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 DownMagnet UP Checked that both polarities gives the same pattern

M1R2 Data/MC ration Magnet DownMagnet UP

M1R3 data/MC ratio Magnet DownMagnet UP

M1R4 data/MC ratio Magnet DownMagnet UP

First conclusions The 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 Z A sketch of how chambers are installed One row contains chamber at Z1/Z2 or Z3/Z4 A column mixes chamber upstream and downstream of the support wall Z1 Z2 Z3 Z4

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

Hits multiplicity vs Z MC Although similar z dependence is observed the entity is much reduced R1 ~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 TDC Spectrum, maybe at different working 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 simulation Standard No Calo No Calo and no Pipe The pipe is not responsible for residual 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 description Test 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 M2R M2R M2R M3R

Spares

Material due to M1 itselself Before first gap of chamber at 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 R4 R1 ~ 1.6 R2 ~1.5 R3 ~1.25 R4 ~ 1.1 Is this pattern in agreement with bakspalsh explanation? I naively imagine that the back splash z dependence is region independent If so backsplash seems to not be the dominant effect Data