experimental overview - mitrolandg/roland_bnl_low_e.pdf · gunther roland bnl workshop march 2006...
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![Page 1: Experimental Overview - MITrolandg/Roland_BNL_low_E.pdf · Gunther Roland BNL Workshop March 2006 Excitation Function: Particle Ratios Non-monotonic behavior at AGS/SPS boundary NA49](https://reader036.vdocuments.us/reader036/viewer/2022081620/611b8974e1162e5365212bd0/html5/thumbnails/1.jpg)
Can we discover the critical point at RHIC?
Experimental Overview
Gunther Roland
BNL March 9 2006
Thanks to Burak Alver, Ed Wenger,
Siarhei Vaurynovich, Wei LI
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Gunther Roland BNL Workshop March 2006
Matter Density µB (GeV)
Tem
pera
ture
(MeV
)
Quark-Gluon Plasma
Hadron Gas
Phase Boundary
0
200
0
Atomic Nuclei
1
Critical Point
Exploring the QCD Phasediagram
Critical Point
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Gunther Roland BNL Workshop March 2006
Exploring the QCD Phasediagram
Matter Density µB (GeV)
Tem
pera
ture
(MeV
)
Quark-Gluon Plasma
Hadron Gas
Phase Boundary
0
200
0
Atomic Nuclei
1
Critical Point
Susceptibilities diverge near critical point
Locate the critical point using correlation/fluctuation measurements
√s
<(X - <X>)2> Enhanced Fluctuationsnear Critical Point
Rajagopal, Shuryak,Stephanov
Critical Point
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Gunther Roland BNL Workshop March 2006
Matter Density µB (GeV)
Tem
pera
ture
(MeV
)
Quark-Gluon Plasma
Hadron Gas
Phase Boundary
0
200
0
Atomic Nuclei
1
Critical Point
Exploring the QCD Phasediagram
Plot from M. Stephanov, Correlations ‘05
Challenge: Guidance on exact location and strength of correlation signals is limited
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Gunther Roland BNL Workshop March 2006
Experimental Search for the Critical Point
• Theoretical guidance is limited
• Experimental strategy:
- Search in different observables, correlate observables
- Maximize experimental sensitivity
- Fine grained exploration of μB, T space
• Side effect:
- Sensitivity to critical phenomena at 1st order transition, Onset of Deconfinement, EOS softest point, changes in bulk dynamics etc
➡NA49
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Gunther Roland BNL Workshop March 2006
Experimental Search for the Critical Point
• This idea/strategy is not new
• This talk (this workshop)
- What is known from excitation functions?
- What could be done better at RHIC (and how good)?
RHIC
SPS
AGS
First of many experimental talks
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Gunther Roland BNL Workshop March 2006
Fixed target vs collider experiments
If rates O(1Hz) or greater: √s scan of hadronic observables feasible
1/γ2
1/γ3
NA49 K/π fluctuations
CERES low mass e+e-
CERES <pT> fluctuations
min-bias
0-5% central
(optimistic)c.f. Todd Satogata c.f. Peter Steinberg (PHENIX)
Harald Appelshaeuser (CERES)
(known)
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Gunther Roland BNL Workshop March 2006
Suitable hadronic observables
• Here: Simple observables
- Multiplicities and multiplicity correlations
- Spectra and momentum correlations
- Net charge correlations
- Elliptic flow
- Particle ratios and ratio fluctuations
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Gunther Roland BNL Workshop March 2006
Excitation Function: Mid-rapidity Multiplicities
RHIC
SPS
AGS
Compilation by PHOBOS
Nucl. Phys. A 757, 28
Cu+Cu PHOBOS QM’05 ?
?
RHIC
SPSAGS
- Logarithmic growth of mid-rapidity particle density- Structure at SPS energy range and/or around √s ≈ 60 GeV?- Precision of ≈ 5-10% - better if doing relative scan in single experiment (≈ 3%)?
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Gunther Roland BNL Workshop March 2006
Excitation Function: Total Multiplicities
RHIC
SPS
AGS
Compilation by PHOBOS
nucl-ex/0301017
submitted to PRC
e+e-
- A+A Nch/participant pair approaches Nch in e+e-
- A+A by itself can be fit with log2(s)- Structure at SPS energy IF compared to e+e- or p+p
RHIC
SPS
AGS
e+e-
log2(s) Wit Busza,
Zakopane ‘04
c.f. Gazdzicki, Steinberg
log2(s) Wit Busza,
Zakopane ‘04
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Gunther Roland BNL Workshop March 2006
Fraction of produced hadrons in Nch
Change from baryon- to meson dominated systemover the energy range of interest!
RHICSPS
AGS
Excitation Function: Total Multiplicities
c.f. Gazdzicki, Steinberg
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Gunther Roland BNL Workshop March 2006
Excitation Function: Momentum SpectraCompilation by NA49
Plot from Claudia Hoehne, QM’05
filled symbol: particleopen symbol: antiparticle
- Structure in energy dependence of <mT>- Reminiscent of Van Hove’s T vs ε prediction (1982)- Surprisingly difficult measurement
● Decay corrections, PID acceptance
“The Kink”
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Gunther Roland BNL Workshop March 2006
RHICSTAR
SPSCERES
AGS?
Compilation by STARSTAR PRC 72 044902 (2005)
Central A+A
Excitation Function: Momentum Fluctuations
“The Kink”
Monotonic energy dependence over measured rangeNo results near “kink” region
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Gunther Roland BNL Workshop March 2006
STAR
STAR preliminary
CERES
STAR
Interpretation connected to choice of variables
Connection to 2-particle
correlations
Scaling: Connectionbetween <pT>, N,
fluctuations?
ΣpT≈
Excitation Function: Momentum Fluctuations
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Gunther Roland BNL Workshop March 2006
QGP
Little (no) √s dependence of charge fluctuations
Excitation Function: Charge Fluctuations
Plot from Claude PruneauRHIC Users meeting workshop ‘04
NA49, PRC 70 064903 (2004) PHENIX: PRL 89 082301 (2002)
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Gunther Roland BNL Workshop March 2006
N.B. Multiplicity Fluctuations
Particles produced independently:
σ2C = 1
Particles produced in clusters of size K:
0-20% central
PHOBOS 200 GeVAu+Au preliminary
effective cluster size ≈ 2-2.5 for 200 GeV Au+Au
Analysis of forward/backward multiplicity correlationsParticles are produced in clusters of 2-3
PHOBOS, Peter Steinberg, QM’05
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Gunther Roland BNL Workshop March 2006
N.B. Multiplicity Fluctuations
0-20% central
PHOBOS 200 GeVAu+Au preliminary
effective cluster size ≈ 2-2.5 for 200 GeV Au+Au
“Cluster” in Δη,Δφ space via2-particle correlations
(pythia p+p @200 GeV, η<3)Lesson:Hadronization cannot be ignored in discussion of early stage fluctuations
PHOBOS, Peter Steinberg, QM’05
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Gunther Roland BNL Workshop March 2006
Low Density Limit:STAR, PRC 66 034904 (2002)
Voloshin, Poskanzer, PLB 474 27 (2000)Heiselberg, Levy, PRC 59 2716, (1999)
Excitation Function: Elliptic flow
Cu+Cu: PHOBOS QM 2005
Cu+Cu
Au+Au
“Participant Eccentricity” provides universal scaling
Approach to equilibrium or sampling different regions of EOS?
“Hydro-Limit”
Collapse of proton flow at 40AGeV?provides universal scaling
c.f. Shuryak, Stoecker
NA49 PRC C68 034903 (2003)
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Gunther Roland BNL Workshop March 2006
Now to the main event.....
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Gunther Roland BNL Workshop March 2006
Excitation Function: Particle Ratios
Non-monotonic behavior at AGS/SPS boundary
NA49 Phys.Rev.C66:054902,2002
Plot from Claudia Hoehne, QM’05
“The Horn”
e+e- (Canonical Ensemble)
“The Horn”
A+A
A+A
A+A
e+e- (Canonical Ensemble)
Becattini et al.
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Gunther Roland BNL Workshop March 2006
Lesson: Keeping acceptance/experimental technique constant is essential for precision studies
“The Horn”
RHICSTAR
Preliminary
SPSNA49
Preliminary
AGS?
NA49, Christof Roland, QM’04 STAR, Supriya Das, VI Workshop ‘05
Excitation Function: K/π Fluctuations
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Gunther Roland BNL Workshop March 2006
RHIC
SPS
AGS?
Normalized by dN/dy
Scaling by dN/dy or (dN/dy)1/2 does not work over full energy range
Excitation Function: K/π Fluctuations
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Gunther Roland BNL Workshop March 2006
Why use a collider?
Can RHIC low-√s scan improve on SPS measurements?
Use particle ratio fluctuations as case study
K/π Fluctuations p/π Fluctuations
NA49, Christof Roland, QM’04
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Gunther Roland BNL Workshop March 2006
Event-by-event fit of K/π (NA49)One Event:Event Ensemble:
<dE/
dx>
<dE/
dx>
log(ptot [GeV]) log(ptot [GeV])
Probability density function:
log(ptot [GeV])
<dE/
dx>
Fit dE/dx spectra in 4D binning
<dE/dx>
• Extract ratios with maximum likelihood fit
• Vary relative normalization of the particle species (K/π,p/π) in the PDF
Slide from Christof Roland,Correlations ‘05, MIT
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Gunther Roland BNL Workshop March 2006
Extracting dynamical fluctuations (NA49)
Compare data to mixed events:
σ2data - σ2mix = σ2dynamic
Process the relative widths of the distributions:σ = RMS/Mean * 100 [%]
+
Dynamical Fluctuations
σ = 2.8%
E-by-E K/π ratio
Even
ts
+
Finite Number Statistics
Experimental Resolution
σ = 15.9% σ = 16.7%
E-by-E K/π ratio E-by-E K/π ratio
Even
ts
Even
ts
Statistical fluctuations
=“mixed” Events
σ = 23.1%
E-by-E K/π ratio
Even
ts
=
“Data” Events
E-by-E K/π ratio
σ = 23.27%
Even
ts
Slide from Christof Roland,Correlations ‘05, MIT
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Gunther Roland BNL Workshop March 2006
Challenge: Changing acceptance (NA49)
20 GeV: 40 GeV: 160 GeV:
Slide from Christof Roland,Correlations ‘05, MIT
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Gunther Roland BNL Workshop March 2006
Mid-rapidity spatial track density
“You prefer your collider”Les Horribles Cernettes
Fixed target
Collider
Collider
Fixed target
Track density only rise logarithmically at collider
from this:OccupancyDouble hitsSpace ChargeBaseline shifts etc
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Gunther Roland BNL Workshop March 2006
What can be achieved at RHIC?
“Ideal Detector”
* >80% tracking + PID efficiency from 0.1 < pT < 2.0 GeV/c, over 2+ units of rapidity* Large acceptance trigger/centrality counters* High resolution vertexing
Assume 100k central sample at each √s
* 2π ToF PID coverage near y=0 possible* Acceptance in (pT,y) independent of √s* Track density grows logarithmically with√s * Consistent centrality determination from Nch
But: give up very low pT , luminosity vs fixed target
PID + trigger
Tracking
Vertexing
TriggerTracking
Vertexing
Trigger
PID + trigger
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Gunther Roland BNL Workshop March 2006
K/π fluctuations at low-√s RHIC
NA49 SPS
Low √s RHIC100k central
events
Relative error on K/π fluctuations
Estimate that RHIC low-√s scan could allow reduction of statistical errors to ~ 1/4 of NA49
Significant reduction of systematics of √s dependence
RHIC
SPS
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Gunther Roland BNL Workshop March 2006
What about low pT?
Median Kaon pT ~ 0.5 GeV
(constant over SPS range)
Critical fluctuations: Long Wavelength ➡ look at low pT
A low pT measurement (0.1 - 0.5 GeV/c) would
capture ~ 45% (75%) of all kaons (pions)
Fraction of particles below pT
based on NA49 <mT>
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Gunther Roland BNL Workshop March 2006
Low pT K/π Fluctuations at √s RHIC
SimulationStatistical errors only
Assumptions:* Ideal RHIC detector (see above)* 100k central Au+Au at each √s* K/π Fluctuations from NA49 are correct* 0.1 < pT < 0.5 GeV/c
Fluctuations only at low pT
Fluctuations at all pT
Conclusion: RHIC low-√s scan should allow precision
measurement of (low pT) K/π fluctuations
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Gunther Roland BNL Workshop March 2006
Summary
• Strong theoretical motivation for A+A at √s from 5-50 GeV
• Rich existing data set in this range
• Non-trivial structure/change in yields, ratios, fluctuations/correlations
• Limited statistical/systematic significance
• Low-√s scan at RHIC could confirm and improve experimental results
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Gunther Roland BNL Workshop March 2006
Summary cntd
• To improve on SPS, low-√s run needs to be done right
• Sufficient run time (e.g. 1 RHIC run)
• Large acceptance ToF PID
• High resolution vertexing
• Careful event selection/triggering
• Sufficient number of energies (≥ 5)
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Gunther Roland BNL Workshop March 2006
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Gunther Roland BNL Workshop March 2006
Correlations and Fluctuations, revisited
centrality →
Central A+A
Text
p+p
Net-charge correlations (c.f. Balance Function)
Net-charge FluctuationsGlobal scaling, even though underlying
correlations change