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 Chiral Symmetry Restoration - 98% of hadron’s mass is attributed to spontaneous breaking of chiral symmetry. - Predictions of chiral symmetry restoration at normal nuclear density ( ρ 0 =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) - Consequences are changes to M and Γ of the hadron 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 = Γ 0 + Γ coll = Γ 0 + γ v ρσ ∗ V N Consequence: increased absorption and reduction in detected yield. Sunday, June 13, 2010

CLAS Experiment With the g7a experiment at Jefferson Lab (JLab), we have access to the in-medium properties of the light vector mesons. Reaction: γ A ➞ 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: R. Nasseripour et al, PRL 99, 262302 (2007), M. H. Wood et al., PRC 78, 015201 (2008) D. P . Weygand, MESON200, http:/ /www.if.uj.edu.pl/konferencje/meson2006/talks/weygand.pdf C. Djalali, MESON2008, http:/ /www.if.uj.edu.pl/konferencje/meson2008/talks/djalali.pdf - consistent with no mass shift ( Δ m < 20 MeV) - width broadening consistent with nuclear many-body effects (~40%) - study of in-medium meson-nucleon interactions becomes important. Sunday, June 13, 2010

Jefferson Lab 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 south linac north linac countries Operational since 1997 injector C A B Sunday, June 13, 2010

CLAS Torus Magnet Electromagnetic 6 superconducting coils Calorimeter for for deflecting charged detecting electrons. particles EC e/ π rejection factor: e- : in-bending tracks 10- 2 e+ : out-bending tracks Gas Cherenkov Counter for e/ π separation. Drift Chambers (Ar-CO 2 ) 6500 channels/sector CC e/ π rejection factor: to measure the path of a 10- 1 charged particle. EC/CC rejection factor: Time-of-Flight 10- 3 Hodoscope 48 scintillators/sector Rejection factor for for measuring a e+e- : 10- 6 particle’s travel time Sunday, June 13, 2010

Event Selection Sample Event Segmented Target Foils of carbon, iron, titanium, lead. Cell of LD 2 as a control. Pb p Fe e + Ti C C C C e - LD2 Sunday, June 13, 2010

e + e - Mass Spectra * + Mass Spectra ,- ! ./ *(' +' with ρ , ω , and φ *'' !"#$%& *' !"#$%& mesons )(' )' )'' simulation (' (' ' ' )' ! );' @< AB ):' @' )*' (< !"#$%& !"#$%& )'' (' =' ?< ;' ?' :' < *' ' ' ! < ';) ';< ';* ';= ';+ ';> ? ?;? ?;( '9: '9( '9; '9< '9= '9> ) )9) )9* -0- ! 12$345/4$%164&&178-9: ,-, ! ./$01231$%.41&&.56,78 Sunday, June 13, 2010

e + e - Mass Spectra * + Mass Spectra ,- ! ./ *(' +' with ρ , ω , and φ *'' !"#$%& *' !"#$%& mesons )(' )' )'' simulation (' (' ' ' )' ! );' @< AB ):' @' Mass Spectra )*' (< !"#$%& !"#$%& )'' after subtraction (' =' of the ρ -meson ?< ;' ?' contribution :' < *' ' ' ! < σ V A ';) ';< ';* ';= ';+ ';> ? ?;? ?;( '9: '9( '9; '9< '9= '9> ) )9) )9* T A = -0- ! 12$345/4$%164&&178-9: ,-, ! ./$01231$%.41&&.56,78 A σ V N Sunday, June 13, 2010

φ Meson Absorption Comparison to other work Comparison to Glauber calculations Normalized to carbon ! Giessen calculations Giessen calculations w/ Spring8 absorption strengths JLab SPring8 Elementary: σ φ N < 10mb SPring8: γ A ➞ φ X ➞ K + K - X E γ =1.5- 2.4 GeV In-medium: σ * φ N = 35mb (SPring8) T. Ishikawa et al., Phys. Lett. B 608, 215 (2006) σ * φ N = 15-70mb (JLab) Sunday, June 13, 2010

ω -Meson Absorption JLab CBELSA-TAPS M. Kotulla et al., PRL 100, 192302 (2008) Giessen Calculations P . Muhlich and U. Mosel, NPA 773 , 156 (2006) Valencia Calculations Kaskulov et al., EPJA 31, 245 (2007) Sunday, June 13, 2010

ρ - ω Interference Interference contribution Data from the 2 H Target after ρ -meson subtraction Sunday, June 13, 2010

g12: Measurement of the Elementary Process Data collected in Hall B in 2008. Bremsstrahlung photon beam on a LH2 target (E γ < 5.5 GeV). The primary focus of the experiment is a search for exotic mesons. An additional trigger allowed for lepton pairs. y r y a r n a i n m Non Interference Fit Interference Fit i m i l χ 2 /ndf = 132/34 e χ 2 /ndf = 46/50 i l r e P r M ρ = 0.721(4) GeV M ρ = 0.769(14) GeV P Γ ρ = 0.140(1) GeV Γ ρ = 0.169(22) GeV M ω = 0.778(1) GeV M ω = 0.784(1) GeV Γ ω = 0.0258(1) GeV Γ ω = 0.026(2) GeV Phase = 5.82(6) rad Sunday, June 13, 2010

Interference Analysis y Work conducted by r a Michael Paolone of Univ. n i m of South Carolina i l e r Fit: ρ BW + ω BW + P 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

K s Meson Analysis Density dependence predictions of the KN potential - K- effective mass decreases - K+ effective mass increases Brown et al, NPA567 , 937 (1994) Weise, NPA610, 35c (1996) Li et al, NPA625 , 372 (1997) Preliminary FOPI Collaboration at GSI Benabderrahmane et al., PRL 102, 182501 (2009) - K 0 production in C and Pb with 1.15 GeV π - beams - Data suggests a 20 MeV repulsive potential in Pb K s → π + π - is a good candidate for JLab analysis - π + π - events are plentiful - Photon beam illuminates the entire nucleus - Target spacings are 2.5 cm - For K 0 , c τ = 2.68 cm Sunday, June 13, 2010

K s Meson Absorption Normalized to deuterium Normalized to carbon Preliminary Preliminary - Analysis is a work in progress - Simulations are needed for detector acceptance and vertex reconstruction - Possible target contamination (c τ = 2.68 cm and target spacing = 2.5 cm) - Analysis of meson momentum dependence is underway Sunday, June 13, 2010

Summary 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. K s ➞ 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

Conclusions 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