Cloud flexibility using DIRAC interware

Communities of different locations are running their computing jobs on dedicated infrastructures without the need to worry about software, hardware or even the site where their programs are going to be executed. Nevertheless, this usually implies that they are restricted to use certain types or versions of an Operating System because either their software needs an definite version of a system library or a specific platform is required by the collaboration to which they belong. On this scenario, if a data center wants to service software to incompatible communities, it has to split its physical resources among those communities. This splitting will inevitably lead to an underuse of resources because the data centers are bound to have periods where one or more of its subclusters are idle. It is, in this situation, where Cloud Computing provides the flexibility and reduction in computational cost that data centers are searching for. This paper describes a set of realistic tests that we ran on one of such implementations. The test comprise software from three different HEP communities (Auger, LHCb and QCD phenomelogists) and the Parsec Benchmark Suite running on one or more of three Linux flavors (SL5, Ubuntu 10.04 and Fedora 13). The implemented infrastructure has, at the cloud level, CloudStack that manages the virtual machines (VM) and the hosts on which they run, and, at the user level, the DIRAC framework along with a VM extension that will submit, monitorize and keep track of the user jobs and also requests CloudStack to start or stop the necessary VM's. In this infrastructure, the community software is distributed via the CernVM-FS, which has been proven to be a reliable and scalable software distribution system. With the resulting infrastructure, users are allowed to send their jobs transparently to the Data Center. The main purpose of this system is the creation of flexible cluster, multiplatform with an scalable method for software distribution for several VOs. Users from different communities do not need to care about the installation of the standard software that is available at the nodes, nor the operating system of the host machine, which is transparent to the userThis work was supported by projects FPA2007-66437- C02-01/02 assigned to UB and FPA2010-21885-C02- 01/02 and TIN 2010-17541 USC. FPA2007-66152-C02-01/02 and FPA2010-21816-C02-01/02, assigned to PICS

Study of the kinematic dependences of Λ 0b production in pp collisions and a measurement of the Λ 0b → Λ +c π − branching fraction

The kinematic dependences of the relative production rates, fΛ0b/fd, of Λ 0b baryons and B 0 mesons are measured using Λ 0b → Λ +c π − and B¯0 →D+π− decays. The measurements use proton-proton collision data, corresponding to an integrated luminosity of 1 fb−1 at a centre-of-mass energy of 7 TeV, recorded in the forward region with the LHCb experiment. The relative production rates are observed to depend on the transverse momentum, p T, and pseudorapidity, η, of the beauty hadron, in the studied kinematic region 1.5 < p T < 40 GeV/c and 2 < η < 5. Using a previous LHCb measurement of fΛ0b/fd in semileptonic decays, the branching fraction ℬ(Λ 0b → Λ +c π −) = (4.30 ± 0.03 + 0.12− 0.11 ± 0.26 ± 0.21) × 10− 3 is obtained, where the first uncertainty is statistical, the second is systematic, the third is from the previous LHCb measurement of fΛ0b/fd and the fourth is due to the b B¯0 →D+π− branching fraction. This is the most precise measurement of a Λ 0b branching fraction to date.S

Evidence for the decay B+c→J/ψ3π+2π−

Evidence is presented for the decay B + c → J/ψ3π +2π − using proton-proton collision data, corresponding to an integrated luminosity of 3 fb−1 , collected with the LHCb detector. A signal yield of 32 ± 8 decays is found with a significance of 4.5 standard deviations. The ratio of the branching fraction of the B + c → J/ψ3π +2π − decay to that of the B+ c → J/ψπ+ decay is measured to be B (B+ c → J/ψ3π +2π −) B B + c → J/ψπ+ = 1.74 ± 0.44 ± 0.24, where the first uncertainty is statistical and the second is systematicS

Effective lifetime measurements in the B0s→K+K−, B0→K+π−and B0s→π+K−decays

Measurements of the effective lifetimes in the B0s→K+K−, B0→K+π−and B0s→π+K−decays are presented using 1.0fb−1of ppcollision data collected at a centre-of-mass energy of 7TeV by the LHCb experiment. The analysis uses a data-driven approach to correct for the decay time acceptance. The measured effective lifetimes are τB0s→K+K−=1.407±0.016(stat)±0.007(syst)ps, τB0→K+π−=1.524±0.011(stat)±0.004(syst)ps, τB0s→π+K−=1.60±0.06(stat)±0.01(syst)ps. This is the most precise determination to date of the effective lifetime in the B0s→K+K−decay and provides constraints on contributions from physics beyond the Standard Model to the B0smixing phase and the width difference Γs.S

Search for the decay D0→π+π−μ+μ−

A search for the D0→π+π−μ+μ− decay, where the muon pair does not originate from a resonance, is performed using proton–proton collision data corresponding to an integrated luminosity of 1.0 fb−1 recorded by the LHCb experiment at a centre-of-mass energy of 7 TeV. No signal is observed and an upper limit on the relative branching fraction with respect to the resonant decay mode D0→π+π− φ(→μ+μ− ), under the assumption of a phase-space model, is found to be B D0→π + π − μ + μ − /B D0→π + π − φ →μ + μ − < 0.96 at 90% confidence level. The upper limit on the absolute branching fraction is evaluated to be B(D0→π+π−μ+μ− ) < 5.5×10−7 at 90% confidence level. This is the most stringent to date.S

Evidence for the decay X(3872) →ψ(2S)γ

Evidence for the decay mode X(3872) →ψ(2S)γin B+→X(3872)K+decays is found with a sig-nificance of 4.4 standard deviations. The analysis is based on adata sample of proton–proton collisions, corresponding to an integrated luminosity of3fb−1, collected with the LHCb detector, at centre-of-mass energies of 7and8TeV. The ratio of the branching fraction of the X(3872) →ψ(2S)γdecay to that of the X(3872) →J/ψγdecay is measured to be B(X(3872)→ψ(2S)γ) B(X(3872)→J/ψγ) = 2.46± 0.64±0.29, where the first uncertainty is statistical and the second is systematic. The measured value does not support apureD¯ D∗molecular interpretation of the X(3872)state.S

Measurement of the Ξ−b and Ω−b baryon lifetimes

Using a data sample of ppcollisions corresponding to an integrated luminosity of 3fb−1, the Ξ−band Ω−bbaryons are reconstructed in the Ξ−b→J/ψΞ−and Ω−b→J/ψΩ−decay modes and their lifetimes measured to be τ Ξ − b = 1.55+0.10 −0.09 (stat)±0.03 (syst) ps, τ Ω − b = 1.54+0.26 −0.21 (stat)± 0.05 (syst) ps. These are the most precise determinations to date. Both measurements are in good agreement with previous experimental results and with theoretical predictionsS

A study of CP violation in B± →DK± and B±→Dπ± decays with D→K0SK±π∓ final states

A first study of CP violation in the decay modes B±→[KS 0 K±π∓] D h±and B±→[KS 0 K∓ π±] D h±, where h labels a K or π meson and D labels a D 0 or D‾ 0 meson, is performed. The analysis uses the LHCb data set collected in pp collisions, corresponding to an integrated luminosity of 3 fb− 1. The analysis is sensitive to the CP-violating CKM phase γ through seven observables: one charge asymmetry in each of the four modes and three ratios of the charge-integrated yields. The results are consistent with measurements of γ using other decay modesS

Measurement of the CKM angle γ using B ± → DK ± with D → K0S π + π −, K0S K + K − decays

A binned Dalitz plot analysis of B± → DK± decays, with D → K0S + − and D → K0S K+K−, is performed to measure the CP-violating observables x± and y±, which are sensitive to the Cabibbo-Kobayashi-Maskawa angle . The analysis exploits a sample of proton-proton collision data corresponding to 3.0 fb−1 collected by the LHCb experiment. Measurements from CLEO-c of the variation of the strong-interaction phase of the D decay over the Dalitz plot are used as inputs. The values of the parameters are found to be x+ = (−7.7 ± 2.4 ± 1.0 ± 0.4) × 10−2, x− = (2.5 ± 2.5 ± 1.0 ± 0.5) × 10−2, y+ = (−2.2 ± 2.5 ± 0.4 ± 1.0) × 10−2, and y− = (7.5 ± 2.9 ± 0.5 ± 1.4) × 10−2. The first, second, and third uncertainties are the statistical, the experimental systematic, and that associated with the precision of the strong-phase parameters. These are the most precise measurements of these observables and correspond to = (62 +15 −14) , with a second solution at γ → γ  + 180 , and rB = 0.080+0.019 −0.021, where rB is the ratio between the suppressed and favoured B decay amplitudesS

Differential branching fractions and isospin asymmetries of B → K (*) μ + μ − decays

The isospin asymmetries of B → Kμ + μ − and B → K * μ + μ − decays and the partial branching fractions of the B 0 → K 0 μ + μ −, B + → K + μ + μ − and B + → K *+ μ + μ − decays are measured as functions of the dimuon mass squared, q 2. The data used correspond to an integrated luminosity of 3 fb−1 from proton-proton collisions collected with the LHCb detector at centre-of-mass energies of 7 TeV and 8 TeV in 2011 and 2012, respectively. The isospin asymmetries are both consistent with the Standard Model expectations. The three measured branching fractions favour lower values than their respective theoretical predictions, however they are all individually consistent with the Standard Model.S