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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. 1. DNP/JPS joint mtg, Maui – Sep. 20, 2005 G. David, BNL. - PowerPoint PPT Presentation
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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
1
DNP/JPS joint mtg, Maui – Sep. 20, 2005 G. David, BNL
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
DNP/JPS joint mtg, Maui – Sep. 20, 2005 G. David, BNL
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
DNP/JPS joint mtg, Maui – Sep. 20, 2005 G. David, BNL
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
DNP/JPS joint mtg, Maui – Sep. 20, 2005 G. David, BNL
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
5
DNP/JPS joint mtg, Maui – Sep. 20, 2005 G. David, BNL
(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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DNP/JPS joint mtg, Maui – Sep. 20, 2005 G. David, BNL
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
7
DNP/JPS joint mtg, Maui – Sep. 20, 2005 G. David, BNL
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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DNP/JPS joint mtg, Maui – Sep. 20, 2005 G. David, BNL
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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DNP/JPS joint mtg, Maui – Sep. 20, 2005 G. David, BNL
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
10
DNP/JPS joint mtg, Maui – Sep. 20, 2005 G. David, BNL
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
11
DNP/JPS joint mtg, Maui – Sep. 20, 2005 G. David, BNL
(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
12
DNP/JPS joint mtg, Maui – Sep. 20, 2005 G. David, BNL
…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
13
DNP/JPS joint mtg, Maui – Sep. 20, 2005 G. David, BNL
Dielectron mass shift or broadening
(Rapp, van Hees)
A Few Examples of What We Expect to See/Rule Out / 2
14
DNP/JPS joint mtg, Maui – Sep. 20, 2005 G. David, BNL
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)
A Few Examples of What We Expect to See/Rule Out / 3
15
DNP/JPS joint mtg, Maui – Sep. 20, 2005 G. David, BNL
A Few Examples of What We Expect to See/Rule Out / 4
16
DNP/JPS joint mtg, Maui – Sep. 20, 2005 G. David, BNL
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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