Lepton Flavor Violations In B Meson Decays Still Seen In Experimental Evidence (updated March 27, 2019)

This is probably the most important discrepancy between theory and experiment in fundamental physics at the moment. The pulls on the Wilson coefficients mentioned exceed five sigma (before any proper look elsewhere effect analysis). There are new theories to explain it, explored below, but not good ones.

B-decay discrepancies after Moriond 2019

Jason Aebischer, Wolfgang Altmannshofer, Diego Guadagnoli, Meril Reboud, Peter Stangl, David M. Straub

(Submitted on 25 Mar 2019)

Following the updated measurement of the lepton flavour universality (LFU) ratio R_K in B -> Kll decays by LHCb, as well as a number of further measurements, e.g. R_K* by Belle and B_s -> mu mu by ATLAS, we analyse the global status of new physics in b -> s transitions in the weak effective theory at the b-quark scale, in the Standard Model effective theory at the electroweak scale, and in simplified models of new physics. 

We find that the data continues to strongly prefer a solution with new physics in semi-leptonic Wilson coefficients. A purely muonic contribution to the combination C_9 = -C_10, well suited to UV-complete interpretations, is now favoured with respect to a muonic contribution to C_9 only. An even better fit is obtained by allowing an additional LFU shift in C_9. Such a shift can be renormalization-group induced from four-fermion operators above the electroweak scale, in particular from semi-tauonic operators, able to account for the potential discrepancies in b -> c transitions. This scenario is naturally realized in the simplified U_1 leptoquark model. We also analyse simplified models where a LFU effect in b -> sll is induced radiatively from four-quark operators and show that such a setup is on the brink of exclusion by LHC di-jet resonance searches.

Comments:	35 pages, 18 figures, 2 tables
Subjects:	High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Experiment (hep-ex)
Cite as:	arXiv:1903.10434 [hep-ph]

From the body text:

Conclusions  

Motivated by the updated measurements of the theoretically clean lepton flavour universality tests RK and RK∗ by the LHCb and Belle experiments, as well as by additional measurements, notably of Bs → µµ by the ATLAS collaboration, we have updated the global EFT analysis of new physics in b → s`` transitions. A new-physics effect in the semi-muonic Wilson coefficient C bsµµ 9 continues to give a much improved fit to the data compared to the SM. However, compared to previous global analyses, we find that there is now also a preference for a non-zero value of the semi-muonic Wilson coefficient C bsµµ 10 , mostly driven by the global combination of the Bs → µ +µ − branching ratio including the ATLAS measurement. The single-coefficient scenario giving the best fit to the data is the one where C bsµµ 9 = −C bsµµ 10 , which is known to be well suited to UV-complete interpretations, and indeed is predicted in several new-physics models with tree-level mediators coupling dominantly to left-handed fermions.  

We have also studied the possibility of a simultaneous interpretation of the b → s`` data and the discrepancies in b → cτν transitions in the framework of a global likelihood in SMEFT Wilson coefficient space. We find one especially compelling scenario, characterised by new physics in all-left-handed semitauonic four-fermion operators. These operators can explain directly the discrepancies in b → cτν transitions, and, at the same time, radiatively induce a lepton flavour universal contribution to the b → s`` Wilson coefficients. An additional nonzero semimuonic Wilson coefficient then allows accommodating the RK(∗) discrepancies. Such picture can be quantitatively realized in the context of the U1 leptoquark simplified model, and we find that indeed an excellent description of the data can be obtained, including the deviations in b → cτν transitions.  

Another logical possibility to generate a lepton flavour universal NP effect in C9 is via RG effects from a four-quark operator. We have investigated this possibility in the SMEFT and in simplified tree-level models. We find that the only potentially viable setup is a colour-octet scalar. Due to its TeV-scale mass and large coupling to quarks, it is strongly constrained by di-jet resonance searches at the LHC and can be tested in the near future. Our study illustrates how the theoretical picture has evolved as a consequence of crucial measurement updates, and how this picture stays coherent in spite of the numerous constraints. We collect in Table 2 a number of predictions directly related to the discussed SMEFT scenario. The situation will only get more exciting due to the host of new analyses using the full Run-2 data set, as well as the Belle-II data set, to which we look forward.  

Note added: After the completion of this work, new preliminary results on RD and RD∗ using semileptonic tags were presented by Belle [109]. The new results, that are slightly closer to the SM predictions compared to an average of previous Belle results, are not yet included in our analysis.

March 27, 2019 papers re lepton-flavor universality violation in 
B meson decays:

[arXiv:1903.10823 (cross-list from hep-ph) [pdf, ps, other]

Simultaneous explanation of K and B anomalies in vectorlike compositeness

Shinya Matsuzaki, Kenji Nishiwaki, Kei Yamamoto

Comments: 12 pages, 4 figures; Contribution to the Proceedings of the Corfu Summer Institute 2018 "School and Workshops on Elementary Particle Physics and Gravity" (CORFU2018), 31 August - 28 September, 2018, Corfu, Greece

Subjects: High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Experiment (hep-ex)

We address the presently reported significant flavor anomalies in the K and B meson systems such as the CP violating Kaon decay (ϵ′/ϵ) and lepton-flavor universality violation in B meson decays (RK(∗), and also commenting RD(∗)), by proposing flavorful and chiral vector bosons as the new physics constitution at ∼1TeV. Interestingly, if the new (composite) vector bosons are quite heavier than ∼1TeV, we face a difficulty in addressing the anomaly in ϵ′/ϵ consistently with the constraint from the K0-K0⎯⎯⎯⎯⎯⎯⎯ mixing. Both of the anomalies can be addressed within 1σ confidence levels individually, where the relevant parameter space will be investigated by the NA62 and KOTO experiments, in addition to direct searches at the large hadron collider.

arXiv:1903.10954 (cross-list from hep-ph) [pdf, other]

Rank-One Flavor Violation and B-meson anomalies

Valerio Gherardi, David Marzocca, Marco Nardecchia, Andrea Romanino

Comments: 28 pages, 8 figures, 7 tables

Subjects: High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Experiment (hep-ex)

We assume that the quark-flavor coefficients matrix of the semileptonic operators addressing the neutral-current B-meson anomalies has rank-one, i.e. it can be described by a single vector in quark-flavor space. By correlating the observed anomalies to other flavor and high-pT   observables, we constrain its possible directions and we show that a large region of the parameter space of this framework will be explored by flavor data from the NA62, LHCb and Belle II experiments. 

Implications for New Physics in b→sμμ transitions after recent measurements by Belle and LHCb

Kamila Kowalska, Dinesh Kumar, Enrico Maria Sessolo

(Submitted on 26 Mar 2019)

We present a Bayesian analysis of the implications for new physics in semileptonic b→s transitions after including new measurements of RK at LHCb and new determinations of RK∗ and RK∗+ at Belle. We perform global fits with 2, 4, and 8 input Wilson coefficients, plus one CKM nuisance parameter to take into account uncertainties that are not factorizable. We infer the 68% and 95.4% credibility regions of the marginalized posterior probability density for all scenarios and perform comparisons of models in pairs by calculating the Bayes factor given a common data set. We then proceed to analyzing a few well known BSM models that can provide a high energy framework for the EFT analysis. These include the exchange of a heavy Z′ boson in models with heavy vector-like fermions and a scalar field, and a model with scalar leptoquarks. We provide predictions for the BSM couplings and expected mass values.

Comments:	32 pages, 5 figures, 23 tables
Subjects:	High Energy Physics - Phenomenology (hep-ph)
Cite as:	arXiv:1903.10932 [hep-ph]
	(or arXiv:1903.10932v1 [hep-ph] for this version)

There is much less notable tension in the charm CP violation sector even though it is more than 4 sigma:

ΔACP within the Standard Model and beyond

Mikael Chala, Alexander Lenz, Aleksey V. Rusov, Jakub Scholtz

(Submitted on 25 Mar 2019)

In light of the recent LHCb observation of CP violation in the charm sector, we review standard model (SM) predictions in the charm sector and in particular for ΔACP. We get as an upper bound in the SM |ΔASMCP|≤3×10−4, which can be compared to the measurement of ΔALHCb2019CP=(−15.4±2.9)×10−4. 

We discuss resolving this tension within an extension of the SM that includes a flavour violating Z′ that couples only to s¯s and c¯u. We show that for masses below 80 GeV and flavour violating coupling of the order of 10−4, this model can successfully resolve the tension and avoid constraints from dijet searches, D0−D⎯⎯⎯⎯0 mixing and measurements of the Z width.

Comments:	11 pages, 1 table, 1 figure
Subjects:	High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Experiment (hep-ex)
Report number:	IPPP/19/25
Cite as:	arXiv:1903.10490 [hep-ph]
	(or arXiv:1903.10490v1 [hep-ph] for this version)

It is less significant because the predicted value is uncertain:

Implications on the first observation of charm CPV at LHCb

Hsiang-nan Li, Cai-Dian Lü, Fu-Sheng Yu

(Submitted on 26 Mar 2019)

Very recently, the LHCb Collaboration observed the CP violation (CPV) in the charm sector for the first time, with ΔAdirCP≡ACP(D0→K+K−)−ACP(D0→π+π−)=(−1.54±0.29)×10−3. This result is consistent with our prediction of ΔASMCP=(−0.57∼−1.87)×10−3 obtained in the factorization-assisted topological-amplitude (FAT) approach in [PRD86,036012(2012)]. It implies that the current understanding of the penguin dynamics in charm decays in the Standard Model is reasonable. Motivated by the success of the FAT approach, we further suggest to measure the D+→K+K−π+ decay, which is the next potential mode to reveal the CPV of the same order as 10−3.

Comments:	10 pages
Subjects:	High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Experiment (hep-ex)
Cite as:	arXiv:1903.10638 [hep-ph]
	(or arXiv:1903.10638v1 [hep-ph] for this version)

And there is a review of muon g-2 research:

The muon g−2: a brief overview of hadronic cross section data

Alexander Keshavarzi

(Submitted on 22 Mar 2019)

The hadronic vacuum polarisation contributions to the anomalous magnetic moment of the muon, ahad,VPμ are evaluated dispersively via a combination of experimentally measured e+e−→hadrons cross section data. Many experiments have dedicated programmes to precisely measure these final states, meaning that a vast amount of data is now available and that, in some cases, overall precision has reached the sub-percent level. However, data tensions are evident between measurements of the same hadronic channels from different experiments, which reduces the overall quality of the data combinations used to determine ahad,VPμ. The inclusion of these data in the KNT18 analysis results in ahad,LOVPμ=(693.26±2.46)×10−10 and ahad,NLOVPμ=(−9.82±0.04)×10−10. The corresponding new estimate for the Standard Model prediction is found to be aSMμ=(11 659 182.04±3.56)×10−10, which is 3.7σ below the current experimental measurement.

Comments:	The 9th International Workshop on Chiral Dynamics. arXiv admin note: text overlap with arXiv:1802.06229
Subjects:	High Energy Physics - Experiment (hep-ex); High Energy Physics - Phenomenology (hep-ph)
Cite as:	arXiv:1903.10349 [hep-ex]
	(or arXiv:1903.10349v1 [hep-ex] for this version) Single pseudoscalar meson pole and pion box contributions to the anomalous magnetic moment of the muon Gernot Eichmann, Christian S. Fischer, Esther Weil, Richard Williams (Submitted on 26 Mar 2019) We present results for single pseudoscalar meson pole contributions and pion box contributions to the hadronic light-by-light (LBL) correction of the muon's anomalous magnetic moment. We follow the recently developed dispersive approach to LBL, where these contributions are evaluated with intermediate mesons on-shell. However, the space-like electromagnetic and transition form factors are not determined from analytic continuation of time-like data, but directly calculated within the functional approach to QCD using Dyson-Schwinger and Bethe-Salpeter equations. This strategy allows for a systematic comparison with a strictly dispersive treatment and also with recent results from lattice QCD. Within error bars, we obtain excellent agreement for the pion electromagnetic and transition form factor and the resulting contributions to LBL. In addition, we present results for the η and η′pole contributions and discuss the dynamical effects in the η−η′ mixing due to the strange quarks. Our result for the total pseudoscalar pole contributions is aPS-poleμ=91.6(1.9)×10−11 and for the pion-box contribution we obtain aπ−boxμ=−16.6(1)(7)×10−11. Comments: 11 pages, 9 figures Subjects: High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Lattice (hep-lat) Cite as: arXiv:1903.10844 [hep-ph]   (or arXiv:1903.10844v1 [hep-ph] for this version)