Production and transport of hadrons generated in nuclear cascades initiated by muons in the rock (exclusive approach)

Monte Carlo calculation of differential distributions of hadrons going into LVD (Large Volume Detector) experimental hall from the rock was performed. Probability of energy transfer into nuclear cascade by muon is taken according to Bezrukov and Bugaev (1981) giving 9.45×10⁻⁶ inelastic muon-nucleus interactions per gram per year at the depth of Gran Sasso. Simulation of hadron cascades in the rock was made using the universal hadron transport code SHIELD. It allowed to calculate transport of hadrons at energy up to 1 TeV providing the exclusive simulation of nuclear reactions in the whole energy range. Differential distributions of neutrons, protons and charged pions are obtained for the roof, walls and floor of the hall separately in absolute units. Total number of hadrons with energy above 15 MeV going into the hall is about 250 particles per m² per year. Number of ingoing neutrons is in good agreement with measurement. The yield of high energy hadrons (>1 GeV) in backward hemisphere is observed. Possible role of K⁰-mesons as a source of background events in LVD is distinguished.     

A new method to determine the electroweak couplings of individual light flavours at LEP

A method is presented for determining the yields and properties of individual light quark flavours in Z ⁰ decays that is essentially free of detailed assumptions about hadronisation. The method uses an equation system with the number of events which are single and double tagged by high energy hadrons as inputs. In addition, SU(2) isospin symmetry and the flavour independence of QCD are used to derive general relations between hadron production from the various primary light quarks. Assuming the branching fractions R _q of the Z ⁰ into down and strange quarks to be the same, five million hadronic Z ⁰ decays may allow precisions of δ(R _d = R _s)/(R _d = R _s) ～ 0.05 and δA _FB(d = s) ～ δA _fb(u) ～ 0.015 for the corresponding asymmetries. The method can be extended to include somewhat more model dependent symmetries of hadron production, which then allows the electroweak observables for each of the individual light quarks to be determined.     

Collective Perspective on Advances in Dyson–Schwinger Equation QCD

We survey contemporary studies of hadrons and strongly interacting quarks using QCD's Dyson-Schwinger equations, addressing the following aspects: confinement and dynamical chiral symmetry breaking; the hadron spectrum; hadron elastic and transition form factors, from small-to large-Q2; parton distribution functions; the physics of hadrons containing one or more heavy quarks; and properties of the quark gluon plasma.     

Collective Perspective on Advances in Dyson-Schwinger Equation QCD

We survey contemporary studies of hadrons and strongly interacting quarks using QCD's Dyson-Schwinger equations, addressing the following aspects: confinement and dynamical chiral symmetry breaking; the hadron spectrum; hadron elastic and transition form factors, from small- to large-Q²; parton distribution functions; the physics of hadrons containing one or more heavy quarks; and properties of the quark gluon plasma.     

Cross section and transverse momentum of hadron interactions with air nuclei at primary cosmic ray energies of 0.3–5 PeV

The Tien Shan experimental data on hadrons with energies exceeding 0.5 TeV in extensive air showers (EAS) from primary cosmic rays with energies from 0.3 to 5 PeV are compared with the results of CORSIKA + QGSJET model simulations. Some conclusions are drawn on the increase of the cross section and transverse momentum in the hadron interactions with air atom nuclei from 0.1 TeV (accelerator with a fixed target) to 5 PeV (EAS) energies.     

Phenomenological constraints on broken supersymmetry

We show that the existence of massless color octet quarks, which appear in a class of broken supersymmetric field theories, implies the existence of additional light (? 1 GeV) unstable hadrons with large $\text{(? 10 μb)}$ production cross sections. We estimate the half-life for these states to be less than 10^?8 s. If it is greater than 10^°10 s, these states are already ruled out experimentally.     

Search for gauge mediated SUSY breaking topologies in ee collisions at centre-of-mass energies up to 209 GeV

A total of 628 bp^-1 of data collected with the ALEPH detector at centre-of-mass energies from 189 to 209 GeV is analysed in the search for gauge mediated SUSY breaking (GMSB) topologies. These topologies include two acoplanar photons, non-pointing single photons, acoplanar leptons, large impact parameter leptons, detached slepton decay vertices, heavy stable charged sleptons and multi-leptons plus missing energy final states. No evidence is found for new phenomena, and lower limits on masses of supersymmetric particles are derived. A scan of a minimal GMSB parameter space is performed and lower limits are set for the next-to-lightest supersymmetric particle (NLSP) mass at 54 GeV/c² and for the mass scale parameter at 10 TeV/c², independently of the NLSP lifetime. Including the results from the neutral Higgs boson searches, a NLSP mass limit of 77 GeV/c² is obtained and values of up to 16 TeV/c² are excluded. Received: 14 March 2002 / Published online: 20 September 2002     

A consistent parametrisation for the production rates of negatively charged hadrons and neutral strange particles in nucleon-nucleon,nucleon-nucleus and nucleus-nucleus collisions

A parametrisation of negative hadron and neutral strange particle production was developed which consistently describes presently available data from nucleon-nucleon, nucleon-nucleus and nucleus-nucleus collisions at a beam energy of 200 GeV per nucleon. Average multiplicities of negative hadrons are found to be proportional to the number of wounded nucleons, averageK _s ⁰ multiplicities proportional to the number of wounded quarks, and average and multiplicities proportional to the number of wounded quarks plus an additional contribution proportional to the number of interactions of secondary produced particles. Predictions are given for lead-lead collisions.On leave from Rudjer Boskovic Institute, Zagreb, Croatia     

The hadronisation of a quark-gluon plasma

We consider two scenarios for the expansion of a quark-gluon plasma. If the evolution is slow enough, the system can remain in equilibrium throughout its entire history up to the freeze-out of a hadron gas; for a very rapid expansion, it may break up into hadrons before or at the confinement transition, without ever going through an equilibrium hadron phase. We compare hadron production rates in the two approaches and show that for a hadronisation temperatureT?200 MeV and baryonic chemical potential μ _B ?500 MeV, their predictions essentially coincide. Present data on strange particle production lead to values in this range and hence cannot provide a distinction between the two scenarios. Pion, nucleon and non-strange meson production seem to require a considerably lower freeze-out temperature and baryonic chemical potential. In the hadron gas picture, this is in accord with the difference in mean free path of the different hadrons in the medium; it suggests a sequential freeze-out, in which strange hadrons stop interacting earlier than non-strange hadrons. In the quark-gluon plasma break-up, the hadronic final state fails to provide the high entropy per baryon observed in non-strange hadron production. The break-up moreover leads to a decrease of the entropy per baryon; hence it must be conceptually modified before it can be considered as a viable hadronisation mechanism.     

Studying the nature of the long-flying component of cosmic rays using X-ray emulsion chambers exposed in the Pamirs and Tien Shan

The origin of an excess of hadrons observed in deep homogeneous lead X-ray emulsion chambers (XRECs) at depths of more than 70 radiation length units is analyzed. Preliminary experimental data on the absorption of cosmic-ray hadrons in a two-storied XREC with a large air gap, exposed in the Tien Shan mountains, are presented. The chamber was designed to test the hypothesis that the main source of the excess of dark spots detected on X-ray films deep inside the XREC was substantial growth of the charmed-particle production cross section at energy E_lab ～ 75 TeV. The experimental data obtained using a two-storied REC and in experiments with deep homogeneous XRECs are compared to the results from calculations using the FANSY 1.0 model. The comparison shows qualitative agreement between the experimental and the model data, assuming high values of the charmed-particle production cross section when E_lab ～ 75 TeV in the forward kinematic region with x_F ≥ 0.1.     

Charm,bottom and top production in high energy electron proton collisions

Differential cross sections for electroproduction of charm, bottom and top quarks are calculated via all contributing 2 → 2 and 2 → 3 QCD subprocesses. Fragmentation of heavy quarks to heavy hadrons and effects due to weak chain decays of the heavy quarks are taken into account. We also calculated background contributions given by the production of two or three light-quark jets both via the neutral and charged current processes. We point out that, similarly to the case of hadron colliders, it will be necessary to require final state lepton(s) to suppress the jet background. To separate charm and bottom production we have to require at least one hard muon or two isolated leptons and one jet in the final state. We show that two or more jet production via the charged current mechanism and bottom production with hard gluon bremssrahlung are the most important background contributions in top search. However, we also show that they become negligible by requiring one lepton, two or three jets and large missing energy in the final state. We estimate that the discovery limit on the top quark mass value is about 70 GeV at HERA.     

Search for single vectorlike quarks in pp ̄ collisions at √s=1.96 TeV

We present a search for hypothetical vectorlike quarks in pp ? collisions at √s=1.96 TeV. The data were collected by the D0 detector at the Fermilab Tevatron Collider and correspond to an integrated luminosity of 5.4 fb(-1). We select events with a final state composed of a W or Z boson and a jet consistent with a heavy object decay. We observe no significant excess in comparison to the background prediction and set limits on production cross sections for vectorlike quarks decaying to W+jet and Z+jet. These are the most stringent limits to date for electroweak single vectorlike quark production at hadron colliders.     

Mass and lifetime limits on new long-lived particles in 300 GeV/c π− interactions

A sensitive search has been done for the production of new long-lived and penetrating particles by 300 GeV/c negative pions. No new state —decaying into at least two charged known particles —has been detected with mass above 1 GeV/c² and lifetime in the range 5·10^?11 s to 5·10^?7s. We give upper limits on production cross sections, and consequences on the existence of heavy “axion-like” particles, heavy neutrinos and supersymmetric particles. In particular, this experiment excludes the existence of light gluinos with lifetime in the range 5·10^?11 to 10^?8s: this closes the last “window of opportunity” for gluinos withM<2 GeV/c² and lifetime measurable in particle physics experiments.     

Jet quenching pattern at LHC in PYQUEN model

The first LHC data on high transverse momentum hadron and dijet spectra in PbPb collisions at center-of-mass energy 2.76 TeV per nucleon pair are analyzed in the frameworks of PYQUEN jet quenching model. The presented studies for the nuclear modification factor of high-p _T hadrons and the imbalance in dijet transverse energy support the supposition that the intensive wide-angular (“out-of-cone”) medium-induced partonic energy loss is seen in central PbPb collisions at the LHC.     

Mass level of heavy flavored hadrons in the heavy-quark effective theory

We have studied the heavy flavored hadron spectroscopy, which is motivated by the heavy quark effective theory. TheQ \(\bar q\) ,Qqq andQQq hadrons have been investigated systematically. Regarding thes-quark as a member of heavy quarks, the predicted mass levels of both theQqq andQQq baryons are quite consistent with experimental ones.     

Heavy flavour hadron spectroscopy: An overview

A comprehensive overview and some of the theoretical attempts towards understanding heavy flavour hadron spectroscopy are presented. Apart from the conventional quark structure (quark, antiquarks structure for the mesons and three-quarks structure of baryons) of hadrons, multiquark hadrons the hadron molecular states etc., also will be reviewed. Various issues and challenges in understanding the physics and dynamics of the quarks at the hadronic dimensions are highlighted. Looking into the present and future experimental prospects at different heavy flavour laboratories like BES-III, CLEO-c, BaBar, Belle, LHC etc., the scope for theoretical extensions of the present knowledge of heavy flavour physics would be very demanding. In this context, many relevant contributions from the forthcoming PANDA Facility are expected. Scopes and outlook of the hadron physics at the heavy flavour sector in view of the future experimental facilities are highlighted.     

The HFT,a Heavy Flavor Tracker for STAR

Determining the degree of termalisation of the medium created in heavy ion collisions at RHIC remains highly debated. Elliptic flow (v₂) measurements at RHIC have already suggested the development of collectivity among partons before hadronization. If heavy flavor hadrons flow with the light flavor hadrons, this indicates frequent interactions between the light (u, d ,s) and heavy (c, b) quarks. Thus, thermalization of light quarks is likely to have been reached through partonic re-scattering. Experimentally this can be probed by making a direct measurement of D-mesons v₂ with sufficient precision at low transverse momentum. Using the Heavy Flavor Tracker (HFT) detector, the STAR experiment at RHIC is proposing to both study this process and also to directly reconstruct charmed hadrons (D⁰, D⁺, D_s, Λ_C, ...), using the displaced vertices of their decay products. The HFT is the first vertex detector to use a new and promising CMOS active pixel sensor technology. It will allow to build a relatively fast, accurate and radiation tolerant detector, while keeping the material budget low (∼0.3%X₀ per layer). Detector design and physics performance simulations are presented.     

The evolution of short distance phase space quanta into hadron jets

A statistical model fore ⁺ e ^? annihilation into hadrons is presented which explains at the same time some short distance phenomena (multiple jet structure, rate of three jet events, scaling) and large distance phenomena (hadron final states, multiplicities). We investigate the change of phase space structure with time under the assumption that the interaction volume expands with velocity of light. At short distancesL?m _π ^?1 elementary quanta in the instantaneous phase space with mass spreadΔm～L ^?1 can be produced. They are unstable and evolve into the jets of hadrons. The time evolution of the system is uniquely determined by sequential application of our principle of equipartition in instantaneous phase space.     

Predicted new class of hadrons and the average parton charge

A semiempirical mass formula of a particular parton model, in which it is assumed that partons are highly charged, requires the existence of a new class of hadrons, at least one of which must be absolutely stable and whose masses are of the order of a few GeV. Several experiments (with accelerators and cosmic rays) appear to support the notions that partons are highly charged and that a new class of hadrons exists. The recently reported particle of Niu et al., with an apparent lifetime ～10^?13 sec, may be a member of the new predicted class.     

Search for displaced vertices arising from decays of new heavy particles in 7 TeV pp collisions at ATLAS

We present the results of a search for new, heavy particles that decay at a significant distance from their production point into a final state containing charged hadrons in association with a high-momentum muon. The search is conducted in a pp-collision data sample with a center-of-mass energy of 7 TeV and an integrated luminosity of 33 pb^?1 collected in 2010 by the ATLAS detector operating at the Large Hadron Collider. Production of such particles is expected in various scenarios of physics beyond the standard model. We observe no signal and place limits on the production cross-section of supersymmetric particles in an R-parity-violating scenario as a function of the neutralino lifetime. Limits are presented for different squark and neutralino masses, enabling extension of the limits to a variety of other models.