Feasibility Study of Forward Calorimeter in ALICE experiment

Sanjib Muhuri

Variable Energy Cyclotron Centre

Kolkata

Possible position in ALICE

PMD

PMD position (A-side at z~360cm) is the most ideal location for the Forward Calorimeter – Phase-1. This is just behind the V0 detector and in front of the vacuum flange and its support.

Issues and Limitation of the Calorimeter

• It is expected to be placed around 360cm away from the interaction point.• • Eta coverage should be such to accept most of the forward region. (ours is

from 2.49 to 4.8 for the detector radius between 6 cm to 60 cm) .

• Full energy deposition should be confirmed for 1GeV to about 200GeV incident particles (photons or electrons) .

• Sampling elements/layers should be large enough to have better energy resolution .

• Tracking with good position resolution needed to track the shower profiles because of close proximity of the showers and also to get a better estimation on the total energy deposition.

• Need a smart algorithm to recognize to very closely spaced clusters (for example, two photons are 5mm apart coming from 200GeV Pi0 ) .

X-Y Si Strip (2 layers) 0.3 mm thickness Strip size 0.475 mm x 6 mm

W thickness 3.5 mm

Si Pad + W(1X0)Si thickness 0.3 mmSi size 1 cm x 1cm

W thickness 3.5 mm

Only Tungsten (W) W thickness 3.5 mm

Forward Calorimeter: Silicon – W Calorimetry

3 layers(W + Si pad)

W: 2X0 2+3+1+3+1+12 = 22 X0

Particle

12 layers (W + Si pad)

11 layers of W+ Si_Pad

3 la

yers

of W

+Si_

Pad

3 la

yers

of W

+Si_

Pad

W+S

i_Pi

xel

W+S

i_Pi

xel

W+S

i_Pi

xel

6.2 cm

6.2 cmGeometry of one small module whose front view is 6.2 cm x 6.2 cm

Total no. of Channels for 62mm x 62mm module is 256 + 36 + 256 + 36 +256 + (36 x 4) = 984 channels

0th Layer -> 2Xo W + 0.6 mm Si_Pixel 1st to 3rd Layers -> 1Xo W + 0.5 mm Si_Pad

4th Layer -> 1Xo W + 0.6 mm Si_Pixel 5th to 7th Layers -> 1Xo W + 0.5 mm Si_Pad

8th Layer -> 1Xo W + 0.6 mm Si_Pixel 9th to 19th Layers -> 1Xo W + 0.5 mm Si_Pad

Geant4 geometry of the Prototype of the Present configuration

This prototype is of Dimension24cm*24cm*21Xo

Longitudinal Shower Profile for gamma at different energies (no weighting)

We have simulated both longitudinal and transverse shower profile using 'gamma' as indent particles of energy 1GeV to 50GeV. From longitudinal profile it has been found that “the position of shower-max vary from 4Xo to 8Xo depending on the incident energy which theoretically verified.

Shower Max

tmax = 3.9 + ln(Eo)

Transverse shower Profile for strip layersTransverse shower Profile for strip layers

Cumulative energy deposition at different (gamma) energies

I have studied layer wise Cumulative Edep profile for 1000 events of 'gamma' of energy 1GeV to 50GeV. From cumulative Edep profile it has been found that depending on the incident energy layer wise added Edep get saturated right from 10th layer to 16th layer suggesting full energy deposition by the the incident particle. So 21Xo length of FoCAL is supposed to be enough to minimize longitudinal leakage.

Calibration Curve for photons

I have found the calibration of Edep with respect to Eincidence . It shows very good linearity of Edep with Eincidence with E(deposited) = 0.0012 + 0.0179 * E(incidence)

Resolution:

~19% resolution

To find the energy resolution I have plotted s/Edep (%) Vs Eincidence and fit it with the function f(x) = a + b/sqrt(S)

where b = 18.9 % shows reasonably good energy resolution. a = 0.416 % shows compactness and less defect of the Calorimeter.

Results of Pi0 clustering0th Layer (Pixel Layer)

Continued……1st Layer (Pad Layer)

Continued……

4th Layer (Pixel Layer)

Continued…..5th Layer (Pad Layer)

Continued…..

8th Layer (Pixel Layer)

Continued……

10th Layer (Pad Layer)

Alpha (asymmetry) parameter and opening angle for10 GeV 0

Left figure shows the asymmetry of decayed photons from Pi0. Though It is supposed to have peak around zero but from reconstructed data we have got it around 0.09.

In the right panel we have plotted separation angle b/w two gammas from Pi0. The angle seems to closely matched with the theoretical prediction

Mass of pi0 obtained

Open angle Vs Incident Energy(for Pi0 decayed to two Photons)

Studying pseudorapidity, =-ln(tan/2), dependence of particle production probes parton distributions at different Bjorken x values and involves different admixtures of gg, qg and qq’ subprocesses.

Assume:

1. Initial partons are collinear2. Partonic interaction is elastic

pT, pT,2

How can Bjorken x values be selected in hard scattering?

Deep inelastic scattering Hard scattering hadroproduction

Forward Physics - KinematicsBackup Slides 1

Mid-rapidity particle detection:

0 and <>0

xq xg xT = 2 pT / s

Large-rapidity particle detection:

>>

xq xT e xF (Feynman x), and

xg xF e(

p+p +X, s = 200 GeV, =01.0

0.8

0.6

0.4

0.2

0.0

frac

tion

0 10 20 30pT,(GeV/c)

qq

qg

gg

Large rapidity particle production and correlations involving large rapidity particle probes low-x parton distributions using valence quarks

NLO pQCD (Vogelsang)

Forward Physics - KinematicsBackup Slides 1