Particle production at HERA

H1 has measured a number of different known particles and compared their production to QCD models and to other reactions such as N-N collisions. ZEUS has also measured the production of K SK 0 S pairs with a view to searching for glueballs. Several resonances are seen which are glueball candidates. The results on the masses and widths are compared to other experiments. At HERA acceleration ring, electron (positron) and proton beams were accelerated and made to collide with a center-of-mass energy of above 300 GeV at two interaction points where the H1 and ZEUS detectors were located. 1. Energy dependence of the charged multiplicity in deep inelastic scattering The production of multi-hadronic final states has been an interesting subject. Charged multiplicity in DIS are measured in both the hadronic center-of-mass (HCM) frame and the Breit frame, using an integrated luminosity of 38.6 pb. Only hadrons in the current fragmentation regions of both frames were used due to detector acceptance limitations. The mean charged multiplicity is shown in Figure 1(left) in the current region of the HCM frame as a function of energy, W, and in the current region of the Breit frame as a function of 2 ·E B . The data are compared and in good agreement with the ARIADNE and LEPTO Monte Carlo predictions, while results from HERWIG Monte Carlo prediction are lower. The data are also compared with results of previously published ZEUS [1] and H1 [2, 3, 4] measurements. The measurements agree within the experimental uncertainties at higher values of 2 ·E B , but differ at low values as a function of Q. The energy scale 2 ·E B gives better agreement in the current region of the Breit frame and results from ee experiment than using Q. The mean charged multiplicities are compared with results from ee [5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16] and fixed-target [17, 18, 19] experiments in Figure 1 (right). Both the current regions of the Breit and HCM frames are used as function of the energy scales, 2 · E B and W, respectively. Good overall agreement is observed among these experiments, presenting the same dependence of the mean charged multiplicity on the respective energy scale. In general conclusion, universality of mean charged multiplicity dependence with energy scale is observed. 2. Strangeness production at low Q in deep inelastic ep scattering The production measurement of strangeness production gives insight into the suppression of strangeness involved in lighter flavours fragmentation process studies. This non-perturbative 1 On behalf of the H1 and ZEUS collaborations