# Presentation: 472584

## The NA60 experiment at the CERN SPS

- “Production of open charm and prompt dimuons
- in collisions of proton and heavy ion beams on nuclear targets”
- Results 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 Research*
*Wako, Saitama 351-0198, Japan*
*For the NA60 Collaboration*

## New and better measurements 

**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?

- NA50

##   Track matching through the muon filter:

-   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.

- muon spectrometer

- beam

- muon filter

- vertex spectrometer

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

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

- Vertex
- spectrometer

## muon track offset resolutionbetter than 35 m for p  15 GeV/c

**prompt****dimuons**

**open charm**

- muon track offset resolutionbetter than 35 m for p  15 GeV/c

- D+ : c = 317 mD0 : c = 124 m

- offset  90 m

- 90  offset  800 m and muons
- away from each other  180 m
- in the transverse plane at Zvertex

- Background

- Background

- Signal

- Signal

## 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**

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

**  ****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/nucleon
- Pb beam profiles(very broad beam)

- timing with1.7 ns accuracy

##   8 double tracking planes of 300 m silicon sensors.

-   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.

## The NA60 Silicon Pixel Detectors

- 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.

- Int. hit map from
- Pb-Pb collisions

******x**** ****= 14.4 ********m**

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

- Spatial resolution

## Results from the June 2002 proton run

- target boxwindow

- 400 GeVprotons

- 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.

- 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

**p****T**** (GeV/c)**

- Much improved comparisonswith CERES dielectrons andwith NA49    results.

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

-  average event
- (36 tracks)

- beam tracking

- beamtrackersensor

- target boxwindows

- Pb targets

- Resolution in the determinationof the interaction vertex     σZ  ~ 190 m     σX  ~   20 m

**Correlation width ~ 30 ****m**

- Beam tracker vs. pixel telescope

**X****vertex**** from pixel telescope (cm)**

**X****vertex**** from beam tracker (cm)**

- pixel detector telescope partly installed

## Summary and Outlook

-     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.

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

-   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 spectrometer

- 8”  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).

## ~50 people, 12 institutes, 7 countries

- 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