Measurement of event shape variables in deep-inelastic scattering at HERA

Deep-inelastic ep scattering data taken with the H1 detector at HERA and corresponding to an integrated luminosity of 106 pb^-1 are used to study the differential distributions of event shape variables. These include thrust, jet broadening, jet mass and the C-parameter. The four-momentum transfer Q is taken to be the relevant energy scale and ranges between 14 GeV and 200 GeV. The event shape distributions are compared with perturbative QCD predictions, which include resummed contributions and analytical power law corrections, the latter accounting for non-perturbative hadronisation effects. The data clearly exhibit the running of the strong coupling α_s(Q) and are consistent with a universal power correction parameter α₀ for all event shape variables. A combined QCD fit using all event shape variables yields α_s(m_Z)=0.1198±0.0013 ^+0.0056_-0.0043 and α₀=0.476±0.008 ^+0.018_-0.059.     

Study of the π+π+π-π- system centrally 0 produced by incident π+ andp beams at 85 GeV/c

The reactions π⁺ p→π⁺(π⁺π⁺π^-π^-)p andpp→p(π⁺π⁺π^-π^-)p, where the (π⁺ π⁺ π^- π^-) system is centrally produced have been studied at 85 GeV/c. The π⁺π⁺π^-π^- mass spectrum shows evidence for thef ₁ (1285) meson with a mass of 1278±2 MeV and width 41±12 MeV which decays mainly through ρ⁰(770)π⁺π^-. Thef ₁(1285) is also observed in the ηπ⁺π^- channel. There is no significant evidence for ηππ or 4π decay modes of thef ₁(1420). The ρ⁰ρ⁰ production is found to be small. A Dalitz plot analysis of the 3π system shows evidence fora ₂ (1320) production and for a large contribution of theJ ^PC=1⁺⁺ ρπ wave.     

ψ(2S)强衰变中的一个新的反常现象

利用在北京正负电子对撞机(BEPC)上北京谱仪(BES)最近采集的127万个(2S)事例,测量了新的强子衰变道(2S)→ωπ+π-,和ωf2(1270)的分支比,发现(2S)→满足理论预言的“14%规则”,而(2S)→ωf2(1270)相对于J/明显抑制,从而首次从实验上观察到粲素衰变为非矢量-赝标量末态出现破坏上述规则的反常行为.     

Search for single leptoquark and squark production in electron-photon scattering at $\sqrt{s_{\rm ee}}=189$ GeV at LEP

A search for first generation scalar and vector leptoquarks (LQ) as well as for squarks () in R-parity violating SUSY models with the direct decay of the into Standard Model particles has been performed using ee collisions collected with the OPAL detector at LEP at an ee centre-of-mass energy of 189 GeV. The data correspond to an integrated luminosity of about 160 pb. The dominant process for this search is , where a photon, which has been radiated by one of the beam electrons, serves as a source of quarks. The numbers of selected events found in the two decay channels are in agreement with the expectations from Standard Model processes. This result allows to set lower limits at the 95% confidence level on the mass of first generation scalar and vector leptoquarks, and of squarks in R-parity violating SUSY models. For Yukawa couplings to fermions larger than , the mass limits range from 121 GeV to GeV ( GeV to GeV) depending on the branching ratio of the scalar (vector) leptoquark state. Furthermore, limits are set on the Yukawa couplings for leptoquarks and for squarks, and on as a function of the scalar leptoquark/squark mass. Received: 22 May 2001 / Published online: 25 January 2002     

Dijet photoproduction at HERA and the structure of the photon

The dijet cross section in photoproduction has been measured with the ZEUS detector at HERA using an integrated luminosity of 38.6 pb. The events were required to have a virtuality of the incoming photon, , of less than 1 GeV and a photon-proton centre-of-mass energy in the range GeV. Each event contains at least two jets satisfying transverse-energy requirements of GeV and GeV and pseudorapidity requirements of \mbox{}. The measurements are compared to next-to-leading-order QCD predictions. The data show particular sensitivity to the density of partons in the photon, allowing the validity of the current parameterisations to be tested. Received: 21 December 2001 / Published online: 5 April 2002     

A direct search for stable magnetic monopoles produced in positron-proton collisions at HERA

A direct search has been made for magnetic monopoles produced in e ⁺ p collisions at a centre of mass energy of 300 GeV at HERA. The beam pipe surrounding the interaction region in 1995-1997 was investigated using a SQUID magnetometer to look for stopped magnetic monopoles. During this time an integrated luminosity of 62 pb^-1 was delivered. No magnetic monopoles were observed and charge and mass dependent upper limits on the e ⁺ p production cross section are set.Received: 25 January 2005, Revised: 13 March 2005, Published online: 12 April 2005     

Single and double dissociation in πp collisions at 11 and 16 GeV/c

The reactions π⁻p → 2π⁻π⁺p, π⁻p → 2π⁻π⁺π^op and π⁻p → 2π⁻2π⁺n are analysed at 11 and 16 GeV/c using longitudinal phase space (LPS) plots. The weighted LPS distributions for π⁻p → 2π⁻π⁺p is dominated by two well separated structures corresponding to single diffraction dissociation of the pion, π⁻p → (2π⁻π⁺)p, and of the proton, π⁻p → π⁻(π⁻π⁺p). The former is more abundant than the latter, and both are approximately constant with energy. In contrast, processes of type π⁻p → (2π)(πp) decrease with increasing energy.

In the five-body reactions the weighted LPS distribution reveals especially at 16 GeV/c a maximum for single dissociation of the proton into 3πp, namely π⁻p → π⁻(π⁻π⁺π^op); this process is likely to be diffractive. The neutron channel has a corresponding maximum displaced toward a multiperipheral configuration π⁻p → π⁻(π⁻2π⁺)n. Another strong maximum corresponds to the pion dissociation π⁻p → (2π⁻π⁺π^o)p. This is interpreted to be an ω-exchange process because no analogous structure occurs in π⁻p → (2π⁻2π⁺)n. Finally, a broad structure reveals double dissociation of both incident particles; it occurs in the two channels π⁻p → (2π⁻π⁺)(π^op) and π⁻p → (2π⁻π⁺)(π⁺n), being stronger in the latter. Further analysis of this process in terms of isospin exchange suggests that it is partially diffractive. Factorization is also discussed.

An appendix gives general aspects of the LPS analysis for the asymptotic study of n-body collisions at very high energy.     

Evolution of the use of relational and NoSQL databases in the ATLAS experiment

The ATLAS experiment used for many years a large database infrastructure based on Oracle to store several different types of non-event data: time-dependent detector configuration and conditions data, calibrations and alignments, configurations of Grid sites, catalogues for data management tools, job records for distributed workload management tools, run and event metadata. The rapid development of “NoSQL” databases (structured storage services) in the last five years allowed an extended and complementary usage of traditional relational databases and new structured storage tools in order to improve the performance of existing applications and to extend their functionalities using the possibilities offered by the modern storage systems. The trend is towards using the best tool for each kind of data, separating for example the intrinsically relational metadata from payload storage, and records that are frequently updated and benefit from transactions from archived information. Access to all components has to be orchestrated by specialised services that run on front-end machines and shield the user from the complexity of data storage infrastructure. This paper describes this technology evolution in the ATLAS database infrastructure and presents a few examples of large database applications that benefit from it.