Discrepancy Between Simulated and Experimental Photon Time Distribution

[chenjianqi (Jianqi Chen)]

Versions

FLUKA: FLUKA 4-5.0
Flair: FLAIR 3.4-2

Description

I used the usdraw entry in mgdraw.f to record the propagation of muons in the scintillator and logged the data at each step. Based on the obtained data, I plotted the distribution of the number of produced photons over time, as shown in the first figure. The red dashed line represents the actual decay time (neutrino production). However, upon zooming in on the two peaks (second and third figures), it was observed that these peaks are highly irregular and differ significantly from the real experimental data (last figure) (EJ200 + PMT + DT5751).
Can you tell me what might be causing this?
ENTRY USDRAW ( ICODE, MREG, XSCO, YSCO, ZSCO )

CALL GEOR2N (MREG, NAMREG, IERR1)
OPEN (10, FILE=“3He_detector_mgdraw.dat”)

IF (NAMREG.EQ.“Box”) THEN
IF (NP.EQ.3 .AND. (KPART(1).EQ.28 .OR. KPART(2).EQ.28
& .OR. KPART(3).EQ.28 .OR. KPART(1).EQ.27 .OR. KPART(2).EQ.27
& .OR. KPART(3).EQ.27)) THEN
WRITE(10,*) NCASE,ATRACK,JTRACK,XSCO,YSCO,ZSCO,
& NAMREG,NP,KPART(1:NP),TKI(1:NP)

  ELSE IF (NP.EQ.2 .AND. (KPART(1).EQ.7 .OR. KPART(2).EQ.7))

& THEN
WRITE(10,*) NCASE,ATRACK,JTRACK,XSCO,YSCO,ZSCO,
& NAMREG,NP,KPART(1:NP),TKI(1:NP)

  ELSE IF (NP.EQ.3 .AND. (KPART(1).EQ.7 .OR. KPART(2).EQ.7

& .OR. KPART(3).EQ.7)) THEN
WRITE(10,*) NCASE,ATRACK,JTRACK,XSCO,YSCO,ZSCO,
& NAMREG,NP,KPART(1:NP),TKI(1:NP)

  END IF

END IF

IF ( .NOT. LFCOPE ) THEN
LFCOPE = .TRUE.
IF ( KOMPUT .EQ. 2 ) THEN
FILNAM = ‘/’//CFDRAW(1:8)//’ DUMP A’
ELSE
FILNAM = CFDRAW
END IF
OPEN ( UNIT = IODRAW, FILE = FILNAM, STATUS = ‘NEW’,
& FORM = ‘UNFORMATTED’ )
END IF

RETURN

END
I have uploaded the .inp and hope you can help me resolve the issues. I would be grateful.

Best
Yongce，

Input files

FLUKA_geometry.inp (2.4 KB)

[dcalzola (Daniele Calzolari)]

Hi Jianqui,

I’m trying to understand the purpose of your simulation, but it’s not entirely clear to me. I see that you’re simulating a 300 TeV muon beam.

It seems that the statistics of your counts are too low to draw meaningful conclusions about the process you’re studying. Assuming a Poisson-like distribution in your bins (which is already a strong assumption), the statistical uncertainties dominate over your peaks.

From your mgdraw output, it looks like you’re recording all discrete events that generate neutrinos or photons. Since muon decay is a stochastic process, I’m not sure what you mean by “actual decay time.” Each muon decay should occur at a different time.
Is your simulation performed with a single muon?

Also, in your experimental plot you mention a “sampling point,” but there should be an absolute time scale if you want to make a proper comparison.

As a general suggestion, I would also double-check your BEAM card (why does the beam have zero width in y and 10 m in x?). In addition, you can use the ICODE variable in mgdraw.f to identify which physical process generated each secondary particle.

Cheers,
Daniele