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

Measurement of forward Z → e+e− production s√s=8 TeV

A measurement of the cross-section for Z-boson production in the forward region of pp collisions at 8 TeV centre-of-mass energy is presented. The measurement is based on a sample of Z → e+e− decays reconstructed using the LHCb detector, corresponding to an integrated luminosity of 2.0 fb−1. The acceptance is defined by the requirements 2.0 20 GeV for the pseudorapidities and transverse momenta of the leptons. Their invariant mass is required to lie in the range 60-120 GeV. The cross-section is determined to beS

Measurement of indirect CP asymmetries in D0 → K−K+ and D0 → π−π+ decays using semileptonic B decays

Time-dependent CP asymmetries in the decay rates of the singly Cabibbo-suppressed decays D0 → K−K+ and D0 → π−π+ are measured in pp collision data corresponding to an integrated luminosity of 3.0 fb−1 collected by the LHCb experiment. The D0 mesons are produced in semileptonic b-hadron decays, where the charge of the accompanying muon is used to determine the initial state as D0 or D¯0. The asymmetries in effective lifetimes between D0 and D¯0 decays, which are sensitive to indirect CP violation, are determined to be AΓ(K−K+)=(−0.134±0.077−0.026−0.034)%,AΓ(π−π+)=(−0.092±0.145−0.025−0.033)%, where the first uncertainties are statistical and the second systematic. This result is in agreement with previous measurements and with the hypothesis of no indirect CP violation in D0 decays.S

Precise measurements of the properties of the B1(5721)0,+ and B *2(5747)0,+ states and observation of B+,0π−,+ mass structures

Invariant mass distributions of B+π− and B0π+ combinations are investigated in order to study excited B mesons. The analysis is based on a data sample corresponding to 3.0 fb−1 of pp collision data, recorded by the LHCb detector at centre-of-mass energies of 7 and 8 TeV. Precise measurements of the masses and widths of the B1(5721)0,+ and B2(5747)0,+ states are reported. Clear enhancements, particularly prominent at high pion transverse momentum, are seen over background in the mass range 5850-6000 MeV in both B+π− and B0π+ combinations. The structures are consistent with the presence of four excited B mesons, labelled B J (5840)0,+ and B J (5960)0,+, whose masses and widths are obtained under different hypotheses for their quantum numbersS

Measurement of CP asymmetries and polarisation fractions in B0s→K∗0K¯∗0 decays

An angular analysis of the decay B0s→K∗0K¯∗0 is performed using pp collisions corresponding to an integrated luminosity of 1.0 fb−1 collected by the LHCb experiment at a centre-of-mass energy s√=7 TeV. A combined angular and mass analysis separates six helicity amplitudes and allows the measurement of the longitudinal polarisation fraction f L = 0.201 ± 0.057 (stat.) ± 0.040 (syst.) for the B0s→K∗(892)0K¯∗(892)0 decay. A large scalar contribution from the K ∗0(1430) and K ∗0(800) resonances is found, allowing the determination of additional CP asymmetries. Triple product and direct CP asymmetries are determined to be compatible with the Standard Model expectations. The branching fraction B(Bs→K∗(892)0K¯∗(892)0) is measured to be (10.8 ± 2.1 (stat.) ± 1.4 (syst.) ± 0.6 (f d /f s )) × 10−6.S

Observation of the B0→ρ0ρ0 decay from an amplitude analysis of B0→(π+π−)(π+π−)decays

Proton–proton collision data recorded in 2011 and 2012 by the LHCb experiment, corresponding to an integrated luminosity of 3.0fb−1, are analysed to search for the charmless B0→ρ0ρ0decay. More than 600 B0→(π+π−)(π+π−)signal decays are selected and used to perform an amplitude analysis, under the assumption of no CP violation in the decay, from which the B0→ρ0ρ0decay is observed for the first time with 7.1 standard deviations significance. The fraction of B0→ρ0ρ0decays yielding a longitudinally polarised final state is measured to be fL=0.745+0.048−0.058(stat) ±0.034(syst). The B0→ρ0ρ0branching fraction, using the B0→φK∗(892)0decay as reference, is also reported as B(B0→ρ0ρ0)=(0.94±0.17(stat)±0.09(syst)±0.06(BF))×10−6S

Search for CP violation in D0→π−π+π0 decays with the energy test

A search for time-integrated CPviolation in the Cabibbo-suppressed decay D0→π−π+π0is performed using for the first time an unbinned model-independent technique known as the energy test. Using proton–proton collision data, corresponding to an integrated luminosity of 2.0fb−1collected by the LHCbdetector at a centre-of-mass energy of √s=8TeV, the world’s best sensitivity to CPviolation in this decay is obtained. The data are found to be consistent with the hypothesis of CPsymmetry with a p-value of (2.6 ±0.5)%S

Study of the rare B0s and B0s decays into the π+π−μ+μ−final state

A search for the rare decays B0s→π+π−μ+μ−and B0→π+π−μ+μ−is performed in a data set corresponding to an integrated luminosity of 3.0fb−1collected by the LHCb detector in proton–proton collisions at centre-of-mass energies of 7 and 8TeV. Decay candidates with pion pairs that have invariant mass in the range 0.5–1.3GeV/c2and with muon pairs that do not originate from a resonance are considered. The first observation of the decay B0s→π+π−μ+μ−and the first evidence of the decay B0→π+π−μ+μ−are obtained and the branching fractions, restricted to the dipion-mass range considered, are measured to be B(B0s→π+π−μ+μ−) =(8.6 ±1.5(stat) ±0.7(syst) ±0.7 (norm)) ×10−8and B(B0→π+π−μ+μ−) =(2.11±0.51(stat)±0.15(syst)±0.16(norm))×10−8, where the third uncertainty is due to the branching fraction of the decay B0→J/ψ(→μ+μ−)K∗(892)0(→K+π−), used as a normalisation.S

Measurement of the CP-violating phase βin B0→J/ψπ+π−decays and limits on penguin effects

Time-dependent CPviolation is measured in the (—)B0→J/ψπ+π−channel for each π+π−resonant final state using data collected with an integrated luminosity of 3.0fb−1in ppcollisions using the LHCb detector. The final state with the largest rate, J/ψρ0(770), is used to measure the CP-violating angle 2βeffto be (41.7 ±9.6+2.8−6.3)◦.This result can be used to limit the size of penguin amplitude contributions to CPviolation measurements in, for example, (—)B0s→J/ψφdecays. Assuming approximate SU(3) flavour symmetry and neglecting higher order diagrams, the shift in the CP-violating phase φsis limited to be within the interval [−1.05◦, +1.18◦] at 95% confidence level. Changes to the limit due to SU(3) symmetry breaking effects are also discussed.S

Measurement of the Z+b-jet cross-section in pp collisions at √s = 7 TeV in the forward region

The associated production of a Z boson or an off-shell photon γ * with a bottom quark in the forward region is studied using proton-proton collisions at a centre-of-mass energy of 7 TeV. The Z bosons are reconstructed in the Z/γ * → μ + μ − final state from muons with a transverse momentum larger than 20 GeV, while two transverse momentum thresholds are considered for jets (10 GeV and 20 GeV). Both muons and jets are reconstructed in the pseudorapidity range 2.0 < η < 4.5. The results are based on data corresponding to 1.0 fb−1 recorded in 2011 with the LHCb detector. The measurement of the Z+b-jet cross-section is normalized to the Z+jet cross-section. The measured cross-sections are σ( Z/γ∗(μ+μ−)+b-jet)=295±60 (stat)±51 (syst)±10 (lumi) fb (0.1) for p T(jet) > 10 GeV, and σ(Z/γ∗(μ+μ−)+b-jet)=128±36 (stat)±22 (syst)±5 (lumi) fb (0.2) for p T(jet) > 20 GeVS