Comprehensive results on the production of unidentified charged particles, π

The p t -differential inclusive production cross sections of the prompt charmed mesons D 0 , D + , and D * + in the rapidity range |y| < 0.5 were measured in proton-proton collisions at √ s = 7 TeV at the LHC using the ALICE detector. Reconstructing the decaysand their charge conjugates, about 8,400 D 0 , 2,900 D + , and 2,600 D * + mesons with 1 < p t < 24 GeV/c were counted, after selection cuts, in a data sample of 3.14×10 8 events collected with a minimum-bias trigger (integrated luminosity L int = 5 nb −1 ). The results are described within uncertainties by predictions based on perturbative QCD.

The first evidence of spin alignment of vector mesons (K Ã0 and ϕ) in heavy-ion collisions at the Large Hadron Collider (LHC) is reported. The spin density matrix element ρ 00 is measured at midrapidity (jyj < 0.5) in Pb-Pb collisions at a center-of-mass energy (ffiffiffiffiffiffiffi ffi s NN p) of 2.76 TeV with the ALICE detector. ρ 00 values are found to be less than 1=3 (1=3 implies no spin alignment) at low transverse momentum (p T < 2 GeV=c) for K Ã0 and ϕ at a level of 3σ and 2σ, respectively. No significant spin alignment is observed for the K 0 S meson (spin ¼ 0) in Pb-Pb collisions and for the vector mesons in pp collisions. The measured spin alignment is unexpectedly large but qualitatively consistent with the expectation from models which attribute it to a polarization of quarks in the presence of angular momentum in heavy-ion collisions and a subsequent hadronization by the process of recombination.

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The differential production cross section of electrons from semileptonic heavy-flavor hadron decays has been measured at midrapidity (jyj < 0:5) in proton-proton collisions at ffiffi ffi s p ¼ 7 TeV with ALICE at the LHC. Electrons were measured in the transverse momentum range 0:5 < p t < 8 GeV=c. Predictions from a fixed-order perturbative QCD calculation with next-to-leading-log resummation agree with the data within the theoretical and experimental uncertainties.