direct photon and high-pt 0 correlations with alice dongjo,kim jyväskylä university, finland

Direct photon and high-pT Direct photon and high-pT 00 correlations with ALICEcorrelations with ALICE

DongJo,Kim Jyväskylä University, Finland

Apr 18, 2023 DongJo Kim 2

Motivation Motivation pQCD jet quenching :

• Similar suppression pattern of high-pT electrons from semi-leptonic D and B mesons decays; PRL 91, 172302 (2003) • No broadening of the associated correlation peak (nucl-ex/051000) in contrast to “standart picture” e.g. Phys. Lett. B630, 78 (2005)• Induced gluon radiation should violate the xT scaling, not seen in 0 seen in h. E.g. Brodsky, Pirner and Raufeisen, hep-ph/0510315.• Why NLO pQCD work without kT ?

Detailed understanding of “unmodified” parton properties in p+p is crucial p+p data @ RHIC and LHC

• Fragmentation function D(z)

• Jet shape

jT jet fragmentation transverse momentum

kT parton transverse momentum


pQCD quenching - modification of pQCD quenching - modification of D(z) D(z)

Fragmentation strongly modified at pThadron~1-5 GeV

even for the highest energy jets

=ln(EJet/phadron)

pThadron~2 GeV for

Ejet=100 GeV

Borghini and Wiedemann, hep-ph/0506218

• MLLA: parton splitting+coherence angle-ordered parton cascade• Theoretically controlled, experimentally verified approach

• Medium effects introduced at parton splitting


Width of Away-Side Peaks - where is broadening Width of Away-Side Peaks - where is broadening ??

• away-side widths similar for central and peripheral

d+Au 0.24+-0.07 rad

Au+Au 20-40% 0.20+-0.02 rad

Au+Au 0-5% 0.22+-0.02 rad

• Where is the jet broadening at RHIC? How about LHC?

STARSTAR

nucl-th/0308028

Leading Particle

Reconstructed Jet

STAR nucl-ex/0604018

8 < pT(trig) < 15 GeV/c

I. Vitev


kkTT physics physics

Reference to heavy ion:

• Broadening in the “punch through” - high-pT ?

• Broadening in the “Mach cone” - low-pT ?

Understanding of (p)QCD phenomena

• k2T evolution with s.

• k2T associated to direct photons.

• Resummation techniques Vogelsang,Sterman,Keusza Nucl

Phys A721,591(2003).

• NLO physics - pout distribution.


Hard scattering – kHard scattering – kT T

LongitudinalLongitudinal

jetjet

jetjet

s

transverse

• acoplanar in PL PT space• acoplanar in PX PY space

LongitudinalLongitudinal

jetjet

jetjet

s

kT measures the accoplanarity of the two back-to-back jets in transverse plane

kT measures the accoplanarity of the two back-to-back jets in transverse plane

dσdy2 y1=0

∝ e−sl⋅xT coshy2

−log2xT

< y2 < log2xT

dσdy2 y1=0

∝ e−sl⋅xT coshy2

−log2xT

< y2 < log2xT


Origin of kOrigin of kTT

Intrinsic kT “fermi motion” Soft QCD NLO radiation. As an example - J/ production.

pTJ/ =1.80.230.16 GeV/c

Phys. Rev. Lett. 92, 051802, (2004).

€

kT2 =

pT ,pair2

2= kT

2

intrinsic+ kT

2

NLO+ kT

2

soft

Power law tail @ large value of pT,pair

Gussian @ pT,pair0 Leading-Log resummation Vogelsang,Sterman,Keusza Nucl Phys A721,591(2003)

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.


Soft Gaussian + Soft Gaussian + hard power lawhard power law

D. Boer and W. Vogelsang,Phys. Rev. D69 (2004) 094025

J. Qiu and I. Vitev,Phys. Lett. B570 (2003) 161

radiative tails

STARp+p

p+p

Phys. Rev., 1981, D23, 604

QuickTime™ and aTIFF (LZW) decompressor



oo - h - h correlation correlation functionsfunctions

p+p p+p s=200 GeVs=200 GeV

d+Au

Corrected for acceptance

σN

σA

σN jT jet fragmentation transverse mom.

σF kT parton transverse momentum

YA folding of D(z) and final state PDF.

p + p jet + jet

pout


Trigger biasTrigger biasThere are ALWAYS two types of trigger biases when correlating pTtriggerpTassoc

z-bias; steeply falling/rising D(z) & PDF(1/z)

ztrig

zassoc

Selecting events with pTt > pTa forces kT vector toward trigger jet:

ˆ ˆTtrigg Tassocp p>

hat-xh bias

kT


Trigger associated spectra are Trigger associated spectra are insensitiveinsensitive to to D(z)D(z)

LEP data

M.J. Tannenbaum Approximation - Incomplete Gamma function when assumed power law for final state PDF and exp for D(z)


kk22TT, , zztt in p+p @ 200 GeV in p+p @ 200 GeV

ISR

We gave up an effort to extract fragmentation function from di-hadron data, direct photon analysis under way. For D(z) the LEP date were used.

PHENIX

€

ˆ x h−1 zt kT

2 = xh−1 pout

2 − jTy2 (1+ xh

2)Iterative solution for each pT bin by varying k2

T

Systematic errors comes from unknown ratio gluon/quark jet => D(z) slope.


NLO at work at RHIC.NLO at work at RHIC.

Good agreementwith NLO pQCD

Phys.Rev.Lett.91:241803,2003

p+p0+X p+pdirect +Xp+p0+X


High pHigh pTT: ref. for HI, resummation, : ref. for HI, resummation, detailed NLO testsdetailed NLO tests

PHENIX measured pTpair=3.360.090.43GeV/c

extrapolation to LHC k2T=34 GeV2/c2


LO pQCD and inclusive yieldLO pQCD and inclusive yield

LO gets the data only when Gaussian smearing of order of k2T3 GeV/c used.LO gets the data only when Gaussian smearing of order of k2

T3 GeV/c used.

P. Levai


Trigger Trigger associated spectra are associated spectra are sensitivesensitive to to D(z)D(z)

ztrig

zassoc

d 2σdpTtdxE

=dpTa

dxE

⊗d2σ

dpTtdpTa

;1xh

D(zt)D(ztpTa)xhpTt

)Σ'

xTt

x.pTt/ pTa

∫ (pTt

zt

)dzt

Di-hadron correlations

Direct photon correlations D(zt) (zt)

d 2σdpTtdxE

=dpTa

dxE

⊗d2σ

dpTtdpTa

;1)pTa

Σ' pTa)pTa

⎛

⎝⎜⎞

⎠⎟D

pTa)pTa

⎛

⎝⎜⎞

⎠⎟

No trigger bias - associated spectra reflect the actual Fragmentation Function


Direct photon measurementDirect photon measurement

hep-ph/0311131hep-ph/0311131

Very Challenging measurement:

/0 < 0.1 in accessible kinematic region

CTEQ5


How to construct direct How to construct direct -h yield -h yield

i. Construct inclusive -h yield

ii. Construct decay -h yield via:

– Pair by pair weighted summation method i. convolutes all 0-h pair contributions

from higher pT

ii. Weight reflects the probability from kinematics for a 0 at given pT to decay into a photon in a given pT range

iii. Subtraction via:

)1

(/11

1hdechinchdir Y

RY

RY −−− −

−=


-h correl. fcn. in p+p @ √s = 200 GeV -h correl. fcn. in p+p @ √s = 200 GeV comparison to PYTHIAcomparison to PYTHIA


Pythia CKIN(3) Triggered Pythia CKIN(3) Triggered 00 yield yield

CKIN(3) values correspond to minimum of hard 22 process.

)pT

Effectively similar effect as online tower threshold cut. The only thing which is not correct is the absolut normalization (xsection). This can be done by matching renormalization in the overlap region (if there is such a region.)

I show 200 GeV p+p data because we know them best.


Pythia 200 GeV Pythia 200 GeV 00 yield yield

Kinematical limit 100 GeV/c!

Below 20 GeV/c the spectrum is power law with n=7 (n=8 in the case of invariant xsection). Phase space factor at pT>20 GeV/c turned the pQCD power low in “non perturbative” exponential.


Cross Check to go for correlationsCross Check to go for correlations

PYTHIA6.323CTEQ5


High pT Direct High pT Direct ’s : for cross check…’s : for cross check…

LO • q+g q+ (Compton scattering) >>• q+q g+ (Annihilation process)@high energy, only the compton process is relevant

NLO• bremsstrahlung, fragmentation


@high pT (Ktmode=1,ckin3=8)@high pT (Ktmode=1,ckin3=8)

16<pTt<20 GeVpTa :2,3,4,5,7,8,10,15,20GeV


XXEE distributions : k distributions : kT T effect (I) effect (I)

There is no difference from

0-h with <kT>2 = 3 GeV

• kT effect is quite clear


QuickTime™ and aTIFF (Uncompressed) decompressor


PYTHIA -h @ 200GeVPHENIX 0-h @ 200GeV

• kT makes xE slope steeper in lower pT but it is not much in higher pT

• Caution : “fitting” is not finalized yet for this study

• Looking at p+p data with strict isolation cuts etc

XXEE distributions : k distributions : kT T effect (II) effect (II)


Conclusion and perspectivesConclusion and perspectives• High pT 0 suppressionin HI itself poorly informs us on how exactly

the produced medium affects the propagation and the hadronization of

high-energy quarks and gluons.

• From 0 -h correlation is not sensitive on the determination of fragmentation

– PHENIX measured pTpair=3.360.090.43GeV/c

– extrapolation to LHC k2T=34 GeV2/c2

– But Trigger bias

• Need -h correlation

• PHENIX used “substraction” method , agreed with PYTHIA

– Need more detail study

• PYTHIA shows kT effect is stronger in low pT < 4, and almost no effect in high pT

• Data are being looked at with more strict isolation cuts etc.

direct photon and high-pt 0 correlations with alice dongjo,kim jyväskylä university, finland

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