Workshop on Precision Physics and Fundamental Physical Constants

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Workshop on Precision Physics and Fundamental
Physical Constants ????????????? ????????? ??
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DIRAC collaboration
CERN Geneva,
Switzerland
Tokyo Metropolitan University
Tokyo, Japan
Czech Technical University
Prague, Czech Republic
IFIN-HH Bucharest,
Romania
Institute of Physics ASCR
Prague, Czech Republic
JINR Dubna,
Russia
Nuclear Physics Institute ASCR
Rez, Czech Republic
IHEP
Protvino, Russia
INFN Laboratori Nazionali di Frascati
Frascati, Italy

SINP of Moscow State University
Moscow, Russia
Santiago de Compostela University
Santiago de Compostela, Spain
Trieste University and INFN-Trieste
Trieste, Italy
Bern University
Bern, Switzerland
University of Messina
Messina,
Italy
KEK Tsukuba,
Japan
Zurich University
Zurich, Switzerland
Kyoto Sangyou University
Kyoto, Japan
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Pionium lifetime
Pionium (A2?) is a hydrogen-like atom consisting
of ? and ?- mesons EB-1.86 keV, rB387 fm,
pB0.5 MeV
The lifetime of ??- atoms is dominated by the
annihilation process into ?0 ?0

Gasser et al (2001)
Uretsky 1961 Bilenkiy 1969
a0 and a2 are the ?? S-wave scattering lengths
for isospin I0 and I2.
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Theoretical Status
In ChPT the effective Lagrangian which describes
the pp interaction is an expansion in (even)
terms
1966 Weinberg (tree) 1984 Gasser-Leutwyler
(1-loop) 1995 Knecht et al. (2-loop) 1996
Bijnens et al. (2-loop) 2001 Colangelo et al. (
Roy)
And the theoretical results for the scattering
lengths up to 2-loops are
Tree (Weinberg) 1-loop (Gass.Leut.) 2-loop (Bijnens et al.) 2loopRoy (Colangelo et al.)
a0 0.16 0.203 0.219 0.220 2.3
a2 -0.045 -0.043 -0.042 -0.044 2.3
These results (precision) depend on the
low-energy constants (LEC) l3 and l4. Because l3
and l4 are sensitive to the quark condensate,
precise measurements of a0, a2 are a way to study
the structure of the QCD vacuum. Lattice gauge
calculations from 2006 provided values for these
l3 and l4.
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Production of pionium
Atoms are Coulomb bound state of two pions
produced in one proton-nucleus collision
Nemenov 1985
Background processes
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Method of A2p observationand lifetime measurement
?(A2p) is too small to be measured directly. E.
m. interaction of A2p in the target A2p ? pp
- Q lt 3MeV/c, Tlablt 3 mrad
Target Ni 98 ?m
p
p
A2p
atomic pairs (nA)
(NA)
24 GeV/c
p-
p
Coulomb from short-lived sources
(NC)
p
p-
NA K(Q0) NC(QltQ0) with known K(Q0)
?,
24 GeV/c
Breakup probability PbrnA/NA
p
p
p
non-Coulomb from long-lived sources
p-
24 GeV/c
?, ?,
p
p0
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Lifetime and breakup probability
The Pbr value depends on the lifetime value, t.
To obtain the precise Pbr(t) 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 anlmnlm coefficients are given
by
if nlm? nlm,
snlmnlm being the pionium-target atom cross
section, N0 the Avogadro Number, r the material
density and A its atomic weight.
The detailed knowledge of the cross sections
(AfanasyevTarasov 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.
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Break-up probability
Solution of the transport equations provides
one-to-one dependence of the measured break-up
probability (Pbr) on pionium lifetime t
dt10 ? dPbr 4
All targets have the same thickness in radiation
lengths 6.710-3 X0
There is an optimal target material for a given
lifetime
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ISO-VIEW
SIDE-VIEW
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DIRAC experimental setup 2007
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DIRAC Spectrometer
Setup features angle to proton beam ?5.7?
channel aperture ?1.2103 sr magnet
2.3 Tm momentum range
1.2?p??7 GeV/c Thin targets 7 103 X0,
Nuclear efficiency 3 10-4 resolution on
relative momentum ?QX ?QY0.3 MeV/c, ? QL0.5
MeV/c Proton beam 1011 proton/spill
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Analysis based on MC
Atoms 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.
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Atomic pairs MC
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Atomic pairs (2001)
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Lifetime of Pionium
Result from DIRAC
ChPT prediction
Phys. Lett. B 619 (2005) 50-60 hep-ex/0504044
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Experimental results 2001-2003
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Experimental results 2001-2003
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DIRAC preliminary results with GEM/MSGC
QL distribution
?All events
?After background subtraction
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DIRAC preliminary results with GEM/MSGC
QT distribution
?After background subtraction for QLlt2MeV/c
QLlt2 MeV/c
QLgt2 MeV/c
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DIRAC Experimental results
A2p lifetime
2005 DIRAC (PL B619, 50)
...based on 2001 data (6530 observed atoms)
2008 DIRAC (SPSC 22/04/08)
...major part 2001-03 data (13300 observed atoms)
Including GEM/MicroStripGasChambers gt number of
reconstructed events is 18000 gt the statistical
error in a0-a2 is 3, and the expected full
error is lt5.
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Comparison with other experimental results
K?3?
...with ChPT constraint between a0 and a2
2006 NA48/2 (PL B633, 173)
2009 NA48/2 (seminar at CERN)
...without constraint (a2 free)
...with ChPT constraint between a0 and a2
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Comparison with other experimental results
Ke4
2008 NA48/2 (EPJ C54, 411)
...without constraint (a2 free)
2009 NA48/2 (seminar at CERN)
...without constraint (a2 free)
...with ChPT constraint between a0 and a2
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a0-a2
DIRAC 2008
G.Colangelo 2009
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Kp- and K-p atoms lifetime
K?-atom (AK?) is a hydrogen-like atom consisting
of K and ?- mesons
EB -2.9 keV rB 248 fm pB 0.8 MeV
The K?-atom lifetime (ground state 1S), ?1/? is
dominated by the annihilation process into K0?0

J. Schweizer (2004)
From Roy-Steiner equations
If
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?K scattering lengths
I. ChPT predicts s-wave scattering lengths
V. Bernard, N. Kaiser, U. Meissner. 1991
A. Rossel. 1999
J. Bijnens, P. Talaver. April 2004
II. Roy-Steiner equations
P.Büttiker et al. - 2004
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?K scattering
What new will be known if ?K scattering length
will be measured?
The measurement of the s-wave pK scattering
lengths would test our understanding of the
chiral SU(3)L ? SU(3)R symmetry breaking of QCD
(u, d and s quarks), while the measurement of pp
scattering lengths checks only the SU(2)L ?
SU(2)R symmetry breaking (u, d quarks).
This is the principal difference between pp and
pK scattering!
Experimental data on the pK low-energy phases are
absent
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Trajectories of p- and K from the AKp break-up
The numbers to the right of the tracks lines are
the p ? and K momenta in GeV/c
The AKp, p - and K momenta are shownin the
following table
Patom (GeV/c) Pp (GeV/c) PK (GeV/c)
5.13 1.13 4.0
5.77 1.27 4.5
6.41 1.41 5.0
10.26 2.26 8.0
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Upgraded DIRAC experimental setup
Modifided parts
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p-K and pK- atom signal
In total 17354 ?K-atomic pairs are observed
with a significance of 3.2?.
B. Adeva et al.,Evidence for pK-atoms with
DIRAC, Physics Letters B 674 (2009) 11 Y.
Allkofer, PhD Thesis, Universität Zürich, 2008.
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QL-distribution for Kp- pairs from 2007 data
QT -distribution for Kp- background pairs from
2007 data
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QL-distribution for pp- pairs from 2008 data
QL-distribution for pK- pairs from 2008 data
QL-distribution for Kp- pairs from 2008 data
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Results of 2009
The comparison of the events collected in years
2008 and 2009 in the DIRAC experiment.
Year Number of spills Number of days Spills/day
2008 7.0 105 95 7400
2009 10.9 105 164 6600
The time correlated events were selected by the
cuts in the transverse and longitudinal
components Qx, Qy and QL
pp Qx 6 MeV/c Qy 6 MeV/c QL 30 MeV/c
pK Qx 8 MeV/c Qy 8 MeV/c QL 30 MeV/c
Year pp- pK- Kp-
2008 4.8 106 2.7 104 4.2 105
2009 7.3 106 3.4 104 7.5 105
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Metastable Atoms
For pA 5.6 GeV/c and ? 20
?1s 2.9 10 ?15 s , ?1s 1.7 10 ?3
cm ?2s 2.3 10 ?14 s , ?2s 1.4 10 ?2
cm ?2p 1.17 10 ?11 s , ?2p 7 cm
?3p ? 23 cm
?4p ? 54 cm
2µ
100µ
Illustration for observation of the A2p
long-lived states with breaking foil.
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Energy splitting between np - ns states in ???
atom
For n 2
(1979) A. Karimkhodzhaev and R. Faustov
(2000) D. Eiras and J. Soto (1983) G. Austen
and J. de Swart
(2004) J. Schweizer, EPJ C36 483 (1986) G.
Efimov et al. A. Rusetsky,
priv. comm. (1999) A. Gashi et al.

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Metastable Atoms
Probabilities of the A2p breakup (Br) and yields
of the long-lived states for different targets
provided the maximum yield of summed population
of the long-lived states S(l 1)
Target Z Thickness µ Br S (l 1) 2p0 3p0 4p0 S (l 1, m 0)
04 100 4.45 5.86 1.05 0.46 0.15 1.90
06 50 5.00 6.92 1.46 0.51 0.16 2.52
13 20 5.28 7.84 1.75 0.57 0.18 2.63
28 5 9.42 9.69 2.40 0.58 0.18 3.29
78 2 18.8 10.5 2.70 0.54 0.16 3.53
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Prospects of DIRAC
Creation of an intense source of pp, pK and other
exotic atoms at SPS proton beam and using them
for accurate measurements of all S-wave pp and pK
scattering length to check the precise low energy
QCD predictions
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Yields of atoms at PS and SPS
DIRAC prospects at SPS CERN
Yield of dimeson atoms per one proton-Ni interaction, detectable by DIRAC upgrade setup at ?L5.7º Yield of dimeson atoms per one proton-Ni interaction, detectable by DIRAC upgrade setup at ?L5.7º Yield of dimeson atoms per one proton-Ni interaction, detectable by DIRAC upgrade setup at ?L5.7º Yield of dimeson atoms per one proton-Ni interaction, detectable by DIRAC upgrade setup at ?L5.7º Yield of dimeson atoms per one proton-Ni interaction, detectable by DIRAC upgrade setup at ?L5.7º Yield of dimeson atoms per one proton-Ni interaction, detectable by DIRAC upgrade setup at ?L5.7º Yield of dimeson atoms per one proton-Ni interaction, detectable by DIRAC upgrade setup at ?L5.7º
24 GeV 24 GeV 24 GeV 450 GeV 450 GeV 450 GeV
Ep A2p AKp- ApK- A2p AKp- ApK-
WA 1.110-9 0.5210-10 0.2910-10 0.1310-7 0.1010-8 0.7110-9
WAN 1. 1. 1. 12. 19. 24.
WA /Wp 3.410-8 16.10-10 9.10-10 1.310-7 1.10-8 7.110-9
WAN /WpN 1. 1. 1. 3.8 6.2 8.
A multiplier due to different spill duration 4 A multiplier due to different spill duration 4 A multiplier due to different spill duration 4
Total gain 1. 1. 1. 15. 25. 32.
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DIRAC prospects at SPS CERN
Present low-energy QCD predictions for pp and pK
scattering lengths
will be improved by Lattice calculations
?K
will be significantly improved by ChPT
Planned results of DIRAC ADDENDUM at PS CERN
after 2008-2009
2010-2011 Observation of metastable pp- atoms
and study of a possibility to measure its Lamb
shift. Study of the possibility to observe
KK- and atoms using 2008-2009 data.
DIRAC at SPS CERN beyond 2011
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Thank you for your attention