The NA60 experiment at the CERN SPSThe NA60 experiment at the CERN SPS““Production of open charm and prompt dimuonsProduction of open charm and prompt dimuons

in collisions of proton and heavy ion beams on nuclear targets”in collisions of proton and heavy ion beams on nuclear targets”

Results and perspectivesResults and perspectives

Detector concept and overview.

Dimuon production in proton-nucleus collisions:

mass resolution, phase space coverage.

Vertex position resolution in Pb-Pb collisions.

Perspectives.

Johann M. Heuser

RIKEN - The Institute of Physical and Chemical ResearchWako, Saitama 351-0198, Japan

For the NA60 Collaboration

NA50

Questions left open by previous SPS experiments

New and better measurements are needed !

What is the origin of the intermediate mass dimuon excess? Thermal dimuons produced from a QGP phase?

Is the open charm yield enhanced in nucleus-nucleus collisions ? How does it compare to the suppression pattern of charmonium states?

Which physics variable drives the onset of ’, c and

J/ suppression ? Energy density ? Cluster density?

What is the normal nuclear absorption pattern of the c?

melting of c?

melting of directly produced J/?

NA50

• Track matching through the muon filter:• Improved dimuon mass resolution.• Improved signal / background ratio (rejection of and K decays).

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

D

{offset

vertex

NA60 detector concept: an “eye” in the vertex region

muon spectrometer

beam

muon filter

vertex spectrometer

with pixels

without pixels

J/

’

The use of a silicon vertex telescope clearly improves the mass resolution(from 70 to ~ 20 MeV at the mass).

Vertexspectrometer

Dimuon mass resolution: simulation

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

promptdimuons

open charm

muon track offset resolution

better than 35 m for p 15 GeV/c

D+ : c = 317 mD0 : c = 124 moffset 90 m

90 offset 800 m and muons away from each other 180 min the transverse plane at Zvertex

Background

Background

Signal

Signal

Separating charm decays from prompt dimuons

Overview of the NA60 detector: the reality

Silicon Micro-Strip Detectors

Muon Spectrometer

beam

Silicon Pixel Detectors

ZDC Quartz Blade

Interaction Counter

Beam Tracker

2.5 T dipole magnet

Target box

vertex tracker

Cryogenic Silicon Beam Tracker

Two stations of back-to-back mounted micro-strip

sensors. Operated at 130 K radiation hard.

24 strips of 50 m pitch per sensor.

20 m resolution on the transverse coordinates

of the interaction point.

20 GeV/nucleonPb beam profiles

(very broad beam)

timing with1.7 ns accuracy

The NA60 Silicon Micro-Strip Detectors

8 double tracking planes of 300 m silicon sensors.

1536 strips of pitch from 60 to 227 m occupancy < 3%.

Tilted lines to improve momentum and angles resolution.

90 mm diameter to cover dimuon acceptance at 40 cm

from target.

Beam hole through sensor wafer.

SCTA read-out chips (from ATLAS) operated at 40 MHz.

track & vertex reconstruction in low multiplicity environment.

Pixel efficiency

X (cm)

preliminary

16 tracking planes in two sizes (4 or 8 chips). ~100 ALICE1LHCb pixel detector assemblies. Matrix of 32 x 256 pixels per assembly. Pixel size 50 x 425 m2 . Ion. radiation hardness: up to ~30 Mrad. Operation at 10 MHz r/o clock.

accurate track and vertex reconstruction in a very high multiplicity environment.

The NA60 Silicon Pixel Detectors

Int. hit map fromPb-Pb collisions

X residual (cm)

preliminary

x = 14.4 m

Convolution of pixel and trackingresolution (including alignment)using only two tracking planes.Full telescope: < 10 m expected.

Spatial resolution

Z-vertex resolution~ 900 μm

target boxwindow

400 GeVprotons

Results from the June 2002 proton run

Dimuon mass spectrum from muon spectrometer

Dimuon mass distributionfor each target

p-Be ~ 30 MeV

~ 25 MeV

J/

vertex identification

muon track matchingbetween vertex telescopeand muon spectrometer

Obtained with the micro-strip detector telescope.

Present mass resolution : ~ 25 MeV at the and ~ 30 MeV at the (it was around 80 MeV in NA50).

A good measurement of the nuclear dependence of and production should be feasible.

Z (cm)-4 -2 0 2 4

0

50

100

150

200

250

In

Be Be Be Be

Pb

NA60 dimuon mass resolution

NA50-like resolution

NA60 low mass dimuon data extendsdown to much lower transverse momentum values than previous measurements(NA38, NA50, Helios-3).

Dimuon phase space coverage

mid-rapidity

pT (

GeV

/c)

pT (

GeV

/c)

Much improved comparisonswith CERES dielectrons andwith NA49 results.

Z (cm)-10 -8 -6 -4 -2 0 2 4 6 8 10

0

500

1000

1500

2000

2500

3000

3500

4000

30 GeV/n

average event(36 tracks)

beam tracking

beamtrackersensor

target boxwindows

Pb targetsResolution in the determinationof the interaction vertex σZ ~ 190 m

σX ~ 20 m

October 2002 Pb-Pb data: 20/30 GeV/nucl. beams

Correlation width ~ 30 m

Beam tracker vs. pixel telescope

Xvertex from pixel telescope (cm)

Xv

ert

ex f

rom

bea

m t

rack

er (

cm)

pixel detector telescope partly installed

NA60 new detectors are almost fully developed.

Completion of the Pixel Detector Telescope for Fall 2003 ongoing.

Data collected in 2002 confirms feasibility of the experiment:

dimuon mass resolution at the and φ peaks ~ 25–30 MeV.

phase space coverage extends down to low pT and masses.

resolution in transverse vertex coordinates ~ 20 m.

In September-October 2003 NA60 will study In-In collisions:

J/ and ’ suppression patterns.

, and φ production.

open charm production.

thermal dimuon production.

Summary and Outlook

Overview of Silicon Tracking Telescope for next runs

Eight small (4 chips) and eight large (8 chips) pixel planes.

Last tracking plane at 32 cm from the center of the target.

Mixed setup : 8 strip tracking stations complemented by pixel planes.

Strip planes : faster read-out, less material and bigger angular coverage.

Pixel planes : much better granularity and signal to noise ratio.

In-In

p-A

Ongoing completion of the pixel detector vertex spectrometer8” ALICE1/LHCb chip wafer prepared for bump-bonding to yield the pixel detectors.

20 µm solder bump bond (VTT, Finland).

Three pixel planes, used in Pb-Pb run 10/2002. Two more planes assembled.

Material for the full telescope:

Ceramic hybrids.

Printed circuit boards.

Readout electronics.

Cooling structure on a module.

Quality check: Pixel detector assemblies on probe station.

5” sensor wafer (layout).

The 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. Devaux, A. Drees, L. Ducroux, H. En’yo, A. de Falco, 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, N. de Marco, A. Masoni, A. Neves, H. Ohnishi, C. Oppedisano, P. Parracho, G. Puddu, E. Radermacher, P. Rosinský,

E. Scomparin, J. Seixas, S. Serci, R. Shahoyan, P. Sonderegger, R. Tieulent, G. Usai,H. Vardanyan, R. Veenhof and H. Wöhri

~50 people, 12 institutes, 7 countries