Projects

• Projects of Slovak Scientific Grant Agency VEGA:

  Number	Principal Investigator	Name of project
  2/5137/25	P. Stríženec	The hadronic energy calibration in the ATLAS calorimetry - the proposal and software implemantation, the assembly, testing and updrade of the electronics
  2/4067/24	J. Ferencei	Study of ep collisions in H1 experiment in the conditions of the HERA increased luminosity
  2/6192/26	I. Králik	Study of nuclear matter at extremal conditions in NA57 and ALICE experiments in CERN
  2/0061/08	D. Bruncko	The study some aspects of the calorimetry in high energy physics
  2/0100/08	J. Bán	The proposal and the radiation hardness tests of the speed electronics based on the SiGe technology and working in the wide temperature region for collider's experiments with high luminisity

• Slovak government projects:

  Number	Principal Investigator	Name of project
  CERN-ALICE	L. Šándor	Study of new forms and phase transition of nuclear matter at at high energy densities. Contribution to the development and building of the electronics for silicon pixel detector (SPD) and for central trigger system of the ALICE experiment
  CERN-ATLAS	D. Bruncko	Development and tests of the calibration system for hadronic end-cap calorimeters for ATLAS detector in CERN
  CERN-NA57	I. Králik	Study of possible quark-gluon plasma production in heavy-ion collisions

  
  
  

• INTAS project:

  Number	Principal Investigator	Name of project
  05-103-7555	D. Bruncko	A Proposal for R&D to establish the limitations on the operation of the ATLAS End-Cap Calorimeters at high LHC Luminosities

  
  
  

• APVV project:

  Number	Principal Investigator	Name of project
  APVV-20-057305	J. Antoš	The advanced top quark physics studies

  
  
  

  Heavy-ion physics experiments

  The main goal of the heavy ion activities is finding an experimental evidence of a possible formation of the new state of matter -- Quark Gluon Plasma -- and investigation of properties of nuclear matter under extreme conditions (high temperatures, high densities). A list of the selected activities and results:
  
  

  • Experiments with Pb ions at the CERN SPS

    • Results on inverse m slopes of different particle species in Pb-Pb collisions at 160 AGeV/c can be interpreted as an indication of the collective transverse flow in heavy ion collisions. WA97 results on (and probably also ) show deviation from the trend followed by particles with zero or one unit of strangeness (see fig. 1). This suggests that multistrange baryons (and antibaryons) are produced in hot and dense central fireball and their production is not much affected by the later hadronic rescattering.
    • Dependence of the hyperon yield on the collision centrality is tried as a promising tool for establishing conditions for possible transition of nuclear matter into a new regime (see fig. 2 with the WA97 results).
    • A new experiment NA57 continues studying the strange particle production in heavy-ion collisions. New aims of this experiment include enlarged centrality coverage (compared with the WA97) and running with Pb beam at lower energy (about 40 GeV/c per nucleon).
      ----------------
      WA97 finished data taking in 1996 and the data analysis is in the progress. NA57 had been commisioned in 1997 and started data taking for physics in 1998.
      
  

  Figure 1: Inverse m slope parameters T for different particle species. Linear dependence of the T parameter on particle mass was suggested as an evidence of the collective transverse flow in Pb-Pb collisions

  

  Figure 2: Hyperon yields as a function of the number of participating nucleons (left) in Pb-Pb interactions. The righthand figure shows the same with all yields normalized to those measured in p-Pb collisions. Dotted lines show the deviation of the observed dependence from the assumption about linear dependence of particle yields on the number of participating nucleons (solid line)

  • Other experiments

    • Observation of the increase of ratio in S-W compared to p-W collisions (HELIOS-3);
    • Finding a ''low mass excess'' in S-W dimuon data which suggests a partial chiral symmetry restoration in nucleus-nucleus collisions (HELIOS-3);

  The heavy-ion subject will be continued in the future on the CERN LHC at the ALICE experiment. At present, various simulations are being performed in order that the detector performance might be optimized. Calculations of radiation conditions in and near the detector are part of our ALICE activities.
  

  Another area of our interest covers design and development of the trigger and data acquisition schemes, which are tested as a part of the NA57 experiment.

  
  
  
  

  H1 experiment

  H1 experiment has profited from the significant increase of the collected luminosity in the last 2 years (1996 - 10 pb^-1, 1997 - 28 pb^-1. This high statistics allowed first deeper look into high Q² physics and even into physics beyond Standard Model.

  The most important results are:

  • in 1997 the results of the analysis of the 1995 data taken with interaction vertex shifted by 70 cm and with an upgraded backward part of the H1 detector (new Spacal calorimeter and backward drift chamber), were published for the kinematical range 0.35 < Q² < 3.5 GeV², x > 6.10^-6 and 0.03 < y < 0.75 [1]. Data show smooth continuation from fixed target measurements, see fig. 3. The rise of F² with decreasing x is still prominent for values of Q² > 2 GeV² but becomes less steep for smaller Q² values.
    Data access the transition region from DIS to photoproduction and a provide powerful constraints on the development of further low Q² phenomenology.
    

    Figure 3: F2p(x,Q2) as a function of x for the different Q2 values

  • The cross section measurement at high inelasticity values of y 0.86 was used for the first determination of the longitudinal structure function F_L. F_L was derived under the assumption that F² measured at low y (y < 0.35) and extrapolated at high values of inelasticity y is accurately determined by the NLO QCD calculation. Most of the data are higher han the QCD expectation but the experimental errors are still relatively large.
  • two indications of the signals physics beyond Standard Model were widely discussed. Despite the present interpretation of slight excess in high Q² region (see fig. 4) with respect to expectations of the Standard Model to be most probably statistical fluctuation, the final answer waits still for more accumulated luminosity.
    Second signal indicating the yield of events with one isolated high-p_T lepton above the expectation of Standard Model also waits for increased accumulated luminosity of the coming years.
    

    Figure 4: Neutral current cross section at fixed x versus Q2 together with the NMC, SLAC and BCDMS data and compared to the MRST parametrisation and the NLO fit all the data for x > 0.7

  • a lot of new results accumulated during the last two years shed the light onto the mechanism of light and heavy vector meson production in photo-production. Figure 5 summarizes the energy dependence of the elastic vector meson cross-sections compared to some power law dependences. In the case of light vector mesons () the weak dependence on center-of-mass energies is consistent with the exchange of a soft Pomeron. For the photo-production of the dependence on is much stronger and is described by QCD based models.
    

    Figure 5: The cross sections dependence of the vector mesons in the photoproduction are shown as a function of the energy in p system

  • new results for the determination of strong coupling constant based on the jet rates in deep inelastic scattering indicate competitiveness with the worldwide available data.
  • for the first time the determination of the gluon density in the virtual photon is plotted in fig. 6 as a function of the momentum fraction x of the parton of the photon entering the hard scattering process.
    

    Figure 6: Gluon density in the virtual photon

  We took also part in the upgrade of the H1 detector. For the transition region between the deep inelastic scattering (DIS) and photoproduction a new detector, the so called Very Low Q² (VLQ) has been constructed, which covers a range of Q²: 0.02 < Q² < 1 GeV².
  Our contribution is connected with the trigger and ToF systems.