Update on the pp → ΞΞ Analysis
Walter Ikegami Andersson
Uppsala Universityon behalf of the PANDA collaboration
PANDA collaboration meetingNovember 05-09, 2018GSI
1 / 20
Outline
Feasibility studies of pp → Ξ+Ξ− at pbeam = 7.0 GeV/c
Spin observables extraction using spin density matrix formalism
Will be presented on Thursday during plenary sessions
In this presentation
Test effects on reconstruction efficiency when changing differentialcross section
Test feasibility of measuring spin observables of pp → Ξ+Ξ− atpbeam = 4.6 GeV/c
2 / 20
Simulation parameters
Simulations are done with:
Release dec17p2b.
fairsoft may16p1
Fairroot v17.10b
Decay of Ξ handled by Geant4:
Ensures propagationof Ξ in B-field
Event sample: ∼ 8.5 · 105
Parameters:
Antiproton beam:pp = 7.0 GeV/cpp = 4.6 GeV/c
Full Detector Setup
Ideal Mass Hypothesis forKalman Filter
Ideal Pattern Recognition
Ideal Particle Identification
3 / 20
Preselection - first set
Preselection criteria:
Combine pπ− to form Λ candidates
Select |mΛ −M(pπ−)| < 50 MeV/c2
Combine Λπ− to form Ξ− candidates
Select |mΞ −M(Λπ−)| < 50 MeV/c2
DTF Ξ− → Λπ− → pπ−π−
Repeat for Ξ+ candidates
Combine Ξ+Ξ− to form pp system
4 / 20
Preselection - second set
Final selection criteria:
Vertex fit Ξ+Ξ−To propagate variablesfrom vertex to IP
Select ∠(Ξ+Ξ−) > 3 rad
Select ∆z = z(Λ)− z(Ξ) > 0 cm
Four constraint fit Ξ+Ξ−
Choose Ξ+Ξ− pair with smallest4C fit χ2
5 / 20
Preselection 1st set at pbeam = 7.0 GeV/c
Sample True False T/F ε
Λ 4.72× 105 4.75× 105 0.90 55%Λ 4.84× 105 5.39× 105 0.99 57%
Ξ+ 3.65× 105 3.71× 105 0.98 43%Ξ− 3.73× 105 3.49× 105 1.1 44%
Ξ+Ξ− 1st 8.9× 104 1.2× 104 7.6 10.4%
Efficiency of 10.4% after first set of preselection
Must impose further selection and choose one candidate per event
Consider background channels
6 / 20
Final Selection - Ξ Invariant Mass at pbeam = 7.0 GeV/c
Gaussian fit: mfit(Ξ+) = 1322.1 MeV/c2
and σfit(Ξ+) = 3.0 MeV/c2
Gaussian fit: mfit(Ξ−) = 1322.0 MeV/c2
and σfit(Ξ−) = 3.0 MeV/c2
Select |mfit(Ξ)−mpdg (Ξ)| < 15 MeV/c2
Black - Ξ+Ξ−
Red - Σ+(1385)
Blue - ΛΛπ+π−
Green - pp2π+2π−
Cyan - Combi.
]2) [GeV/c+
Ξ(fitm1.27 1.28 1.29 1.3 1.31 1.32 1.33 1.34 1.35 1.36 1.37
10
210
310
410
]2) [GeV/c-Ξ(fitm1.27 1.28 1.29 1.3 1.31 1.32 1.33 1.34 1.35 1.36 1.37
10
210
310
410
7 / 20
Final Selection - Displaced Vertex at pbeam = 7.0 GeV/c
I.P reconstructed with vertex fit
Ξ displaced from I.P
Select(z(Ξ+)− z(V0)) + (z(Ξ−)− z(V0)) > 3
Black - Ξ+Ξ−
Red - Σ+(1385)
Blue - ΛΛπ+π−
Green - pp2π+2π−
Cyan - Combi.
) [cm]0V - z-Ξ
) + (z0V - z+
Ξ(z
0 10 20 30 40 50 60 70 80 90 100
S+
BS
/
0
50
100
150
200
250
) [cm]0V - z-Ξ
) + (z0V - z+
Ξ(z
0 10 20 30 40 50 60 70 80 90 100
Ent
ries
10
210
310
8 / 20
Final Efficiencies
Limits are 90% C.L.
Channel Ξ+Ξ− Σ(1385)+Σ(1385)− ΛΛ2π+2π− pp2π+2π− DPMSample 8.5 × 105 10 × 107 10 × 107 10 × 107 10 × 107
σeff [µb] 0.123 4.33 24.1 390 58 300Weight factor 1 3.06 17.06 278 41 214
Preselection 2nd 7.83 × 104 3.15 × 104 3.51 × 103 1 14Final selection 6.76 × 104 3 14 0 0
N weighted 6.76 × 104 9 239 0 0S/B 420 7.4 × 103 283 > 106 > 0.7
Final signal efficiency of ε = 7.9%
High purity, S/B > 100 across relevant background channels
9 / 20
Differential cross section
Introduce forward-peaking distribution andsee change in final efficiency
10 / 20
Forward peaking distributions
Angular dsitribution modeled with empirical function, t ′ reducedmomentum transfer
I ∝ abe−bt′ + cde−dt′
h_d0thtcmEntries 852765Mean 0.5411Std Dev 0.4985
+Ξ
θcos 1− 0.8− 0.6− 0.4− 0.2− 0 0.2 0.4 0.6 0.8 1
0
10000
20000
30000
40000
50000
h_d0thtcmEntries 852765Mean 0.5411Std Dev 0.4985
+Ξ
θcos
More lenient caseε = 7.5%
h_d0thtcmEntries 843918Mean 0.9248Std Dev 0.094
+Ξ
θcos 1− 0.8− 0.6− 0.4− 0.2− 0 0.2 0.4 0.6 0.8 1
0
50
100
150
200
250
310× h_d0thtcm
Entries 843918Mean 0.9248Std Dev 0.094
+Ξ
θcos
Extreme case, parameters similar topp → Σ0Λ at pbeam = 6.0 GeV/c
ε = 5.0%
11 / 20
Spin Observables at pbeam = 4.6 GeV/c
Feasibility of measuring spin observables atpbeam = 4.6 GeV/c
12 / 20
Preselection 1st set at pbeam = 4.6 GeV/c
Sample True False T/F ε
Λ 5.14× 105 5.43× 105 0.95 60%Λ 5.25× 105 6.15× 105 0.85 62%
Ξ+ 3.87× 105 4.07× 105 0.95 46%Ξ− 3.95× 105 4.41× 105 0.90 46%
Ξ+Ξ− 1st 9.7× 104 8.9× 103 11 11.4%
Efficiency of 11.4% after first set of preselection
Must impose further selection and choose one candidate per event
Consider background channels
13 / 20
Final Selection - Ξ Invariant Mass at pbeam = 4.6 GeV/c
Gaussian fit: mfit(Ξ+) = 1322.2 MeV/c2
and σfit(Ξ+) = 2.8 MeV/c2
Gaussian fit: mfit(Ξ−) = 1322.2 MeV/c2
and σfit(Ξ−) = 2.8 MeV/c2
Select |mfit(Ξ)−mpdg (Ξ)| < 15 MeV/c2
Black - Ξ+Ξ−
Red - Σ+(1385)
Blue - ΛΛπ+π−
Green - pp2π+2π−
Cyan - Combi.
]2) [GeV/c+
Ξ(fitm1.27 1.28 1.29 1.3 1.31 1.32 1.33 1.34 1.35 1.36 1.37
10
210
310
410
]2) [GeV/c-Ξ(fitm1.27 1.28 1.29 1.3 1.31 1.32 1.33 1.34 1.35 1.36 1.37
10
210
310
410
14 / 20
Final Selection - Displaced Vertex at pbeam = 4.6 GeV/c
I.P reconstructed with vertex fit
Ξ displaced from I.P
Select(z(Ξ+)− z(V0)) + (z(Ξ−)− z(V0)) > 3
Black - Ξ+Ξ−
Red - Σ+(1385)
Blue - ΛΛπ+π−
Green - pp2π+2π−
Cyan - Combi.
) [cm]0V - z-Ξ
) + (z0V - z+
Ξ(z
0 10 20 30 40 50 60 70 80 90 100
S+
BS
/
0
50
100
150
200
250
) [cm]0V - z-Ξ
) + (z0V - z+
Ξ(z
0 10 20 30 40 50 60 70 80 90 100
Ent
ries
1
10
210
310
15 / 20
Final Efficiencies at pbeam = 4.6 GeV/c
Limits are 90% C.L.
Channel Ξ+Ξ− Σ(1385)+Σ(1385)− ΛΛ2π+2π− pp2π+2π− DPMSample 8.5 × 105 10 × 107 10 × 107 10 × 107 10 × 107
σeff [µb] 0.41 4.33 14.7 130 68 800Weight factor 1 0.946 3.21 28.6 15 087
Preselection 2nd 8.65 × 104 3.29 × 104 2.61 × 104 105 5Final selection 7.23 × 104 1 39 0 0
N weighted 7.23 × 104 0.9 125 0 0S/B 527 7.63 × 104 576 > 1.1 × 103 > 2.1
Final signal efficiency of ε = 8.5%, higher than pbeam = 4.6 GeV/ccase
High purity, S/B > 500 across relevant background channels, purerthan pbeam = 4.6 GeV/c case
16 / 20
Polarisation Py at pbeam = 4.6 GeV/c
Simulate sample of 107 signal events to construct acceptancecorrection matrices
Acceptance correct and extract spin observables with method ofmoments
ΛθCos 1− 0.8− 0.6− 0.4− 0.2− 0 0.2 0.4 0.6 0.8 1
Pol
aris
atio
n
1−
0.5−
0
0.5
1
YP
YPInputPRELIMINARY
ANDAPMC simulation
ΛθCos 1− 0.8− 0.6− 0.4− 0.2− 0 0.2 0.4 0.6 0.8 1
)/2
Y +
PY
(P
1−
0.5−
0
0.5
1
)/2Y
+ PY
(P
InputPRELIMINARY
ANDAPMC simulation
17 / 20
Spin Correlation Cii at pbeam = 4.6 GeV/c
Simulate sample of 107 signal events to construct acceptancecorrection matrices
Acceptance correct and extract spin observables with method ofmoments
ΛθCos 1− 0.5− 0 0.5 1
Spi
n co
rrel
atio
n C
xx
0.2−
0
0.2
0.4
0.6
0.8
1
1.2
1.4
xxC
InputPRELIMINARY
ANDAPMC simulation
ΛθCos 1− 0.5− 0 0.5 1
Spi
n co
rrel
atio
n C
yy
0.2−
0
0.2
0.4
0.6
0.8
1
1.2
1.4
yyC
InputPRELIMINARY
ANDAPMC simulation
ΛθCos 1− 0.5− 0 0.5 1
Spi
n co
rrel
atio
n C
zz
0.2−
0
0.2
0.4
0.6
0.8
1
1.2
1.4
zzC
InputPRELIMINARY
ANDAPMC simulation
18 / 20
Spin Correlation Cij at pbeam = 4.6 GeV/c
Simulate sample of 107 signal events to construct acceptancecorrection matrices
Acceptance correct and extract spin observables with method ofmoments
ΛθCos 1− 0.5− 0 0.5 1
Spi
n co
rrel
atio
n C
xz
0.2−
0
0.2
0.4
0.6
0.8
1
1.2
1.4
xzC
zxCInputPRELIMINARY
ANDAPMC simulation
ΛθCos 1− 0.5− 0 0.5 1
)/2
zx +
Cxz
(C
0.2−
0
0.2
0.4
0.6
0.8
1
1.2
1.4
)/2zx + Cxz
(C
InputPRELIMINARY
ANDAPMC simulation
19 / 20
Summary & Outlook
Analysis at pbeam = 7.0 GeV/c yields a signal efficiency of ε = 7.9%
Testing two forward peaking distributions yield ε = 7.5% andε = 5.0%
Spin observables analysis also tested at pbeam = 4.6 GeV/c- Signal efficiency of ε = 8.5%- Spin observables can be extracted
Thank you for your attention!
20 / 20
Summary & Outlook
Analysis at pbeam = 7.0 GeV/c yields a signal efficiency of ε = 7.9%
Testing two forward peaking distributions yield ε = 7.5% andε = 5.0%
Spin observables analysis also tested at pbeam = 4.6 GeV/c- Signal efficiency of ε = 8.5%- Spin observables can be extracted
Thank you for your attention!
20 / 20
Backup
20 / 20
Acceptance functions
Acceptance used forCxx
xk1− 0.5− 0 0.5 1xk
1−0.5−00.5
10
0.1
0.2
xk1− 0.5− 0 0.5 1xk
1−0.5−00.5
10
0.1
0.2
xk1− 0.5− 0 0.5 1xk
1−0.5−00.5
10
0.1
0.2
xk1− 0.5− 0 0.5 1xk
1−0.5−00.5
10
0.1
0.2
xk1− 0.5− 0 0.5 1xk
1−0.5−00.510
0.1
0.2
xk1− 0.5− 0 0.5 1xk
1−0.5−00.510
0.1
0.2
xk1− 0.5− 0 0.5 1xk
1−0.5−00.510
0.1
0.2
xk1− 0.5− 0 0.5 1xk
1−0.5−00.510
0.1
0.2
20 / 20
Acceptance functions
Acceptance used forCyy
yk1− 0.5− 0 0.5 1yk
1−0.5−00.5
10
0.1
0.2
yk1− 0.5− 0 0.5 1yk
1−0.5−00.5
10
0.1
0.2
yk1− 0.5− 0 0.5 1yk
1−0.5−00.5
10
0.1
0.2
yk1− 0.5− 0 0.5 1yk
1−0.5−00.5
10
0.1
0.2
yk1− 0.5− 0 0.5 1yk
1−0.5−00.510
0.1
0.2
yk1− 0.5− 0 0.5 1yk
1−0.5−00.510
0.1
0.2
yk1− 0.5− 0 0.5 1yk
1−0.5−00.510
0.1
0.2
yk1− 0.5− 0 0.5 1yk
1−0.5−00.510
0.1
0.2
20 / 20
Acceptance functions
Acceptance used forCzz
zk1− 0.5− 0 0.5 1zk
1−0.5−00.5
10
0.1
0.2
zk1− 0.5− 0 0.5 1zk
1−0.5−00.5
10
0.1
0.2
zk1− 0.5− 0 0.5 1zk
1−0.5−00.5
10
0.1
0.2
zk1− 0.5− 0 0.5 1zk
1−0.5−00.5
10
0.1
0.2
zk1− 0.5− 0 0.5 1zk
1−0.5−00.510
0.1
0.2
zk1− 0.5− 0 0.5 1zk
1−0.5−00.510
0.1
0.2
zk1− 0.5− 0 0.5 1zk
1−0.5−00.510
0.1
0.2
zk1− 0.5− 0 0.5 1zk
1−0.5−00.510
0.1
0.2
20 / 20
Acceptance functions
Acceptance used forCxz
xk1− 0.5− 0 0.5 1zk
1−0.5−00.5
10
0.1
0.2
xk1− 0.5− 0 0.5 1zk
1−0.5−00.5
10
0.1
0.2
xk1− 0.5− 0 0.5 1zk
1−0.5−00.5
10
0.1
0.2
xk1− 0.5− 0 0.5 1zk
1−0.5−00.5
10
0.1
0.2
xk1− 0.5− 0 0.5 1zk
1−0.5−00.510
0.1
0.2
xk1− 0.5− 0 0.5 1zk
1−0.5−00.510
0.1
0.2
xk1− 0.5− 0 0.5 1zk
1−0.5−00.510
0.1
0.2
xk1− 0.5− 0 0.5 1zk
1−0.5−00.510
0.1
0.2
20 / 20
Acceptance functions
Acceptance used forCzx
zk1− 0.5− 0 0.5 1xk
1−0.5−00.5
10
0.1
0.2
zk1− 0.5− 0 0.5 1xk
1−0.5−00.5
10
0.1
0.2
zk1− 0.5− 0 0.5 1xk
1−0.5−00.5
10
0.1
0.2
zk1− 0.5− 0 0.5 1xk
1−0.5−00.5
10
0.1
0.2
zk1− 0.5− 0 0.5 1xk
1−0.5−00.510
0.1
0.2
zk1− 0.5− 0 0.5 1xk
1−0.5−00.510
0.1
0.2
zk1− 0.5− 0 0.5 1xk
1−0.5−00.510
0.1
0.2
zk1− 0.5− 0 0.5 1xk
1−0.5−00.510
0.1
0.2
20 / 20
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