• Energy Research

We present results obtained from a study of the structure of hadronic events recorded by the L3 detector at various centre-of-mass energies. The distributions of event shape variables and the energy dependence of their mean values are measured from 30GeV to 189GeV and compared with various QCD models. The energy dependence of the moments of event shape variables is used to test a power law ansatz for the non-perturbative component. We obtain a universal value of the non-perturbative parameter alpha_0 = 0.537 +/- 0.073. From a comparison with resummed O(alpha_s^2) QCD calculations, we determine the strong coupling constant at each of the selected energies. The measurements demonstrate the running of alpha_s as expected in QCD with a value of alpha_s(m_Z) = 0.1215 +/- 0.0012 (exp) +/- 0.0061 (th).

AbstractIn this paper, we report the measurement of the energy flow, the cross section and the average inelasticity of forward neutrons (+ antineutrons) produced in$$ \sqrt{s} $$s= 13 TeV proton-proton collisions. These quantities are obtained from the inclusive differential production cross section, measured using the LHCf Arm2 detector at the CERN Large Hadron Collider. The measurements are performed in six pseudorapidity regions: three of them (η >10.75, 8.99< η <9.21 and 8.80< η <8.99), albeit with smaller acceptance and larger uncertainties, were already published in a previous work, whereas the remaining three (10.06< η <10.75, 9.65< η <10.06 and 8.65< η <8.80) are presented here for the first time. The analysis was carried out using a data set acquired in June 2015 with a corresponding integrated luminosity of 0.194 nb−1. Comparing the experimental measurements with the expectations of several hadronic interaction models used to simulate cosmic ray air showers, none of these generators resulted to have a satisfactory agreement in all the phase space selected for the analysis. The inclusive differential production cross section forη >10.75 is not reproduced by any model, whereas the results still indicate a significant but less serious deviation at lower pseudorapidities. Depending on the pseudorapidity region, the generators showing the best overall agreement with data are either SIBYLL 2.3 or EPOS-LHC. Furthermore, apart from the most forward region, the derived energy flow and cross section distributions are best reproduced by EPOS-LHC. Finally, even if none of the models describe the elasticity distribution in a satisfactory way, the extracted average inelasticity is consistent with the QGSJET II-04 value, while most of the other generators give values that lie just outside the experimental uncertainties.

We present a study of the structure of hadronic events recorded by the L3 detector at LEP at the center of mass energies of 161 and 172 GeV. The data sample corresponds to an integrated luminosity of 21.25 pb-1 collected during the high energy runs of 1996. The distributions of event shape variables and the energy dependence of their mean values are well reproduced by QCD models. From a comparison of the data with resummed second order QCD calculations, we determine the strong coupling constant at the two energies. Combining with our earlier measurements we find that the strong coupling constant decreases with increasing energy as expected in QCD.

The main aim of the LHCf experiment is to provide precise measurements of the production spectra relative to neutral particles produced in the very forward region by high energy proton-proton and proton-ion collisions. This information is necessary in order to test and tune hadronic interaction models used by ground-based cosmic rays experiments. In order to reach this goal, LHCf makes use of two small sampling calorimeters installed in the LHC tunnel at $\pm 140$ m from IP1, able to detect neutral particles having pseudo-rapidity $\eta > 8.4$. After the operations relative to p-p collisions at $\mathrm{\sqrt{s} = 13~TeV}$, the collaboration focused the activity on the study of forward photons and neutrons production at this energy. In this paper, we discuss the recent results relative to the photons analysis, regarding, in particular, the inclusive production cross section, the role of diffractive and non-diffractive processes in forward photons production (investigated thanks to the LHCf-ATLAS joint analysis) and the forward differential energy flow.