PHENIX Single Non-Photonic Electron Spectra and v 2

4/12/2006N. Grau, Journal Club 1

4/12/2006

PHENIX Single Non-Photonic Electron Spectra

and v2

Nathan Grau

Journal Club

April 12, 2006


4/12/2006

Outline

• What do single electrons tell us?– Light quarks, heavy quarks, direct production

• Why is that interesting?– Heavy quarks have a perturbative scale mQ

– Light vs. heavy quark differences

• How do we measure them?– Need to remove large backgrounds

• What do we conclude?


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Sources of electrons

• Physics sources of electrons– Light quarks/hadrons

e+e-, e+e-

• Ke, etc.• Dalitz decay 0 e+e-, etc.

– Heavy quarks/hadrons• J/ e+e-, Y e+e-

• D Ke, etc.

– Direct production• •

• Other sources of electrons– Internal conversion of

photons in material

• Note: almost everything here is true about muons as well.

eeqq eqeqqg


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Two definitions

• Inclusive electrons are all of these sources• Non-photonic electrons are those not from light hadron

decay and from internal conversions and virtual direct photon production– Primarily from heavy flavor decays and Drell-Yan

– Drell-Yan is small component down by a factor of 100 because of EM

– New sources of electrons in A+A?• Enhancement of low mass dileptions?

• Thermal radiation?


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Why not just measure heavy quarks directly?

• Typically charm and bottom are measured from their quarkonia spectra– PHENIX does this at least for J/

• Open charm and bottom are also typically measured from displaced vertices– c ~ 100 mm for D and ~200 mm for B– PHENIX can’t do this yet

• Measure open charm in the hadronic decay channel– DK, D– After three years still don’t see it (but STAR does)

• Measuring electrons maximizes usage of statistics– Catch more of the branching ratio


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Interest in Heavy Flavors

• In HIC we would like a probe that is– Strongly interacting with the medium

• Heavy quarks have color charge

– Survive the hadronization process of the plasma• See the next couple of slides

• Heavy flavors compared to jets– Can be calculated perturbatively: S(mQ) << QCD

– Auto-generated in the interaction in similar processes.


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But this i

s a long and complicated story that T

atia

will probably fil

l us in on in a couple of w

eeks!


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Initial Expectations for Heavy Quark Energy Loss

• Heavy quarks from hard scattering traverse the medium and lose energy– Survives QGP hadronization.

• “Dead cone” effect– Can someone please explain the dead cone effect to me.

I really couldn’t find a clear explanation in the literature.


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Heavy-to-Light Comparison

• Ratio of heavy quark RAA to light quark RAA.

• 20% higher RAA predicted for heavy quarks at 5 GeV.

RA

AQ/R

AA

q

Dokshitzer & Kharzeev PLB 519 199 (2001)

quark pT


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Anisotropy of Heavy Quarks (I)

• Flow results from 2 sources– Pressure gradients in the overlap region of the nuclei

• Low pT, hydrodynamics

– Path length dependent energy loss• High pT

• Question: Do heavy quarks couple as strongly to the medium as light quarks?– We should measure it!


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Anisotropy of Heavy Quarks (II)

• Another question: Less energy loss for heavy quarks, but does that necessarily reduce the anisotropy?

yx

yx

lightpp

pp

lightheavy fpp if

light

yx

yx

heavyfpfp

fpfp

! We should measure it!

(Good to <10% from Dokshitzer and Kharzeev)


4/12/2006

Electrons in PHENIX

• Identification by– Charged track in DC/PC

• Momentum, charge, position

– Associated hit in RICH• Electrons only fire up to 3.5 GeV

• Muons and pions then fire– Muons are rare

– Associated EM cluster in calorimeter


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Final Spectra

• Inclusive Electrons

• Need to determine the photonic contribution

0-10% 10-20% 60-80%


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Cocktail Method

• Parameterize the measured 0 spectrum as a function of centrality

• Assume that all other light mesons mT scale, confirmed by spectrum

• Conversion photon spectrum determined from PISA simulation

• Direct photons parameterized from NLO fit

• Kaon spectrum parameterized from data

• Run EXODUS which randomly picks from the given distribution and decays if necessary


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Non-Photonic Spectrum (I)

• Comparison of the minimum bias cocktail and converter spectra– Note that the cocktail is

much more precise

• Excellent agreement


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Non-Photonic Spectrum (II)

• Published spectrum– The line

indicates a fit to the p+p spectra

– Note no centrality above 60%?

– Suppression observed at high-pT in all centrality


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RAA

• A dramatic suppression is seen at high pT.– Comparable to suppression

of 0

• Is this misleading, shouldn’t we shift the electron spectrum to the left in order to compare heavy and light quark suppression?


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What about >60% Centrality?

• We have spectra that compares well to the converter method• But RAA looks terrible! Was PHENIX just sneaky?• The paper claims “More peripheral collisions have insufficient

electron statistics to reach pT = 5 GeV/c.”• The 0 spectra do not reach to the same pT in all centrality bins…


4/12/2006

What can we say about heavy quark Eloss?

• Comparison of data to theory• 1a-1c BDMPS (next weeks talk)

calculation of charm only for– a: no medium, only Cronin– b: – c:

• 2a-2b GLV calculation with charm and bottom, bottom pulls up the RAA because of dead cone.– a: – b:

• Very extreme range of densities and opacities!

/fmGeV 4ˆ 2q

/fmGeV 14ˆ 2q

1000/ dydN g

3500/ dydN g


4/12/2006

Gluon Contribution to Spectrum?

• A hard gluon from a hard process could split (fragment?) to Q-Qbar and create two hard mesons

• If the formation time for such a splitting is longer than say the lifetime of the plasma, the gluon would lose the energy and this would be reflected in the resulting charm hadrons.– Because the gluon is fast, gamma is large and there will be a time

dilation in it’s “decay”

• No calculation of this I have found• p+p spectrum errors leave room for this production• Is it implemented in pythia?


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Summary on Spectra

• This is an open topic at the moment

• No calculation can reproduce the observed spectra based on both charm and bottom contributions

• On the face it seems that the charm and bottom loose as much energy as light quarks and gluons…

• What about the coupling to the medium– i.e. do heavy quarks flow?


4/12/2006

Extracting Inclusive Electron v2

• Measure the azimuthal angle wrt for both candidates and background

• Subtract background from total to get signal and fit

2cos21 20 vN


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Inclusive Electron v2


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Obtaining Non-photonic electron v2

photnonphot

photnonphotnonphotphotinc

photnonphotinc

incincinc

photnonphotnonphotphotinc

photnonphotinc

NN

vNvNv

NNN

vNd

dN

vNvNd

dN

d

dN

d

dN

d

dN

222

2

22

2cos21

2cos212cos21

Inclusive electron v2 is a weighted average of the components. True for any v2!


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Obtaining Photonic v2

• Just use a cocktail similar to the singles spectra

• EXODUS modified to produce a random RP and distribution of the generated particles.

• Study electron v2 given input v2 and spectra

+/- and 0 as input


4/12/2006

Cocktail Sources

• Cocktail sources (in order of importance) 0 Dalitz(previous slide) and conversion (run through

PISA)• Not suprisingly similar v2.

Dalitz decay, assume v2 = kaon v2, spectrum mT scales– K decay, use measured v2 and spectra of K and STAR’s

Ks0

• Nothing else without further assuming about heavier particle v2 (J, etc.)


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Cocktail Results

• The resulting v2 for the different components

• Relative contribution to the total is also known from the cocktail

e v2 from 0 Dalitz e v2 from K

e v2 from Dalitz


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Non-photonic Electron v2 Results

• The paper claims a 90% confidence level that non-photonic electron v2 !=0– Why does that

seem too low?

– All points except on are >0 at 1.5?


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But I’m Missing the Point

• Non-zero non-photonic electron v2!

• And it is consistent with charm flow!

• Is recombination believable?


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The Summary

• PHENIX has measured single non-photonic electron spectra and v2 and found that– High-pT electrons are suppressed wrt binary scaled p+p collisions to the level of 0

– There is a non-zero v2.

• In RUN-4 these results have been extended to

– Better the stats

– Centrality binning

• Other things that are necessary– Extending the pT reach of the electron spectra

• Only reason stopping them at 5 GeV/c was pion turnon in RICH

• Need to do this in p+p as well

– Measure charmed hadrons and measure there v2

• J/ v2 ongoing analysis (but Tatia will let us know if we can distriminate between partonic flow + recombination, etc. with the J/)


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Backup Slides


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Electron ID details

• Exactly the same cuts for both analyses– High quality tracks

• Excellent p resolution, S/B?

– 2 matching to EMCal• Cluster association, multiple

scattering

– n0>=3, n3>=1 (number of pmts with good timing fired)

• ?

– -2 < E/p < 3

Overall S/B for 0.5-5 GeV/c is very good ~10/1


4/12/2006

Electron ID Background

• Background is determined by the swap variables– z -z of hits reassociate RICH and EMCal hits– Good for determining random association

• Why is the background not the same shape as the tails?

• Effect on the single particle spectrum and for the flow analysis– Just subtract off the background spectrum and

dn/dshape from the measured spectrum and dn/d


4/12/2006

Acceptance and Efficiency

• Acceptance– Amount of dead area within

the fiducial region– Study by PISA with detector

response tuned to data

• Efficiency– In active area probability for

finding the electrons given the cuts in the analysis

– Study by embedding single particles into real events

1/(A

cc*E

ff)

pT


4/12/2006

Measuring the RP

• wi are weights, could be n for number of particles in the ith bin, pT for pT flow correlations

Qn n

=0

Documents

PHENIX Single Non-Photonic Electron Spectra and v 2