It was the beginning of a warm summer in Geneva when Dr. S. Kailas, Director of the Nuclear Physics Division of BARC (the Bhaba Atomic Research Centre), received the warm greeting of ALICE during his visit, on 14th May. Dr. Kailas is an Indian physicist renowned in nuclear science for his contribution to the areas of Nuclear Structure, Nuclear Reaction, Radioactive Ion Beam, Accelerator Physics and more.
BARC is situated on the outskirts of Mumbai, on the shores of the Arabian Sea. The “father of [the] Indian nuclear programme", Homi Jehangir Bhabha, founded the Trombay Atomic Energy Establishment in 1944. It became BARC after he passed away, in order to commemorate his contribution to the nation. Over the decades, BARC has emerged as a multi- disciplinary research institute. It has become a nodal institute of the Indian Nuclear Energy Programme, controlling the funds and activity of all nuclear research in India.
Photo courtesy of Subhash Singha, PhD student of VECCFrom left to right:
Dr. Dipanwita Dutta of BARC, Dr. Ajit Mohanty of BARC, PhD student Sudipan De of VECC, Dr. Rashmi Raniwala of University of Rajasthan, ALICE Spokesperson Paolo Giubellino, Director of Physics Division of BARC S. Kailas, previous ALICE Spokesperson Jurgen Schukraft, and Post Doctoral Researcher Indranil Das of IPN d'Orsay.
Dr. Kailas was curious about the comparison between the four LHC experiments when Paolo Giubellino confirmed to him that ALICE is the second heaviest experiment. Being composed of 18 different types of detectors makes ALICE more challenging to operate than any other LHC experiment. Dr. Kailas was then led to the ALICE Control Room (ACR), where Rashmi Raniwala explained to him the ALICE central data taking components, such as the High Level Trigger, Detector Control System, Experiment Control System, Data Acquisition and Central Trigger Processor. Being an active experimentalist, Dr Kailas promptly queried how the quality of the recorded data is monitored. Dr. Raniwala described the role of the Data Quality Monitor (DQM) and assured him that we are not storing the garbage data. Jurgen Schukraft took a step further and showed him the T0 DQM plots, which clearly differentiates the debris of the particles from beam-beam and beam- gas collisions. Dr. Kailas asked about the present vacuum level in the ALICE region. It took some time to find out the answer since the tuning of vacuum at different places of the LHC is solely controlled by the LHC operator. Dr. Kailas also had some confusion about the observation of Quark Gluon Plasma (QGP), but Paolo quickly replied that we have already passed through the cross-over region close to the temperature axis of the phase diagram. On the whiteboard, Jurgen explained to him further the QGP phase diagram and the position of ALICE with respect to the baryon chemical potential and temperature axis.
Following this discussion in the ACR, Dr. Kailas was led to the exhibition at point 2, where Paolo described the evolution of the universe since the Big Bang and the interest of ALICE to study the matter that is produced a micro-second after the creation of the universe. Dr. Kailas was then shown the ALICE model in the exhibition, with the emphasis that on both sides of the detector there are Indian contributions. On one side, at the Muon Spectrometer, the main Indian contribution is the fabrication and the operation of the Second Muon Tracking Station, which has around 226,000 readout pads made by the Saha Institute of Nuclear Physics (SINP) and Aligarh Muslim University. In addition, SINP has designed and delivered 108,000 MANAS chips. These are ASIC (Application Specific Integrated Circuit) based readout chips, which are presently used for muon tracking and measurement of photon multiplicity in the large rapidities of ALICE. Apart from detector responsibilities, SINP is also involved in the High Level Trigger (HLT) project of ALICE, and played a key role to develop the fast algorithm of clustering, tracking, Quality Assurance and online event display for the Muon Spectrometer. SINP had also provided materials for the front absorber of the Muon Spectrometer.
On the other side of ALICE, the Photon Multiplicity Detector (PMD) is another large effort of several universities from the different corners of India (see full list). The PMD collaboration built 221,184 honeycomb shaped proportional counters of 0.25 cm2 cross section. Each counter has a honeycomb shaped cathode extended towards a 20 micron thick gold-plated tungsten wire kept at ground potential at the centre of the cell. The PMD cells are arranged in two independent equal halves, one serves as veto detector and other is used as preshower plane with a lead converter in between. Dr. Kailas was excited when he came to know that one Indian detector is the largest cathode pad chamber detector and another is the smallest honeycomb detector in the world. Jurgen and Paolo then moved on to the other ALICE detectors such as the Photon Spectrometer (PHOS), V0, T0, and Time of Flight (TOF), and detection technologies such as the PHOS crystals and scintillators, whereupon Ajit Mohanty and Dipanwita Dutta also joined the discussion.
After the discussion in the exhibition, Dr. Kailas had explained to him the operation of the HLT, with the focus on the HLT of the Muon Spectrometer. He expressed interest in the beauty of the different tracking algorithms for fast data processing. Dr. Kailas also visited the HLT computing PC farm and admitted that the level of complexity of the HLT in ALICE is really high.
When the visit of Dr. Kailas was about to end and we were coming out of the SX2 building at point 2, he asked “Tell me, how much is the noise pickup of the detector?" Though I replied that the noise level is within one ADC channel for the Muon Tracking system, which we have managed with proper grounding shield, it shows that one short visit to ALICE was not enough for an inquisitive physicist.