In June and July, 2016 a group of young scientists of MEPhI Department “Physics of elementary particles” under the supervision of Professor Anatoliy Romaniuk has conducted the testing of detector prototypes for future experiments at the Large Hadron Collider with the participation of colleagues from LPI (Russia), MSU (Russia), the University of Bonn (Germany), and the University of Bari (Italy).

The researched prototypes should allow accomplish the division of different types of particles, such as protons and kaons, on energies of several teraelectronvolt (TeV). A sharp growth in high-energy particles’ production in proton collisions on the LHC is connected with the growth of energy of colliding particle beams. Since 2015 the collision energy on the accelerator has grown up to 13 TeV. Together with the decrease of the interval between collisions this change should allow expand the horizons of existing research up to the scale of energies and conditions, achievable only during the Big Bang, that marked the birth of our Universe.

Studying physics, arising in such extreme conditions, scientists from all over the world hope to answer the most relevant questions from the field of physics of high energies, such as the origin of the dark matter or the existence of supersymmetry and to confirm or dismiss the predictions of the most reliable at the moment theory of particles and fields – the Standard Model.

The control room of the experiment on testing of new prototypes of transition radiation detector. From left to right Jochen Kaminsky, Daniil Ponomarenko, Sergey Konovalov, Dmitriy Schukin

The conditions on the experiments have strict requirements to the measuring equipment. The methods of registration and particle detectors require updates and modification to guarantee high efficiency and productivity during the registration of physical processes.

MEPhI group provides for the working capacity and the development of the ATLAS Transition Radiation Tracker (TRT). In the process of work MEPhI employees get the valuable experience of work in conditions of growing requirements to the equipment, connected with the growth of accelerator’s luminosity.

Professor Anatoliy Romaniuk, who has been the Head of MEPhI ATLAS group and ATLAS TRT collaboration for several years, has told about the ideas, which are in the basis of TRT and new prototypes:

“ATLAS Transition Radiation Tracker (TRT) is a part of ATLAS inner detector and is aimed at the registration of traces (tracks) of particles, measuring of their impulses and their identification on the basis of transition radiation phenomenon. Transition radiation is the radiation by charged particles of photons (quantums of electromagnetic interaction) at the moment of passing the border between two environments with different refraction indexes. Its peculiarity is that its probability (intensity) is measured in dependence on the Lorentz factor, which is different for particles of different mass and same energy. This peculiarity allows, for example, successfully separate electrons from pi-mesons in ATLAS experiment using the information from TRT. TRT detector, created by employees of our university, doesn’t have analogues in the world. Many developments have found application in other international experiments in physics of high energies and astrophysics, where our employees have taken part: transition radiation detector for HERA-B (DESY) experiment, transition radiation detector for TRT AMS experiment (International Space Station), front tracking detector for ZEUS (DESY) experiment and others.

Graphic representation of the Higgs boson decay into 4 electrons (red and blue lines), recorded at the ATLAS experiment. In the central part we can clearly see changed TRT (red and white dots) on the tracks of charged particles (orange curves), including tracks on registered electrons.

The next step can be made in the development of transition radiation detectors. In the tests with new prototypes we researched new concepts of transition radiation detectors, which should allow widen the field of particle identification up to the highest energies, possible on modern accelerators”.

The scheme of the experiment was described by MEPhI young specialist in detectors 28-year old Konstantin Vorobiev, who has 5 years of work experience at ATLAS.

“The whole facility consisted of several parts and included: Cherenkov counter, used as an input flip-flop, aimed at the identification of electrons and Yukawa mesons; the system of the beam stabilization; gas-pixel set-up; two prototypes of a future gas detector, consisting of the gas discharge tubes (straw set-ups), working on the effect of transition radiation; two transition radiation detectors; system of scintillation units for the adjustment of the beam geometry and the coincidence circuit with an input trigger and, finally, a calorimeter for the division of electrons and pi-mesons on return. The coincidence scheme is a useful tool, signaling, that a particle beam goes through all the elements of the facility. As we can see, there are other elements on the facility, apart from new prototypes, which are able to divide particles according to the type, but they have a smaller efficiency, than tested prototypes, and are used to check the quality of the beam.

The experiment scheme

We needed to answer the questions:

1 Can transition radiation detectors be used for the identification of particles under extremely high energies?

2 If yes, what should the geometry of the detector and radiator be like?

3 Is there a possibility to use the information about exit angle of transition radiation for the improvement of identification?

We had two prototypes on the basis of straw set-ups, the assembly of which we started long before the start of the experiments. The main differences of these prototypes are in geometrical peculiarity of the straw position. The main difference is that the signal from the ionizing radiation in one prototype was read summarily in each layer, while in another prototype the reading happened separately for each straw. The first option allows capture more precisely the projection of particles after radiators and minimize possible losses – particles missing the detectors.

The prototypes and radiators have been set up on the beam and are ready for work

The first tests have been conducted in the laboratory with radioactive sources. We also had several transition radiation detectors with different geometry. Tests with different radiators should allow detect optimal density and the length of the radiator for the future detector. Gas-pixel detector was used in tests for the detection of the possibility of using of information about exit angles of photons for particle identification.

The tests have been conducted at the beams of electrons and muons, which come to us from SPS accelerator, that is one of the elements of LHC accelerator system. The energies have reached hundreds of gigaelectronvolt. It’s not TeV, but a small mass of electrons and muons allows research Lorentz factors, which can have protons and kaons under extremely high energies. We had one week for all the tests, which was preceded by a month of works on installation and assembly of all the equipment.

In the first days, when the session of statistics assembly started, there were a lot of things to do. We needed to tune our equipment, the beam geometry, correct faults of the assembly and perform the calibration of the prototypes.

Konstantin Vorobiev checks the readiness of all the facility’s components before the first session of the data assembly

Judging by the first data, which were available during the experiment, our facility was assembled in a right way. Some expected effects could be observed during the work of prototypes with the help of an up-to-date system of data collection. After the demolition of the equipment for the experiment the prototypes have been installed in the laboratory, where there is a system of reading off and recording of the signals from detectors, similar to the one which was on the beam. It can be useful in future interpretation of results.” says Konstantin.

Daniil Ponomarenko, Department 40 post-graduate student, told us about the primary processing of data from prototypes.

“The long period of preparation of the equipment and software in the lab preceded data assembly. Data acquisition systems play the key role in any experiment. They should meet the requirements of the fault tolerance, stability and the speed of work. The efficiency of the record of chosen events should be close to 100%.

We took as the basis the software, which we inherited from previous text research of gaseous mixtures, conducted last year. Then it was necessary to adapt all the programs to the new configuration of detectors and improve the functionality of the interface, used by operators. We made the maximum automation of the errors’ processing, sending crash reports to the experts, the primary processing of the data and their transfer to the RAID long-term storage. Practically full cycle of the program development has been conducted: from the idea to the testing. The second task was the creation of a simple and clear service for online data tracking for the estimation of its quality.

Electronic measuring equipment for the experiment on testing of new prototypes

The work was conducted in a team with participation of TDAQ (Trigger&DAQ) of LHC experts. In future it is planned to use the software for other experiments.”

Some young post-graduate students, like Dimitriy Krasnopevtsev from Dep.40, had a chance to move from physical data analysis on the computer to the participation in the assembly and testing of detectors.

“It is necessary for us now to update calibrations for transition radiation detectors in connections with the change of conditions in the second session of work on the LHC. Some parts of the new prototypes are similar to the acting elements of transition radiation detectors, that’s why it was useful to work with them in real life before setting computer programs for them.”

Dimitriy Krasnopevtsev traces gas pipeline to the facility

Dimitriy Krasnopevtsev (on the left) and Dmitriy Shulga (on the right) prepare supporting area for prototypes

First year Master’s degree student of the Dep.40 tells about his experience:

“My first shift was at night. I checked the main parametres of the facility and conducted measurings according to the program of actions.

Dmitriy Schukin, Oleg Meshkov and Evgeny Soldatov install high-voltage wires from the control room to the facility

I was really pleased with the participation in the real experiment on particle physics.”

“The obtained data should be processed and compared to the predicted one,” says leading LPI employee, Associate Professor of Dep.40. V.O. Tikhomirov

“The data accumulation was successful, we met the deadline, which is important in CERN laboratories,” said Professor Anatoliy Romaniuk.

MEPhI participants at the experiment:

1. Dep. 40 Professor Anatoliy Romaniuk

2. Associate Professor of Dep.40 Vladimir Tikhomirov

3. Engineer, post-graduate student, Dep. 40 Konstantin Vorobiev

4. Engineer, post-graduate student, Dep. 40 Konstantin Philippov

5. Engineer, post-graduate student, Dep. 40 Dimitriy Krasnopevtsev

6. Post-graduate student, Dep. 40 Evgeniy Shulga

7. Post-graduate student, Dep. 40 Daniil Ponomarenko

8. Post-graduate student, Dep. 40 Nadezhda Proklova

9. Post-graduate student, Dep. 40 Evgeniy Soldatov

10. Master’s degree student, Dep. 40 Dmitriy Schukin

11. Engineer, Dep. 40 Nikita Vozniuk.