Measuring the J / -Nucleon dissociation cross section with PANDA . - PowerPoint PPT Presentation

Measuring the J / Ψ -Nucleon dissociation cross section with PANDA . Bühler 1 P on behalf of PANDA collaboration 1 Stefan Meyer Institute, Vienna logo P . Bühler (SMI) Hadron 2011, 14.06.2011 1 / 15

Motivation J / Ψ -nucleon dissociation cross: Probability of J / Ψ to break up when moving through nuclear matter. Charme in medium - fundamental parameter Issue in heavy ion research Anomalous suppression observed in central HI collisions Probable indication of existence of Quark-Gluon-Plasma logo P . Bühler (SMI) Hadron 2011, 14.06.2011 2 / 15

Experimental approaches Nucleus (Z,A) J / Ψ in J / Ψ out σ diss logo P . Bühler (SMI) Hadron 2011, 14.06.2011 3 / 15

Experimental approaches Nucleus (Z,A) J / Ψ out σ diss logo P . Bühler (SMI) Hadron 2011, 14.06.2011 3 / 15

Experimental approaches NA50 collaboration , Eur. Phys.J.C Nucleus (Z,A) 48 (2006) 329 Production of J / Ψ p ( 400 GeV ) J / Ψ out Interpretation of results ambiguous because mixed with other effects σ diss Large momenta, feed down from other states, interaction with co-movers ✞ ☎ σ diss ≈ 4 . 5 mb ( 1 − 7 mb ) ✝ ✆ logo P . Bühler (SMI) Hadron 2011, 14.06.2011 3 / 15

Experimental approaches K.K. Seth , A Unique way to Nucleus (Z,A) Measure Charmonium-Nucleon Cross Sections, Hirschegg, 2001 p ( E res ) Formation of J / Ψ Avoid effects from large momenta, feed down, co-movers σ diss ✄ � At FAIR with PANDA ✂ ✁ J / Ψ out logo P . Bühler (SMI) Hadron 2011, 14.06.2011 3 / 15

Measurement of σ diss # esc = # form · ( 1 − σ diss · � ρ L � ) 1 » 1 − # esc – σ diss = � ρ L � · # form modeling measurement Nucleus (Z,A) # obs = # esc · br · f eff p ( E res ) P Fermi # form = F ( ., ., ., . ) · # in σ diss J / Ψ out # in # form # esc , # obs logo P . Bühler (SMI) Hadron 2011, 14.06.2011 4 / 15

HESR and PANDA at FAIR HESR PANDA P p : 1 . 5 - 15 GeV/c 4 π coverage HI and HR mode Charged and neutral particle ∆ P p identification P p ≥ 2 · 10 − 5 Cluster jet and solid targets L ≤ 10 32 1 / cm 2 / s logo P . Bühler (SMI) Hadron 2011, 14.06.2011 5 / 15

Questions to answer How can # in be determined How can # esc be measured How accurately can # form and � ρ L � be computed logo P . Bühler (SMI) Hadron 2011, 14.06.2011 6 / 15

Measurement of # esc p + A → J / Ψ → l + l − cross sections in the order of 100 pb total cross section in the order of 1 b → need background suppression of > 10 10 exploit topology of signal events to enhance S / N Combination of cuts allows to efficiently suppress background ( < 10 − 10 ) PANDA Physics Performance Report , arXiv:0903.3905 How long will it take? ◮ σ obs ≈ 100 pb , L ≈ 10 30 ✞ ☎ → a few J / Ψ per day! ✝ ✆ logo P . Bühler (SMI) Hadron 2011, 14.06.2011 7 / 15

Computation of # form ideal case: ∆ P p = 0, P p = 0 (Γ / 2 ) 2 � � 2 J + 1 4 π σ BW ( E cm ) = B in B out ( E cm − m J / Ψ ) 2 + (Γ / 2 ) 2 ( 2 S 1 + 1 )( 2 S 2 + 1 ) k 2 m J / Ψ = 3096 . 916 ± 0 . 011 MeV, Γ = 0 . 0932 ± 0 . 0021 MeV ( Particle Data Group , Physics Letters B667, 1 (2008) B in B out = ( 1 . 14 ± 0 . 2 ) × 10 − 4 ( E760 collaboration , Phys. Rev. D 47 (1993) 772) → BW ( m J / Ψ ) = 280 nb logo P . Bühler (SMI) Hadron 2011, 14.06.2011 8 / 15

Computation of # form relative BW(P ) 1 1. complication: ∆ P p � = 0 p HI mode HR mode -1 10 10 -2 10 -3 -0.1 -0.05 0 0.05 0.1 (P -P ) res p [%] P res Atomic mass A 2. complication: Nuclear binding 200 energy, in-medium mass shift? 150 100 50 0 4.06 4.07 4.08 4.09 4.1 4.11 P [GeV/c] p res V ) 1 / 3 ≈ 250 MeV / c P F = � ( 3 π 2 Z 3. complication: P p � = 0, Fermi motion logo P . Bühler (SMI) Hadron 2011, 14.06.2011 9 / 15

Computation of # form p Nucleus logo P . Bühler (SMI) Hadron 2011, 14.06.2011 10 / 15

Computation of # form H. de Vries et al. Atomic Data and Nuclear Tables 36 (1987) 495 0.2 ] -3 A = 56 (r) [fm ρ 0.15 normal nuclear density 0.1 3pG 2pF I 2pF II 0.05 0 0 1 2 3 4 5 6 r [fm] p Nucleus logo P . Bühler (SMI) Hadron 2011, 14.06.2011 10 / 15

Computation of # form H. de Vries et al. Atomic Data and Nuclear Tables 36 (1987) 495 0.2 ] -3 A = 56 (r) [fm ρ 0.15 normal nuclear density 0.1 3pG 2pF I 2pF II 0.05 0 0 1 2 3 4 5 6 r [fm] p Nucleus -6 x f -4 -2 0 2 4 6 logo dx f ∝ dN / dz P . Bühler (SMI) Hadron 2011, 14.06.2011 10 / 15

Computation of # form H. de Vries et al. Atomic Data and Nuclear Tables 36 (1987) 495 P F ∝ ρ 1 / 3 0.2 ] -3 A = 56 (r) [fm ρ 0.15 0.01 normalized distribution A = 40 normal nuclear density dN/dz 0.008 0.1 3pG 2pF I 2pF II 0.006 0.05 0.004 0 0 1 2 3 4 5 6 0.002 r [fm] p Nucleus -6 0 0 50 100 150 200 250 300 pF [MeV/c] x f -4 -2 0 2 4 6 logo dx f ∝ dN / dz P . Bühler (SMI) Hadron 2011, 14.06.2011 10 / 15

Computation of # form H. de Vries et al. Atomic Data and Nuclear Tables 36 (1987) 495 P F ∝ ρ 1 / 3 0.2 ] -3 A = 56 (r) [fm ρ 0.15 0.01 normalized distribution A = 40 normal nuclear density dN/dz 0.008 0.1 3pG 2pF I 2pF II 0.006 0.05 0.004 0 0 1 2 3 4 5 6 0.002 r [fm] p Nucleus -6 0 0 50 100 150 200 250 300 pF [MeV/c] x f -4 -2 0 � r A f diss ∝ x f ρ ( l ) dl 2 4 P J / Ψ = P p + P F 6 logo dx f ∝ dN / dz P . Bühler (SMI) Hadron 2011, 14.06.2011 10 / 15

Computation of # form × -3 10 1.2 4 normalized distribution res ∆ ∆ P = 0, P = 0 BW HI mode A = 40 p p ∆ HR mode, P = 0 A = 40 /# HR mode p esc ∆ 1 HI mode, P = 0 3.5 BW(m ) p # Ψ ∆ J/ HR mode, P = P p F ∆ HI mode, P = P p F 0.8 3 0.6 2.5 0.4 2 0.2 1.5 0 1 3.095 3.0955 3.096 3.0965 3.097 3.0975 4.11 4.112 4.114 4.116 4.118 S [GeV] p momentum [GeV/c] First step in simulations more sophisticated models required logo P . Bühler (SMI) Hadron 2011, 14.06.2011 11 / 15

Computation of � ρ L � 1 � 1 − # esc � σ diss = � ρ L � · # form modeling measurement p cross section 1 according to p p cross section formed escaped p fraction of -1 10 -2 10 -3 10 50 100 150 200 logo A P . Bühler (SMI) Hadron 2011, 14.06.2011 12 / 15

Computation of � ρ L � �� ∞ � � ρ L � = x f ρ ( l ) dl depends on . ρ ( r ) . distribution of formation points, d( x f ) . Fermi-momentum distribution compute by MC with high statistics logo P . Bühler (SMI) Hadron 2011, 14.06.2011 13 / 15

Computation of � ρ L � � � 1 1 − # esc σ diss = � ρ L � · # form 1.2 <rho.L> [1/fm^2] dN/dz 1 0.8 0.6 0.4 0.2 <rho.L> = -2.23e-01 + 1.76e-01 * A^(1/3) 0 2.5 3 3.5 4 4.5 5 5.5 6 1/3 A logo P . Bühler (SMI) Hadron 2011, 14.06.2011 14 / 15

Computation of � ρ L � � � 1 − # esc σ diss · � ρ L � = # form 1.2 0.5 <rho.L> [1/fm^2] #form #esc dN/dz 1 - 1 0.4 0.8 0.3 0.6 0.2 0.4 0.1 0.2 <rho.L> = -2.23e-01 + 1.76e-01 * A^(1/3) 0 0 2.5 3 3.5 4 4.5 5 5.5 6 2 2.5 3 3.5 4 4.5 5 5.5 6 1/3 1/3 A A logo P . Bühler (SMI) Hadron 2011, 14.06.2011 14 / 15

Computation of � ρ L � � � 1 − # esc σ diss · � ρ L � = # form 1.2 0.5 <rho.L> [1/fm^2] #form #esc dN/dz 1 - 1 0.4 0.8 0.3 0.6 0.2 0.4 0.1 0.2 #esc × 1 - [ ](A) = 4.24e-01 <rho.L>(A) <rho.L> = -2.23e-01 + 1.76e-01 * A^(1/3) #form 0 0 2.5 3 3.5 4 4.5 5 5.5 6 2 2.5 3 3.5 4 4.5 5 5.5 6 1/3 1/3 A A → σ diss = 4 . 2 mb logo P . Bühler (SMI) Hadron 2011, 14.06.2011 14 / 15

Summary With PANDA pA → J / Ψ → l + + l − can be efficiently measured ≈ a few J / Ψ per day To determine σ diss one needs to ◮ Scan resonance and determine shape and number of J / Ψ ( # esc ) ◮ Compute number of formed J / Ψ ( # form ) h i ◮ Fit 1 − # esc ( A ) with � ρ L � ( A ) # form � � Parameters to select P p i , HR/HI, { ( A , Z ) j } Parameters to measure # in , # esc Parameters to model # form logo P . Bühler (SMI) Hadron 2011, 14.06.2011 15 / 15