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![Page 1: Laboratory of Nuclear Problems, Joint Institute for Nuclear Research, Dubna Measurement of atom lifetime at DIRAC. ICHEP02 Amsterdam, 25–31 July,](https://reader036.vdocument.in/reader036/viewer/2022083007/56649e865503460f94b8926e/html5/thumbnails/1.jpg)
Laboratory of Nuclear Problems,
Joint Institute for Nuclear Research, Dubna
Measurement of atom lifetime
at DIRAC.
ICHEP02
Amsterdam, 25–31 July, 2002.
Leonid Afanasyev on behalf of DIRAC collaboration
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83 Physicists from 19 Institutes
Basel Univ., Bern Univ., Bucharest IAP, CERN, Dubna JINR, Frascati LNF-INFN, Ioannina Univ., Kyoto-Sangyo Univ., Kyushu Univ. Fukuoka,
Moscow NPI, Paris VI Univ., Prague TU, Prague FZU-IP ASCR, Protvino IHEP, Santiago de Compostela Univ., Tokyo Metropolitan Univ., Trieste
Univ./INFN, Tsukuba KEK, Waseda Univ.
Lifetime Measurement of +- atoms to test low energy QCD predictions.
DImeson Relativistic Atomic Complexes
DIRACDIRAC
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The goal of the DIRAC Experiment is to measure the +- atom
lifetime of order 3·10-15 s with 10% precision. This measurement will
provide in a model independent way the difference between
Swave scattering lengths |a2a0 | with 5 % precision. Low energy
QCD - chiral perturbation theory - predicts nowadays scattering
lengths with very high accuracy ~ 2 % . Therefore, such a
measurement will be a sensitive check of the understanding of
chiral symmetry breaking of QCD by giving an indication about the
value of the quark condensate, an order parameter of QCD.
The GoalThe Goal
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Theoretical MotivationTheoretical Motivation+ atoms (A2 in the ground state decay by strong interaction mainly into 00.
3
2
222 104
1
0
0
Chiral Perturbation Theory (ChPt), which describes the strong interaction at low energies provides, at NLO in isospin symmetry breaking, a precise relation between 2 and the scattering lengths:
)1(|| 000 22
2202
LONLOLO
aaC
(Deser et al) (Gall et al., Jalloli et al, Ivanov et al)
a0 and a2 are the strong S-wave scattering lengths for isospin I=0 and I=2.
s1510)1.09.2()%2.18.5(
%5)/()(%10/ 2020 aaaa
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Theoretical StatusTheoretical StatusIn ChPT the effective Lagrangian which describes the interaction is an expansion in (even) terms:
)4()4()2( LLLLeff
%)5.1(004.0265.0%)3(258.0
gChPT01.025.0
20.0
20)6(
20)6(
)6(20
)4(20
)2(
aaLaaL
LaaLaaL1966 Weinberg (tree):
1984 Gasser-Leutwyler (1-loop):1995 Knecht et al. (2-loop):1996 Bijnens et al. (2-loop):2001 Colangelo et al. (& Roy):
Tree
(Weinberg)
1-loop
(Gass.&Leut.)
2-loop
(Bijnens et al.)
2loop+Roy
(Colangelo et al.)
a0 0.16 0.203 0.219 0.220
a2 -0.045 -0.043 -0.042 -0.044
And the theoretical results for the scattering lengths up to 2-loops are:
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Experimental StatusExperimental StatusExperimental data on scattering lengths can be obtained via the following indirect processes:
shold near thre :dependent Model NN
)( t,independen Model 4ee KeK
05.028.00 a L. Rosselet et al., Phys. Rev. D 15 (1977) 574
(theor)005.0syst)(004.0013.0216.00
a New measurement at BNL (E865)
S.Pislak et al., Phys.Rev.Lett. 87 (2001) 221801
C.D. Froggatt, J.L. Petersen, Nucl. Phys. B 129 (1977) 89
M. Kermani et al., Phys. Rev. C 58 (1998) 3431
10 05.026.0 ma
)syst(008.0014.0204.00 a
05.026.00 a M.Nagels et al., Nucl.Phys. B 147 (1979) 189Combined analysis of Ke4, Roy equation and peripheral reaction
NN data
…
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AA22ππ production production•The pionic atoms are produced by the Coulomb interaction of a pion pair in proton-target collisions (Nemenov):
•Also free Coulomb pairs are created in the proton-target collisions.
•The atom production is proportional to the low relative momentum Coulomb pairs production (NA=KNC).
•The pionic atoms evolve in the target and some of them (nA) are broken. The broken atomic pairs are emitted with small C.M.S. relative momentum (Q < 3 MeV/c) and opening angle <0.3 mrad.
•DIRAC aims to detect and identify Coulomb and atomic pairs samples to calculate the break-up probability
Pbr=nA/NA.
qp
sCnlm
Anlm
qdpd
d
M
E
Pd
d
0
2)(3 )0()2(
Lorentz Center of Mass to Laboratory factor.
Wave function at origin (accounts for Coulomb interaction).
Pion pair production from short lived sources.
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Lifetime and breakup probabilityLifetime and breakup probability
mln
mln
mln
nlm
nlm spads
sdp)(
)(
AN
amln
nlmmln
nlm
0
.00
.0/20
l
lPcMA
Na n
totnlmnlm
nlm
The Pbr value depends on the lifetime value, . To obtain the precise Pbr() curve a large differential equation system must be solved:
where s is the position in the target, pnlm is the population of a definite hydrogen-like state of pionium. The anlm
n´l´m´ coefficients are given by:
nlmn´l´m´ being the electro-magnetic
pionium-target atom cross section, N0 the Avogadro Number, the material density and A its atomic weight.
, if nlm n´l´m´,
The detailed knowledge of the cross sections (Afanasyev&Tarasov; Trautmann et al) (Born and Glauber approach) together with the accurate solution of the differential equation system permits us to know the curves within 1%.
=10% Pbr =4%
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DIRAC SpectrometerDIRAC Spectrometer
Upstream detectors: MSGCs, SciFi, IH.
Downstream detectors: DCs, VH, HH, C, PSh, Mu.
Setup features:angel to proton beam =5.7 channel aperture =1.2·10–3 srmagnet 1.85 T·mmomentum range 1.2p7 GeV/cresolution on relative momentum QX= QY=0.4 MeV/c QL=0.6 MeV/c
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CalibrationCalibration
Time difference spectrum at VH with e+e- T1 trigger.
Mass distribution of p- pairs from decay. =0.43 MeV/c2 <0.49 MeV/c2 (Hartouni et al.).
Positive arm mass spectrum, obtained by time difference at VHs, under - hypothesis in the negative arm.
These results show that our set-up fulfils the needs in time and momentum resolution.
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Atoms detectionAtoms detection
Accidentals:
dQdN
acc
Non-Coulomb pairs:
dQdN
dQdN
acc
NC
corr
Coulomb pairs:
dQ
dNQA
dQ
dN accC
Ccorr )(
fQAN
dQdN
dQdN
dQdN
dQdNdQ
dN
QR Cacc
Ccorr
NCcorr
acc
corr
)()(
N and f are obtained from a fit to the pion pairs Q spectrum in the range without atomic pairs Q > 3 MeV/c
The time spectrum at VH provides us the criterion to select real (time correlated) and accidental (non correlated) pairs.
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Atoms detectionAtoms detectionNi 2001 data
Corr.FunctQ
R(Q
)
0123456789
0 2.5 5 7.5 10 12.5 15 17.5 20
0
10000
20000
30000
0 2.5 5 7.5 10 12.5 15 17.5 20
010000
200003000040000
0 2.5 5 7.5 10 12.5 15 17.5 20
Real+Accidental
Entries 712418
Q
N
Accidental
Entries 1220603
Q
N
Real
Entries 646538
Q
N
0
10000
20000
30000
0 2.5 5 7.5 10 12.5 15 17.5 20
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Atomic PairsAtomic Pairs
Atomic pairsQ
N
-200
0
200
400
600
800
1000
0 2.5 5 7.5 10 12.5 15 17.5 20 22.5
Pt 1999
Ti 2000+2001
Ni 2000
Ni 2001
Ni 2002
Target Z Thick (m)
Pt 78 28
Ni 2000
Ni 2001
28 94
98
Ti 22 251
Atomic pairsQ
N
-20
0
20
40
60
80
100
120
140
0 2.5 5 7.5 10 12.5 15 17.5 20
Atomic pairsQ
N
-200
0
200
400
600
800
0 2.5 5 7.5 10 12.5 15 17.5 20
Atomic pairsQ
N
-100
0
100
200
300
0 2.5 5 7.5 10 12.5 15 17.5 20
Atomic pairsQ
N
-250
0
250
500
750
1000
1250
1500
1750
2000
0 2.5 5 7.5 10 12.5 15 17.5 20
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Atomic pairsAtomic pairs
SampleTriggers 106
na at Q<2MeV/c
na at
Q<3MeV/c
Pt 1999 55.713043
(3.)
20777
(2.7)
Ni 2000 896920170 (5.4)
1335300
(4)
Ti 2000+01
9101170190 (6.2)
1495340 (4.4)
Ni 2001 6472686310 (8.7)
3500510 (6.9)
Ni 2002
(15 day)77
400100
(4)
545170
(3.2)+- relative c.m. momentum MeV/c
Ent
ries
/0.5
MeV
/c
Atomic Pairs
Monte Carlo
0
200
400
600
800
1000
1200
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
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Conclusions and resultsConclusions and results
Ni +Ti
Ti 2000/1
Ni 2000
Statistical error
Lifetime 10-15 s
Sample
1.1
8.08.2
5.1
3.14.5
9.0
7.06.3
%34
%26
%22
DIRAC collaboration has built up the double arm spectrometer which achieves 1 MeV/c resolution at low relative momentum (Q<30MeV/c) of particle pairs and has successfully demonstrated its capability to detect atoms after 2 years of running time.
Some preliminary lifetime results have been achieved with a 5000 atoms sample reaching an statistical accuracy of 22% in lifetime determination.
The accurate determination of systematical errors requires a measurement of the background.
A 10% accuracy on the atom lifetime value (goal of the experiment) will require running beyond 2002.