The ALICE High Level Trigger comprises a large computing cluster, dedicated interfaces and software applications. It allows on-line event reconstruction of the full data stream of the ALICE ...experiment at up to 25 GByte/s. The commissioning campaign has passed an important phase since the startup of the Large Hadron Collider in November 2009. The system has been transferred into continuous operation with focus on the event reconstruction and first simple trigger applications. The paper reports for the first time on the achieved event reconstruction performance in the ALICE central barrel region.
Abstract Measurements of $$K^{*}(892)^0$$ K ∗ ( 892 ) 0 resonance production via its $$K^{+}\pi ^{-}$$ K + π - decay mode in inelastic p+p collisions at beam momenta 40 and 80 $$\text{ GeV }\!/\!c$$ ...GeV / c ( $$\sqrt{s_{NN}}=8.8$$ s NN = 8.8 and 12.3 $$\text{ GeV }$$ GeV ) are presented. The data were recorded by the NA61/SHINE hadron spectrometer at the CERN Super Proton Synchrotron. The template method was used to extract the $$K^{*}(892)^0$$ K ∗ ( 892 ) 0 signal. Transverse momentum and rapidity spectra were obtained. The mean multiplicities of $$K^{*}(892)^0$$ K ∗ ( 892 ) 0 mesons were found to be $$(35.1 \pm 1.3 \mathrm {(stat)} \pm 3.6 \mathrm {(sys))} \cdot 10^{-3}$$ ( 35.1 ± 1.3 ( stat ) ± 3.6 ( sys ) ) · 10 - 3 at 40 $$\text{ GeV }\!/\!c$$ GeV / c and $$(58.3 \pm 1.9 \mathrm {(stat)} \pm 4.9 \mathrm {(sys))} \cdot 10^{-3}$$ ( 58.3 ± 1.9 ( stat ) ± 4.9 ( sys ) ) · 10 - 3 at 80 $$\text{ GeV }\!/\!c$$ GeV / c . The NA61/SHINE results are compared with the Epos1.99 and Hadron Resonance Gas models as well as with world data. The transverse mass spectra of $$K^{*}(892)^0$$ K ∗ ( 892 ) 0 mesons and other particles previously reported by NA61/SHINE were fitted within the Blast-Wave model. The transverse flow velocities are close to 0.1–0.2 of the speed of light and are significantly smaller than the ones determined in heavy nucleus-nucleus interactions at the same beam momenta.
The multiplicity and pseudorapidity distributions of inclusive photons have been measured at forward rapidities ( ) in proton-proton collisions at three center-of-mass energies, Formula omitted 0.9, ...2.76 and 7 TeV using the ALICE detector. It is observed that the increase in the average photon multiplicity as a function of beam energy is compatible with both a logarithmic and a power-law dependence. The relative increase in average photon multiplicity produced in inelastic pp collisions at 2.76 and 7 TeV center-of-mass energies with respect to 0.9 TeV are 37.2 Formula omitted 0.3 % (stat) 8.8 % (sys) and 61.2 Formula omitted 0.3 % (stat) 7.6 % (sys), respectively. The photon multiplicity distributions for all center-of-mass energies are well described by negative binomial distributions. The multiplicity distributions are also presented in terms of KNO variables. The results are compared to model predictions, which are found in general to underestimate the data at large photon multiplicities, in particular at the highest center-of-mass energy. Limiting fragmentation behavior of photons has been explored with the data, but is not observed in the measured pseudorapidity range.
We present spectra of charged pions and protons in 0–10% central Au+Au collisions at sNN=200 GeV at mid-rapidity (y=0) and forward pseudorapidity (η=2.2) measured with the BRAHMS experiment at RHIC. ...The spectra are compared to spectra from p+p collisions at the same energy scaled by the number of binary collisions. The resulting nuclear modification factors for central Au+Au collisions at both y=0 and η=2.2 exhibit suppression for charged pions but not for (anti-) protons at intermediate pT. The p¯/π− ratios have been measured up to pT∼3 GeV/c at the two rapidities and the results indicate that a significant fraction of the charged hadrons produced at intermediate pT range are (anti-) protons at both mid-rapidity and η=2.2.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image) The production of the strange and double-strange baryon resonances (..., ...) has been measured at mid-rapidity (... ...) ...in proton-proton collisions at ... ... 7 TeV with the ALICE detector at the LHC. Transverse momentum spectra for inelastic collisions are compared to QCD-inspired models, which in general underpredict the data. A search for the ... pentaquark, decaying in the ... channel, has been carried out but no evidence is seen.
The production of the strange and double-strange baryon resonances (Formula: see text, Formula: see text) has been measured at mid-rapidity (Formula: see textFormula: see text) in proton-proton ...collisions at Formula: see text Formula: see text 7 TeV with the ALICE detector at the LHC. Transverse momentum spectra for inelastic collisions are compared to QCD-inspired models, which in general underpredict the data. A search for the Formula: see text pentaquark, decaying in the Formula: see text channel, has been carried out but no evidence is seen.
We present the first measurement at the LHC of exclusive J/ψ photoproduction off protons, in ultraperipheral proton-lead collisions at sqrts_{NN}=5.02 TeV. Events are selected with a dimuon pair ...produced either in the rapidity interval, in the laboratory frame, 2.5<y<4 (p-Pb) or -3.6<y<-2.6 (Pb-p), and no other particles observed in the ALICE acceptance. The measured cross sections σ(γ+p→J/ψ+p) are 33.2±2.2(stat)±3.2(syst)±0.7(theor) nb in p-Pb and 284±36(stat)_{-32}^{+27}(syst)±26(theor) nb in Pb-p collisions. We measure this process up to about 700 GeV in the γp center of mass, which is a factor of two larger than the highest energy studied at HERA. The data are consistent with a power law dependence of the J/ψ photoproduction cross section in γp energies from about 20 to 700 GeV, or equivalently, from Bjorken x scaling variable between ∼2×10^{-2} and ∼2×10^{-5}, thus indicating no significant change in the gluon density behavior of the proton between HERA and LHC energies.
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