University of Santiago de Compostela, Spain |a |a 0 0 -a -a 2 2 | | Measurement Measurement from from Pionium Lifetime by DIRAC Pionium Lifetime by DIRAC Bernardo Adeva on behalf of DIRAC collaboration IVth INTERNATIONAL CONFERENCE ON QUARKS AND NUCLEAR PHYSICS 5 - 10 June 2006, Madrid, Spain
|a 0 -a 2 | Measurement from Pionium Lifetime by DIRAC. Bernardo Adeva on behalf of DIRAC collaboration. University of Santiago de Compostela, Spain. IVth INTERNATIONAL CONFERENCE ON QUARKS AND NUCLEAR PHYSICS 5 - 10 June 2006, Madrid, Spain. DIRAC. - PowerPoint PPT Presentation
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University of Santiago de Compostela, Spain
|a|a00-a-a22|| MeasurementMeasurement from from
Pionium Lifetime by DIRACPionium Lifetime by DIRAC
Bernardo Adeva on behalf of DIRAC collaboration
IVth INTERNATIONAL CONFERENCE ON QUARKSAND NUCLEAR PHYSICS
L. Rosselet et al., Phys. Rev. D 15 (1977) 574a0=0.26±0.05
N→N near threshold
M. Kermani et al., Phys. Rev. C 58 (1998) 3431a0=0.204±0.014 ±0.008(syst)
C.D. Froggatt, J.L. Petersen, Nucl. Phys. B 129 (1977) 89a0=0.26±0.05
N.Cabibbo, Phys. Rev. Lett. 93, 121801 (2004)N.Cabibbo, G.Isidori, hep-ph/0502130
|a0-a2|= 0.281 ± 0.007 (stat.) ±0.014 (syst.)
K+→+00 and KL→30 NA48
The pionium is a Coulomb bound state:
MeV1fm387)(0keV858.1
2
B
PCB
PARJE
+ and - originating from short lived sources (, K*, ,...) and resonance decays may form a pionium atom. The differential cross section is:
Lorentz Center of Mass to Laboratory factor.
Wave function at origin (accounts for Coulomb interaction).
Pion pair production from short lived sources.
Production of pioniumProduction of pionium
Method of pionium detectionMethod of pionium detection
Pionium is created in nS states then it interacts with target material:
decay 15 for 17c m
L.Nemenov, Sov.J.Nucl.Phys. 41 (1985) 629
Annihilation: A2→00
Excitation: transitions between atomic levels
Break-up(ionisation): characteristic “atomic” pairs nA
• Qcms<3MeV/c • → in laboratory system E+≈E-, small opening angle θ<3mrad
Coulomb and atomic pairs are detected simultaneously:
Niforμmλ S 201int
C
Ath
A
ABr N
nKN
nP 1
Production of pioniumProduction of pioniumAtoms are Coulomb bound state of two pions produced in one proton-nucleus collision
Background processes:Coulomb pairs. They are produced in one proton nucleus collision from fragmentation or short lived resonances resonances (, K*, ,...) and exhibit Coulomb interaction in the final state:
Non-Coulomb pairs. They are produced in one proton nucleus collision. At least one pion originates from a long lived resonance. No Coulomb interaction in the final state
Accidental pairs. They are produced in two independent proton nucleus collision. They do not exhibit Coulomb interaction in the final state
α/q)Mπ2exp(1α/qMπ2(q)A
dpdpσd(q)A
dpdpσd
π
πC
0S
2
CC
2
DIRAC SpectrometerDIRAC Spectrometer
Upstream detectors: MSGCs, SciFi, IH.
Downstream detectors: DCs, VH, HH, C, PSh, Mu.
Tracking principles Tracking principles •Precison time-of-flight to reduce accidental and proton background
•Strong e+e- rejection by Čerenkov counters
•Unambiguous transverse momentum QT by upstream tracking (MSGC+SFD)
•Longitudinal momentum QL measured by fast drift chambers and upstream tracks
DIRAC Spectrometer DIRAC Spectrometer High high irradiation
Time difference spectrum at VH with e+e- T1 trigger.
Mass distribution of p- pairs from decay. =0.39 MeV/c2
Positive arm mass spectrum, obtained by TOF difference, under - hypothesis in the negative arm.
Accidental pairs, different proton interactions in the target
Coulomb pairs. From short lived sources.r < 3 fm, < R(A2
Non Coulomb pairs. From long lived sources.r ~ 1000 fm.
t= 174 ps +- pairs
Time-of-Flight spectrumTime-of-Flight spectrum
Analysis based on MCAnalysis based on MCAtoms are generated in nS states using measured momentum distribution for short-lived sources. The atomic pairs are generated according to the evolution of the atom while propagating through the target
Background processes:
Coulomb pairs are generated according to AC(Q)Q2 using measured momentum distribution for short-lived sources.
Non-Coulomb pairs are generated according to Q2 using measured momentum distribution for long-lived sources.
Monte Carlo simulation is restricted to detector response only withoutrelying on specific asumptions from proton-nucleus collision models
Qddn
Qddn
Qddn
Qddn
Qddn ATACNCCCp
22322212
Qddn
NQddn i
i
i22
1 LT dQdQQd 2
2D 2 FIT TO (QT, QL) SPECTRUM
3 (accidentals fraction) measured from TOF
1 and free parameters in 10 independent 600 MeV/c +- momentum bins
Atom signal defined as difference between prompt data and Monte Carlo with = 0
1321
PIONIUM BREAK-UP SIGNAL IN +- SPECTRUM
LongitudinalTransverse
· cos
Pionium signal in Q =√ QL2+ QT
2
PIONIUM TRANSVERSE SIGNAL
QL > 2 MeV/c
QL < 2 MeV/c
PIONIUM LONGITUDINAL SIGNAL
)(K1
)(N)(NP exp
CC
ATBr
Qd(Q)A
/n1π
)παM(2)(K2
C
33πth
)(K)(ε)(εK th
AT
CCexp
)Q(0,)Q(0,Ω CL
CT
DETERMINATION OF BREAK-UP PROBABILITY
Different extrapolation domains:
QM analytical factor:
Coulomb-pair background NCC determined from fit 1 parameter:
Acceptance factors i determined by Monte Carlo simulation
Standard choice is QLC = 2 MeV/c and QT
C = 5 MeV/c
fs0.260.22S1 2.58τ
Break-up probability as function of pionium momentum