35 research outputs found
LSS Layout Optimizations for Low-beta Optics for the HL-LHC
The High Luminosity LHC (HL-LHC) project aims to upgrade the existing LHC to a peak luminosity of the order 10³⁵cm⁻²s^{−1}, while retaining as much of the nominal layout and hardware as possible. The current baseline for this upgrade is the use of the Achromatic Telescopic Squeeze (ATS) concept, which allows mini-Beta squeeze in IRs 1 and 5 (ATLAS and CMS respectively) far below that possible with nominal optics. However it is useful to both explore the parameter space of the ATS scheme while also attempting to push the boundaries of the nominal layout. This paper presents a study into maximising optical flexibility of the nominal LHC Long Straight Sections (LSSs) around IPs 1 and 5. This involves replacing, moving or adding magnets within the LSS to investigate feasibility of exploiting a more conventional optical scheme than the ATS scheme. In particular the option of replacing single LSS quadrupoles with doublets is explored. The study also looks at making similar changes to the LSS while also implementing the ATS scheme, to further explore the ATS parameter space with the benefit of experience gained into flexibility of a modified nominal LHC optical scheme
Search for dark photon decays to at NA62
International audienceThe NA62 experiment at CERN, designed to study the ultra-rare decay , has also collected data in beam-dump mode. In this configuration, dark photons may be produced by protons dumped on an absorber and reach a decay volume beginning 80 m downstream. A search for dark photons decaying in flight to pairs is reported, based on a sample of protons on dump collected in 2021. No evidence for a dark photon signal is observed. A region of the parameter space is excluded at 90% CL, improving on previous experimental limits for dark photon masses between 215 and 550 MeV
Search for leptonic decays of the dark photon at NA62
International audienceThe NA62 experiment at CERN, configured in beam-dump mode, has searched for dark photon decays in flight to electron-positron pairs using a sample of protons on dump collected in 2021. No evidence for a dark photon signal is observed. The combined result for dark photon searches in lepton-antilepton final states is presented and a region of the parameter space is excluded at 90% CL, improving on previous experimental limits for dark photon mass values between 50 and 600 MeV and coupling values in the range to . An interpretation of the search result in terms of the emission and decay of an axion-like particle is also presented
Search for leptonic decays of the dark photon at NA62
International audienceThe NA62 experiment at CERN, configured in beam-dump mode, has searched for dark photon decays in flight to electron-positron pairs using a sample of protons on dump collected in 2021. No evidence for a dark photon signal is observed. The combined result for dark photon searches in lepton-antilepton final states is presented and a region of the parameter space is excluded at 90% CL, improving on previous experimental limits for dark photon mass values between 50 and 600 MeV and coupling values in the range to . An interpretation of the search result in terms of the emission and decay of an axion-like particle is also presented
A search for the decay
A search for the decay, forbidden within the Standard Model by either lepton number or lepton flavour conservation depending on the flavour of the emitted neutrino, has been performed using the dataset collected by the NA62 experiment at CERN in 2016--2018. An upper limit of is obtained for the decay branching fraction at 90% CL, improving by a factor of 250 over the previous search
Search for lepton number and flavour violation in and decays
Searches for the lepton number violating decay and the lepton flavour violating and decays are reported using data collected by the NA62 experiment at CERN in 20172018. No evidence for these decays is found and upper limits of the branching ratios are obtained at 90% confidence level: B() K^{+} \rightarrow \pi^{-} \mu^{+} e^{+}K^{+} \rightarrow \pi^{+} \mu^{-} e^{+}\pi^{0} \rightarrow \mu^{-} e^{+}20172018\mathcal{B}(K^{+}\rightarrow\pi^{-}\mu^{+}e^{+})<4.2\times 10^{-11}\mathcal{B}(K^{+}\rightarrow\pi^{+}\mu^{-}e^{+})<6.6\times10^{-11}\mathcal{B}(\pi^{0}\rightarrow\mu^{-}e^{+})<3.2\times 10^{-10}$. These results improve by one order of magnitude over previous results for these decay modes
Measurement of the very rare decay
The NA62 experiment reports the branching ratio measurement BR at 68% CL, based on the observation of 20 signal candidates with an expected background of 7.0 events from the total data sample collected at the CERN SPS during 2016-2018. This provides evidence for the very rare decay, observed with a significance of 3.4. The experiment achieves a single event sensitivity of , corresponding to 10.0 events assuming the Standard Model branching ratio of . This measurement is also used to set limits on BR(), where is a scalar or pseudo-scalar particle. Details are given of the analysis of the 2018 data sample, which corresponds to about 80% of the total data sample
Search for decays to invisible particles
The NA62 experiment at the CERN SPS reports a study of a sample of tagged mesons from , searching for the decay of the to invisible particles. No signal is observed in excess of the expected background fluctuations. An upper limit of is set on the branching ratio at 90% confidence level, improving on previous results by a factor of 60. This result can also be interpreted as a model-independent upper limit on the branching ratio for the decay where is a particle escaping detection with mass in the range GeV/ and rest lifetime greater than 100 ps. Model- dependent upper limits are obtained assuming to be an axion-like particle with dominant fermion couplings or a dark scalar mixing with the Standard Model Higgs.The NA62 experiment at the CERN SPS reports a study of a sample of tagged mesons from , searching for the decay of the to invisible particles. No signal is observed in excess of the expected background fluctuations. An upper limit of is set on the branching ratio at 90% confidence level, improving on previous results by a factor of 60. This result can also be interpreted as a model-independent upper limit on the branching ratio for the decay , where is a particle escaping detection with mass in the range 0.110-0.155 GeV and rest lifetime greater than 100 ps. Model-dependent upper limits are obtained assuming to be an axion-like particle with dominant fermion couplings or a dark scalar mixing with the Standard Model Higgs boson