Study of Prompt Dimuon and Charm Productionwith Proton and Heavy Ion Beams at the CERN SPS

The NA60 experiment

Carlos Lourenço and Gianluca Usaion behalf of the NA60 Collaboration

• Reminder of the physics motivation and plans of NA60

• Evolution with respect to the proposal

– Experimental apparatus

– Readout electronics, DAQ and detector control

Excess production of intermediate mass dimuons

NA38+NA50

• The p-A data is properly described by Drell-Yan and charm decays

• The required charm cross-section agrees with previous direct measurements

• In heavy ion collisions the yield of produced dimuons exceeds the expected sources

• The excess increases with the centrality of the nuclear collisions

NA50

Charm enhancement ?

The measured yields can be reproduced by scaling up the expected charm contribution by up to a factor 3

L. Capelli, NA50, at QM2001

Thermal model of Rapp and Shuryak(central collisions only)explicit introduction of a QGP phase

Integration over space-time history :

fireball lifetime : 14 fm/c

initial temperature : Ti = 192 MeV

critical temperature : Tc = 175 MeV

Thermal dimuons production ?

L. Capelli, NA50, at QM2001

The measured yields can also be reproduced by addingthermal radiation to the Drell-Yan and open charm

sources

+

-

Low mass dilepton production

• The p-Be and p-Au data are properly described by the standard cocktail of hadronic decays but there is an excess in the Pb-Au data !

• The excess increases with the square of the charged particle multiplicity and is more pronounced at low pT

• Chiral symmetry restoration ? Better statistics, signal to background ratio and mass resolution are needed !

J/ suppression in S-U and Pb-Pb (1987-1998)

melting of c ? melting of direct J/ ?

Color screening prevents charmonia formation in a deconfined medium. Binding energies :

’ 50 MeV, c 250 MeV, J/ 650 MeV

The thresholds are only visible in the Pb-Pb data !

A new collision system is needed to check onset

PLB 477 (2000) 28

NA50

NA50QM2001

’ suppression in S-U collisions

melting of ’ ?

Drop byfactor ~ 3

The ’ suppression pattern is very different between p-A and S-U data !

Color screening ? If so, what is the ’ melting temperature ( value of Tc ) ?

A new collision system is needed with points below and above L = 4-5 fm

Physics motivation

What is the origin of the intermediate mass dimuon excess ? Thermal dimuons ?

Is the open charm yield enhanced in nucleus-nucleus collisions ?

Is the meson modified by the medium ? observe the reference peak !

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

What is the physical origin of the ’ suppression ? Color screening ?

What fraction of J/ come from c decays ?

What is the nuclear dependence of c production in p-A collisions ?

Detector concept

• 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

D

{offset

vertex

Adding silicon detectors to track the muons before they traverse

the hadron absorber

Improved measurement of prompt dimuon production and

open charm in heavy ion collisions

The silicon vertex spectrometer proposed in P316

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

Silicon pixel telescope

1.7 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

Dimuon mass resolution : simulation

• Clear improvement in mass resolution and signal / background ratio

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

NA50

NA60

Vertexspectrometer

with pixels

without pixels

J/

’

• 4 “half” planes• 33 LHC1 chips• ~ 60’000 channels

1998 feasibility tests

absorber

target

pixel box

TC8 magnet

1.7 T dipolemagnetic field

Dimuon mass resolution : April 1998 data

• few hours at ~ 10 8 protons / burst on a 10 mm Be target• half acceptance, bump-bonding, radiation damage low detector efficiency• only 600 dimuon events in the final analysis data sample

without pixels

M = 70 MeV

with pixels

M = 20 MeV

Measurement of the muon track offset

Determination of the interaction vertex

Impact parameter of themuon tracks

D+ : c = 317 m

D0 : c = 124 m

D

IMR excess : charm or thermal dimuons ?

• 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

c production in p-Be and p-Pb

photon converter

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

e+e pairs from different events

c e+e

• What fraction of J/ ’s come from c decays ?

• Does it change from p-Be to p-Pb ?

B = 1.7 T

Developments since the proposal

• Offline software advancing well : AliRoot framework, from Fortran to C++

• Beamscope tested in Sept. - Nov. 2000 : 42 days of high intensity Pb beam

• New detector : beamscope for proton running, with new fast amplifier chip

• New target dipole magnet : higher field ; much better integration of detectors

• Better detectors to reject bad triggers : quartz blade, interaction counter, P2

• New gas system for the muon chambers

• New readout electronics and DAQ : increased bandwidth

We benefit from the critical help provided by the ALICE offline software team,the RD39 collaboration and the cryo lab,the EP-MIC group, W. Flegel and F. Bergsma,the LHC gas group (F. Hahn et al.),the EP-ED group and the EP-AID group

Status of the offline software

Detector setup :• The whole detector geometry and materials are described using GEANT

Event generation :• Soft signals with Genesis code (thermal distributions)• Hard processes with PYTHIA• Underlying hadronic background with VENUS

Algorithms :• Trigger logic implemented• Detector response done up to the hit level• Track and vertex reconstruction under development• Everything must be ready for the October 2001 run

The beamscope detector

CryogenicModule

Amplifier Cards

200 mm

Vacuumchamber

CCE (in %)

Heavily irradiated silicon detectors continue working when operated at cryogenic temperatures

beam

Beamscope test in November 1999

Exposed for 3 days to the 40 A GeV Pb beamAverage beam intensity: 5106 ions per 4.5 s burstTotal dose: ~ 1 Grad

Beamscope test in Sept.-Nov. 2000

Exposed 42 days in the NA50 Pb beamAverage beam intensity: 710 7 ions per 4.5 s burstTotal fluence : 5 ± 2 1014 ions / cm2 ( 90 ± 40 Grad )Electronics suffered from radiation in the beam area

Pb ion signal shape

8 Gs/s

time (ns)

amp

litu

de

(mV

)

200 V

2 Gs/s

time (ns)am

pli

tud

e (m

V)

200 V

• Very fast rise time ( < 500 ps)• Long tail (~ 20 ns)• Shaping (signal width ~ 4 ns) improves double-pulse resolution

• Signal is broader• Amplitude ~ 20 times lower

but still visible !

Non-irradiated After ~ 40 Grad

Beam profile and cluster correlations

hit

s (

103

)

strip number

Day 38

1.2 mm

hit

s (

103

)

Time accuracy of thereadout electronics system

integrating all the stripsover several spills

= 1.0 ± 0.1 ns

Day 42

y2 (m)

y 4 (m

)

Correlation of clusters inthe 2 vertical measurements

Beamscope for proton running

Chip CERN_NA60_32_ch• Measuring the interaction point with few prompt tracks• ~ 100 % sub-target reconstruction efficiency• Improved Z and X-Y vertex resolutions

Increased tagging efficiency forD mesons and prompt muons

• New CMOS readout chip for the proton beamscope• 32 channels ; runs at around T = 130 K• Simulated double peak resolution : 10 ns at room T• High gain : 1 mip = 60 mV• Power dissipation = 275 mW• Design submitted for production• Tests and module assembly start mid June• Use on the beam in October 2001

Improvement in the vertex magnet

The new dipole magnet, PT7, has a field of 2.5 T (for I = 900 A).

The mass resolution of the c peak, dominated by the momentum measurement

of the electron and positron tracks, improves from 43 MeV to 25 MeV.The signal to background ratio improves by around factor of 2.The integration of the detectors is much easier than with TC8.

Field along beam axis

NA60 target region

Front view

PT7 Beamscope modulesat 45 degrees

BeOabsorber

The integration and installation studies have started, including mechanical supports, alignment, cooling systems, vacuum, readout cables, etc.Care must be taken with the strong magnetic field and the high radiation load.

Critical concerns

• The NA60 physics program relies heavily on the intermediate mass ion beam

Indium-Indium collisions should be available as soon as possible

• The operation of the muon spectrometer demands the support of IN2P3• The construction of the silicon vertex spectrometer and the successful operation

of NA60 requires a strong CERN participation

The NA60 collaboration is weaker than anticipated one year ago

• Successive time delays in the availability of the Alice1 pixel readout chips• Only around 15 good assemblies are expected per wafer

Silicon pixel telescope will not be ready before the ion run of 2002

Silicon microstrip telescope for proton physics

Each detector is one wafer; inner part = A-D zones; outer part = E-F zonesOnly the ~ 300 m thickness of the sensors on the way of the particlesSmall detectors (only inner part is read) = 384 channels per half planeBig detectors (all strips are read) = 768 channels per half planeOne readout chip, SCTA3, reads 128 stripsFull telescope = 4 small and 3 big X-Y stations = 120 readout chipsOne hybrid (3 or 6 chips) and DAQ adapter card per half plane; total = 2814 ADC cards, 6 channels each (3 ADCs per hybrid)Data rate around 30 Mbyte per burst ; 2 PCI-FLIC cards needed in 1 PCRequires only 28 working pixel chips to build 3 small and 1 big pixel planes

6.5 charged particles per average p-Pb collision : less than 2 or 3 % occupancyResolution in impact parameter of muon tracks is around 25 m

VME readout electronics for pixel telescope

2 VME crates

VME to PCIMXI-2 interface

20 Mbyte/s

721 000 channels

Limitations : required bandwidth beyond VME limit (12 Mbyte/s) number of events / burst limited to 4000 non scalable system bad ratio performance / cost (VME crates) pixel chips readout frequency limited to 10 MHz

64 pixel chips24 pixel chips

VME Pilot board

Zero sup

32 bit FIFO

Hit encoding

20 bitFIFO

VMEVM

E b

us

pixchip pixchip pixchip

Readout of muon chambers and trigger hodoscopes

22 RMH modules / crate

System encoder 16 bit words

To VME buffer 4 Mbyte

Cascaded CAMACcrates

RMH32 hit channels

20 000 channels

Limitations :

memory limit on the RMH to VME interface buffer : 4 Mbyte

slow word transmission protocol (500 ns) number of events / burst < 4000

PCI - FLIC readout electronics

PCI - FLIC card

Mezzanine outline

User connector ;46 signals for pixel data

Pixel Readout Board(PCI mezzanine card)

To / from front-endelectronics (LVDS)

FPGA on PRB

Mezzanine

area

F

I

F

O

32 Mbytespill-buffer

PCI bus 100 Mbyte/s

RAM

Zero suppression & hit encoding -pixel chips readout control

F

I

F

O

PCI readout electronics for the pixel telescope

PCI cards(up to 5 cards perPC motherboard)

Local data concentrators(under DATE software control)

Parallel readoutscalable system

74 Mbyte/s

Linux PCs

Pixel telescope data throughput

10 K x 16 bit words 20 Kbyte / event

PCI :20 Kbyte / event @ 74 Mbyte / s

270 s to acquire one event

VME :20 Kbyte / event @ 20 Mbyte / s 1000 s to acquire one event

Pixel plane number

Ave

rage

hit

nu

mb

erSmall planes

Large planes

Pixel telescope readout performance

Pixel chip :4 Event Buffers

VME :1000 s / event

pixCLK @ 10 MHz

PCI :270 s / eventpixCLK @ 20

MHz

We can take ~ 8000 events on tape / burstwith less than 10 % dead time

MultiEvent Buffer :dead time 1/4 of SingleEvent Buffer

triggers per second

dea

d t

ime

PCI readout electronics for RMH

RMH cable adapter mezzanine

RMH NIM signals

ECL TTL convertersDifferential 2*22 ECL

32 MB spill-buffer

RMH cable handshake

Word cycle 350 ns6 MB/s bandwidth

16 bit word handshake

10..15 sec readout from burst buffer5 sec fill buffer

Muon spectrometer readout performance

320 (16 bit) words / event 0.7 Kbyte / event RMH PCI buffer bandwidth 6 Mbyte / s

NA50

NA60

dea

d t

ime

triggers per second

NA50 : 500 ns/word x 320 words = 160 sone partition : 160 s service time700 triggers/s, with 10 % dead time, spill of 5 s : 3150 events on tape / burst

NA60 : 350 ns/word x 320 words = 100 stwo partitions : 50-60 s service time1800 triggers/s, with 10 % dead time, spill of 5 s : 8000 events on tape / burst

10 %

From VME to PCI detector readout : summary

General : easy readout partitioning (up to 5 PCI cards per PC)

PCI spill-buffer directly mappable into the DAQ software

Pixel detector : PCI cards readout in parallel (sequential readout with VME)

74 Mbyte/s bandwidth (20 Mbyte/s with VME)

pixel chips clocked @ 10 - 20 - 40 MHz (on board PLL)

Muon spectrometer : PCI spill buffer increased to 32 Mbyte (4 Mbyte with VME)

hit readout time 350 ns (500 ns with VME)

The data acquisition system

60 MB/burst 80 MB/burst 1.2 MB/burst 8 MB/burst Total: 150 MB/burst

FastEthernet 11 MB/s

GbitEthernet 110 MB/s

All nodes :Linux/DATE

Run control

Beamarea

LDC pix2

LDC pix10.12 MB/s 0.8 MB/s

8 MB/s

Fast/Gbit switch

3+4 PCI-FLIC/PRB

Online monitoring

GDC

tape

Disk server

LDC BS+ZDC LDC MS

6 MB/s

15 MB/s

15 MB/s

DAQ softwareDATE

The detector control system

Pixelcooling

Tmon(20 chan)

Interlock(2 chan)

Cryoflows

Cryo/pixelcontrol

Gas control

mixer

distributor

Gas PLC

Permanent storage

CAEN SY2527 CAEN SY403

HV, LVpixels

HV, LVbeamscope

HVZDC(2 crates)

HVhodoscopes(14 crates)

CAEN frontend(Linux)

PVSS/SCADA with OPC (WinNT)

Summary

• NA60 will clarify the origin of the intermediate mass dimuon excess and measure the yield of charmed mesons produced in heavy ion collisions.

• Considerable technical improvements were made since the proposal : new detectors, new vertex magnet, new readout electronics and DAQ, etc.

• Severe lack of resources (people and budget) keep the collaboration much weaker than anticipated. Stronger support from CERN and other institutes is mandatory to allow the experiment to take good physics data in 2002.

• Data with good statistics, mass resolution and signal to background ratio will allow to study the production of , and mesons, as well as the charmonia resonances.

The NA60 Collaboration

Brookhaven

R. Arnaldi, A. Baldit, K. Banicz, K. Borer, L. Casagrande, J. Castor, B. Chaurand*, W. Chen, B. Cheynis, P. Chochula, C. Cicalò, M.P. Comets, P. Cortese, V. Danielyan, A. David, A. De Falco, N. De Marco, A. Devaux, B. Dezillie, 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, D. Jouan, L. Kluberg*, Y. Le Bornec, B. Lenkeit,

Z. Li, C. Lourenço, M.P. Macciotta, M. Mac Cormick, F. Manso, D. Marras, A. Masoni, S. Mehrabyan, H. Muller, A. Musso, A. Neves, B. Pes, S. Popescu, G. Puddu, P. Ramalhete,

P. Rosinsky, P. Saturnini, E. Scomparin, J. Seixas, S. Serci, R. Shahoyan, E. Siddi, P. Sonderegger, G. Usai, G. Vandoni, H. Vardanyan, N. Willis, H. Wöhri and M. Zagiba

Lisbon

Orsay

CERN Bern

Bratislava

Torino

Yerevan

CagliariLyonClermont

11 institutesbut very few financing agencies

*) personal commitment