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Azimuthal symmetry of HCAL readouts. O. Kodolova (SINP MSU). f symmetry: goal and data stream choice. Goal is to install the relative scale within each eta-ring. - using the phi-symmetric events equalize the response of HCAL readouts

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Azimuthal symmetry of HCAL readouts

O. Kodolova (SINP MSU)

f symmetry: goal and data stream choice

Goal is to install the relative scale within each eta-ring.

- using the phi-symmetric events equalize the response of HCAL


- choice of data stream may be different for the different eta

regions: HB/HE/HF

Current data stream choices:

- minbias events

- low momentum isolated tracks (10-15-25 GeV)

Both choices have + and - features

symmetry with minbias events

The estimation of mean energy per readout:

<Ereadout> = <Esignal>+<Enoise>

The variance estimation:

<Vreadout> = <Vsignal>+<Vnoise>

The mean energy and variance in the ring:

<Ering> = <Esignal>+<Enoise>


Noise mean values and variances have to be estimated either from the same event using first time slices (startup scenario) or from pedestal runs (when pileup starts).

symmetry with minbias events: calibration procedure

Coefficients are derived from non-calibrated sample for each

readout i in each -ring j after Noise subtraction

Mean values:

Cij = <Eij>/<Ej>

or variances:

Cij = sqrt(<Vij>/<Vj>)

Coefficients are applied and the new readout response is:

Note: to avoid noise/signal

correlations special runs

without zero-suppression


Eij corrected = Eij/Cij

Project was started in 2006 and was tested

with CSA06/CSA07/CSA08/CRAFT

symmetry with minbias events: noise contribution




10 mln (noise+signal)

Vreadout, GeV2

Signal is much

less then noise

in barrel


2 mln (noise)

CSA07 data

Vreadout, GeV2


symmetry with minbias events:

needed statistics estimation

Depends on the noise value, i.e. Most critical for the central barrel


1. Calibration with mean value: Mean noise = 10-5 with RMS=0.2-0.3 GeV

Mean signal

HB: 0.002 GeV (ieta=1)

HB: 0.008 GeV (ieta=14)

HE: 0.03 GeV (ieta=21)

HF: 0.5 GeV (ieta=35)

2. Calibration with variance: Mean Noise variance =0.084, RMS=0.24 GeV2

fluctuates channel-to-channel

Mean variance

HB: 0.005 GeV2 (ieta=1)

HB: 0.008 GeV2 (ieta=14)

HE: 0.059 GeV2 (ieta=21)

Error of noise RMS/sqrt(N)

< 0.02 * Esignal

N=25 mlns events for HB, ieta=1

Error of noise RMS/sqrt(N)

< 0.02 * Vsignal

N=6 mlns events for HB, ieta=1

Coefficients (ideal calibration) with variances

for 9 mlns events

HB, ieta=1

HE, ieta=23

Material effects

Channels with large noise RMS

require higher statistics

(optimistic) or can not be included

in f-symmetry if noise distribution

is essentially non-gausian

HF, ieta=32

Accuracy vs number of events (IDEAL calibration)


Black: 90K

Red: 900K

Green: 1.8mln

Pink: 8.9mlns

Large noise channels

were extracted from the





The best accuracy

that can be achieved

with 9 mlns of events

and current noise map

Azimuthal symmetry jobs with CRAFT

L1 trigger : EG and Muon

AlCaRAW is created at HLT step to be sent to Tier0

only HCAL RAW data (without zero-suppression)

Special reconstruction at Tier0 followed by

AlCARECO production

Time slices 1-4 for noise reconstruction

Time slices 5-8 for signal reconstruction

160 mlns events are at CAF: same amount for noise and signal events.

50 mlns were analyzed:

4 days of data collected from 29st of Oct to 1st of Nov.

~2 days with HF on.

It can be used to study

the level of noise and

noise stability

Variance distributions in HB (50 mlns NZSP events)









Var(ieta,iphi) with



Same noise


were in


Slides 1-8



Energy distribution in the readout

iphi=70, ieta=-1

twice wider then “normal” readouts

due to small conversion factor.

Peak 4

E, GeV

Peaks origin (example with HB)

Peak 1

Peak 2

Peak 3

Peak 4

Problematic HPD, iphi=70


Variance stability

From 29th Oct to 1st of Nov

HF was on later (on 30th Oct?)

HB, iph=70. ieta=-1

HF, ieta=36, iphi=3



HF, ieta=36

Variances are stable, but

sometimes we observe fluctuations

that required the additional study.

Phi symmetry with Isotracks


cell-by-cell calibration with isotracks


- statistics for tracks with P>15 GeV/c

we need a few hundreds MIP tracks per cell

- material effects which depend on track energy

- shower profile vs energy ?

We will use the interval from 15 to 25 GeV or from

10 to 25 GeV

- Zero suppression affects low momentum tracks ?

Cell by cell calibration with 50 GeV

~45 tracks/cell

~22 tracks/cell

Material effects

~100 tracks/cell

From G.Safronov,


~900 tr/cell


Phi symmetry in high -h region (outside tracker) can be done with

minbias events with accuracy less than 1 %. For HB we can reach

3-3.5% in rings ieta<5 and 2% in ieta=5-14 and in HE. ~10 mlns events

have to be collected in special NZSP run.

The possibility was checked with CSA07/CSA08/Latest generation with

CMSSW219(IDEAL calibration)/CRAFT.

Phi symmetry in HB/HE can be done/cross-checked with isolated tracks

sample. However this possibility needs some additional study.

More study need to be done with Cosmic (noise stability) and with new

simulation with the latest noise/gains.

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