M.E. Sadler, D. Soboyede, E. Walker, S. Watson. Abilene Christian University, Abilene, Texas 79699, USA.
Dima Svirida (ITEP)
Inspired by + indications and high interest to the pentaquark matter Search for the neutral cryptoexotic member of the baryon antidecuplet ½+ based solely on the predictions for it’s small width No current experimental data can reveal such a resonance with a width of several MeV Latest detailed investigations of the “modified”
“EPECUR”* Proposal (hep-ex/0509032)
Dima Svirida (ITEP)
n(1650) ???(
p or K0)
____________________
* “EPECUR” is the transliteration of the Russian abbreviation for “Experiment for Pentaquark search in the Elastic Scattering (and –pK0 reaction)”
10N
FA02 PWA allow narrow resonant structures near 1680 and 1730 MeV Theoretical predictions for the mass 1650-1690 MeV, width 2-20 MeV Experiment idea: very precise cross-section measurements with very fine energy steps (0.6 MeV in terms of invariant mass) Extremely favorable experimental conditions: large cross-sections, high sensitivity, “ideal” pion beam-line at ITEP
Weak sensitivity in total elastic cross-section Yet high effect in differential cross-section in the area of minimum at 40o-90o c.m. Sensitivity estimates from PWA data: 15% effect in d/d for el/=5% -- coupling to the elastic channel
Stage I: p Elastic
Dima Svirida (ITEP)
Measurements in the pbeam
range 900-1200 MeV/c (s=1610-1770 MeV) Beam energy resolution <0.1% in the range 2% at a time 25 cm LiH target 0.5% statistical error in (1 MeV/c 20oc.m.) bins in the cross-section minimum after 20 days of running
d/d
c.m.
Cross-section minimum 0.2mb/sr
10N
M=1671 MeV=6 MeVel/=5%
Stage I: p Elastic Setup
Dima Svirida (ITEP)
Beam momentum resolution measured 0.07% in early 70’s Minimize matter in the beam-line Beam trigger from proportional chambers Reasonable Landau widening inside the LiH target Dipole field measurements with NMR Mean beam momentum monitored with TOF
Proportional chambers PC1–PC3 located in first focus of the ITEP beam-line 322 for the incident pion momentum measurement Proportional chambers PC4–PC6 for the tracking of the incident pions Liquid hydrogen target with 1 mm beryllium cover, 4 cm, 25 cm long Sets of drift chambers DC1–DC4 for the reaction products tracking Beam scintillation counters S1, S2, trigger hodoscopes H2,H3 with TOF features, anti- and beam TOF counter A1.
Events TG
T
middle
TG
T
entranceTG
T
exit
Beam Resolution Tests
Dima Svirida (ITEP)
Using p9Be scattering to 10,5o at 1.4957 GeV/c on the internal accelerator target and 1 mm proportional chambers 9Be excitation levels structure well seen Dispersion in the first focus 57 mm/% Beam momentum resolution: 0.07% best measured, 0.10% at average conditions
= (4-6) mm or (0.07-0.10)%
0 2.43 MeV
2.43 MeV 6.76 MeV
Stage II: pK0
Dima Svirida (ITEP)
Very attractive for search and baryon spectroscopy in general:
Predicted branching K/2*–p/ Reaction total cross-section is significantly smaller than that of elastic scattering, making the resonant effect more pronounced Energy range under study close to the reaction threshold – resonant effect enhanced 15% resonant effect in the total reaction cross-section assuming K/=10%, –p/=5%
In addition: Pure isotopic state ½ High analyzing power of p weak decay =0.642 – important byproduct polarization measurement
Convenient for detection: Relatively large cross-section ~0.9 mb Significant fraction 22% of the charged mode pK0 + + p
10N
10N
Kp
KKK
resK
kkl
4
)12(1
pK0 Detection Features (MC)
Dima Svirida (ITEP)
Detection of 4 particles in the final state requires rather “hermetic” acceptance With no magnetic field the tracking detector accuracy must be 150-200 m in order to reliably reconstruct K0 and decay vertices Protons are concentrated in a narrow forward cone, while pions from both decays have wide angular distributions including backward areas Most of the 4-charged events have either all four particles going forward (~20%) or a proton and 2 pions going forward, the third pion at large angle (~80%) The identification of a single proton is highly important for the background suppression as well as for polarization measurement; TOF technique may be used for this purpose Reliable separation of K0 and K00 final states can be achieved above 0 production threshold The setup can cover nearly 2 of production angles in the whole energy range under study
protons from
pions from
pions from K0
lab
TOFpTOF@1m
ns
0 8ns
Stage II: pK0 setup
Dima Svirida (ITEP)
The beam part the same as in “Stage I” 4 of 5 middle size drift chambers inherited from “Stage I” (DC1-5) Additionally need 4 smaller DCs (DC6-9) and one large DC10 XY-segmented hodoscope H1,2 at 2 m from the target for trigger logic and proton TOF identification; need 10x10 cm2 cell size in the central area of 1x1 m2
Even with only backward angles lost for tracking, the acceptance for the charged mode is 20-30%
Event reconstruction -- no magnetic field, proton identification: 4 unknown momentum absolute values in the final state 4 projections of conservation laws Overconstraints from 2 vertex information allow background suppression and K00 separation Naturally decay angles can be determined for asymmetry measurement
pK0 MC Simulations
Dima Svirida (ITEP)
MC simulation is under development at Abilene Christian University Acceptance optimization Multiple scattering effects and chamber accuracy TOF and/or dE/dx optimization for particle ID Event reconstruction for off-line data processing
EventsTOTAL
Events with at least one side chamber crossed
Forward chamber
Side (up/dn) chambers
Polarization – Planned accuracy
Dima Svirida (ITEP)
1% statistical accuracy in tot
K in 1 MeV energy bins in 23 days of running More than twice better accuracy than in NIMROD polarization data, but in 285 energy bins 10 times better equivalent statistical error Possible resonant singularities in the energy behavior of the polarization
NIMROD Data
EPECUR Planned
Milestones and Plans
Dima Svirida (ITEP)
Milestones passed June 2004 Proposal submitted at ITEP and PNPI September 2004 Proposal approved by ITEP scientific council November 2004 MOU with PNPI was signed, PNPI taking the responsibility for proportional and drift
chambers production; ITEP is responsible for the beam, target and the chamber electronics December 2004 322 beamline at ITEP was resurrected and beam adjustments and tests started, technical
project of LiH target modification finished March 2005 Adjustment of beam focusing and first tests of the momentum resolution;
prototype proportional chamber and electronics production started. Started MC simulations for the elastic setup.
April 2005 LiH target moving to the experiment area started The project is supported by the Russian Fund for Basic Research, grant 05-02-17005
June 2005 Successful tests of prototypes of proportional and drift chambers and their electronics October 2005 DAQ and trigger distribution electronics production and DAQ code development started June 2006 Proportional chambers mounted in the first focus of the beamline, accurate tests of the
beam momentum resolution completed August 2006 PC electronics mass production ended, DC electronics mass production started September 2006 MOU with ACU signed, MC simulations for the second stage started
Milestones to pass November 2006 Liquid neon test run of the target March 2007 Liquid hydrogen run of the target. Tests of the 2 full-scale prototypes of drift chambers November 2007 Tests of 4 drift chambers for the elastic setup 2008 Production of additional drift chambers for KΛ March 2008 The first data run for the elastic scattering November 2008 The second data run for the elastic scattering 2009 Data runs for KΛ
Conclusions
Dima Svirida (ITEP)
A completely new experimental setup is under construction at the ITEP synchrotron beam-line 322 in collaboration with PNPI EPECUR experiment has sufficient chances to reveal the cryptoexotic member of the baryon antidecuplet ½+ if it exists In all cases, new excellent data on p elastic scattering and pK0 reaction will be obtained, overriding current experimental accuracy by an order of magnitude and more, and significantly contributing to the PWA database polarization measurement in pK0 -- valuable byproduct of the experiment Yet the manpower and financial resources of the collaboration are limited, that’s why
COLLABORATORS ARE EXTREMELY WELCOME !!!Thanks
The authors are grateful to the great number of people who support the proposal and took part in its discussion; special thanks for this to I.I.Strakovsky (GWU) and Ya.I.Azimov (PNPI). The work is partially supported by the RFBR grant 05-02-17005
