Studies of control samples and backgrounds for the measurement of direct CP violation with interferometric methods at KLOE
Author: Szymon Gamrat
Supervisor: dr Eryk Czerwiński
abstract
Defence year: 2023
The main goal of these studies is to determine a correction factor for the efficiency of selection obtained using KSKL -> pi+pi-pi0pi0 Monte Carlo events using experimentally collected data in the function of time difference Deltat between decays of kaons. It constitutes a continuation of an analysis for Re(epsilon'/epsilon) and Im(epsilon'/epsilon) parameters, which began in [1].
Measurement principle is based on the selection of background channels having common properties with KSKL -> pi+pi-pi0pi0. The chosen decays were KSKL -> pi+/-l-/+nipi0pi0, KSKL -> pi+pi-3pi0 and KSKL -> pi+pi-pi+pi- corresponding to signal-like parts K -> pi0pi0, K -> pi+pi-, respectively.
The first step was to perform a selection under the hypothesis of each tagging decay (K -> pi+/-l-/+nipi0pi0, KL -> 3pi0 and KS -> pi+pi-) and reach the highest possible purity. Then, the number of tagging events was weighted with a branching ratio for each signal-like part to obtain so-called expected distributions of the time difference. The additional selection under the hypothesis of K -> pi0pi0 or K -> pi+pi- was imposed on the events after tagging to mimic the selection performed for KSKL -> pi+pi-pi0pi0 using MC. Importantly, independence between charged and neutral parts of decay had to be conserved, so the method of trilateration was adapted to reconstruct a neutral vertex. Finally, having determined the expected and selected distributions of Deltat, a correction factor can be calculated via the division of efficiency obtained from data by the efficiency from MC. The result is not
a uniform distribution, so there exists a specific factor for each bin of the Deltat histogram. Final uncertainties were determined using a standard propagation of a measurement error. A measured correction will be used in the further studies over CP symmetry breaking in the entangled kaons? systems.
Measurement of the charge asymmetry for the KS -> pi e nu decay with the KLOE detector
Author: Daria Kamińska
Supervisor: prof. Paweł Moskal, dr Eryk Czerwiński
abstract
Defence year: 2014
The aim of this work is a determination of the charge asymmetry in semileptonic decays of KS meson. The measurement was performed using KLOE detector localized at DAFNE accelerator in the National Laboratory in Frascati, Italy. The experimental data used in this thesis has been collected during 2004-2005 data campaign of KLOE. The final values of charge asymmetry determined for KS meson semileptonic decays, obtained by registering the phi -> KL KS -> KL pi e nu process, amount to AS = (1.5 ? 5.8 stat ) 10^(-3). Obtained result does not indicate the CPT violation and received statistical uncertainty is, as expected, about two times better with respect to previous measurement.
A novel algorithm for the K->pi0pi0->gggg decay vertex reconstruction for the KLOE-2 experiment
Author: Aleksander Gajos
Supervisor: prof. Paweł Moskal, dr Eryk Czerwiński
abstract
Defence year: 2013
The aim of this work is to devise an auxiliary method of reconstruction of the K->pi0pi0 decay vertex for the KLOE experiment. The requirement for reconstruction is not to depend on quantities that may be affected by kaon regeneration and thus to allow for its rejection as background for the phi->KsKl->pi+pi-pi0pi0 process. A new reconstruction algorithm is proposed and implemented which uses four photons from the K->pi0pi0->gggg decay chain recorded by an electromagnetic calorimeter and is based on finding their common origin point. A kinematic fit is included in the algorithm in order to tune the quantities used as input to vertex reconstruction and thus increase spatial resolution of vertex location. The final resolution achieved by the new reconstruction algorithm was found to be about 0.5cm in each spatial coordinate for vertices of kaons decaying very close to their production point and about 2.5cm for the most interesting region where the spherical beam pipe is present. The prospects of application of the new algorithm to rejection of regeneration background were tested in several ways.
Measurement of the neutral kaon regeneration cross-section in beryllium at P=110 MeV/c with the KLOE detector
Author: Izabela Balwierz
Supervisor: prof. Paweł Moskal
abstract
Defence year: 2011
The main result of this thesis is determination of the neutral kaon regeneration cross-section in beryllium for momentum of p_K=110 MeV/c. It was obtained by analyzing data for K_L->K_S regeneration in the cylindrical beam pipe of the KLOE detector. The corresponding cross-sections for the KLOE drift chamber inner wall and the spherical beam pipe were also evaluated as well as values for aluminium and carbon. The K_L mesons were produced in the center of the detector in the collision region of e^+ and e^- beams of the DAFNE collider that worked at the phi meson resonance peak. The analysis was based on identification of regenerated events e^+ e^- -> phi -> K_S K_L -> pi^+ pi^- K_S^reg -> pi^+ pi^- pi^+ pi^- and their extraction from the distributions of the vertex position of the K_L meson decays into pi^+ pi^-. The regeneration cross-sections were determined based on the extracted number of regenerated events and number of the K_L mesons passing through the regenerator. Obtained results are equal to: sigma_reg^Be=(50.0 +/- 0.7^stat +/- 5.0^syst)mbarn for beryllium, sigma_reg^BP=(77.6 +/- 0.3^stat +/- 7.8^syst)mbarn for the beam pipe, sigma_reg^DC=(75.7 +/- 0.3^stat +/- 7.6^syst)mbarn for the drift chamber inner wall, sigma_reg^Al=(170 +/- 3^stat +/- 38^syst)mbarn for aluminium and sigma_reg^C=(61 +/- 1^stat +/- 11^syst)mbarn for carbon.
Investigations of the time interval distributions between the decays of quantum entangled neutral kaons
Author: Tomasz Twaróg
Supervisor: prof. Paweł Moskal
abstract
Defence year: 2010
Merging and splitting of clusters in the electromagnetic calorimeter of the KLOE detector
Author: Jarosław Zdebik
Supervisor: prof. Paweł Moskal
abstract
Defence year: 2008
The work was carried out in the framework of the KLOE collaboration studying the decays of the phi meson produced in the DAFNE accelerator in the collisions of electron and positron. The main aim of this thesis was investigation of the influence of the merging and splitting of clusters in decays with the high multiplicity of gamma quanta, which are at most biased by these effects. For this aim we implemented the full geometry and realistic material composition of the barrel electromagnetic calorimeter in FLUKA package. The prepared Monte Carlo based simulation program permits to achieve a fast generation of the detector response separately for each interested reaction. The program was used to study the reconstruction efficiency with the KLOE clustering algorithm as a function of the photocathode quantum efficiency. It was also used to investigate merging and splitting probabilities as a function of the quantum efficiency. The conducted studies indicated that the increase of quantum efficiency does not improve significantly the identification of clusters. The influence of these effects was estimated for eta meson decays into 3 neutral pions and K_short meson into 2 neutral pions.
Studies of CPT symmetry violation in matter-antimatter systems
Author: Daria Kisielewska
Supervisor: prof. Paweł Moskal
Auxilliary supervisor: dr Eryk Czerwiński
abstract
Defence year: 2019
In this thesis systems made of quark-antiquark and lepton-antilepton were studied for CPT symmetry violation effects.
The first study was preformed in neutral K meson pairs by comparing the asymmetries constructed from the decay rates into the two CP conjugated semileptonic final states, pi- e+ nu and pi+e-ar(nu). If the CPT symmetry holds, then the asymmetry constructed for short-lived kaon (A S ) and long-lived kaon (A L ) are expected to be identical. At present, the most precise measurement of A L has been performed by the KTeV collaboration: A L = ( 3.322 pm 0.058 stat pm 0.047 syst ) 10^(-3) . The measurement of its counterpart is experimentally more difficult since it requires a very pure K S beam which can be realised only by exploiting the entangled neutral kaons pairs produced at a phi-factory. The first measurement of A S has been performed by the KLOE collaboration in 2006 using 410 pb^(-1) of integrated luminosity: A S = ( 1.5 pm 9.6 stat pm 2.9 syst ) 10^(-3) , with an accuracy dominated by the statistical uncertainty. The new measurement reported in this thesis is based on a four times
larger data sample, corresponding to an integrated luminosity of 1.63 fb^(-1) . The final value A S = ( ?4.9 pm 5.7 stat pm 2.6 syst ) 10^(-3) improves statistical accuracy by a factor of almost two with respect to the previous KLOE result. The combination of these two measurements gives A S = ( ?3.8 pm 5.0 stat pm 2.6 syst ) 10^(-3) and allows to determine the new limits on CPT violating parameters Re ( x ? ) = ( ?2.0 pm 1.4 ) 10^(-3) , and Re ( y ) = ( 1.7 pm 1.4 ) 10^(-3) . The obtained results are in agreement with CPT invariance and with statistical uncertainty almost a factor of two smaller with
respect to the former measurements.
The second part of this work comprised a demonstration of the feasibility of using the J-PET detector to test the CPT violation in correlations of momenta of photons originating from ortho-positronium annihilation and the spin of ortho-positronium.
For this purpose simulations of the o-Ps formation and its annihilation into three photons were performed taking into account distributions of photons? momenta as predicted by quantum electrodynamics and the response of the J-PET tomograph.
The results indicate that the J-PET detector has a realistic chance to improve best present limits established for CPT symmetry violations in decays of positronium by more than an order of magnitude. This can be achieved by the application
of plastic scintillators which have superior time resolution and allow to create a setup with high granularity of detection strips and low detection pile-ups, which allows to overcome the limitation on the source activity. In addition, the improved
angular resolution combined with the excellent timing, and with the possibility of triggerless registration of all events allow for suppression and monitoring of background events.
Investigations of fundamental symmetries with the electron-positron systems
Author: Aleksander Gajos
Supervisor: prof. Paweł Moskal
Auxilliary supervisor: dr Eryk Czerwiński
abstract
Defence year: 2018
This work concerned two experimental searches for the violation of fundamental discrete symmetries in physical systems originating from electron-positron interactions. The first study was a direct test of the symmetry under reversal in time in transitions of neutral K mesons, performed with quantum-entangled neutral kaon pairs produced in the e+e->KsKl process. Data collected by the KLOE experiment operating at the DAFNE collider in 2004-2005 were studied to select events of the KsKl->pi e nu 3pi0 and KsKl->pi+pi- pi e nu processes and compare their rates. For the Kl->3pi0 decay involving only neutral particles, a dedicated reconstruction technique based on trilateration was devised. Rates of each process identified by two time-ordered neutral kaon decays, determined as a function of a difference between kaon decays, were used to measure the asymptotic level of two T-violation sensitive ratios of double kaon decay rates, yielding the values of R2 = 1.020 +/- 0.017stat +/- 0.035syst and R4 = 0.990 +/- 0.017stat +/- 0.039syst. In agreement with expectation based on the size of the the dataset used, these results do not reach the sensitivity needed to probe T violation. However, this measurement proves that the required reconstruction and analysis of the data is feasible and prospects exist for a statistically significant test of the T symmetry with a larger dataset collected by the KLOE-2 experiment is certain systematic effects are eliminated.
The second part of this work comprised a demonstration of the feasibility of using the J-PET detector to search for non-vanishing angular correlations in the decays of ortho-positronium atoms, the lightest purely leptonic systems decaying into photons. The trilateration based reconstruction method prepared for Kl->3pi0 decay at KLOE was adapted to the ortho-positronium annihilations into three photons. Its performance was validated using Monte Carlo simulations proving it may be applied to determination of spin direction of positrons forming the positronium atoms, thus allowing for control of their polarization in the experiment. Moreover, the feasibility of identification of 3gamma events as well as reconstruction of their origin points was demonstrated using a test measurement performed with the J-PET detector.
Study of the phi->eta e+e- dalitz decay using KLOE detector
Author: Jarosław Zdebik
Supervisor: prof. Paweł Moskal
abstract
Defence year: 2013
In this thesis the results of the investigation of the phi -> eta e+ e- -> pi+ pi- pi0 e+ e- reaction are presented. The goal of this work is to extract the branching ratio of the phi -> eta e+ e- decay, the slope of an electromagnetic transition form factor of phi-eta mesons and a charge radius of the phi meson. For this aim the phi mesons were produced in the electron-positron collisions and the eta mesons were identified via the eta -> pi0 pi+ pi- decay channel. The measurement was performed using the KLOE detector and the electron-positron beams circulated in the DAPhiNE accelerator. The experimental data used in this thesis has been collected in 2004-2005 years. After selection of the final sample, we reconstructed around 13000 events coming from phi -> eta e+e- -> pi0 pi+ pi- e+ e- decay with less than 2% background. Thus improving the statisticscollected by previous experiments by about two orders of magnitude. The extracted values of form factor slope parameter,b , branching ratio, BR and the radius of phi meson for analyzed reaction are: b = 1.32 +/- 0.23stat +/- 0.02syst GeV-2 , BR = (1.170 +/- 0.035stat +/- 0.008syst ) * 10-4 , radius = 0.56 +/- 0.05 fm, respectively. The results for slope of transition form factor, branching ratio and the charge radius of phi meson are delivered with the biggest precision ever.
Search for the CP symmetry violation in the decays of Ks mesons using the KLOE detector
Author: Michał Silarski
Supervisor: prof. Paweł Moskal
abstract
Defence year: 2012
The aim of this work was to determine the KS ->3pi0 decay branching ratio and a modulus of the eta_000 parameter, defined as the ratio of amplitudes for KS ->3pi0 to KL -> 3pi0 decays, which characterizes the CP symmetry violation in this decay. The measurement has been carried out with the KLOE detector operating at the phi?factory DAFNE in the Italian National Center for Nuclear Physics in Frascati. DAFNE collides the e+ and e- beams at the center of mass energy s = 1019.45 MeV. The e+e? collisions result in the phi meson creation which is almost at rest and decay predominantly to kaon pairs. The decay products are registered using the KLOE detection setup, which consists of large cylindrical drift chamber surrounded by the electromagnetic calorimeter. The detectors are placed in a magnetic field of B = 0.52 T generated
by superconducting solenoid.
The KS mesons were identified with high efficiency via registration of these KL mesons which crossed the drift chamber without decaying and then interacted with the KLOE electromagnetic calorimeter . The KS four-momentum vector was then determined using the registered position of the KL meson and the known momentum of phi. Next, the search for the KS -> 3pi0 -> 6gamma decay was carried out by the selection of events with six gamma quanta which momenta were reconstructed using time and energy measured by the electromagnetic calorimeter. To increase the signal over background ratio after identification of the KS meson and requiring six reconstructed photons a discriminant analysis was performed. It was based on kinematical fit, testing of the signal and background hypotheses and exploiting of the differences in kinematics of the KS decays into 2pi0 and 3pi0. The search for the KS ->3pi0 decay presented in this work failed to detect a signal of sufficient statistical significance. Hence, we have obtained the upper limit on the KS -> 3pi0 branching ratio at the 90% confidence level: BR(KS -> 3pi0) < 2.7*10^{-8},which is almost five times lower than the latest published result. This upper limit can be translated into a limit on the modulus of the eta_000 parameter amounting to:|eta_000| < 0.009 at the 90% confidence level. This corresponds to an improvement of the |eta_000| uncertainty by a factor of two with respect to the latest direct measurement. The upper limit on the KS ->3pi0 branching ratio determined in this work is still about one order of magnitude larger than the prediction based on the Standard Model. Hence, the search for this decay will be continued with the upgraded KLOE detector, which has realistic chances to observe the KS ->3pi0 decay for the first time in the near future.
