K 0 and 0 0 production in ppbar

K 0 and Λ 0/Λ 0 production in p-pbar collisions at s=1800 and 630 Ge. V For the two energies and for the full MB data sample, analyses of: Ø K 0 and Λ 0 multiplicities and p. T inclusive distributions; Ø Dependence of the ‹p. T (V 0)> and of the mean number of V 0 from the event charged multiplicity. F. Rimondi – QCD Meeting Aug 8, 2002 1

K 0/Λ 0 production in Min Bias events Data analyzed: 1800 Ge. V 630 Ge. V run 1 A + 1 B +1 C run 1 C ~ 3, 300, 000 triggers ~ 2, 600, 000 triggers Offline event selection: reject -events containing cosmic rays (central calorimeter, TOF) - events with no tracks -events with calorimeter problems - events with a single CTC track, but no central calorimeter tower with at least 100 Me. V - events with more than one primary vertex - events with a primary vertex more than 60 cm from the detector center - events with no primary vertex F. Rimondi – QCD Meeting Aug 8, 2002 2

K 0/Λ 0 production in Min Bias events After selection: 2, 079, 154 events @ 1800 Ge. V 2, 091, 599 events @ 630 Ge. V Track selection: - standard CTCSEL selection - |d| ‹ 0. 5 cm - |z 0 trk - zver|‹ 5 cm Mult = n. of good CTC tracks = Nch* F. Rimondi – QCD Meeting Aug 8, 2002 1 ‹ p T> = Nch* p. Ti 3

K 0/Λ 0 production in Min Bias events K 0/Λ 0 selection - use full sample of reconstructed CTC tracks - make opposite sign pairs and look for pairs converging to a common secondary vertex - fit secondary vertex with the hypothesis of K 0/Λ 0 decay F. Rimondi – QCD Meeting Aug 8, 2002 4

K 0/Λ 0 production in Min Bias events K 0/Λ 0 were accepted if: - secondary vertex 3 -C fit has probability > 5% - the fitted mass is within 3 from K 0/Λ 0 mass - the projected vertex displacement in xy plane Lxy > 1 cm - the decay track |η|< 1. 5 and p. T(V 0) 0. 250 Ge. V/c - |z 0(V 0)-zvertex| < 6 cm - p. T(V 0) > 0. 4 Ge. V/c - |η(V 0)| < 1. 5 F. Rimondi – QCD Meeting Aug 8, 2002 5

K 0/Λ 0 production in Min Bias events K 0/Λ 0 efficiency correction Efficiency for finding K 0/Λ 0 evaluated in two ways: - simulated V 0 embedded in real MB events; - full MB events with K 0/Λ 0 generated with Pythia, then simulated (QFL simulation) and reconstructed. CDFnote: CDF/ANAL/MIN_BIAS/CDFR/6043 F. Rimondi – QCD Meeting Aug 8, 2002 6

K 0/Λ 0 production in Min Bias events Efficiency evaluated inclusively for each single distribution Experimental distribution N/ I vs I is corrected for: (I) = Rec. ( N/ I) Gen. ( N/ I) vs I where I is a generic inclusive variable (p. T, , mult) and N either the number of events or tracks in I (I) is so integrated over all the other variables F. Rimondi – QCD Meeting Aug 8, 2002 7

K 0/Λ 0 production in Min Bias events Efficiency for 1 V 0 almost constant, ~60%, in the phase space region |η| < 1 and |p. T| > 2 Ge. V/c Strongly decreasing outside this region Efficiency for 2, 3, … V 0 also decreases F. Rimondi – QCD Meeting Aug 8, 2002 8

K 0/Λ 0 production in Min Bias events Soft and Hard Interactions Soft: events with no cluster of minimum energy of 1. 1 Ge. V in the whole calorimeter Hard: events with at least one cluster of minimum energy of 1. 1 Ge. V anywhere in the calorimeter A track cluster algorithm is used to compensate energy loss in the cracks F. Rimondi – QCD Meeting Aug 8, 2002 9

K 0/Λ 0 production in Min Bias events Number of K 0 s and Soft sample Hard sample : 1800 Ge. V 630 Ge. V 57787 54581 Λ 0/Λ 0 15407 12596 K 0 s 11200(~19%) 15850(~29%) Λ 0/Λ 0 1973(~13%) 2578(~21%) K 0 s 46587 38731 13434 10018 K 0 s Full MB sample Λ 0/Λ 0 F. Rimondi – QCD Meeting Aug 8, 2002 10