The Top Quark Mass From ATLAS 13 TeV Data

A summary and review of ATLAS 13 TeV data at the Large Hadron Collider (LHC) from a talk presented at a recent conference, explains this direct measurement of the top quark mass from fully leptonic decays. It notes that: "this top-mass extraction turns out to be the most precise single measurement from the reconstruction of the top-decay products, i.e. m(t) = 174.41 ± 0.39 (stat.) ± 0.66 (syst.) ± 0.25 (recoil)." Combining all three sources of uncertainty in quadrature, this is 174.41 ± 0.81 GeV. The brief paper recaps an earlier disclosure of this measurement published on June 5, 2023.

This top quark mass is at the high end of recent top quark measurements. The Particle Data Group value is 172.57 ± 0.29 GeV (determined by inflating uncertainty estimates by a factor of 1.5 because they otherwise wouldn't all be reasonably consistent). But this result, which is included in the PDG world average, is still consistent with the world average as it is just 1.2 sigma above the PDG value.

This result is close to the Tevatron combined measurement from 2016 of 174.30 ± 0.64 GeV. But seven CMS experiment measurements (and one different ATLAS measurement from 2019) over the time period from 2016 to 2023 measure values ranging from 171.77 ± 0.37 GeV to 173.06 ± 0.84 GeV which drag down the world average.

A determination of the top quark pole mass from cross-section measurements is close to the world average from direct measurements and is competitive in precision. The world average top quark pole mass from cross-section measurements is 172.4 ± 0.7 GeV.

The inverse error average weighted average top quark mass from direct measurements and cross-section measurements combined (which is arguably more robust) is 172.52 GeV, with an uncertainty of a bit less than ± 0.29 GeV (probably something like ± 0.25 GeV).

I suspect that the true value is probably about 173 GeV.

The Common Cold Is Old

The common cold virus is much older than modern humans. 

The origins of viral pathogens and the age of their association with humans remains largely elusive. To date, there is no direct evidence about the diversity of viral infections in early modern humans pre-dating the Holocene. We recovered two near-complete genomes (5.2X and 0.7X) of human adenovirus C (HAdV-C), as well as low-coverage genomes from four distinct species of human herpesvirus obtained from two 31,630-year-old milk teeth excavated at Yana, in northeastern Siberia. 

Phylogenetic analysis of the two HAdV-C genomes suggests an evolutionary origin around 700,000 years ago consistent with a common evolutionary history with hominin hosts. 

Our findings push back the earliest direct molecular evidence for human viral infections by ∼25,000 years, and demonstrate that viral species causing common childhood viral infections today have been in circulation in humans at least since the Pleistocene.

From Sofie Holtsmark Nielsen, et al., "31,600-year-old human virus genomes support a Pleistocene origin for common childhood infections" bioRxiv (June 28, 2021).

A 7.9 Sigma Tension In Measuring V(cb) Of The CKM Matrix

In February 2020, a post at this blog reviewed the values of nine CKM matrix elements (which in turn can be derived from not more than four parameters, which are experimentally determined in the Standard Model).

The square of the absolute value of each element is equal to the probability of the transition described in the element to the second type of quark in the subscript taking place, given that a W+ boson has been emitted by a quark of the type of the first type of quark shown in the subscript.

One of those nine elements is V(cb) which has a global best fit value of:

(41.47 ± 0.70) *10^-3

Unitarity constraints (since the sum of the probabilities of all possible transitions from a single quark should equal 100%) suggest that V(cb) may be a bit high.

A new study, limited to fits to decays of neutral B mesons to a negatively charged vector D meson (D∗− (2010), which has as valence quarks an anti-charm quark and a d quark) together with a positively charged lepton (i.e. a positron, anti-muon, or anti-tau lepton) and a neutrino corresponding to it, using new methods, comes up with a lower value for element V(cb) at quite high precision. The result from this study is:

 (35.10 ± 0.41) * 10^-3.

This is a 7.9 sigma tension between this measurement and the global average which is a serious tension.

There could be a methodological error or an error in estimating the margin of error in the new measurement, but given the stark difference, this tension deserves further study.

[Submitted on 21 Aug 2020]

Revisiting fits to B0→D∗−ℓ+νℓ to measure |Vcb| with novel methods and preliminary LQCD data at non-zero recoil

Daniel Ferlewicz, Phillip Urquijo, Eiasha Waheed

We present a study of fits to exclusive B0→D∗−ℓ+νℓ measurements for the determination of the Cabbibo-Kobayashi-Maskawa matrix element magnitude |Vcb|, based on the most recent Belle untagged measurement. Results are obtained with the Caprini-Lellouch-Neubert (CLN) and Boyd-Grinstein-Lebed (BGL) form factor parameterisations, with and without the inclusion of preliminary Lattice QCD measurements of form factors at non-zero hadronic recoil from the JLQCD collaboration. The CLN and BGL fits are also studied in different scenarios with reduced theoretical assumptions, and at higher order expansions respectively. To avoid bias from high systematic uncertainty correlations we use a toy MC approach with a Cholesky decomposition of the covariance matrix. We find that (1)ηEW|Vcb|=(35.2±0.2±0.8)×10−3 for CLN and (34.9±0.3±1.0)×10−3 for BGL(1,0,2) without input from Lattice QCD. The errors quoted correspond to statistical and systematic uncertainties, respectively. We find no evidence to support lepton flavour dependence on the measurement of |Vcb| but find some tension in the results associated with the ratio of form factors R1. We show how input from JLQCD allows for well defined fit results with reduced model dependence in CLN and BGL. The results obtained using preliminary values are consistent between different orders of parameterisations, ultimately providing a method for a model-independent exclusive measurement of |Vcb|. Using preliminary inputs from the JLQCD collaboration, (1)ηEW|Vcb| is found to be approximately (35.1±0.07±0.4)×10−3 in BGL(2,2,2).

Hunter-gatherers 7kya had stronger bones

Hunter-gatherers from 7,000 years ago had stronger bones than farmers from 1,000 years ago, probably due to the amount of strength building exercise they had.

In other news: archaeological traces of H. Erectus tools from 1.2 mya have been found in Turkey.

Eurogenes meanwhile has a refined thee autosomal population model of West Eurasians that suggests that Near Eastern Neolithic individuals probably has less Western European Hunter-Gatherer admixture than the Early European Farmer component derived from ancient DNA in the leading model of the kind.