scholarly journals On measurement of photon polarization in radiative penguin B decays to baryons

2021 ◽  
Vol 81 (8) ◽  
Author(s):  
P. Pakhlov ◽  
T. Uglov
Keyword(s):  
Standard Model ◽  
Standard Model Prediction ◽  
Branching Fraction ◽  
New Physics ◽  
Photon Polarization ◽  
Left Handed ◽  
The Standard Model ◽  
Stringent Test ◽  
Model Independent ◽  
Near Future

AbstractA measurement of the photon polarization in radiative penguin B decays provides a test of the Standard Model and a probe for New Physics, that can lead to a deviation from the Standard Model prediction of left-handed photons in $$b\rightarrow s \gamma $$ b → s γ . We propose a new method to measure the photon polarization using the baryonic decay $$B^- \rightarrow \Lambda \bar{p} \gamma $$ B - → Λ p ¯ γ . The P-violating $$\Lambda $$ Λ -hyperon decay allows a measurement of the $$\Lambda $$ Λ helicity to be performed, which can be uniquely related to the photon polarization in a model-independent way. The $$B^- \rightarrow \Lambda \bar{p} \gamma $$ B - → Λ p ¯ γ decay was recently measured to have a large branching fraction providing a possibility to get meaningful results with the data already available at LHC and B-factory experiments. An increase of the B-meson sample at high luminosity LHC experiments and Belle II should provide a really stringent test by using this method already in the near future.

scholarly journals The role of mesons in muon g − 2

2019 ◽  
Vol 199 ◽  
pp. 01010 ◽  
Author(s):  
Fred Jegerlehner
Keyword(s):  
Standard Model ◽  
Standard Model Prediction ◽  
Meson Production ◽  
Form Factors ◽  
New Physics ◽  
Production Data ◽  
The Standard Model ◽  
Near Future ◽  
Deviation Effect

The muon anomaly aμ=(gμ-2)/2 showing a persisting 3 to 4 σ deviation between the SM prediction and the experiment is one of the most promising signals for physics beyond the SM. As is well known, the hadronic uncertainties are limiting the accuracy of the Standard Model prediction. Therefore a big effort is going on to improve the evaluations of hadronic effects in order to keep up with the 4-fold improved precision expected from the new Fermilab measurement in the near future. A novel complementary type experiment planned at J-PARC in Japan, operating with ultra cold muons, is expected to be able to achieve the same accuracy but with completely different systematics. So exciting times in searching for New Physics are under way. I discuss the role of meson physics in calculations of the hadronic part of the muon g-2. The improvement is expected to substantiate the present deviation $\Delta a_\mu ^{{\rm{New}}\,{\rm{physics}}} = \Delta a_\mu ^{{\rm{Experiment}}} - \Delta a_\mu ^{{\rm{Standard Model}}}$ to a 6 to 10 standard deviation effect, provided hadronic uncertainties can be reduce by a factor two. This concerns the hadronic vacuum polarization as well as the hadronic light-by-light scattering contributions, both to a large extent determined by the low lying meson spectrum. Better meson production data and progress in modeling meson form factors could greatly help to improve the precision and reliability of the SM prediction of aμ and thereby provide more information on what is missing in the SM.

scholarly journals Standard Model prediction of the Bc lifetime

2021 ◽  
Vol 2021 (7) ◽  
Author(s):  
Jason Aebischer ◽  
Benjamín Grinstein
Keyword(s):  
Standard Model ◽  
Model Prediction ◽  
Strange Quark ◽  
Standard Model Prediction ◽  
New Physics ◽  
Operator Product ◽  
Special Focus ◽  
Third Order ◽  
Clear Cut ◽  
The Standard Model

Abstract Applying an operator product expansion approach we update the Standard Model prediction of the Bc lifetime from over 20 years ago. The non-perturbative velocity expansion is carried out up to third order in the relative velocity of the heavy quarks. The scheme dependence is studied using three different mass schemes for the $$ \overline{b} $$ b ¯ and c quarks, resulting in three different values consistent with each other and with experiment. Special focus has been laid on renormalon cancellation in the computation. Uncertainties resulting from scale dependence, neglecting the strange quark mass, non-perturbative matrix elements and parametric uncertainties are discussed in detail. The resulting uncertainties are still rather large compared to the experimental ones, and therefore do not allow for clear-cut conclusions concerning New Physics effects in the Bc decay.

scholarly journals Disentangling QCD and new physics in D → πℓ+ℓ−

2021 ◽  
Vol 2021 (4) ◽  
Author(s):  
Aoife Bharucha ◽  
Diogo Boito ◽  
Cédric Méaux
Keyword(s):  
Standard Model ◽  
Branching Ratio ◽  
Branching Ratios ◽  
New Physics ◽  
Operator Product ◽  
Beyond The Standard Model ◽  
Spectral Functions ◽  
The Standard Model ◽  
Model Independent ◽  
Weak Annihilation

Abstract In this paper we consider the decay D+ → π+ℓ+ℓ−, addressing in particular the resonance contributions as well as the relatively large contributions from the weak annihilation diagrams. For the weak annihilation diagrams we include known results from QCD factorisation at low q2 and at high q2, adapting the existing calculation for B decays in the Operator Product Expansion. The hadronic resonance contributions are obtained through a dispersion relation, modelling the spectral functions as towers of Regge-like resonances in each channel, as suggested by Shifman, imposing the partonic behaviour in the deep Euclidean. The parameters of the model are extracted using e+e− → (hadrons) and τ → (hadrons) + ντ data as well as the branching ratios for the resonant decays D+ → π+R(R → ℓ+ℓ−), with R = ρ, ω, and ϕ. We perform a thorough error analysis, and present our results for the Standard Model differential branching ratio as a function of q2. Focusing then on the observables FH and AFB, we consider the sensitivity of this channel to effects of physics beyond the Standard Model, both in a model independent way and for the case of leptoquarks.

SEARCH FOR NEW PHYSICS IN eμX DATA AT THE TEVATRON USING SLEUTH: A QUASI-MODEL-INDEPENDENT SEARCH STRATEGY FOR NEW PHYSICS

2001 ◽  
Vol 16 (supp01b) ◽  
pp. 888-890
Author(s):  
◽  
BRUCE KNUTESON
Keyword(s):  
Standard Model ◽  
Search Strategy ◽  
New Physics ◽  
Beyond The Standard Model ◽  
Final States ◽  
Final State ◽  
The Standard Model ◽  
Model Independent

We present a quasi-model-independent search for physics beyond the standard model. We define final states to be studied, and construct a rule that identifies a set of variables appropriate for any particular final state. A new algorithm ("Sleuth") searches for regions of excess in the space of those variables and quantifies the significance of any detected excess. After demonstrating the sensititvity of the method, we apply it to the semi-inclusive channel eμX collected in ≈108 pb -1 of [Formula: see text] collisions at [Formula: see text] at the DØ experiment at the Fermilab Tevatron. We find no evidence of new high pT physics in this sample.

scholarly journals Searching for new physics in charm radiative decays

2018 ◽  
Vol 33 (32) ◽  
pp. 1850194
Author(s):  
Aritra Biswas ◽  
Sanjoy Mandal ◽  
Nita Sinha
Keyword(s):  
Standard Model ◽  
Branching Ratio ◽  
New Physics ◽  
Radiative Decays ◽  
Symmetric Model ◽  
Leading Order ◽  
Photon Polarization ◽  
Long Distance ◽  
The Standard Model ◽  
Distance Effects

We show that for a heavy vector-like quark model with a down type isosinglet, branching ratio for [Formula: see text] decay is enhanced by more than [Formula: see text] as compared to that in the Standard model when QCD corrections to next-to-leading order are incorporated. In a left–right symmetric model (LRSM) along with a heavy vector-like fermion, enhancement of this order can be achieved at the bare (QCD uncorrected) level itself. We propose that a measurement of the photon polarization could be used to signal the presence of such new physics in spite of the large long distance effects. We find that there is a large region within the allowed parameter space of the model with a vector-like quark and an additional left–right symmetry, where, the photon polarization can be dominantly right-handed.

scholarly journals Flavor physics: Precision as an avenue to discovery

2020 ◽  
Vol 35 (01) ◽  
pp. 1930018
Author(s):  
Diego Guadagnoli
Keyword(s):  
Cp Violation ◽  
Standard Model ◽  
Flavor Physics ◽  
Standard Model Prediction ◽  
New Physics ◽  
Effective Theory ◽  
Theory Approach ◽  
Long Distance ◽  
The Standard Model ◽  
The Impact

This paper describes the work pursued in the years 2008–2013 on improving the Standard Model prediction of selected flavor-physics observables. The latter includes: (1) [Formula: see text], that quantifies indirect CP violation in the [Formula: see text] system and (2) the very rare decay [Formula: see text], recently measured at the LHC. Concerning point (1), the paper describes our reappraisal of the long-distance contributions to [Formula: see text],[Formula: see text] that have permitted to unveil a potential tension between CP violation in the [Formula: see text]- and [Formula: see text]-system. Concerning point (2), the paper gives a detailed account of various systematic effects pointed out in Ref. 4 and affecting the Standard Model [Formula: see text] decay rate at the level of 10% — hence large enough to be potentially misinterpreted as nonstandard physics, if not properly included. The paper further describes the multifaceted importance of the [Formula: see text] decays as new physics probes, for instance how they compare with [Formula: see text]-peak observables at LEP, following the effective-theory approach of Ref. 5. Both cases (1) and (2) offer clear examples in which the pursuit of precision in Standard Model predictions offered potential avenues to discovery. Finally, this paper describes the impact of the above results on the literature, and what is the further progress to be expected on these and related observables.

scholarly journals Detailed study of the Λb → Λcτν̄τ decay

2018 ◽  
Vol 33 (29) ◽  
pp. 1850169 ◽  
Author(s):  
E. Di Salvo ◽  
F. Fontanelli ◽  
Z. J. Ajaltouni
Keyword(s):  
Standard Model ◽  
Semileptonic Decay ◽  
Form Factors ◽  
Higgs Doublet ◽  
New Physics ◽  
Beyond The Standard Model ◽  
Left Handed ◽  
The Standard Model ◽  
Analogous Formula ◽  
Two Higgs Doublet Model

We examine in detail the semileptonic decay [Formula: see text], which may confirm previous hints, from the analogous [Formula: see text] decay, of a new physics beyond the Standard Model. First of all, starting from rather general assumptions, we predict the partial width of the decay. Then we analyze the effects of five possible new physics interactions, adopting in each case five different form factors. In particular, for each term beyond the Standard Model, we find some constraints on the strength and phase of the coupling, which we combine with those found by other authors in analyzing the analogous semileptonic decays of [Formula: see text]. Our analysis involves some dimensionless quantities, substantially independent of the form factor, but which, owing to the constraints, turn out to be strongly sensitive to the kind of nonstandard interaction. We also introduce a criterion thanks to which one can discriminate among the various new physics terms: the left-handed current and the two-Higgs-doublet model appear privileged, with a neat preference for the former interaction. Finally, we suggest a differential observable that could, in principle, help to distinguish between the two cases.

scholarly journals Long-lived heavy neutral leptons at the LHC: four-fermion single-NR operators

2022 ◽  
Vol 2022 (1) ◽  
Author(s):  
Rebeca Beltrán ◽  
Giovanna Cottin ◽  
Juan Carlos Helo ◽  
Martin Hirsch ◽  
Arsenii Titov ◽  
...  
Keyword(s):  
Field Theory ◽  
Standard Model ◽  
Effective Field Theory ◽  
New Physics ◽  
Effective Field ◽  
High Luminosity ◽  
The Past ◽  
The Standard Model ◽  
Model Independent

Abstract Interest in searches for heavy neutral leptons (HNLs) at the LHC has increased considerably in the past few years. In the minimal scenario, HNLs are produced and decay via their mixing with active neutrinos in the Standard Model (SM) spectrum. However, many SM extensions with HNLs have been discussed in the literature, which sometimes change expectations for LHC sensitivities drastically. In the NRSMEFT, one extends the SM effective field theory with operators including SM singlet fermions, which allows to study HNL phenomenology in a “model independent” way. In this paper, we study the sensitivity of ATLAS to HNLs in the NRSMEFT for four-fermion operators with a single HNL. These operators might dominate both production and decay of HNLs, and we find that new physics scales in excess of 20 TeV could be probed at the high-luminosity LHC.

scholarly journals Search for single production of vectorlike top partners through th channel at the HE-LHC and FCC-hh

2021 ◽  
Vol 81 (7) ◽  
Author(s):  
Xi-Yan Tian ◽  
Liu-Feng Du ◽  
Yao-Bei Liu
Keyword(s):  
Standard Model ◽  
Production Cross ◽  
Branching Fraction ◽  
Hadron Collider ◽  
High Energy ◽  
New Physics ◽  
Beyond The Standard Model ◽  
The Standard Model ◽  
Single Production ◽  
Integrated Luminosity

AbstractThe vectorlike top partners are potential signature of some new physics beyond the Standard Model at the TeV scale. In this paper, we propose to search for the vectorlike T quark with charge 2/3 in the framework of a simplified model where the top partners only couples with the third generation of Standard Model quarks. We investigate the observability for electroweak production of a vectorlike T quark in association with a standard model bottom quark through the process $$pp \rightarrow T\bar{b}j$$ p p → T b ¯ j with the subsequent decay mode of $$T\rightarrow t(\rightarrow b W^+\rightarrow b \ell ^{+} \nu _{\ell })h( \rightarrow \gamma \gamma )$$ T → t ( → b W + → b ℓ + ν ℓ ) h ( → γ γ ) , at the proposed High Energy Large Hadron Collider (HE-LHC) and Future Circular Collider in hadron-hadron mode (FCC-hh) including the realistic detector effects. The 95% confidence level excluded regions and the $$5\sigma $$ 5 σ discovery reach in the parameter plane of $$\kappa _{T}-m_T$$ κ T - m T , are respectively obtained at the HE-LHC with the integrated luminosity of 15 ab$$^{-1}$$ - 1 and the FCC-hh with the integrated luminosity of 30 ab$$^{-1}$$ - 1 . We also analyze the projected sensitivity in terms of the production cross section times branching fraction at the HE-LHC and FCC-hh.

scholarly journals Presymmetry in the Standard Model with adulterated Dirac neutrinos

2015 ◽  
Vol 30 (31) ◽  
pp. 1550160 ◽  
Author(s):  
Ernesto A. Matute
Keyword(s):  
Standard Model ◽  
High Energy ◽  
New Physics ◽  
Boson Mass ◽  
Effective Theory ◽  
Type I ◽  
Electroweak Symmetry ◽  
Seesaw Mechanism ◽  
Left Handed ◽  
The Standard Model

Recently we proposed a model for light Dirac neutrinos in which two right-handed (RH) neutrinos per generation are added to the particles of the Standard Model (SM), implemented with the symmetry of fermionic contents. The ordinary one is decoupled via the high scale type-I seesaw mechanism, while the extra pairs off with its left-handed (LH) partner. The symmetry of lepton and quark contents was merely used as a guideline to the choice of parameters because it is not a proper symmetry. Here we argue that the underlying symmetry to take for this correspondence is presymmetry, the hidden electroweak symmetry of the SM extended with RH neutrinos defined by transformations which exchange lepton and quark bare states with the same electroweak charges and no Majorana mass terms in the underlying Lagrangian. It gives a topological character to fractional charges, relates the number of families to the number of quark colors, and now guarantees the great disparity between the couplings of the two RH neutrinos. Thus, Dirac neutrinos with extremely small masses appear as natural predictions of presymmetry, satisfying the ’t Hooft’s naturalness conditions in the extended seesaw where the extra RH neutrinos serve to adulterate the mass properties in the low scale effective theory, which retains without extensions the gauge and Higgs sectors of the SM. However, the high energy threshold for the seesaw implies new physics to stabilize the quantum corrections to the Higgs boson mass in agreement with the naturalness requirement.

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