Tracking(1) Kp2 decay-in-flight BG simulation

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Tracking(1)Kp2 decay-in-flight BG simulation
Sep. 1, 2007 JPARC TREK Collaboration meeting at
Saskatchewan

• K. Horie
• Osaka University

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Simple estimation of Kp2 BG fraction

• Fraction of Kp2 decay-in-flight in the target is
  BR(Kp2)/BR(Km3) decay probability
  (1.- exp (target
  radius / bgct) ) 1.
• momentum of Kp2 p 205MeV/c b 0.84
• bgct 100cm
• target radius 10cm
• 1- exp(-10/100) 0.1
• The number of Kp2 decay-in-flight in the target
  is comparable to the number of Km3 events

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Target and tracking

• Last meeting at KEK
• Source of Kp2 BG(1)scatter in the
  spectrometer(2)dif in the spectrometer can be
  rejected by installing C0.
• (3)dif before C0
• to be rejected by target fiber.

This talk MC simulation (GEANT3) for Kp2 BG
rejection (1) fiber size (2) target
thickness (3) Kp2 BG fraction
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Analysis of target fiber
Maximum energy deposit in 1 fiber (MeV)
Energy deposit in each fiber (MeV)

• fiber geometry square type ?2mm20 cm
  lengthtarget radius 3cm
• K beam800 MeV/c, pencil beam
• 2 different type of ADC or amplifier are needed.

total energy deposit (MeV)
number of hit fiber
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Fiber size and spatial resolution of K stopping
position

• K stopping position was determined as a function
  of fiber size by GEANT3.
• Analysis method Method 1 K stopping position
  was determined by 1 fiber position which has the
  maximum energy deposit.Method 2K stopping
  position was determined by energy weighted
  average of 2 fiber positions which has the
  maximum and 2nd maximum energy deposit.

x
x
x
Method 1
Method 2
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Spatial resolution of K stopping position as a
function of fiber size
rdiff true measured
method 1L1.5mm
method 1L2mm
L

• open method 1 (using 1 fiber info.)
• closed method 2 (using 2 fibers info.)K
  stopping position was obtained to be 0.07cm in
  RMS.

method 1L2.5mm
L (cm)
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Kp2-dif fraction in Km3 sample

• Kp2 decay-in-flight fraction was obtained as a
  function of target radius by a GEANT3 code.
• C0(GEM) position was fixed and more realistic
  than the previous study.rGEM 8cm, s0.01cm

tracking c2

• 4 point tracking (C0, C2, C3, C4) with a c2 cut
• m requirement by TOF
• Pgt185 MeV/c or back-to-back events are rejected.
  

Km3
Kp2
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Target diff. spectra
K stop. pos. (hit-fit) (cm)

• Most of survived Kp2 events after Km3 selection
  is p decay-in-flight before C0 chamber.
• Resolution of K stopping position (s0.07cm) is
  not considered.

rtarg3cm
rtarg3cm
rtarg3cm
rtarg5cm
rtarg5cm
rtarg5cm
rtarg5cm
Km3
0.12 cm in RMS
0.07 cm in RMS
Kp2
Kp2 BG could be rejected by target diff. cut.
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Results of Kp2 BG fraction
event survive factor for target diff. cut
red 5cm radius blue 3 cm radius
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Summary

• Fraction of Kp2 dif BG is estimated by using a
  GEANT3 for target radius of 3cm and 5cm .
• Most of survived Kp2 events after Km3 selection
  is p decay-in-flight before C0
  chamber.Arrangement of target fiber with C0 is
  key point to reject.
• Resolution of K stopping position is evaluated.
  0.07cm in RMS
• Fraction of Kp2 BG is controlled to be 0.1-0.5
  level.

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backup
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Consistency of Kpi2 BG fraction between last
reported value and this talk

• previous reported at KEKBG fraction 0.3
• Difference Feb.
  Aug.GEM s200micron
  100micron r 5cm
  8cmtarget r3cm 3cm, 5cmtracking c2
  cut adequate adequatetarget diff.
  cut loose adequate

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Simple estimation of Kp2 BG events

• momentum of Kp2 p 205MeV/c b 0.84
• bgct is nearly 100cm
• target radius is neary 10cm
• 1- exp(-10/100) is nearly prob 0.1
• fraction of Kp2 decay in flight in the target is
  BR(Kp2)/BR(Km3) prob is neary 1.
• The number of Kp2 decay-in-flight in the target
  is comparable to the number of Kmu3 events