direct photon interferometry

Direct photon interferometry

D.Peressounko

RRC “Kurchatov Institute”

D.Peressounko, WPCF, Kromeriz, 2005 2

Outlook Photons are special:

Penetrating => Specific R(KT) dependence Massless => Unusual Rinv and inv interpretation Rare => Strong background

Experimental review Completed experiments

TAPS,WA98 Ongoing

PHENIX,STAR Developing

ALICE

Conclusions


Accessing space-time dimensions of different stages of the collision

Pb+Pb @ 17.2 AGeV

Rout Rside Rlong

•3+1 hydro with first order phase transition.•QGP phase includes pre-equilibrium pQCD contribution

D.P. Phys.Rev.Lett.93:022301,2004

QGP

mixed

hadr


KT dependence of photon correlation radii

RHIC Au+Au @ 200 AGeV

D.P. Phys.Rev.Lett.93:022301,2004

D.Srivastava, Phys.Rev.C71:034905,2005

T.Renk, hep-ph/0408218


Predictions for correlation radii

System Rout(fm) Rside(fm) Rlong(fm) Rinv(fm)

4.4 4.2 0.2 D.Srivastava, Phys.Rev.C71:034905,2005

4.3 3.9 1.2 3.0 D.Peressounko, Phys.Rev.Lett.93:022301,2004

ee

KT=1 GeV6.0 3.2 3.3* 3.2 J.Alam et al., Phys.Rev.C70:054901,2004

5.5 3.0 1.6* 3.0 J.Alam et al., Phys.Rev.C67:054902,2003

5.1 4.3 2.8 - T.Renk, hep-ph/0408218

*Not LCMS system

RHIC, Au+Au@200 AGeV, KT=2GeV


Qinv parameterization for massless particles

S(x) = exp( - t2/2 – x2/Ro2 - y2/Rs

2 - z2/Rl2),

C2(qo,qs,ql)=1 + exp( -qo2(Ro

2 +22) -qs2Rs

2 -ql2Rl

2)

C2(Qinv)=

∫d3q/qe C2(qo,qs,ql) (Qinv2+q2)

∫d3q/qe (Qinv2+q2)

= 1/(4)∫[1+ exp{-Qinv2(K0

2/M2cos2 (Ro2+22) + Rs

2 sin2sin2 + Rl2sin2cos2 ) }] d

= 1+invexp{-Qinv2Rinv

2)

Rinv = <Rs,Rl> (not Ro!) inv = 1/(4) ∫exp{ - 4KT2(Ro

2 + 2)cos2}d

For massless particles (,e) Qinv parameterization is very special!

(integrate in CM frame of the pair)


Qinv parameterization for massless particles (MC)

Set 1: Ro = 6 Rs = 6 Rl = 6

Set 2: Ro = 4 Rs = 6 Rl = 6

Set 3: Ro = 2 Rs = 6 Rl = 6

Set 4: Ro = 6 Rs = 4 Rl = 6

Set 5: Ro = 6 Rs = 2 Rl = 6

Set 6: Ro = 6 Rs = 4 Rl = 4

Set 7: Ro = 4 Rs = 4 Rl = 4

Set 8: Ro = 2 Rs = 4 Rl = 4

Set 9: Ro = 6 Rs = 2 Rl = 2

inv = Erf(2KT√Ro2 + 2)/(2KT√Ro

2 + 2)

inv=1/(2KT√Ro2 + 2)


Background photon correlations Bose-Einstein 0 correlations

Resonance decays

Collective flow

0

0

}

0

0

0

}


0 BE residual correlations

D.P. Phys.Rev.Lett.93:022301,2004

R=4 fm

R=5 fm

R=6 fm

C2=1+exp(-Qinv

2R2)



A.Deloff and T.Siemiarczuk,ALICE internal note INT-98-50

=1/2(k1-k2)

C2()=1+/(1+2R

2)2

dN/dp=p·epx(-p/[3GeV])



O.V.Utyuzh, G.Wilk, Nukleonika 49:S15 (2004), hep-ph/0312364

Varying width (and strength) Varying strength


TAPS: detector setup

BaF2 25 cm long (12 X0) prism of hexagonal cross section, the diameter of the inner circle being 5.9 cm (69% of the Moliere radius).

Min angle cut between photons 8.30

Distance to IP 62 cm

Typical photon energy ~10 MeV


TAPS: m distribution and C2

Geantsimulations

86Kr+natNi @ 60 AMeV 181Ta+197Au @ 40 AMeV

Comparison to BUU calculations


Number of events collected: Peripheral (20% min bias) 3897935Central (10% min bias) 5817217

WA98 setup


Two photon correlation functions


WA98: apparatus effectsLmin = 20 cm (5 modules)

Lmin = 25 cm (6 modules)



200 < KT < 300 MeV

100 < KT < 200 MeV

100 < KT < 200 MeV

200 < KT < 300 MeV


Hadrons and photon conversion

“Narrow” (16 + 1)% (4 + 1)%

“Neutral” ( 1 + 4)% (1 + 4)%

“All” (37 + 4)% (22 + 4)%

“Narrow neutral” (1 + 1)% (1 + 1)%

obs = =1 (N

dir)2

2 (Ntot + cont)2

Contamination, (charged + neutral)

100<KT<200 200<KT<300pid

true

(1+ cont/ Ntot)2


Photon background correlations

00 Bose-Einstein correlations:

Slope: -(4.5±0.4)·10-3 (GeV-1)

Elliptic flow:

Slope: -(3.1±0.4)·10-3 (GeV-1)

Decays of resonances:

K0s→20→4

K0L→30→6

→30→6→0→3


C2(Qinv) =1 + /(4) ∫ do exp{ - Qinv2 (Rs

2 sin2 sin2 + Rl2 sin2 cos2 )

- (Qinv2 + 4KT

2)cos2 Ro2 } R

Rlong

Rside

Rinv = f(Rs,Rl)

inv = Erf(2KTRo)

2KTRo

(for massless particles!)

Invariant correlation radius


Subtraction method,upper limit

Yield of direct photons

Correlation method:

Subtraction method

Predictions

hadronic gasQGP

sumpQCD

Predictions:S. Turbide, R. Rapp, and C. Gale, hep-ph/0308085.

Ndir = N

total √2

inv = Erf(2KTRo)

2KTRo

Most probable yield (Ro=6 fm)The lowest yield (Ro=0)


PHENIX setup

Lead ScintillatorLead + scintillatingplates of 5.5*5.5 cm2 at a distance 510 cm from IP.

Lead GlassPbGl crystals4*4 cm2 cross sectiondistance 550 cm from IP


PHENIX: Comparison to data

d+Au collisions at √sNN=200 GeV


STAR

Use 1 gamma in TPC, 1 gamma in calorimeter.

A procedure has been developed which permits the measurement of gamma-gamma HBT signals despite the large background of gammas from π0 mesons

Gamma energy > 1.0 GeV is required for the residual π0 correlation to be “small”

“No HBT” calculation may be needed but appears to be doable.

Conclusions from the talk of J. Sandweiss on “RHIC-AGS users meeting”, June 21, 2005, BNL:


ALICE setup

PHOS:crystals PbW04

2*2 cm cross section Distance to IP 460 cm


ALICE: unfolding and resolution


ALICE: photon correlations in HIJING event

Kt=200 MeV


Summary Direct photon and electron interferometry is

rather special subject due to penetrating nature, zero mass and low yield.

Two-photon correlations were observed in two experiments up to now.

Photon correlations are analyzed now at PHENIX and STAR.

PHOS detector at ALICE is very promising tool due to fine granularity and high spatial and energy resolutions.


PHENIX: MC simulations

Kt = 0.2 GeV

Using measured spectra and yields for 0, kaons and

K+→

K0S→

K0L→30

→30

c=4.7 m

c=15. m

c=0.02 m


Jan-e Alam et al., ee correlations

J.Alam et al., Phys.Rev.C70:054901,2004

KT=1 GeV

Not LCMS


T.RenkSide

Long

side

out

T.Renk, hep-ph/0408218


Penetrating probes: probe all stages?

RHIC Au+Au @ 200 AGeV

D.P. Phys.Rev.Lett.93:022301,2004


Possible sources of distortion of correlation function

Apparatus effects (cluster splitting and merging) Hadron misidentification Photon conversion Photon background correlations:

Bose-Einstein correlations of parent 0; Collective (elliptic) flow; Residual correlations due to decays of resonances;

direct photon interferometry

Documents

mev100 kt

14p1 exp

mev200 kt

modules200 kt

photon conversionnarrow

massless particles mc

massless particles g

cmtypical photon energy