The Jagiellonian Positron Emission Tomograph (J-PET) is a detector for
medical imaging of the whole human body as well as for physics studies
involving detection of electron-positron annihilation into photons. J-PET has
high angular and time resolution and allows for measurement of spin of the
positronium and the momenta and polarization vectors of annihilation quanta. In
this article, we present the potential of the J-PET system for background
rejection in the decays of positronium atoms.Comment: Presented at the 2nd Jagiellonian Symposium on Fundamental and
  Applied Subatomic Physics, Krak\'ow, Poland, June 4-9, 2017. To be published
  in Acta Phys. Pol. 

Białas, P.

Curceanu, C.

Czerwiński, E.

Dulski, K.

Gajos, A.

Gorgol, M.

Głowacz, B.

Hiesmayr, B. C.

Jasińska, B.

Kisielewska, D.

Korcyl, G.

Kowalski, P.

Kozik, T.

Krawczyk, N.

Krzemień, W.

Kubicz, E.

Mohammed, M.

Moskal, P.

Niedźwiecki, Sz.

Pawlik-Niedźwiecka, M.

Pałka, M.

Raczyński, L.

Rudy, Z.

Sharma, N. G.

Sharma, S.

Shopa, R. Y.

Silarski, M.

Skurzok, M.

Wieczorek, A.

Wiślicki, W.

Zgardzińska, B.

Zieliński, M.

Acta Physica Polonica B

English

arXiv

E. Czerwiński

K. Dulski

P. Białas

C. Curceanu

A. Gajos

B. Głowacz

M. Gorgol

B.C. Hiesmayr

B. Jasińska

D. Kisielewska

G. Korcyl

P. Kowalski

T. Kozik

N. Krawczyk

W. Krzemień

E. Kubicz

M. Mohammed

Sz. Niedźwiecki

M. Pałka

M. Pawlik-Niedźwiecka

L. Raczyński

Z. Rudy

N.G. Sharma

S. Sharma

R.Y. Shopa

M. Silarski

M. Skurzok

A. Wieczorek

W. Wiślicki

B. Zgardzińska

M. Zieliński

P. Moskal

Crossref

Commissioning of the J-PET Detector for Studies of Decays of Positronium Atoms

The Jagiellonian Positron Emission Tomograph (J-PET) is a detector for medical imaging of the whole human body as well as for physics studies involving detection of electron-positron annihilation into photons. J-PET has high angular and time resolution and allows for measurement of spin of the positronium and the momenta and polarization vectors of annihilation quanta. In this article, we present the potential of the J-PET system for background rejection in the decays of positronium atoms

Czerwiński, Eryk

Dulski, Kamil

Białas, Piotr

Gajos, Aleksander

Głowacz, Bartosz

Kisielewska, Daria

Korcyl, Grzegorz

Kozik, Tomasz

Krawczyk, Nikodem

Krzemień, Wojciech

Kubicz, Ewelina

Mohammed, Muhsin

Niedźwiecki, Szymon

Pałka, Marek

Pawlik-Niedźwiecka, Monika

Rudy, Zbigniew

Gupta-Sharma, Neha

Sharma, Sushil

Silarski, Michał

Skurzok, Magdalena

Wieczorek, Anna

Zieliński, Marcin

Moskal, Paweł

Jagiellonian Univeristy Repository

Vol. 48 (2017) ACTA PHYSICA POLONICA B No 10COMMISSIONING OF THE J-PET DETECTOR FORSTUDIES OF DECAYS OF POSITRONIUM ATOMS∗E. Czerwińskia, K. Dulskia, P. Białasa, C. Curceanub, A. GajosaB. Głowacza, M. Gorgolc, B.C. Hiesmayrd, B. JasińskacD. Kisielewskaa, G. Korcyla, P. Kowalskie, T. KozikaN. Krawczyka, W. Krzemieńf , E. Kubicza, M. Mohammeda,gSz. Niedźwieckia, M. Pałkaa, M. Pawlik-NiedźwieckaaL. Raczyńskie, Z. Rudya, N.G. Sharmaa, S. Sharmaa, R.Y. ShopaeM. Silarskia, M. Skurzoka, A. Wieczoreka, W. WiślickieB. Zgardzińskac, M. Zielińskia P. MoskalaaFaculty of Physics, Astronomy and Applied Computer ScienceJagiellonian University, Łojasiewicza 11, 30-348 Kraków, PolandbINFN, Laboratori Nazionali di FrascatiCP 13, Via E. Fermi 40, 00044, Frascati, ItalycDepartment of Nuclear Methods, Institute of PhysicsMaria Curie-Skłodowska Universitypl. Marii Curie-Skłodowskiej 1, 20-031 Lublin, PolanddFaculty of Physics, University of ViennaBoltzmanngasse 5, 1090 Vienna, AustriaeŚwierk Computing Center, National Centre for Nuclear Research05-400 Otwock-Świerk, PolandfHigh Energy Physics Division, National Center for Nuclear Research05-400 Otwock-Świerk, PolandgDepartment of Physics, College of Education for Pure SciencesUniversity of Mosul, Mosul, Iraq(Received October 3, 2017)The Jagiellonian Positron Emission Tomograph (J-PET) is a detectorfor medical imaging of the whole human body as well as for physics studiesinvolving detection of electron–positron annihilation into photons. J-PEThas high angular and time resolution, and allows for measurement of spin ofthe positronium and the momenta and polarization vectors of annihilationquanta. In this article, we present the potential of the J-PET system forthe background rejection in the decays of positronium atoms.DOI:10.5506/APhysPolB.48.1961∗ Presented at the 2nd Jagiellonian Symposium on Fundamental and Applied Sub-atomic Physics, Kraków, Poland, June 3–11, 2017.(1961)1962 E. Czerwiński et al.1. IntroductionDiscrete symmetries C (charge conjugation), P (parity) and T (time re-versal) and their combinations are subject of vigorous investigation in varioussystems, such as nuclei [1] or mesons [2]. This interest is motivated amongothers by matter and anti-matter abundance asymmetry in the Universe(CP symmetry), Lorenz invariance, unitarity and locality of quantum fieldtheory (CPT symmetry), and uniqueness of time itself (T symmetry). Testsof these symmetries are also performed in lepton systems. At present, thehypothesis of CP symmetry conservation is excluded at 90% confidence levelin the accelerator neutrino oscillations and should reach sensitivity greaterthan 3σ by 2026 [3]. Decays of positronium (a bound state of electron andpositron) were investigated in search of CP and CPT violation [4, 5] resultingin upper limits at the level of 10−3.The Jagiellonian Positron Emission Tomograph (J-PET) system will,apart from medical applications, contribute to studies of discrete symmetriesin decays of positronium [6]. Search of forbidden decays of the positroniumtriplet state, so-called ortho-positronium o-Ps → 4γ and singlet state, so-called para-positronium p-Ps → 3γ will test the C symmetry. Tests of theother fundamental symmetries and their combinations will be performedby the measurement of the expectation values of symmetry-odd operatorsconstructed using o-Ps spin (~S), momentum of annihilation quantum (~ki)and its polarization (~i). Table I contains a list of such operators. It is worthto mention that operators constructed with photons polarization vectors arealso available at J-PET system.TABLE IDiscrete symmetries test operators for the o-Ps → 3γ process [6]. The odd-symmetric operators are marked with “−” and are available for studies at theJ-PET system.Operator C P T CP CPT~S · ~k1 + − + − −~S ·(~k1 × ~k2)+ + − + −(~S · ~k1)(~S ·(~k1 × ~k2))+ − − − +~k1 · ~2 + − − − +~S · ~1 + + − + −~S ·(~k2 × ~1)+ − + − −Commissioning of the J-PET Detector for Studies of Decays . . . 19632. Measurement techniqueThe J-PET detector consists of 192 plastic scintillator strips (500× 19×7 mm3 each) made of EJ-230 organized in layers forming three cylinders (48modules on radius 425 mm, 48 modules on radius 467.5 mm and 96 moduleson radius 575 mm) [7]. Each scintillator at both of its ends is equippedwith a R9800 Hamamatsu photomultiplier. In the first test, a point-like22Na source was placed in the center and was covered by the XAD-4 porouspolymer [8]. A test with the aluminum cylinder surrounding the sourcewas also performed1. The positrons emitted from 22Na →22Ne∗ + e+ + ν¯eand 22Ne∗ →22Ne + γ reaction chain with the γ carrying 1274 keV of en-ergy are stopped in the cylinder wall producing o-Ps which may annihilateemitting 3γ. Detection of prompt photons with 1274 keV energy from Nedeexcitation can be used as a start signal for the positronium lifetime mea-surement. Gamma quanta from o-Ps annihilation are registered by means ofthe Compton scattering inside the scintillator strips. Two coordinates of theinteraction point are determined from the known strip position, while theposition along the module is reconstructed from the time difference of signalsregistered by two photomultipliers connected to the ends of that scintilla-tor [9–13]. Annihilation point and time of o-Ps is then reconstructed usingthe trilateration technique [14] taking advantage of the coplanarity of ~ki. Theknown location of positron emission with reconstructed annihilation placeallows for straightforward velocity (~v ) direction determination. The emittedpositrons are longitudinally polarized (~P = ~vc ) due to the parity violationin the β-decay. Since the polarization of positron is to a large extent pre-served during the thermalization process [15, 16], the known spin directionof positron provides the determination of o-Ps spin. Gamma quanta undergoCompton scattering at J-PET plastic scintillators. Since the Compton scat-tering is most likely to occur in the plane perpendicular to the electric vec-tor of the photon [17, 18], registration of annihilation and scattered quantapairs allows to reconstruction of its linear polarization ~i = ~ki× ~k′i, where ~kiand ~k′i denote momentum vectors of ith gamma quantum before and afterthe Compton scattering, respectively [6]. For annihilation into 3γ with aknown ~ki, it is possible to calculate the energy loss of each γ as describedin Ref. [19]. The energies of gamma quanta can be also estimated usingindependent method. At the J-PET system, the electric signals from pho-tomultipliers are probed in time domain at 4 different amplitude thresholdsresulting in up to 8 time measurements (leading and trailing edge of thesignal at each threshold) [20, 21]. Measured Time-Over-Threshold (TOT)1 For the future experiments, the inner wall of the cylinder will be covered by the porousmaterial presently under development at the Maria Curie-Skłodowska University inLublin.1964 E. Czerwiński et al.value depends on the amount of light registered by photomultiplier, whilenumber of photons in the scintillator depends on the energy deposited bygamma quantum. This method is especially useful to distinguish betweenprompt (Eγ = 1274 keV) and annihilation quanta (Eγ ≤ 511 keV).3. Selection of dataThree data-taking campaigns are already concluded with the J-PETexperiment for commissioning and physics studies which is equivalent toapprox. 700 h of data taking with different configuration and settings ofdetection system2. Apart of threshold synchronization and calibration mea-surements, the data were collected also for performance studies accordingto NEMA standards which were so far evaluated based on the simulationsonly [22, 23]. Measurements were performed also with XAD-4 polymer tar-get and 6 different polymer samples. Data is acquired in the triggerlessmode, therefore, an oﬄine reconstruction and signal selection is required forbackground rejection [20, 21, 24]. For o-Ps data sample, the main back-ground contribution is the detector-based scattering when 2 annihilationgamma quanta from p-Ps are registered together with a single scatteringor 1 annihilation γ from p-Ps undergoing 2 scatterings are registered, asschematically presented in Fig. 1.Fig. 1. Colour on-line) Definition of angles in XY view between registered gammaquanta with indexing fulfilling the condition θ12 ≤ θ23 ≤ θ13. Light rectanglesrepresent scintillators, dark rectangles — scintillators with registered hit and yellowcircle in the middle — annihilation region.These scattered events can be rejected in the process of the oﬄine datareconstruction [24]. Here, we present the preliminary results obtained fromthe second J-PET data-taking campaign for a 1 h 40 min measurement withthe XAD-4 target of radius R ≈ 1 cm with only two following criteria appliedoﬄine:2 The fourth campaign is ongoing.Commissioning of the J-PET Detector for Studies of Decays . . . 19651. Number of registered hits in 200 ns time window equals 3.2. TOT values for 2 hits correspond to annihilation quantum energy lossand TOT value for the 3rd hit corresponds to prompt energy loss.The momentum vectors of all three gamma quanta, generated from o-Psannihilation, lie in one plane. Although the direction of prompt γ emission isnot correlated with such an annihilation plane, in theXY view an o-Ps eventfulfilling the two above-mentioned criteria would have the same topology asthe left scheme in Fig. 1 and, therefore, will occupy the region of θ12 +θ23 >180◦ in Fig. 2. The registered annihilation of p-Ps with single scatteringoccurs as a line around θ12 + θ23 ≈ 180◦, while double scattered events arevisible close to (0◦, 0◦). The enhanced number of events close to (100◦, 100◦)corresponds to scatterings by close to 90◦. Registration of such scatterings isat most probable due to the geometry of the J-PET detector. The conclusionFig. 2. Distribution of registered events for θ23+θ12 and θ23−θ12 angles as definedin Fig. 1. Statistics collected during 1 h 40 min of measurement.from the distribution presented in Fig. 2 is that a significant part of thebackground can be rejected based on the angular correlations. Anotherconstraint to reject single scattered events is based on the plane constructedwith three interaction points of gamma quanta with scintillators as shownin Fig. 3. For registered 3 annihilation γ from o-Ps, such a plane shouldbe close to annihilation place. However, for a selection of events with twoannihilation and one prompt photon, such a plane would not be close todetector center, while p-Ps events with single scatterings would create aplane crossing the center. Distribution of such a distance is presented in1966 E. Czerwiński et al.Fig. 4 with visible maximum at distances below about 5 cm. The enhancednumber of events for few bins of higher distance is due to the geometry ofthe detector.Fig. 3. Distance between plane constructed with 3 hits and the source placed atthe center of the detector.Fig. 4. Distribution of the hit-plane distance from detector center. Statistics col-lected during 1 h 40 min of measurement.4. SummaryThe investigation of discrete symmetries is continuously performed inmany systems. So far, no CP-violation effects were discovered for the purelyleptonic bound state such as positronium. The Jagiellonian PET, presentlyCommissioning of the J-PET Detector for Studies of Decays . . . 1967in commissioning stage, will contribute to these studies. The unique prop-erties of the J-PET system are the usage of plastic scintillators for gammaquanta detection and capability of positronium spin determination togetherwith measurement of γ polarization. High accuracy of time measurementtogether with rejection of background based on the event geometry shouldallow for reaching a sensitivity of 10−5 for CP symmetry violation with theJ-PET detector [6].The authors acknowledge the technical support by A. Heczko, W. Migdałand the financial support from the Polish National Centre for Research andDevelopment through grants INNOTECH-K1/IN1/64/159174/NCBR/12and LIDER-274/L-6/14/NCBR/2015, the EU and MSHE grant No. POIG.02.03.00-161 00-013/09, National Science Centre, Poland (NCN) throughgrant No. UMO-2016/21/B/ST2/01222, and the Ministry for Science andHigher Education through grant 7150/E-388/SPUB/2017/1. B.C. Hiesmayracknowledges gratefully the Austrian Science Fund FWF-P26783.REFERENCES[1] A. Aksentyev et al., Acta Phys. Pol. B 48, 1925 (2017), this issue.[2] G. Amelino-Camelia et al., Eur. Phys. J. C 68, 619 (2010)[arXiv:1003.3868 [hep-ex]].[3] T. Wachala, Acta Phys. Pol. B 48, 1969 (2017), this issue.[4] T. Yamazaki et al., Phys. Rev. Lett. 104, 083401 (2010)[arXiv:0912.0843 [hep-ex]].[5] P.A. Vetter, S.J. Freedman, Phys. Rev. Lett. 91, 263401 (2003).[6] P. Moskal et al., Acta Phys. Pol. B 47, 509 (2016)[arXiv:1602.05226 [nucl-ex]].[7] S. Niedźwiecki et al., Acta Phys. Pol. 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Commissioning of the J-PET detector for studies of decays of positronium atoms

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Commissioning of the J-PET detector for studies of decays of positronium
  atoms

Commissioning of the J-PET detector for studies of decays of positronium atoms

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