I was asked by the Physics Dept of Padova to make a design for the Muon detection In CMS in fall At that time CMS was considering two option one from NIKHEF (exagonal tubes) and a second from Aachen (the walless drift chambers,an evolution of the Aachen MU chambers of UA1). The key request was that the detector had to be able to identify the beam crossing that originated the MU. This required a time resolution better than 5~ 10 nsec. The two submitted projects planned to couple drift chambers to RPC layers. I tried to make a design that gets rid of the RPC and capable of identify the time and position of the track simultaneously. For the MU detector of ZEUS I had designed a delay line that could in principle to be used to perform at once meantime operation and the time digitization. What we had to find was a drift cell with a linear space time relation. The rectangular and very simple cell designed for L3 was a good candidate to start with.

aluminium noril Copper graphite NIKHEF AACHEN PADOVA 20 mm 11 mm Sense wire Field Shaping wires

We started to design a rectangular tube with a cross section of 1 cmx 2cm,than we moved to 1x4 cm2. We used plastic tubes (NORIL) with the idea of exploiting the know how gained with the Iarocci tubes in ZEUS. They were cheap and a full machinery and tools was already developped and available for the construction and assembly of large Chambers. Field shaping electrodes were obtained by painting with graphite, layers of tubes were separated by copper foils acting as ground planes. Plastic polarization and charging up helped to shape a very good drift field

A ZEUS Barrel MU Chamber transporting a young colleague 10 m 2 to 4 m

1 2 3 For a perpendicular track T’ = (T1+T2)/2 + T/2 = T if T1+T2 = T For an inclined track T’1= T1+d and T’3 = T3-d T’= T+d and T” = T-d a second MT operation on the two output T’” = (T+d + T-d)/2 +T = 3/2 T i.e. a fixed time output

The proposal was submitted in May1992 CMS was ready to include it in the LOI in case We had convincing results in a test beam (in August 1992!!!) Results were very good Time resolution in the identification of the time of passage of the tracks 2 ns for perp. Tracks up to 4 ns at 20 deg. Efficiency of time identification was around 75% due to generation of delta rays inside the cell : a delta between the parent track and the wire mimics a shorter Drift time. The rate of delta generation (and MT failures) was studied in a next trial using 4 Layers and making MT operation in two groups of 3 layers (1,2,3) and (2.3.4). It was decided to make chambers with modules of four planes and to design a MT circuit capable of making the MT operation on any group of 3 layers. Inefficiency was reduced below 3% :the fraction of cases in which delta affects two of the four layers.

These studies required several test beam in the RD5 set up and were done in tight collaboration with Dubna people testing their first CSC chambers (ME1/1). Like us they were looking to the effects of delta and showering muons to fix the better chamber and electronics parameters and number of layers to cope with. It was amusing,even not fully surprising,that In spite of the different technologies the findings were fully compatible and in some case identical. A very exciting and lovely time. At that time the endcap was planned to use CSC in the small cone covered by ME1/1. At larger ETA the choice between DT and CSC was still debated. After these studies we made, with Dubna, the proposal to extend the coverage with CSC to the full end cap.

After a detailed comparison and a public debate CMS made the choice in favor of the Padova design. But, quite surprisingly, decided to keep RPC as a Trigger back up. In the following months new things happened one after the other: 1)NEUTRONS: It was discovered that LHC exp. Area will be filled by a gas of low energy neutrons Generated by the interaction of beam halo with the beam collimators. Plastic is a lovely target for LE neutrons,and we (but not RPC!) decided after hard Internal discussion to move to a metal design. This was not harmless because it moved the center of gravity of the technical know how from Padova (plastic/ZEUS) to Aachen (metal/L3). The CMS DT will follow the L3 scheme :cells made by large Aluminum foils separated by arrays of I beams to shape the tubes………. 2) SSC cancellation: With the income of a large US community the full Mu (and HCal) project was deeply revised. The barrel was shortened to house a layer of CSCs between the barrel an FWD yokes. This,together with a more accurate study of the services, had the result of a creation of a new,and an increase of the old, air gaps inside the iron Yoke. And unfortunately the magnetic field in large areas of the barrel increased by a factor two (the radial component fro.5 to up 1 Tesla, and the longitud. from.2 up to.5 Tesla) 3) And a bit late some weakness was discovered in the DT structure

Electron paths at Bz =.3 T

The third event : a structural problem

And the I-Beam design change

old new

The debate on gas enclosure and supporting fixtures

To summarize we had three revolution in the project: 1)From plastic to metal (neutrons) 2)Change of field shaping ( magnetic field) 3)Change in I-Beams ( mechanical stiffness) They were not minor adjustments because they forced to change deeply the construction process and associated tools, invent new tools for I-Beams assembly and strip deposition on the plates. They required lot of work and severe tests, and increased a lot the work load for construction. We had to find collaborators for the difficult task of I-Beams and plates preparation and to enlarge the number of assembly site. Dubna for plates,Protvino for I-beams, CIEMAT and Torino joined for assembly. But the project was finalized and suddenly in 1998 we started to place huge (for my previous experience) contracts for material purchase and tool construction. (9000 KChf, i.e. 45% of the foreseen budget, were committed in two years for Al plates,I-Beams,HComb etc, 4000 for chamber,plates and I-Beams tools) To do what?

Legnaro Assembly Hall Aachen Assembly Hall CIEMAT Assembly Hall Torino Assembly Hall

The DUBNA plant: ~3500 plates~ strips The Protvino plants ~ I-Beams HVB in IHEP (2X11000 boards from 2000-Sept.2005)

SLayers and chambers Assembly ~ finished I-Beams in Protvino May 2001-June 2004 Plates in Dubna Oct.2001-June 2005

Chambers stored at CERN ISR Chambers installed in YB+2 (65 chambers installed in YB+1 and YB+2, full YB+2 is commissioned) First installation Aug.03

Magnetic field does not affect efficiency, but it affects the resolution because of the change of the apparent drift velocity due to the Lorentz Angle. The displayed data are corrected for. An average correction is possible also at Trigger level B variations from 0.2 to 0.8 T in the same chamber DT Chamber performance (one cell)

DriftTubes Local-Trigger

SLAYER 1 SLAYER 2 SLAYER 3 ~ 1.5 m 10 cm

BX identification efficiency (one chamber) 2% difference between emulator and data. Emulator result is similar to TB2003. Angle wrt chamber plane: RMS is 2~3 mrad Track position :RMS 650~ 800 micron tracks hitting 2 I-beams trig. at 14bx efficiency = total # of events Event= scintillator + 2 hits in beam region Reconstructed tracks EFFICIENCY FOR BX ID and reconstr. tracks

1 Dead tube angular distribution of the tracks Cell precision is affected by the random time of arrival of the cosmic MU wrt the electronics clock PHI THETA COMMISSIONING with COSMIC RAYS Asking the trigger to select HH patterns only (8 hits out of 8 laters), allows a large rate of events (~ 100 Hz) The reconstruction efficiency of the parent track is better than 90% 1 DT Standalone Trigger Horizontal Chamber: density of population

TIME Box of hits (SL1 38 KEvents) hits TIME Box of hits of reco. tracks hits

Lot of energy will be injected by LHC into billions of collisions to excite the Higgs field, and lot of work and ingenuity by us to catch its long awaited and rare QUANTUM