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Reconstructing energy from HERD

beam test dataZheng QUAN

IHEP3rd HERD work shopXi’an, 20 Jan.2016

What does ICCD raw data look like

• Images of 250 WLS fibers on 300×400 pixels CCDs• Each pixel has a

digitized gray value proportional to the light intensity

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Crystal/WLSF array coordinate

One frame of 40GeV electron run

• C2X crystals: center of crystal array, directly hit by beam particles, most probably deposited high energy ;

• Higher deposited energy means larger spot, needs more space to weaken or avoid overlapping.

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Fitting or merging

a. Fitting the shape of 1MIP spot with gaussian function: sigma~1.3 pixels, maybe the bin size is not small enough to make a precise fitting

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b. Change of shape: high energy deposited, over saturated;

c. Unsymmetrical shape.

Energy reconstruction step 1: Summing gray values(merging pixels)

• Merging area: approximated circle, radius = 5 pixels, center = COG(gray value weighted) • Light intensity distribution on CCD

doesn’t change with Light intensity;

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• Fitting:Lan×Gaus(left peak) + Lan×Gaus(right peak),MIP = MPV(right) – MPV(left)

Energy reconstruction step 2: Calibrating low range ICCD using pion beam

• Event Selection: ~40% incident particles do not initiate showers

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1MIP ≈ 0.03GeV

Energy reconstruction step 3: Fitting baseline

Low range ICCD High range ICCD

The pixels on high range ICCD have a larger fluctuation of response, indicating a wider baseline distribution

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The MPV of baseline peak always deviates from 0 after baseline calibration. Fortunately, We can observe the baseline peak in every run.

Low range baseline of A02

High range baseline of C24

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Baseline

Energy reconstruction step 4: Image overlap(crosstalk) correction

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Construct a Correction Matrix

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Relative Crosstalk Value doesn’t change with light intensity.

Very rough estimate Beam

GeV

Energy reconstruction step 5: Calibrating high range ICCD

Calibration factors: Great difference among CALO units…

Expected factor: 0.025~0.033

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Event Selection 1: Time dependent

Good events: Before PS trigger, in a period of 3.3ms, no self trigger event comes

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, depends on beam intensity

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Event Selection 2: Shower shape

For 100GeV electron:

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100GeV electron beam: contains 13% hadrons, 90% of hadronic events are excluded after selecting.

Problem: What’s in this peak?

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10GeV 50GeV

100GeV 200GeV

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Electron energy

Slope<1, due to energy deposition in carbon structure and energy leakage.

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Energy resolution Electron

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Angle reconstruction

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𝒀𝒁 𝑷𝒓𝒐𝒋𝒆𝒄𝒕𝒊𝒐𝒏𝑿𝒁 𝑷𝒓𝒐𝒋𝒆𝒄𝒕𝒊𝒐𝒏

𝟒𝟎𝑮𝒆𝑽 𝑬𝒍𝒆𝒄𝒕𝒓𝒐𝒏

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Gap = 5mm Gap = 2mm

Proton Event Selection:• Enough valid hits to exclude MIP events;• Shower maximum is contained;• Shower starts at first few layers;

Scale

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𝑬𝒇𝒇𝒊𝒄𝒊𝒆𝒏𝒄𝒚 𝟎 .𝟔

𝝈𝑬 𝟓𝟎%

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Problems and discussions: Longitudinal Shower Shape

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Electron 100GeV

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For layer 2, layer 3: Energy deposited in central units are higher than expected(C21,C22);For layer 4, layer 5: Energy deposited in CALO units around the central units are lower than expected.

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C20 C21 C22

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Problems and discussions: Strange excess on the right of main peak

Main peak

Right peak

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Self trigger system: no peak on the right

Self Trigger system VS reconstructed energy from ICCD

Right peak Right peak disappearsafter excluding E>120GeV events

So the right peak is probably from ICCD

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Problems and discussions: charge detection

C20: the first layer of central CALO Units

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Quenching?

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Problems and discussions: About energy resolution…

Slightly saturated

Fitting with

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With high range Without high range

Summary• Performances of HERD prototype: Energy resolution :5%@100GeV(e-), 50%(proton);Angular resolution: 1.5deg @100GeV(e-);• Shower shapes: not agree with simulation well;• Reasons of unexpected : Readout noise of ICCD,

crosstalk correction.

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