-- PeterKicsiny - 2021-02-08

FLUKA Run 2 simulation benchmark with beam loss monitors in the CMS forward region

Abstract

In 2018 two Beam Loss Monitors (BLM) were located on both ends of CMS in the rotating shield region (N2 filled, 1.1 bar pressure, 1.5 l sensitive volume). Their measurement data (running sum: 10 - window width: 5242.88 ms - refresh time: 81.92 ms - log frequency: 1 Hz [1]) are used for a FLUKA benchmark study. Detectors are represented by air cylinders in two FLUKA CMS Run 2 models (v3.40.0.0 and v3.40.1.0). Particle fluences inside the cylinders are simulated and converted into charge quantities using pre-simulated detector response functions [2]. Benchmark results are reported as simulated over measured charge ratios for the proton-proton fills in 2018.


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Figure Caption
pdf version
brildata 2018 offline.png

Simulation over measurement data ratios of the BLM detectors per proton fill in 2018. The simulated charges were calculated using CMS FLUKA Run 2 model v3.40.0.0 (BLM -Z) and v3.40.1.0 (BLM +Z) and are normalized by the total delivered luminosity of each fill using the latest offline normalization tag, accessed on 14/12/2020, and the inelastic cross section of σ_inel=79.5 mb [3]. Blue dots represent ratios for the BLM on the negative end, whereas red dots show them for the BLM on the positive end. Statistical uncertainties are up to 1% and omitted for clarity. Offset between the two bands of ratios is ascribed to various systematic uncertainties including the assumed response functions of the detectors and the modeling of the surrounding geometry. Fills with no available or less than 10e38 cm-2 total integrated luminosity data are excluded from the benchmark study. In general, outliers below the main bands correspond to higher measured charge than expected from simulation. In case of these fills, the BLM tubes have relatively low instantaneous current readout values (often below 10e-9 A) and thus higher signal to noise ratio where the excess measured charge comes from noise contribution. In other cases the excess charge is a contribution of a tail current pile-up due to a high density of consecutive fills, which increases the baseline level. On the contrary, outliers above the bands are scarce and correspond to fills where measured charge is lower than simulated charge. In these cases, parts of the measurement data are missing, which could be because data were not sent or recorded correctly thus they do not correspond to the total delivered luminosity measured by BRIL luminometers. The above mentioned luminosity cut is applied to filter most of these outliers from the analysis.

pdf version
positive nonlinearity 2018.png

Current response (running sum 10) of the BLM ionization chamber on the positive end of CMS as a function of instantaneous luminosity for all proton-proton fills in 2018 with available delivered luminosity data. Luminosity is calculated using the latest offline calibration normalization tag as of 14/12/2020. Data is binned into 10 equal sections along the luminosity axis and for each bin the mean and standard deviation of the current response are plotted. The abscissa of the plotted points is determined as the mean abscissa of raw data values within the corresponding bin. Nonlinearity of the detector response is inferred from the uncertainty of the parameter of a linear fit and estimated to be up to 1%.

pdf version
negative nonlinearity 2018.png

Current response (running sum 10) of the BLM ionization chamber on the negative end of CMS as a function of instantaneous luminosity for all proton-proton fills in 2018 with available delivered luminosity data. Luminosity is calculated using the latest offline calibration normalization tag as of 14/12/2020. Data is binned into 10 equal sections along the luminosity axis and for each bin the mean and standard deviation of the current response are plotted. The abscissa of the plotted points is determined as the mean abscissa of raw data values within the corresponding bin. Nonlinearity of the detector response is inferred from the uncertainty of the parameter of a linear fit and estimated to be up to 1%.

Topic attachments
I Attachment History Action Size Date Who Comment
PDFpdf brildata_2018_offline.pdf r1 manage 36.3 K 2021-02-17 - 18:58 PeterKicsiny  
PNGpng brildata_2018_offline.png r1 manage 22.3 K 2021-02-17 - 18:58 PeterKicsiny  
PDFpdf negative_nonlinearity_2018.pdf r1 manage 43.0 K 2021-02-17 - 18:58 PeterKicsiny  
PNGpng negative_nonlinearity_2018.png r1 manage 30.6 K 2021-02-17 - 18:58 PeterKicsiny  
PDFpdf positive_nonlinearity_2018.pdf r1 manage 42.5 K 2021-02-17 - 18:58 PeterKicsiny  
PNGpng positive_nonlinearity_2018.png r1 manage 29.5 K 2021-02-17 - 18:58 PeterKicsiny  
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Topic revision: r7 - 2021-03-08 - PeterKicsiny
 
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