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Title: The


1
The Underlying Event in Run 2 (CDF)
The underlying event consists of hard initial
final-state radiation plus the beam-beam
remnants and possible multiple parton
interactions.
Studying the Underlying Event
  • Two Classes of Events Leading Jet and
    Back-to-Back.
  • Two Transverse regions transMAX, transMIN,
    transDIF.
  • PTmax and PTmaxT distributions and averages.
  • Df Distributions Density and Associated
    Density.
  • ltpTgt versus charged multiplicity min-bias and
    the transverse region.
  • Correlations between the two transverse
    regions trans1 vs trans2.
  • Studying the Underlying Event in Drell-Yan
    Production.
  • Extrapolations to the LHC.

UEMB_at_CMS
Florida-Perugia
CMS at the LHC
2
The Transverse Regionsas defined by the
Leading Jet
Charged Particle Df Correlations pT gt 0.5 GeV/c
h lt 1
Look at the charged particle density in the
transverse region!
Transverse region is very sensitive to the
underlying event!
  • Look at charged particle correlations in the
    azimuthal angle Df relative to the leading
    calorimeter jet (JetClu R 0.7, h lt 2).
  • Define Df lt 60o as Toward, 60o lt -Df lt 120o
    and 60o lt Df lt 120o as Transverse 1 and
    Transverse 2, and Df gt 120o as Away. Each
    of the two transverse regions have area DhDf
    2x60o 4p/6. The overall transverse region is
    the sum of the two transverse regions (DhDf
    2x120o 4p/3).

3
Particle Densities
Charged Particles pT gt 0.5 GeV/c h lt 1
CDF Run 2 Min-Bias
DhDf 4p 12.6
CDF Run 2 Min-Bias Observable Average Average Density per unit h-f
Nchg Number of Charged Particles (pT gt 0.5 GeV/c, h lt 1) 3.17 /- 0.31 0.252 /- 0.025
PTsum (GeV/c) Scalar pT sum of Charged Particles (pT gt 0.5 GeV/c, h lt 1) 2.97 /- 0.23 0.236 /- 0.018
  • Study the charged particles (pT gt 0.5 GeV/c, h
    lt 1) and form the charged particle density,
    dNchg/dhdf, and the charged scalar pT sum
    density, dPTsum/dhdf.

4
Transverse Particle Densities
Charged Particles pT gt 0.5 GeV/c h lt 1
Area 4p/6
  • Study the charged particles (pT gt 0.5 GeV/c, h
    lt 1) in the Transverse 1 and Transverse 2 and
    form the charged particle density, dNchg/dhdf,
    and the charged scalar pT sum density,
    dPTsum/dhdf.
  • The average transverse density is the average
    of transverse 1 and transverse 2.

5
Charged Particle Density Df Dependence
Log Scale!
Min-Bias 0.25 per unit h-f
  • Shows the Df dependence of the charged particle
    density, dNchg/dhdf, for charged particles in the
    range pT gt 0.5 GeV/c and h lt 1 relative to
    jet1 (rotated to 270o) for leading jet events
    30 lt ET(jet1) lt 70 GeV.
  • Also shows charged particle density, dNchg/dhdf,
    for charged particles in the range pT gt 0.5 GeV/c
    and h lt 1 for min-bias collisions.

6
Charged Particle Density Df Dependence
Refer to this as a Leading Jet event
Subset
Refer to this as a Back-to-Back event
  • Look at the transverse region as defined by the
    leading jet (JetClu R 0.7, h lt 2) or by the
    leading two jets (JetClu R 0.7, h lt 2).
    Back-to-Back events are selected to have at
    least two jets with Jet1 and Jet2 nearly
    back-to-back (Df12 gt 150o) with almost equal
    transverse energies (ET(jet2)/ET(jet1) gt 0.8)
    and with ET(jet3) lt 15 GeV.
  • Shows the Df dependence of the charged particle
    density, dNchg/dhdf, for charged particles in the
    range pT gt 0.5 GeV/c and h lt 1 relative to
    jet1 (rotated to 270o) for 30 lt ET(jet1) lt 70
    GeV for Leading Jet and Back-to-Back events.

7
Charged Particle Density Df Dependence
Leading Jet
Back-to-Back
Polar Plot
  • Shows the Df dependence of the charged particle
    density, dNchg/dhdf, for charged particles in the
    range pT gt 0.5 GeV/c and h lt 1 relative to
    jet1 (rotated to 270o) for 30 lt ET(jet1) lt 70
    GeV for Leading Jet and Back-to-Back events.

8
Transverse PTsum Density versus ET(jet1)
Leading Jet
Back-to-Back
Min-Bias 0.24 GeV/c per unit h-f
  • Shows the average charged PTsum density,
    dPTsum/dhdf, in the transverse region (pT gt 0.5
    GeV/c, h lt 1) versus ET(jet1) for Leading
    Jet and Back-to-Back events.
  • Compares the (uncorrected) data with PYTHIA Tune
    A and HERWIG after CDFSIM.

9
Transverse PTsum Density versus ET(jet1)
30-70 GeV
95-130 GeV
Very little dependence on ET(jet1) in the
transverse region for back-to-back events!
10
TransDIF PTsum Density versus ET(jet1)
Leading Jet
Back-to-Back
MAX-MIN is very sensitive to the hard
scattering component of the underlying event!
  • Use the leading jet to define the MAX and MIN
    transverse regions on an event-by-event basis
    with MAX (MIN) having the largest (smallest)
    charged PTsum density.
  • Shows the transDIF MAX-MIN charge PTsum
    density, dPTsum/dhdf, for pT gt 0.5 GeV/c, h lt 1
    versus ET(jet1) for Leading Jet and
    Back-to-Back events.

11
TransMIN PTsum Density versus ET(jet1)
Leading Jet
Back-to-Back
transMIN is very sensitive to the beam-beam
remnant component of the underlying event!
  • Use the leading jet to define the MAX and MIN
    transverse regions on an event-by-event basis
    with MAX (MIN) having the largest (smallest)
    charged particle density.
  • Shows the transMIN charge particle density,
    dNchg/dhdf, for pT gt 0.5 GeV/c, h lt 1 versus
    ET(jet1) for Leading Jet and Back-to-Back
    events.

12
Transverse PTsum Density PYTHIA Tune A vs
HERWIG
Leading Jet
Back-to-Back
Now look in detail at back-to-back events in
the region 30 lt ET(jet1) lt 70 GeV!
  • Shows the average charged PTsum density,
    dPTsum/dhdf, in the transverse region (pT gt 0.5
    GeV/c, h lt 1) versus ET(jet1) for Leading
    Jet and Back-to-Back events.
  • Compares the (uncorrected) data with PYTHIA Tune
    A and HERWIG after CDFSIM.

13
Charged PTsum DensityPYTHIA Tune A vs HERWIG
HERWIG (without multiple parton interactions)
does not produces enough PTsum in the
transverse region for 30 lt ET(jet1) lt 70 GeV!
14
Transverse PTsum Density PYTHIA Tune A vs
HERWIG
Leading Jet
Back-to-Back
Now look in detail at back-to-back events in
the region 95 lt ET(jet1) lt 130 GeV!
  • Shows the average charged PTsum density,
    dPTsum/dhdf, in the transverse region (pT gt 0.5
    GeV/c, h lt 1) versus ET(jet1) for Leading
    Jet and Back-to-Back events compared with
    PYTHIA Tune A and HERWIG after CDFSIM.

15
Charged PTsum DensityPYTHIA Tune A vs HERWIG
HERWIG (without multiple parton interactions)
agrees much better in the transverse region for
95 lt ET(jet1) lt 130 GeV!
16
Transverse ltpTgt versusTransverse Nchg
Leading Jet
Back-to-Back
Min-Bias
  • Look at the ltpTgt of particles in the transverse
    region (pT gt 0.5 GeV/c, h lt 1) versus the
    number of particles in the transverse region
    ltpTgt vs Nchg.
  • Shows ltpTgt versus Nchg in the transverse region
    (pT gt 0.5 GeV/c, h lt 1) for Leading Jet and
    Back-to-Back events with 30 lt ET(jet1) lt 70
    GeV compared with min-bias collisions.

17
Transverse PTmax versus ET(jet1)
Leading Jet
Back-to-Back
Min-Bias
  • Use the leading jet to define the transverse
    region and look at the maximum pT charged
    particle in the transverse region, PTmaxT.
  • Shows the average PTmaxT, in the transverse
    region (pT gt 0.5 GeV/c, h lt 1) versus ET(jet1)
    for Leading Jet and Back-to-Back events
    compared with the average maximum pT particle,
    PTmax, in min-bias collisions (pT gt 0.5 GeV/c,
    h lt 1).

18
Back-to-Back AssociatedCharged Particle
Densities
Maximum pT particle in the transverse region!
Associated densities do not include PTmaxT!
  • Use the leading jet in back-to-back events to
    define the transverse region and look at the
    maximum pT charged particle in the transverse
    region, PTmaxT.
  • Look at the Df dependence of the associated
    charged particle and PTsum densities, dNchg/dhdf
    and dPTsum/dhdf for charged particles (pT gt 0.5
    GeV/c, h lt 1, not including PTmaxT) relative to
    PTmaxT.
  • Rotate so that PTmaxT is at the center of the
    plot (i.e. 180o).

19
Back-to-Back AssociatedCharged Particle
Densities
Associated densities do not include PTmaxT!
Jet2 Region
??
Log Scale!
  • Look at the Df dependence of the associated
    charged particle density, dNchg/dhdf for charged
    particles (pT gt 0.5 GeV/c, h lt 1, not including
    PTmaxT) relative to PTmaxT (rotated to 180o) for
    PTmaxT gt 0.5 GeV/c, PTmaxT gt 1.0 GeV/c and PTmaxT
    gt 2.0 GeV/c, for back-to-back events with 30 lt
    ET(jet1) lt 70 GeV.
  • Shows jet structure in the transverse region
    (i.e. the birth of the 3rd 4th jet).

20
Back-to-Back AssociatedCharged PTsum Density
Associated densities do not include PTmaxT!
Jet2 Region
??
Log Scale!
  • Look at the Df dependence of the associated
    charged particle density, dPTsum/dhdf for charged
    particles (pT gt 0.5 GeV/c, h lt 1, not including
    PTmaxT) relative to PTmaxT (rotated to 180o) for
    PTmaxT gt 0.5 GeV/c, PTmaxT gt 1.0 GeV/c and PTmaxT
    gt 2.0 GeV/c, for back-to-back events with 30 lt
    ET(jet1) lt 70 GeV.
  • Shows jet structure in the transverse region
    (i.e. the birth of the 3rd 4th jet).

21
Back-to-Back AssociatedCharged Particle
Densities
Back-to-Back charge density
Back-to-Back associated density
  • Shows the Df dependence of the associated
    charged particle density, dNchg/dhdf for charged
    particles (pT gt 0.5 GeV/c, h lt 1, not including
    PTmaxT) relative to PTmaxT (rotated to 180o) for
    PTmaxT gt 0.5 GeV/c, PTmaxT gt 1.0 GeV/c and PTmaxT
    gt 2.0 GeV/c, for back-to-back events with 30 lt
    ET(jet1) lt 70 GeV.

It is more probable to find a particle
accompanying PTmaxT than it is to find a particle
in the transverse region!
  • Shows Df dependence of the charged particle
    density, dNchg/dhdf for charged particles (pT gt
    0.5 GeV/c, h lt 1) relative to jet1 (rotated to
    270o) for back-to-back events with 30 lt
    ET(jet1) lt 70 GeV.

22
Back-to-Back AssociatedCharged Particle
Densities
Back-to-Back charge density
Back-to-Back associated density
Polar Plot
  • Shows the Df dependence of the associated
    charged particle density, dNchg/dhdf, pT gt 0.5
    GeV/c, h lt 1 (not including PTmaxT) relative to
    PTmaxT (rotated to 180o) and the charged particle
    density, dNchg/dhdf, pT gt 0.5 GeV/c, h lt 1
    relative to jet1 (rotated to 270o) for
    back-to-back events with 30 lt ET(jet1) lt 70
    GeV.

23
Back-to-Back AssociatedCharged Particle
Densities
Back-to-Back charge density
Back-to-Back associated density
Polar Plot
  • Shows the Df dependence of the associated
    charged particle density, dNchg/dhdf, pT gt 0.5
    GeV/c, h lt 1, PTmaxT gt 2.0 GeV/c (not including
    PTmaxT) relative to PTmaxT (rotated to 180o) and
    the charged particle density, dNchg/dhdf, pT gt
    0.5 GeV/c, h lt 1, relative to jet1 (rotated to
    270o) for back-to-back events with 30 lt
    ET(jet1) lt 70 GeV.

24
Jet Topologies
QCD Four Jet Topology
QCD Three Jet Topology
Polar Plot
  • Shows the Df dependence of the associated
    charged particle density, dNchg/dhdf, pT gt 0.5
    GeV/c, h lt 1, PTmaxT gt 2.0 GeV/c (not including
    PTmaxT) relative to PTmaxT (rotated to 180o) and
    the charged particle density, dNchg/dhdf, pT gt
    0.5 GeV/c, h lt 1, relative to jet1 (rotated to
    270o) for back-to-back events with 30 lt
    ET(jet1) lt 70 GeV.

25
Back-to-Back AssociatedCharged Particle
Density
Jet2 Region
Log Scale!
  • Look at the Df dependence of the associated
    charged particle density, dNchg/dhdf, pT gt 0.5
    GeV/c, h lt 1 (not including PTmaxT) relative to
    PTmaxT (rotated to 180o) for PTmaxT gt 2.0 GeV/c
    for back-to-back events with 30 lt ET(jet1) lt
    70 GeV and 95 lt ET(jet1) lt 130 GeV.
  • Very little dependence on ET(jet1) in the
    transverse region for back-to-back events!

26
Back-to-Back vs Min-BiasAssociated Charge
Density
Birth of jet3 in the transverse region!
Back-to-Back Associated Density
Min-Bias Associated Density
Log Scale!
Birth of jet1 in min-bias collisions!
  • Shows the Df dependence of the associated
    charged particle density, dNchg/dhdf for pT gt 0.5
    GeV/c, h lt 1 (not including PTmaxT) relative to
    PTmaxT (rotated to 180o) for PTmaxT gt 2.0 GeV/c,
    for back-to-back events with 30 lt ET(jet1) lt
    70 GeV.
  • Shows the data on the Df dependence of the
    associated charged particle density,
    dNchg/dhdf, pT gt 0.5 GeV/c, h lt 1 (not
    including PTmax) relative to PTmax (rotated to
    180o) for min-bias events with PTmax gt 2.0
    GeV/c.

27
Back-to-Back vs Min-BiasAssociated PTsum
Density
Birth of jet3 in the transverse region!
Back-to-Back Associated Density
Min-Bias Associated Density
Log Scale!
Birth of jet1 in min-bias collisions!
  • Shows the Df dependence of the associated
    charged particle density, dNchg/dhdf for pT gt 0.5
    GeV/c, h lt 1 (not including PTmaxT) relative to
    PTmaxT (rotated to 180o) for PTmaxT gt 2.0 GeV/c,
    for back-to-back events with 30 lt ET(jet1) lt
    70 GeV.
  • Shows the data on the Df dependence of the
    associated charged particle density,
    dNchg/dhdf, pT gt 0.5 GeV/c, h lt 1 (not
    including PTmax) relative to PTmax (rotated to
    180o) for min-bias events with PTmax gt 2.0
    GeV/c.

28
Associated PTsum DensityPYTHIA Tune A vs HERWIG
HERWIG (without multiple parton interactions)
does not produce enough associated PTsum in the
direction of PTmaxT!
PTmaxT gt 0.5 GeV/c
And HERWIG (without multiple parton interactions)
does not produce enough PTsum in the direction
opposite of PTmaxT!
29
Associated PTsum DensityPYTHIA Tune A vs HERWIG
PTmaxT gt 2 GeV/c
But HERWIG (without multiple parton interactions)
produces too few particles in the direction
opposite of PTmaxT!
30
Jet Multiplicity
Max pT in the transverse region!
HERWIG (without multiple parton interactions)
does not have equal amounts of 3 and 4 jet
topologies!
Data have about equal amounts of 3 and 4 jet
topologies!
  • Shows the data on the number of jets (JetClu, R
    0.7, h lt 2, ET(jet) gt 3 GeV) for back-to-back
    events with 30 lt ET(jet1) lt 70 GeV and PTmaxT gt
    2.0 GeV/c.
  • Compares the (uncorrected) data with PYTHIA Tune
    A after CDFSIM.
  • Compares the (uncorrected) data with HERWIG after
    CDFSIM.

31
Transverse 1 Region vsTransverse 2 Region
Leading Jet
Back-to-Back
  • Use the leading jet to define two transverse
    regions and look at the correlations between
    transverse 1 and transverse 2.
  • Shows the average number of charged particles in
    the transverse 2 region versus the number of
    charged particles in the transverse 1 region
    for pT gt 0.5 GeV/c and h lt 1 for Leading Jet
    and Back-to-Back events.
  • Shows the average pT of charged particles in the
    transverse 2 region versus the number of
    charged particles in the transverse 1 region
    for pT gt 0.5 GeV/c and h lt 1 for Leading Jet
    and Back-to-Back events.

32
Transverse 1 Region vsTransverse 2 Region
33
The Central Regionin Drell-Yan Production
Look at the charged particle density and the
PTsum density in the central region!
Charged Particles (pT gt 0.5 GeV/c, h lt 1)
After removing the lepton-pair everything else is
the underlying event!
  • Look at the central region after removing the
    lepton-pair.
  • Study the charged particles (pT gt 0.5 GeV/c, h
    lt 1) and form the charged particle density,
    dNchg/dhdf, and the charged scalar pT sum
    density, dPTsum/dhdf, by dividing by the area in
    h-f space.

34
CDF Run 1 PT(Z)
PYTHIA 6.2 CTEQ5L
Parameter Tune A Tune A25 Tune A50
MSTP(81) 1 1 1
MSTP(82) 4 4 4
PARP(82) 2.0 GeV 2.0 GeV 2.0 GeV
PARP(83) 0.5 0.5 0.5
PARP(84) 0.4 0.4 0.4
PARP(85) 0.9 0.9 0.9
PARP(86) 0.95 0.95 0.95
PARP(89) 1.8 TeV 1.8 TeV 1.8 TeV
PARP(90) 0.25 0.25 0.25
PARP(67) 4.0 4.0 4.0
MSTP(91) 1 1 1
PARP(91) 1.0 2.5 5.0
PARP(93) 5.0 15.0 25.0
UE Parameters
ISR Parameter
  • Shows the Run 1 Z-boson pT distribution (ltpT(Z)gt
    11.5 GeV/c) compared with PYTHIA Tune A
    (ltpT(Z)gt 9.7 GeV/c), Tune A25 (ltpT(Z)gt
    10.1 GeV/c), and Tune A50 (ltpT(Z)gt 11.2
    GeV/c).

Intrensic KT
35
CDF Run 1 PT(Z)
PYTHIA 6.2 CTEQ5L
Parameter Tune A Tune AW
MSTP(81) 1 1
MSTP(82) 4 4
PARP(82) 2.0 GeV 2.0 GeV
PARP(83) 0.5 0.5
PARP(84) 0.4 0.4
PARP(85) 0.9 0.9
PARP(86) 0.95 0.95
PARP(89) 1.8 TeV 1.8 TeV
PARP(90) 0.25 0.25
PARP(62) 1.0 1.25
PARP(64) 1.0 0.2
PARP(67) 4.0 4.0
MSTP(91) 1 1
PARP(91) 1.0 2.1
PARP(93) 5.0 15.0
UE Parameters
ISR Parameters
  • Shows the Run 1 Z-boson pT distribution (ltpT(Z)gt
    11.5 GeV/c) compared with PYTHIA Tune AW
    (ltpT(Z)gt 11.7 GeV/c).

Effective Q cut-off, below which space-like
showers are not evolved.
The Q2 kT2 in as for space-like showers is
scaled by PARP(64)!
Intrensic KT
36
Drell-Yan Productionat the Tevatron
ltPT(pair)gt versus M(pair)
Lepton-Pair Transverse Momentum
Z
Z
  • Shows the lepton-pair average PT versus the
    lepton-pair invariant mass at 1.96 TeV for PYTHIA
    Tune AW and PYTHIA Tune A.
  • Shows the lepton-pair average PT versus the
    lepton-pair invariant mass at 1.96 TeV for PYTHIA
    Tune AW and HERWIG.

37
Drell-Yan Productionat the LHC
ltPT(pair)gt versus M(pair)
Lepton-Pair Transverse Momentum
The lepton-pair ltPTgt much larger at the LHC!
Z
Z
  • Shows the lepton-pair average PT versus the
    lepton-pair invariant mass at 1.96 TeV for PYTHIA
    Tune AW and HERWIG.
  • Shows the lepton-pair average PT versus the
    lepton-pair invariant mass at 14 TeV for PYTHIA
    Tune AW and HERWIG.

38
The Underlying Event inDrell-Yan Production
(Tevatron)
Charged particle density versus M(pair)
The Underlying Event
HERWIG (without MPI) is much less active than PY
Tune AW (with MPI)!
Z
Z
  • Shows the charged particle density versus the
    lepton-pair invariant mass at 1.96 TeV for PYTHIA
    Tune AW and PYTHIA Tune A.
  • Shows the charged particle density versus the
    lepton-pair invariant mass at 1.96 TeV for PYTHIA
    Tune AW and HERWIG (with no MPI).

39
The Underlying Event inDrell-Yan Production
(LHC)
Charged particle density versus M(pair)
The Underlying Event
HERWIG (without MPI) is much less active than PY
Tune AW (with MPI)!
Underlying event much more active at the LHC!
Z
Z
  • Charged particle density versus the lepton-pair
    invariant mass at 1.96 TeV for PYTHIA Tune AW and
    HERWIG (without MPI).
  • Charged particle density versus the lepton-pair
    invariant mass at 14 TeV for PYTHIA Tune AW and
    HERWIG (without MPI).

40
The Underlying Event inHigh PT Jet Production
(LHC)
Charged particle density versus PT(jet1)
The Underlying Event
Underlying event much more active at the LHC!
  • Charged particle density in the Transverse
    region versus PT(jet1) at 1.96 TeV for PY Tune
    AW and HERWIG (without MPI).
  • Charged particle density in the Transverse
    region versus PT(jet1) at 14 TeV for PY Tune AW
    and HERWIG (without MPI).

41
The Underlying Event inHigh PT Jet Production
(LHC)
Charged PTsum density versus PT(jet1)
The Underlying Event
Underlying event much more active at the LHC!
  • Charged PTsum density in the Transverse region
    versus PT(jet1) at 1.96 TeV for PY Tune AW and
    HERWIG (without MPI).
  • Charged PTsum density in the Transverse region
    versus PT(jet1) at 14 TeV for PY Tune AW and
    HERWIG (without MPI).

42
UEMB_at_CMS
UEMB_at_CMS Rick Field (Florida) Darin Acosta
(Florida) Paolo Bartalini (Florida) Albert De
Roeck (CERN) Livio Fano' (INFN/Perugia at
CERN) Filippo Ambroglini (INFN/Perugia at
CERN) Khristian Kotov (UF Student, Acosta)
Me at CMS!
  • Measure Min-Bias and the Underlying Event at CMS
  • The plan involves two phases.
  • Phase 1 would be to measure min-bias and the
    underlying event as soon as possible (when the
    luminosity is low), perhaps during commissioning.
    We would then tune the QCD Monte-Carlo models
    for all the other CMS analyses. Phase 1 would be
    a service to the rest of the collaboration. As
    the measurements become more reliable we would
    re-tune the QCD Monte-Carlo models if necessary
    and begin Phase 2.
  • Phase 2 is physics and would include comparing
    the min-bias and underlying event measurements
    at the LHC with the measurements we have done
    (and am doing now) at CDF and then writing a
    physics publication.

Darin
UEMB_at_CMS
43
UEMB_at_CMS
UEMB_at_CMS
  • Min-Bias Studies Charged particle distributions
    and correlations. Construct charged particle
    jets and look at mini-jet structure and the
    onset of the underlying event. (requires only
    charged tracks)

Study charged particles and muons using the CMS
detector at the LHC!
  • Underlying Event Studies The transverse
    region in leading Jet and back-to-back
    charged particle jet production and the central
    region in Drell-Yan production. (requires
    charged tracks and muons for Drell-Yan)
  • Drell-Yan Studies Transverse momentum
    distribution of the lepton-pair versus the mass
    of the lepton-pair, ltpT(pair)gt, ltpT2(pair)gt,
    ds/dpT(pair) (only requires muons). Event
    structure for large lepton-pair pT (i.e. mm
    jets, requires muons).
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