Mesons in the Medium: Experiments with CLAS at Jefferson Lab M. H. - - PowerPoint PPT Presentation
Mesons in the Medium: Experiments with CLAS at Jefferson Lab M. H. Wood (Canisius College, Buffalo, NY , USA), M. Paolone, R. Nasseripour, D. P . Weygand, and C. Djalali for the CLAS Collaboration Sunday, June 13, 2010 Medium Modifications
, USA),
. Weygand, and C. Djalali for the CLAS Collaboration
Sunday, June 13, 2010
Chiral Symmetry Restoration
breaking of chiral symmetry.
nuclear density (ρ0=0.16 fm-3)
Bernard and Meissner, NPA 489, 647 (1988) Brown and Rho, PRL 66, 2720 (1991) Hatsuda and Lee, PRC 46, R34 (1992)
in the nucleus, such as 20% drop in ρ-meson mass in Pb.
In-medium Hadronic Interactions
In the nuclear medium, the meson-nucleon cross section is modified
Leupold et al., arXiv:nucl-th/0907 .2388 (2009)
This modification is manifested as collisional broadening or a change to the collisional width.
Γ = Γ0 + Γcoll = Γ0 + γvρσ∗
V N
Consequence: increased absorption and reduction in detected yield.
Sunday, June 13, 2010
With the g7a experiment at Jefferson Lab (JLab), we have access to the in-medium properties of the light vector mesons. Reaction: γA ➞VX➞ e+e-X (no FSI) (Eg < 4 GeV)
Meson Mass (MeV) Width (MeV) ρ 768 149 ω 782 8 φ 1020 4
Results of the ρ meson search:
. Weygand, MESON200, http:/ /www.if.uj.edu.pl/konferencje/meson2006/talks/weygand.pdf
/www.if.uj.edu.pl/konferencje/meson2008/talks/djalali.pdf
Sunday, June 13, 2010
Superconducting e- Accelerator Max I=200mA Max E=6 GeV, dE/E=10-4 Run 3 experiments simultaneously (Halls A,B,C) 1500 physicists from ~30 countries Operational since 1997
C B A south linac north linac injector
Sunday, June 13, 2010
Gas Cherenkov Counter for e/π separation. CC e/π rejection factor: 10-1 Electromagnetic Calorimeter for detecting electrons. EC e/π rejection factor: 10-2 EC/CC rejection factor: 10-3 Rejection factor for e+e- : 10-6 Drift Chambers (Ar-CO2) 6500 channels/sector to measure the path of a charged particle. Torus Magnet 6 superconducting coils for deflecting charged particles Time-of-Flight Hodoscope 48 scintillators/sector for measuring a particle’s travel time e- : in-bending tracks e+ : out-bending tracks
Sunday, June 13, 2010
e+ e- p
LD2 C C C C Fe Ti Pb
Sample Event Segmented Target
Foils of carbon, iron, titanium, lead. Cell of LD2 as a control.
Sunday, June 13, 2010
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Mass Spectra with ρ, ω, and φ mesons simulation
Sunday, June 13, 2010
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Mass Spectra with ρ, ω, and φ mesons simulation
Mass Spectra after subtraction
contribution
TA = σV A AσV N
Sunday, June 13, 2010
JLab SPring8 Giessen calculations Giessen calculations w/ Spring8 absorption strengths
Normalized to carbon! Comparison to other work Comparison to Glauber calculations
Elementary: σφN < 10mb In-medium: σ*φN = 35mb (SPring8) σ*φN = 15-70mb (JLab)
SPring8: γA ➞ φX ➞ K+K-X Eγ=1.5- 2.4 GeV
Sunday, June 13, 2010
Giessen Calculations
P . Muhlich and U. Mosel, NPA 773 , 156 (2006)
Valencia Calculations
Kaskulov et al., EPJA 31, 245 (2007)
JLab CBELSA-TAPS
192302 (2008)
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Data from the 2H Target Interference contribution after ρ-meson subtraction
Sunday, June 13, 2010
Data collected in Hall B in 2008. Bremsstrahlung photon beam on a LH2 target (Eγ < 5.5 GeV). The primary focus of the experiment is a search for exotic mesons. An additional trigger allowed for lepton pairs.
Non Interference Fit χ2/ndf = 132/34 Mρ = 0.721(4) GeV Γρ = 0.140(1) GeV Mω = 0.778(1) GeV Γω = 0.0258(1) GeV Interference Fit χ2/ndf = 46/50 Mρ = 0.769(14) GeV Γρ = 0.169(22) GeV Mω = 0.784(1) GeV Γω = 0.026(2) GeV Phase = 5.82(6) rad
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Work conducted by Michael Paolone of Univ.
Fit: ρ BW + ω BW + interference term Need to do a full study of Bethe-Heitler background Need to do a full Monte Carlo simulation with interference
Sunday, June 13, 2010
Density dependence predictions
Brown et al, NPA567 , 937 (1994) Weise, NPA610, 35c (1996) Li et al, NPA625 , 372 (1997)
FOPI Collaboration at GSI
Benabderrahmane et al., PRL 102, 182501 (2009)
GeV π- beams
potential in Pb
Ks→π+π- is a good candidate for JLab analysis
entire nucleus
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Normalized to deuterium Normalized to carbon
Sunday, June 13, 2010
Exciting program of in-medium meson modifications with γ beams with CLAS at JLab. ρ meson: consistent with no mass shift in cold nuclear medium at JLab kinematics Transmission/absorption studies φ meson: consistent with Spring8 result. The in-medium cross section is 2-3 times greater than the elementary cross section. ω meson: large absorption (collisional width > 200 MeV). The discrepancy with CB-ELSA/TAPS and theoretical calculations may be due to ρ-ω interference. Ks➞π+π-: preliminary analysis underway. Working on momentum dependence and decay vertex reconstruction. Indication of less absorption than the ω and φ mesons. A second CLAS measurement is planned to
✓ increase the statistics ✓ Momentum dependence of in-medium modifications for the vector mesons ✓ Improved target: replace Pb with Nb and increase the target spacing for
absorption studies.
Sunday, June 13, 2010
What started out as a search for chiral symmetry restoration has turned into a rich field of study. Chiral symmetry restoration can only be proven once the in-medium hadronic interactions are understood. The transmission or absorption studies provide the needed information.
Sunday, June 13, 2010