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  • 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 �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/c2and 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 × 107σeff [µb] 0.123 4.33 24.1 390 58 300

    Weight factor 1 3.06 17.06 278 41 214Preselection 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 � = 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

    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

    θcos

    More lenient case� = 7.5%

    h_d0thtcmEntries 843918Mean 0.9248Std Dev 0.094

    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

    θcos

    Extreme case, parameters similar topp → Σ0Λ at pbeam = 6.0 GeV/c

    � = 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 �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/c2and 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 × 107σeff [µb] 0.41 4.33 14.7 130 68 800

    Weight factor 1 0.946 3.21 28.6 15 087Preselection 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 � = 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

    YPInputPR

    ELIMIN

    ARY

    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

    InputPRELI

    MINAR

    Y

    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

    InputPRELI

    MINAR

    Y

    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

    InputPRELI

    MINAR

    Y

    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

    InputPRELI

    MINAR

    Y

    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

    zxCInputPR

    ELIMIN

    ARY

    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

    InputPRELI

    MINAR

    Y

    ANDAPMC simulation

    19 / 20

  • Summary & Outlook

    Analysis at pbeam = 7.0 GeV/c yields a signal efficiency of � = 7.9%

    Testing two forward peaking distributions yield � = 7.5% and� = 5.0%

    Spin observables analysis also tested at pbeam = 4.6 GeV/c- Signal efficiency of � = 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 � = 7.9%

    Testing two forward peaking distributions yield � = 7.5% and� = 5.0%

    Spin observables analysis also tested at pbeam = 4.6 GeV/c- Signal efficiency of � = 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

    1−0.5−0

    0.510

    0.1

    0.2

    xk1− 0.5−0 0.5

    1xk

    1−0.5−0

    0.510

    0.1

    0.2

    xk1− 0.5−0 0.5

    1xk

    1−0.5−0

    0.510

    0.1

    0.2

    xk1− 0.5−0 0.5

    1xk

    1−0.5−0

    0.510

    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

    1−0.5−0

    0.510

    0.1

    0.2

    yk1− 0.5−0 0.5

    1yk

    1−0.5−0

    0.510

    0.1

    0.2

    yk1− 0.5−0 0.5

    1yk

    1−0.5−0

    0.510

    0.1

    0.2

    yk1− 0.5−0 0.5

    1yk

    1−0.5−0

    0.510

    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

    1−0.5−0

    0.510

    0.1

    0.2

    zk1− 0.5−0 0.5

    1zk

    1−0.5−0

    0.510

    0.1

    0.2

    zk1− 0.5−0 0.5

    1zk

    1−0.5−0

    0.510

    0.1

    0.2

    zk1− 0.5−0 0.5

    1zk

    1−0.5−0

    0.510

    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

    1−0.5−0

    0.510

    0.1

    0.2

    xk1− 0.5−0 0.5

    1zk

    1−0.5−0

    0.510

    0.1

    0.2

    xk1− 0.5−0 0.5

    1zk

    1−0.5−0

    0.510

    0.1

    0.2

    xk1− 0.5−0 0.5

    1zk

    1−0.5−0

    0.510

    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

    1−0.5−0

    0.510

    0.1

    0.2

    zk1− 0.5−0 0.5

    1xk

    1−0.5−0

    0.510

    0.1

    0.2

    zk1− 0.5−0 0.5

    1xk

    1−0.5−0

    0.510

    0.1

    0.2

    zk1− 0.5−0 0.5

    1xk

    1−0.5−0

    0.510

    0.1

    0.2

    20 / 20