In a supersymmetry scenario with R-parity violation (RPV), neutralinos with GeV-scale mass, which are necessarily bino-like, are allowed by all constraints and can be produced in association with a baryon in $\textit{B}$-meson decays via certain $$ \overline{U}\overline{D}\overline{D} $$ operators. In this work, we investigate this scenario with two non-vanishing RPV couplings at the low-energy scale. With one RPV coupling governing the neutralino production rate and another determining its lifetime, this scenario can lead to observable signals with displaced-vertex signatures in the tracking volume of $\textit{B}$-factories. To maximize the sensitivity to such signals, we develop a new partial-reconstruction technique that yields high efficiency and utilizes most of the decays of relatively heavy, long-lived particles, achieving much better sensitivity than standard full reconstruction. We consider potential background sources and devise selection criteria to suppress their event yields to very low levels. Using a parameterized model of the detector, we estimate in detail the displaced-vertex reconstruction efficiency as a function of neutralino lifetime and mass. For squark masses beyond the LHC limits, we calculate the signal sensitivity of Belle II, showing that the experiment can probe the RPV couplings well beyond the present bounds, obtained from searches for dinucleon decays, baryon-antibaryon oscillations, and $\textit{B}$ → $\textit{p}$ + missing.

Israel

Emilie Bertholet

Chile

Claudio Dib

Sara Gandelman

Juan Helo

Germany

Valery Lyubovitskij

India

Minakshi Nayak

Nicolás Neill

Abner Soffer

China

Zeren Wang

Searching for long-lived light neutralinos from $\textit{B}$-meson decays with baryonic R-parity violation at Belle II

We study light neutralinos $$ \left({\overset{\sim }{\chi}}_1^0\right) $$ with masses ranging from 10 GeV to several hundred GeV within the framework of R-parity-violating (RPV) supersymmetry. These light neutralinos can be long-lived, decaying with a macroscopic displacement (order cm) inside the LHC main detectors. Complementing previous works on the subject, here we focus on their production through the electroweak pair production of left-chiral sleptons $$ \left({\tilde{e}}_L\right) $$ , with the signal process $\textit{pp}$ → $$ {\tilde{e}}_L^{+}{\tilde{e}}_L^{-} $$ → $$ {e}^{+}{\overset{\sim }{\chi}}_1^0{e}^{-}{\overset{\sim }{\chi}}_1^0 $$ . In contrast to the previous study with a singly produced slepton, where the RPV coupling $$ {\lambda}_{111}^{\prime } $$ induces $\textit{both}$ the production and decay of the light neutralino, in our scenario the production proceeds through Drell-Yan-like processes that are essentially independent of RPV couplings. Correspondingly, we implement a displaced-vertex search strategy for which our numerical analysis shows that the high-luminosity LHC can probe $$ {\lambda}_{111}^{\prime } $$ values up to three orders of magnitude smaller, and neutralino masses up to about four times larger than those accessible in the previously studied single-slepton production scenario.

Giovanna Cottin

Fabián Hernández-Pinto

Probing light neutralinos from pair-produced sleptons with displaced vertices at the high-luminosity LHC

Neutrino masses and dark matter (DM) might have a common origin. The $\textit{scotogenic}$ model can be considered the proto-type model realizing this idea, but many other variants exist. In this paper we explore the phenomemology of a particular DM neutrino mass model, containing a triplet scalar. We calculate the relic density and check for constraints from direct detection experiments. The parameter space of the model, allowed by these constraints, contains typically a long-lived or quasi-stable doubly charged scalar, that can be searched for at the LHC. We reinterpret existing searches to derive limits on the masses of the scalars of the model and estimate future sensitivities in the high-luminosity phase of the LHC. The searches we discuss can serve to constrain also many other 1-loop neutrino mass models.

Carolina Arbeláez

Spain

Martin Hirsch

Téssio Melo

Long-lived particle phenomenology in one-loop neutrino mass models with dark matter

Taiwan

Erratum to: Searching for light neutralinos with a displaced vertex at the LHC

We propose a search for B meson decays to a baryon plus missing energy at the Belle II experiment to probe supersymmetry with a GeV-scale lightest neutralino   <math> <msubsup> <mover> <mi>χ</mi> <mo>~</mo> </mover> <mn>1</mn> <mn>0</mn> </msubsup> </math>  $$ {\overset{\sim }{\chi}}_1^0 $$  and R-parity violation (RPV). We perform analytic computations of the signal branching fractions in the framework of effective field theory, with a single nonzero RPV operator   <math> <msubsup> <mi>λ</mi> <mrow> <mi>ij</mi> <mn>3</mn> </mrow> <mrow> <mo>′</mo> <mo>′</mo> </mrow> </msubsup> <msubsup> <mover> <mi>U</mi> <mo>¯</mo> </mover> <mi>i</mi> <mi>c</mi> </msubsup> <msubsup> <mover> <mi>D</mi> <mo>¯</mo> </mover> <mi>j</mi> <mi>c</mi> </msubsup> <msubsup> <mover> <mi>D</mi> <mo>¯</mo> </mover> <mn>3</mn> <mi>c</mi> </msubsup> </math>  $$ {\lambda}_{ij3}^{\prime \prime }{\overline{U}}_i^c{\overline{D}}_j^c{\overline{D}}_3^c $$ , where i, j = 1, 2. The hadronic form factors are calculated using an SU(3) phenomenological Lagrangian approach for the proton, as well as several hyperons and charmed baryons. Since the decay of the neutralino is kinematically and CKM suppressed in this theoretical scenario, it decays outside the detector and appears experimentally only as missing energy. We detail the analysis techniques at the experimental level and estimate the background in the   <math> <msup> <mi>B</mi> <mo>+</mo> </msup> <mo>→</mo> <mi>p</mi> <msubsup> <mover> <mi>χ</mi> <mo>~</mo> </mover> <mn>1</mn> <mn>0</mn> </msubsup> </math>  $$ {B}^{+}\to p{\overset{\sim }{\chi}}_1^0 $$  search using published results for   <math> <msup> <mi>B</mi> <mo>+</mo> </msup> <mo>→</mo> <msup> <mi>K</mi> <mo>+</mo> </msup> <mi>ν</mi> <mover> <mi>ν</mi> <mo>¯</mo> </mover> </math>  $$ {B}^{+}\to {K}^{+}\nu \overline{\nu} $$ . Our final sensitivity plots are shown for both   <math> <msubsup> <mi>λ</mi> <mn>113</mn> <mrow> <mo>′</mo> <mo>′</mo> </mrow> </msubsup> </math>  $$ {\lambda}_{113}^{\prime \prime } $$  versus the squark mass   <math> <msub> <mi>m</mi> <mover> <mi>q</mi> <mo>~</mo> </mover> </msub> </math>  $$ {m}_{\tilde{q}} $$  and   <math> <msubsup> <mi>λ</mi> <mn>113</mn> <mrow> <mo>′</mo> <mo>′</mo> </mrow> </msubsup> <mo>/</mo> <msubsup> <mi>m</mi> <mover> <mi>q</mi> <mo>~</mo> </mover> <mn>2</mn> </msubsup> </math>  $$ {\lambda}_{113}^{\prime \prime }/{m}_{\tilde{q}}^2 $$  versus the neutralino mass   <math> <msub> <mi>m</mi> <msubsup> <mover> <mi>χ</mi> <mo>~</mo> </mover> <mn>1</mn> <mn>0</mn> </msubsup> </msub> </math>  $$ {m}_{{\overset{\sim }{\chi}}_1^0} $$ . We find that the search at Belle II could probe   <math> <msubsup> <mi>λ</mi> <mn>113</mn> <mrow> <mo>′</mo> <mo>′</mo> </mrow> </msubsup> <mo>/</mo> <msubsup> <mi>m</mi> <mover> <mi>q</mi> <mo>~</mo> </mover> <mn>2</mn> </msubsup> </math>  $$ {\lambda}_{113}^{\prime \prime }/{m}_{\tilde{q}}^2 $$  down to the order of 10 −8 GeV −2 in the kinematically allowed   <math> <msub> <mi>m</mi> <msubsup> <mover> <mi>χ</mi> <mo>~</mo> </mover> <mn>1</mn> <mn>0</mn> </msubsup> </msub> </math>  $$ {m}_{{\overset{\sim }{\chi}}_1^0} $$  range. We also obtain current limits on   <math> <msubsup> <mi>λ</mi> <mn>123</mn> <mrow> <mo>′</mo> <mo>′</mo> </mrow> </msubsup> </math>  $$ {\lambda}_{123}^{\prime \prime } $$  by recasting an existing search interpreted as   <math> <msup> <mi>B</mi> <mn>0</mn> </msup> <mo>→</mo> <msup> <mi>Λ</mi> <mn>0</mn> </msup> <msubsup> <mover> <mi>χ</mi> <mo>~</mo> </mover> <mn>1</mn> <mn>0</mn> </msubsup> </math>  $$ {B}^0\to {\Lambda}^0{\overset{\sim }{\chi}}_1^0 $$ , and comment about searches for   <math> <msup> <mi>B</mi> <mo>+</mo> </msup> <mo>→</mo> <msup> <mi>Σ</mi> <mo>+</mo> </msup> <msubsup> <mover> <mi>χ</mi> <mo>~</mo> </mover> <mn>1</mn> <mn>0</mn> </msubsup> </math>  $$ {B}^{+}\to {\Sigma}^{+}{\overset{\sim }{\chi}}_1^0 $$ ,   <math> <msup> <mi>B</mi> <mn>0</mn> </msup> <mo>→</mo> <msup> <mi>Σ</mi> <mn>0</mn> </msup> <msubsup> <mi>χ</mi> <mn>1</mn> <mn>0</mn> </msubsup> </math>  $$ {B}^0\to {\Sigma}^0{\chi}_1^0 $$ ,   <math> <msup> <mi>B</mi> <mo>+</mo> </msup> <mo>→</mo> <msubsup> <mi>Λ</mi> <mi>c</mi> <mo>+</mo> </msubsup> <msubsup> <mover> <mi>χ</mi> <mo>~</mo> </mover> <mn>1</mn> <mn>0</mn> </msubsup> </math>  $$ {B}^{+}\to {\Lambda}_c^{+}{\overset{\sim }{\chi}}_1^0 $$ , and   <math> <msup> <mi>B</mi> <mo>+</mo> </msup> <mo>→</mo> <msubsup> <mi>Ξ</mi> <mi>c</mi> <mo>+</mo> </msubsup> <msubsup> <mover> <mi>χ</mi> <mo>~</mo> </mover> <mn>1</mn> <mn>0</mn> </msubsup> </math>  $$ {B}^{+}\to {\Xi}_c^{+}{\overset{\sim }{\chi}}_1^0 $$ . In closing, we briefly discuss potential searches at the LHCb and BESIII experiments.

Probing R-parity violation in B-meson decays to a baryon and a light neutralino

We study the LHC discovery potential in the search for heavy neutral leptons (HNL) with a new signature: a displaced shower in the CMS muon detector, giving rise to a large cluster of hits forming a displaced shower. A new Delphes module is used to model the CMS detector response for such displaced decays. We reinterpret a dedicated CMS search for neutral long-lived particles decaying in the CMS muon endcap detectors for the minimal HNL scenario. We demonstrate that this new strategy is particularly sensitive to active-sterile mixings with τ leptons, due to hadronic τ decays. HNL masses between ~ 1–6 GeV can be accessed for mixings as low as |V  τN |2~10−7, probing unique regions of parameter space in the τ sector.

United States

Cristián Peña

Christina Wang

Si Xie

Long-lived heavy neutral leptons with a displaced shower signature at CMS

In the framework of the low-energy effective field theory of the Standard Model extended with heavy neutral leptons (HNLs), we calculate the production rates of HNLs from meson decays triggered by dimension-six operators. We consider both lepton-number-conserving and lepton-number-violating four-fermion operators involving either a pair of HNLs or a single HNL. Assuming that HNLs are long-lived, we perform simulations and investigate the reach of the proposed far detectors at the high-luminosity LHC to (i) active-heavy neutrino mixing and (ii) the Wilson coefficients associated with the effective operators, for HNL masses below the mass of the B-meson. We further convert the latter to the associated new-physics scales. Our results show that scales in excess of hundreds of TeV and the active-heavy mixing squared as small as 10 −15 can be probed by these experiments.

Rebeca Beltrán

Arsenii Titov

Long-lived heavy neutral leptons from mesons in effective field theory

We study a bino-like light neutralino (  <math> <msubsup> <mover> <mi>χ</mi> <mo>~</mo> </mover> <mn>1</mn> <mn>0</mn> </msubsup> </math>  $$ {\overset{\sim }{\chi}}_1^0 $$ ) produced at the LHC from the decay of a scalar lepton (  <math> <msub> <mover> <mi>e</mi> <mo>~</mo> </mover> <mi>L</mi> </msub> </math>  $$ \tilde{e}_L $$ ) through the process pp →   <math> <msub> <mover> <mi>e</mi> <mo>~</mo> </mover> <mi>L</mi> </msub> </math>  $$ \tilde{e}_L $$  →   <math> <mi>e</mi> <msubsup> <mover> <mi>χ</mi> <mo>~</mo> </mover> <mn>1</mn> <mn>0</mn> </msubsup> </math>  $$ e{\overset{\sim }{\chi}}_1^0 $$  in the context of R-parity-violating (RPV) supersymmetry where   <math> <msubsup> <mover> <mi>χ</mi> <mo>~</mo> </mover> <mn>1</mn> <mn>0</mn> </msubsup> </math>  $$ {\overset{\sim }{\chi}}_1^0 $$  is the lightest supersymmetric particle. For small masses and RPV couplings, the neutralino is naturally long-lived and its decay products can be identified as displaced tracks. Following existing searches, we propose a displaced-vertex search strategy for such a light neutralino with a single RPV coupling switched on,   <math> <msubsup> <mi>λ</mi> <mn>111</mn> <mo>′</mo> </msubsup> </math>  $$ {\lambda}_{111}^{\prime } $$ , in the mass range 10 GeV ≲   <math> <msub> <mi>m</mi> <msubsup> <mover> <mi>χ</mi> <mo>~</mo> </mover> <mn>1</mn> <mn>0</mn> </msubsup> </msub> </math>  $$ {m}_{{\overset{\sim }{\chi}}_1^0} $$  ≲ 230 GeV. We perform Monte Carlo simulations and conclude that at the high-luminosity LHC, the proposed search can probe values of   <math> <msubsup> <mi>λ</mi> <mn>111</mn> <mo>′</mo> </msubsup> </math>  $$ {\lambda}_{111}^{\prime } $$  down to two orders of magnitude smaller than current bounds and up to 40 times smaller than projected limits from monolepton searches.

Searching for light neutralinos with a displaced vertex at the LHC

It is well-known that at tree-level the d = 5 Weinberg operator can be generated in exactly three different ways, the famous seesaw models. In this paper we study the related question of how many phenomenologically consistent 1-loop models one can construct at d=5. First, we discuss that there are two possible classes of 1-loop neutrino mass models, that allow avoiding stable charged relics: (i) models with dark matter candidates and (ii) models with “exits”. Here, we define “exits” as particles that can decay into standard model fields. Considering 1-loop models with new scalars and fermions, we find in the dark matter class a total of (115+203) models, while in the exit class we find (38+368) models. Here, 115 is the number of DM models, which require a stabilizing symmetry, while 203 is the number of models which contain a dark matter candidate, which maybe accidentally stable. In the exit class the 38 refers to models, for which one (or two) of the internal particles in the loop is a SM field, while the 368 models contain only fields beyond the SM (BSM) in the neutrino mass diagram. We then study the RGE evolution of the gauge couplings in all our 1-loop models. Many of the models in our list lead to Landau poles in some gauge coupling at rather low energies and there is exactly one model which unifies the gauge couplings at energies above 1015 GeV in a numerically acceptable way.

Ricardo Cepedello

Sergey Kovalenko

How many 1-loop neutrino mass models are there?

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 N  R SMEFT, 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 N  R SMEFT 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.

Long-lived heavy neutral leptons at the LHC: four-fermion single-N  R  operators