CR009 $pp \to l^+ l^- \,\text{(high-mass tail, EFT contact-operator)}\,$
Drell-Yan high-mass tail as EFT contact-operator bound Status REVIEWED VERIFIED High Code: NO Priority Medium
PDG / equivalent values
| Observable | Value | Year | Experiment / source | Provenance |
|---|---|---|---|---|
| llqq contact-interaction scale $\Lambda$, combined dielectron+dimuon LL constructive | Lambda_LL^+ > 35.8 TeV 95% CL (lower_limit) | 2025 | ATLAS | source ↑ |
| llqq contact-interaction scale $\Lambda$, combined dielectron+dimuon LL destructive | Lambda_LL^- > 26.0 TeV 95% CL (lower_limit) | 2025 | ATLAS | source ↑ |
| llqq contact-interaction scale $\Lambda$, combined dielectron+dimuon RR constructive | Lambda_RR^+ > 35.5 TeV 95% CL (lower_limit) | 2025 | ATLAS | source ↑ |
| llqq contact-interaction scale $\Lambda$, combined dielectron+dimuon RR destructive | Lambda_RR^- > 26.5 TeV 95% CL (lower_limit) | 2025 | ATLAS | source ↑ |
| llqq contact-interaction scale $\Lambda$, combined dielectron+dimuon LR constructive | Lambda_LR^+ > 32.5 TeV 95% CL (lower_limit) | 2025 | ATLAS | source ↑ |
| llqq contact-interaction scale $\Lambda$, combined dielectron+dimuon LR destructive | Lambda_LR^- > 28.8 TeV 95% CL (lower_limit) | 2025 | ATLAS | source ↑ |
| llqq contact-interaction scale $\Lambda$, CMS lower endpoint, LL destructive | Lambda_LL > 23.9 TeV 95% CL (lower_limit) | 2025 | CMS | source ↑ |
| llqq contact-interaction scale $\Lambda$, CMS upper endpoint, RR constructive | Lambda_RR > 36.4 TeV 95% CL (lower_limit) | 2025 | CMS | source ↑ |
Why this constrains the RS scan
In a 5D RS interpretation, this is primarily a constraint on neutral heavy
vector exchange that induces semileptonic operators of the form
\((\bar q\gamma_\mu q)(\bar\ell\gamma^\mu\ell)\). It is not a direct
KK-gluon mass limit, since a color-octet KK gluon does not mediate
\(\ell^+\ell^-\) at tree level. It constrains the electroweak KK tower, a
\(Z^\prime\)-like custodial vector, or a more generic compositeness sector
only after specifying the light-quark and lepton couplings.
With the usual contact-interaction convention,
\(4\pi/\Lambda^2 \sim |g_q g_\ell|/M_V^2\). Therefore the ATLAS
\(\Lambda_{\rm LL}^{+}>35.8~\mathrm{TeV}\) limit corresponds only
schematically to
\[
M_V \gtrsim \sqrt{|g_q g_\ell|/(4\pi)}\,35.8~\mathrm{TeV},
\]
not to a universal \(35.8~\mathrm{TeV}\) resonance mass bound. For
\(|g_q g_\ell|\sim 1\), this is an \(O(10~\mathrm{TeV})\) neutral-vector
scale; for strongly coupled light fermions it can be higher, while for
UV-localized light fermions it is weaker. The quark-scan methodology note
already finds the low-energy anarchic-flavor median scale
\(\Mkk^{\min,p50}=47.26~\mathrm{TeV}\) at \(\gs=3\), with a
95\%-acceptance crossing at \(127.13~\mathrm{TeV}\). CR009 is therefore a
cross-check and a handle on non-anarchic or non-universal RS variants, not the
leading anarchic-flavor constraint.
What's changed since the original paper
The LHC history is a steady increase in energy, luminosity, and analysis
sophistication. ATLAS started with 7 TeV dielectron and dimuon data in
arXiv:1112.4462, establishing early LL isoscalar contact-scale sensitivity.
ATLAS then used the 8 TeV dilepton spectrum and forward-backward asymmetry in
arXiv:1407.2410, improving the same contact-interaction program. CMS's 8 TeV
spectrum analysis in arXiv:1412.6302 provided comparable same-flavor contact
limits and model-independent resonance information.
Run 2 changed the reach. ATLAS's first 13 TeV result with 3.2
\(\mathrm{fb}^{-1}\), arXiv:1607.03669, extended the early Run-2
sensitivity. The 36.1 \(\mathrm{fb}^{-1}\) ATLAS search,
arXiv:1707.02424, and CMS's 36 \(\mathrm{fb}^{-1}\) result,
arXiv:1812.10443, pushed the model-dependent reach into higher
tens-of-TeV \(\Lambda\) scales in comparable patterns. The current
full-Run-2 anchors are ATLAS arXiv:2006.12946 and CMS arXiv:2103.02708.
The SMEFT literature clarified how to use these tails. Falkowski,
Gonzalez-Alonso, and Mimouni compiled low-energy four-fermion constraints in
arXiv:1706.03783, while later high-energy Drell--Yan SMEFT work treats the
tails as energy-growing probes of semileptonic dimension-six operators
(
smeft\_theory\_arxiv\_extracts.txt).Validity and model dependence
The quoted \(\Lambda\) limits are measured exclusions, but the map to RS is
not model-independent. The experimental interpretation assumes a particular
helicity current, an interference sign, and the conventional
\(g_{\rm contact}^2=4\pi\) normalization. The CMS combination assumes a
universal contact interaction for electrons and muons. ATLAS and CMS also
use different background strategies, and the high-mass tail is sensitive to
PDF and electroweak corrections.
For RS, the largest ambiguity is the light-fermion coupling pattern. A
minimal light-fermion UV localization suppresses the contact operator, while
non-anarchic lepton localization, partial compositeness of light quarks, or an
extra neutral vector with sizable dilepton branching can make the bound much
more relevant. EFT validity also requires the mediator to be heavier than the
dilepton masses driving the fit; otherwise the correct object is a resonance
or broad-resonance likelihood, not the contact-limit number alone.
Code coverage in this repo
NO. The required grep over
quarkConstraints/, qcd/,
flavorConstraints/, neutrinos/, yukawa/,
warpConfig/, solvers/, scanParams/, and
tests/ found no Drell--Yan, dilepton-tail, contact-interaction,
collider-reinterpretation, CheckMATE, MadAnalysis5, SModelS, Delphes,
Pythia, or MadGraph implementation. The only CMS match was the
unrelated RunDec alpha-s test at tests/test\_alpha\_s.py:88.
Adjacent evidence shows that the scan computes \(M_{KK}\) and low-energy
\(\Delta F=2\) ratios, not collider direct-search filters:
quarkConstraints/scan.py:359 maps \(\Lambda_{\rm IR}\) to \(M_{KK}\),
quarkConstraints/scan.py:376 evaluates flavor diagnostics,
quarkConstraints/scan.py:377 calls the \(\Delta F=2\) evaluator, and
quarkConstraints/deltaf2.py:320 states that the implemented
Wilsons are tree-level KK-gluon-inspired \(\Delta F=2\) coefficients matched
at \(M_{KK}\).Implementation difficulty
HIGH. Recording the bound is easy; using it as a live scan
constraint is not. A faithful implementation would need either a public
likelihood or a recreated binned dilepton-tail likelihood with correlations,
PDF and electroweak systematics, an RS-to-SMEFT matching layer for the
neutral electroweak KK vectors, and validity logic deciding when a point
should be treated as a contact interaction rather than a resolved resonance.
External reinterpretation infrastructure such as MadAnalysis5, CheckMATE, or
a dedicated high-\(p_T\) SMEFT tool would be the pragmatic route.
Reason: Requires a binned high-mass dilepton likelihood or external reinterpretation, RS neutral-vector matching to semileptonic SMEFT operators, PDF/electroweak systematics, and EFT-validity/resonance-region logic.
Key references
PDG2025\_QuarkLeptonCompositeness;
ATLAS2020\_NonResonantDilepton;
CMS2021\_HighMassDilepton;
CMS2021\_HEPData\_CILimits;
FalkowskiGonzalezAlonsoMimouni2017\_SMEFT4F;
DawsonGiardinoIsmail2018\_DYSMEFT.