Most important project achievements.

1. Search for supersymmetric particles (new limits and new signatures) - Task 1,2
   • papers 5, 8, 13, 17, 20, 22, 24, 27, 43, 71
2. New results on the origin of Dark Matter (supersymmetric and non-supersymmetric) and search for it - Task 1,2
   • papers 12, 14, 19, 25, 26, 65, 75, 83
3. New results on CP violation and BSM physics in Yukawa couplings - Task 4
   • papers 2, 23, 37, 63, 67, 68, 76, 79, 84
4. Development of Machine Learning Techniques and its application to the sphaleron and microscopic black holes production - Task 5
   • papers 66, 73, 77, 80
5. New results on electroweak phase transitions (with a Higgs particle as a pseudo-Nambu-Goldstone boson, with vector-like fermions) - Task 3
   • papers 35, 41, 64, 74, 78, 82, 85
6. Search for long-lived particles with displaced vertices - Task 1,2
   • papers 3, 9, 19, 21, 40, 41
7. New theoretical tools for Effective Field Theories - related to all tasks of this project
   • papers 69, 70
8. Developing tau lepton reconstruction methods necessary to control tau lepton background in many processes - Task 2,3,4
   • papers 30, 31, 32, 33, 34, 36, 38, 39, 44, 48, 51, 52, 53, 54, 59, 60, 61, 62, 81

Short description of the project results.

The project publication list includes 4 joint Warsaw-Bergen papers (publications 20,26,63,66), 28 papers by the Warsaw team and 52 papers reported by the Bergen team. Bergen group contributes to all ATLAS publications via Operational Tasks. The Operational Tasks linked to this project are: reconstruction of tau leptons with subsequent studies of efficiency and bacground, tau leptons energy callibration, designing tau trigger algorihtms with subsequent studies of the triggger efficienty and background. Trigger algorithms are typically redisigned and retuned for each running period of the Large Hadron Collider. In addition, one of the project members is presently responsible for the maintenance and developement of the statistical tool of ATLAS, so called HISTFITTER thus her work is exploited in all ATLAS publications with searches for new particls. The present project is acknowledged in all ATLAS publications from 2023 and 2024 and in a large number of publications from 2021. Only a selection of publications that have closer links to the project tasks has been reported in the project reports.They are characterized by the direct contribution of the team members employed by this project to the ATLAS data analysis which is or will be used in the research conducted in the project. Bergen succeeded to align the compulsory ATLAS technical work with the tasks of this project. The work concerns mostly identification, measurement and calibration of the energy of the tau leptons in the detector and triggering on tau leptons. Several ML methods are exploited by the project members in this task. Whenever tau leptons are a signal or a background, be it real data or simulation the work of the Bergen project members is involved in all ATLAS publications. Experimental usability and precise reconstruction of tau leptons is pertinent to tasks 2,3,4 of this project and many tools were developed by Fomin and Aakvaag in the context of task 2. In the task 1 tau leptons are a background.

Joint Papers:

• In paper 20, "Monojet signatures from gluino and squark decays", by T. Buanes, I. Lara, R. Masełek, M. Nojiri, K. Rolbiecki and K. Sakuari, JHEP 10(2022)150 (Task 1)
  There is investigated the discovery potential at the LHC in the monojet channel for the associated production of squarks and gluinos, followed by the decay of the lighter coloured particle to a stable neutralino with its mass almost degenerate with the decaying object. In the second scenario, the associated production of a squark and electroweakino is analysed, assuming the eletroweakino is a member of SU(2) multiplet. A small mass difference between the members of the multiplet makes the analysis particularly interesting and demanding. Both analyses significantly increase the excluded by the LHC data parameter range and give predictions for the HL-LHC and HE-LHC.
• In paper 26, "LHC constraints on electroweakino dark matter revisited", by T. Buanes, I. Lara, K. Rolbiecki and K. Sakurai, PRD.107.095021 (Task 1)
  A mono-jet signal and possible multi-jet signals produced when several energetic partons are produced from the initial state radiation are analysed to compare the detection prospects of the dark matter production in several simplified models. Particularly interesting results are obtained for searching for light charginos and neutralinos, covering the mass region with the mass difference between LSP and NLSP between 0.5 to 5 GeV, not accessible by other searches. The paper gives for the first time the limits on the production of light winos.
• In paper 63, "Exploring CP violation in H->tau tau gamma decay", E. Aakvaag, N. Fomin, A. Lipniacka, S. Pokorski, J. Rosiek and D. Sahoo, Eur. Phys. J. C 84 (2024) no.3, 341 (Task 4)
  A method of measuring the CP-odd part of the Yukawa interaction of Higgs boson and tau leptons by observing the forward–backward asymmetry in the Higgs decay into two tau leptons and a photon is proposed. The source of such asymmetry is the interference of the CP-even loop-level contribution coming from the decay channel of the Higgs into Z boson and a photon, with subsequent decay of the Z into lepton pairs, with the contribution from tree-level CP-odd Yukawa interaction. It is found that the CP violating effect is maximum when the invariant mass of the pair of tau leptons is equal to the mass of the Z boson. We propose and utilise various Dalitz plot asymmetries to quantify the maximal size of the asymmetry and perform Monte Carlo simulations to study the feasibility of measuring it in the high luminosity phase of the Large Hadron Collider (HL-LHC).
• In paper 66, "Machine learning classification of sphalerons and black holes at the LHC", by S. Grefsrud, T. Buanes, F. Koutroulis, A. Lipniacka, R. Masełek, A. Papaefstathiou, K. Sakurai, T. B. Sjursen and I. Slazyk, Eur. Phys. J. C 84 (2024) no.4, 442 (Task 5)
  In this publication it is demonstrated that the image recognition based Convolution Neural Network (CNN) can distinquish between Sphalerons and Black Holes at high confidence level, by looking at just few pictures on the events in the ATLAS Detector. These pictures are clearly undistiquishable by the human eye. The results from CNN have been cross-checked by a "more standard" Machine Learning method, Boosted Decision Tree. Since the classification by Boosted Decision Tree can be translated to a (long) list of simple selections, comparing the results of image recognition by CNN and the Boosted Decision Tree is a step towards achieving "explainability" of the CNN results. Moreover, image recognition by CNN is able to classify the number of extra dimensions for Black Hole events, albeit looking at larger number of events. This seems to be the most competitive method of recognising the number of extra dimensions in Black Hole events so far.

Other papers mentioned in the project most important achievements:

The research of both teams has contributed to all tasks of the project:

Task 1 is focused on mono-jet analysis in search for dark matter and new electrically neutral stable particles and its theoretical interpretation, assisted by machine learning techniques.
Task 2 is focused on Discriminating theories by joint mono-higgs and mono-higgs analyses.
Task 3 devoted to the Mechanism of the first order electroweak phase transition and its probes by di-higgs boson production and Task 4 on Probing new sources of CP violation in the Higgs-fermion sector are strongly interconnected,as they deal with two famous Sacharov conditions for a successful electroweak baryogenesis.
Task 5 is devoted to investigating on the sphaleron and microscopic black hole production at the LHC.

• In paper 21, a comprehensive and model-independent study for the prospects of multi-charged long-lived particle searches at the LHC and HL-LHC is performed. This covers an important counterpart of the Task 1 scenario. The analyses dedicated to the anomalous charged tracks and diphoton resonances are supported by the Grieg grant.
• In paper 22, the possibility to explain the observed theory-experimental discrepancy (anomaly) in supersymmetric theories is investigated. is found that a significant part of the parameter space has been excluded by LHC constraints from the jets+MET and mono-Higgs (e.g. WH+MET final state) channels. The part of the study analyzing these LHC constraints was supported by the Grieg grant.
• In paper 23, the contraints and future prospects for discovering beyond the Standard Model effects in the complex Yukawa couplings has been analyzed.
• In paper 24, there are analyzed relevant signals expected at the LHC for a stop as the lightest supersymmetric particle (LSP).
• In paper25, the distinctive cosmological dynamics in multi-component dark matter scenarios and its impact in probing a sub-dominant component of dark matter are investigated. It is found that contrary to a naive expectation, it can be easier to detect the sub-component with smaller abundance fractions in direct/indirect-detection experiments and cosmological observations.
• In paper 27, a scenario with singlino-like dark matter and a long-lived electroweakino NLSP is investigated in the framework of the NMSSM. Several new experimental signatures are identified.
• In paper 28, an anlysis of signatures with exotic Higgs decays is performed, relevant for task 2.
• In paper 30: In this measurements, that intends to use electrons and muons , W decays to taus are a background. This background is removed due to tools developed primarily by the project members (Aakvaag, Fomin, Latour) in the context of task 2,3,4.
• In papers 31,32,33,34,36,38,39,44,48,51,52,53,54,59,60,61,62 as in 30 the tau background was removed thanks to procedures developed by the Bergen team members.
• Paper 35: This publication is pertinent in the context of task 3.
• Paper 37: This publication is pertinent to task 4, the results serve as a partial cross-check of calculations that is used in task 4 publication.
• Paper 40: This publication is interesting in the context of task 1, the results can be reinterpreted and combined.
• Paper 41: Higgs pair production is testing the triple Higgs couplings, relevant for electroweak baryogenesis (Task 3)
• Paper 43: This process is an important background to searches performed in task 1 and 2. Project member Latour had a major contribution to this publication.
• In paper 64, the phase transitions have been studied for the so-called Gegenbuer scalar (Higgs) potentials.
• In paper 74, the effects of vector-like fermions in the spectrum on the electroweak phase transitions have been investigated
• In paper 76, similar methods as in [63] are used to reconstruct the Higgs boson decaying to the Z boson and another particle .
• In paper 77, one of the processes that forms bockground to the possible observation of lepton number violation was measured. Lepton number violation is related to the Task 5. It is exploited, among other observables, by Machine Learning methods in publication [66].
• In paper 78, several measurements were combined to set limits on the self-coupling of the Higgs boson. These measurements are directly related to the Task 3.
• In paper 79, the production of the Higgs boson decaying to Z is confirmed experimentally. This is the process that is at the base of CP-violation measurement proposed by project members in [63] as a part of Task 4. The next step will be to analyse the ATLAS data in a similar was as in [79] to set experimental limits on the CP violation in this channel.
• In paper 80, a complementary method to look for Black Holes to that used in Task 5, in [66] is presented. Unlike the method in [66], this method is however not sensitive to the number of extra-dimensions.
• In paper 81, decays of the Higgs boson to the pair of tau leptons are exploited. The tools for this signature are build by project members.
• The paper 75 is entirely produced by this project members as a part of the Task 2. It forms a part of the PhD thesis of Erlend Aakvaag and project post-doc Nikolai Fomin was the main person responsible for this work. The search for Dark Matter achieved in this work is further used in another publication to set more comprehensive limits on Dark Matter.
• The results in 85 and 82 are directly related to the Task 3 as they are sensitive the the Higgs-boson self-coupling.
• The results in 83 are directly related to the Task 1, as they can be interpreted in the same type of models and provide complementary information.
• The results in 84 use tools developed by the group members and provide benchmark and complementary information to the work performed in Task 4, presented in [63].