Calibration and performance of the LHCb calorimeters in Run 1 and 2 at the LHC

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LHCb-DP-2020-001
arXiv:2008.11556 [PDF]

(Submitted on 26 Aug 2020)
Inspire 1813379

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Abstract

The calibration and performance of the LHCb Calorimeter system in Run 1 and 2 at the LHC are described. After a brief description of the sub-detectors and of their role in the trigger, the calibration methods used for each part of the system are reviewed. The changes which occurred with the increase of beam energy in Run 2 are explained. The performances of the calorimetry for $\gamma$ and $\pi^0$ are detailed. A few results from collisions recorded at $\sqrt {s}$ = 7, 8 and 13 TeV are shown.

Figures and captions

Layout of the LHCb experiment.	fig1.pdf [152 KiB] HiDef png [1 MiB] Thumbnail [448 KiB]
Layout of the calorimeter system.	fig2.pdf [33 KiB] HiDef png [1018 KiB] Thumbnail [602 KiB]
Calorimeter cells segmentation of the SPD , PS , and ECAL (left), and the HCAL (right).	fig3a.pdf [24 KiB] HiDef png [659 KiB] Thumbnail [144 KiB]
	fig3b.pdf [20 KiB] HiDef png [284 KiB] Thumbnail [58 KiB]
SPD cell.	fig4.jpg [34 KiB] HiDef png [768 KiB] Thumbnail [169 KiB]
ECAL cell.	fig5.pdf [86 KiB] HiDef png [538 KiB] Thumbnail [290 KiB]
HCAL cell.	fig6.pdf [103 KiB] HiDef png [917 KiB] Thumbnail [387 KiB]
Expected efficiency of the SPD response to particles as a function of the threshold value, obtained from the integration of convoluted Poisson and Landau distributions. The solid line corresponds to the position of the averaged minimum energy ionisation (MIP), the dashed one to the threshold set at $0.5 E_{\rm MIP}$.	fig7.pdf [19 KiB] HiDef png [77 KiB] Thumbnail [71 KiB]
Examples of efficiency curves for individual SPD cell fits covering the whole correction factor range.	fig8.pdf [49 KiB] HiDef png [270 KiB] Thumbnail [235 KiB]
Distribution of the cell efficiencies in the SPD in 2011.	fig9.pdf [24 KiB] HiDef png [69 KiB] Thumbnail [41 KiB]
Distribution of the energies, expressed in ADC counts, recorded in a PS cell with a charged track pointing to it. The result of the fit with the model discussed in the text is superimposed.	fig10.pdf [31 KiB] HiDef png [224 KiB] Thumbnail [162 KiB]
Measurement of the MIP-calibrated energy deposit in 2011 data. The distributions in the three PS regions are superimposed as well as the fit of a Gaussian function to each of these data distributions.	fig11.pdf [29 KiB] HiDef png [661 KiB] Thumbnail [258 KiB]
Example of a ECAL PMT regulation curve. The two bold vertical lines mark the working range of ECAL high voltages.	fig12.pdf [38 KiB] HiDef png [303 KiB] Thumbnail [309 KiB]
Miscalibration (black), calibration (red) and residuals (blue) of the energy flow calibration procedure for an initial mis-calibration of 10% (left) and 2% (right), obtained on simulated samples. The left (right) plot corresponds to the situation after the initial (final) calibration. In both cases a significant improvement of the calibration is obtained.	fig13a.pdf [81 KiB] HiDef png [298 KiB] Thumbnail [253 KiB]
	fig13b.pdf [33 KiB] HiDef png [292 KiB] Thumbnail [256 KiB]
Value of the fitted $\pi ^0$ mass as a function of time (run number, 2011 data). The decrease observed is due to the ECAL ageing (left). $\pi ^0$ mass fit value as a function of time (run number) after applying the gain correction (right).	fig14a.pdf [52 KiB] HiDef png [287 KiB] Thumbnail [198 KiB]
	fig14b.pdf [32 KiB] HiDef png [441 KiB] Thumbnail [378 KiB]
Distribution of $E/p$ in the ECAL for electrons (red) and hadrons (blue) using 2011 data (left). Fraction of gain lost for electrons in the ECAL as a function of the integrated luminosity (right). The two first steps correspond to the HV changes done during the data taking period, the third one is due to annealing during one month without beam.	fig15a.pdf [18 KiB] HiDef png [248 KiB] Thumbnail [171 KiB]
	fig15b.pdf [17 KiB] HiDef png [117 KiB] Thumbnail [99 KiB]
Invariant mass distribution for $\pi ^0 \rightarrow \gamma\gamma$ candidates upon which the fine calibration algorithm is applied. The red curve corresponds to the distribution before applying the method, while the blue curve is the final one. Values in the red (blue) box are the mean and sigma of the signal peak distribution in $ {\mathrm{ Me V /}c^2}$ before (after) applying the fine calibration method.	fig16.pdf [200 KiB] HiDef png [181 KiB] Thumbnail [148 KiB]
$\pi ^0$ mass as a function of time in summer 2017. The red (blue) lines correspond to HV changes from the LED system ( $\pi ^0$ calibration).	fig17.pdf [38 KiB] HiDef png [371 KiB] Thumbnail [269 KiB]
Values of PMT gain corrections, obtained from a typical $^{137}{\rm Cs}$ calibration run (left). Relative variations in gain obtained from two measurements with the $^{137}{\rm Cs}$ source with respect to the LED measurement variation (right).	fig18a.pdf [27 KiB] HiDef png [612 KiB] Thumbnail [488 KiB]
Variation of the sensitivities of the HCAL cells in 2011.	fig19.pdf [202 KiB] HiDef png [539 KiB] Thumbnail [443 KiB]
PMT gain degradation as a function of the integrated anode current measured at lab (left). Integrated PMT anode currents accumulated during 2011 (right).	fig20a.pdf [14 KiB] HiDef png [217 KiB] Thumbnail [179 KiB]
	fig20b.pdf [26 KiB] HiDef png [580 KiB] Thumbnail [484 KiB]
Light yield $Y^r_i$ averaged over the 44 HCAL most central cells as a function of the delivered luminosity.	fig21.pdf [20 KiB] HiDef png [424 KiB] Thumbnail [308 KiB]
$E_{\rm HCAL }$ and $p_{\rm track}$ distributions for track selected in different cells, for the HCAL calibration based on $E/p$. The lines show the cuts applied for the $E/p$ calculations.	fig22.pdf [962 KiB] HiDef png [490 KiB] Thumbnail [368 KiB]
Averaged $E_{\rm HCAL }/p_{\rm track}$ values in the HCAL cells, right after a $^{137}$Cs calibration (left). Ratio between $E/p$-based calibration coefficients in a 5 week time period and the corresponding ratio of the LED corrections for the same period (right).	fig23a.pdf [42 KiB] HiDef png [266 KiB] Thumbnail [308 KiB]
	fig23b.pdf [6 KiB] HiDef png [236 KiB] Thumbnail [194 KiB]
Distribution of the muon energy deposition in the outer cells (left) and in the most central cells (right) of the HCAL .	fig24a.pdf [33 KiB] HiDef png [248 KiB] Thumbnail [286 KiB]
	fig24b.pdf [27 KiB] HiDef png [253 KiB] Thumbnail [282 KiB]
Invariant mass distribution of $ B ^0 \rightarrow K ^{0} ( K ^+ \pi ^- )\gamma$ candidates in Run 1. The blue curve corresponds to the mass fit. The $ K ^{0} \gamma$ signal component of the fit function (red line) and the various background contaminations are shown.	fig25.pdf [22 KiB] HiDef png [328 KiB] Thumbnail [242 KiB]
$B\rightarrow K^* \gamma$ mass resolution in terms of photon mis-calibration from simulation for high energy photons. The comparison with the actual value suggests an intrinsic resolution in the photon energy of $2$%.	fig26.png [116 KiB] HiDef png [182 KiB] Thumbnail [95 KiB]
Mass distribution of the reconstructed $ D ^0 \rightarrow K ^- \pi ^+ \pi ^0 $ candidates with resolved $\pi ^0$ (left) and merged $\pi ^0$ (right) obtained from the 2011 data sample. The blue curve corresponds to a fit. The signal component of the fit function (red dashed line) and the background (green dash-dotted line) contributions are shown.	fig27a.pdf [26 KiB] HiDef png [232 KiB] Thumbnail [173 KiB]
	fig27b.pdf [25 KiB] HiDef png [229 KiB] Thumbnail [170 KiB]
Electron identification estimators (open histogram for electrons, shaded histogram for hadrons): a) energy deposited in the PS , b) value of the $\chi^2_{\rm 2D}$ estimator in ECAL , c) energy deposited in the HCAL . Data taken in 2011.	fig28a.pdf [14 KiB] HiDef png [145 KiB] Thumbnail [108 KiB]
	fig28b.pdf [18 KiB] HiDef png [508 KiB] Thumbnail [289 KiB]
	fig28c.pdf [17 KiB] HiDef png [214 KiB] Thumbnail [145 KiB]
Photon identification efficiencies as a function of the applied cut for IsNotH (hadron rejection) (left) and IsNotE (electron rejection) (right) with $ B ^0 \rightarrow K ^{*0} \gamma$ data (red dashed line) and simulation (blue solid line).	fig29a.png [15 KiB] HiDef png [95 KiB] Thumbnail [39 KiB]
	fig29b.png [15 KiB] HiDef png [98 KiB] Thumbnail [41 KiB]
Purity as a function of efficiency for (green) the full photon candidate sample, (blue) converted candidates according to the SPD information and (red) non-converted candidates (left). Photon identification efficiency as a function of $\pi ^0$ rejection efficiency for the $\gamma - \pi ^0 $ separation tool for simulation (red curve), and data (blue curve) (right).	fig30.pdf [36 KiB] HiDef png [147 KiB] Thumbnail [104 KiB]
Ratio of photon detection efficiencies $\epsilon (\gamma \rightarrow ee)/\epsilon(\gamma_{CALO})$ from the decay of $\pi ^0$ mesons in data (red) and simulations (blue).	fig31.pdf [37 KiB] HiDef png [110 KiB] Thumbnail [94 KiB]
Distribution of $\Delta M = M(\mu ^+ \mu ^- \gamma)-M(\mu ^+ \mu ^- )$ for $p_{ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} }$ in the $ p_{\mathrm{T}}$ -range 4-5 $ {\mathrm{ Ge V /}c}$ . Fits are also shown, with the total fitted function (blue solid curve), the $\chi _{ c 1}$ signal (green dashed curve), the $\chi _{ c 2}$ signal (red dot-dashed curve) and the $\chi _{ c 0}$ signal (purple long-dashed curve).	fig32.pdf [37 KiB] HiDef png [239 KiB] Thumbnail [169 KiB]
Electron identification efficiency versus mis-identification rate.	fig33.pdf [22 KiB] HiDef png [487 KiB] Thumbnail [336 KiB]
Performance of the calorimeter for electron identification with $\Delta\log{\mathcal L}_{e/h}^{\rm CALO}$ cuts: efficiency as a function of momentum (left) and mis-identification rate (right) as a function of momentum.	fig34.pdf [98 KiB] HiDef png [177 KiB] Thumbnail [112 KiB]
Distribution of $E/p$ from electrons coming from converted photons with $E_{\rm PS }>50\mathrm{ Me V} $, with at least one hit on the SPD and a track with $ p_{\mathrm{T}} > 200 {\mathrm{ Me V /}c} $ pointing into the ECAL cluster ($\chi^2_{2D}<25$), and a matching positron to forming invariant mass $M(ee) < 100$ $ {\mathrm{ Me V /}c^2}$ (left). Resolution for $\sigma(E/p)$ as a function of energy (right).	fig35a.pdf [71 KiB] HiDef png [245 KiB] Thumbnail [191 KiB]
	fig35b.pdf [15 KiB] HiDef png [108 KiB] Thumbnail [104 KiB]
Distribution of $E/p$ from simulations (left). Resolution $\sigma(E/p)$ as a function of energy, obtained from simulations (right).	fig36a.pdf [35 KiB] HiDef png [241 KiB] Thumbnail [192 KiB]
	fig36b.pdf [15 KiB] HiDef png [114 KiB] Thumbnail [112 KiB]
Invariant mass distributions for selected $ B ^0_ s \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \eta^{\left(\prime\right)}$ candidates. Black dots are the data, thin solid orange lines are the $ B ^0_ s $ contributions and orange dot-dashed lines are the $ B ^0 $ contributions. The blue dashed lines show the combinatorial background contributions and the dotted blue lines show the partially reconstructed background components. The total fit functions are drawn as solid blue lines.	fig37.pdf [151 KiB] HiDef png [477 KiB] Thumbnail [359 KiB]
Mass distribution of the reconstructed $ B ^0 \rightarrow K ^{0} ( K ^+ \pi ^- )\gamma$ candidates in Run 2. The blue curve corresponds to the mass fit. The $ K ^{0} \gamma$ signal component of the fit function (red line) and the various background contaminations are shown.	fig38.pdf [22 KiB] HiDef png [332 KiB] Thumbnail [246 KiB]
Distribution of $\Delta M = M( D ^0 \pi ^+ )-M( K ^- \pi ^+ \pi ^0 )$ with resolved (left) and merged $\pi ^0 $ (right) in 2017-2018.	fig39a.pdf [123 KiB] HiDef png [186 KiB] Thumbnail [133 KiB]
	fig39b.pdf [122 KiB] HiDef png [192 KiB] Thumbnail [134 KiB]
Animated gif made out of all figures.	DP-2020-001.gif Thumbnail