The NA60 experiment at the CERN SPS
first results and future perspectives
Chiara Oppedisano
for the NA60 Collaboration
Study of prompt dimuon and charm production
with proton and heavy ion beams at the CERN SPS
Detector concept and physics programme
Dimuon production in p-A collisions
Charged particle pseudorapidity densities in Pb-Pb collisions
Future perspectives
SQM 2003, Atlantic Beach, NC, USA
C. Oppedisano
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Detector concept
MUON SPECTROMETER
~1m
Muon filter
TARGET
AREA
ZDC and
Quartz Blade
Tracking
MWPCs
Toroidal Magnet
Fe
wall
Trigger
hodoscopes
GOAL  accurate measurement of muon kinematics
Hadron absorber + muon spectrometer (NA50)
 no information at vertex level to distinguish prompt
from decay muons
Dipole field
2.5 T
TARGET
BOX
BEAM
BEAM
TRACKER
MUON
FILTER
TELESCOPE
IC
VERTEX TELESCOPE  matching tracks in muon
spectrometer and in vertex spectrometer
MAGNETIC FIELD measurement of muon track
momentum at vertex
BEAM TRACKER  measurement of interaction point
to determine impact parameter of muon tracks
SQM 2003, Atlantic Beach, NC, USA
C. Oppedisano
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Beam tracker and target system
BEAM TRACKER
 Silicon micro-strip detectors
2 x-y stations upstream of target box
cryogenic detector (T = 130K)
 radiation hardness
20 mm resolution on transverse
coordinates of interaction point
Online monitoring of beam profile  Pb @ 20 A GeV
TARGET SYSTEM
Proton beam  Be, In and Pb targets
same beam normalization for all the nuclear targets
Ion beams  several thin sub-targets
interaction rate comparable to a thick target
reduced material traversed by muon in the angular acceptance of muon spectrometer
SQM 2003, Atlantic Beach, NC, USA
C. Oppedisano
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Vertex telescope
Vertex spectrometer placed in magnetic field  accurate measurement of angle and
momentum of tracks at the vertex, covering muon spectrometer angular acceptance
p-A collisions Silicon MICROSTRIP and PIXEL detectors
sensors divided in regions of variable strip pitch and length
 occupancy <3%
16 microstrip planes grouped in 8 tracking stations
~40 cm
A-A collisions  Silicon PIXEL detectors
high occupancy  high granularity and radiation hardness
tracking planes  10 four-chip planes and 3 sixteen-chip planes
Y (cm)
ALICE1LHCB chips, pixel size (50  425) mm2
~32 cm
 Expected mass resolution: 20 MeV at w peak
Hitmap (Pb-Pb collision)
SQM 2003, Atlantic Beach, NC, USA
C. Oppedisano
X (cm)4
Intermediate mass region excess
With enhanced
charm
p-A collisions
 data described by Drell-Yan + charm decays
Peripheral
collisions
S-U and Pb-Pb collisions
 dimuon yield exceeds the superposition of
expected sources
With expected
charm yield
IMR dimuon yields can be reproduced by:
adding thermal radiation to Drell-Yan and open
charm
OR
scaling up of charm contribution vs. centrality
by up to a factor 3
dN/dM
M(GeV)
Central
collisions
NA60
separate open charm from thermal contribution
SQM 2003, Atlantic Beach, NC, USA
C. Oppedisano
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Open charm tagging
measure impact parameter of muon tracks
 separation of the two main contributions to IMR dimuon spectra:
prompt dimuon sample from interaction vertex
muon pairs from D decays with offset w.r.t. interaction point
µ
~10 cm
Muon filter
vertex
, K  µ
offset
<1mm
Dµ
prompt dimuons
Background
PROMPT
dN/dM
dN/dM
Offset distribution
Background
CHARM
open charm
Charm
Prompt
0
100 200 300 400 500 600 700
Offset (mm)
SQM 2003, Atlantic Beach, NC, USA
C. Oppedisano M(GeV)
M(GeV)
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Charmonium production
NA50
CHARMONIUM SUPPRESSION
NA50  J/y suppression  indication for onset of deconfinement
cc melting
NA60
better mass resolution  yI and J/y clearly separated
In-In collisions  identification of the physics variable with
threshold behavior
D production is the best reference for J/y production study
s(p-A) = s0 Aa
A-DEPENDENCE OF cc PRODUCTION IN p-A COLLISIONS
Around 30-40% of J/y comes from cc radiative decays
E866
NA50  cc anomalously suppressed in semi-central Pb-Pb
collisions
p-A 800 GeV
NA60
normal absorption pattern of cc
measuring the cc to J/y ratio from p-Be to p-Pb
SQM 2003, Atlantic Beach, NC, USA
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Results from p-A data (I)
Dimuon mass spectrum
from muon spectrometer
Data collected in June 2002
6 targets (1 In, 3 Be, 1 Pb, 1 Be) 2 mm thick
Vertex telescope: 14 strip planes + 1 pixel plane
 Zvertex resolution ~ 900 mm
Target identified by
vertex telescope
Dimuon spectrum
for each target
Zvertex distribution
Muon track matching
between vertex telescope
and muon spectrometer
Pb
250
p-Be
200
sw ~ 25 MeV
In
150
sf ~ 30 MeV
100
Be Be Be
Be
50
0
-4
-2
024
Z (cm)(cm)
Zvertex
SQM 2003, Atlantic Beach, NC, USA
C. Oppedisano
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Results from p-A data (II)
Dimuon spectra after muon track matching: In and Pb targets
p-In
p-Pb
 dimuon mass resolution: ~ 25 MeV at the w peak and ~ 30 MeV at the f
 precise A-dependence of the w and f production
(NA50 mass resolution for low masses ~ 90 MeV)
Muon offset study  little statistics to extract charm A-dependence
SQM 2003, Atlantic Beach, NC, USA
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Results from Pb-Pb data
Pb-Pb collisions at 20 and 30 A GeV (October 2002)
3 Pb targets: 1.5, 1.0 and 0.5 mm thick
dN/dZ
Resolution on interaction vertex
determination: σZ ~190 mm σX ~20 mm
Pb targets
Beam
tracker
sensor
Target box
window
Xvertex from beam tracker
(cm)
Beam tracker vs. pixel telescope
Xvertex from telescope (cm)
Zvertex (cm)
SQM 2003, Atlantic Beach, NC, USA
Correlation width ~ 30 mm
C. Oppedisano
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Charged particle multiplicity measurement
Multiplicities evaluated from clusters
to access midrapidity
Plane 1 - Target 1
Plane 1 - Target 3
Magnetic field switched off
midrapidity
midrapidity
Geometrical acceptances depend
on the considered plane-target set
Centrality measured by ZDC
dN/dh (0.1 h units)
ZDC spectrum @ 30 GeV
Beam trigger
Interaction trigger
1
2
3
Plane 1
Data corrected
for acceptance
EZDC<1685 GeV  5% of total geometrical x-section
SQM 2003, Atlantic Beach, NC, USA
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dN/dh (0.1 h units)
Corrections
d rays (Pb+fragments)
Plane 1 - Target 3
(worst case)
d rays from Pb beam  simulations with GEANT3.21
MC reliability tested with beam-trigger data
Corrections factors calculated for each plane-target set
d rays from fragments  evaluated vs. centrality
Correction factor for
re-interaction from MC
Plane 1 - Target 1
SQM 2003, Atlantic Beach, NC, USA
dN/dh (0.1 h units)
dN/dh (0.1 h units)
Secondaries from re-interactions  evaluated using
UrQMD 1.2, leads to correction factors from 1.1 to 1.8
1
2
3
Plane 1
After MC corrections
 distributions in
good agreement
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Charged particle distributions
Fit of dNch/dh distributions at 30 GeV  hmax from data compatible with event generator value
Systematic error ~11% (4% from residual data spread at same h, 9% on d-rays contribution,
(dN/dh)/(0.5 Npart)
dN/dh (0.1 h units)
3% on re-interaction factors, 5% on pixel plane efficiency)
30 GeV
Npart
h
Centrality bin
hmax
(dN/dh)hmax
0-5 %
5-10%
10-20%
20-35%
2.1 ± 0.1
2.1 ± 0.1
1.9 ± 0.2
1.8 ± 0.2
172 ± 4
129 ± 4
98 ± 4
74 ± 6
SQM 2003, Atlantic Beach, NC, USA
(dN/dh)/(0.5*Npart)
0.98 ± 0.02 (stat.) ± 0.11 (syst.)
0.87 ± 0.03 (stat.) ± 0.10 (syst.)
0.85 ± 0.03 (stat.) ± 0.09 (syst.)
0.91 ± 0.07 (stat.) ± 0.10 (syst.)
C. Oppedisano
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(dNch/dh)/(0.5*Npart)
 Npart estimated from Glauber fit to EZDC spectrum
 translation from laboratory to CMS frame
Charged particle multiplicity per participant in Pb-Pb collisions for 5% most central events:
30 A GeV  (dNch/dh)/(0.5*Npart) = 0.81 ± 0.02 (stat.) ± 0.09 (syst.)
SQM 2003, Atlantic Beach, NC, USA
C. Oppedisano
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Summary and future perspectives
Summary on data collected in 2002
p-A collisions:
 vertex telescope made of silicon strip (and pixel) planes
 dimuon mass resolution: ~25 MeV at the w peak, ~ 30 MeV for the f confirming
expectation from simulations
Pb-Pb collisions:
 vertex telescope in a partial configuration (only 3 pixel planes)
 resolution on coordinates of interaction point:
~190 mm on Zvertex
~ 20 mm on transverse coordinates
 measurement of charged particle pseudorapidity densities at 30 A GeV
These results confirm the feasibility of the experiment and give
good perspectives for next runs with proton and Indium beams
SQM 2003, Atlantic Beach, NC, USA
C. Oppedisano
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NA60 Collaboration
R. Arnaldi, K. Banicz, K. Borer, J. Buytaert, J. Castor, B. Chaurand, W. Chen, B. Cheynis,
C. Cicalò, A. Colla, P. Cortese, A. David, A. de Falco, N. de Marco, A. Devaux, A. Devismes,
A. Drees, L. Ducroux, H. En’yo, A. Ferretti, M. Floris, P. Force, A. Grigorian, J.Y. Grossiord,
N. Guettet, A. Guichard, H. Gulkanian, J. Heuser, M. Keil, L. Kluberg, Z. Li, C. Lourenço,
J. Lozano, F. Manso, A. Masoni, A. Neves, H. Ohnishi, C. Oppedisano, G. Puddu,
E. Radermacher, P. Rosinský, E. Scomparin, J. Seixas, S. Serci, R. Shahoyan, E. Siddi,
P. Sonderegger, G. Usai, H. Vardanyan and H. Wöhri
50 people, 12 institutes, 7 countries
CERN
Bern
Palaiseau
Riken
BNL
Yerevan
Stony Brook
Torino
Lisbon
Cagliari
Clermont
Lyon
SQM 2003, Atlantic Beach, NC, USA
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