Transcript Slide 1
Physics Program
A.N.Sissakian, A.S.Sorin
Round Table Discussion II Searching for the mixed phase of strongly interacting matter at the JINR Nuclotron: Nuclotron facility development JINR, Dubna, October 6 – 7, 2006
(shut down) AGS (shut down ) (shut down) AGS BNL Au+Au 1985 −1990 SPS CERN Pb+Pb 2003 2002 2000 2000 1994 − 2000 RHIC BNL Au+Au 2000 − ? E (GeV) S 1/2 (GeV) 2
11 20 30 40 80 160 2.1•10 4 2.3
4.7 6.3 7.6 8.3 12.3 17.4
200
NUCLOTRON JINR
Project parameters: maximum energy 5 GeV/nucl. for nuclei with А ~ 200.
PHASE DIAGRAMS
Y.B.Ivanov, V.N.Russkikh, V.D.Toneev, Phys. Rev. C73 044904 (2006)
For central collisions at the Nuclotron energy even if an average state of the whole strongly interacting system does not approach the mixed phase, an essential part of the system volume will spend a certain time in the mixed phase.
Round Table Discussion Searching for the mixed phase of strongly interacting matter at the JINR Nuclotron
July 7 - 9, 2005
Program Talks Organizing Committee Photographs Research Program & Expert's Report
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/
Phases of strongly interacting matter
Nuclotron
http://www.gsi.de/
FAIR GSI
Nuclotron
Nuclotron facility development
Accelerator/experiment options under discussion: 1. Synchrotron with a beam energy of up to 10 AGeV, beam intensity of Au/Pb/U ions more than 10
6
/s, internal fixed target.
2. Collider with c.m. energy of
s
NN
= 7 GeV (equivalent to a fixed target energy of about 24 AGeV) and luminosity of 10
27
cm
-2
s
-1
(corresponding to a reaction rate of 6 kHz for Au beams).
Required parameters The following basic initial parameters have been accepted in designing physical installation: Kinetic energy of each colliding beam The setup covers solid angle close to Average luminosity of colliding beams Total cross section of heavy ion interaction (U+U) The mean multiplicity of charged particles in a central collision Fraction of central collisions Fraction of events with strange particles Fraction of events with lepton pairs in domain of
meson 2.5 A GeV 4
1
10 27 cm -2
s -1 .
7 b 600 5% 6% 10 -4 The following interaction rate characterizes the setup capability: - Frequency of interaction Total number of interactions per year assuming the statistics is being collected for 50% of the calendar time 1
10 11 A number of central interactions per year A number of central interactions with strange particles per year of
A number of central interactions with lepton pairs in the domain meson per year 7 3
10 10 3 8 /s 5
10 5
10 5 9 From these estimations it is possible to conclude that luminosity 10 27 cm -2
s -1 may be sufficient for the decision of the above form
1.
2.
Advantages I. Collider
Convenient experimental conditions: symmetry (kinematics of collisions), “simple” data analysis.
1.
High intensity and high brightness of the beam:To reach the peak luminosity level of 10 order of 10 28 11 cm
s
, one needs of the ions
beam at small emittance and large bunching factor.
2.
Disadvantages
Strong requirements to vacuum conditions in the Nuclotron at injection Relatively small magnetic rigidity of the collider rings at large E
lab
: 2.5
2.5 GeV/u can be realized at 30 Tm, it is equivalent to 24 GeV/u for fixed target. Experiment can be performed without acceleration in the collider rings, using Nuclotron as an accelerator: superconducting magnets of a modest field, small ring circumference Increase of the rigidity to 45 Tm permits experiment energy to 5 x 5 GeV/u.
increase in
3
Usage of the collider ring for ion stripping at intermediate energy allows one to accelerate them afterwards in the Nuclotron up to 6 GeV/u and perform fixed target experiments with an extracted beam. High intensity of the stored beam permits setting up experiments with radioactive isotopes
3.
Nuclotron has to accelerate ions at large charge state: for U the charge has to be larger than 60+, stripping has to be provided at intermediate energy that leads to pure stripping efficiency
.
4
Required intensity can be reached using vacuum arc or EBIS ion sources only.
Usage of vacuum arc source requires a very long linear accelerator (~80 m) and booster. EBIS, in principle, can provide required intensity with a much simpler linear accelerator, but the parameters have not been demonstrated experimentally yet.
.
5
Luminosity life-time is limited by IBS in the ion beam, rather high injection repetition rate is necessary, the ratio between mean and peak luminosity is relatively small.
.
1 .
2 .
3
II. Internal target experiment High luminosity at relatively small beam intensity. High brightness of the beam is not necessary. Luminosity level of 10 30 сm
s
is achievable at beam intensity of 108 -109 ions/beam. One can use a large variety of target and beam nuclei.
Final stripping is provided after acceleration in the Nuclotron before injection into the new synchrotron at 100% efficiency Simple injection complex. Beam storage Required is not intensity necessary.
can be provided by ion sources of different types at experimentally demonstrated intensity.
.
1 .
2 .
3
Experimental condition is worse than in the collider mode.
Maximum achievable energy in the centre-of-mass is sufficiently smaller than in the collider mode.
Limited possibility of the energy increase (10 T magnets ) One needs to build a synchrotron at magnetic rigidity of about 90 Tm: ring circumference is equal to the Nuclotron one, magnetic field is of about 6 T.
Heavy element gas or fibber target of small effective density.
Complicated design of the interaction point: “snake” for the primary beam and so on.
III. Experiments with extracted beam One can use radioactive ion beams, but it requires sufficiently higher intensities of a primary beam: 10 11
10 12 ions/beam.
.
1
Experimental conditions are worse than in the internal target. To have the same luminosity level, one needs to use large thickness of the target that leads to uncertainties in interaction co-ordinates and momentum determination
.
2
In contrast with point II one needs slow extraction at 10 GeV/u.
From the accelerator hand of the project the scheme I differs from schemes II and III mainly in one point only: scheme I presumes the construction of two new storage rings operating at a fixed magnetic field, schemes II and III require creation of a new synchrotron of maximum energy of 10 GeV/u. The price of two storage rings is comparable with the cost of a new synchrotron. New linear injector for the Nuclotron may have the same structure and price for all the schemes if EBIS ion source is applied.
Owing to wider experimental possibilities preference is given the collider version of the new facility and this scheme is described in the project.
The collider option permits to scan a larger region of the QCD phase diagram, and is preferable with respect to the fixed target option. The project has to be realized within 5-6 years in order to be operational well before the FAIR project. This boundary condition limits the size of the project and restricts the technology of the accelerator and of the experimental setup to available solutions.
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The NICA project is dedicated to the design and construction at JINR of a new relativistic heavy ion superconducting collider based on the Nuclotron accelerator complex. General goal of the project is to start in the coming 5
6 years experimental study of hot and dense strongly interacting QCD matter and search for possible manifestation of signs of the mixed phase and critical endpoint in heavy ion collisions. The MPD is proposed for these goals.
Additionally, as a result of the project realisation, the potentials of the Nuclotron accelerator complex will be sufficiently increased in all the fields of its current physics program and the facility creation will open new fields of experimental studies.
The project realization presumes fulfilment of the following tasks: - Upgrade of the Nuclotron and reaching its design parameters, - Development of highly charged heavy ion sources, - Creation of a new linear injector,
-
Creation of two new superconducting storage rings to provide collider experiment with heavy ions like Au or U at energy 2.5 x 2.5 GeV/u (equivalent fixed target energy is 24 GeV/u ) with average luminosity of 10 27 cm -2
s -1 ; if magnetic rigidity of the collider rings is chosen to be equal to the Nuclotron project one, the maximum experiment energy reaches 5 x 5 GeV/u (equivalent fixed target energy is 70 GeV/u ).
There are two versions of the collider and detector projects. In the first collider version, one of the new storage rings will be used as an ion beam accumulator at intermediate energy that permits generation of intensive beams of completely stripped heavy ions and then provides acceleration in the Nuclotron up to maximum energy of 5
6 GeV/u (depending on the Z/A ratio) for fixed target experiments.
The project of a new linear injector allows also an effective acceleration of light ions to Nuclotron injection energy in order to increase intensity of polarized ion beams.
The physics program:
1. The nuclear matter equation-of-state at high densities.
2. In-medium properties of hadrons.
3. Space-time evolution of nuclear interaction.
4. The first order deconfinement and/or chiral symmetry restoration phase transitions.
5. The QCD critical endpoint
.
Future heavy-ion experiments in the beam energy range between 2 and 24 AGeV: 1. Multistrange hyperons. The yields, spectra and collective flow of (multi) strange hyperons are expected to provide information on the early and dense phase of the collision as they are produced close to threshold. Therefore, these particles are promising probes of the nuclear matter equation-of-state at high baryon density. 2. Event-by-event fluctuations. The hadron yields and momenta should be analyzed event-wise in order to search for nonstatistical fluctuations which are predicted to occur in the vicinity of the critical endpoint and when penetrating the coexistence phase of the first order deconfinement and/or chiral phase transition. In order to subtract the (dominant) contributions from resonance decays one should measure the yields of the relevant short-lived particles such as the φ and the K* mesons. 3. HBT correlations. Measurement of short correlations between hadrons π, K, p, Λ allows one to estimate the space-time size of a system formed in nucleus-nucleus interactions. Alongside with the increase of fluctuations, the spatial size of the system is expected to be getting smaller near the deconfinement phase transition due to softening of the equation of state (the “softest point” effect).
4. Penetrating probes. Measurements of dilepton pairs make it possible to investigate in-medium spectral functions of low-mass vector mesons which are expected to be noticeably modified due to effects of chiral symmetry restoration in dense and hot matter. (Note that for dilepton production processes there is an suppression by 3-4 orders of magnitude. For average luminosity of colliding beams 10 27 cm -2 s -1 a number of central interactions with lepton pairs in the domain of rho-meson is 10 5 -10 6 per year, assuming the statistics is being collected for 50% of the calendar time). Specific properties of the sigma-meson as a chiral partner of pions, which characterizes a degree of chiral symmetry violation, may be in principle detected near the phase boundary via a particular channel of sigma-decay into dileptons or correlated gamma-gamma pairs. Above a beam energy of about 15 AGeV also charmonium might be detectable. J/Psi mesons are a promising probe for the deconfinement phase transition (needs additional consideration).
5. Open charm (above 15 AGeV). D-mesons probe the early phase of the collision and are sensitive to in-medium effects due to chiral symmetry restoration. Alongside with a low yield these mesons have some particularities in their detection what should be considered later in more details. Possibly it is a good task when higher colliding energy will be reached.
Experiments at AGS have studied hadron production (π, K, p, Λ) in Au+Au collisions at beam energies between 2 and 10 AGeV. At 6 AGeV also Ξ hyperons have been observed. Event-by-event fluctuations have not been analysed. No dilepton data have been measured. Therefore, new experiments in this energy range should concentrate on the excitation function of (multi)strange hyperons and on event-by-event observables. In the beam energy range between 10 and 20 AGeV no collision experiments with beams of heavy nuclei have been performed. Therefore, the collider option offers the unique opportunity to perform pioneering experiments which should measure all hadrons including multi-strange hyperons, their phase-space distributions and collective flow. This includes also event-by-event observables.
Theoretical (model and lattice) predictions for the location of the critical end-point. Points are calculated in different models specified in M. Stephanov, Int. J. Mod. Phys. A20, 4387 (2005)[hep-ph/0402115].
Conclusions
1. A study of the phase diagram in the domain populated by heavy-ion collisions with the bombarding energy ~ 5 ÷ 24 GeV/nucleon to search for the mixed phase seems to be a very attractive task. 2. The use of the isospin asymmetry as an additional conserving parameter to characterize the created hot and dense system attracts new interest in this problem ( critical end-boundary hypersurface ? ).
3. The available theoretical predictions are strongly model dependent giving rather dispersive results . There are no lattice QCD predictions for this highly nonpertubative region. Much theoretical work should be done and only future experiments may disentangle these models.
4. A JINR Nuclotron possibility of accelerating heavy ions to the project energy of 5A GeV and increasing it up to 24A GeV can be realized in 5 - 6 years . This will enable us to effort a unique opportunity for scanning heavy-ion interactions in energy, centrality and isospin asymmetry . It seems to be optimal to have the gold and uranium beams in order to scan in isospin asymmetry in both central and semi-central collisions at not so high temperatures .