1. Lc+ Status Report Heavy Flavor Working Group
Manuel Calderon de la Barca
Indiana University
08-Mar-05

2. Manuel Calderon de la Barca
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 = 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?
08-Mar-05
Manuel Calderon de la Barca

3. Manuel Calderon de la Barca
GEANT Simulations
Overall acceptance = 17%
Acc == (all 3 daughters leave 10 hits in TPC)
Thrown
Accepted
08-Mar-05
Manuel Calderon de la Barca

4. Manuel Calderon de la Barca
GEANT Acceptance
vs. pT (~20% at 1 GeV/c), vs. y (~40% at y=0)
08-Mar-05
Manuel Calderon de la Barca

5. Where are the daughters?
Proton
Pion
Kaon
Original <pt>
Accepted <pt> p
0.376
0.385 K
0.495
0.583
0.597
0.677
08-Mar-05
Manuel Calderon de la Barca

6. Manuel Calderon de la Barca
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 = 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+ = x 0.17 = 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 % central events.
1 Lc+ in 1000 minbias events.
08-Mar-05
Manuel Calderon de la Barca

7. Manuel Calderon de la Barca
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
08-Mar-05
Manuel Calderon de la Barca

8. Manuel Calderon de la Barca
PID Checks
More events!
Hey, what’s all this stuff??
Few events
Deuterons visible, other tracks
are possible merged tracks, but their
contribution is small.
08-Mar-05
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?
08-Mar-05
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)
08-Mar-05
Manuel Calderon de la Barca

11. Invariant mass plots (minbias).
(Signal)
(Signal)
Background estimate from 118K minbias events.
12 counts per event: S/B = /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)
08-Mar-05
Manuel Calderon de la Barca

12. Background subtraction
If we flip the sign of the pion, can that give us a background histogram if p+/p- = 1 ?
Doesn’t work!
08-Mar-05
Manuel Calderon de la Barca

13. Manuel Calderon de la Barca
Why doesn’t it work?
Ratio is not exactly 1.
08-Mar-05
Manuel Calderon de la Barca

14. Manuel Calderon de la Barca
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.
08-Mar-05
Manuel Calderon de la Barca

15. Manuel Calderon de la Barca
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.)
08-Mar-05
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
08-Mar-05
Manuel Calderon de la Barca

17. Manuel Calderon de la Barca
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.
08-Mar-05
Manuel Calderon de la Barca