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IFAE 2007 Napoli Eugenio Nappi
Incontri di Fisica delle Alte Energie 2007 Incontri di Fisica delle Alte Energie 2007
IFAE 2007 Napoli Eugenio Nappi
N. Cabibbo and G. Parisi, Phys. Lett. B59 (1975) 67
“In high-energy physics we have concentrated on experiments in which we distribute a higher and higher amount of energy into a region with smaller and smaller dimensions.
In order to study the question of ‘vacuum’‘vacuum’, we must turn to a different direction; we should investigate some ‘bulk’ phenomena by distributing high energy over a distributing high energy over a relatively large volumerelatively large volume.”
To understand the strong force and the phenomenon of confinement:we must create and study a system of deconfined quarks
by colliding heavy nuclei at ultrarelativistic energies
The pioneering papersThe pioneering papers
T.D. Lee Rev. Mod. Phys. 47 (1975) 267
IFAE 2007 Napoli Eugenio Nappi
Heavy Ion Physics: – starting in the 80’s at Bevalac by a few physicists mostly from US, Germany and Japan– more than 2000 nuclear and high energy physicists active worldwide today – energy increase by factor 104 in ~ 25 years with LHC in 2008
mostly by (re-)using particle physics machines
Heavy Ion AcceleratorsHeavy Ion Accelerators
1.E+00
1.E+01
1.E+02
1.E+03
1.E+04
1.E+05
1.E+06
1.E+07
1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
Year
sq
rt(s
) -
2m
(G
eV
)
SppS
ISR
FNAL
AGS
TeV LHC
AGS Si/Au
SPS S/Pb
Bevalac
LHC Pb
RHIC
Total center-of-mass energy versus time
x5.5x5.5
x 13x 13
x 28x 28
AGS
SPS
RHIC
LHC
IFAE 2007 Napoli Eugenio Nappi
μB
“Warning” in the Cabibbo and Parisi’s paper:The true phase diagram may actually be substantially more complex, due to other kinds of transition
The actual phase diagramThe actual phase diagram
Temperature
Quark-Gluon Plasma
ColorSuperconductor
Hadronic Fluid
Vacuum
CriticalEnd point
Triplepoint ?Ordinary
matter
Big Bang
~ 173 MeV
IFAE 2007 Napoli Eugenio Nappi
/T4 ~ number of degrees of
freedom
hadronicmatter:
few d.o.f.
deconfinedQCD matter:many d.o.f.
• Critical temperature: Tc 173 MeV• Critical energy density: 6 normal nuclear matter• The phase transition coincides with the restoration of the chiral symmetry• Pressure changes slowly at the phase boundary• The deconfined system does not behave like a weakly interacting parton gas
Expectations from Lattice QCD calculationsExpectations from Lattice QCD calculations
Tc 173 MeV ~ 2 1012 K
(T at the center of the Sun ~ 15 106 K)
Not yet a Stefan Boltzmann gas
IFAE 2007 Napoli Eugenio Nappi
The initial goal was to probe experimentally the phase diagram of nuclear matter (nuclear physics). The scope is now wider: Cosmologynature of QCD under the kind of extreme conditions which occurred in the earliest stages of the evolution of the Universe (~ 1 s)
Astrophysics stability of neutron stars
High energy physics symmetry breaking mechanism origin of (constituent) masses (chiral symmetry restoration)
The scope of heavy ion physicsThe scope of heavy ion physics
IFAE 2007 Napoli Eugenio Nappi
Main results from SPS and RHIC
Future prospects at LHC
ALICE physics potential
Outline
Physics of heavy ion collisions at ultrarelativistic energiesPhysics of heavy ion collisions at ultrarelativistic energies
IFAE 2007 Napoli Eugenio Nappi
reactions traverse two orders of magnitude of energy density and three phases in few fm/c
Aim: to study the dynamical evolution (intermediate phase) through the knowledge of the initial
conditions and the measurement of the particle yield
Heavy Ion CollisionsHeavy Ion Collisions
Colliding ionsColliding ions Bang! Bang! ? ? Freeze-out Freeze-out
IFAE 2007 Napoli Eugenio Nappi
• Chemical freeze-out (at Tch Tc): end of inelastic scatterings; no new particles (except from decays)
• Kinetic freeze-out (at Tfo Tch): end of elastic scatterings; kinematical distributions stop changing
hard (high-pT) probesearly signals (direct,but rare), keepmemory of QGP formation time
soft physics regimelate signals (indirect, but very abundant) created throughout collision history and decoupled late
The time evolution of the matter produced in HI collisionsThe time evolution of the matter produced in HI collisions
IFAE 2007 Napoli Eugenio Nappi
Pb-Pb collision seen by the NA49 TPCs
at the CERN SPS
STARSTAR
dNch/dη = 1200
dNch/dη = 2600
Challenge: selecting and calibrating the probesChallenge: selecting and calibrating the probesHigh multiplicity →Large combinatorialbackgroundEvent by event physics:- chemical composition (exploration of T,B)- dynamical fluctuations, …
Question: how do we recognize that the QGP has been formed?
▪ evidence extracted from a careful and systematic comparison of nucleon-nucleon, nucleon-nucleus and nucleus-nucleus reactions;
▪ simultaneous observation of several
(QGP) signatures
dNch/dy ~ 500
dNch/dy ~ 800
IFAE 2007 Napoli Eugenio Nappi
AGS : 1986 - 2000• Si and Au beams ; up to 14.6 A GeV• only hadronic observables
RHIC : 2000 - • Au, Cu beams ; up to s = 200 GeV• four experiments• hadrons, photons and dileptons
SPS : 1986 - • O, S and Pb beams ; up to 200 A GeV• sixteen experiments (two still running)• hadrons, photons and dileptons
LHC : 2008 - • Pb beams ; up to s = 5.5 TeV• three experiments• hadrons, photons and dileptons
Two labs to recreate the Big-BangTwo labs to recreate the Big-Bang
IFAE 2007 Napoli Eugenio Nappi
New state of matter at the SPSNew state of matter at the SPS
• J/ suppression. Indication of deconfinement?– J/ loosely bound system melts in QGP due to Debye screening
• Strangeness enhancement– Mass of strange quark decreases in QGP therefore easier to produce
• Melting of the – Ifdecays in QGP medium its mass is modified
NA50
April 2000, CERN press office announcement:
compelling evidence that a new state of matter has indeed been created
IFAE 2007 Napoli Eugenio Nappi
RHIC revenge RHIC revenge
IFAE 2007 Napoli Eugenio Nappi
the energy density is at least 7 times larger than needed for color deconfinement and temperature is about two times the critical temperature predicted by lattice QCD; matter thermalizes in an unexpectedly short time (< 1 fm/c) and exhibites collective motion with ideal hydrodynamic properties: a perfect liquid that appears to flow with a near-zero viscosity to entropy ratio, lower than any previously observed fluid (close to a universal lower bound); anomalous enhancement of baryon and anti-baryon production rates relative to mesons suggesting that hadrons form by quark coalescence after the flow occurs; dramatic energy loss of partons traversing matter of very high color charge density.
Heavy ion physics at RHICHeavy ion physics at RHIC
IFAE 2007 Napoli Eugenio Nappi
the energy density is at least 7 times larger than needed for color deconfinement and temperature is about two times the critical temperature predicted by lattice QCD; matter thermalizes in an unexpectedly short time (< 1 fm/c) and exhibites collective motion with ideal hydrodynamic properties: a perfect liquid that appears to flow with a near-zero viscosity to entropy ratio, lower than any previously observed fluid (close to a universal lower bound); anomalous enhancement of baryon and anti-baryon production rates relative to mesons suggesting that hadrons form by quark coalescence after the flow occurs; dramatic energy loss of partons traversing matter of very high color charge density.
Heavy ion physics at RHICHeavy ion physics at RHIC
IFAE 2007 Napoli Eugenio Nappi
Particle distribution in the transverse plane Particle distribution in the transverse plane
b
x
y z
Coordinate space: initial asymmetry
Momentum space: final asymmetry
Collective motion → asymmetric pressure gradients are more effective at pushing particles out along the “reaction plane” direction rather than perpendicular to it, as measured by the elliptic flow v2
spectators
participantsnucleons in
nuclear overlap
nn
TT
ndpdN
ddpdN
)cos(v21 v2 is the 2nd harmonic Fourier coefficientof the particle distribution in the x-y plane
22
22
2 2cosyx
yx
pp
ppv
IFAE 2007 Napoli Eugenio Nappi
Elliptical flow @ RHICElliptical flow @ RHIC
v2 as large as predicted by perfect fluid dynamics strong (collective) pressure large and fast rescattering (early thermalization)
v2 dependent on mass (as predicted by P. Huovinen et al, PLB 503 (2001) 58)
viscosity/entropy = /s ~ 0 (perfect fluid)
0/ /s s
IFAE 2007 Napoli Eugenio Nappi
Scaling with valence quark number n supports a Scaling with valence quark number n supports a quark-coalescence picture of hadronizationquark-coalescence picture of hadronization
2 2v vhad partn
had partT Tp np
Coalescence vs fragmentationCoalescence vs fragmentation
Elliptic flow saturates at pt ~ 1 GeV/c, just at the constituent quark scale
IFAE 2007 Napoli Eugenio Nappi
the energy density is at least 7 times larger than needed for color deconfinement and temperature is about two times the critical temperature predicted by lattice QCD; matter thermalizes in an unexpectedly short time (< 1 fm/c) and exhibites collective motion with ideal hydrodynamic properties: a perfect liquid that appears to flow with a near-zero viscosity to entropy ratio, lower than any previously observed fluid (close to a universal lower bound); anomalous enhancement of baryon and anti-baryon production rates relative to mesons suggesting that hadrons form by quark coalescence after the flow occurs; dramatic energy loss of partons traversing matter of very high color charge density.
Heavy ion physics at RHICHeavy ion physics at RHIC
IFAE 2007 Napoli Eugenio Nappi
• Recombination models assume particles are formed by the coalescence of “constituent” quarks
• Explain baryon excess by simple counting of valence quark content
Particle production ratioParticle production ratio
Au+Au: p/ ~ 1 Λ/K0S ~ 1.8
p+p: p/ ~ 0.3 Λ/K0S ~ 0.6
e++e-: p/ ~ 0.1-0.2
large enhancement in Au+Au relative to p+p collisions (max at pT~3 GeV/c)
IFAE 2007 Napoli Eugenio Nappi
the energy density is at least 7 times larger than needed for color deconfinement and temperature is about two times the critical temperature predicted by lattice QCD; matter thermalizes in an unexpectedly short time (< 1 fm/c) and exhibites collective motion with ideal hydrodynamic properties: a perfect liquid that appears to flow with a near-zero viscosity to entropy ratio, lower than any previously observed fluid (close to a universal lower bound); anomalous enhancement of baryon and anti-baryon production rates relative to mesons suggesting that hadrons form by quark coalescence after the flow occurs; dramatic energy loss of partons traversing matter of very high color charge density.
Heavy ion physics at RHICHeavy ion physics at RHIC
IFAE 2007 Napoli Eugenio Nappi
back-to-back jets in pp and d-Au collisionsthe jet opposite to the high-pT trigger particle
disappears in central Au-Au collisions being absorbed by the dense QCD medium
Jet quenching @ RHICJet quenching @ RHIC
- pp d-Aucentral Au-Au
Two-particle azimuthal correlations
the high-pT hadrons are strongly suppressed with
respect to the expected scaling from pp collisions, photons are not affected by the dense medium
jet quenching: fast particles lose energy by traveling through the dense medium
nu
clea
r m
od
ific
atio
n f
acto
r
ppin yield 197 x 197
AuAuin yieldAAR
matter created in heavy-ion collisions is of extreme density and thus very opaque to hard partons
If A+A = p+p, then RAA
=1
IFAE 2007 Napoli Eugenio Nappi
Experimental evidence for « liquid » rather
than « gaseous » behavior
Strong correspondence with cosmology RHIC results, if confirmed at LHC,
would imply:
early Universe was a low viscosity liquid (400 times less than water) at T = 2000 109 K
Art due to Hatsuda and S. Bass
QGP @ RHIC QGP @ RHIC
The matter created in heavy ion collisions forms a highly color opaque plasma of quarks and gluons, which is possibly permeated by turbulent color fields, especially at early times, when the expansion is most rapid→→ sQGPsQGP
Berndt MBerndt Mueueller – ller – Duke UniversityDuke University
……it is clear that the matter created it is clear that the matter created
at RHIC differs from anything that at RHIC differs from anything that
has been seen before. Its precisehas been seen before. Its precise
description must await our deeperdescription must await our deeper
understanding… BRAHMS collab. understanding… BRAHMS collab.
IFAE 2007 Napoli Eugenio Nappi
LHC heavy ion programmeLHC heavy ion programme– Machine:– energy:
• Ebeam = 7 x Z/A [TeV] => s = 5.5 TeV/A or 1.14 PeV (Pb-Pb)
– beams:• possible combinations: pp, pA, AA (constant beam rigidity)
– Running time:• ~ 4 weeks/year (106 s effective); typically after pp running (like at SPS)• first HI run expected end 2008 (1/20th design luminosity)
– Luminosity: • 1027 (Pb) to >1030 (light ions) cm-2s-1 => rate from 10 kHz to several 100 kHz• integrated luminosity 0.5 nb-1/year (Pb-Pb)
– Detector(s)
– one single dedicated ‘general purpose’ HI expt at LHC: ALICE
– ATLAS/CMS will participate, but priority is pp physics
IFAE 2007 Napoli Eugenio Nappi
Why ultra-relativistic nuclear collisions at LHC? Why ultra-relativistic nuclear collisions at LHC?
<0.2~0.3~10 (fm/c)
4–101.5–4.0<1QGP (fm/c)
2x1047x103103Vf(fm3)
15–504–52.5 (GeV/fm3)
1200-2600800500dNch/dy
550020017s1/2(GeV)
LHCRHICSPSCentral collisionsHigher energy densities over larger volumes and increased lifetime of QGP phase (~10 fm/c) QGP more dominant over final-state hadron interactions
LHC is the first machine that will produce a long-lived quark-gluon plasma
transition from strongly coupled QGP -> ideal QGP ?
Much larger “dynamic range” compared to RHIC
IFAE 2007 Napoli Eugenio Nappi
• LHC allows to probe initial partonic state in a novel Bjorken-x range (10-2-10-5) where strong nuclear gluon shadowing is expected (saturation of the available phase-space) • At LHC, the central region is expected to be essentially baryon free more direct comparison with lattice QCD calculations and with the conditions of the primordial Universe
Novel aspects of nucleus-nucleus collisions at LHCNovel aspects of nucleus-nucleus collisions at LHC
10-6 10-4 10-2 100
x
108
106
104
102
100M
2 (
GeV
2)
RHIC
High density (saturated) gluon distribution
M = 3 GeV
M = 10 GeV
IFAE 2007 Napoli Eugenio Nappi
Hard Processes at LHCHard Processes at LHCMain novelty of the LHC: large hard cross section (scale with s !)
~2% at SPS
~50% at RHIC
~98% at LHC
tothard /
Hard processes ( i.e. jets, heavy flavours) are extremely useful tools:– have large Q and small “formation
time” t 1/Q• probe matter at very early
times – extend the range of matter probes
into regimes that allow for more reliable calculations (pQCD)
X 2000X 2000
Pion Production
Very hard probes
copiously produced
More than 1 jet > 20 GeV per central collision (more than 100 > 2 GeV)More than 4.0 104 jets with ET > 200 GeV in 1 month Pb-Pb run
IFAE 2007 Napoli Eugenio Nappi
Heavy quarksHeavy quarks
bbRHIC
bbLHC
ccRHIC
ccLHC
100
10
NLO calculations with MNR code: Mangano, Nason, Ridolfi, Nucl. Phys. B 373 (1992) 295.
NLO predictions (ALICE baseline for charm & beauty)
theoretical uncertainties of a factor 23
[mb] QQNNQQ
totN
system, s pp, 14 TeV Pb-Pb (0-5%), 5.5 TeV
11.2 / 0.5 4.3 / 0.2
0.16 / 0.007 115 / 4.6
SPS RHIC LHC
J/ melting
J/ regeneration
H. Satz, CERN Heavy Ion Forum, 09/06/05
?
Cancellation between J/suppression and regeneration(recombination) in a QGP ?
If more than one c-quark pair is formed within y 1, and if the c-quarks are thermalized, J/ may be formed by recombination.
IFAE 2007 Napoli Eugenio Nappi
Guideline: to measure flavor content and phase-space distribution event-by-event– Track and identify most (2 * 1.8 units) of the hadrons from very
low (< 100 MeV/c; soft processes) up to fairly high pT (~100 GeV/c; hard processes)
– Vertex recognition of hyperons and D/B mesons in an environment of very high charged-particles density (up to dN/d = 8000)
– Dedicated & complementary systems for di-electrons and di-muons– Excellent photon detection ( in Δφ =45° and 0.1 η units)– High throughput DAQ system + powerful online intelligence ('PC
farm')
ALICE ( A Large Ion Collider Experiment) is the only LHC detector specifically designed to investigate nucleus-nucleus collisions
Compromise: the fragmentation region is not addressed (difficult at LHC, ybeam=9)
ALICE Design ParametersALICE Design Parameters
IFAE 2007 Napoli Eugenio Nappi
The Alice CollaborationThe Alice Collaboration
~ ½ ATLAS,CMS; ~ 2x LHCb
30 Countries
90 Institutions
~1000 collaborators total (63% from CERN MS)
A large community which has been
constantly growing over the years, and still
grows
Italian participation: 190 researchers CORE share ~ 24 M€ ≈ 27%
IFAE 2007 Napoli Eugenio Nappi
ALICE Experimental LayoutALICE Experimental Layout
L3 magnet
B ≤ 0.5 T
Total weight : 9,800 tonsOverall diameter : 16 mOverall length : 26 m 130 MCHF CORE
Muon Forward Spectrometer
2.4 < < 4
IFAE 2007 Napoli Eugenio Nappi
Lepton AcceptanceLepton Acceptance
ATLAS & CMS present a large lepton acceptance ||<2.4
ALICE combines muonic and electronic channels
- covers the low pT region (quarkonia)
- covers the forward region 2.5<<4.0
IFAE 2007 Napoli Eugenio Nappi
J/Ψ family family
Mμμ (GeV/c)Mμμ (GeV/c)
– μ+μ- channel (muon arm)– 1 month PbPb data taking
State S[103] B[103] S/B S/(S+B)1/2
J/ 130 680 0.20 150
’ 3.7 300 0.01 6.7
(1S) 1.3 0.8 1.7 29
(2S) 0.35 0.54 0.65 12
(3S) 0.20 0.42 0.48 8.1
QuarkoniaQuarkonia
e+e- channel (TRD)
2 x 108 PbPb
IFAE 2007 Napoli Eugenio Nappi
• Essential jet measurements: modification of fragmentation in dense matter + response of the medium to the jet– cross sections are huge: rate is not a
primary issue– calorimetry alone insufficient:
physics lies in detailed changes of fragmentation patterns and correlations, including low pT
• Requirements for jet measurements:– precise tracking over very broad
kinematic range (TPC+ITS)– PID over broad kinematic range – detailed correlations of soft and hard
physics– jet trigger (EMCAL)
EMCAL EMCAL
Joint project between US and Europe (Italy and France)
It will enhance the ALICE capabilitiesfor jet measurement. It enables triggering on high energy jets (enhancement factor 10-15), reduces the bias for jet studies and improves the jet energy resolution.
IFAE 2007 Napoli Eugenio Nappi
August 2006August 2006 Detector InstallationDetector Installation
SEPTEMBER 2006SEPTEMBER 2006SEPTEMBER 2006SEPTEMBER 2006January 2007January 2007March 2006March 2006
IFAE 2007 Napoli Eugenio Nappi
Tracking PerformanceTracking Performance
p (GeV/c)
For track densities dN/dy = 2000 – 4000, combined tracking efficiency well above 90% with <5% fake track
probability
dN/dy = 4000, B=0.4 T
resolution ~ 5% at 100 GeV/c excellent performance in hard region!
IFAE 2007 Napoli Eugenio Nappi
0 1 2 3 4 5 p (GeV/c)
TPC + ITS (dE/dx)
/K
/K
K/p
K/p
e /
HMPID (RICH)
TOF
1 10 100 p (GeV/c)
TRD e /Rejection factor 100
/K
K/p
HADRON-ID 3 separation power
ITS
kaons
pions
protons
dE/d
x (M
IP u
nits
)
TPC
P(GeV/c)
All known PID techniques used in ALICE
dE/dx = 6.8% at dN/dy=8000 (5.5% for isolated tracks)
Charged Particle IdentificationCharged Particle Identification
IFAE 2007 Napoli Eugenio Nappi
Extension of PID by dE/dx to higher momentaExtension of PID by dE/dx to higher momenta
Combine TPC and TRD dE/dx capabilities (similar number of samples/track) to get statistical ID in the relativistic rise region
8<p<10GeV/c
IFAE 2007 Napoli Eugenio Nappi
Secondary vertex and cascade finding
Pb-Pb central
13 recons./event
pT dependent cuts -> optimizeefficiency over the whole pT range
Statistical limit : pT ~8 - 10 GeV/c for K+, K-, K0s, ; 3 - 6 GeV/c for
Reconst. rates: : 0.1/event : 0.01/eventpT: 1 to 3-6 GeV
300 Hijingevents
8-10 GeV
106
Topological identification of strange particlesTopological identification of strange particles
IFAE 2007 Napoli Eugenio Nappi
Invariant mass reconstruction, background subtracted (like-sign method) mass resolutions ~ 1.5 - 3 MeV and pT stat. limits from 5 () to 12 GeV/c (,K*)
central Pb-Pb
Mass resolution ~ 2-3 MeV
K*(892)0 K 15000 central Pb-Pb
K+K-Mass resolution ~ 1.2 MeV
Invariant mass (GeV/c2)
ResonancesResonances
IFAE 2007 Napoli Eugenio Nappi
Open Charm Detection in Hadronic DecaysOpen Charm Detection in Hadronic Decays
Mass 1.864 GeV/c2 c=124 m
~0.55 D0K-+ accepted/event important also for J/ normalization
Overall significance for 106 events ~10
1<pT<2 GeV/c
High precision open charm measurement
IFAE 2007 Napoli Eugenio Nappi
Proton-proton physics with ALICE
The ALICE detector works even better for pp collisions, because of the low occupancy (10–4 to 10–3), even if there is a significant number of events overlapping.
The first physics with ALICE will be proton-proton collisions, which correspond to a major part of the ALICE programme for several reasons:– to provide “reference” data to understand heavy ion collisions. In a new
energy domain, each signal in HI has to be compared to pp;– For genuine proton-proton physics whenever ALICE is unique or
competitive; note that ALICE can reach rather “high” pT, up to ~ 100 GeV/c, ensuring overlap with other LHC experiments.
– The possibility of taking proton data at several center of mass energies (0.9 TeV, 2.4 TeV, perhaps 5.5 TeV, and 14 TeV), will provide ALICE with the possibility to understand the evolution of many of the properties of pp collisions as a function of the center of mass energy, and also to add to the measurements from previous experiments using proton-antiprotons.
IFAE 2007 Napoli Eugenio Nappi
Minimum Bias trigger is provided by coincidence between V0 counters covering a pseudo-rapidity range from -1.7 to -3.7 and from 2.8 to 5.1.
excellent measurement in the central region
(charged particles)
Global event properties: charged particle multiplicity
IFAE 2007 Napoli Eugenio Nappi
Strange and baryonic particle studies• based on Pythia simulation, ALICE will be able to acquire a significant sample of strange based on Pythia simulation, ALICE will be able to acquire a significant sample of strange
particles produced in pp minimum bias events:particles produced in pp minimum bias events:
• heavy flavour baryons (heavy flavour baryons (bb, , bb, , bb, ...) which are poorly known. , ...) which are poorly known.
Br.(Br.(bb J/ J/ = (4.7 ± 2.8) = (4.7 ± 2.8)1010–4–4, 10, 1099 events, triggered on J/ events, triggered on J/ using the TRD detector, should using the TRD detector, should
produce a few thousand produce a few thousand bb
IFAE 2007 Napoli Eugenio Nappi
LHC will provide a quantitative LHC will provide a quantitative understanding of Relativistic understanding of Relativistic Heavy Ion collision dynamics Heavy Ion collision dynamics
and QGP properties likely and QGP properties likely enabling enabling to assess the current to assess the current
theoretical uncertaintiestheoretical uncertainties
ConclusionConclusion