pNb hadron2011 v3 - SLAC National Accelerator · PDF filep) MDC((Magnet)) β) TOF(ino))...

Probing cold nuclear ma0er with virtual photons

1

Michael Weber, Manuel Lorenz, Anar Rustamov and Pavel Tlusty for the HADES collaboraAon

HADRON 2011 -‐ 17.06.11

Outline: •  Virtual photons in cold nuclear ma0er •  HADES •  Slow and fast e+e-‐ pairs •  Nuclear modificaKon factor •  Conclusion

Virtual photons in cold nuclear ma0er

•  EM structure / Vector mesons in ma0er •  Decay in e+e-‐:

–  Weak interacKons with surrounding medium –  Other sources (conversion, Dalitz decays)

•  Experiments: –  Shape measurements (spectral funcKon) –  AbsorpKon (total width)

•  Results (Spring8, KEK -‐ E328, JLab – CLAS, CB/TAPS@ELSA, ANKE) –  Broadening –  Pole mass shi`? –  Difficult interpretaKon (Differences in Background determinaKon, ρ contribuKon, decay kinemaKcs, …)

2

e+

e-

Heavy nucleus γ*

HADRON 2011 -‐ 17.06.11

HADES@GSI

HADRON 2011 -‐ 17.06.11 3

Observable Detector p MDC (Magnet) β TOF(ino)

dE/dx MDC TOF(ino)

e+/e-‐ RICH Pre-‐Shower

High Acceptance Di-‐Electron Spectrometer[ EPJ A41 243 ]

Data sets: protons with Ekin = 3.5 GeV •  pNb (cold nuclear ma0er) •  pp (reference)

HADES@GSI

HADRON 2011 -‐ 17.06.11 4

High Acceptance Di-‐Electron Spectrometer[ EPJ A41 243 ]

Data sets: protons with Ekin = 3.5 GeV •  pNb (cold nuclear ma0er) •  pp (reference)

See also: •  „In-‐medium modificaKon

of hadrons”, Piotr Salabura

•  „Neutral kaon producKon in pp and pNb collisions”, Kirill Lapidus

e+e-‐ Invariant Mass

•  Signal = all e+e-‐ pairs – same event Like Sign CB •  S/B ~ 10 in vector meson mass region •  Mass resoluKon: σω~15 MeV/c2

•  2 independent PID: Hard Cuts and MulK Variate Analysis HADRON 2011 -‐ 17.06.11 5

)2 (MeV/ceeM

0 200 400 600 800 1000 1200

)-1 )2 ((

MeV

/cee

dN/d

M

-110

1

10

210

310

410

- e+ eCB (LS)

p+Nb (3.5 GeV) > 9 ̊

Signal

α

Reference: pp (Ekin = 3.5 GeV)

HADRON 2011 -‐ 17.06.11 6

Separate 4 mass regions: •  π0 :

0.00 < Mee (GeV/c2) < 0.15 •  η :

0.15 < Mee (GeV/c2) < 0.47 •  Δ, ρ, ω Dalitz :

0.47 < Mee (GeV/c2) < 0.70 •  ω, ρ, φ :

0.70 < Mee (GeV/c2) < 1.20

PRELIMINARY

Cold nuclear ma0er: pNb (Ekin = 3.5 GeV)

HADRON 2011 -‐ 17.06.11 7

•  NormalizaKon: –  pp: elasKc collisions –  pNb: negaKve pion yield

•  Pion scale with ~ A0.7 –  Expected for surface

producKon

•  Shape analysis: –  RelaKve to π0 yield

•  Nuclear modificaKon factor PRELIMINARY

]2 [GeV/ceeM0 0.2 0.4 0.6 0.8 1 1.2

)]2 [1

/(GeV

/cee

dN

/dM

0π

1/N

-510

-410

-310

-210

-110

1p+Nb 3.5 GeV

p+p 3.5 GeV

Comparison: pNb vs. pp

HADRON 2011 -‐ 17.06.11 8

•  Shape analysis •  Scaled with the number of π0

•  Different producKon and/or absorpKon processes dominant

for different e+e-‐ sources

PRELIMINARY

Pair momenta

HADRON 2011 -‐ 17.06.11 9

HS

D S

imulation

Momentum cut

•  Enrich in-‐medium decays of vector mesons

Pair momenta

HADRON 2011 -‐ 17.06.11 10

•  Enrich in-‐medium decays of vector mesons •  HADES: Significant e+e-‐ yield with pee< 800 MeV/c ( ~ 35 % in VM mass region)

S.Leupold, V.Metag and U.Mosel, nucl-th 0907.2388

JLAB-CLAS HADES

]2 [GeV/ceeM0 0.2 0.4 0.6 0.8 1 1.2

)]2 [1

/(GeV

/cee

dN

/dM

0π

1/N

-510

-410

-310

-210

-110

1p+Nb

p+p

]2 [GeV/ceeM0 0.2 0.4 0.6 0.8 1 1.2

)]2 [1

/(GeV

/cee

dN

/dM

0π

1/N

-510

-410

-310

-210

-110p+Nb

p+p

Slow and fast pairs

HADRON 2011 -‐ 17.06.11 11

pee> 800 MeV/c pee< 800 MeV/c

PRELIMINARY PRELIMINARY

Slow and fast pairs

HADRON 2011 -‐ 17.06.11 12


•  High p: free p+p producKon •  Low p: overshoot over p+p -‐ different for ρ, ω, and φ


Nuclear modificaKon factor

HADRON 2011 -‐ 17.06.11 13

RpA =Apppart !dN / dp

pNb

ApNbpart !dN / dp

pp

=Apppart !! reaction( pp) !d! / dp

pNb

ApNbpart !! reaction( pNb) !d! / dp

pp

! reaction( pNb)

! reaction( pp)

= 20,5= (A)0.67

HADRON 2011 -‐ 14.06.11

PRELIMINARY RpA = 1: No In-‐Medium effects

RpA > 1: Excess

RpA < 1: Suppression

[GeV/c]eeP0 0.5 1 1.5

pAR

0

1

2

3

4 <0.15 eeM<0.47 ee0.15<M<0.7 ee0.47<M

ee0.7<M

ωidentified

Nuclear modificaKon factor

HADRON 2011 -‐ 17.06.11 14

At low pair momenta: •  Pions ~ const

•  Strong excess of ρ, Δ type sources –  Secondary reacKons –  Isospin dependence

•  ω: Trend to absorpKon

PRELIMINARY

Transport model calculaKons

HADRON 2011 -‐ 17.06.11 15 J. Weil, GIBUU [hCp://arxiv.org/abs/1106.1344]




HADRON 2011 -‐ 17.06.11 16 J. Weil, GIBUU [hCp://arxiv.org/abs/1106.1344] Pee (GeV/c)

R pA

R pA


HADRON 2011 -‐ 17.06.11 17 J. Weil, GIBUU [hCp://arxiv.org/abs/1106.1344]

10-1

100

101

102

103

0 0.2 0.4 0.6 0.8 1

d!/dµ

[µb/

GeV

]

dilepton mass mee [GeV]

all momenta

datano mesonic FSI

FSI, K" = 1K" = 2K" = 3K" = 4K" = 5

CB/TAPS@ELSA

•  RelaKve yield

•  Fast and slow pairs

•  Nuclear modificaKon factor

•  Have to understand producKon mechanisms in primary and secondary reacKons: – Transport models – π beam experiments

Conclusion

18

In π0/ω region ~ 1.0 Other sources ~ 1.5

High p: p+Nb = p+p Low p: excess (secondary reacKons)

ω absorpKon?

High p: RpNb = 0.8 – 0.9 Low p: RpNb = 0.8 – 2.5

HADRON 2011 -‐ 17.06.11

BACKUP

HADRON 2011 -‐ 17.06.11 19

[GeV/c]tP0 0.2 0.4 0.6 0.8 1 1.2

[1/(G

eV/c

)]t

dN

/dP

0 π1/

N

-510

-410

-310

-210

-110

1

2<0.150 GeV/ceeM

[GeV/c]tP0 0.2 0.4 0.6 0.8 1 1.2

[1/(G

eV/c

)]t

dN

/dP

0 π1/

N

-510

-410

-310

-210

2<470 GeV/cee0.150 <M

[GeV/c]tP0 0.2 0.4 0.6 0.8 1 1.2

[1/(G

eV/c

)]t

dN

/dP

0 π1/

N

-610

-510

-410

-310

2<700 GeV/cee0.470 <M

[GeV/c]tP0 0.2 0.4 0.6 0.8 1 1.2

[1/(G

eV/c

)]t

dN

/dP

0 π1/

N

-510

-410

p+Nb

p+p

2>700 GeV/ceeM

Transverse momenta

HADRON 2011 -‐ 17.06.11 20


eeY0 0.5 1 1.5 2 2.5

dN

/dY

0 π1/

N

-410

-310

-210

-110

2<0.150 GeV/ceeM

eeY0 0.5 1 1.5 2 2.5

dN

/dY

0 π1/

N

-510

-410

-310

-210

2<470 GeV/cee0.150 <M

eeY0 0.5 1 1.5 2 2.5

dN

/dY

0 π1/

N

-510

-410

2<700 GeV/cee0.470 <M

eeY0 0.5 1 1.5 2 2.5

dN

/dY

0 π1/

N

-610

-510

-410

p+Nb

p+p

2>700 GeV/ceeM

RapidiKes

HADRON 2011 -‐ 17.06.11 21


Isospin dependence

•  Dielectron cross sections in p+p and p+d at beam energies from 1.04 to 4.88 GeV measured with DLS

•  Decreasing mass dependence of pd/pp with increasing beam energy

•  pd cross section becomes approximately twice the pp cross section at all masses with increasing beam energy

W.K.Wilson et al., PRC 57 (1997) 1865

HADRON 2011 -‐ 17.06.11 22

Transparency ratio ? γ + A à ω/ρ + X p + A à ω/ρ + X

Low interaction probability à  Production in whole volume à  ~ Aα, α = 1

Strong interaction à  Production on surface à  ~ Aα, α = 2/3 BUT: secondary proction via pions à ~ Aα, α > 2/3

TA à absorption in nucleus à in medium width

TA à disentanglement of production and absorption à Model dependence

g A

p A

π

HADRON 2011 -‐ 17.06.11 23

pNb hadron2011 v3 - SLAC National Accelerator · PDF filep) MDC((Magnet)) β) TOF(ino))...

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