Abstract
The standard model of particle physics currently provides our best description of fundamental particles and their interactions. The theory predicts that the different charged leptons, the ...electron, muon and tau, have identical electroweak interaction strengths. Previous measurements have shown that a wide range of particle decays are consistent with this principle of lepton universality. This article presents evidence for the breaking of lepton universality in beauty-quark decays, with a significance of 3.1 standard deviations, based on proton–proton collision data collected with the LHCb detector at CERN’s Large Hadron Collider. The measurements are of processes in which a beauty meson transforms into a strange meson with the emission of either an electron and a positron, or a muon and an antimuon. If confirmed by future measurements, this violation of lepton universality would imply physics beyond the standard model, such as a new fundamental interaction between quarks and leptons.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
We investigate all potentially viable scenarios that can produce the chiral enhancement required to simultaneously explain the (g − 2)e and (g − 2)u data with either a single scalar leptoquark or a ...pair of scalar leptoquarks. We provide a classification of these scenarios in terms of their ability to satisfy the existing limits on the branching ratio for the μ → eγ process. The simultaneous explanation of the (g − 2)e,μ discrepancies, coupled with the current experimental data, implies that the (g − 2)e loops are exclusively due to the charm-quark propagation, whereas the (g − 2)u loops are due to the top-quark propagation. The scenarios where the (g − 2)e loops are due to the top (bottom) quark propagation are, at best, approximately 9 (3) orders of magnitude away from the experimental limit on the μ → eγ branching ratio. All in all, there are only three particular scenarios that can pass the μ → eγ test and simultaneously create a large enough impact on the (g − 2)e,μ discrepancies when the new physics is based on the Standard Model fermion content. These are the S1, R2, and S1 & S3 scenarios, where the first two are already known to be phenomenologically viable candidates with respect to all other flavor and collider data constraints. We show that the third scenario-where the right-chiral couplings to charged leptons are due to S1, the leftchiral couplings to charged leptons are due to S3, and the two leptoquarks mix through the Standard Model Higgs field-cannot address the (g − 2)e and (g − 2)u discrepancies at the 1σ level due to an interplay between ..., and Z → μ+μ− data despite the ability of that scenario to avoid the μ → eγ limit. (ProQuest: ... denotes formula omitted.)
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FLAG Review 2021 Aoki, Y.; Blum, T.; Colangelo, G. ...
The European physical journal. C, Particles and fields,
10/2022, Volume:
82, Issue:
10
Journal Article
Peer reviewed
Open access
We review lattice results related to pion, kaon,
D
-meson,
B
-meson, and nucleon physics with the aim of making them easily accessible to the nuclear and particle physics communities. More ...specifically, we report on the determination of the light-quark masses, the form factor
f
+
(
0
)
arising in the semileptonic
K
→
π
transition at zero momentum transfer, as well as the decay constant ratio
f
K
/
f
π
and its consequences for the CKM matrix elements
V
us
and
V
ud
. Furthermore, we describe the results obtained on the lattice for some of the low-energy constants of
S
U
(
2
)
L
×
S
U
(
2
)
R
and
S
U
(
3
)
L
×
S
U
(
3
)
R
Chiral Perturbation Theory. We review the determination of the
B
K
parameter of neutral kaon mixing as well as the additional four
B
parameters that arise in theories of physics beyond the Standard Model. For the heavy-quark sector, we provide results for
m
c
and
m
b
as well as those for the decay constants, form factors, and mixing parameters of charmed and bottom mesons and baryons. These are the heavy-quark quantities most relevant for the determination of CKM matrix elements and the global CKM unitarity-triangle fit. We review the status of lattice determinations of the strong coupling constant
α
s
. We consider nucleon matrix elements, and review the determinations of the axial, scalar and tensor bilinears, both isovector and flavor diagonal. Finally, in this review we have added a new section reviewing determinations of scale-setting quantities.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We present a measurement of R_{K^{*}}, the branching fraction ratio B(B→K^{*}μ^{+}μ^{-})/B(B→K^{*}e^{+}e^{-}), for both charged and neutral B mesons. The ratio for the charged case R_{K^{*+}} is the ...first measurement ever performed. In addition, we report absolute branching fractions for the individual modes in bins of the squared dilepton invariant mass q^{2}. The analysis is based on a data sample of 711 fb^{-1}, containing 772×10^{6} BBover ¯ events, recorded at the ϒ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e^{+}e^{-} collider. The obtained results are consistent with standard model expectations.
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Bold ideas, daunting challenges Halpern, Paul
Science (American Association for the Advancement of Science),
12/2023, Volume:
382, Issue:
6674
Journal Article
Peer reviewed
A vibrant history traces the triumphs and missteps of quantum, nuclear, and particle physics
Abstract
Conventional, hadronic matter consists of baryons and mesons made of three quarks and a quark–antiquark pair, respectively
1,2
. Here, we report the observation of a hadronic state ...containing four quarks in the Large Hadron Collider beauty experiment. This so-called tetraquark contains two charm quarks, a
$$\overline{{{u}}}$$
u
¯
and a
$$\overline{{{d}}}$$
d
¯
quark. This exotic state has a mass of approximately 3,875 MeV and manifests as a narrow peak in the mass spectrum of
D
0
D
0
π
+
mesons just below the
D
*+
D
0
mass threshold. The near-threshold mass together with the narrow width reveals the resonance nature of the state.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
7.
FLAG Review 2019 Aoki, S; Aoki, Y; Bečirević, D ...
The European physical journal. C, Particles and fields,
02/2020, Volume:
80, Issue:
2
Journal Article
Peer reviewed
Open access
We review lattice results related to pion, kaon, D-meson, B-meson, and nucleon physics with the aim of making them easily accessible to the nuclear and particle physics communities. More ...specifically, we report on the determination of the light-quark masses, the form factor f+(0) arising in the semileptonic K→π transition at zero momentum transfer, as well as the decay constant ratio fK/fπ and its consequences for the CKM matrix elements Vus and Vud. Furthermore, we describe the results obtained on the lattice for some of the low-energy constants of SU(2)L×SU(2)R and SU(3)L×SU(3)R Chiral Perturbation Theory. We review the determination of the BK parameter of neutral kaon mixing as well as the additional four B parameters that arise in theories of physics beyond the Standard Model. For the heavy-quark sector, we provide results for mc and mb as well as those for D- and B-meson decay constants, form factors, and mixing parameters. These are the heavy-quark quantities most relevant for the determination of CKM matrix elements and the global CKM unitarity-triangle fit. We review the status of lattice determinations of the strong coupling constant αs. Finally, in this review we have added a new section reviewing results for nucleon matrix elements of the axial, scalar and tensor bilinears, both isovector and flavor diagonal.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The elliptic azimuthal anisotropy coefficient (v2) is measured for charm (D0) and strange (KS0, Λ, Ξ−, and Ω−) hadrons, using a data sample of p+Pb collisions collected by the CMS experiment, at a ...nucleon-nucleon center-of-mass energy of sNN=8.16 TeV. A significant positive v2 signal from long-range azimuthal correlations is observed for all particle species in high-multiplicity p+Pb collisions. The measurement represents the first observation of possible long-range collectivity for open heavy flavor hadrons in small systems. The results suggest that charm quarks have a smaller v2 than the lighter quarks, probably reflecting a weaker collective behavior. This effect is not seen in the larger PbPb collision system at sNN=5.02 TeV, also presented.
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A search for charge-parity (CP) violation in D^{0}→K^{-}K^{+} and D^{0}→π^{-}π^{+} decays is reported, using pp collision data corresponding to an integrated luminosity of 5.9 fb^{-1} collected at a ...center-of-mass energy of 13 TeV with the LHCb detector. The flavor of the charm meson is inferred from the charge of the pion in D^{*}(2010)^{+}→D^{0}π^{+} decays or from the charge of the muon in Bover ¯→D^{0}μ^{-}νover ¯_{μ}X decays. The difference between the CP asymmetries in D^{0}→K^{-}K^{+} and D^{0}→π^{-}π^{+} decays is measured to be ΔA_{CP}=-18.2±3.2(stat)±0.9(syst)×10^{-4} for π-tagged and ΔA_{CP}=-9±8(stat)±5(syst)×10^{-4} for μ-tagged D^{0} mesons. Combining these with previous LHCb results leads to ΔA_{CP}=(-15.4±2.9)×10^{-4}, where the uncertainty includes both statistical and systematic contributions. The measured value differs from zero by more than 5 standard deviations. This is the first observation of CP violation in the decay of charm hadrons.
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Muon g − 2 and Δα connection Keshavarzi, Alexander; Marciano, William J; Passera, Massimo ...
Physical review. D,
08/2020, Volume:
102, Issue:
3
Journal Article
Peer reviewed
The discrepancy between the Standard Model theory and experimental measurement of the muon magnetic moment anomaly, aμ = (gμ − 2)/2, is connected to precision electroweak (EW) predictions via their ...common dependence on hadronic vacuum polarization effects. The same data for the total e+e− → hadrons cross section, σhad(s), are used as input into dispersion relations to estimate the hadronic vacuum polarization contributions, aμhad,VP, as well as the five-flavor hadronic contribution to the running QED coupling at the Z -pole, Δα(5)had(M2Z), which enters natural relations and global EW fits. The EW fit prediction of Δα(5)had(M2Z) = 0.02722(41) agrees well with Δα(5)had(M2Z) = 0.02761 ( 11 ) obtained from the dispersion relation approach, but exhibits a smaller central value suggestive of a larger discrepancy Δaμ = aexpμ − aSMμ than currently expected. Postulating that the Δaμ difference may be due to unforeseen missing σhad(s) contributions, implications for MW, sin2 θlepeff and MH obtained from global EW fits are investigated. Shifts in σhad(s) needed to bridge Δaμ are found to be excluded above √s ≳ 0.7 GeV at the 95% C.L. Moreover, prospects for Δaμ originating below that energy are deemed improbable given the required increases in the hadronic cross section. Such hypothetical changes to the hadronic data are also found to affect other related observables, such as the electron anomaly, aSMe, the rescaled ratio Re/μ = (mμ/me)2 (aehad,LO VP / aμhad, LO VP), and the running of the weak mixing angle at low energies, although the consequences of these are currently less constraining.
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