it missed? Leave a comment, highlight any passage above to comment on it, or challenge this review formally.