LHCb tops off the wall

The LHCb electromagnetic calorimeter wall has been erected and the hadron calorimeter is being assembled.


The electromagnetic calorimeter, completely assembled, is a wall more than 6 m high and 7 m wide, consisting of 3300 blocks of scintillator, fibre optics and lead.


The wall of the LHCb electromagnetic calorimeter has been assembled within only a month, a fine feat that will be followed by the assembly of the hadron calorimeter, which will be completed in June. Thus LHCb will soon have erected two of the key elements of its detector.

LHCb's objective is to study CP violation, an effect that would enable it to elucidate Nature's very slight preference for matter over antimatter. This phenomenon would explain the infinitesimal surplus of matter of which we are the result, as is everything else that we see in the Universe.

The experiment started the installation work by positioning its monumental magnet (see Bulletins No. 18 and 50/2004). Now, the time has come for the calorimeters to be assembled.

The modules of the LHCb electromagnetic calorimeter have been manufactured by the Russian Institute of Theoretical and Experimental Physics (ITEP) in Moscow and delivery started at the end of 2002. This detector, which is based on "shashlik" technology, consists of 3300 modules each with a cross section of 12 centimetres x 12 centimetres and measuring 80 centimetres in length. Each module is a sandwich (hence the name which denotes a popular type of Russian kebab sandwich) alternating lead absorbent plates with layers of scintillator forming the detector material. Fibre optics run through these slices perpendicular to the axis.

For the assembly in the cavern, a team of three to five people from ITEP worked around the clock to install all the modules, weighing 30 kilos, by hand. The calorimeter was assembled using a method similar to that employed for laying bricks in a wall, but with great precision. The modules had to be aligned to an accuracy of about 1.5 millimetres. Their alignment was confirmed by the surveyors. Rolf Linder, the LHCb Installation Co-ordinator, is pleased with the result: "The assembly work, which took two months, progressed twice as quickly as planned." The lengthy cabling work can now start, as amongst other things the electromagnetic calorimeter has 6000 read-out channels.

The first wall had barely been completed when another Russian team from the Institute of High Energy Physics (IHEP) in Protvino started work on building the hadron calorimeter. Again, the modules had to be stacked on top of one another, although this time they are even bigger. Each module is 4.2 metres in length, 1.66 metres wide and 26 centimetres thick, and weighs a mere 9.5 tonnes. So this time the detector cannot be assembled by hand and an overhead travelling crane has to be used.

52 modules consisting of steel plates and scintillator material manufactured at IHEP have to be assembled. Construction should be completed in mid-June. "The philosophy behind the assembly of this detector is different", explains Andreas Schopper, the Head of the LHCb calorimeter project. "Each module is already fully operational as the photomultipliers and cabling are already fitted."

The assembly of the two walls is restricting the amount of space in the cavern. This lack of space is one of the difficulties encountered by the Russian teams whose work was co-ordinated by the installation team led by Bernard Chadaj.

These large detectors are being assembled on large metal structures designed by the LAPP Laboratory in Annecy, France.


The installation team for the electromagnetic calorimeter. Top, from left to right, Serge Deckert, Robert Kristic, Bernard Chadaj, and below, Salvatore Lampis, Tengiz Kvaratskheliya, Alexandre Aref'Ev, Bruno Lieunard, Jerôme Dech, Christophe Mazeau, Cedric Fournier.



The assembly team for the hadron calorimeter: from top to bottom, Rustem Dzhelyadin, Robert Kristic, Patrick Vallet, then left to right Vitaly Polyakov, Evgeny Chernov and Kirill Kachnov, and lastly Frank Lamour.