Simulation study for Forward Calorimeter in LHC-ALICE experiment Y.Hori, H.Hamagaki, T.Gunji University of Tokyo, CNS

Outline Physics Motivation and Measurement Items Detector Requirements and its Design Simulation study of performance Hardware considerations Summary and Outlook

Physics Motivation Gluon PDF in small-x Gluon saturation Nuclear dependence of saturation scale, shadowing

Measurement items (x, Q2) map covered by FOCAL Measurement items Prompt g at h=3~4(5) p0-jets or dijets at h=3~4(5) || h=-1~1 Both in p+p,p+Pb collisions x and pt range of prompt g production (LO level 90% compton) large-x parton (quark) Small-x parton (gluon)

Requirement for the detector Large dynamic range ( Energy 1 ~ 200GeV) p0/g separation (two g separation ~ 6mm)　FOCAL z position =4.5m Fine segmentation  0.01 particle/cm2 at h~4 in 8.8TeV p+Pb central collisions Pt (GeV/c) 1 3 7 P(GeV/c) 27.3 81.9 191 2g distance (cm) 4.6 1.5 0.66 p0 kinematics h= 3.5~4 Inclusive g number at FOCAL (z=450) p+Pb 8.8TeV collisions by HIJING Inclusive g Pt > 0.5 GeV/c Pt > 1 GeV/c

IP - 4.5 m ALICE

Conceptual Design of FOCAL Module Particle electronics Silicon Tungsten sampling Calorimeter like PHENIX FOCAL W is a good absorber ( radiation length X0 = 3.5 mm, Moliere radius = 9 mm) With Silicon Strip detector for 2 g separation from p0 Fine segment (Si Pad 1cm x 1cm) X-Y Si Strip Si Pad + W Silicon 0.3 mm thickness 2 layers Strip pitch 0.5 - 1 mm Si thickness 0.5 mm W thickness 3.5 mm Pad 1 cm x 1cm 7 layers x 3 segments = 21 layers total depth 21X0 Charged VETO Same detector as Si Strip

Basic performance and g ID Linearity up to 200 GeV g < 1% Sampling fraction ~ 1.4% detection efficiency > 95% Energy resolution ~ % Position resolution ~ 1.5 mm at 10 GeV Charged hadron/g separation using longitudinal shower profile p+ rejection 250 @ g efficiency 90% at 100 GeV

　p0 inv. Mass in HIJING Two g invariant mass at 3<h<3.5 from HIJING p+Pb event at 8.8 TeV. (Energy and position are smeared according to the resolution.) S/N ratio

p0 reconstruction efficiency By Invariant mass method using Si Pad detector Reconstruction efficiency Reconstruction efficiency with energy asymmetry cut (<0.8). Merging Probability [%] Probability that two g go into neighboring pad. Probability that two g go into same pad. p0 up to 70 GeV (pT=7 at h=3) can be measured by invariant mass method. For the p0 with more than E>70 GeV, we have to use alternative method.

High Energy p02g kinematics Minimum 2 g distance at FOCAL - 12mm for 100 GeV p0 - 6mm for 200 GeV p0 2g distance from 100 - 200 GeV p0 is constant for energy asymmetry < 0.8. Position measurement of 2 g by Si Strip detector and merged energy measurement by Si Pad detector are useful to identify p0 10 GeV 50,100,200 GeV

p0 reconstruction using Si Strip detector Locate a cluster with large energy deposit in the Si Pad & define search region in the Si Strip Search for 2 clusters in the Si Strip & obtain distance between the clusters Applied cut with total energy deposit and 2 clusters distance Second cluster Mask area First cluster Strip position (/0.5mm) 200GeV 150GeV 100GeV 70GeV

p0 reconstruction using Si Strip detector Efficiency vs. position of the strip layer Efficiency vs. p0 energy for 1mm, 0.5mm strip pitch 200GeVp0 100GeVp0 0.5 mm pitch strip at 6X0 1 mm pitch strip at 6X0 Parameters used in reconstruction algorithm is optimized so that the contamination is < 1% 50% of the identification efficiency of high energy p0 (>100 GeV) is achieved using the one strip layer around 5-7X0.

R&D of Si Pad detector and Conceptual design of readout electronics 9 inch wafer, 8 x 8 Pad with the size of 1.1 cm x 1.1cm Heavy alloy 94W-4Ni-2Cu(non-magnetic, density = 17.9g/cm3) dual amplifier ASIC charge divide type requirement - dynamic range 50fC – 500pC - S/N at MIP = 10 under developed ADC ALTRO chip 25MHz, 10bit ADC and digital firmware We begin to construct prototype C high C low

Summary and Outlook LHC is suitable place to study small-x physics. prompt g and jets at forward rapidity are good probe for this study. Simulation study was conducted to evaluate the possible detector design. In terms of occupancy and p0/g separation, Si - W Calorimeter with Si Strip is a good choice. Basics performance was carefully checked. p0 identification algorithm is developed and the efficiency is calculated. Next, we will do full simulation and construct a prototype Hardware issue - how to realize large dynamic range ⇒　may lead severe cross talk - how to assemble readout electronics

p0 and g yield

Prompt g BG

Isolation Prompt g Fragment g g from eta g from pi0 Isolation : pT (sum of associated particles in R<0.7) < 0.2*pT(photon) [R = cone radius defined by sqrt(dh2 + df2)] Efficiency for isolation cut (0.2): Prompt g Fragment g g from eta g from pi0 Rejection (efficiency): pi0 = 50 (2%) @ 5 GeV eta = 20 (5%) @ 5 GeV Efficiency for photons Prompt = 80% @ 5 GeV Frag. Photons = 30% @ 5GeV S/N w/o isolation = 0.02 (0.1) @ 5 GeV (10 GeV) S/N with isolation = 0.8 (4) @ 5 GeV (10GeV)

Simulation Study Longitudinal shower profile Good EM shower profile Linearity : -1% up to 200 GeV Dynamic range: 1.2MeV (MIP) - 3 GeV (200GeV g)

Si-pad design 9 inch wafer 8x8 pads with 1cm x 1cm