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