-nucleus optical potential and the search for mesic states in - - PowerPoint PPT Presentation

η’-nucleus optical potential and the search for η’ mesic states in photo nuclear reactions

*funded by the DFG within SFB/TR16

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YITP Workshop on Hadron in Nucleus, 31st Oct.-2nd Nov. 2013, Kyoto, Japan Mariana Nanova

• II. Physikalisches Institut

for CBELSA/TAPS Collaboration Outline: ◆ motivation ◆ experimental approaches for determining the η’-nucleus optical potential:

• imaginary part of the potential - transparency ratio measurement
• real part of the potential:

excitation function of the η’-meson momentum distribution ◆ search for η’-nucleus bound states ◆ summary

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search for η’-meson-nucleus bound states

prediction of η’-12C bound states and their width for different η’ -meson nucleus potentials

• D. Jido et al., PRC 85 (2012) 032201

U(ρ) = V(ρ) + i W(ρ) more strongly bound states for deeper potentials W(ρ0) ≈ -10 MeV from M. Nanova et al., PLB 710 (2012) 600 many states with width Γ << binding energy predicted

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meson absorption meson mass shift Experimental approaches to determine the meson-nucleus optical potential meson-nucleus optical potential W(r) = −Γ0/2 · ρ(r)

ρ0

= − 1

2 · ~c · ρ(r) · σinel · β

V (r) = ∆m(ρ0) · ρ(r)

ρ0

Transparency ratio measurement

experimental observable to extract the in-medium width of the meson

TA =

σγA!η0X A·σγN!η0X

line shape analysis: direct determination of Δm excitation function: provides information about the depth of V(r) meson momentum distribution: provides information about the depth of V(r) meson-nucleus-bound states: direct determination of Ebin (Δm)

U(r) = V (r) + iW(r)

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Crystal Barrel/TAPS@ELSA Experiment

http://www.cb.uni-bonn.de 4π photon detector: ideally suited for identification of multiphoton final states photoproduction of η’ meson

photon beam

Eγ=0.5-2.6 GeV

Crystal Barrel TAPS

solid target: 12C, 40Ca, 93Nb and 208Pb

MiniTAPS Crystal Barrel photon beam

Eγ=0.7-3.1 GeV

Forward Plug

solid target: 12C

η’→π0π0η→6γ

BR 8.1% beamtime 2003 beamtime 2009

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photoproduction of η’ meson off 12C, 40Ca, 93Nb and 208Pb Eγ = 1500 - 2200 MeV;

The imaginary part of the η’-nucleus potential

• M. Nanova et al., PLB 710 (2012) 600

E=1.7 GeV

A TA

’exp data (0)=10 MeV (0)=15 MeV (0)=20 MeV (0)=25 MeV (0)=30 MeV (0)=35 MeV (0)=40 MeV

0.6 0.7 0.8 0.9 1 10 10

2

C

normalized to carbon

T C

A = 12·σγA!η0X A·σγC!η0X

➱ Γη’(<⎮pη’⎮> ≈1.05 GeV/c ) ≈ 15-25 MeV; ρ0=0.17 fm-3; ση’inel ≈ 3 -10 mb

at low density approximation:

Γ(ρ) = Γ(ρ0) ρ ρ0 Γ(ρ) = −ImΠ(ρ) E ∼ ρvσinel ;

W(ρ=ρ0)= -Γ0/2 = - (7.5-12.5) MeV

’

A TA

• 0.3

0.4 0.5 0.6 0.7 0.8 0.9 1 10 10

2

comparison with other mesons

η’ interaction with nuclear matter much weaker than for η, ω mesons

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The real part of the η’-nucleus potential

• J. Weil, U. Mosel and
• V. Metag, PLB 723 (2013 ) 120
• measurement of the excitation function of

the meson: in case of dropping mass - higher meson yield for given √s because of increased phase space due to lowering of the production threshold

Ethr

γN

1.0 1.2 1.4 1.6 1.8 2.0 2.2 1E-3 0.01 0.1 1 10

• Coll. Broadening

(ση’N=8 mb)

• Coll. Broadening +

Mass Shift (-5%)

γ

12C->η’X

1.0 1.2 1.4 1.6 1.8 2.0 2.2 0.01 0.1 1 10 100

• Coll. Broadening

(ση’N=8 mb)

• Coll. Broadening +

Mass Shift (-5%)

σγNb->η’X [µb] σγC->η’X [µb] γ

93Nb->η’X

Eγ [GeV] Eγ [GeV]

Ethr

γN

• E. Paryev, J. Phys. G: Nucl. Part. Phys. 40 (2013) 025201

based on γp→ η’p and γn→ η’n exp. data

0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 0.1 1 10

• Coll. Broadening

(ση’N=8 mb)

• Coll. Broadening +

Mass Shift (-5%) Eγ=1.5-2.2 GeV

γ

12C->η’X

0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 1 10 100

• Coll. Broadening

(ση’N=8 mb)

• Coll. Broadening +

Mass Shift (-5%) dσγNb->η’X/dpη’ [µb/(GeV/c)] dσγC->η’X/dpη’ [µb/(GeV/c)]

γ

93Nb->η’X

Eγ=1.5-2.2 GeV pη’ [GeV/c] pη’ [GeV/c]

• measurement of the momentum distribution
• f the meson:

in case of dropping mass - when leaving the nucleus hadron has to become on-shell; mass generated at the expense of kinetic energy ➯ downward shift of momentum distribution

excitation function for η’ photoproduction off C

decay mode: η’ → π0π0η comparison of CBELSA/TAPS data with calculations by E. Paryev, J. Phys. G: Nucl. Part. Phys. 40 (2013) 025201 and priv. communication

strong mass shift not supported by data

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excitation function

calculations normalized to data for Eγ = 2000-2500 MeV; downscaled by 1.2

• exp. data and the 5 scenarios divided by the

calculation for scenario V(ρ=ρ0)=0 MeV

E[MeV] ’ [µb]

V(=0) = 0 MeV V(=0) = -75 MeV V(=0) = -100 MeV V(=0) = -150 MeV V(=0) = -50 MeV V(=0) = -25 MeV

E[MeV] ’ [µb]

tot C data diff Ethr

10

• 1

1 10 1000 1500 2000 2500 E[MeV] ratio

V(=0) = 0 MeV V(=0) = -75 MeV V(=0) = -100 MeV V(=0) = -150 MeV V(=0) = -50 MeV V(=0) = -25 MeV Ethr

1 2 3 4 5 1500 2000 2500

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V(ρ=ρ0) = -40±6 MeV

estimation of the real part of the η’-nucleus potential from the η’ excitation function

significance test

potential depth [MeV] 2/f 5 10 15 20 25 30

• 150
• 100
• 50

χ2-fit of the data with the calculated excitation functions for the 6 scenarios

E[MeV] ’ [µb]

V(=0) = 0 MeV V(=0) = -75 MeV V(=0) = -100 MeV V(=0) = -150 MeV V(=0) = -50 MeV V(=0) = -25 MeV

E[MeV] ’ [µb]

tot C data diff Ethr

10

• 1

1 10 1000 1500 2000 2500

ση’N=11mb excitation function

• M. N. et al., paper accepted for publication in PLB

V = 0 MeV V = -25 MeV; V = -50 MeV V = -75 MeV V = -100 MeV; V = -150 MeV

1 2 1250-1350 MeV 1350-1450 MeV

d/d(cos’) [µb]

1450-1550 MeV

cos(’)cm

2

• 1
• 0.5

0.5 1

below threshold

2 4 2.5 5 1550-1600 MeV 1600-1700 MeV

d/d(cos’) [µb]

1700-1800 MeV

cos(’)cm

2.5 5

• 1
• 0.5

0.5 1

at threshold

2 4 2.5 5 1800-1900 MeV 1900-2000 MeV

d/d(cos’) [µb]

2100-2200 MeV

cos(’)cm

2.5 5

• 1
• 0.5

0.5 1

above threshold

high sensitivity to different scenarios at threshold η’→π0π0η→6γ

BR: 8.1% Eγ = 1250 - 2600 MeV

experimental data on η’ photoproduction off 12C

sensitivity to different scenarios

• E. Ya. Paryev, priv. communication

strong mass shift not supported by data

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data favour V(ρ=ρ0) ≈-50 MeV ➯ attractive!

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momentum distribution

p’ [GeV/c ] d’/dp’ [µb/GeV/c]

C data E=1500-2200 MeV V(=0) = 0 MeV V(=0) = -75 MeV V(=0) = -25 MeV V(=0) = -100 MeV V(=0) = -150 MeV V(=0) = -50 MeV

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• 1

1 0.25 0.5 0.75 1 1.25 1.5 1.75 2

calculation normalized to data in p = 1.5-1.8 GeV/c, downscaled by 1.2

η’ momentum distribution off C

comparison of CBELSA/TAPS data with calculations by

• E. Paryev, J. Phys. G: Nucl. Part. Phys. 40 (2013) 025201 and priv. communication

p’ [GeV/c ] ratio

C data E=1500-2200 MeV V(=0) = 0 MeV V(=0) = -75 MeV V(=0) = -25 MeV V(=0) = -100 MeV V(=0) = -150 MeV V(=0) = -50 MeV

2 4 6 8 10 0.5 1 1.5

• exp. data and the 5 scenarios divided by the

calculation for scenario V(ρ=ρ0)=0 MeV

consistent with predictions by:

• S. Bass and A.W.Thomas, Acta Phys. Pol. B 41 (2010) 2239
• H. Nagahiro et al., PLB 709 (2012) 87.

W(ρ=ρ0) = -10±2.5 MeV, M. Nanova et al., PLB 710 (2012) 600. ⎮V ⎮>> ⎮W⎮ ! ➯ search for η’ mesic states promising

estimation of the of η’-nucleus potential depth from the η’ momentum distribution

p’ [GeV/c ] d’/dp’ [µb/GeV/c]

C data E=1500-2200 MeV V(=0) = 0 MeV V(=0) = -75 MeV V(=0) = -25 MeV V(=0) = -100 MeV V(=0) = -150 MeV V(=0) = -50 MeV

10

• 1

1 0.25 0.5 0.75 1 1.25 1.5 1.75 2

potential depth [MeV] 2/f 2 4 6 8 10

• 150
• 100
• 50

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V(ρ=ρ0) = -32±11 MeV

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excitation function for η’ photoproduction off Nb

data will be taken with CB/TAPS detector system at ELSA

• Nov. 2013 / Jan. 2014
• E. Paryev, private communication

ση’N=11mb

V(=0) = 0 MeV V(=0) = -25 MeV V(=0) = -50 MeV V(=0) = -75 MeV V(=0) = -100 MeV V(=0) = -150 MeV Nb

E[MeV] ’ [µb] 10

• 1

1 10 1 1.5 2 2.5 3

excitation function

p’ [GeV/c ] d’/dp’ [µb/GeV/c] Nb

E=1500-2200 MeV V(=0) = 0 MeV V(=0) = -75 MeV V(=0) = -25 MeV V(=0) = -100 MeV V(=0) = -150 MeV V(=0) = -50 MeV 1 10 10 2 0.25 0.5 0.75 1 1.25 1.5 1.75 2

momentum distribution

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summary

η’ promising candidate for mesic states ⎮V ⎮>> ⎮W⎮ ! ➯

• 1. Imaginary part of the η’- nucleus optical potential determined from

transparency ratio measurements:

• 2. Real part of the η’- nucleus optical potential determined from:
• a. measurement of the excitation function of the η’-meson
• b. measurement of the momentum distribution of the η’-meson
• 3. η’-nucleus optical potential - experiment needed off Nb to confirm the

result W(ρ=ρ0)=−Γ0/2 = -10±2.5 MeV V(ρ=ρ0) = -32±11 MeV V(ρ=ρ0) = -40±6 MeV Uη’A(ρ=ρ0) = -(37±10(stat) ±10(syst)+i(10±2.5)) MeV first (indirect) observation of in-medium mass shift of η’ at ρ=ρ0 and T=0

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forward going proton takes up momentum of incoming photon beam, leaving meson almost at rest ⇒ captured by nucleus in case of an attractive interaction

γ

η’, ω, η p

population of η’, ω, η-mesic states in photo induced reactions

two ways of measuring excitation energy of mesic nucleus: 1.) missing mass spectrometry: measure spectrum of forward going proton 2.) measure kinetic energy of decay products

• f mesic state

Eex-E0 [MeV] d2/dEd [nb/sr/MeV]

E = 2.2 GeV (V0,W0) = -(55,10) MeV (V0,W0) = -(0,10) MeV

5 10 15 20

• 80
• 60
• 40
• 20

20 40 60 80

• H. Nagahiro, private communication

12C(γ,p) η’X

bound state region quasi free production

• utlook

1) FRS@GSI missing mass spectrometry:

K . I t a h a s h i e t a l . , P r

• g

. T h e

• .

P h y s . 1 2 8 ( 2 1 2 ) 6 1

12C(p,d) η’X @ 2.5 GeV

2) BGO-OD@ELSA

12C(γ,p) η’X @ 2.8 GeV

Incoming Photon Energy [MeV] Momentum of ’ [MeV/c] proton = 10o 1o 5o

200 400 600 800 1000 1500 2000 2500 3000

a potential of 37 MeV depth will support η’ momenta up to 270 MeV/c

momentum transfer to η’

approved proposal: ELSA/3-2012-BGO

next talk: Y. Tanaka

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search for η’-mesic states in photo nuclear reaction

12C(γ,p) η’X @ 2.8 GeV

Δp/p ≈ 1-2 %

BGO-OD@ELSA

• H. Schmieden, P. Levi Sandri

BGO-OD ideally suited for inclusive and semi-exclusive measurement 4π acceptance charged and neutral particle ID

• BGO ball:

a highly segmented calorimeter- ideal for neutral meson detection

• Forward spectrometer:

tracking detectors, dipole magnet, drift chambers and TOF walls - charged particle ID and momentum reconstruction

approved proposal: ELSA/3-2012-BGO

measurement of η’N formation and decay

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search for η’-mesic states in photo nuclear reactions

BGO-OD ideally suited for measurement of η in coincidence with forward going proton

measurement of formation and decay of η’-nucleus bound state

η’N → M B η’N → ηN

• 2. semi-exclusive measurement:

measurement of p in coincidence with decay of η’-mesic state

about 70% of all η’-mesic states decay by emission of lighter mesons; predominantly by η’N→ηN

• E. Oset and A. Ramos, PLB 704 (2011) 334

12C(γ,p) η’X @ 2.8 GeV with BGO-OD@ELSA

Δp/p ≈ 1-2 %

• 1. inclusive measurement: missing mass spectrometry

measurement of p momentum η’ p

γ