[PPT] - Determination of the - and '-nucleus optical potential Mariana PowerPoint Presentation

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Mariana Nanova for the CBELSA/TAPS Collaboration

*funded by the DFG within SFB/TR16

Outline: ◆ motivation ◆ exp. approaches to study the in-medium properties of mesons ◆ experimental results on the real and imaginary part of the ω- and η’-nucleus optical potential ◆ summary & outlook

MESON2016 Cracow, 2th - 7th June 2016

Determination of the ω- and η'-nucleus optical potential

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2

if the QCD ground state changes in a medium ⇒ properties of hadrons (“excited states”) are also expected to change

baryons and mesons

◆ QCD vacuum as a Bose-Einstein condensate of qq ◆ all states (particles) are created out of the vacuum state (“excitations of the QCD-vacuum”) ◆ the ground-state structure influences the particle properties

−

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3

widespread theoretical and experimental activities to search for in-medium modifications of hadrons how do the hadron properties (mass, width) change in a dense nuclear medium ??

hadrons in the medium

G.E.Brown and M. Rho, PRL 66 (1991) 2720

m? m ≈ < ¯ qq >? < ¯ qq >0 ≈ 0.8(ρ ≈ ρ0)

“Brown-Rho Scaling”

T.Hatsuda and S. Lee, PRC 46 (1992) R34

m

V

mV = (1 − α ρ ρ0 ); α ≈ 0.18

QCD sum rule approach: drop of ρ, ω mass by about 15% at ρ=ρ0

V. Bernard and U.-G. Meißner,

NPA 489 (1988) 647

pioneering papers:

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4

V. Bernard and U.-G. Meissner,
Phys. Rev.D 38 (1988) 1551

almost no dependence of η’ mass on density

S. Bass and A. Thomas,

PLB 634 (2006) 368

Δmη’ (ρ0)≈−40 MeV for θηη’ = −200 Δmη’ (ρ0)≈−150 MeV Δmη (ρ0) ≈ +20 MeV

H. Nagahiro et. al,
Phys. Rev. C 74 (2006) 045203

SU(2) SU(3)

S. Sakai and D. Jido

PRC 88 (2013) 064906

Δmη’ (ρ0)≈−80 MeV NJL-model NJL-model linear σ model QMC-model

hadronic models: predictions for η’ in-medium mass

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5

hadronic models: predictions for ω-spectral functions

F. Klingl et al.,

NPA 610 (1997) 297; NPA 650 (1999) 299

◆ lowering of in-medium mass ◆ broadening of resonance

with increasing nuclear density Re(U) ≠0; Im(U) ≠0

M. Lutz et al.,

NPA 706 (2002) 437

splitting into ω-like and N*N-1 mode due to coupling to nucleon resonances

P . Mühlich et al., NPA 780 (2006) 187

spectral function for ω meson at rest: almost no mass shift; strong in-medium broadening Re(U) ≈0; Im(U) large

experimental task: search for {

}

mass shift ? broadening? structures?

f hadronic spectral functions

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meson-nucleus optical potential U(r) = V (r) + iW(r)

mass and lifetime (width) may be changed in the medium

V (r) = ∆m(ρ0) · ρ(r)

ρ0

real part in-medium mass modification

⬄

W(r) = −Γ0/2 · ρ(r)

ρ0

= − 1

2 · ~c · ρ(r) · σinel · β

imaginary part in-medium width, absorption inelastic cross section lifetime shortened

⬄

H. Nagahiro an S. Hirenzaki,

PRL 94 (2005) 232503

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experimental approaches to determine the meson-nucleus optical potential U(r) = V (r) + iW(r) V (r) = ∆m(ρ0) · ρ(r)

ρ0

real part

W(r) = −Γ0/2 · ρ(r)

ρ0

= − 1

2 · ~c · ρ(r) · σinel · β

imaginary part

◆ transparency ratio measurement

TA = σγA→η0X A · σγN→η0X

D. Cabrera et al., NPA 733 (2004)130

◆ line shape analysis ◆ excitation function ◆ momentum distribution ◆ meson-nucleus bound states

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CBELSA/TAPS experiment

MiniTAPS Crystal Barrel photon beam

Eγ=0.7-3.1 GeV

Forward Plug

solid target: 12C

and 93Nb

Eγ=0.7 - 3.1 GeV

1320 CsI 216 BaF2

4π photon detector: ideally suited for identification of multi-photon final states

η’→π0π0η→6γ

BR 8.5%

ω→π0γ→ 3γ BR 8.2%

≈ 3% σm m

η’→π0π0η→6γ

]

2

[MeV/c

η π π

M 850 900 950 1000 1050 1100 1150 )]

2

[1/(6 MeV/c

η π π

N 200 400 600 800 1000 1200 1400 1600 1800 3177 counts

Nb

2

0.3 MeV/c ± =11.8 σ

2

0.5 MeV/c ± m=957.6

≈ 1% σm m

]

2

[MeV/c

γ π

M 600 650 700 750 800 850 900 950 )]

2

[1/(4 MeV/c

γ π

N

3

10

4

10 64456 counts

C

2

0.3 MeV/c ± =25.8 σ

2

0.4 MeV/c ± m=792.5

ω→π0γ→ 3γ

≈ 3% σm m

64456 counts 3177 counts

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The real part of the meson-nucleus

ptical potential

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J. Weil, U. Mosel and
V. Metag, PLB 723 (2013 ) 120

the real part of the ω-nucleus potential

ω→π0γ

sensitive to nuclear density at production point and not at decay point

γ+93Nb→π0γ+X Eγ=0.9-1.3 GeV

π0γ momentum distribution

◆ momentum distribution of 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

10

➯ cross section enhancement

π0γ excitation function

◆ measurement of the excitation function

f 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

Eγthr

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Eγthr

excitation function for ω photoproduction off C comparison with GiBUU calculation

CB/TAPS @ MAMI

V. Metag et al., PPNP

, 67 (2012) 530

data not consistent with strong mass shift scenario (Δm/m≈-16%)

vacuum collisional broadening(CB) CB+mass shift (-16%) mass shift (-16%)

M. Thiel et al., EPJA 49 (2013) 132

momentum distribution V(ρ=ρ0) = −(42±17(stat)±20(syst)) MeV

[GeV]

γ

E 0.9 1 1.1 1.2 1.3 1.4 b] µ /A [ σ

2

10

1

10

Carbon

★CB/TAPS@MAMI

CBELSA/TAPS

GiBUU

collisional broad. and mass shift V = 0 MeV V = -20 MeV V = -40 MeV V = -55 MeV V = -94 MeV V = -125 MeV

Carbon

excitation function

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data: M. Nanova et al., PLB 727 (2013) 417

data disfavour strong mass shifts

Eγ[MeV] ση’ [µb]

V(ρ=ρ0) = 0 MeV V(ρ=ρ0) = -75 MeV V(ρ=ρ0) = -100 MeV V(ρ=ρ0) = -150 MeV V(ρ=ρ0) = -50 MeV V(ρ=ρ0) = -25 MeV

Eγ[MeV] ση’ [µb]

σtot C data σdiff Eγthr

10

1

1 10 1000 1500 2000 2500

Vη’(ρ=ρ0) = −(40±6) MeV

ση’N=11 mb

CBELSA/TAPS @ ELSA

pη’ [GeV/c ] dση’/dpη’ [µb/GeV/c]

C data Eγ=1500-2200 MeV V(ρ=ρ0) = 0 MeV V(ρ=ρ0) = -75 MeV V(ρ=ρ0) = -25 MeV V(ρ=ρ0) = -100 MeV V(ρ=ρ0) = -150 MeV V(ρ=ρ0) = -50 MeV

10

1

1 0.25 0.5 0.75 1 1.25 1.5 1.75 2

Vη’(pη’≈1.1 GeV/c;ρ=ρ0) = −(32±11) MeV

ση’N=11 mb

excitation function and momentum distribution for η' photoproduction off C

calc.: E. Paryev, J. Phys. G 40 (2013) 025201

γ C →η’X

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excitation function and momentum distribution for η' photoproduction off Nb

CBELSA/TAPS @ ELSA

[GeV/c]

' η

p

0.5 1 1.5 2 2.5

b/GeV/c] µ / [

' η

/dp σ d

1 10

Nb =1.3 - 2.6 GeV

γ

E

= 14 mb

inel ' η

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

P R E L I M I N A R Y

Vη'(pη'≈1.14 GeV/c;ρ=ρ0) = −(41±22) MeV

M. Nanova et al., submitted to PRC for publication

[GeV]

γ

E

1 1.5 2 2.5

b] µ [

' η

σ

1 10

Nb

tot

σ

diff

σ

= 14 mb

inel ' η

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

' thr η γ

E

P R E L I M I N A R Y

Vη'(ρ=ρ0) = −(46±15) MeV

data disfavour strong mass shifts γ Nb →η’X

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real part of ω-nucleus potential from ω kinetic energy

10≤θp≤110

the higher the attraction the lower the kinetic energy of the ω meson

γ ω p

Eγ=1.25-3.1 GeV CBELSA/TAPS @ ELSA

782 [MeV]

γ π

E 20 30 40 50 60 70 80 90 [nb/MeV/sr] Ω d

kin

/dE

γ π

σ

2

d 1.4 1.5 1.6 1.7 1.8 1.9 2 2.1 2.2

) , W (V

(156,70) MeV
(100,70) MeV
( 50,70) MeV
( 0,70) MeV
(-20,70) MeV
(-50,70) MeV
H. Nagahiro, priv. com.
782 [MeV]
E
300 -200 -100

100 200 300 400 [nb/MeV/sr]

d

kin

/dE

2

d

0.5

0.5 1 1.5

Carbon

S. Friedrich et al., PLB 736 (2014) 26

Ekin=(60.5±7)MeV

Vω(pω≈300 MeV/c; ρ=ρ0) = −(15±35) MeV

potential depth [MeV]

150
100
50

50 peak position [MeV] 30 40 50 60 70 80 90

d)

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compilation of results for the real part of the ω- and η’-nucleus optical potential

Vη’A(ρ=ρ0) =

−(40±8(stat)±15(syst)) MeV VωA(ρ=ρ0) = −(29±19(stat)±20(syst)) MeV

ω η’

[MeV]

'A η

V 80 − 60 − 40 − 20 −

excitation function

mom. distribution

weighted average C Nb

[MeV]

'A η

V 80 − 60 − 40 − 20 − 20

excitation function

kin

peak E average C

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The imaginary part of the meson-nucleus

ptical potential: momentum dependence

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[MeV/c]

ω

p 500 1000 1500 2000 2500 b/(GeV/c)] µ /A [

ω

/dp σ d 0.5 1 1.5 2 2.5

Nb C

momentum differential cross section for ω, η’ produced off C, Nb

ω η’

γ C,Nb → ωX

Eγ = 1.2- 2.9 GeV

TNb/C (pm) = 12 ⦁σγNb→mX (pm) 93 ⦁σγC→mX (pm)

m

momentum differential cross sections ⇒

P R E L I M I N A R Y

[MeV/c]

' η

p 500 1000 1500 2000 2500 b/(GeV/c)] µ /A [

' η

/dp σ d 0.05 0.1 0.15 0.2 0.25

Nb C

P R E L I M I N A R Y

γ C,Nb →η’X

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ω η’

momentum dependence of transparency ratio for ω, η’

absorption of η’ mesons much weaker than for ω mesons !!

TNb/C (pm) = 12 ⦁σγNb→mX(pm) 93 ⦁σγC→mX (pm)

m

M. Kotulla et al., PRL 100 (2008) 192302

bbbbbbbbbbbb

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

blablabla

TNb/C ≈ 0.7-0.8

η’

TNb/C ≈ 0.4-0.6

ω

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imaginary part of the potential for ω, η’

Glauber model: high energy Eikonal approximation TNb/C (pm)

⇒ Γ0 (ρ=ρ0) (pm) = - 2 Im U0 (pm)

m m m

ω η’

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

Im U0(ρ=ρ0,pω=0) = −(30±10) MeV

ω

◆ extrapolation to production threshold: ◆ extension to higher energies allows for dispersion relation analysis,

providing link between real and imaginary part of potential

M. Kotulla et al., PRL 114 (2015) 199903

PRELIMINARY

[MeV]

thr

s

ω

s 200 400 600 800 1000 1200 1400 1600 ) [MeV]

ω

(Im U

20 40 60 80 100 120

PRL 114 (2015) 199903 this experiment

PRELIMINARY

Im U0(ρ=ρ0,pη’=0) = −(10±3) MeV

η’

[MeV]

thr

s

'

η

s 200 400 600 800 1000 1200 1400 ) [MeV]

' η

(Im U

5 10 15 20 25 30 35 40 45

PLB 710 (2012) 600 this experiment

blablabla blablabla

S. Friedrich et al., submitted to EPJA for publication

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compilation of results for real and imaginary part of the ω, η’ -nucleus optical potential

UωA(ρ=ρ0)= −((29±19(stat)±20(syst) + i(30±10)) MeV Uη’A(ρ=ρ0)= −((40±8(stat)±15(syst) + i(10±3)) MeV

ω not a good candidate to search for meson-nucleus bound states!

⎮Im U ⎮≈⎮Re U⎮; ➯

first (indirect) observation of in-medium mass shift of η’ at ρ=ρ0 and T=0 in good agreement with QMC model predictions (S. Bass et al. , PLB 634 (2006) 368)

η’ promising

candidate to search for mesic states ⎮Re U⎮ >>⎮Im U⎮; ➯

ω η’

potential depth [MeV] 10 20 30 40 50 imaginary part [MeV] 10 20 30 40 50 60

ω ' η

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utlook: search for η’-mesic states in photo-nuclear reactions

12C(γ,p) η’X @ 1.5-2.8 GeV

Δp/p ≈ 1-2 %

B1: BGO-OD@ELSA

BGO-OD ideally suited for exclusive measurement

approved proposal: ELSA/3-2012-BGO

η’

γ

p

formation and decay of η’-mesic state

N

η

LEPS2@SPring-8

12C(γ,p) η’X @ 1.5-2.4 GeV

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,)

missing mass spectrometry: Δmm =2.5 MeV/c2

12C target

S2 S4 2.5 GeV protons 2 . 7

2

. 9 G e V / c d e u t e r

n

s ( p r

t
n

s ) MWDC aerogel Cerenkov aerogel Cerenkov p/d separation by aerogel Cerenkov TOF S2-S4 (diff.≈20 ns) plastic scintillators

search for η’-mesic states in hadronic reactions FRS@GSI:

12C(p,d)η’⦻11C

K. Itahashi et al., PETP 128 (2012) 601
H. Nagahiro et al., PRC 87 (2013) 045201

particle identification by time-of-flight

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Summary & Outlook

how do the hadron properties (mass, width) change in a dense nuclear medium ?? ◆ all mesons are broadened; their lifetime is shortened through inelastic collisions Γω(ρ=ρ0; p=0) ≈ 60 MeV; Γη’(ρ=ρ0; p=0) ≈ 15 MeV; ◆ large mass modifications Δm > 100 MeV (as predicted by some calculations) have not been observed ◆ for the η’ meson an in-medium mass drop of Δm (ρ=ρ0) ≈ −40 MeV has been determined ◆ the η’ meson is a good candidate for forming meson-nucleus bound states since Im U << Re U ◆ search for η’ mesic states ongoing ◆ in-medium effects described within meson-nucleus optical

meson properties do change in a strongly interacting medium !!

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BACKUP

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[MeV]

ω

Γ 50 100 150 200 250 300 350 400

ω Nb/C

T 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

= 200 MeV/c

ω

p = 400 MeV/c

ω

p = 600 MeV/c

ω

p = 800 MeV/c

ω

p = 1000 MeV/c

ω

p = 1200 MeV/c

ω

p = 1600 MeV/c

ω

p = 2400 MeV/c

ω

p

ω

[MeV]

' η

Γ 50 100 150 200 250 300 350 400

' η Nb/C

T 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

= 275 MeV/c

' η

p = 525 MeV/c

' η

p = 750 MeV/c

' η

p = 1075 MeV/c

' η

p = 1225 MeV/c

' η

p = 1525 MeV/c

' η

p = 1825 MeV/c

' η

p = 2275 MeV/c

' η

p

' η

in-medium width from transparency ratio

Glauber model in high energy eikonal approximation TNb/C(p) ⟷ Γ0(p)

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[MeV/c]

' η

p 500 1000 1500 2000 [MeV]

' η

Γ 10 20 30 40 50 60 70 80 90

PLB 710 (2012) 600 this experiment

momentum dependence of ω, η’ in-medium width

P . Mühlich et al.,NPA 780 (2006) 187

O. Buss et al., Phys. Rep. 512 (2012) 1

[MeV/c]

ω

p 500 1000 1500 2000 [MeV]

ω

Γ 50 100 150 200 250

PRL 114 (2015) 199903 this experiment

GiBUU

A. Ramos et al., EPJA 49 (2013)148
D. Cabrera and R. Rapp, PLB 729 (2014)67
S. Friedrich
M. Kotulla et al., PRL 114 (2015) 199903
M. Nanova et al., PLB 710 (2012) 600

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[MeV/c]

' η

p 500 1000 1500 2000 [mb]

' η inel

σ 5 10 15 20 25 30 35 40

PLB 710 (2012) 600 this experiment

[MeV/c]

ω

p 500 1000 1500 2000 [mb]

ω inel

σ 50 100 150 200

PRL 114 (2015) 199903 this experiment

inelastic absorption cross section σinel

a=0.0±6.2 b=31±4 a=8.1±9.5 b=6.8±9.8

⟨σinel(p)⟩ = (14±3) mb

E. Oset and A. Ramos, PLB 704 (2012) 334

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if self-energy Σ of the meson is an analytic function then imaginary and real part related up to a constant by: work in progress (Horst Lenske (B7)) + const