L c + Status Report

1. Lc+ Status Report Heavy Flavor Working Group Manuel Calderon de la Barca Indiana University

2. Why? How? • Lc+ : lightest charmed baryon. • Never measured in heavy ion collisions before. • ~15 – 20% of charm production goes into Lc+. • If (signal) then {yield? spectra? Centrality dep?} • Does recombination work for charm as well? • Lc+p K-p+ (+ c.c. mode for Lc-) • M = 2.285 GeV, BR (5 ± 1.3) %, ct=60 mm, (udc) • 3-body decay: large combinatorical background • Momenta of daughters in good PID region • Maybe there’s a chance? Manuel Calderon de la Barca

3. GEANT Simulations • Overall acceptance = 17% • Acc == (all 3 daughters leave 10 hits in TPC) Thrown Accepted Manuel Calderon de la Barca

4. GEANT Acceptance • vs. pT (~20% at 1 GeV/c), vs. y (~40% at y=0) Manuel Calderon de la Barca

5. Where are the daughters? Proton Pion Kaon Manuel Calderon de la Barca

6. Rough Yield Estimate • Lc/(D0+D+) = 0.3, Ds/(D0+D+) = 0.2 • If scc=sDD + sLc + sDs then • sLc/scc = 0.2 • If scc=600 mb and : • Taa=23 mb-1 for 10% central • Taa=5.5 mb-1 for minbias • i.e. assuming binary collision scaling • ccbar yield per 10% central = .023 x 600 = 14 • ccbar yield per minbias = .0055 x 600 = 3.3 • Lc+ yield per 10% central = 14x0.2x0.5 = 1.4 • Lc+ yield per minbias = 3.3x0.2x0.5 = 0.33 • Branching ratio 5%: 1.4x0.05=0.07 central, 0.33x0.05=1.65 e-2 • Accepted Lc+ = 0.07 x 0.17 = 0.012 central, 2.8 e-3 minbias • Efficiency 0.8 (single track) : .012x(0.83) = .006 central, 1.44 e-3 • 1 Lc+ in the right decay mode in our acceptance per 200 10% central events. • 1 Lc+ in 1000 minbias events. Manuel Calderon de la Barca

7. Analysis Cuts • Fit points >=24 • dE/dx points >=20 • Dca < 1.5 cm • |h|<1.0 • PID cuts: • |nSigma_X|<1 && |nSigma_Y|>3 && |nSigma_Z|>3 • Where x,y,z == pion,kaon,proton Manuel Calderon de la Barca

8. Hey, what’s all this stuff?? PID Checks More events! Few events Deuterons visible, other tracks are possible merged tracks, but their contribution is small. Manuel Calderon de la Barca

9. Data: pt of candidate daughters • This is the right kinematic range for the Lc+. • Can we beat the background? Manuel Calderon de la Barca

10. Invariant mass plots central. (Signal) (Signal) • Background estimate from 3.2 M central events. • 23 counts per event: S/B = 0.006/23 = 2.6x10-4 • For a 3s signal, need : 9 x 2(3833) = 69K Lc+ • Nevents = 69K/0.006 = 11.5 M central events (sufficient in Run IV) Manuel Calderon de la Barca

11. Invariant mass plots (minbias). (Signal) (Signal) • Background estimate from 118K minbias events. • 12 counts per event: S/B = 0.00144/23 = 6.2x10-5 • For a 3s signal, need : 9 x 2(16014) = 288K Lc+ • Nevents = 288K/0.006 = 48 M minbias events (not sufficient in Run IV) Manuel Calderon de la Barca

12. Doesn’t work! Background subtraction • If we flip the sign of the pion, can that give us a background histogram if p+/p- = 1 ? Manuel Calderon de la Barca

13. Why doesn’t it work? • Ratio is not exactly 1. Manuel Calderon de la Barca

14. p+/p- expanded scale • Ratio not flat and not =1 to few per mil. • Important when need to model background in millons of events! • Contamination above 0.6 GeV plays a role. Manuel Calderon de la Barca

15. Fitting the shape. • Approach: • polinomial fit in 2.1 < M < 2.5 • Add a gaussian and see if chi2 improves. • (for later, i.e. no signal there, statistics is still too low.) Manuel Calderon de la Barca

16. In pT bins, does subtraction work? pK+p- (Lc+) 0<pt<0.5 3.6 M Central Events c2/dof=0.99 Invariant mass. Subtraction of pol6 fit. pK-p+ (Lc-) 1<pt<1.5 3.6 M Central Events c2/dof=0.79 Manuel Calderon de la Barca

17. Conclusions • From rough signal and background numbers, possible signal in Run 4 • 15 M events for ~3s signal in central events. • To do: • Process data as it comes, check for pt dependence. • Will process minbias, central events. Manuel Calderon de la Barca