Conceptual design of the lambda disks detector for the PANDA experiment

Abstract

PANDA (antiProton ANnihilations at DArmstadt) is a future experiment in the FAIR (Facility for Antiproton and Ion Research) facility located next to GSI, Darmstadt, Germany. The HESR (High Energy Storage Ring) of the FAIR facility will provide antiproton beam of any momentum between 1.5 GeV/c and 15 GeV/c. Main physics motivation of PANDA is to explore the low energy regime of Quantum Chromodynamics (QCD). Mainly it will focus on the following areas: charmonium spectroscopy, search for the gluonic states, hadrons in nuclear matter, hypernuclei physics and electromagnetic processes. The PANDA detector setup is made up of two major parts - target spectrometer and forward spectrometer. Target spectrometer consists of tracking detectors, particle identification detectors, electromagnetic calorimeter. Micro Vertex Detector (MVD) is the innermost tracking detector of the target spectrometer. It has four barrel layers and six disks layers. After the last disk layer of MVD and first layer of Gas Electron Multipliers (GEM), there is a large detector free volume. By including the Lambda Disks Detector (LDD) into the PANDA setup, there is a possibility to extend hyperon study in the PANDA physics program. Hyperons have a large decay length of the order of a few centimeters. Therefore, they travel a large distance before decaying into other particles. The LDD will have the capability to improve the reconstruction probability of hyperons having a longer decay length. Also present database of hyperon physics is not complete. PS185 experiment at the LEAR (Low Energy Antiproton Ring) facility had measured ⇤¯⇤ cross-section from its beam production threshold momentum (1.436 GeV/c) to 2 GeV/c and Bubble Chamber experiment provides crosssection above 2 GeV/c with low statistics and there is no data available above 7 GeV/c. Not only addition of LDD will verify previous measured cross-section below 7 GeV/c, it may also provide data above 7 GeV/c with large statistics. In the proposed geometry of the Lambda Disks Detector, the outer and inner ring of these disks are both made up of Double-sided Silicon Strip Sensors. The outer ring has been kept similar to the outermost layers of the MVD forward disks. Both sides of the trapezoidal silicon strip sensors for the outer ring of the Lambda Disks have 512 strips with a pitch of 67.5 μm. Each sensor has a stereo angle of 150 between the two long edges and the sensor thickness is 285 μm. Inner ring of the disks has 768 strips per side with a pitch of 45 μm. Each sensor of inner ring has a stereo angle of 25.1380 with sensor height of 46 mm.To test the capability of LDD, we have simulated and reconstructed ¯pp ! ⇤¯⇤ channel under the PANDA simulation framework at beam momentum 1.8 GeV/c that is near threshold beam momentum of the reaction and other at 4 GeV/c to compare the performance of the detector with increasing beam momentum. In order to perform the feasibility studies for the Lambda Disks Detector of the PANDA experiment, we have studied the angular distributions from the daughter particles of Lambda (⇤) hyperons to map the direction of the final state particles inside the target spectrometer.The decay length of the produced hyperons is studied which is in good agreement with the PDG value (c⌧ = 7.89 cm). Momentum correlations (pz versus pT ) of ⇤ hyperons as well as their decay products are studied to understand the kinematics of these particles. The decay vertex positions of produced ⇤ hyperons are studied to make estimate of events decaying before the LDD since this detector detects final state particles (p, ¯p, ⇡−, ⇡+) from this decay channel. We have also studied vertex and momentum resolution from ¯pp ! ⇤¯⇤ channel with and without the LDD. We have found that vertex resolution of ⇤ and ¯⇤ remain unchanged after the addition of LDD. However, we observed that the addition of LDD spoils the momentum resolution in the z-direction and remain unchanged in transverse direction. Hit count studies of the daughter particles from both hyperons are performed and observed that hit counts are increased after the addition of LDD to the detectorset up. At low beam momentum (1.8 GeV/c), the most significant e↵ect is the increment in the number of hits of protons in the angular range of the Lambda Disks. The average number of hit points per track rises above four, which allows individual tracking of the particle. At a higher beam momentum (4.0 GeV/c), antiprotons are forward boosted in comparison to protons and usually have more than six hits in angular coverage of the Lambda Disks. Final state pions (⇡+ and ⇡−) register more than six hits after the addition of LDD to the PANDA. The increment in the particle hits after adding the LDD is a positive sign towards its development. We have estimated mass resolution and reconstruction efficiency of ⇤ and ¯⇤ hyperons with and without the LDD, which are most important parameters for the feasibility studies of this detector. A double Gaussian function is fitted to the mass distribution of hyperons because the combinatorial background is also Gaussian in nature.