Docstoc

PPT - DIRAC - CERN

Document Sample
PPT - DIRAC - CERN Powered By Docstoc
					FINAL CORRECTIONS TO PIONIUM LIFETIME

        WITH Ni 2001 DATA




         A. Romero, B. Adeva, O. Vázquez Doce, C. Mariñas
                            GENERAL COMMENTS
Two topics were not addressed in DIRAC Note 2006-03
“ Measurement of Pionium Lifetime” , namely :

 possible K+K- contamination in the final state

 influence of lower-Z contamination in the target chemical composition

They are small contributions in principle
(DIRAC Proposal CERN/SPSLC 95-1 , pag. 92, estimated 0.25 % K+K- error )


A. Kuptsov “DIRAC Targets”, 5 March 2005, is the main reference for the latter

K+K- Coulomb interaction can be simulated since it is described by
Sakharov factor at first order


we know the corrections for breakup probability have opposite signs:

 negative for K+K-
 positive for target contamination
K+K- Monte Carlo was simulated and processed thorough the standard
generator/ GEANT-DIRAC/ ARIANE chain.


Monte Carlo for Coulomb pairs was modified
to include a fraction of K+K- pairs in agreement with
the experimental measurements, as function of pair momentum p.


2 values of global 2D-fit in (QT, QL) slightly improved in all momentum bins


Breakup probability was re-determined as function of p,
and pionium lifetime re-fitted.
Preliminary result :



                        before K+K- correction

                        after K+K- correction




                       after K+K- and lower-Z
                       target correction
PBr   Stability with QT and QL cut-off parameters slightly improved




PBr                                          MeV/c                    QT (MeV/c)




                                             MeV/c                    QT (MeV/c)

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:0
posted:4/20/2013
language:Unknown
pages:5