SQM 2003, Atlantic Beach, NC, USA C. Oppedisano 1

Chiara OppedisanoChiara Oppedisanofor 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

The NA60 experiment at the CERN SPSfirst results and future perspectives

SQM 2003, Atlantic Beach, NC, USA C. Oppedisano 2

Detector concept

GOAL accurate measurement of muon kinematics

Hadron absorber + muon spectrometer (NA50) no information at vertex level to distinguish prompt from decay muons

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

Tracking MWPCs

Trigger hodoscopes

Toroidal Magnet

FewallMuon filter

ZDC and Quartz Blade

TARGET AREA

MUON SPECTROMETER~1m

MUON FILTER

BEAMTRACKER

TARGETBOX

TELESCOPE

Dipole field2.5 T

BEAM

IC

SQM 2003, Atlantic Beach, NC, USA C. Oppedisano 3

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 m 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 4

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

Expected mass resolution: 20 MeV at peak

A-A collisions Silicon PIXEL detectors

high occupancy high granularity and radiation hardness

tracking planes 10 four-chip planes and 3 sixteen-chip planes

ALICE1LHCB chips, pixel size (50 425) m2

~32 cm

X (cm)Y

(cm

)

Hitmap (Pb-Pb collision)

SQM 2003, Atlantic Beach, NC, USA C. Oppedisano 5

Intermediate mass region excess

dN

/dM

Centralcollisions

Peripheralcollisions

M(GeV)

With expected charm yield

With enhanced charmp-A collisions

data described by Drell-Yan + charm decays S-U and Pb-Pb collisions dimuon yield exceeds the superposition of expected sources

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

NA60 separate open charm from thermal contribution

SQM 2003, Atlantic Beach, NC, USA C. Oppedisano 6

Open charm tagging

measure impact parameter of muon tracks separation of the two main contributions to IMR dimuon spectra:

prompt dimuon sample from interaction vertexmuon pairs from D decays with offset w.r.t. interaction point µ

D µ

, K µoffset<1mm

~10 cm

vertex Muon filter

0 100 200 300 400 500 600 700Offset (m)

Offset distribution

open charm

prompt dimuons

M(GeV)

dN

/dM

Background

Prompt

CHARM

M(GeV)

dN

/dM

Background

PROMPT

Charm

SQM 2003, Atlantic Beach, NC, USA C. Oppedisano 7

E866

p-A 800 GeV

c melting

Charmonium production

(p-A) = 0 A A-DEPENDENCE OF c PRODUCTION IN p-A COLLISIONS

Around 30-40% of J/comes from c radiative decays

NA50 c anomalously suppressed in semi-central Pb-Pb collisions

NA60 normal absorption pattern of c

measuring the c to J/ ratio from p-Be to p-Pb

CHARMONIUM SUPPRESSION

NA50 J/ suppression indication for onset of deconfinement

NA60

better mass resolution I and J/ clearly separated

In-In collisions identification of the physics variable with threshold behavior

D production is the best reference for J/production study

NA50

SQM 2003, Atlantic Beach, NC, USA C. Oppedisano 8

Muon track matching between vertex telescope and muon spectrometer

Results from p-A data (I)

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 m

Dimuon mass spectrum from muon spectrometer

Target identified by vertex telescope

Dimuon spectrum for each target

Z (cm)-4 -2 0 2 4

0

50

100

150

200

250

In

Be Be Be Be

Pb

Zvertex distribution

Zvertex (cm)

p-Be

~ 30 MeV

~ 25 MeV

SQM 2003, Atlantic Beach, NC, USA C. Oppedisano 9

Results from p-A data (II)

dimuon mass resolution: ~ 25 MeV at the peak and ~ 30 MeV at the

precise A-dependence of the and production (NA50 mass resolution for low masses ~ 90 MeV)

Muon offset study little statistics to extract charm A-dependence

Dimuon spectra after muon track matching: In and Pb targets

p-Pbp-In

SQM 2003, Atlantic Beach, NC, USA C. Oppedisano 10

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

Zvertex (cm)

dN

/dZ

Resolution on interaction vertex determination: σZ ~190 m σX ~20 m

Pb targets

Target boxwindow

Beam tracker sensor

Correlation width ~ 30 m

Beam tracker vs. pixel telescope

Xvertex from telescope (cm)

Xv

ert

ex f

rom

be

am

tra

ck

er

(cm

)

SQM 2003, Atlantic Beach, NC, USA C. Oppedisano 11

Charged particle multiplicity measurement

Multiplicities evaluated from clusters to access midrapidity

Magnetic field switched off

Geometrical acceptances depend on the considered plane-target set

EZDC<1685 GeV 5% of total geometrical x-section

Beam trigger

Interaction trigger

ZDC spectrum @ 30 GeV

midrapiditymidrapidity

Plane 1 - Target 1 Plane 1 - Target 3

Centrality measured by ZDC

Data corrected for acceptance

123

Plane 1

dN

/d

(0.1

u

nit

s)

SQM 2003, Atlantic Beach, NC, USA C. Oppedisano 12

123

dN

/d

(0.1

u

nit

s)

Corrections

rays from Pb beam simulations with GEANT3.21MC reliability tested with beam-trigger dataCorrections factors calculated for each plane-target set

rays from fragments evaluated vs. centrality

Secondaries from re-interactions evaluated using UrQMD 1.2, leads to correction factors from 1.1 to 1.8

Plane 1

dN

/d

(0.1

u

nit

s)

Correction factor for re-interaction from MCPlane 1 - Target 1

rays (Pb+fragments)Plane 1 - Target 3

(worst case)

dN

/d

(0.1

u

nit

s)

After MC corrections distributions in good agreement

SQM 2003, Atlantic Beach, NC, USA C. Oppedisano 13

Charged particle distributions

30 GeV

dN

/d

(0.1

un

its)

Fit of dNch/d distributions at 30 GeV max from data compatible with event generator value

Systematic error ~11% (4% from residual data spread at same , 9% on -rays contribution, 3% on re-interaction factors, 5% on pixel plane efficiency)

Centrality bin max (dN/d)max (dN/d)/(0.5*Npart)

0-5 % 2.1 ± 0.1 172 ± 4 0.98 ± 0.02 (stat.) ± 0.11 (syst.) 5-10% 2.1 ± 0.1 129 ± 4 0.87 ± 0.03 (stat.) ± 0.10 (syst.) 10-20% 1.9 ± 0.2 98 ± 4 0.85 ± 0.03 (stat.) ± 0.09 (syst.) 20-35% 1.8 ± 0.2 74 ± 6 0.91 ± 0.07 (stat.) ± 0.10 (syst.)

(dN

/d)

/(0.

5 N

par

t)

Npart

SQM 2003, Atlantic Beach, NC, USA C. Oppedisano 14

(dNch/d)/(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/d)/(0.5*Npart) = 0.81 ± 0.02 (stat.) ±0.09 (syst.)

SQM 2003, Atlantic Beach, NC, USA C. Oppedisano 15

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 peak, ~ 30 MeV for the confirming

expectation from simulations

Pb-Pb collisions:

vertex telescope in a partial configuration (only 3 pixel planes)

resolution on coordinates of interaction point:

~190 m on Zvertex

~ 20 m 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 16

50 people, 12 institutes, 7 countries

Lisbon

CERN Bern

Torino

Yerevan

Cagliari

LyonClermont

BNLRiken

Stony Brook

Palaiseau

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