status report of the dirac experiment (ps 212)
DESCRIPTION
Status report of the DIRAC experiment (PS 212). L.Nemenov. SPS Committee, April 5, 2011. DIRAC collaboration. CERN Geneva, Switzerland. Tokyo Metropolitan University Tokyo, Japan. Czech Technical University Prague , Czech Republic. - PowerPoint PPT PresentationTRANSCRIPT
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Status report of the DIRAC experiment (PS 212)
SPS Committee, April 5, 2011.
L.Nemenov
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CERN Geneva, Switzerland
Kyoto University Kyoto, Japan
Bern University Bern, Switzerland
KEK Tsukuba, Japan
Santiago de Compostela University Santiago de Compostela, Spain
University of Messina Messina, Italy
IHEP Protvino, Russia
INFN-Laboratori Nazionali di Frascati Frascati, Italy
SINP of Moscow State University Moscow, Russia
JINR Dubna, Russia
Nuclear Physics Institute ASCR Rez, Czech Republic
IFIN-HH Bucharest, Romania
Institute of Physics ASCR Prague, Czech Republic
Tokyo Metropolitan University Tokyo, Japan
Czech Technical University Prague, Czech Republic
DIRAC collaborationDIRAC collaboration
Zurich University Zurich, SwitzerlandKyoto Sangyou University
Kyoto, Japan
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1. Status of 2008–2010 data process on K+π− and K−π+ atoms.
2. Schedule of data analysis of K+π− and K−π+ atoms in 2011.
3. Status of the publication about π+π− atom lifetime measurement on 2001-2003 data
4. Status of 2008–2010 data process on π+π− atoms.
5. Multiple-scattering measurement during 2011 run.
6. Long-lived π+π− atoms and data taking in 2011 for their observation.
7. K+K− and πμ Coulomb pairs.
ContentContent
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Modifided parts MDC - microdrift gas chambers, SFD - scintillating fiber detector, IH – ionization hodoscope. DC - drift chambers , VH – vertical hodoscopes, HH – horizontal hodoscopes, Ch – nitrogen Cherenkov , PSh - preshower detectors , Mu - muon detectors
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Upgraded DIRAC setup
DIRAC setupDIRAC setup
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Extrapolation to the targetExtrapolation to the target
target
DC
Y X
target
SFD
X-plane
The area where hits are
expecting
SFD
magnet
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ππ++KK−− e experimental data 2008, 2009 xperimental data 2008, 2009
Experimental distribution of π+K− pairs with low background (points with error bar) are fitted with a sum of “atomic pairs” (red line), “Coulomb pairs” (blue line), “non-Coulomb pairs” (magenta line). A sum of “Coulomb” and “non-Coulomb” pairs is presented with black line. The cut on QT<4 MeV/c.
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KK++ππ−− e experimental dataxperimental data 2008, 2009 2008, 2009
Experimental distribution of K+π− pairs with low background (points with error bar) are fitted with a sum of “atomic pairs” (red line), “Coulomb pairs” (blue line), “non-Coulomb pairs” (magenta line). A sum of “Coulomb” and “non-Coulomb” pairs is presented with black line. The cut on QT<4 MeV/c.
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ππ++KK−− e experimental dataxperimental data 2009 2009
Comparison of the reconstructed π+K − events with low background and 2 SFD planes (red line) and events with medium background and 3 SFD planes (black line). The number of reconstructed events increased by 1.22.
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KK++ππ−− e experimental dataxperimental data 2009 2009
Comparison of the reconstructed K+π− events with low background and 2 SFD planes (magenta line) and events with medium background and 3 SFD planes (blue line).The number of reconstructed events increased by 1.34.
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All All ππKK e experimental dataxperimental data
π+K−
Year NA nA
2008 44 ± 13 23 ± 19
2009 66 ± 16 39 ± 23
2010 190% from 2008
K+π−
Year NA nA
2008
2009
66 ± 18 44 ± 26
150% from 2008
190% from 20082010
Sum of π+K− and K+π−*
NA nA
Ready
Expexted
176 ± 28 106 ± 39
170% from analyzed data
Numbers of generated πK atoms (NA) and numbers of “atomic pairs” (nA) found for data samples of 2008, 2009 and expected for 2010 for data with the low background.
* The expected number for events with the medium background will be higher by factor of 1.3
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All All ππKK e experimental dataxperimental data
Expected ratio of signal to error for data with the the low background.
There is 40% of data with a higher background which implication is under investigation
4.5A
A
N
n
Accounting of events with medium background increase number of reconstructed events by factor 1.3 and the ratio becomes
5.2A
A
N
n
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Schedule of data analysis of Schedule of data analysis of ππKK atoms in 2011 atoms in 2011
I. End of June 2011 1. Preparation of ntuples for 2008, 2009 and 2010 data.2. Preliminary results on atomic pairs extraction using 2008, 2009 data with low back-ground and two dimension spectra analysis. II End of October 2011 1. Search for πK atomic pairs using two dimension spectra and all statistic with low level background 2. Presentation of preliminary results on the analysis of statistic with low and medium level of back-ground.
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ππ++ππ−− e experimental dataxperimental data 2008, 20092008, 2009
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ππ++ππ−− datadata
Statistic for measurement of |a0-a2| scattering length difference and expected precision
Year nA δstat (%) δsyst
(%)
δsyst (%) MS δtot (%)
2001-2003 21000 3.1 3.0 2.5 4.3
2008
2009
2010
4800
7100
9000
2008-2010* exp.21000
(27000)
3.1
(2.7)
3.0
(2.1)
2.5
(1.25)
4.3
(3.4)
2001-2003 2008-2010
42000
(48000)
2.2
(2.0)
3.0
(2.1)
2.5
(1.25)
3.7
(2.9)
* There is 40% of data with a higher background which implication is under investigation
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Results: lifetime & scattering lengthResults: lifetime & scattering length
DIRAC data
1ss
value stat syst theo* tot
|a0 – a2|
value stat syst theo* tot
Reference
2001 PL B 619 (2005) 50
2001-03 CERN-PH-EP-2011-028 (preprint)
91.2 49.062.0
264.0
0.0200.033
15.3 28.026.0
2533.0
0.01110.0106
NA48 K-decaya0 – a2
value stat syst theo tot
Reference
2009 K3 EPJ C64 (2009) 589
2010 Ke4 & K3 EPJ C70 (2010) 6350015.00020.02639.0
* theoretical uncertainty included in systematic error
45.038.0
19.049.0
20.019.0
20.018.0
017.0020.0
022.0009.0
0072.00077.0
0078.00080.0
0088.00029.00048.02571.0
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Multiple-scattering measurement
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- 4 planes DC- scatterer- 2 planes DC
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Multiple-scattering measurement
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Observation of long-lived π+π− atoms
em vac strnl nl nl nlE E E E
0 0
0 0 22strn nE A a a
0 0
2
0 2
1W R a a
2 2 0.59 0.0120 20 21 20 21
s p str em em vac vacE E E E E E eV
A2π decay dominated by annihilation process:
A2π lifetime depends on the ππ scattering length difference |a0 – a2|
Energy shift contributions
Strong interaction contribution
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…opens future possibility to measure the energy splitting E(ns-np).
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191919
For pA = 4.5 GeV/c ( = 16.1)
1s = 2.9 × 10 15 s , 1s = 1.4 × 10 3 cm2s = 2.3 × 10 14 s , 2s = 1.1 × 10 2 cm2p = 1.17 × 10 11 s , 2p = 5.7 cm, 3p 19 cm,
4p 43 cm
The A2π decay in the p-state is forbidden by angular momentum conservation. So the lifetime of the A2π atom in the 2p state (τ2p=1.17 ·10-11 s) is determined by the 2p–1s radiative transition with a subsequent annihilation in 1s state (τ1s=3 ·10-15 s): π+ + π- π0 + π0
The lifetime of the np-states is about 103 larger than the ns-states, so it is possible to measure the energy difference of these levels by exerting an electric field (Stark effect) on the atom and tracking the field dependence of the decay probability.The influence of an magnetic field on the A2π atom lifetime opens the possibility to measure the splitting between 2s and 2p levels.
Observation method
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Production yields of A2π long-lived states
Probability of A2π breakup (Br) and production yields of the long-lived states 2p, 3p, 4p, 5p, 6p (m=0) as a function of the target thickness, for Beryllium (Z=4) target.
The A2π ground state lifetime is assumed to be 3.0·10-15s and the atom momentum 4.5 GeV/c.
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Production yields of A2π long-lived states
Target material characteristics for production of long-lived atomic
states
- target thickness, chosen to provide maximum production yield of long-
lived states
- A2π breakup probability
- Σ (l ≥ 1): total yield of long-lived states including states with n ≤ 7
- 2p0, 3p0, 4p0, production yield of p-states with magnetic quantum number
m = 0
- Σ (l =1, m = 0): sum of the p-states up to n = 7
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Part of the atoms, which were created in the Be target and then broken up in the Pt foil, as a function of the distance between Be target and Pt foil for all metastable states (n >1, l >0) and for some individual states with l=1. The foil thickness is 2μ.
Simulation of all π+π- pairs at experimental conditions
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Tokyo Metropolitan University & Kyoto University
Neodymium magnetic piece=70x60x5mm3: Gap=60mm; BL=0.01Tm Time of delivery to CERN: before 4 May 2011
yz
x
150mm
90mm
60mm
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Arrangement of Beryllium target, permanent magnet and Platinum foil.
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Simulation of long-lived A2π observation
Simulated distribution of π+ π- pairs over QY with criteria: QX <1 MeV/c, QL < 1MeV/c. Additional magnet is implemented. “Atomic pairs” from long-lived atoms (light area) above background produced in Beryllium target (hatched area)
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Simulation of long-lived A2π observation
Simulated distribution of π+π- pairs over QL, with criterion QT < 1 MeV/c. “Experimental” data (points with error bars) are fitted by a sum of “atomic pairs” from long-lived states, “Coulomb pairs” and “non-Coulomb pairs”. The background sum is shown by the solid line.
The number of atomic pairs are found to be
281 48longAn
atomic pairs from long-lived states
Coulomb pairs
non-Coulomb pairs
281 48longAn
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Q and F for BeQ and F for Be 222LYX QQQQ
2
2
2
2
2
2
LYX Q
L
Q
Y
Q
X QQQF
0.5 /XQ MeV c
0.56 /LQ MeV c
0.32 /YQ MeV c
Qx
QL
Qy Q<1MeV/c
F<2
Simulation of long-lived A2π observation
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Simulation of long-lived A2π observation
Simulated distribution of π+π- pairs over F, with criterion QT < 2 MeV/c. “Experimental” data (points with error bars) are fitted by a sum of “atomic pairs” from long-lived states, “Coulomb pairs”, “non-Coulomb pairs”. The background sum is shown by the solid line.
n =327 37 ; 8.8A
long AA
n
n
2 2 2
F= 0.50 0.32 0.56
X Y LQ Q Q
where 0.50, 0.32 and 0.56 Mev/c are RMS’s of the atomic pairs distribution over correspondingcomponents of the relative momentum Q. Now,
327 37longAn
Coulomb pairs
non-Coulomb pairs
atomic pairs from long-lived states
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Long-lived π+π− atoms
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The observation of ππ atom long-lived states opens the future possibility to measure the energy difference between ns and np states E(ns-np) and the value of ππ scattering lengths |2a0+a2|.
If a resonance method can be applied for the E(ns-np) measurement, then the precision of ππ scattering length measurement can be improved by one order of magnitude relative to the precision of other methods.
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Thank you for your attention
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≡ relative distance between + and mesons in A2 atom
r
≡ laboratory magnetic field
≡ electric field in the CM system of an A2 atom
F
BLab
Lab LabF B B
Atom beams are influenced by external magnetic field and the relativistic Lorentz factor γ
F
LabB
p
A
+
r
A2 ,v
c
z
L.Nemenov, V.Ovsiannikov, Phys.Lett. B514 (2001)
Measurements of the Lamb shift using external magnetic and electric fields
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2p 2p
2 2
2p
2s
1 1201
4
eff
where: 2
2
22 2p s
F
E E
BLab = 2 Tesla
2p
2p
20 , 0.025 1.3
40 , 0.05 2.25
eff
eff
2(0) p
t
A AN N e
(0) eff
t
A AN N e
The dependence of A2π life time eff for 2p-states of the electric field F strength
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3333
Resonant enhancement of the annihilation rate of AResonant enhancement of the annihilation rate of A22
L.Nemenov, V.Ovsiannikov, E.Tchaplyguine, Nucl. Phys. (2002)
Ap
Ap ,Lab LLaabbB
In CM System:2 2, cos , p s
Lab LLaabb
E Et
at resonance: res Lab resLab
In Lab. System:0 2
,Lab LabLab
lT
c T
l0
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Resonant enhancementResonant enhancement
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Charged secondaryCharged secondaryCharged secondaryCharged secondary
Proton beamProton beamProton beamProton beam
p
ResonatorsResonatorsResonatorsResonators
γres1 γres2 γres3 γres4
0
Pt foilPt foilPt foilPt foil
0
0 0
0
0
+
-A*
2 A* A*K
Resonant methodResonant method
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The production yield strongly increases for smaller Q
pnucleus
+
-
Strong interaction
For small Q there are Coulomb pairs :
pp, pK, K+K-, πµ C-pairs
pp, pK, K+K-, πµ atoms
Coulomb pairs and atomsCoulomb pairs and atoms
+ +
-
+
- -
+
-
+
-
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Yield of dimeson atoms per one proton-Ni interaction, detectable by DIRAC upgrade setup at L=5.7º
24 GeV 450 GeV
EpA2π AK+π− Aπ+K− A2π AK+π− Aπ+K−
WA 1.1·10-9 0.52·10-10 0.29·10-10 0.13·10-7 0.10·10-8 0.71·10-9
WAN 1. 1. 1. 12. 19. 24.
WA /Wπ3.4·10-8 16.·10-10 9.·10-10 1.3·10-7 1.·10-8 7.1·10-9
WAN
/WπN
1. 1. 1. 3.8 6.2 8.
A multiplier due to different spill duration ~4
Total gain 1. 1. 1. 15. 25. 32.
DIRAC prospects at SPS CERN
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Target Ni 98 m
A2π
p
24 GeV/c
p
24 GeV/c
π+
π−
π−π+
p
24 GeV/c π−
π+
π+
π0
π+
,,,…
η, η’,…
(NC)
(NA)Atomic pairs(nA)
p π−
π+
24 GeV/c
p
Coulomb correlatedpairs
Non-Coulomb pairs
Accidental pairs
Interaction point
Interaction point
Method of Method of AA2π2π observation and measurement observation and measurement
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3939
Upgraded DIRAC experimental setupUpgraded DIRAC experimental setup