REVIEW
Search for high-mass diphoton resonances in $pp$ collisions at $\sqrt{s}=8$ TeV with the ATLAS detector
High Energy Physics - Experiment · Submitted 21 Apr 2015 · 39 references
Pith's verdict: A clean, well-documented 8 TeV diphoton null result with real but acknowledged softness in how the RS mass limit is quoted.
T0 · AI review
Why Pith says this
Highlight any text to comment on it.
Referee report
The paper
The paper claims
ATLAS finds no diphoton resonance in 20.3 fb$^{-1}$ of 8 TeV data, and sets a lower limit of 2.66 TeV on the lightest Randall-Sundrum graviton mass at coupling $k/\overline{M}_{\mathrm{Pl}} = 0.1$.
The reading
What carries the argument
The load-bearing device is the background model in the signal region. Because sidebands at high mass are too sparse to constrain the background directly, the irreducible $\gamma\gamma$ shape is taken from a Pythia plus Diphox simulation and normalized to data in a low-mass control region, 179 to 409 GeV, after a template fit to the photon isolation energy $E_T^{\mathrm{iso}}$ determines how much of that control region is genuine photons versus misidentified jets. The reducible $\gamma + j$, $j + \gamma$ and $j + j$ shapes come from data control samples and are extrapolated with a three-parameter form $f(m_{\gamma\gamma}) = p_1 \times (m_{\gamma\gamma})^{p_2 + p_3 \log(m_{\gamma\gamma})}$. A binned Poisson likelihood over the search-region spectrum, with Gaussian nuisance parameters for systematic uncertainties and a uniform positive prior on the signal rate, is then integrated to give the 95% confidence bound. The tight photon identification and the $E_T^{\mathrm{iso}} < 8$ GeV requirement, whose efficiency is 96% per photon, are what keep the reducible background from swamping the high-mass bins.
Extended reading notes
Core claim
The claim is a null result with teeth. The observed diphoton mass spectrum, binned logarithmically from 179 GeV to 3 TeV, shows no localized excess over the predicted background: the largest bump the BumpHunter scan finds anywhere in the 409 to 3000 GeV search region sits between 494 and 745 GeV, and the probability that background fluctuations would produce an excess at least that significant somewhere in the region is 58%. Event yields in the coarser mass bins of Table 3 track the expectation closely, including zero observed events against $3.69 \pm 0.25$ expected in the 1312 to 1415 GeV window. From this agreement the authors derive 95% confidence upper limits on $\sigma \times \mathrm{BR}(G^* \to \gamma\gamma)$ as a function of graviton mass, and, using the model's predicted cross section for each coupling, translate them into the mass limits quoted above. The authors also note that these limits do not fold in theory uncertainties on the signal prediction, and that the PDF uncertainty alone, shown as a band in the cross-section limit figure, is comparable in size to the missing higher-order uncertainty.
Load-bearing premise
The background expected at 1 to 3 TeV is assumed to be correctly predicted by extrapolating a simulation-based photon-photon shape and a fitted three-parameter reducible shape, both anchored in a control region below 409 GeV, without independent validation at high mass.
Editorial extensions
If this is right
- Any model predicting a narrow diphoton resonance below roughly 2.7 TeV with a Randall-Sundrum-like coupling of 0.1 is excluded by this dataset; the corresponding bar for weakly coupled ($0.01$) gravitons is about 1.4 TeV.
- The upper limits on $\sigma \times \mathrm{BR}(G^* \to \gamma\gamma)$ improve on the earlier 7 TeV ATLAS diphoton search by factors of 2.1 at 0.5 TeV and 3.6 at 2.75 TeV, and are quoted against the larger 8 TeV production cross section.
- Because the exclusion is expressed as a limit on coupling versus mass, the result can be read as a boundary in the $(m_{G^*}, k/\overline{M}_{\mathrm{Pl}})$ plane: couplings above roughly 0.1 are excluded for graviton masses up to 2.66 TeV.
- The data-driven background method demonstrated here, simulation-normalized irreducible plus fitted reducible shapes anchored at low mass, is reusable for any high-mass diphoton search where high-mass sidebands are statistically exhausted.
Reading between the lines
- The 58% BumpHunter probability and the mild upward fluctuation in the 494 to 745 GeV region are the kind of residual that a future higher-luminosity or higher-energy dataset could either kill or promote; the natural next check is whether that region sharpens into a resonance at 13 TeV.
- Since the exclusion curve is a coupling-versus-mass boundary, a modest improvement in integrated luminosity or center-of-mass energy buys more in reach at low coupling than at high coupling, because the weaker-coupling curves are the ones closest to the current limit.
- The stated omission of theory uncertainties on the signal cross section means the quoted mass limits are, strictly, limits on the experimental rate; a reader comparing these numbers to other experiments should fold in the PDF and higher-order uncertainty band before treating the boundary as sharp.
Original abstract
This article describes a search for high-mass resonances decaying to a pair of photons using a sample of $20.3$ fb$^{-1}$ of $pp$ collisions at $\sqrt{s}=8$ TeV recorded with the ATLAS detector at the Large Hadron Collider. The data are found to be in agreement with the Standard Model prediction, and limits are reported in the framework of the Randall-Sundrum model. This theory leads to the prediction of graviton states, the lightest of which could be observed at the Large Hadron Collider. A lower limit of $2.66$ ($1.41$) TeV at 95% confidence level is set on the mass of the lightest graviton for couplings of $k/\overline{M}_{\mathrm{Pl}} = 0.1$ ($0.01$).
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
This article describes a search for high-mass resonances decaying to a pair of photons using a sample of $20.3$ fb$^{-1}$ of $pp$ collisions at $\sqrt{s}=8$ TeV recorded with the ATLAS detector at the Large Hadron Collider. The data are found to be in agreement with the Standard Model prediction, and limits are reported in the framework of the Randall-Sundrum model. This theory leads to the prediction of graviton states, the lightest of which could be observed at the Large Hadron Collider. A lower limit of $2.66$ ($1.41$) TeV at 95% confidence level is set on the mass of the lightest graviton for couplings of $k/\overline{M}_{\mathrm{Pl}} = 0.1$ ($0.01$).
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | This article describes a search for high-mass resonances decaying to a pair of photons using a sample of $20.3$ fb$^{-1}$ of $pp$ collisions at $\sqrt{s}=8$ TeV recorded with the ATLAS detector at the Large Hadron Collider. | contribution 0.81 | 0.94 | 0.03 | asserted 0.91 |
| s1 | The data are found to be in agreement with the Standard Model prediction, and limits are reported in the framework of the Randall-Sundrum model. | result 0.99 | 0.94 | 0.89 | asserted 0.99 |
| s2 | This theory leads to the prediction of graviton states, the lightest of which could be observed at the Large Hadron Collider. | background 0.93 | 0.06 | 0.03 | hedged possibility 0.97 |
| s3 | A lower limit of $2.66$ ($1.41$) TeV at 95% confidence level is set on the mass of the lightest graviton for couplings of $k/\overline{M}_{\mathrm{Pl}} = 0.1$ ($0.01$). | result 1.00 | 0.94 | 0.65 | 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
Figures reproduced from arXiv:1504.05511 by the authors.
References
How later papers used it
92 later papers cite it
3 later papers by other authors are listed below: 3 used its data or values.
Uses its data or values 3 of 40 papers with this label
-
Used this paper's 8 TeV diphoton search with 20.3 fb^-1 of data to interpret the excess.
Phenomenology of a 750 GeV Singlet (2015) · 1.00 · paraphrased: the licence does not allow quoting
-
Obtained its curves using the 95% C.L. limits given in this paper, which refer to the 8 TeV ATLAS data at 20.3 fb^-1.
Collider Tests of (Composite) Diphoton Resonances (2016) · 0.94 · paraphrased: the licence does not allow quoting
-
Excluded the light green region using this paper's constraints on the diphoton channel of about 0.3 fb or less.
Diboson Resonance as a Portal to Hidden Strong Dynamics (2015) · 0.97 · paraphrased: the licence does not allow quoting
How the literature uses it
92 arXiv papers cite this in 121 sentences
Papers citing it · 63 sentences without a confident label
Uses its data or values 40 papers
-
We read in the predicted backgrounds and observed data from the reported plots in Refs. [ref] .
How Resonance-Continuum Interference Changes 750 GeV Diphoton Excess: Signal Enhancement and Peak Shift · Dataset and Method · 0.99
-
Corresponding upper bounds at $95%$ confidence level yield $σ^8 TeV_pp→jj<2.5$ pb [ref] and $σ^8 TeV_pp→γγ<1.5$ fb [ref] , respectively.
Interpreting $750$ GeV Diphoton Excess with R-parity Violating Supersymmetry · Introduction · 0.97
-
(3) The ATLAS [ref] and CMS [ref] searches for a resonance decaying to $γγ$ at $√(s)=8$ TeV give a $95%$ CL upper limit on the production cross section: [equation]
750 GeV diphoton resonance in a top and bottom seesaw model · Numerical Calculations and Results · 0.96
Compares with it 5 papers
-
This gives $σ_pp →s B_s →γγ$ close to the upper limit from the $8 TeV$ data [ref] .
Composite Models for the 750 GeV Diphoton Excess · Hidden Glueball: Minimal Model · 0.90
-
We find that these limits are much stronger than the ones obtained in the LHC-8 analysis from ATLAS [ref] with 20.3 fb$^-1$ and CMS [ref] with 19.7 fb$^-1$.
Diphoton Resonances at the LHC · Photon fusion production · 0.97
-
Interestingly, the signal is in tentative agreement with results from the similar CMS search, which sees a local excess of 2 $σ$ for the same width, employing 2.6 fb$^-1$ of data [ref] .[For a narrow width, which seems to be preferred in CMS, the significance increases to 2.6 $σ$.] There were also less significant upward fluctuations in this mass region in the run I data collected at 8 TeV [ref] .
Indirect Constraints on the Scalar Di-Photon Resonance at the LHC · Introduction · 0.81
Cites it as background 8 papers
-
Over the past decades, there has been an intense search for resonant heavy gravitons both at Tevatron [ref] and LHC in the diphoton and dilepton channels [ref] , as well as in massive gauge bosons and di-Higgs channels [ref] .
LHC Constraints on Resonant Kaluza-Klein Gravitons · Introduction · 0.94
-
Previous LHC searches for spin-2 resonances were performed by the ATLAS [ref] and CMS [ref] collaborations using proton-proton (pp) collisions at $√(s) = 8$ and $13$ TeV [ref] .
Probing Heavy Spin-2 Bosons with $\gamma \gamma$ final states from Vector Boson Fusion Processes at the LHC · Introduction · 0.93
-
Over the course of the past few years the CMS and ATLAS experiments produced several searches for $X →γγ$ decays in Run 1 and Run 2 data [ref] .
Hadron Collider Searches for Diboson Resonances · Searches for $γγ$ Resonances · 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.