Periodic Reporting for period 4 - BSMFLEET (Challenging the Standard Model using an extended Physics program in LHCb)
Periodo di rendicontazione: 2019-10-01 al 2020-03-31
We know that the Standard Model (SM) of Particle Physics is not the ultimate theory of Nature. It misses a quantum description of gravity, it does not offer any explanation to the composition of Dark Matter, and the matter-antimatter unbalance of the Universe is predicted to be significantly smaller than what we actually see. Those are fundamental questions that still need an answer. Alternative models to SM exist, based on ideas such as SuperSymmetry or extra dimensions, and are currently being tested at the Large Hadron Collider (LHC) at CERN. But after the first run of the LHC the SM is yet unbeaten at accelerators, which imposes severe constraints in Physics beyond the SM (BSM). From this point, I see two further working directions: on one side, we must increase our precision in the previous measurements in order to access smaller BSM effects. On the other hand; we should attack the SM with a new fleet of observables sensitive to different BSM scenarios, and make sure that we are making full use of what the LHC offers to us. I propose to create a team at Universidade de Santiago de Compostela that will expand the use of LHCb beyond its original design, while reinforcing the core LHCb analyses in which I played a leading role so far. LHCb has up to now collected world-leading samples of decays of b and c quarks. My proposal implies to use LHCb for collecting and analysing also world-leading samples of rare s quarks complementary to those of NA62. In the rare s decays the SM sources of Flavour Violation have a stronger suppression than anywhere else, and therefore those decays are excellent places to search for new Flavour Violating sources that otherwise would be hidden behind the SM contributions. It is very important to do this now, since we may not have a similar opportunity in years. In addition, the team will also exploit LHCb to search for μμ resonances predicted in models like NMSSM, and for which LHCb also offers a unique potential that must be used.
During this project, the trigger efficiency for the 2016-2019 period was improved by about an order of magnitude compared to the state prior to the project. This allowed a very precise search for Ks->μμ, which showed no signal evidence. Other strange decays into dimuons are being searched in the same dataset. The trigger efficiency for the LHCb upgrade (2021-) has been improved by yet another order of magnitude thanks to the use of GPU instead of the previous, hardware-based, L0. This improvement will allow to get very close to the SM prediction for KS->μμ. In addition, we provided the world best limits in NMSSM higgses in the Y mass region.
During this project, the trigger efficiency for the 2016-2019 period was improved by about an order of magnitude compared to the state prior to the project. This allowed a very precise search for Ks->μμ, which showed no signal evidence. Other strange decays into dimuons are being searched in the same dataset. The trigger efficiency for the LHCb upgrade (2021-) has been improved by yet another order of magnitude thanks to the use of GPU instead of the previous, hardware-based, L0. This improvement will allow to get very close to the SM prediction for KS->μμ. In addition, we provided the world best limits in NMSSM higgses in the Y mass region.
The BSMFLEET project is divided in four main work packages. The main of them WP1, aims for adapting the trigger system of LHCb and LHCb upgrade to select rare decays of strange particles, and analyse those decays.
The project has published four CERN-LHCb public notes, two CERN-LHCb conference note, and 19 publications peer-reviewed journals. The team members have given tens of talks at international conferences. The main results
of the WP1 were highlighted at CERN Courier. WP2 was designed to search for NMSSM A1 Higgs bosons near the Y mass region. No signal was found, so we set world best upper limits on that mass region. WP3 and WP4 were
meant to develop roadmap analyses of Bs mesons, most notably providing an improved measurement of the CP violating phase φs. To achieve this result we made a GPU analysis framework for HEP, which we later use for several other measurements.
The project has published four CERN-LHCb public notes, two CERN-LHCb conference note, and 19 publications peer-reviewed journals. The team members have given tens of talks at international conferences. The main results
of the WP1 were highlighted at CERN Courier. WP2 was designed to search for NMSSM A1 Higgs bosons near the Y mass region. No signal was found, so we set world best upper limits on that mass region. WP3 and WP4 were
meant to develop roadmap analyses of Bs mesons, most notably providing an improved measurement of the CP violating phase φs. To achieve this result we made a GPU analysis framework for HEP, which we later use for several other measurements.
The impact of the project surpased the most optimistic expectations. The capabilities of LHCb and its upgrade to study s->dmumu transitions have been improved beyond the 'best' scenario shown in the proposals. The number of public results is above what was expected, and the interest of the community in the kaon physics program of LHCb has grown substantially. In fact, this new program has triggered other relevant researches of the field to request ERC funding for related activities.