September 6, 2001Heavy ion physics at CERN after 2000 and before LHC 1 E. Scomparin, INFN-Torino (Italy) NA60 collaboration International Workshop on the.

September 6, 2001 Heavy ion physics at CERN after 2000 and before LHC

1

Heavy ion physics at CERN after 2000 and before LHC

E. Scomparin, INFN-Torino (Italy)

NA60 collaboration

International Workshop on the Physics of QGP Palaiseau, September 4-7, 2001

•The success of the SPS program•Turning “compelling evidence” into solid proof: specific questions which require specific answers•The extension of the heavy ion program (2002-2003)•Dimuon physics: the NA60 experiment•Studies in the hadronic sector•Conclusions


2

Actual status of the SPS program•Observed signals (and theoretical calculations) seem to indicate that SPS energy region is the one where deconfinement starts to occur •At 158 GeV/c:

•charmonia suppression pattern (NA50)steep onset seen in peripheral PbPb

•strangeness enhancement (WA97/NA57, NA49) smooth onset for peripheral PbPb

•At 40 GeV/c:•Strangeness enhancement is higher than at top SPS energy(NA49)

•How to get a clearer view of how deconfinement sets in ?•Study, in the SPS energy range:

•excitation functions for various observables•system size dependence (lighter projectiles)

•Also other observations need clarification/confirmationhas thermal radiation been detected (WA98,NA50)?


3

Plans for next years

NA35 NA36

NA49

NA34(Helios-2)

NA34/3(Helios-3)

NA44

NA45(Ceres)

NA38

NA50

NA60

WA80

WA98

WA85

WA97

NA57

NA52

WA94

HADRONS LEPTONS, PHOTONS

S

multistrange

photons

electrons

1986

1994

2000

exoticsstrangeness,

hadron spectra

strangeness

muons

2003

muonsstrangeness,

hadron spectra

Pb

2001: p beam only2002-2003: p and ion beams (Pb at various energies, In)


4

Open questions on dimuon physics

•What is the origin of the excess production of intermediate mass dimuons ?Thermal dimuon production or open charm enhancement ?

•What is the open charm production cross section in nucleus-nucleus collisions ?

•What is the physics variable that rules the onset of J/ suppression ?

•Are the and mesons modified by the medium ?

•Which fraction of the J/ yield comes from c decays ?What is the nuclear dependence of c production in p-A collisions ?

•NA60, approved to run in the years 2001-2003, will try to answer these questions•Based on an upgrade of the existing NA50 set-up (muon spectrometer+centrality detectors)


5

The NA60 collaborationR. Arnaldi, A. Baldit, K. Banicz, K. Borer, L. Casagrande, J. Castor, B. Chaurand, W. Chen, E. Chesi, B. Cheynis, C. Cicalò, P. Cortese, V. Danielyan, A. David, A. De Falco, N. De Marco,A. Devaux, B. Dezillie, D. Dominguez, L. Ducroux, B. Espagnon, P. Force, E. Gangler, V. Granata, A. Grigorian, S. Grigorian, J.Y. Grossiord, A. Guichard, H. Gulkanian, R. Hakobyan, E. Heijne, M. Hess, P. Jarron, L. Kluberg, B. Lenkeit, Z. Li, C. Lourenço, J. Lozano, M.P. Macciotta, F. Manso, D. Marras, A. Masoni, S. Mehrabyan, H. Muller, A. Musso, A. Neves, B. Pes, S. Popescu, G. Puddu, E. Radermacher, P. Ramalhete, P. Rosinsky, P. Saturnini, E. Scomparin, J. Seixas, S. Serci, R. Shahoyan, E. Siddi, P. Sonderegger, G. Usai, G. Vandoni, H. Vardanyan and H. Wöhri

Brookhaven

Lisbon

CERN Bern

Torino

Yerevan

CagliariLyonClermont


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NA60: detector concept (1)

• Drawbacks of NA50 set-up: •Multiple scattering limits mass resolution, no prompt muon tagging

• Start from existing NA50 set-up:• Muon spectrometer : NA10 NA38 NA50 NA60• ET + EZDC + Nch detailed scan in centrality from peripheral to central collisions• Small production cross sections extremely selective dimuon trigger !• High intensity beams (more than 107 ions per second) radiation hard detectors• More than 1010 Pb-Pb collisions are probed every running day


7

NA60: detector concept (2)

D

{offset

vertex

Adding silicon detectors to track the muons before they traverse the

hadron absorber

• Track matching through the muon filter• Improved mass resolution• Improved signal / background ratio (rejection of and K decays)• Improved systematical uncertainties (vertex reconstruction)

• Muon track offset measurement • Separate charm from prompt (thermal) dimuons


8

NA60: overview of new detectors

• 10 planes• 88 pixel readout chips• 720 000 channels• pixel size : 50425 m2

Silicon pixel telescope

2.5 Tdipole field

• 2 x-y stations of -strip Si detectors at T = 130 K• ~ 20 m resolution on the transverse coordinates of the beam ions

Beamscope


9

The muon spectrometer•Working since 1977 : NA10, NA38, NA50, NA60

•Upgrade of gas system

•New DAQ and controls

•R/O electronics interface changing from VME to PCI


10

The zero degree calorimeter•Working; developed for use in NA50 ; it only works for ion runs•New DAQ and controls •R/O electronics interface will change to PCI in 2002, before ion run•A quartz blade will be placed just upstream of the ZDC, to identify beam fragments


11

The target region

Hadronabsorbers

Tracking volume

Target box

Beamscope

PT7 Magnet

beam

•Several advantages with respect to the original 1.7 T TC8 magnet:•C-shapedeasier integration of target detectors•Larger gap (106 mm) better coverage of muon spectrometer acceptance•Higher magnetic field improve track matching efficiency

Field along beam axis

•2.5 T dipole field at 900 A •BdL = 1 Tm •very homogeneous field


12

Performance of new detectors: beamscope

= 1.0 ± 0.1 ns •October 2000: exposed 42 days in the NA50 Pb beam•Average beam intensity: 710 7 ions per 4.5 s burst•Total fluence : 5 ± 2 1014 ions / cm2 ( 90 ± 40 Grad )


13

Performance of new detectors: pixel telescope

4 “half” planes33 LHC1 chips~ 60’000 channels

absorber

target

Pixel box

coil

1.7 T dipolemagnetic field


14

Dimuon mass resolution

Clear improvement in mass resolution, thanks to the vertex spectrometer

M at M = 1 GeV : 70 MeV in NA50; 20 MeV in NA60

Good agreement data simulation

Data: 450 GeV,3 days, ~10 8 protons / burst,

10 mm Be target ( 5 % int )


15

Low mass dileptons: where are we?

NA50

•CERES sees, in Pb-Pb collisions, a strong dielectron enhancement:2.6 0.5(stat) 0.6(syst), for 0.25<mee<0.7 GeV/c2 (1996 data), concentrated at low pT

•NA50 sees practically no excess, but has a strong mT cut, due to the optimization of the set-up for J/ studies•Rather poor mass resolution and signal/background for both experiments


16

NA60: low mass dimuon physics

•Statistics corresponding to :•1 week of data taking at 107 ions/burst•0.17 I target

•About 1.5·105 , ,

•Evident gain in mass resolution, S/B and statistics with respect to existing CERES & NA50 data


17

Intermediate mass dimuons: where are we?

•Excess of dimuon production in A-A collisions (Helios-3, NA38/NA50) compatible with an enhancement (~factor 3) of open charm production

•Result based on •Mass shape analysis•Transverse momentum analysis

•Theoretical explanation difficult


18

Looking for thermal dimuons

•NA50 excess has been found to be compatible also with the production of thermal dimuons (central collisions), in a model which assumes :

•fireball lifetime : 14 fm/c•initial temperature : Ti = 192 MeV•Presence of a QGP phase with critical temperature : Tc = 175 MeV

see Rapp and Shuryak, PLB473(2000)13


19

Impact parameter resolution

Determination of the interaction vertex

Impact parameter of the muon tracks


20

Intermediate mass dimuons in NA60

Prompt dimuons selection : events with muon track offset < 90 m

Charm selection : events with muon track offset in the range 90 800 m and muons > 180 m away from each other in the transverse plane at zv

•Statistics corresponding to:30 days of data taking at 5·107 ions/burst, with 5 Pb sub-targets (1.5 mm each)


21

J/: where are we ?

melting of c ?

melting of directly produced J/ ?

PLB 477 (2000) 28

•A specific prediction to be checked by NA60: the J/ suppression pattern in In-In collisions exhibits a break at an impact parameter ~ 3.5 fm (M. Nardi & H. Satz)


22

J/ physics in NA60

•NA60: improved mass resolution•J/ mass resolution:

•90 MeV (no pixel) 55 MeV (pixel)’ mass resolution:

•120 MeV (no pixel) 75 MeV (pixel)•NA60 can study the onset of ’ suppression (between p-A and peripheral S-U collisions)

•NA50•Mass resolution ~ 100 MeV @ M~3 GeV’ production rate small compared to J/ •Systematic errors not negligible when studying ’/ J/


23

pA physics: study of c yield

•4 Be and 1 Pb targets; ~ 30 days of protons•Background subtracted by mixing J/ and

e+e pairs from different events

•Important to correctly separate, in nucleus-nucleus collisions, J/ from radiative c decays from direct J/ •Study the ratio c/ J/ for light and heavy targets•Measure c e+e

•Match muon tracks in the spectrometer with tracks in the vertex spectrometer to identify J/ (~80%)•Look for a dielectron (common vertex, correct mass) between remaining tracks•Global reconstruction efficiency~5%

B = 1.7 T


24

NA60 pA runs: 2001 setup

40 cm

•8 double planes of silicon micro-strips ; sensors from BNL

• Hybrids and SCTA128 readout chips developed for ATLAS

• New ADC readout card (also for LHC-B)

• Occupancies always below 3 %

• Mass resolution : ~15 MeV, c~25 MeV (with B=2.5 T)

Beamscope available also for p-Athanks to a recent CERN-EP/MIC development of a fast amplifier


25

NA60: summary

• Third generation experiment to separately study the production of prompt dimuons and of muons coming from the decay of charmed mesons

• NA60 will clarify the origin of the excess IM dimuon production and measure the yield of charmed mesons produced in heavy ion collisions• By accurately measuring the J/ and ’ production in In-In collisions, NA60 will put to a stringent test the current interpretations of the step-wise pattern measured by NA50 in Pb-Pb collision• Low mass dimuon data with good statistics, mass resolution and signal to background ratio will allow to study the production of , and mesons

• NA60 will contribute to the understanding of the present results and will clarify if a deconfined state of matter is produced in heavy ion collisions at the SPS


26

Study of low energy Pb-Pb collisions: NA49•Non-monotonic energy dependence of the strangeness to pion ratio•At 40 A·GeV, higher by ~30% than at top AGS and SPS energies

10 days of data taking in 2002 at 20 and 30 A·GeV to look for a structure in Es

(80 A·GeV data already collected in 2000)


27

Conclusions

•In the years 1986-2000 several SPS experiments have seen what they were looking for

•Available results (J/ suppression, strangeness enhancement, possible emissionof thermal radiation, in-medium modification of vector mesons) show that thehypothesis of QGP formation at SPS energies holds

•In the final three years the SPS program will be focussed on very specific topics.

•A measurement of open charm, useful as a reference for the study of charmonia suppression, and interesting for the study of the mechanisms involved in heavy quark production in the nucleus-nucleus environment, will be performed•The study of charmonia suppression pattern (NA60) and strangeness production (NA49) will be continued, using energy scans and intermediate mass projectiles (In). The aim is to deepen our understanding of how deconfinement sets in

September 6, 2001Heavy ion physics at CERN after 2000 and before LHC 1 E. Scomparin, INFN-Torino (Italy) NA60 collaboration International Workshop on the.

Documents

heavy ion physics

dimuon physics

heavy ion program

physics variable

sps program

physics of qgp palaiseau

muons strangeness

ion beams pb