dnp/jps joint mtg, maui – sep. 20, 2005 g. david, bnl

DNP/JPS joint mtg, Maui – Sep. 20, 2005 G. David, BNL

Direct Photons(Electromagnetic Probes) at RHIC-II

Joint DNP/JPS Meeting, Sep. 18-22, Kahului, Maui

G. David, BNL

Inspired by and based largely upon the work done in the RHIC-II Electromagnetic Probes Physics Working Group

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At RHIC we created a new form of matter - there’s no arguing about this

So far its properties seem to be quite different from the ones anticipated

Plethora of data, rapid evolution of theory – but quite far from a coherent picture

Fast transition from phenomenological (bulk) description to dynamical (mechanisms) and the number of question marks is rising (no surprise)

Case in point:

What Is Certain and What Isn’t

S.Turbide, R.Rapp and C.Gale, Phys. Rev. C 69, 014903 (2004). 2


Two Groups of Questions / 1

When and how does deconfinement occur?

So far we have seen the “ no sQGP” and the “fully developed sQGP” -- but where exactly is the transition (system size, energy density)? -- what makes it thermalize in incredibly short times (~0.1-0.5 fm/c)? -- is chiral symmetry restored (at least partially)? ( e.m. probes! )

EoS with phase transition

EoS without phase transition

D.d'Enterria and D.Peressounko,nucl-th/05030543


Two Groups of Questions / 2 What are the properties (physics mechanisms) in the new matter?

We know it has a large degree of collectivity and it is very opaque -- but what exactly causes jet quenching? ( e.m. probes an important clue! ) -- does it harbor bound states, resonances? ( e.m. probes unique! ) -- do vector meson masses drop or broaden? What happens to the yields? ( e.m. probes! ) -- …

Zakharov (hep-ph/0405101)

No quenching

w/ quenching

– Bremsstrahlung contribution only!

– Potential increase in bremsstrahlung yield in medium.

– More important:

• Energy & kT

spectrum will directly reflect medium properties.

•Jet conversion will produce more photons out-of-plane than in-plane

Negative v2 for these “jet quenching” photons

(Brian Cole)4


RHIC – II - a Process to Explore What We Found

RHIC-II is not so much a milestone as a process -- detector upgrades (higher precision, signals currently not accessible) -- luminosity upgrades (rare probes, more systematic studies – species, energy) -- path to a “QCDLAB”

Upgrades High T QCD…. QGP Spin Low-x

PHENIX

e+e- heavy jet quarkonia

flavor tomog.

W ΔG/G

Hadron blind detector

Vertex Tracker

Muon Trigger

Forward cal. (NCC)

X

X X O O

O

O O

X X

O

O

X

STAR

Time of Flight (TOF)

MicroVtx (HFT)

Forward Tracker

Forward Cal (FMS)

DAQ 1000

O X O

X X

O

O X X

X O

O

O O

X

O

RHIC Luminosity O O X X O O O

(Axel Drees)X OCritical Significant improvement

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(Craig Woody)

PHENIX dielectrons: expected improvement with HBD

Exploration Means Detector Upgrades

Goal: reduce

combinatorial background

to a level where

background from charm

dominates the

signal

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Na60 – Damjanovic, QM2005

For the first time, and peaks clearly visible in dilepton channel

Mass resolution:23 MeV at the position

μμ channel also seen

Exploration Means Precision / 1

Baseline for the future:

perform as well as this – or better!

A shining (and recent) example I couldn’t resist showing

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Predictions for In-In by Rapp et al (2003) for ⟨dNch/d⟩ = 140, covering all scenarios

Theoretical yields, folded with acceptance of NA60 and normalized to data in mass interval < 0.9 GeV

Only broadening of (RW) observed, no mass shift (BR)

High quality data to differentiate between theories

Exploration Means Precision / 2

Disclaimer: BR have an

argument with this calculation!

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Exploration Means Luminosity Upgrades

PHENIX published direct photon excess

200 GeV AuAu – direct photons, photon and 0 RAA

Run-2 Run-4

Although the message is clear, the measurement is starving for statistics even in Run-4 (and this is just one system, one energy!)

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Exploration Means Novel Approaches / 1 • Calculate ratios of various Minv bins to lowest one: Rdata

• If no direct photons: ratios correspond to Dalitz decays• If excess: direct photons

0

0

direct

data

incl.

direct

*

*

RR

RR

incl.

direct

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Direct photons measured by internal conversion compared to the new (Run-4) “classic” photon excess measurementBeing a low efficiency method it would benefit from much higher statistics!

(Yasuyuki Akiba)

Exploration Means Novel Approaches / 2

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(Dave Morrison)

Npart

Ncoll

eccentricity

b(fm)

At RHIC we can turn quite a few “knobs” by varying the energy, species and

making asymmetric collisions

One of RHIC’s Strengths: Play With Geometry

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…with the detector and luminosity upgrades

Turbide et al Jet conversion – need v2 at very high pT!

A Few Examples of What We Expect to See/Rule Out / 1

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Dielectron mass shift or broadening

(Rapp, van Hees)


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suppression of low mass dileptons (???)

in sharp contradiction with perturbative expectations predicting enhancement at low energyBraaten, Pisarski, Yuan, PRL 64 (90) 2242

(Petreczky)

qMM /

R

MeVq 10

qMM /

R

MeVq 100

dM

dNdM

dN

R pert

ll

ll

(Casalderrey-Solana)


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Summary

RHIC – the accelerator and the experiments – are successful beyond all

prior expectations

We’ve seen something completely new and already our first results

revolutionized theory

Detailed exploration of the transition and the properties of the medium with

high precision measurements will mean a quantum leap in our

quantitative understanding of strong interactions

We need additional tools in order to fully utilize RHIC’s tremendous possibilities

Remember: that’s not in the sky -- we already delivered!

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dnp/jps joint mtg, maui – sep. 20, 2005 g. david, bnl

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