in proton-nucleus collisions Andrey Polyanskiy (FZ Jlich/ITEP - PowerPoint PPT Presentation

Mitglied der Helmholtz-Gemeinschaft Measurement of the in-medium Φ-meson width in proton-nucleus collisions Andrey Polyanskiy (FZ Jülich/ITEP Moscow) for the ANKE collaboration Hadron 2011, Munich, June 14 th 2011

Scope of the talk  Physics motivation  Experiment at ANKE  Data analysis  Results and discussion 2

Φ in free space  Meson spectral function: Γ 0 / 2 S ( m )= 1 2 , π 2 +(Γ 0 / 2 ) ( m − m 0 ) m 0 – pole mass, Γ 0 – meson width m 0 = 1.0195 GeV (PDG 2008) Γ 0 = 4.26 MeV  Φ is a long-lived meson: λ dec = ħc/Γ 0 = 44 fm >> R(Au) 3

Φ in nuclear matter ∗  Meson spectral function:  (Γ 0 − 2Im U opt )/ 2 ∗ ( m )= 1 S 2 , π 2 +((Γ 0 − 2ImU opt )/ 2 ) ( m −( m 0 + ReU opt )) ∗   A general picture of numerous studies in different approaches, e.g. effective Lagrangians and QCD sum rules: - mass modification is small - main medium effect on the Ф is significant increase of its width up to an order of magnitude 4

Methods of Φ in-medium width measurement I  Study of the meson spectral function – measurement of low momentum Φ's: - Φ→e + e - (BR = 3·10 -4 ) - Φ→K + K - (BR = 0.49, K - FSI, hadronic potential)  Experiments: KEK-PS-E325: Reaction: pA→ΦX, Φ→e + e - p-Energy: 12 GeV Targets: C, Cu Result: Γ*/Γ 0 = 3.6, Γ* ≈ 11 MeV for <p Φ > = 1 GeV/c Δm/m 0 = -3.4% at ρ=ρ 0 R.Muto et al. , PRL 98 (2007) 042501 5

Methods of Φ in-medium width measurement II  Attenuation measurement of the Φ flux – analysis of the target mass dependence for the Φ production cross section The Φ survival probability D in the nucleus matter rest frame: D = exp ( − ∫ z ) , ∗ ( p Φ , ρ( r )) m 0 dl Γ ∞ ρ(r) – local nuclear density. p Φ  Experiments: JLab/CLAS: COSY/ANKE: Spring-8/LEPS: Reaction: γA→ΦX, Φ→e + e - Reaction: pA→ΦX, Φ→K + K - Reaction: γA→ΦX, Φ→K + K - γ-Energy: up to 4 GeV p-Energy: 2.83 GeV ( ε NN ≈76MeV ) γ-Energy: 1.5 - 2.4 GeV Targets: 2 H, C, Ti-Fe, Pb Targets: Li, C, Al, Cu Targets: C, Cu, Ag, Au Result: σ* ΦN = 16-70 mb Result: σ* ΦN = 35 +17 -11 mb Result: Γ * = 33-50 MeV Γ* ≈ 100 MeV for <p Φ > = 1.1 GeV/c for <p Φ > = 1.8 GeV/c T. Ishikawa et al. , M.H. Wood et al. , A.Polyanskiy et al. , PLB 608 (2005) 215 PRL 105 (2010) 112301 PLB 695 (2011) 74 * (ρ 0 )= p Φ * Γ lab E σ Φ N ρ 0 In low density approximation: 6

ANKE – forward angle magnetic spectrometer at internal target position of COSY Pd – positive detector system Nd Nd – negative detector system Fd – forward detector system Fd Φ momentum (0.6 ― 1.6) GeV/c, and angular range: 0 o ≤ Θ Φ ≤ 8 o Pd 7

Analysis: K + selection  Delayed Veto Technique  TOF Stop-Start w/o delayed veto delayed 8

Analysis: Φ/K + K - pairs identification C Φ pA→ΦX pA→K + K - X “+” background Au 7000-10000 Φ's for each target (C, Cu, Ag Au) 9

A-dependence of Φ production cross section  A-dependence in the form: A A T A =   R = T A   = 12 T A – nuclear transparency ratio N C T C A A      Absolute and relative normalization of the Φ production cross section – use of the know pion data: relative normalization: C =  12  A A C A A       C = N  N    π + : p = 0.5 GeV/c, θ ~ 0 0 A α π = 0.38 +/- 0.02 C A C   N  N      J. Papp et al., Phys. Rev. Lett. 34 (1975) 601; V. V. Abaev et al., J. Phys. G 14 (1988) 903; Yu. T. Kiselev et al., Preprint ITEP 56-96, Moscow (1996). 10

Transparency ratio: experiment ANKE(preliminary) 11

Transparency ratio: experiment and models Valencia/E.Oset et al. ANKE(preliminary) MC & Chiral Unitary Approach D. Cabrera et al. , NPA 733 (2004) 130 Prediction: 28 MeV for Φ at rest for ρ = ρ 0 V.Magas et al ., PRC 71 (2005) 065202; L.Roca (private 12 communication)

Transparency ratio: experiment and models Moscow/E.Paryev Valencia/E.Oset et al. ANKE(preliminary) MC & Chiral Unitary Nuclear Spectral Function Approach Approach V.Magas et al ., PRC E.Paryev, J.Phys. G 71 (2005) 065202; 36 (2009) 015103 L.Roca (private 13 communication)

Transparency ratio: experiment and models Moscow/E.Paryev Rossendorf/ Valencia/E.Oset et al. ANKE(preliminary) MC & Chiral Unitary Nuclear Spectral Function B.Kämpfer et al. Approach Approach BUU H.Schade, B.Kämpfer V.Magas et al ., PRC E.Paryev, J.Phys. G (private communication); 71 (2005) 065202; 36 (2009) 015103 cf. PRC 81 (2010) 034902: L.Roca (private 14 communication)

Transparency ratio: experiment and models Moscow/E.Paryev Rossendorf/ Valencia/E.Oset et al. ANKE(preliminary) MC & Chiral Unitary Nuclear Spectral Function B.Kämpfer et al. Approach Approach BUU Relevant features for models: • forward acceptance • two-step production processes • σ pn→pnΦ /σ pp→ppΦ ≈ 4 H.Schade, B.Kämpfer V.Magas et al ., PRC E.Paryev, J.Phys. G (private communication); 71 (2005) 065202; 36 (2009) 015103 cf. PRC 81 (2010) 034902: L.Roca (private 15 communication)

In-medium width Γ Φ and σ * ΦN cross section (preliminary) lab (ρ 0 )= p Φ * Γ Φ E σ Φ N ρ 0 LDA: Γ Φ lab ≈ 33-50 MeV ( <p Φ > = 1.1 GeV/c, ρ 0 = 0.16 fm -3 ) A.Polyanskiy et al. , PLB 695 (2011) 74 16

Double differential cross section of Φ production (preliminary) Excess in low momentum part + common systematics ~ 20 % 17

In-medium width Γ Φ and σ * ΦN cross section (preliminary) lab ≈ 45 MeV and/or σ * for p Φ > 1.1 GeV/c Γ Φ Φ N ≈ 17 mb 18

Summary Momentum dependence of the Φ-meson production under the forward angles has been studied at ANKE:  Large in-medium Φ width is extracted from high momentum part of spectrum  Preliminary differential cross sections are not completely reproduced by current model calculations in low momentum part 19

Thank You! 20

Extra Slides 21

Invariant mass spectra for 6 momentum bins 22

Comparison with three model calculations → Φ in-medium width, and … Relevant features: model A • two-step production • σ pn→pnΦ /σ pp→ppΦ ≈ 4 R • forward acceptance model C model B A) V.Magas et al., PRC 71, 065202 (2005): MC & Chiral unitary approach B) E.Paryev, J.Phys.G. 36 (2009) 015103: Nuclear spectral function C) H. Schade, B. Kaempfer (private communication) (cf. PRC 81 (2010) 034902): BUU-Rossendorf lab ≈ 33-50 MeV ( <p Φ > = 1.1 GeV/c, ρ 0 = 0.16 fm -3 ) Γ Φ A.Polyanskiy et al. , PLB 695 (2011) 74 23

BUU-Rossen- dorf (prelimi- nary) B. Kaempfer & H. Schade 24

BUU-Rossendorf (preliminary) 25

… its momentum dependence (preliminary) BUU/Rossendorf(preliminary): Au R including secondary production processes only primary production 26