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 mm x 6 mm W thickness 3.5 mm Si Pad + W(1X 0 ) Si thickness 0.3 mm Si 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: 2X = 22 X 0 Particle 12 layers (W + Si pad)

11 layers of W+ Si_Pad 3 layers of W+Si_Pad W+Si_Pixel 6.2 cm Geometry 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 (36 x 4) = 984 channels 0 th Layer -> 2Xo W mm Si_Pixel1 st to 3 rd Layers -> 1Xo W mm Si_Pad 4 th Layer -> 1Xo W mm Si_Pixel5 th to 7 th Layers -> 1Xo W mm Si_Pad 8 th Layer -> 1Xo W mm Si_Pixel 9 th to 19 th Layers -> 1Xo W mm Si_Pad

Geant4 geometry of the Prototype of the Present configuration This prototype is of Dimension 24cm*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 = ln(Eo)

Transverse 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) = * 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 = % shows compactness and less defect of the Calorimeter.

Results of Pi0 clustering 0 th 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 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 collinear 2.Partonic interaction is elastic  p T,   p T,2  How can Bjorken x values be selected in hard scattering? Deep inelastic scatteringHard scattering hadroproduction Forward Physics - Kinematics Backup Slides 1

Mid-rapidity particle detection:    0 and  0  x q  x g  x T = 2 p T /  s Large-rapidity particle detection:   >>    x q  x T e    x F (Feynman x), and x g  x F e  (      p+p    +X,  s = 200 GeV,  = fraction p T,   (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 - Kinematics Backup Slides 1