1. Tanja Susa Kreso Kadija Tome Anticic Vedran Nikolic
Production of hyperon and hyperon resonances in p+p collisions (and status of pA analysis)
Tanja Susa
Kreso Kadija
Tome Anticic
Vedran Nikolic
Rudjer Boskovic Institute
Zagreb, Croatia
NA49 collaboration meeting, CERN, 2008

2. Inclusive cross section
But Nbeam hard to determine
Instead, use ratio N trigger/Nbeam and N trigger
≈1% difference
Used before
Use exact formula

3. Negligible difference
Trigger cross section
From full and empty data sample
Take into account beam attenuation
Before
≈2% difference
Negligible difference
p+p pion paper

4. Ntrigger sF sE s2 s1 x2 x1 l Very complicated…
From full and empty data sample
Take into account beam attenuation
Very complicated…
≈1% difference sF sE s1 s2 x1 x2 l

5. nx nx = nxdet CF VENUS . nx number of particles x produced in hydrogen
nxdet number of detected particles x (xi/v0) after vertex cuts
CF ... correction factor:
branching ratio
acceptance and efficiency
v0/xi cuts
trigger loss correction
vertex cuts losses
VENUS .

6. Data sets All p+p data sets Changes with respect to old analysis
Improve geometry and correct
residual distortions
1996
1999
2000
2001
2002
1.03 M
1.21 M
2.67 M
0.67 M
2.84 M
Correct bugs in reconstruction
clients
R3D
tpc_error
Open cuts and/or correct bugs
in V0 fitter/finder and Ξ finder
and use new 13 par. Ξ fitter

7. all tracks are +- 3 s (dE/dX)
 cuts
(by)2 + (bx/2)2 < x2
proton p 
rap < -2.25
z - zmain < 0 cm
x = 1
-2.35 < rap < -2.25
z - zmain < 1 cm
x = 1
all tracks are +- 3 s (dE/dX)
-1.75 < rap < 0.25
z - zmain < 3 cm
x = 1
2 MeV/bin
0.25< rap < 0.75
z - zmain < 5 cm
x = 1
about 125k
0.75 < rap < 1.25
z - zmain < 5 cm
x = 0.25
1.25 < rap < 1.75
z - zmain < 10 cm
x = 0.25
Minv(pπ-)[GeV]

8.  signal comparison 96 + 99 + 00 data sets New Old about 68 k
2 MeV/bin
2 MeV/bin
New
Old
Minv(pπ-)[GeV]
Minv(pπ-)[GeV]
about 68 k
about 35k

9. Both include losses due
 correction factors
1./CF
New
Old
rat
Both include losses due
to the vertex cut

10.  signal - rapidity dσ/dpt[mb/GeV] dσ/dy[mb] w/o feed. corr.
pt[GeV]

11.  rapidity comparison feed. corr. dσ/dy[mb] new old rapidity

12.  pt comparison y=-1.5 y=-1 y=-0.5 y=0 new old y=1.5 y=1 y=0.5

13.  signal – inv. xf dσ/dpt[mb/GeV] dσ/dy[mb] w/o feed. corr.
pt[GeV]

14.  inv. xf comparison feed. corr. dσ/dy[mb] new old xf

15. Comparison with world data

16. Some quality checks on the new data
Check sensitivity of L yield on behaviour of:
Vertex cut
S4 trigger loss
Geometry and residual distorsion corrections
Stability across years

17. Vertex cut CUT nev/nevorig vtx. fitted 81%
≈ 18% of data: background interactions
CUT nev/nevorig
vtx. fitted %
|z-zcent| < 9 cm % (|z-zcent| < 5.5 cm, 96 )
x2+y2 < 1 cm %
Loss of the p+p event ≈ 25% (10% geom. effect)
Corrected with VENUS

18. Non-reconstructed vertex (2000)
rec. vtx.
non-rec. vtx.
FULL
# of Λ in hydrogen
nnorec/nrec ≈ 3.1%
EMPTY

19. Non-reconstructed vertex (2002)
rec. vtx.
non-rec. vtx.
FULL
# of Λ in hydrogen
nnorec/nrec ≈ 1.2%
EMPTY

20. Non-reconstructed vertex (MC)
rec. vtx.
non-rec. vtx.
minv(pπ-)[GeV]
# of Λ in hydrogen
nnorec/nrec ≈ 1.8 %
Good agreement with data

21. In ideal case, FT-ET should be flat. Good agreement. Systematics on
Reconstructed vertex
VENUS corrected
|z-znom|[cm]
σΛ/σΛ(9 cm cut) FT
FT-ET
All rapidities
|y| < 0.25
In ideal case, FT-ET should be flat.
Good agreement. Systematics on
the order of about 1-2 %

22. Reconstructed vertex (MC)
Data (FT -ET)
VENUS (MB)
z[cm] n
Additional check
Good agreement of data with MC

23.  trigger loss (VENUS S4 correction)
S4 correction comparison
between VENUS and data (2002 using GAP TPC data)
data
VENUS
Good agreement

24. Stability across the years
Midrapidity  yield
ds/dy
feed. corr.
year
Max difference 1996 (7%)

25. Geometry and residual distortion correction
w/o geom.corr.
old V0
new V0
with geom. corr.
Reconstructed 2000 data w/o geom. and res.corr.
improved clients included
MC data not corrected for residual distortion
Run both old & new V0, Ξ finders/fitters mb
Analysis type
pt [GeV]
Yield stable, geom., res. corr. and V0 finder/fitter not a source of differences

26. pA analysis status Geometry/Residuals corrected for 1999 and 2001
Data run for 1999
2001 in progress
Analysis proceeding
1999
2001
events
Centralities:
events
Centralities:

27. 1999 pA geometry After corrections in: Geometry Residuals BPD
x residuals (cm)
Before
y residuals (cm)
z (cm)

28. 1999 pA impact paramters Main vertex tracks L cm cm cm cm
x impact parameter cm
y impact parameter cm cm cm
Main vertex tracks L

29. L invariant mass
About 15% more Ls
GeV

30. Conclusion L analysis in good progress
Systematic influence found small for: S4
main vertex
geometry and distortion correction
V0 finder/fitter
pA analysis in progress