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Title: Recent results of the NA48/2 experiment

Abstract

The main goals of the NA48/2 experiment are a search for direct CP - violation in the charged kaon decays, a measurement of the pion scattering lengths using Ke4 decays and an investigation of some rare decays. By using large samples of K{+-} {yields} {pi}{+-}{pi}+{pi}- and K{+-} {yields} {pi}{+-}{pi}0{pi}0 decays, the asymmetries in the linear Dalitz plot slopes Ag = (g+ - g-)/(g+ + g-) were measured with high accuracy for both decay modes. The design of the experiment and the method of analysis provide good control of instrumental charge asymmetries in this measurement. Investigating the two neutral pion effective mass distribution in the K{+-} {yields} {pi}{+-}{pi}0{pi}0 decays, we observed cusp-like anomaly. This anomaly, never observed before, can be interpreted as an effect due to the final state charge exchange process {pi}+{pi}- {yields} {pi}0{pi}0 in the K{+-} {yields} {pi}{+-}{pi}+{pi}- decay. Comparison with theoretical models allowed to obtain a measurement of the pion-pion scattering length with a new technique which has a high precision.

Authors:
 [1]
  1. University of Sofia 'St. Kliment Ohridski', Faculty of Physics, 5 James Bourchier Blvd. 1164 Sofia (Bulgaria)
Publication Date:
OSTI Identifier:
21057128
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 899; Journal Issue: 1; Conference: 6. international conference of the Balkan Physical Union, Istanbul (Turkey), 22-26 Aug 2006; Other Information: DOI: 10.1063/1.2733108; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA). NA48-CERN Collaboration
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; ACCURACY; ASYMMETRY; CHARGE EXCHANGE; COMPARATIVE EVALUATIONS; CP INVARIANCE; DALITZ PLOT; EFFECTIVE MASS; KAONS MINUS; KAONS PLUS; MULTIPARTICLE SPECTROMETERS; PARTICLE DECAY; PARTICLE IDENTIFICATION; PION-KAON INTERACTIONS; PION-PION INTERACTIONS; PIONS MINUS; PIONS NEUTRAL; PIONS PLUS; SCATTERING LENGTHS

Citation Formats

Marinova, Evelina. Recent results of the NA48/2 experiment. United States: N. p., 2007. Web. doi:10.1063/1.2733108.
Marinova, Evelina. Recent results of the NA48/2 experiment. United States. doi:10.1063/1.2733108.
Marinova, Evelina. Mon . "Recent results of the NA48/2 experiment". United States. doi:10.1063/1.2733108.
@article{osti_21057128,
title = {Recent results of the NA48/2 experiment},
author = {Marinova, Evelina},
abstractNote = {The main goals of the NA48/2 experiment are a search for direct CP - violation in the charged kaon decays, a measurement of the pion scattering lengths using Ke4 decays and an investigation of some rare decays. By using large samples of K{+-} {yields} {pi}{+-}{pi}+{pi}- and K{+-} {yields} {pi}{+-}{pi}0{pi}0 decays, the asymmetries in the linear Dalitz plot slopes Ag = (g+ - g-)/(g+ + g-) were measured with high accuracy for both decay modes. The design of the experiment and the method of analysis provide good control of instrumental charge asymmetries in this measurement. Investigating the two neutral pion effective mass distribution in the K{+-} {yields} {pi}{+-}{pi}0{pi}0 decays, we observed cusp-like anomaly. This anomaly, never observed before, can be interpreted as an effect due to the final state charge exchange process {pi}+{pi}- {yields} {pi}0{pi}0 in the K{+-} {yields} {pi}{+-}{pi}+{pi}- decay. Comparison with theoretical models allowed to obtain a measurement of the pion-pion scattering length with a new technique which has a high precision.},
doi = {10.1063/1.2733108},
journal = {AIP Conference Proceedings},
number = 1,
volume = 899,
place = {United States},
year = {Mon Apr 23 00:00:00 EDT 2007},
month = {Mon Apr 23 00:00:00 EDT 2007}
}
  • NA48/2 is devoted to study direct CP violation in three charged pions kaon decay. A novel design for the beam line and an upgrade of the NA48 detector are adopted to allow the simultaneous detection of decays from K+/K- unseparated beams. The first preliminary measurement of the direct CP violating parameter Ag is presented. A value for the charge asymmetry in the K{+-} {yields} {pi}{+-}{pi}+{pi}- of Ag = (0.5 {+-} 3.8) {center_dot} 10-4 has been measured using using 1.6 billions K+/K- decays. The analysis of the charge asymmetry in the 'neutral' channel K{+-} {yields} {pi}{+-}{pi}0{pi}0 and a new method tomore » extract the {pi}{pi} scattering length studying accurately the Dalitz Plot in the 'neutral' mode are also shortly discussed. The future program on kaon physics at CERN is briefly outlined.« less
  • Preliminary results of the measurement of charged CP violating asymmetry A{sub g} = (g{sup +} - g{sup -}/g{sup +} + g{sup -}) in both 3{pi} decay modes, based on the whole accumulated statistics in 2003 and 2004, are presented.A new unexpected anomaly in the 2{pi}0 mass subsystem spectrum in K{+-} {yields} {pi}{+-}{pi}0{pi}0 decay, so called ''cusp'', due to charge exchange re-scattering process ({pi}+{pi}- {yields} {pi}0{pi}0) is discussed.A preliminary result indicates the observation of direct emission amplitude and first observation of an interference term in the non-leptonic radiative rare decay K{+-} {yields} {pi}{+-}{pi}0{gamma} is presented.
  • The computation of pion scattering lengths a{sub 0}{sup 0} and a{sub 0}{sup 2} has been addressed in two independent analyses by the NA48/2 collaboration: the variation of the phase shift {delta} = {delta}{sub 0}{sup 0}-{delta}{sub 1}{sup 1} in K{sup {+-}}{yields}{pi}{sup {+-}}{pi}{sup {+-}}e{sup {+-}}{nu} (Ke4) decay and the fit of a cusp-like structure in the M{sub {pi}{sup 0}}{sub {pi}{sup 0}}{sup 2} distribution of the K{sup {+-}}{yields}{pi}{sup {+-}}{pi}{sup 0}{pi}{sup 0} decay.
  • The NA48 experiment aims to measure the direct CP violation parameter Re({epsilon}{sup '}/{epsilon}) using the method of the double ratio with a precision of 2x10{sup -4}. The experiment has collected data during 1997 and during 1998 and plans to produce a result based on the 1997 statistics soon. The status of the analysis and the perspectives for the future are outlined in this paper.
  • A first level trigger system based on a 40 MHz digital pipeline has been developed for the CERN NA48 experiment, aiming at measuring CP violation in K{sup 0} {r_arrow} 2{pi} decays. The outputs of the 13340 cells of the 10 m{sup 3} liquid krypton calorimeter are summed into 64 X and 64 Y projection strips and continuously digitized with 40 MHz FADCs. This information is used to reconstruct at each clock cycle and for the two calorimeter projections, the number of clusters, the impact time of each of them (with a precision of about 3 ns), their total energy andmore » the first and second moments of the energy distribution. Based on the quantities listed above, a programmable look-up table system subsequently computes online the longitudinal position of the kaon decay vertex and performs an event selection. The system is described.« less