Physics with the ATLAS detector on LHC (JINR participation)

1. Physics with the ATLAS detector on LHC (JINR participation) V. Bednyakov, N. Russakovich

2. The ATLAS detector Over the last decade JINR-ATLAS team was deeply involved in designing, construction, tests and assembly of major systems of ATLAS: Inner Detector Tile Calorimeter Liquid Argon End Cap Calorimeter Muon detector Common Items (Toroid Warm Structure and others) Participation in the Physics Program was always considered as the most important target. Till 2003 this work has been performed mainly in “background” regime, essentially based on individual efforts, promoted with limited resources case-by-case (as well as for software developments and general computing infrastructure of ATLAS).

3. Workshops on the ATLAS Physics Program • Early 2004 the JINR-ATLAS team management decided to establish a regular framework (series of workshops) to promote physics-oriented activities at home, aimed to: • Open the door for new ideas (also attract new collaborators, interested in future physics at LHC); • Monitoring of ongoing activities and select most promising ones to provide the necessary support, in particular for visiting conferences and dedicated ATLAS meetings; • Enrich “home community” by involving physicists from JINR member countries who have less possibilities in computing and networking, to make JINR-ATLAS resources and experience widely available; • Keep people informed about recent software developments and dedicated computing infrastructure at JINR. • Web site: http://www.atlas-jinr.ru/

4. Higgs boson • Search for the SM Higgs boson with the ATLAS detector (G.Chekov, I.Boiko, K.Nikolaev, R.Sadikov) • The process H→4μ was investigated on the basis of the full ATLAS detector simulation. Further investigation of the identical muons effect on the decay H→4μ was also carried out. • The proposals were made to study in Dubna the ATLAS large-mass Higgs discovery potential by means of reactions H→2W→2lν,or H→2W→lνjj (Yu.Kulchitsky) and H→2Z→2lν, or H→2Z→lljj(V.Vinogradov) on the basis of the already simulated ATLAS DC1 and DC2 data. The proposals rely on the Higgs boson production via the Vector Boson Fusion mechanism (the two accompanying forward jets allows very good background reduction) and on the maximal Higgs boson decay rates into WW- or ZZ-pair at MH=400--1000 GeV. At the moment the works are still on the step of these proposals.

5. Quark-gluon structure functions, VHM • The possibilities of measuring at the LHC energiesthe gluon distributions in the proton by means of simultaneous registration of the direct photons (or Z-bosons) and jets (so called "gamma/Z+jet" events) were carried out by D.Bandurin and N.Skachkov. The correspondent talks are given at the both Workshops. The task is under investigation also at the Tevatron energies (D0 project). • Study of Very High Multiplicity Events at LHC (J.Budagov, Yu.Kulchitsky, I.Manjavigze, A.Sissakian,).

6. SANC • Project SANC (Support of Analytical and Numerical Calculations for Experiments at Colliders). D.Bardin, L.Kalinovskaya, P.Christova, G.Nanava A.Andonov (DLNP, JINR), A.Arbuzov, S.Bondarenko (BLTP, JINR). The status of HEP (semi-)analytical calculation tool for LHC was presented by its leader D.Bardin. At the moment this very ambitious and quickly progressing project is not yet ready for practical investigations of the prospects for observation of the physical phenomena at the LHC with ATLAS detector. Nevertheless it promises to be much more useful for development of the JINR-ATLAS physical program right in the near future. http://brg.jinr.ru/

7. Top quark physics N.Russakovich, V.Bednyakov, E.Khramov, S.Tokar, A.Tonoyan • Verification of the of the top-quark charge With the help of the PYTHIA and ATLFAST simulations the prospects for correct verification of the statement that the top-quark electric charge indeed equals to +2/3 is performed on the basis of the lepton-jet top decay channels. • Search for ttbar resonance with ATLAS Resonances with several masses are considered (500, 1000, 1500… GeV) with PYTHIA 6.203 event generator and processed with ATLFAST integrated in ATHENA framework.

8. Theoretical calculations and estimates • Evaluation of the next-to-leading order QCD corrections to the single top- and top-anti-top quarks production together with an estimate of the associate top-Higgs production (in pp-interactions) were given by A.Akhmedov. Some aspects of research of the top- and Higgs boson production and the search for the exotic phenomena at LHC were discussed by Z.Usubov. Theory and phenomenology of the ATLAS physics with the Higgs bosons, the extra gauge bosons and (very) heavy quarkonia states as well as a theory of the multi-particle correlations during particle productions were given by G.Kozlov. Just an idea about monopole search with the ATLAS detector was presented by Yu.Kurochkin (Minsk). The diffractive Higgs production and search for the virtual electroweak effects with ATLAS were discussed by I.Satsunkevich (Minsk). V.Gilevsky (Minsk) gave report on general parameterization of 4-boson vertex and its importance for the collider physics.

9. Theoretical calculations and estimates • Supersymmetry and Dark Matter search at LHC ( V.Bednyakov, S.Kovalenko). The highest importance of the SUSY search at LHC (especially in connection with cosmology and astrophysics via famous problem of the Dark Matter) needs no any extra arguments Unfortunately, till now there is no any Dubna-based “ATLAS simulation” activity in the field. The situation will be improved in the nearest future. • P.Starovoitov (Minsk) considered two-photon mechanism of Drell-Yan lepton pair production in pp-collisions and demonstrated that its contribution is not negligible.

10. Search for gravitons (extra dimensions) • The possibility of observation of the graviton exchange effects on dijet production was studied by Z.Usubov on the basis of ATLAS detector simulation with PYTHIA and ATLFAST. A sensitivity of the LHC to a main parameter of the graviton production model is estimated. • The search for and identification of the direct and indirect manifestations of the graviton-like Kaluza-Klein states in the lepton-pair production at LHC A.Pankov (Gomel). The new Center-edge asymmetry was introduced to isolate the spin-2 graviton contribution. This well developed and attractive theoretical proposal now is ready to enter the ATLAS-simulation phase.

11. Conclusions • We have more than enough fresh attractive ideas which can be and should be incorporated into the ATLAS research program. • Only very few of above proposals have passed a way from initial idea to clear experimental procedure through simulation, background estimates and so on. We have to work intensively – LHC start up is approaching! • My proposal to other Dubna-LHC groups (CMS, ALICE) and their leaders would be:let us arrange a common framework – joint home workshops on LHC physics. Despite of some differences like detector particularities and software used we all (I believe) could get a lot of benefit from mutual discussions.