Physics with the ATLAS detector on LHC

(JINR participation)

V. Bednyakov, N. Russakovich

N.Russakovich

21 January 2005

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).

N.Russakovich

21 January 2005

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/ N.Russakovich

21 January 2005

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. H  Z Z*  4μ

7500 events (15600 fb -1

H

) PYTHIA

 Z Z*  4μ

30000 events (8265 fb -1 ) PYTHIA

tt  (Wb)(Wb)  (μν)(μJet)(μν)(μJet)

20000 events (8265 fb -1 ) PYTHIA

Zbb  (μμ)(μJet)(μJet)

22500 events ACERMC

Z Z*  4μ • The applied criteria ensure ~30% efficiency (20-50)% background level.

• Pile-Up events included (firstly in ATLAS) • ~100 fb -1 of luminosity is required for the Higgs discovery.

(JINR preprint Р1-2004-44) .

 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.

N.Russakovich

21 January 2005

Quark-gluon structure functions, VHM

 The possibilities of measuring at the LHC energies the

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

,).

PITHYA Prediction for Ratio of K3/K2 correlators for ATLAS at 14 TeV A. One may conclude that the dynamical models built into the PITHYA can not predict thermalization.

B. The transition region to thermalized state. VHM may belong to it.

C. The limiting thermalization region:

|

K

3

K

2 3 / 2 ~ 1

n

ON CORRELATORS FOR HIGH MULTIPLICITY EVENTS.

J. Budagov , Y. Kulchitsky , J.Mandzhavidze

, N. Rusakovich , A.Sissakian

Phys.Atom.Nucl.67:69-71,2004

N.Russakovich

21 January 2005

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/ N.Russakovich

21 January 2005

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.

• •

Verification of the SM electric charge of the top quark at ATLAS detector at LHC (pp collider

S

=14 TeV)

It is generally accepted, that the particle discovered at Fermilab in 1995 is the Standard Model (SM) top quark with 2/3 charge. But in the analysis carried out by the CDF and D0 collaborations the top charge was not in fact measured (till now) due to insufficient statistics. There is an alternative interpretation. One can assume that the particle discovered at Fermilab is an “exotic” quark with charge 4/3.

(D. Chang et al. Phys.Rev.D59, 091503 (1999) and Phys.Rev.D61, 037301 (2000)) t t

the LHC (pp-collider

s



14 TeV

) Resonances with several masses are considered (500, 1000, 1500… GeV) with PYTHIA 6.203 event generator and processed with AtlFast integrated in ATHENA framework

N.Russakovich

21 January 2005

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

as a theory of the

multi-particle correlations

states as well 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

collider physics. and its importance for the N.Russakovich

21 January 2005

Theoretical calculations and estimates



P.Starovoitov

(Minsk) considered negligible.

two-photon mechanism of Drell-Yan

lepton pair production in pp collisions and demonstrated that its contribution is not

Two-photon creation of lepton pairs in pp-collisions N. Shumeiko, A. Soroko, P. Starovoitov We study another possibility to produce lepton pairs in hadron collisions, namely, the two-photon exchange

•

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.

N.Russakovich

21 January 2005

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.

There are many very different NP scenarios that predict new particle exchanges which can lead to contact interaction (CI) below direct production threshold.

A partial list of know candidates: - compositeness

- Z'

- scalar or vector leptoquarks

- R

-parity violating sneutrino exchange

- graviton KK towers in extra dimensional models

- gauge boson

KK

towers - etc.

In the case of indirect discovery many different NP scenarios may lead to the same or very similar experimental signatures.

N.Russakovich

21 January 2005

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.

N.Russakovich

21 January 2005