Transcript Heavy flavor measurements at RHIC energies … present and

Non-photonic leptons and
charm production at RHIC
an experimental overview
Alexandre Suaide
University of São Paulo – Brazil
RHIC white papers: many new things…
... and still many questions.
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RHIC has produced matter that behaves differently
from anything we have seen previously...
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Can we fully describe it?
Can we see the phase transition/critical point?
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... is dense (many times cold nuclear matter
density)...
... is dissipative...
... exhibits strong collective behavior...
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Lower energies, different system sizes?
Does dissipation and collective behavior both occur at the
partonic stage? How partons interact with matter?
... and seems to be thermally equilibrated
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Is it?
Alexandre Suaide
University of São Paulo, Brazil
Quark Matter 2006
Shanghai, China
2
How heavy flavors can help in this search?
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Heavy quarks are ideal
probes for medium created
at RHIC
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Two ways of doing that
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Quarkonium investigation
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Deconfinement
Medium thermometer
B. Mueller, nucl-th/0404015
D mesons
Open heavy flavor
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Production mechanisms
thermalization
Interaction with the medium
tomography
Alexandre Suaide
University of São Paulo, Brazil
Quark Matter 2006
Shanghai, China
, Y’, c
3
Open heavy flavors
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Useful tool to probe the
medium
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(or m)
Yield, spectra, correlations, jets…
How do we do it?
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Hadronic reconstruction
 Clean probe, but difficult in
high multiplicity environments
Semi-leptonic decays
 Easier, but depends on ‘magic’
to disentangle flavors
Alexandre Suaide
University of São Paulo, Brazil
Quark Matter 2006
Shanghai, China
4
How do we measure it?
• Designed for leptonic
measurements
• Low radiation length
• Open heavy flavors
• Electron
measurements
and muons
• Quarkonia states
Alexandre Suaide
University of São Paulo, Brazil
• Large acceptance and
efficiency
• Good particle identification
• dE/dx, EMC and ToF
• Open heavy flavors
• hadronic
reconstruction, muons
and electrons
• Quarkonia states depend
on special triggers
Quark Matter 2006
Shanghai, China
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How do we measure it?
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Phenix
 Electrons
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Muons
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Electromagnetic calorimeter
and RICH at mid rapidity
Muon arms at forward
rapidities
STAR
 Hadronic reconstruction of Dmesons
 Muon identification with
TPC/ToF
 Electrons
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p
m
ToF + TPC for low momentum
(pT<4 GeV/c)
EMC + TPC for high
momentum (pT>1.5 GeV/c)
Alexandre Suaide
University of São Paulo, Brazil
Quark Matter 2006
Shanghai, China
6
Not all electrons come from heavy flavor
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Most of electrons are originated from
sources other than heavy flavors
 g  e+ + e- (small for Phenix)
 p0  g + e+ + e h, w, f, etc.
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Phenix is almost material free, so their
background is highly reduced when
compared to STAR
So,
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PHENIX
keep in mind that electrons
go through a lot of plastic surgery
Phenix applies two different methods
with very good consistency between
them
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Converter method
Cocktail method
STAR has the advantage of being
capable of measuring the background
despite the amount of material
Alexandre Suaide
University of São Paulo, Brazil
Quark Matter 2006
Shanghai, China
Mass (GeV/c2)
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Knowing that experiments are
capable of measuring heavy
flavors at RHIC, lets go through
some findings.
3 main topics to discuss
1. Total charm cross section
2. Interactions of heavy flavors with the medium
3. Separation of charm from bottom at RHIC
Alexandre Suaide
University of São Paulo, Brazil
Quark Matter 2006
Shanghai, China
8
Production mechanisms
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Charm quarks are
believed to be
produced at early
stage by initial gluon
fusions.
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(M. Gyulassy & Z. Lin,
PRC 51 (1995) 2177)
Sensitive to initial
gluon distribution
Nuclear and medium
effects in the initial
state
Alexandre Suaide
University of São Paulo, Brazil
Quark Matter 2006
Shanghai, China
9
Baseline – production in p+p collisions
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depends on:
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M. Cacciari et al., PRL 95:122001,2005
Heavy Quark production is a
“hard” process pQCD
Calculation on NLO
Quark mass mc, mb
Factorization scale mF
(typically mF = mT or 2mT)
Renormalization scale mR
(typically mR = mF)
Parton density functions
(PDF)
Fragmentation functions
(FF) – plays important role
Fixed-Order plus Next-toLeading-Log (FONLL)
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designed to cure large logs
for pT >> mq where mass is
not relevant
Alexandre Suaide
University of São Paulo, Brazil
Quark Matter 2006
Shanghai, China
10
Charm cross section from STAR
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Use all possible signals
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D mesons
Electrons
Muons
Y. Zhang (STAR), Hard Probes 2006
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Charm cross section is
well constrained
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95% of the total cross
section
Direct measurement m
D-mesons and muons
constrain the low-pT
region
Alexandre Suaide
University of São Paulo, Brazil
p
Quark Matter 2006
Shanghai, China
11
Charm cross section from PHENIX
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Many different
datasets
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Non-photonic
electron spectra
Improving statistics
over time
Reducing pT cut
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hep-ex/0609010
Reduces extrapolation
uncertainties
Alexandre Suaide
University of São Paulo, Brazil
Quark Matter 2006
Shanghai, China
12
Charm production at RHIC: total cross section
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FONLL as baseline
 Large uncertainties due
to quark masses,
factorization and
renormalization scale
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Phenix about a factor of 2
higher but consistent within
errors
 Only electrons but less
background
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STAR data about a factor of
5 higher
 More material but it is the
only direct measurement
of D-mesons
 95% of the total cross
section is measured
Alexandre Suaide
University of São Paulo, Brazil
Quark Matter 2006
Shanghai, China
13
Charm production at RHIC: total cross section
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Data from both
experiments
independently
indicate total cross
section follow Nbin
scaling
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Charm is produced by
initial collisions
No room for thermal
production in the
sQGP
Alexandre Suaide
University of São Paulo, Brazil
Quark Matter 2006
Shanghai, China
14
Charm production at RHIC: spectra shape
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Does FONLL describe
the spectral shape
despite of any
normalization
discrepancy?
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Both STAR and
PHENIX recently
submitted electron
spectra up to about 10
GeV/c
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How do they compare
to FONLL?
Alexandre Suaide
University of São Paulo, Brazil
Quark Matter 2006
Shanghai, China
15
Charm production at RHIC: spectra shape
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Experiments do not agree
to each other
 Low material in Phenix
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-2
FONLL describes the
shape well
Less electron
background to subtract
Direct measurement of
D-mesons at STAR and
low-pT m
Is this shown only at
high-pT?
2
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1/(2pNevpT)d N/dpTdy [(GeV/c) ]
10
0
STAR Combined fit MB
m, electrons and D-mesons
10
-1
10
-2
10
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10
-4
10
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0,0
Phenix MB Au+Au data
0,5
1,0
1,5
2,0
2,5
3,0
pT [GeV/c]
Alexandre Suaide
University of São Paulo, Brazil
Quark Matter 2006
Shanghai, China
16
Charm cross section: the issue
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STAR and PHENIX reported charm cross
section in different collision configurations
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Data are self-consistent within experiments
Both cross section and spectral shapes
Are
the
discrepancies
stoppers
 Both
suggest
Nbin scaling in show
the cross
section
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on
the understanding of the interaction between
heavy quarks and the medium created at RHIC?
 But experiments do not agree to each other
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PHENIX is a factor of ~2 lower than STAR
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D-mesons/muons/electrons measurement vs. Lower
electron background
Very important issue to be addressed in the next months
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Low material run at STAR and more precise D-mesons
measurements are needed
Alexandre Suaide
University of São Paulo, Brazil
Quark Matter 2006
Shanghai, China
17
Energy loss in the medium
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Light quarks
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High pT suppression / quenching of away-side jet
for light quark hadrons
Pedestal&flow subtracted
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Can we learn something about the medium?
Alexandre Suaide
University of São Paulo, Brazil
Quark Matter 2006
Shanghai, China
18
Energy loss in the medium
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Strong suppression observed for light quarks
creates bias towards surface emission
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Medium is extremely opaque for light quarks
K.J. Eskola, H. Honkanken, C.A. Salgado, U.A. Wiedemann, Nucl. Phys. A747 (2005) 511
Increasing density
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What about heavy quarks?
Alexandre Suaide
University of São Paulo, Brazil
Quark Matter 2006
Shanghai, China
19
Open Heavy Flavors – Energy Loss in Medium
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In vacuum, gluon radiation
suppressed at q < mQ/EQ
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“dead cone” effect implies
lower energy loss (DokshitzerKharzeev, ‘01)
light
(M.Djordjevic PRL 94 (2004))
Q
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energy distribution w dI/dw of
radiated gluons suppressed
by angle-dependent factor
Smaller energy loss would
probe inside the medium
Collisional E-loss: qg  qg,
qq  qq
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dE/dx  ln p - small?
Alexandre Suaide
University of São Paulo, Brazil
Quark Matter 2006
Shanghai, China
20
Collisional EL for heavy quarks
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Collisional and radiative energy losses are comparable!
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M.G.Mustafa,Phys.Rev.C72:014905
A. K. Dutt-Mazumder et al.,Phys.Rev.D71:094016,2005
Should strongly affect heavy quark RAA
M. Djordjevic, nucl-th/0603066
Alexandre Suaide
University of São Paulo, Brazil
Quark Matter 2006
Shanghai, China
21
High-pT electrons and energy loss
STAR
PHENIX nucl-ex/0611018
Alexandre Suaide
University of São Paulo, Brazil
STAR nucl-ex/0607012 (*)
Quark Matter 2006
Shanghai, China
(*) updated data
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Electron RAA from d+Au to central Au+Au
PHENIX nucl-ex/0611018
STAR nucl-ex/0607012
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Use of non-photonic
electron spectra as proxy
for energy loss study
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RAA show increasing
suppression from peripheral
to central Au+Au
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First evidence of heavy
quark EL
Differences between
STAR and PHENIX
disappear in RAA
Is it smaller than for lightquark hadrons?
Alexandre Suaide
University of São Paulo, Brazil
Quark Matter 2006
Shanghai, China
23
Understanding NPE suppression
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Radiative EL with
reasonable gluon
densities do not explain
the observed
suppression
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Djordjevic, Phys. Lett. B632
81 (2006)
Even extreme
conditions with high
transport coefficient do
not account for the
observed suppression
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PHENIX nucl-ex/0611018
STAR nucl-ex/0607012
Armesto, Phys. Lett. B637
362 (2006)
Other EL mechanisms?
Alexandre Suaide
University of São Paulo, Brazil
Quark Matter 2006
Shanghai, China
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Understanding NPE suppression
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Collisional EL may
be significant for
heavy quarks
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PHENIX nucl-ex/0611018
STAR nucl-ex/0607012
Wicks, nuclth/0512076
van Hess, Phys.
Rev. C73 034913
(2006)
Still marginal at
high-pT
Alexandre Suaide
University of São Paulo, Brazil
Quark Matter 2006
Shanghai, China
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Understanding NPE suppression
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Charm alone
seems to
describe better
the suppression
at high-pT
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Dead cone more
significant for
bottom quark 
larger collisional
(relative) EL
Alexandre Suaide
University of São Paulo, Brazil
PHENIX nucl-ex/0611018
STAR nucl-ex/0607012
Quark Matter 2006
Shanghai, China
26
Understanding NPE suppression
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PHENIX nucl-ex/0611018
STAR nucl-ex/0607012
Other effects may
contribute to the
observed
suppression
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What if heavy quarks
fragment inside the
medium and are
suppressed by
dissociation?
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Adil and Vitev, hepph/0611109
Similar suppression
for B and D at highpT
Alexandre Suaide
University of São Paulo, Brazil
Quark Matter 2006
Shanghai, China
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Open Heavy Flavors – Elliptic Flow
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Observed large elliptic flow of
light/s quark mesons at RHIC
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V.Greco, C.M. Ko
nucl-th/0405040
solid: STAR
open: PHENIX
PRL91(03)
Strong evidence for thermalization
What about charm?
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Naïve kinematical argument: need
mq/T ~ 7 times more collisions to
thermalize
v2 of charm closely related to RAA
Van Hees & Rapp,
PRC 71, 034907:
resonant heavy-light
quark scattering via
scalar, pseudoscalar,
vector, and axial
vector D-like-mesons
Alexandre Suaide
University of São Paulo, Brazil
Quark Matter 2006
Shanghai, China
28
Do heavy quarks flow?
PHENIX nucl-ex/0611018
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Study of non-photonic
single electrons (from
semileptonic D decays)
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First hint of strong charm
v2 for pT<2 GeV/c
 Compatible with
v2charm = v2light-q
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Seems to decrease at
higher-pT (????)
 Does the suppression
of charm makes bottom
evident in this region in
Au+Au?
Alexandre Suaide
University of São Paulo, Brazil
Quark Matter 2006
Shanghai, China
Increase statistics
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Many questions…
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The NPE RAA and v2 shows
interesting results
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Suppression is very large when
compared to the expectation
from radiative energy loss that
seems to work well for light
quark hadrons
Other possible mechanisms?
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Collisional EL, resonances,
in medium fragmentation…
Need to investigate in detail
different aspects of the
suppression
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Centrality dependence,
system size, …
But, very important, need to
disentangle charm from
bottom!
Alexandre Suaide
University of São Paulo, Brazil
Quark Matter 2006
Shanghai, China
PHENIX nucl-ex/0611018
STAR nucl-ex/0607012
30
e-h correlations in p+p: bottom vs. charm
See Xiaoyan Lin’s talk for STAR
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Understand charm and bottom
production is a key point to
understand suppression and flow
Direct measurement is very
complicated
One possible idea: electronhadron correlations
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Near side peak dominated by
decay kinematics
Preliminary e-h correlations from
p+p collisions in STAR
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Extract relative bottom contribution
for different electrons pT
fexp  R fB  1 R) fC
Alexandre Suaide
University of São Paulo, Brazil
Quark Matter 2006
Shanghai, China
31
e-h correlations in p+p: bottom vs. charm
See Xiaoyan Lin’s talk for STAR
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FONLL has large
uncertainties in the
b/(c+b) ratio
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Could the data nail it
down?
First measurement of
open-bottom at RHIC
 Non-zero
contribution of
bottom
 Very close to
FONLL predictions
Alexandre Suaide
University of São Paulo, Brazil
Quark Matter 2006
Shanghai, China
32
Some considerations…
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Heavy flavor is an important tool to understand HI
physics at RHIC
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First RHIC results are interesting and challenging
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Large differences in cross section between Phenix and
STAR
Why so much suppression at high-pT?
Do heavy flavors flow?
Charm and bottom relative production. Where bottom
starts dominating?
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First attempts from STAR indicates a non-zero contribution of
bottom to the NPE spectra
Very first step on the understanding of heavy quark EL
Alexandre Suaide
University of São Paulo, Brazil
Quark Matter 2006
Shanghai, China
33
We are just in the beginning…
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Heavy flavor is challenging
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Measurements are complicated and hungry for
statistics
The future is promising…
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STAR and PHENIX upgrades visioning heavy
flavor measurements
RHIC II upgrades will provide more luminosity
Alexandre Suaide
University of São Paulo, Brazil
Quark Matter 2006
Shanghai, China
34
Extras
Alexandre Suaide
University of São Paulo, Brazil
Quark Matter 2006
Shanghai, China
35
Open Heavy Flavor – Goals and Requirements
Physics Motivation
Probes
Studies
Baseline
D/B mesons, nonphotonic electrons
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Thermalization,
Transport
properties of the
medium
D mesons, B?
non-photonic
electrons (D+B)
Elliptic flow v2
pT spectra
as above
Properties of the
medium
Initial conditions
D, B (B  J/y + X)
mesons, nonphotonic electrons
RAA(pT), RCP of D ,
B as a function of
pT for various √s
as above
Properties of the
medium
Heavy Flavor
Production
D mesons, nonphotonic electrons
Correlations:
 charm-charm
 charm-hadron
 J/y-hadron
HIGH luminosity (eff2 !)
Large coverage
Trigger ?
Alexandre Suaide
University of São Paulo, Brazil
Rapidity y(xF)
and pT spectra in
AA, pA as a
function of A, √s
Quark Matter 2006
Shanghai, China
Requirements
High Luminosity
High resolution vertex
detectors (ct(D) ~ 100300 mm)
High-pT PID (DKp)
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How to do it?
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RHIC-II: increased luminosity (RHIC-II ≈ 40 × RHIC)
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collision diamond s = 20 cm at RHIC and s = 10 cm at RHIC II
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gain in usable luminosity is larger than “nominal” increase
PHENIX & STAR: more powerful upgraded detectors crucial to
the Heavy Flavor physics program - completed in mid/near term
~5 years.
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STAR:
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DAQ upgrade increases rate to 1 KHz, triggered data has ~ 0 dead time.
Silicon tracking upgrade for heavy flavor, jet physics, spin physics.
Barrel TOF for hadron PID, heavy flavor decay electron PID.
EMCAL + TOF J/y trigger useful in Au+Au collisions.
Forward Meson Detector
PHENIX:
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Silicon tracker for heavy flavor, jet physics, spin physics.
Forward muon trigger for high rate pp + improved pattern recognition.
Nose cone calorimeter for heavy flavor measurements.
Aerogel + new MRP TOF detectors for hadron PID.
Hadron-blind detector for light vector meson e+e- measurements.
Alexandre Suaide
University of São Paulo, Brazil
Quark Matter 2006
Shanghai, China
37
Charm production at RHIC: spectra shape
FONLL describe the shape well, despite normalization
Alexandre Suaide
University of São Paulo, Brazil
Quark Matter 2006
Shanghai, China
38
Systematic of charm cross section data
pp
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Exp. discrepancy is not a
new event
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Theory has towith
dealtheory
with many choices of parameters
Discrepancy
pp
has also a long history
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Experiments
need
to deal with many corrections
Only recently data
and
onthe
data
if measuring NPE
theory touched
bases
Knowledge evolves in both sides with time!
Alexandre Suaide
University of São Paulo, Brazil
Quark Matter 2006
Shanghai, China
39
Where bottom become significant?
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Large uncertainties
in FONLL prediction
on the relative b/c
yield
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It is important to
reduce the
uncertainties by
measuring the
relative contribution
Alexandre Suaide
University of São Paulo, Brazil
Quark Matter 2006
Shanghai, China
40