1. Claudia Höhne, GSI Darmstadt CBM collaboration
Das CBM Experiment bei FAIR - Untersuchungen des QCD Phasendiagrams bei hohen Baryonendichten -
Claudia Höhne, GSI Darmstadt
CBM collaboration

2. Outline Introduction & motivation
phase diagram of strongly interacting matter
A+A collisions
theoretical status
experimental status
CBM experiment
observables
detector layout
detector R&D
feasibility studies
Summary & Outlook

3. Phasediagram of water
H2O

4. Phasediagram of strongly interacting matter
baryochemical potential (~b/0)
temperature
hadron liquid
QGP
critical point ?
super conductivity
nucleus
K.Rajagopal, Nucl. Phys. A661 (1999) 150
hadron gas
heat
compression

5. Strongly interacting matter
quark gluon plasma
big bang & early universe T
hadron gas
How to access ???
neutron stars r
"normal" nuclear matter
r=r0=0.17 fm-3

6. Heavy ion collisions simulation of a U+U collision at 23 GeV/A (UrQMD)
nucleons mesons excited baryons

7. Heavy ion collisions (II)
UrQMD 160 GeV Au+Au
before collision
compression and heating (T >> Tchem ~ 160 MeV)
thermalization of the "fireball"
(high T and r reached for ~10fm/c = s)
expansion
chemical freezeout (number and type of particles frozen)
kinetic freezeout (particle momenta frozen)
Tchem ~ 160 MeV ~ 2∙1012 K)
(kT unit system, k=8.6∙10-5 eV K-1 → 100 MeV = 1.16∙1012 K !!!)

8. Heavy ion collisions (III)
simulation of Au+Au collisions at different beam energies
→ maximum baryon densities r increase with beam energy
→ energy densities also increase with beam energy
[CBM physics group, E. Bratkovskaya, C. Fuchs priv. com.]

9. Heavy ion collisions (IV)
in heavy ion collisions nuclear matter can be compressed and heated
statistical ansatz: describe "final state" hadron gas as grandcanonical ensemble
→ temperature T, baryochemical potential mb (relation to baryon density r)
→ higher beam energy: higher T, lower mb
QCD calculations: difficult ....
temperature
critical point ?
QGP
beam energy
hadron gas
nucleus
baryochemical potential (~b/0)
K.Rajagopal, Nucl. Phys. A661 (1999) 150
[Andronic et al. Nucl. Phys. A 772, 167 (2006).

10. Theoretical status QGP cSB CSC Lattice QCD Perturbative QCD
Ginzburg-Landau + RG
Nuclear theory
Perturbative QCD
effective models
cSB
CSC
QGP

11. Lattice - QCD T calculations limited to certain observables
and regions of the QCD phase diagram
in particular calculations for m ≠ 0 are difficult and conceptual problems could only be solved a few years ago! mb
mb = 0
→ transition to deconfinement above a certain Tc!
Tc ~ 175 MeV
driven by energy density
ec ~ 1 GeV/fm3
quarks and gluons become relevant degrees of freedom

12. Lattice – QCD (II) phase transition at mb = 0 : crossover
= rapid change of properties but no clearly defined phase boundary
mb > 0 not yet completely settled ... but:
first order phase transition at large mb
→ e.g. latent heat
phase coexistence region
critical point
Tcrit ~ 160 MeV mcrit ~ 360 MeV
chiral symmetry restoration at high T, large mb
[F.Karsch, Z. Fodor, S.D.Katz]

13. Experimental status
since 1980s heavy ion collision experiments at AGS, SPS
2000 start of RHIC, 2008 LHC
RHIC Brookhaven
√s = GeV/nucleon
future: LHC
SPS CERN
GeV/nucleon
AGS Brookhaven
2-10 GeV/nucleon
[Andronic et al. Nucl. Phys. A 772, 167 (2006).

14. Experimental Status (II)
fireball in chemical equilibrium
hadron production successfully described by a statistical model ansatz
→ all hadron yields (even strangeness!) in chemical equilibrium
SPS, RHIC
"limiting temperature" T~160 MeV
→ phase boundary reached, additional energy goes into heating the QGP
[Andronic et al. Nucl. Phys. A 772, 167 (2006).

15. Experimental status (III)
energy dedendence of hadron production
→ changes in SPS energy regime
discussions ongoing:
hadron gas → partonic phase
baryon dominated → meson dominated matter
hadron gas
transition
QGP ?

16. Experimental status – CERN
New State of Matter created at CERN
                                                                                                                                                                                                                                                                                                                                
At a special seminar on 10 February, spokespersons from the experiments on CERN* 's Heavy Ion programme presented compelling evidence for the existence of a new state of matter in which quarks, instead of being bound up into more complex particles such as protons and neutrons, are liberated to roam freely.

17. elliptic flow v2
particle emission pattern in plane transverse to the reaction plane
initial overlap eccentricity is transformed in momentum anisotropy
driven by pressure from overlap region
Fourier expansion of the dN/dϕ distribution: v2 f

18. Experimental status (IV)
all flow observations scale extremely well if taking the underlying number of quarks into account!
flow also seen for charm quarks!
→ like (all!) quarks flow and combine to hadrons at a later stage (hadronisation)
data can only be explained assuming a large, early built up pressure in a nearly ideal liquid (low viscosity!)
baryons n=3
mesons n=2

19. Experimental status (V)
partons should loose energy in a dense and hot medium
→ jet suppression!
→ results imply huge gluon densities corresponding to an initial temperature of ~2Tcrit and e ~ GeV/fm-3 in the fireball!

20. Experimental status – RHIC
RHIC Scientists Serve Up "Perfect" Liquid
New state of matter more remarkable than predicted - raising many new questions
April 18, 2005
TAMPA, FL -- The four detector groups conducting research at the Relativistic Heavy Ion Collider (RHIC) -- a giant atom "smasher" located at the U.S. Department of Energy's Brookhaven National Laboratory -- say they've created a new state of hot, dense matter out of the quarks and gluons that are the basic particles of atomic nuclei, but it is a state quite different and even more remarkable than had been predicted. In peer-reviewed papers summarizing the first three years of RHIC findings, the scientists say that instead of behaving like a gas of free quarks and gluons, as was expected, the matter created in RHIC's heavy ion collisions appears to be more like a liquid.

21. Experimental status - summary
partonic phase created in the early phase of A+A collisions for SPS + RHIC energies
characterization of this phase?
→ RHIC: more an ideal liquid than a gas of quarks and gluons, crossover?
→ LHC: weakly coupled QGP reachable?
→ high baryon density region?
where is deconfinement reached first?
order of the phase transition? critical point?
characteristics of high baryon density matter?
2nd generation experiment!
CBM at FAIR!
10-45 GeV/nucleon
[Andronic et al. Nucl. Phys. A 772, 167 (2006).

22. CBM
... should be in the right energy range for the "onset of deconfinement", the first order phase transition (and the critical point)
... as a 2nd generation experiment can built on the knowledge gained over the last 20 years (observables, experimental techniques)
... will be able to use probes never measured before at these energies but expected to be sensitive to the created matter
[Bratkovskaya et al., PRC 69 (2004) ]
UrQMD calculation of T, mB as function of reaction time
(open symbols – nonequilibrium,
full symbols – appr. pressure equilibrium)

23. FAIR at GSI SIS 300 p beam 2 – 90 GeV Ca beam 2 – 45 AGeV
Au beam 2 – 35 AGeV
max. beam intensity 109 ions/s
high intensity ion beam
Compressed Baryonic Matter
Ion and Laser induced plasmas: High energy density in matter
Cooled antiproton beam: hadron spectroscopy - PANDA
So, just to remind you: CBM will be one of the major experiments at the future FAIR facility next to the existing GSI facility at Darmstadt. FAIR will cover a wide range of physics: From the study of nuclei far from stability with the NUSTAR experiments via hadron spectroscopy with PANDA and plasma physics to the investigation of compressed baryonic matter in nucleus-nucleus collisions with the CBM experiment. With CBM we thus will make use in particular of the high intensity ion beam which will be delivered by the SIS 300 synchrotron. Available beam energies for ions will spread a range from 2 to 35 AGeV for gold ions at beam intensities of up to 10-to-9 ions per second.
Structure of nuclei far from stability - NUSTAR
November 7-8, 2007
FAIR Kick-Off Event !

24. CBM: Physics topics and Observables
The equation-of-state at high B
collective flow of identified hadrons
particle production at threshold energies (open charm)
rare probes!
systematic measurements!
→ comprehensive picture with CBM as 2nd generation experiment!
Deconfinement phase transition at high B
excitation function and flow of strangeness (K, , , , )
excitation function and flow of charm (J/ψ, ψ', D0, D, c)
charmonium suppression, sequential for J/ψ and ψ' ?
QCD critical endpoint
excitation function of event-by-event fluctuations (K/π,...)
Onset of chiral symmetry restoration at high B
in-medium modifications of hadrons (,, e+e-(μ+μ-), D)
mostly new measurements
CBM Physics Book (theory) in preparation

25. Chiral symmetry restoration
chiral broken world:
→ chiral partners show different spectral functions!
for example: nonstrange I=J=1 multiplet: r- and a1 - meson
chiral symmetry restoration requires that vector and axialvector spectral functions become degenerate
→ dramatic reshaping of spectral functions expected!

26. r – meson n  p p  ++ r e+, μ+ e-, μ-
hadronic properties are expected to be affected by the high density matter
r-meson couples to the medium, direct radiation from the early phase
vector-meson dominance!
vacuum lifetime t0 = 1.3 fm/c → dileptons = penetrating probe
connection to chiral symmetry restoration? n  
e+, μ+
e-, μ- r p p
++
r-meson
spectral function
[Rapp, Wambach, Adv. Nucl. Phys. 25 (2000) 1,
hep-ph/ ]

27. Charm production at threshold
CBM will measure charm production at threshold
→ after primordial production, the survival and momentum of the charm quarks depends on the interactions with the dense and hot medium!
→ direct probe of the medium!
D/p ~ 10-7 → experimental challenge!
[W. Cassing et al., Nucl. Phys. A 691 (2001) 753]
do c and c quarks behave differently in baryon-rich matter?
charmonium (cc) in hot and dense matter?
relation to deconfinement?
HSD simulations

28. interaction rates
FAIR will provide high intensity beams up to 109 ions/s
high availability of beam due to parallel operation of FAIR
1% interaction target → 10 MHz interaction rate
→ rare probes!
(rates for D limited because of readout speed of silicon pixel detectors)
BR = branching ratio e = efficiency
T = trigger? Y/10w = yield in 10 weeks

29. STS tracking – heart of CBM
Challenge: high track density
 600 charged particles in  25o
→ trigger on D-mesons for background rejection!
Task
track reconstruction:
0.1 GeV/c < p  GeV/c
Dp/p ~ 1% (p=1 GeV/c)
primary and secondary vertex reconstruction (resolution  50 mm)
V0 track pattern recognition
silicon pixel
and strip detectors
D+ → p+p+K- (ct = 317 mm)
D0 → K-p+ (ct = 124 mm)
D0+D0 ~ 1.5∙10-4 central Au+Au, 25 GeV/nucleon

30. CBM – detector concept fixed target experiment, "medium" energies
→ large solid angle to be covered
high rate, multipurpose detector including open charm reconstruction
→ fast, excellent tracking based on silicon pixel and strip detectors directly behind the target and inside a magnetic field
→ add particle identification afterwards (leptons, hadrons)
drives layout
beam
RICH
TRD
TOF
magnet
STS

31. The CBM experiment
tracking, momentum determination, vertex reconstruction: radiation hard silicon pixel/strip detectors (STS) in a magnetic dipole field
hadron ID: TOF (& RICH)
photons, p0, h: ECAL
PSD for event characterization
high speed DAQ and trigger (up to 10 MHz int. rates) → rare probes!
electron ID: RICH & TRD
 p suppression  104
muon ID: absorber + detector layer sandwich
 move out absorbers for hadron runs
MVD + STS
... measuring both channels would be the best crosscheck of results we can ever do!

32. DAQ & FEE for rare probes highly efficient triggers needed!
D-meson → online tracking and 2ndary vertex finding
DAQ and FEE concept based on "self triggered readout" electronics
FEE provides self-triggered
hit detection, pre-processing
FEE
CNet
BNet
HNet
to archive
TNet
FEE boards
CNet links
DCB: data combiner boards
CDL: CBM detector links
ABB: active buffer boards
EB Switch
Backend processors
General Network
Clock/Trigger distribution
data are shipped to PC
farm with a time stamp
online event reconstruction:
trigger decision
system throughput limited!
archiving rate 25 kHz
storage: 1Gb/s

33. STS and FEE R&D
Fast self-triggered readout chip n-XYTER in collaboration with DETNI
prospect: CBM-XYTER
Strip sensor development with CIS Erfurt
First test sensor delivered spring 2007

34. Detector R&D – TRD main issue for many detectors: high rates!
for example: TRDs → reduce gas gap/ operate with pad plane in the middle of gas gap

35. CbmRoot simulation framework
detector simulation (GEANT3)
full event reconstruction: track reconstruction, add RICH, TRD and TOF info
result from feasibility studies in the following: central Au+Au collisions at 25 AGeV beam energy (UrQMD)

36. Hadrons and Hyperons 25 AGeV central AuAu
layout of CBM provides also good hyperon (tracking in the STS) and hadron (TOF) identification
→ flow, correlations, fluctuations .... p p K

37. Open charm production 25 AGeV central AuAu
D0 → K-p+ and D0 → K+p- (ct = 124 mm), full event reconstruction
<D0 + D0> = 1.5 ∙ 10-4 (central Au+Au collisions, 25 AGeV)
first pixel detector (MAPS) at 10cm
~53 mm secondary vertex resolution
proton identification with TOF
1012 central Au+Au collisions, 25 AGeV

38. Low mass vector mesons 25 AGeV central AuAu invariant mass spectra
electrons: pt > 0.2 GeV/c
background dominated by physical sources (75%)
muons: intrinsic p>1.5 GeV cut (125 cm Fe absorber), use TOF information
background dominated by misidentified muons
electrons: 200k events
background 4 ∙108 events – signal 20k ev.
All e+e-
Comb. bg
ρ  e+e-   e+e- φ  e+e-
π0  γe+e-   π0e+e- η  γe+e-
w,f sm = 14 MeV/c2
w,f sm = 11 MeV/c2

39. J/y and y' 25 AGeV central AuAu invariant mass spectra
electrons: p < 11 GeV/c, pt > 1 GeV, 1‰ interaction target (25 mm Au)
muons: 225 cm Fe absorber, no pt-cut
electrons: 2.4 ∙1010 events
J/y sm = 38 MeV/c2
y' sm = 45 MeV/c2
muons: 4 ∙108 events
J/y sm = 22 MeV/c2
y' sm = 33 MeV/c2

40. CBM CBM@FAIR – high mB, moderate T:
searching for the landmarks of the QCD phase diagram
first order deconfinement phase transition
chiral phase transition
QCD critical endpoint
characterizing properties
of baryon dense matter
in medium
properties of hadrons?
in A+A collisions from
10-45 AGeV
(√sNN = 4.5 – 9.3 GeV)
starting in 2015

41. CBM collaboration 51 institutions, > 400 members China: CCNU Wuhan
USTC Hefei
Croatia:
University of Split
RBI, Zagreb
Univ. Münster
FZ Rossendorf
GSI Darmstadt
Korea:
Korea Univ. Seoul
Pusan National Univ.
Russia:
IHEP Protvino
INR Troitzk
ITEP Moscow
KRI, St. Petersburg
Hungaria:
KFKI Budapest
Eötvös Univ. Budapest
Norway:
Univ. Bergen
Kurchatov Inst. Moscow
LHE, JINR Dubna
LPP, JINR Dubna
Poland:
Krakow Univ.
Warsaw Univ.
Silesia Univ. Katowice
Nucl. Phys. Inst. Krakow
Cyprus:
Nikosia Univ.
India:
Aligarh Muslim Univ., Aligarh
IOP Bhubaneswar
Panjab Univ., Chandigarh
Univ. Rajasthan, Jaipur
Univ. Jammu, Jammu
IIT Kharagpur
SAHA Kolkata
Univ Calcutta, Kolkata
VECC Kolkata
Univ. Kashmir, Srinagar
Banaras Hindu Univ., Varanasi
Czech Republic:
CAS, Rez
Techn. Univ. Prague
France:
IPHC Strasbourg
LIT, JINR Dubna
MEPHI Moscow
Obninsk State Univ.
PNPI Gatchina
SINP, Moscow State Univ.
St. Petersburg Polytec. U.
Portugal:
LIP Coimbra
Romania:
NIPNE Bucharest
Germany:
Univ. Heidelberg, Phys. Inst.
Univ. HD, Kirchhoff Inst.
Univ. Frankfurt
Univ. Mannheim
Ukraine:
Shevchenko Univ. , Kiev
51 institutions, > 400 members
Dresden, September 2007

42. additional slides

43. STS R&D Microstrip Sensors Tracking Stations layout studies
module design

44. fast self-triggered readout electronics
NXYTER chip produced; DETNI − GSI
micro-strip sensor
test system under construction

45. Sequential dissociation of charmonium?
Quarkonium dissociation temperatures – Digal, Karsch, Satz
(J/)/DY = 29.2  2.3
L = 3.4 fm
Preliminary!
Preliminary!
[NA60]

46. Collective flow elliptic flow v2:
collapse of elliptic flow of protons at lower energies signal for first order phase transition?! [e.g. Stoecker, NPA 750 (2005) 121, E. Shuryak, hep-ph/ ]
full energy dependence needed!
elliptic flow v2:
initial overlap eccentricity → particle azimuthal distributions v2
central
midcentral
peripheral f
[NA49, PRC68, (2003)]

47. K/p fluctuations 2nd order phase transition at the critical point
→ fluctuations expected
measure e.g. particle ratios (K/p) event-by-event and compare to an event average
increase of K/p fluctuations for lower energies observed
interpretation open

48. Even charm quarks flow!
even charm quarks participate in the flow!

49. Relation to EOS
maximum mass in dependence on radius depends strongly on underlying EOS (compressibility of neutron matter!)
→ compare with measurements!
same for maximum mass and density in the center
try to use constraints on EOS from A+A collisions!
Grigorian, Blaschke, Klähn, astro-ph/

50. Detector R&D – RPC R&D HADES
main issue for many detectors: high rates!
RPC development together with HADES, FOPI
upgrades
study different materials!