More Like this

1. Heavy neutral leptons at the Electron-Ion Collider

   https://doi.org/10.1007/JHEP03(2023)020  

   Batell, Brian; Ghosh, Tathagata; Han, Tao; Xie, Keping (March 2023, Journal of High Energy Physics)

   A bstract The future Electron-Ion Collider (EIC) at Brookhaven National Laboratory, along with its primary capacity to elucidate the nuclear structure, will offer new opportunities to probe physics beyond the Standard Model coupled to the electroweak sector. Among the best motivated examples of such new physics are new heavy neutral leptons (HNLs), which are likely to play a key role in neutrino mass generation and lepton number violation. We study the capability of the EIC to search for HNLs, which can be produced in electron- proton collisions through charged current interactions as a consequence of their mixing with light neutrinos. We find that, with the EIC design energy and integrated luminosity, one is able to probe HNLs in the mass range of 1 – 100 GeV with mixing angles down to the order of 10 − 4 − 10 − 3 through the prompt decay signatures, and in the mass range of 1 10 GeV with | U e | 2 ~ 10 − 6 – 10 − 4 via the displaced decay signatures. We also consider the invisible mode where an HNL is undetected or decaying to dark sector particles. One could potentially probe heavy HNLs for mixing angles in the window 10 − 3 – 10 − 2 , provided SM background systematics can be brought under control. These searches are complementary to other probes of HNLs, such as neutrino-less double- β decay, meson decay, fixed-target, and high-energy collider experiments. 

   more » « less
2. Heavy Neutral Leptons via Axionlike Particles at Neutrino Facilities

   https://doi.org/10.1103/PhysRevLett.133.261802  

   Abdullahi, Asli M; de_Gouvêa, André; Dutta, Bhaskar; Shoemaker, Ian M; Tabrizi, Zahra (December 2024, Physical Review Letters)

   Heavy neutral leptons (HNLs) are often among the hypothetical ingredients behind nonzero neutrino masses. If sufficiently light, they can be produced and detected in fixed-target-like experiments. We show that if the HNLs belong to a richer—but rather generic—dark sector, their production mechanism can deviate dramatically from expectations associated with the standard-model weak interactions. In more detail, we postulate that the dark sector contains an axionlike particle (ALP) that naturally decays into HNLs. Since ALPs mix with the pseudoscalar hadrons, the HNL flux might be predominantly associated with the production of neutral mesons (e.g., ${\pi }^0$, $\eta$) as opposed to charge hadrons (e.g., ${\pi }^{\pm }$, $K^{\pm }$). In this case, the physics responsible for HNL production and decay are not directly related and experiments like DUNE might be sensitive to HNLs that are too weakly coupled to the standard model to be produced via weak interactions, as is generically the case of HNLs that play a direct role in the type-I seesaw mechanism. Published by the American Physical Society2024 

   more » « less
3. Heavy neutral leptons at beam dump experiments of future lepton colliders

   https://doi.org/10.1007/JHEP04(2023)046  

   Giffin, Pierce; Gori, Stefania; Tsai, Yu-Dai; Tuckler, Douglas (April 2023, Journal of High Energy Physics)

   A bstract A new beam dump experiment that utilizes the beam of future high energy electron-positron colliders could be an excellent avenue to search for dark sector particles due to its unprecedented high energy and intensity. We consider heavy neutral leptons (HNLs) as a specific example to demonstrate the sensitivity of searches for dark sector particles at future electron-positron collider beam dump experiments. This includes the study of the reach at the International Linear Collider (ILC), the Cool Copper Collider (C 3 ), and the Compact Linear Collider (CLIC). We comprehensively examine the HNL production and detector acceptance at these electron beam dump experiments. We show that these experiments will probe regions of HNL parameter space, not yet probed by past experiments, as well as by future approved experiments. Our study also motivates a more detailed analysis of heavy meson productions in high-energy electron-nucleon collisions in thick targets. 

   more » « less
4. Search for long-lived heavy neutral leptons in proton-proton collision events with a lepton-jet pair associated with a secondary vertex at $$ \sqrt{s} $$ = 13 TeV

   https://doi.org/10.1007/JHEP02(2025)036  

   Hayrapetyan, A; Tumasyan, A; Adam, W; Andrejkovic, J W; Bergauer, T; Chatterjee, S; Damanakis, K; Dragicevic, M; Hussain, P S; Jeitler, M; et al (February 2025, Journal of High Energy Physics)

   A<sc>bstract</sc> A search for long-lived heavy neutral leptons (HNLs) using proton-proton collision data corresponding to an integrated luminosity of 138 fb⁻¹collected at$$ \sqrt{s} $$ $\sqrt{s}$= 13 TeV with the CMS detector at the CERN LHC is presented. Events are selected with a charged lepton originating from the primary vertex associated with the proton-proton interaction, as well as a second charged lepton and a hadronic jet associated with a secondary vertex that corresponds to the semileptonic decay of a long-lived HNL. No excess of events above the standard model expectation is observed. Exclusion limits at 95% confidence level are evaluated for HNLs that mix with electron and/or muon neutrinos. Limits are presented in the mass range of 1–16.5 GeV, with excluded square mixing parameter values reaching as low as 2 × 10⁻⁷. For masses above 11 GeV, the presented limits exceed all previous results in the semileptonic decay channel, and for some of the considered scenarios are the strongest to date. 

   more » « less
5. Search for long-lived heavy neutral leptons decaying in the CMS muon detectors in proton-proton collisions at $\sqrt{s}=13\mathrm{TeV}$

   https://doi.org/10.1103/PhysRevD.110.012004  

   Hayrapetyan, A; Tumasyan, A; Adam, W; Andrejkovic, J W; Bergauer, T; Chatterjee, S; Damanakis, K; Dragicevic, M; Hussain, P S; Jeitler, M; et al (July 2024, Physical Review D)

   A search for heavy neutral leptons (HNLs) decaying in the CMS muon system is presented. A data sample is used corresponding to an integrated luminosity of $138{\mathrm{fb}}^{-1}$of proton-proton collisions at $\sqrt{s}=13\mathrm{TeV}$, recorded at the CERN LHC in 2016–2018. Decay products of long-lived HNLs could interact with the shielding materials in the CMS muon system and create hadronic and electromagnetic showers detected in the muon chambers. This distinctive signature provides a unique handle to search for HNLs with masses below 4 GeV and proper decay lengths of the order of meters. The signature is sensitive to HNL couplings to all three generations of leptons. Candidate events are required to contain a prompt electron or muon originating from a vertex on the beam axis and a displaced shower in the muon chambers. No significant deviations from the standard model background expectation are observed. In the electron (muon) channel, the most stringent limits to date are set for HNLs in the mass range of 2.1–3.0 (1.9–3.3) GeV, reaching mixing matrix element squared values as low as $8.6\left(4.6\right)\times {10}^{-6}$. © 2024 CERN, for the CMS Collaboration2024CERN 

   more » « less