1. Some results of test beam studies of Transition Radiation Detector prototypes at CERN. V.O.Tikhomirov P.N.Lebedev Physical Institute of the Russian Academy of Sciences and National Research Nuclear University “MEPhI” On behalf of Collaboration of: Bari INFN – Bari University – Bonn University – Bogazici University – CERN – Istanbul Bilgi University – Louisiana State University – LPI – MEPhI – SINP Moscow State University – Polish Academy of Sciences 2nd International Conference on Particle Physics and Astrophysics. Moscow, October 2016
V.O.Tikhomirov. Some results of test beam studies of TRD prototypes at CERN. ICPPA-2016, Moscow, 11 October 2016

2. Motivation
Test beam studies of particle detectors is an required step during new detectors development or existed detectors upgrade. We are long-term developers and supporters of detectors based on transition radiation registration principles – TRDs.
Very intensive program was realized during test beam 2015 and 2016 at CERN SPS accelerator: thin proportional chambers (straw) prototype with different gas mixtures and type of radiators, GasPixel detector prototype with and without magnetic filed. Data processing and corresponding Monte Carlo programs development are in progress.
The goal is to find radiator/detector parameters which can provide better particle identification at different Lorentz gamma-factor.
Here we observe some results obtained in 2015 with straw prototype with different types of TR radiators.
Another topic: investigation of enlarged gas pressure in the straw chambers effect.
V.O.Tikhomirov. Some results of test beam studies of TRD prototypes at CERN. ICPPA-2016, Moscow, 11 October 2016

3. Test beam 2015 straw prototype setup
Several different radiators (PP foils, fibers, carbon paper, graphen monolayers
vapor deposited on PP foils) and gas mixtures (Xe, Ar and Kr based) were studied.
Only Xe-based mixture with different radiators and straw gas pressure data are considered here.
V.O.Tikhomirov. Some results of test beam studies of TRD prototypes at CERN. ICPPA-2016, Moscow, 11 October 2016

4. Test beam conditions Pions and electrons with energy 20 GeV.
Thin proportional chambers (straws) of 4 mm diameter.
Xe-based mixture (Xe/CO2/O2 = 71.8%/25.6%/2.6%),
100 eV threshold on energy deposition in straw.
Several different types of TR radiators:
10 PP1 radiators: 8 mm, 36 polypropylene foils 15 µm, 213 µm gap between foils.
5 PP2 radiators: the same as PP1, but thick mesh between foils for spacing
Polypropylene fiber (irregular) radiator
graphene paper radiators
graphene monolayer on polyethylene foil
V.O.Tikhomirov. Some results of test beam studies of TRD prototypes at CERN. ICPPA-2016, Moscow, 11 October 2016

5. Absorbed TR photons region
dE/dx ionization peak region
Absorbed TR photons region
V.O.Tikhomirov. Some results of test beam studies of TRD prototypes at CERN. ICPPA-2016, Moscow, 11 October 2016

6. (Inverse) integral spectra – probability to register in straw an energy above some threshold.
V.O.Tikhomirov. Some results of test beam studies of TRD prototypes at CERN. ICPPA-2016, Moscow, 11 October 2016

7. Rejection power – 1/P, where P - probability to (false) identification of pion at some efficiency of electron identification
Better rejection
V.O.Tikhomirov. Some results of test beam studies of TRD prototypes at CERN. ICPPA-2016, Moscow, 11 October 2016

8. Xe, PP1 radiator, electrons
Straw number along beam
TR accumulation effect:
TR photons, generated in some
radiator, can pass neighbor straw and be absorbed in next straw layers.
V.O.Tikhomirov. Some results of test beam studies of TRD prototypes at CERN. ICPPA-2016, Moscow, 11 October 2016

9. Xe, no radiator, electrons
straws along the beam
Data
MC with TR on straw walls
MC without TR on straw walls
Very interesting effect: TR on straw walls: clearly seen in data and is described in MC.
V.O.Tikhomirov. Some results of test beam studies of TRD prototypes at CERN. ICPPA-2016, Moscow, 11 October 2016

10. Regular polypropylene foils vs fiber radiator comparison: better rejection with regular PP, as expected.
Fiber radiators have some technological advantages and are used when regular foils usage is uneasy, e.g. in ATLAS barrel TRT detector.
V.O.Tikhomirov. Some results of test beam studies of TRD prototypes at CERN. ICPPA-2016, Moscow, 11 October 2016

11. Some dedicated radiators were produced and tested in the beam.
There is some theory prediction concerning possible rise of TR yield in graphene.
Some dedicated radiators were produced and tested in the beam.
Graphene paper radiator:
36 foils of ~10 μm (two graphene paper foils of 5 μm thick) separated by 230 μm mesh spacers.
V.O.Tikhomirov. Some results of test beam studies of TRD prototypes at CERN. ICPPA-2016, Moscow, 11 October 2016

12. Here the comparison between regular polypropylene foils and “graphene paper” radiator is shown.
Graphene paper radaiator demonstrates the same performance like PP one, acting like pure carbon.
V.O.Tikhomirov. Some results of test beam studies of TRD prototypes at CERN. ICPPA-2016, Moscow, 11 October 2016

13. Graphene monolayer radiator:
Polyethylene - PE (10 mm 41 foils 12.5 μm thick) with monolayer of graphene on one side
Two different orientation with respect to beam particle: direct (REGr) – graphene layer in face to beam, and reverse (REGr_rev) – polyethylene foil in face to beam
V.O.Tikhomirov. Some results of test beam studies of TRD prototypes at CERN. ICPPA-2016, Moscow, 11 October 2016

14. Practically no difference in performance between pure polyethylene and graphene monolayer with direct (face to beam) orientation
V.O.Tikhomirov. Some results of test beam studies of TRD prototypes at CERN. ICPPA-2016, Moscow, 11 October 2016

15. Small excess in TR production for reverse graphene monolayer orientation with respect to pure polyethylene radiator
V.O.Tikhomirov. Some results of test beam studies of TRD prototypes at CERN. ICPPA-2016, Moscow, 11 October 2016

16. Another possible solution to improve rejection power – to enlarge gas pressure in the straws. It will lead to better absorption of TR photons.
On the other hand, pure ionization losses (which are background in our case) will also rise. The resulting balance is not evident.
V.O.Tikhomirov. Some results of test beam studies of TRD prototypes at CERN. ICPPA-2016, Moscow, 11 October 2016

17. Due to higher gas pressure the corresponding prototype can absob harder part of incident TR spectra.
V.O.Tikhomirov. Some results of test beam studies of TRD prototypes at CERN. ICPPA-2016, Moscow, 11 October 2016

18. Due to better TR absorption, higher pressure prototype provided better rejection power compared to normal pressure.
V.O.Tikhomirov. Some results of test beam studies of TRD prototypes at CERN. ICPPA-2016, Moscow, 11 October 2016

19. As the high-pressure straw chambers can absorb TR photons more effectively, it has a sense to enlarge radiator thickness in front of straw’s layer. Here is the case of double (i.e. 8 mm + 8 mm) PP radiators in front of last 5 straw layers.
Again higher pressure straw chambers provide better rejection compared to normal pressure.
V.O.Tikhomirov. Some results of test beam studies of TRD prototypes at CERN. ICPPA-2016, Moscow, 11 October 2016

20. Conclusions Several different radiators were investigated in test beam
Regular foil radiators provide better rejection power compared to fibre radiator
No essential difference between ordinary polyethylene/polypropylene radiators and graphene radiators was found
Small excess in TR production for reverse graphene monolayer orientation with respect to pure polyethylene radiator is found
Enlarge rejection power can be reached with 0.5 bar overpressure in straw gas mixture
V.O.Tikhomirov. Some results of test beam studies of TRD prototypes at CERN. ICPPA-2016, Moscow, 11 October 2016