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