HadAtom03 13-17 October 2003, Trento, Italy
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Transcript of HadAtom03 13-17 October 2003, Trento, Italy
Experimental Physics Department,
Institute for High Energy Physics (Protvino)
Observation of atoms at DIRAC and its lifetime
estimation.
Valery Brekhovskikh on behalf of DIRAC collaboration
HadAtom03 13-17 October 2003, Trento, Italy
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
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
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:
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)002.0syst)(002.0013.0216.00
a New measurement at BNL (E865)
S.Pislak et al., Phys.Rev. D 67 (2003) 072004
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
…
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, give 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
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.
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%
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 2.3 T·mmomentum range 1.2p7 GeV/cresolution on relative momentum QX= QY=0.4 MeV/c QL=0.6 MeV/c
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.
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
NCcorr
Ccorr
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.
Single and multilayer Single and multilayer measurementsmeasurementsSingle Target Setup Multilayer Setup
Pro
ton b
eam
Atomic
pairs
Coulomb
pairs
2s,3s,...
1s
2s,3s,...
1s
1s
Pro
ton b
eam
pi0
Atomic
pairs
Atomic
pairs
Atomic
pairs
Coulomb
pairs
2piA
2piA
2piA
2piA
2piA
2piApi0
pi0
pi0
1s
Atoms pairsAtoms pairsNi 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
Target Z Thick (m)
Pt 78 28
Ni 2000Ni 2001Ni 2002
andNi 2003
28 949498
(single)12x8
(multi)Ti 22 251
Atomic pairsAtomic pairs
SampleTriggers 106
na at F<2MeV/c
na at
Ql<1MeV/c
Pt 1999 55.713043
(3.0)
20777
(2.7)
Ni 2000+
2001+
2002+
2003
28008994443 (20.3)
13086738
(17.7)
Ti 2000+
2001911
1110159 (7.0)
1492319 (4.7)
+- 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
Effect
-200
0
200
400
600
0 5 10 15 20 25 30
NA(F<2.0)= 1473.9± 230.0N
Effect
-150
-100
-50
0
50
100
150
200
250
0 5 10 15 20 25 30
NA(F<2.0)= 311.3± 103.4N
Effect
-100
0
100
200
300
400
0 5 10 15 20 25 30
NA(F<2.0)= 761.9± 107.1N
Atomic pairs (F)Atomic pairs (F)
Effect
-100
0
100
200
300
400
0 5 10 15 20 25 30
NA(F<2.0)= 688.1± 144.6N
Effect
-250
0
250
500
750
1000
1250
1500
0 5 10 15 20 25 30
NA(F<2.0)= 3631.9± 237.5N
Effect
-200
0
200
400
600
0 5 10 15 20 25 30
NA(F<2.0)= 1636.1± 156.3N
Ni 2000
Ni 2003 (S)
Ni 2001
Ni 2003 (M)
Ni 2002 (20)
Ni 2002 (S)
Effect
0
200
400
600
800
1000
1200
0 2.5 5 7.5 10 12.5 15 17.5 20
NA(Ql<1.0)= 1468.5± 257.0N
Effect
0
500
1000
1500
2000
2500
3000
3500
4000
0 2.5 5 7.5 10 12.5 15 17.5 20
NA(Ql<1.0)= 5193.8± 392.7N
Atomic pairs (QAtomic pairs (QLL))
Ni 2000
Ni 2003 (S)
Ni 2001
Ni 2003 (M)
Ni 2002 (20)
Ni 2002 (S)
Effect
-250
0
250
500
750
1000
1250
1500
1750
0 2.5 5 7.5 10 12.5 15 17.5 20
NA(Ql<1.0)= 1795.6± 266.5
N
Effect
0
500
1000
1500
2000
0 2.5 5 7.5 10 12.5 15 17.5 20
NA(Ql<1.0)= 2560.1± 369.8N
Effect
0
200
400
600
800
0 2.5 5 7.5 10 12.5 15 17.5 20
NA(Ql<1.0)= 1145.7 ± 178.2N
Effect
-100
-50
0
50
100
150
200
250
300
350
0 2.5 5 7.5 10 12.5 15 17.5 20
NA(Ql<1.0)= 384.0± 172.7N
Effect
0
200
400
600
800
0 2.5 5 7.5 10 12.5 15 17.5 20
NA(Ql<1.0)= 1074.0± 220.5N
Effect
0
500
1000
1500
2000
2500
0 2.5 5 7.5 10 12.5 15 17.5 20
NA(Ql<1.0)= 3421.8± 443.8N
Effect
0
1000
2000
3000
4000
5000
6000
0 2.5 5 7.5 10 12.5 15 17.5 20
NA(Ql<1.0)= 8022.0± 630.4
N
Effect
0
500
1000
1500
2000
0 2.5 5 7.5 10 12.5 15 17.5 20
NA(Ql<1.0)= 2937.9± 412.7N
Atoms pairs (noUP)Atoms pairs (noUP)
Effect
0
200
400
600
800
1000
1200
0 2.5 5 7.5 10 12.5 15 17.5 20
NA(Ql<1.0)= 1468.5± 257.0N
Effect
0
500
1000
1500
2000
2500
3000
3500
4000
0 2.5 5 7.5 10 12.5 15 17.5 20
NA(Ql<1.0)= 5193.8± 392.7N
Ni 2000 Ni 2001 Ti 2001
Ni 2000 noUp Ni 2001 noUP Ti 2001 noUP
Atoms pairs (S-M)Atoms pairs (S-M)
In the end of 2002 run there was introduced a segmented Ni target consisting of 12 planes with 1 mm gap between each. The combined thickness of all planes is approximately equal to that of the single layer 98 micron Ni target.
Single and multilayer target event distributions are identical in all respects but one: the multilayer target yields a lower number of dissociated pairs due to the annihilations in the interlayer gaps. One can at once obtain the signal from the difference between the single and multilayer distributions
2003: Difference Single - Multi Ql (MeV)
-100
0
100
200
300
400
0 2.5 5 7.5 10 12.5 15 17.5 20
2002+2003: Difference Single - Multi Ql (MeV)
-200
0
200
400
600
800
1000
0 2.5 5 7.5 10 12.5 15 17.5 202002: Difference Single - Multi Ql (MeV)
-100
0
100
200
300
400
500
600
700
0 2.5 5 7.5 10 12.5 15 17.5 20
Atomic pairs (Table)Atomic pairs (Table)Number of Atomic pairs
Ni2000(24 GeV)
Ni2001(24 GeV)
Ni2002(20 GeV)
Ni2002(24 Gev S)
Ni2002(24 Gev M)
Ni2003(20 GeV S)
Ni2003(20 GeV M)
F<2 688 ±
144
3632 ±
237
1636 ±
156
1474 ±
230
491 ±
143
762 ±
107
311 ±
103
QL<1
QT<3
1468 ±
257
5193 ±
392
1796 ±
266
2560 ±
370
539 ±
237
1146 ±
178
384 ±
172
Ratio of Atomic pairs to Coulomb pairsF<2 0.1296 ±
0.0299
0.2771 ±
0.0219
0.2933 ±
0.0341
0.1578 ±
0.0273
0.1212 ±
0.0384
0.2697 ±
0.0457
0.1141 ±
0.0412
QL<1
QT<3
0.1237 ±
0.0246
0.1912 ±
0.0175
0.1474 ±
0.0255
0.1391 ±
0.0232
0.0638 ±
0.0302
0.2002 ±
0.0380
0.0701 ±
0.0340
Q and FQ and F
222LYX QQQQ
2
2
2
2
2
2
LYX Q
L
Q
Y
Q
X QQQF
cMevYX QQ /1
cMevLQ /65.0
F<1
Q<1MeV/c
)/0.2()3.2( cMeVQNFN aa
Q<2MeV/c
F<2.3
)/0.2()3.2( cMevQNFN bb
Conclusions and resultsConclusions and results
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.
In order to decrease systematic errors, the dedicated measurements with a multi-layer nickel target and measurements of multiple scattering all detectors and setup elements are performing at the end 2002 and during present run of 2003.
Preliminary results have been achieved by analyzing data collected in 2001. The statistical accuracy in the lifetime determination reaches 25% and the systematic one is 26%. Analysis of data collected in 2000 and 2003 together with the systematic error reduction allows us to improve accuracy up to the level of 14%.
Ni2001
10-1 5 s
Pbr
0.3
0 .35
0 .4
0 .45
0 .5
0 .55
0 .6
1 2 3 4 5 6 7 8
ssyststat 1592.072.0 10)(8.0)(12.3