Data/MC discrepancy study

Alessia Satta

Roma

9 october 2014

A reminder of what already shown by Giacomo and me

M1R1 data/MC ratio

Magnet Down Magnet UP

Checked that both polarities gives the same pattern

M1R2 Data/MC ration

Magnet Down Magnet UP

M1R3 data/MC ratio

Magnet Down Magnet UP

M1R4 data/MC ratio

Magnet Down Magnet UP

First conclusionsThe discrepancy data/MC has a chamber “pattern”.

It is smaller for chambers placed upstream and larger for chamber installed downstream

Giacomo suggested calorimeter back splash as explanation for the dependent Z discrepancy

Before asking calo people to look at it I tried to have more clues

M1 Z

Y

X

ZA sketch of how chambersare installedOne row containschamber at Z1/Z2 or Z3/Z4A column mixes chamberupstream and downstream of thesupport wall

Z1

Z2

Z3

Z4

Hits multiplicity vs Z

The Z dependence of hit multiplicity decreased from R1 to R4R1 ~ 1.6 R2 ~1.5 R3 ~1.25 R4 ~ 1.1Is this pattern in agreement with back splash explanation?

Data

Hits multiplicity vs Z

MC

Although similar z dependence is observed the entity is much reducedR1 ~1.2 R2 ~1.1 R3 ~1.07 R4 ~1.03

Using TDC to understand the Z pattern in M1

● We do not have many handles in muon detector data. Try to look ad TDC.

● If z pattern is due to back splash naively we expect that the arrival time of those hits is smaller in Z4 chambers and larger in Z1 chambers. If back splashed particles are at small angles than Z4-Z1 ~ 35 cm so the delay in Z1 wrt Z4 is 70cm/c ~ 2ns ~ 1.5 TDC bin.

● Due to back splash component we expect that average time of hits is larger in Z1 than Z4

Time hit vs z in M1R1

All 12 chambers

TDC average vs Z

The 4 chambers in the equatorial plane

TDC distribution in 4 chambers

The chamber at Z2 has strange TDCSpectrum, maybe at differentworking condition

Time hit vs z in M1R2

the expected pattern due to back splash

Time hit vs z in M1R3

the expected pattern due to back splash

Conclusions part II

● The TDC distributions seems to point in the direction of back splash

● Unfortunately not proved yet it is the main effect of the discrepancy

Go back to MonteCarlo

● Assume current MC knows back splash but underestimates the rate

● Remove Calorimeter from simulation and compare with standard one. If Z dependent rate is due to (mainly) back splash it should disappear in MC w/o calorimeter

In MC there is a source of Z dependent rate apart from Calorimeter back splash

Still using MonteCarlo

● If calorimeter back splash is not the only source of Z dependence which other is present?

● Since Zdependence is higher in R1 an smaller in R4 , could it be related to the pipe?

● Remove Pipe from simulationStandardNo CaloNo Calo and no Pipe

The pipe is not responsible forresidual Z dependence

Std vs no Calo simulation

● For all regions removing calorimeter reduces a lot the effect but not cancel

What else????

● The other possibility is the material of M1 (chamber,wall, etc). Chambers downstream sees more material

Average material upstream on M1 is 40% X0

M1 material

● M1R1 chambers material non negligible, large variation in x-y plane

● For non perpendicular tracks the effective material is spreadout in x-y

● For z1 ~1.5% for z4~10%

● The chamber frame are more important in R1 that R4 since frame area wrt panel area is larger

Summary

● We see z dependent rate

● The amount is region dependent

● Some hint from TDC that back splash is a component of the z dependent rate

● From MC we see the back splash is present but also some other source of z dependent rate is in: not Pipe

● The last hipotesis is chamber material itself

M2 plug description

● Thanks to Robert we have now a realistic description of M2 plugs

● Test the effect using low threshold simulation

M2 plug descriptionTest the effect using low threshold simulation

● Compare Robert precise description with a simplified description I wrote: only X and Y outer box dimension

● The z opening implemented by Robert seems to not increase the rate. Why? Not intuitive to me

High thr. Low thr. low+my plug description

low+robert description

M2R1 11.5 16.9 17.9 17.3

M2R2 10.2 16.6 16.8 16.3

M2R3 5.2 10.6 10.6 10.3

M3R4 5.8 9.2 9.1 9.1

Spares

Material due to M1 itselself

Before first gap of chamberat Z1 ~1.5% x0 Before first gap of chamber

at Z4 ~9.0% x0

Hits multiplicity at different Z

The Z dependence of hit multiplicity decreased from R1 to R4R1 ~ 1.6 R2 ~1.5 R3 ~1.25 R4 ~ 1.1Is this pattern in agreement with bakspalsh explanation?I naively imagine that the back splash z dependence is region independentIf so backsplash seems to not be the dominant effect

Data