Quick Hits

* The Sumerians had different number words and symbols to count numbers of different kinds of things. So, for example, the word for five pieces of fruit would be different than the word for five logs.

* Egyptian pyramids were built as trapezoids and then cut down to pyramids with the left over rock used to make new pyramids.

* Reputedly, Emperor Basil II of the Byzantine Empire was cruel.

* The Anglo-Saxons kept slaves in the middle ages.

* According to Gerald of Wales ca. 1316 CE, at that time the Irish were predominantly herders.

* Harsh murder sentences for newborns killed or neglected in the throes of unattended child birth are still common today even though the death penalty is almost never sought now in these circumstances.

* The TYRP1 gene variant discovered in 2012, is the cause of blond hair in the Solomon Islands in Melanesia, which is a different gene than the one that causes blond hair in Europeans.

* Before 1480, India and Sri Lanka were nearly connected by a land bridge known as Adam’s Bridge.

* There were once oceans on Mars.

High-resolution orbital images of Mars' largest canyon reveal ancient river deltas, proving the Red Planet once held an ocean the size of Earth's Arctic.

New high-resolution imagery from the European Space Agency’s ExoMars Trace Gas Orbiter has provided the most definitive evidence to date that Mars was once a blue planet. Researchers at the University of Bern identified distinct fan-shaped sediment deposits in the southeast Coprates Chasma region, part of the massive Valles Marineris canyon system. These structures, remarkably similar to river deltas on Earth, all sit at a consistent elevation between 3,650 and 3,750 meters. This geological alignment points to one unmistakable conclusion: the presence of an ancient coastline where rivers once emptied into a vast, stable sea approximately 3.37 billion years ago.

While previous theories about Martian oceans relied on lower-resolution data, this study offers direct geomorphological proof of a shoreline. The findings suggest that a massive body of water, comparable in size to Earth’s Arctic Ocean, once covered the entirety of Mars’ northern hemisphere. Though today these ancient deltas are buried beneath wind-sculpted dust and dunes, their distinctive shapes remain preserved. This discovery drastically alters our view of Martian history; the existence of a planet-wide water cycle and a stable ocean suggests that the conditions necessary for life were not isolated occurrences but a global phenomenon.

Source: Argadestya, P., et al. "Geomorphological and sedimentological evidence of a coastline in Southeast Coprates Chasma." npj Space Exploration (2026).

* There are social octopi that build homes for themselves off the coast of Australia.

* This very little bugger ,who is part of this clade of animals (and more specifically this one) is kind of cute in a Disney monsters way. They are the most heat-tolerant complex animal known to science after tardigrades (or water bears), which are able to survive temperatures over 150 °C. They were discovered in 1980 off the Galapagos islands.

When they grow up, they look like this (the "fur" is a symbiotic species of bacteria):

* A photograph of the February 19, 2026 solar eclipse in Antarctica (not AI).

* Nature can be amazing (also not AI).

* In West Texas, ca. 4500 BCE, hunter-gatherers used non-returnable boomerang sticks for small game and atlatl to throw their carefully crafted spears further for big game.

A cache of ancient weapons, more than 6,000 years old, has been uncovered in a remote rock shelter in West Texas, offering one of the clearest pictures yet of early life in North America.

The discovery was made at the San Esteban rock shelter in the Big Bend region, an area known for its dry climate and rugged desert landscape. That dryness turned out to be a gift to archaeologists. Items that would normally rot away wood, leather bindings, plant fibers remained intact for thousands of years. Inside the shelter, researchers found a carefully stored hunting kit dating to around 4,500 B.C., including wooden spear shafts wrapped in leather, stone projectile points, and parts of atlatls, the spear-throwing tools that dramatically increased a hunter’s range and power.

An atlatl works like a lever, giving a thrown spear greater speed and force. With it, hunters could strike animals from distances that would otherwise be impossible with a simple hand throw. Tests and prior studies show these tools could send projectiles well over 100 feet with deadly accuracy. The craftsmanship seen in the newly uncovered pieces shows careful shaping, balance, and planning. These were not rough survival tools; they were refined hunting systems built by people who deeply understood their environment.

Researchers also identified curved wooden throwing weapons often described as straight or non-returning boomerangs. Unlike the returning boomerangs many people picture today, these were designed to fly straight and hit small game with strong impact. Their presence adds another layer to what appears to have been a well-organized toolkit, likely stored together for repeated use.

The San Esteban site has a long history of human occupation stretching back thousands of years. Findings from this latest excavation reinforce the idea that the Big Bend region was not a temporary stop for wandering groups but a place where people lived, adapted, and developed sophisticated survival strategies. The tools show planning, skill, and an ability to work with available materials in smart, efficient ways.

Archaeologists involved in the project say the discovery helps rewrite outdated ideas about early North American societies. These communities were not primitive in the way older textbooks sometimes suggested. They engineered effective hunting technology, understood animal behavior, and created tools built to last.

As research continues, scientists hope to learn more about how these weapons were used, how they were stored, and what they reveal about daily life 6,000 years ago. For now, the dry rock shelter in West Texas has delivered something rare: a direct, tangible connection to hunters who once stood in the same desert landscape, preparing their tools for the next expedition.

* Maize farmers in Peru’s Chincha Valley were fertilizing their crops with seabird poop as early as the year 1250 CE.

* According to this source:

Around 3,800 years ago, a magnitude-9.5 megaquake struck northern Chile's coast, creating the largest earthquake known in human history. The rupture extended roughly 620 miles along the fault line—longer than the devastating 1960 Valdivia earthquake—and generated tsunamis with waves reaching 66 feet that traveled 5,000 miles across the Pacific Ocean to New Zealand. Archaeologists discovered marine deposits, boulders, shells, and sea life displaced far inland in the Atacama Desert, along with toppled stone structures buried beneath tsunami sediment, all radiocarbon-dated to this single catastrophic event.

The disaster forced complete coastal abandonment. Communities that depended on the ocean for survival relocated inland, staying away from the coast for over 1,000 years—an extraordinary response that demonstrates the quake's devastating impact on human populations. Researchers now recognize this megathrust earthquake, caused when tectonic plates suddenly unlocked after building massive strain, as both the oldest discovered earthquake-tsunami disaster in the Southern Hemisphere and a critical warning for modern coastal populations across the Pacific.

* Every recorded earthquake worldwide, 2015 to 2025 (my source didn't cite a source).

 

Another Challenge To ΛCDM That Dispenses With Cosmological Inflation

I have no idea why it took almost two weeks from submission for this preprint to be released by arXiv.

Recent discoveries, e.g., by JWST and DESI, have elevated the level of tension with inflationary ΛCDM. For example, the empirical evidence now suggests that the standard model violates at least one of the energy conditions from general relativity, which were designed to ensure that systems have positive energy, attractive gravity and non-superluminal energy flows.  

In this Letter, we use a recently compiled Type Ia supernova sample to examine whether ΛCDM violates the energy conditions in the local Universe, and carry out model selection with its principal competitor, the Rh=ct universe. We derive model-independent constraints on the distance modulus based on the energy conditions and compare these with the Hubble diagram predicted by both ΛCDM and Rh=ct, using the Pantheon+ Type Ia supernova catalog. 

We find that ΛCDM violates the strong energy condition over the redshift range z⊂(0,2), whereas Rh=ct satisfies all four energy constraints. At the same time, Rh=ct is favored by these data over ΛCDM with a likelihood of ∼89.5% versus ∼10.5%. The Rh=ct model without inflation is strongly favored by the Type Ia supernova data over the currrent standard model, while simultaneously adhering to the general relativistic energy conditions at both high and low redshifts.

Namit Chandak, Fulvio Melia, Junjie Wei, "Model selection with the Pantheon+ Type Ia SN sample" arXiv:2602.15047 (February 5, 2026) (4 pages, accepted for publication in A&A Letters).

Grab Bag Physics Articles

It may be possible to increase the precision with which the top quark mass is measured by a factor of ten to an uncertainty of plus or minus 30 MeV at a next generation positron-electron collider.

Constraints from Big Bang Nucleosynthesis significantly constrain the possibility of heavy neutral leptons (i.e. basically heavy, sterile neutrinos), allowing for the possible parameter space to be constrained from both above and below, potentially making it possible to rule out these hypothetical particles entirely, and in the meantime, focusing the search for them.

The Big Picture In Astrophysics Research

It is more statistical than an analytic description of the most important scientific advances, but it is still a notable overview. Certainly, there is no room to dispute that there has been a surge in astrophysics papers.

Over the past few years, Astrophysics has experienced an unprecedented increase in research output, as is evident from the year-over-year increase in the number of research papers put onto the arXiv. As a result, keeping up with progress happening outside our respective sub-fields can be exhausting. While it is impossible to be informed on every single aspect of every sub-field, this paper aims to be the next best thing. 

We present a summary of statistics for every paper uploaded onto the Astrophysics arXiv over the past year - 2025. We analyse a host of metadata ranging from simple metrics like the number of pages and the most used keywords, as well as deeper, more interesting statistics like the distribution of journals to which papers are submitted, the most used telescopes, the most studied astrophysical objects including GW, GRB, FRB events, exoplanets and much more. We also indexed the authors' affiliations to put into context the global distribution of research and collaboration. 

Combining this data with the citation information of each paper allows us to understand how influential different papers have been on the progress of the field this year. Overall, these statistics highlight the general current state of the field, the hot topics people are working on and the different research communities across the globe and how they function. 

We also delve into the costs involved in publications and what it means for the community. We hope that this is helpful for both students and professionals alike to adapt their current trajectories to better benefit the field.

Rommulus Francis Lewis, Hetansh Shah, Amruth Alfred, "Astrophysics Wrapped 2025: Year-in-Review of Every Astrophysics arXiv Paper from 2025" arXiv:2602.12303 (February 11, 2026).

X17 News

The viable parameter space for the hypothetic X17 particle (with a mass of about 17 MeV) proposed to explain some unexpected nuclear physics is very nearly null.

In recent years, the ATOMKI collaboration has performed a series of measurements of excited nuclei, observing a resonant excess of electron-positron pairs at large opening angles compared to the Standard Model prediction. 

The excess has been hypothesized to be due to the production of a new spin-1 or spin-0 particle, X17, with a mass of about 17 MeV. 

Recently, the PADME experiment has reported an excess in the e+e− cross section at center-of-mass energies near 17 MeV, perhaps further hinting at the existence of a new state. Studies of the spin-1 case have hitherto focused on either vector or axial-vector couplings to quarks and leptons, whereas UV theories more naturally produce both vector and axial-vector i.e. chiral couplings, analogous to the Standard Model weak interactions. 

We consider the ATOMKI anomalies in the context of an X with chiral couplings to quarks and explore the parameter space that can explain the ATOMKI anomalies, contrasting them with experimental constraints. 

We find that it is possible to accommodate the reported ATOMKI signals. However, the 99% CL region is in tension with null results from searches for atomic parity violation and direct searches for new low mass physics coupled to electrons. This tension is found to be driven by the magnitude of the reported excess in the transition of 12C(17.23), which drives the best-fit region towards excluded couplings.

Max H. Fieg, Toni Mäkelä, Tim M.P. Tait, Miša Toman, "The X17 with Chiral Couplings" arXiv:2602.11263 (February 11, 2026).

A Provocative Emergent Gravity Theory

This essay argues that gravity emerges from the running of physical constants with energy scale (called the Renormalization Group flow), and that this viewpoint can guide us to a viable theory of quantum gravity. It explains why this approach is not ruled out by "no go" theorems in the quantum gravity field, and what the existing paradigm for trying to develop a theory of quantum gravity may ge futile.

It's only ten pages long and more readable than many papers on the topic, so give it a read.

In this essay and utilizing the holographic Renormalization Group (RG) flow, we demonstrate how the effective action of a non-gravitating quantum field theory in the ultraviolet (UV) develops an Einstein-Hilbert term in the infrared (IR). That is, gravity is induced by the RG flow. 

An inherent outcome of holography that plays a crucial role in our analysis is the RG flow of boundary conditions: the rigid Dirichlet conditions on the background metric in the UV become an admixture of Dirichlet and Neumann as we flow to the IR, thereby ``unfreezing'' the metric and transforming it from a non-dynamical background into a dynamical field. 

This mechanism, which is a conceptually new addition to the standard Wilsonian RG flow, also provides the mechanism to evade the Weinberg-Witten no-go theorem. 

Within the GR from RG picture outlined here, the search for a quantum theory of gravity by treating the metric as a fundamental field may be a hunt for a phantom -- akin to seeking the atomic structure of water by quantizing the equations of hydrodynamics.

M.M. Sheikh-Jabbari, V. Taghiloo, "GR from RG: Gravity Is Induced From Renormalization Group Flow In The Infrared" arXiv:2602.11806 (February 12, 2026) (Essay written for the Gravity Research Foundation 2026 Awards for Essays on Gravitation).

The S8 Tension

The parameter S(8) quantifies how homogeneous the entire Universe is in terms of matter density, with lower values being more homogeneous than larger values. At higher values, matter is more concentrated in clumps and webs of high matter density, while comparative cosmic voids are bigger and more deep. At lower values, the amount of matter in a volume of space doesn't vary as much across the universe.

S(8) appears to vary between the early-universe and late universe, even though in the paradigmatic ΛCDM model of cosmology, which has been battered by numerous contradictions with astronomy observations, this parameter should remain the same. This tension has also been parallel to the Hubble tension, causing many astrophysicists to suspect that  they have a common cause.

The S8 tension between the early-universe and late universe, however, may be substantially a function of systemic measurement errors, rather than a real phenomena, as a new review article observes.

The parameter S(8)≡σ(8)*(Ωm/0.3)^0.5 quantifies the amplitude of matter density fluctuations. A persistent discrepancy exists between early-universe CMB observations and late-universe probes. 

This review assesses the ``S8 tension'' against a new 2026 baseline: a unified ``Combined CMB'' framework incorporating Planck, ACT DR6, and SPT-3G. This combined analysis yields S(8) = 0.836 + 0.012 − 0.013, providing a higher central value and reduced uncertainties compared to Planck alone. 

Compiling measurements from 2019-2026, we reveal a striking bifurcation: 

DES Year 6 results exhibit a statistically significant tension of 2.4σ--2.7σ (DESY6), whereas KiDS Legacy results demonstrate statistical consistency at <1σ (Wright2025). 

We examine systematic origins of this dichotomy, including photometric redshift calibration, intrinsic alignment modeling, and shear measurement pipelines. We further contextualize these findings with cluster counts (where eROSITA favors high values while SPT favors low), galaxy-galaxy lensing, and redshift-space distortions. The heterogeneous landscape suggests survey-specific systematic effects contribute substantially to observed discrepancies, though new physics beyond ΛCDM cannot be excluded.

Ioannis Pantos, Leandros Perivolaropoulos, "Status of the S8 Tension: A 2026 Review of Probe Discrepancies" arXiv:2602.12238 (February 12, 2026).

The Amazon Is Older Than The Andes

 The fascinating deep history of the Amazon River.

Experimental Bounds On Baryon And Lepton Number Non-Conservation

Baryon number (B) conservation means that the number of quarks minus the number of anti-quarks in any interaction remains constant. Lepton number (L) conservation means that the number of leptons (electrons, muons, tau leptons, and neutrinos) minus the number of anti-leptons in any interaction remains constant.

The Standard Model separately conserves B and L in all interactions except sphaleron interactions, which have been never observed and are theoretically confined to extremely high energy scales and mass-energy densities, which the Large Hadron Collider (LHC) (the most powerful particle collider of all time), cannot reach.

The conservation of baryon number and lepton number is established remarkably robustly in experiments.

Some of the main experimental searches that have not detected B and L non-conservation are the searches for neutrinoless double beta decay, the search for tree-level flavor changing neutral currents, and the search for proton decay. These non-detections have ruled out or tightly constrained many theories in physics including Majorana neutrino mass and most of the simpler grand unified theories (GUTs), such as SU(5).

Baryon number (B) conservation underlies the apparent stability of ordinary matter by forbidding the decay of nucleons, while lepton number (L) conservation plays a central role in the structure of lepton interactions and the possible origin of neutrino mass. 

In the Standard Model, B and L are accidental global symmetries rather than imposed fundamental principles. However, they are expected to be violated in many extensions of the theory, including frameworks of unification and processes in the early Universe. 

This review summarizes the status of experimental tests of B and L conservation and discusses them within a unified framework for interpreting current and future searches across different processes and experimental approaches, outlining historical and theoretical motivation, key physical processes, as well as their broader connections and complementarity to other searches.

Volodymyr Takhistov, "Experimental Tests of Baryon and Lepton Number Conservation" arXiv:2602.09097 (February 9, 2026).

A Catalog Of WISP Theories

A new preprint has a catalog (with references) of beyond the Standard Model theories that are "Weakly Interacting Slim Particle" (WISP) theories. Wikipedia explains the concept, which the abstract and introduction fail to do:

In particle physics, the acronym WISP refers to a largely hypothetical weakly interacting sub-eV particle, or weakly interacting slender particle, or weakly interacting slim particle – low-mass particles which rarely interact with conventional particles.

The term is used to generally categorize a type of dark matter candidate, and is essentially synonymous with axion-like particle (ALP). WISPs are generally hypothetical particles.

WISPs are the low-mass counterpart of weakly interacting massive particles (WIMPs).

The goal of the project is as follows: 

The search for physics beyond the Standard Model (SM) has led to the proposal of a vast landscape of theoretical frameworks. Among them, the family of Weakly Interacting Slim Particles (WISPs) has emerged as a particularly rich and versatile class of candidates, capable of addressing open questions in cosmology, astrophysics and particle physics. 

These particles, ranging from axions and axion-like particles to hidden photons, scalars, pseudoscalars, sterile neutrinos and spin-2 particles, illustrate the growing diversity of ideas within the field.  

The WISPedia is motivated by the need for a unified and systematic reference that organises this rapidly expanding model space. While numerous reviews exist on specific Weakly Interacting Slim Particle (WISP) candidates or experimental searches, the goal of this work is different: to provide a concise, model-oriented encyclopedia that outlines the essential ingredients of each framework– its particle content, interactions and phenomenological role, while pointing the reader toward the original literature and key complementary resources. Rather than serving as an exhaustive review, the WISPedia aims to serve as a quick, structured gateway into the theory landscape of light, weakly coupled particles. It also provides some information on bounds for each of them in a succinct way.

It's top level categorization is by the spin (a.k.a. intrinsic angular momentum a.k.a. "J") and parity of each kind of the Beyond the Standard Model (BSM) particles. 

It also has a very cute table of contents that summarizes some of the high points of each model. It uses emojis to annotate it. This cute legend is what inspired me to make this post, even though, like any catalog of BSM theories, the vast majority of theories discussed don't reflect reality and are "garbage theories" (not in the sense of being technically unsound, but in the sense of being ill-motivated and improbable).

This list of models currently in the catalog, envisioned as a Wikipedia-like or Particle Data Group-like encyclopedia of BSM particle theories that fit the (ill-defined) WISP paradigm, is as follows:

MOND Better In Clusters Than Previously Believed

The discovery that there is more non-stellar ordinary mass in galaxies and galaxy clusters than previously known makes MOND perform better than than previously believed.

In the framework of Milgromian dynamics (MOND), galaxy clusters are known to exhibit a residual missing mass problem, with the baryonic mass falling short of the dynamical mass by about a factor of two. 

The baryon content of clusters is dominated by the intracluster medium (ICM), while the stellar contribution depends sensitively on the assumed stellar initial mass function (IMF). 

We re-evaluate the stellar and remnant masses in galaxy clusters by adopting the integrated galaxy-wide initial mass function (IGIMF) theory, which accounts for the dependence of the IMF on galaxy properties and star formation histories. Massive elliptical galaxies, characterized by high metallicities and short formation timescales, are inferred to form with top-heavy IMFs, leading to a substantial population of stellar remnants. 

Using observational data from WINGS and 2MASS for 46 nearby (z < 0.1) galaxy clusters, we compute stellar, remnant, and intracluster light masses and combine them with previously derived ICM masses. The resulting total baryonic masses are compared to MOND dynamical masses inferred from hydrostatic equilibrium. 

We find that the baryonic mass in stars, remnants and the ICM accounts for at least 88+5+2−4−1% of the MOND dynamical mass. This constrains the kick velocities of the remnants and substantially alleviates the missing mass problem for galaxy clusters in MOND.

Dong Zhang, Akram Hasani Zonoozi, Pavel Kroupa, "Revisiting the missing mass problem in MOND for nearby galaxy clusters" arXiv:2602.06082 (February 4, 2026) (accepted by PDR).

My name is Bond. Molecular Bond.

Ian Fleming*, "Molecular Orbitals and Organic Chemical Reactions" (2009).

*not the James Bond author.

The Physicists And Mr. Epstein

Not my usual fare, but it belongs here, from Matt Strassler's blog:

The Physicists and Mr. Epstein

Mr. Epstein was not only a world-class child abuser, he was a big fan of theoretical high-energy physics and of theoretical physicists. Some of my colleagues, unfortunately, got to know him. A number who were famous and/or had John Brockman as a book agent were even invited to a physics conference on Epstein's private island, well before he was first arrested.... 

More Evidence That The Standard Model Still Works

The ATLAS Paper

Once again, a search for beyond the Standard Model particles comes up empty and places strict limits on the parameter space of such particles. Also, the author list for this 27 page long paper is 17 pages long.

A model-independent search for low-mass resonances decaying into pairs of oppositely charged muons is presented. The analysis uses proton-proton collision data corresponding to an integrated luminosity of 140 fb−1, recorded by the ATLAS detector at the Large Hadron Collider between 2015 and 2018.

The search targets hypothetical dimuon resonances in the invariant mass range from 35 GeV to 75 GeV. The modelling of this mass region is particularly challenging for conventional analytic background parameterisations. To address this, a Gaussian process regression technique is used to model the background. 

The dimuon mass spectrum is analysed for potential signals, and no statistically significant excess is observed. Upper limits at the 95% confidence level are set on the fiducial production cross-section of new resonances decaying promptly into muons, ranging from 20 fb to 110 fb, depending on the resonance mass. These results are further interpreted in the context of dark-photon and dark-matter-mediator models, leading to new constraints on their parameter spaces.

ATLAS Collaboration, "Search for dimuon resonance in the 35 to 75 GeV mass range using 140 fb−1 of 13 TeV pp collisions with the ATLAS detector" arXiv:2601.21361 (February 2, 2026) (44 pages in total, author list starting page 27, 9 figures, 3 tables, submitted to JHEP).

The introduction to the body text of the paper notes that:

Searches for low-mass dimuon resonances have been performed by the CMS and LHCb Collaborations, covering mass ranges of 1.1–7.9 GeV, 11.5–75 GeV and 110–200 GeV for CMS, and 30.214–70 GeV for LHCb.

Those searches also came up empty. 

The trickiest mass range to study of those already studied is the 1.1-7.9 GeV mass range which has lots of different hadron resonances that decay in a great many different ways, with each decay having its own probably of occurring, generating substantial background noise, even though the backgrounds are well understood.

The range from 11.5-75 GeV has very little background noise, because it exceeds all but the heaviest hadron resonance masses (with most hadrons predicted to have masses above 11.5 GeV having never been definitively observed even in the numerous and extremely high energy collisions of the LHC), but it is comfortably less than the W boson mass (roughly 80.4 GeV), the Z boson mass (roughly 91.2 GeV), or the Standard Model Higgs boson mass (roughly 125.1 GeV).

In the 110-200 GeV mass range, the only significant backgrounds that can have dimuon decays are single Standard Model Higgs bosons (roughly 125.1 GeV), W boson pairs (roughly 160.8 GeV), and Z boson pairs (roughly 182.4 GeV). 

So, the total observations of dimuon resonances should have three very precisely predictable bumps and can often be confirmed to be background events because additional decay products in addition to the dimuons are observed. The decays of these background processes to particles other than dimuon pairs can also be used to calibrate the expected number of background dimuons for each of these three resonances.

For example, you can estimate the total Higgs boson production from the number of b quark pair decays that are observed by using that to determine how many dimuon decays from Higgs bosons should be expected, since the ratio of the b quark pair branching fraction of Higgs boson decays to the dimuon branching fraction of Higgs boson decays can be theoretically predicted to high precision. And, when you know how many background dimuon events you expect to see from Higgs boson decays, you can subtract that background from the observed number of dimuon events to determine if there is any beyond the Standard Model particle decay signal in the vicinity of the 125.1 GeV Higgs boson mass. 

You can do something similar for W boson pair decays and Z boson pair decays.

The 110-200 GeV mass range range is far more massive than any predicted Standard Model hadrons or any single W or Z boson, however. But, it is also far less than than the combined mass of a Higgs boson pair (roughly 250.2 GeV) or a top quark-antitop quark pair (which is roughly 345 GeV) or a Toponium meson (which is just a bit more massive that an unbound pair of oppositely charged top quarks).

Charged leptons, like those found in dimuon decays (which also only decay in turn to electrons quite slowly compared to other conceivable decay products with their roughly one microsecond mean lifetime, that turns out to be longer from an outside observer's perspective due to special relativity) are easy for the detectors at the LHC to see, so there are few false negatives. 

The rest mass of a dimuon pair is about 0.21 GeV, so even with an invariant mass of 1.1 GeV, the special relativistic kinetic energy of the dimuon pair is about four times its rest mass, so the pair of charged leptons will be traveling at very close to the speed of light, and the closer to the speed of light that the muons are traveling at is, the slower time passes in their rest frame relative to the rest frame of an outside observer. So, from the perspective of an outside observer, the dimuon pair takes much more than the microsecond of a muon at rest to decay.

Furthermore, a lot of false positive dimuon decays would be accompanied by additional detectible decay products that could distinguish those events from the pure dimuon decay signal that the experimenters were looking for in this paper and its companion papers over other invariant mass ranges.

So, these measurements can be quite precise, and can rule out even quite small beyond the Standard Model signals in these mass ranges.

The CMS Paper

In another recent paper, not only does the data on W boson pair production at the LHC confirm the Standard Model, it also strongly suggests that both the experimental and theoretical uncertainties are highly conservative estimates that greatly overstate the true uncertainty (something that is commonly seen in measurements of electroweak phenomena in high energy physics experiments). 

The first measurement is 0.08 sigma away from the predicted value, and the second is 0.10 sigma away from the predicted value. If a prediction and experiment were repeatedly conducted at random and had those uncertainties, the difference would average 1 sigma. So, the results are 10-12 times closer to each other than would be predicted by random chance given the stated uncertainties. It is very unlikely that this particular experiment is such a statistical fluke. 

This particularly unlikely given that this unexpected closeness between the experimentally measured value and the predicted value is seen in a large share of all high energy physics experiments involving electroweak phenomena but not the strong force, which prevents this seemingly fluke result being due to look elsewhere effects that would undermine their global statistical significance.

So, while the stated experimental uncertainties in the total production cross-section are on the order of ± 12%, the actual uncertainties are closer to being on the order of ± 1%. And, while the stated experimental uncertainties in the fiducial production cross-section are on the order of 20%, the actual uncertainties are closer to being on the order of ± 2%.

This analysis presents an observation of the photon-fusion production of W boson pairs using the CMS detector at the LHC. The total cross section of the W+W− production in photon fusion is measured using proton-proton collision data with an integrated luminosity of 138 fb−1 collected with the CMS detector in 2016−2018 at a center-of-mass energy of s√ = 13 TeV. Events are selected in the final state with one isolated electron and one isolated muon, and no additional tracks associated with the electron-muon production vertex. 

The total and fiducial production cross sections are 643 +82 −78 fb and 3.96 +0.53 −0.51 fb, respectively, in agreement with the standard model predictions of 631 ± 126 fb and 3.87 ± 0.77 fb. 

This agreement enables stringent constraints to be imposed on anomalous quartic gauge couplings within a dimension-8 effective field theory framework.

CMS Collaboration, "Measurement and effective field theory interpretation of the photon-fusion production cross section of a pair of W bosons in proton-proton collisions at s√ = 13 TeV" arXiv:2601.21574 (January 29, 2026).