SPIN 2012, Dubna, September 17-22, 2012
I.G. Alekseeva,*, V.A. Andreevb, I.G. Bordyuzhina, D.A. Fedina, Ye.A. Filimonovb, V.V. Golubevb, A.B. Gridnevb, E.A. Konovalovab, L.I. Korolevaa, N.G. Kozlenkob, V.S. Kozlovb, A.G. Krivshichb, B.V. Morozova, V.M. Nesterova, D.V. Novinskyb,
V.V. Ryltsova, M. Sadlerc, A.D. Sulimova, V.V. Sumachevb, D.N. Sviridaa, V.I. Tarakanovb, V.Yu. Trautmanb
a Institute for Theoretical and Experimental Physics, B. Cheremushkinskaya 25, Moscow, Russia. b Petersburg Nuclear Physics Institute, Gatchina, Leningrad district, Russia
c Abilene Christian University, Abilene, Texas, USA* [email protected]
High precision measurements of the pion-
proton elastic scattering and kaon-lambda
production in the EPECUR experiment
Pentaquark antidecuplet
2
?
Original prediction – N***(1710)From modified PWA – 1680 or 17301
1) R. Arndt et al., Phys.Rev. C69 (2004) 035208SPIN’2012
Igor Alekseev (ITEP, Moscow)
N(1685)
3
NNR’2009, Edinburg, June 8-10, 2009 http://2009physicsevents.org
η-photoproduction off neutron
GRAAL:
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Igor Alekseev (ITEP, Moscow)
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4Igor Alekseev (ITEP, Moscow)
M.J Amaryan et al. Phys.Rev. C85 (2012) 035209
MC
MCcor
The same CLAS statistics of 2004 (g11a run period) as in R. De Vita et al., [CLAS Collaboration], Phys. Rev. D74, 032001 (2006) A narrow structure at KS missing mass MX(KS) = 1.543 GeV with a Gaussian width = 0.006 GeV for the reaction γp→pKSKL
when M(KSKL) = mϕ and −tΘ<0.45 GeV2 with 5.4σ statistical significance.
S+MCcor
S. Naohito @ SPIN 2010
6Igor Alekseev (ITEP, Moscow)
Resonance parameters within safe reach by the experiment:
This provides a good coverage of both theoretical and experimental expectations.
Elastic scattering
K-production
Width (2-20) MeV (2-20) MeV Elastic width, Гel >0.1 MeV >0.02 MeV Elasticity, X >0.05 >0.01
pp 0SKpand
• “Formation” – type experiment.• Extremely high invariant mass resolution (~0.6 MeV), provided by high momentum resolution of the magneto-optic channel 0.1%.• High statistical precision: 0.5% for elastic scattering and 1% for K-production.• Magnetless spectrometer with drift chambers.• Liquid hydrogen target.• Very small amount of matter on the particle paths.
EPECUR:
Not narrow resonances only …• Precise cross section measurements:p p: d/d – 0.5% statistical precision and 1 MeV momentum stepp K0: REAC – 1% statistical precision and the same step
Very important data for PWA• “Usual” resonace P11 N(1710)***• -polarization in the reaction p K0 - an order of magnitude better precision then the best data available now - NIMROD (78)
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Setup for elastic scattering
7Igor Alekseev (ITEP, Moscow)
Proportional chambers with 1mm pitch and 40 um aluminum foil potential electrode in the first focus (1FCH1-4) and in front of the target (2FCH1-4). Momentum of each incident pion is tagged with the precision better 0.1%. Liquid hydrogen target with beryllium outer shell and mylar hydrogen container. The target diameter is 40 mm and the length along the beam ~250 mm. 8 modules of drift chambers with hexagonal structure to measure tracks of particles produced. Trigger scintillation counters S1, S2, A1. NMR system for measurement field in the magneto-optic channel dipoles with precision better 0.1%. Triggers:
Main = S1∙1FCH ∙S2 ∙2FCH ∙(!A1)With prescale:Mom1F = S1∙1FCH ∙S2 ∙2FCH BeamPos = S1∙1FCH∙2FCH ∙ A1
pp
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I.G Alekseev (ITEP) 8
Drift chambers
Proportional chambers
Hodoscope
Liquid hydrogen target heat exchanger
Engineering run (December 2008)7 millions of triggers were written with the liquid
hydrogen target
8Igor Alekseev (ITEP, Moscow)SPIN’2012
9
0
10
20
30
40
50
6013
3013
1513
0012
8512
7012
5512
4012
2512
1011
9511
8011
6511
5011
3511
2011
0510
9010
7510
6010
4510
3010
1510
00 985
970
955
940
925
910
895
880
865
850
835
820
April 09 pi-, 453 mln. trg.April 10 pi-, 1250 mln. trg.June 10 pi+, 688 mln. trg.February 11 pi+, 275 mln. trg.February 11 pi-, 292 mln. trg.
Statistics so far 2.97 billion triggers
Pbeam, MeV/c
Many thanks to ITEP accelerator!
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Igor Alekseev (ITEP, Moscow)
10
Elastic events selectionHypothesis – pion scattered to the left arm
θцм=84о
The hypothesis is true
The hypothesis is false
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Igor Alekseev (ITEP, Moscow)
Track reconstruction efficiencyWe require 3 hits on the track out of 4 possible in each projection
100%
99%
11SPIN’2012
Igor Alekseev (ITEP, Moscow)
Preliminary
Corrected to the acceptance, efficiency and decays
12Igor Alekseev (ITEP, Moscow)SPIN’2012
Statistical errors only
Preliminary
Corrected to the acceptance, efficiency and decays
13Igor Alekseev (ITEP, Moscow)SPIN’2012
Statistical errors only
Preliminary
Corrected to the acceptance, efficiency and decays
14Igor Alekseev (ITEP, Moscow)SPIN’2012
Statistical errors only
Preliminary
Corrected to the acceptance, efficiency and decays
15Igor Alekseev (ITEP, Moscow)SPIN’2012
Statistical errors only
Resonances and channel thresholds in the differential cross sectionResonance influence on the cross section
Other channel threshold influence on the cross section
π-p→K0Σ0 – Minv=1690.2 MeV Pbeam = 1033 MeV/cπ-p→K+Σ- – Minv=1691.1 MeV Pbeam = 1035 MeV/cπ-p→ωn – Minv=1722.3 MeV Pbeam = 1092 MeV/cπ+p→K+Σ+ – Minv=1683.1 MeV Pbeam = 1021 MeV/c
S-wave only
Any wave
N(1685) – Minv=1685 МэВ → Pbeam = 1024 MeV/cEnergy
16Igor Alekseev (ITEP, Moscow)
A.I. Baz, ZETF 33 (1957) 923
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17Igor Alekseev (ITEP, Moscow)
Statistical errors only
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18Igor Alekseev (ITEP, Moscow)
Statistical errors only
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19Igor Alekseev (ITEP, Moscow)
Statistical errors only
Some irregularity is seen in the region of the most interest (1020-1040 MeV) in several θCM bins
Only one half of the statistics in this region was already analyzed
We plan to get more statistics in the narrow energy range
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20Igor Alekseev (ITEP, Moscow)
Statistical errors only
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21Igor Alekseev (ITEP, Moscow)
Statistical errors only
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22Igor Alekseev (ITEP, Moscow)
Statistical errors only
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23Igor Alekseev (ITEP, Moscow)
Statistical errors only
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24Igor Alekseev (ITEP, Moscow)
Statistical errors only
–pK0S +––p
We keep the target and the beam equipment
The drift chambers we already have
New wide-aperture drift chambers
New hodoscopes
Most of the events have either all 4 particles going forward or 3 particles including the proton going forward and one pion going in some other direction
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25Igor Alekseev (ITEP, Moscow)
26Igor Alekseev (ITEP, Moscow)
The new wide-apperture drift chamber tests at PNPI
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Status and plans
27Igor Alekseev (ITEP, Moscow)
Elastic scattering Detector EPECUR for precision measurement of elastic πp-scattering was built and comissioned:
track efficiency in the drift chambers > 99% beam momentum tagging is better 0.1%
We took 4 physics runs and 2.97 billions of triggers are collected. The analysis is under way. The preliminary results show some irregularity at Pbeam=1020-1040 MeV/c. We plan to take more data in the narrow region of interest as well as extend the measurement till 2 GeV/c The beam composition will be determined using Cherenkov counter and Monte-Carlo simulations
K0Λ-production The first out of 4 required wide-aperture drift chambers is manufactured and is being tested at PNPI We have full front-end and DAQ electronic Engineering of mechanical structure as well as of TOF forward hodoscope is under way.
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