Tracking(1) K p 2 decay-in-flight BG simulation
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Tracking(1)K2 decay-in-flight BG simulation
K. Horie
Osaka University
Sep. 1, 2007JPARC TREK Collaboration meeting at Saskatchewan
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Simple estimation of K2 BG fraction
Fraction of K2 decay-in-flight in the target is BR(K2)/BR(K3) * decay probability ~ * (1. exp (target radius / c
momentum of K2 + 205MeV/c; = 0.84c ~ 100cmtarget radius ~ 10cm1- exp(-10/100) ~ 0.1
The number of K2 decay-in-flight in the target is comparable to the number of K3 events
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Target and tracking
Last meeting at KEK
Source of K2 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 K2 BG rejection (1) fiber size
(2) target thickness
(3) K2 BG fraction
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Analysis of target fiber
• fiber geometry square type □2mm20 cm lengthtarget radius : 3cm
• K+ beam800 MeV/c, pencil beam
2 different type of ADC or amplifier are needed.
Energy deposit in each fiber (MeV)
Maximum energy deposit in 1 fiber (MeV)
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 2:K+ stopping position was determined by energy weighted average of 2 fiber positions which has the maximum and 2nd maximum energy deposit.
Energy deposit
H
L Method 1 Method 2
x xx
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Spatial resolution of K+ stopping position as a function of fiber size
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.
L
method 1L=1.5mm
method 1L=2.5mm
method 1L=2mm
rdiff =true – measured
L (cm)
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K2-dif fraction in K3 sample
• K2 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, =0.01cm
4 point tracking (C0, C2, C3, C4) with a 2 cut
requirement by TOF P>185 MeV/c or back-to-b
ack events are rejected.
K3K2
tracking2
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Target diff. spectra
rtarg=5cm rtarg=3cm• Most of survived K2 events
after K3 selection is + decay-in-flight before C0 chamber.
• Resolution of K+ stopping position (=0.07cm) is not considered.
rtarg=5cm rtarg=3cmrtarg=5cm
K+ stop. pos. (hit-fit) (cm)
rtarg=3cmrtarg=5cm
K3
K2
0.12 cm in RMS
0.07 cm in RMS
K2 BG could be rejected by target diff. cut.
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Results of K2 BG fraction
red: 5cm radiusblue: 3 cm radius
• K2 background fraction can be obtained as
BG fraction=
• Ω is the detector acceptance with K3 selection conditions.
Br(K2)* Ω(K)
Br(K3)* Ω(K3)
event survive factor for target diff. cut
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Summary
• Fraction of K2 dif BG is estimated by using a GEANT3 for target radius of 3cm and 5cm .
• Most of survived K2 events after K3 selection is + 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 K2 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 =200micron 100micron r= 5cm 8cmtarget r=3cm 3cm, 5cmtracking 2 cut adequate adequatetarget diff. cut loose adequate
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Simple estimation of K2 BG events
• momentum of K2 + 205MeV/c; = 0.84 c is nearly 100cm• target radius is neary 10cm• 1- exp(-10/100) is nearly prob= 0.1• fraction of K2 decay in flight in the target is
BR(K2)/BR(K3) * prob is neary 1.
The number of K2 decay-in-flight in the target is comparable to the number of Kmu3 events