Dear friends

Last week was a major milestone for CMS. One of the principal technical design features of the detector is that it is constructed on the surface before being lowered, in large pieces, underground. The most critical element of CMS is the central barrel ring, which, in addition to supporting layers of muon chambers, also supports the superconducting solenoid and the inner detectors. On 28th February this ring, including the solenoid, was lowered into the UXC55 underground cavern. The 1920 tonne piece took about 10 hours to be lowered and attracted an unprecedented amount of interest from the world press (see list of reporters etc. here). Indeed there have been newspaper articles, radio shows and even television interviews and features. One important thing to note was that the presence of the media in the CMS assembly site did not disrupt the normal working operation, in particular the lowering.

Some members of the press early Wednesday morning.

The CERN multimedia team also spent the whole day (from around 5:30am!) photographing and filming the descent of YB0. A movie of the lowering (courtesy of Jacques Fichet et al) is already available and can be downloaded here (mp4 format, ~30 Mbytes). In the near future this movie will also be available in high definition format! Watch this space for information!

With best wishes,

Dave Barney
Marzena Lapka

The HEP group of Çukurova University (Turkey) in CMS

A part of the HEP group of Çukurova University with Gulsen Onengut (the leader of the group) in the right top corner.

The HEP group of Çukurova University has been a member of the CMS experiment  for almost 10  years. Our group has 7 professors, 5 PhD candidates and around 10 students who  are working for their MSc degree. Our group has mainly contributed to the Hadronic Forward (HF) calorimeter. Among other things w e: investigated the radiation hardness of quartz fibers, used as the active element of HF; constructed and tested the HF online radiation damage monitoring system; took part in the calibration of HB and HF with LEDs and a radioactive source; took part in data taking and analysis of MTCC runs and almost all beam tests of HF. Our group recently started contributing to  the CASTOR project; we tested the timing parameters and measured dark current and gain for the PMTs of  the CASTOR calorimeter. We have also participated in CASTOR beam test and data analysis .  

Our students working with the FNAL CMS group contributed to the testing of CMS TOB silicon detector modules and physics and detector simulation, i.e. GEANT4 simulations of the CMS Hadronic Forward Calorimeter in the 2004 beam test, CMS sensitivity to quark contact interactions with dijets and CMS Hadron Calorimeter response studies, searches for SUSY in missing transverse energy plus multijet topologies at , Centrality Measurement in heavy ion collisions for HF, jet shape studies, validation of calorimeter tower simulation using CMSSW.

Fatih Kisoglu

My name is Hasan Fatih Kisoglu. I usually use "Fatih". I am  a master student in High Energy Physics at Cukurova University in Adana, Turkey.
Two weeks ago I started a new experience out of my country. I had the opportunity to come to CERN to work for HF+ in HCAL, part of CMS

This is the begining of my 10 months stay and I wish to familiarize myself with the Geneva region and the people here. I live in St.Genis-Pouilly in France. After work or in my free time I usually read books in physics. Sometimes, I also go downtown to  Geneva to discover new places.
I like the area and have toured around a little. Of course, here is a little bit different from my country: for example, the streets, the roads, the buildings, the houses,… The people here are very kind . When I asked something , like an address, a bus stop, etc. they answer immediately and very kindly. At first I was reluctant to ask something, but now I am accustomed.

So, I am at CERN until 15 of December and I hope I will enjoy my time here .

Download a podcast with Fatih
(~16 Mbyte mp4 file)

The CMS collaboration is currently constructing the largest silicon tracking device ever built, with about 17000 detector modules covering an active area of more than 200 m2. To exploit the capabilities of this precision detector, the positions of the individual sensors have to be known to the mum level. Tight mechanical tolerances are enforced during construction and a laser based alignment system is used to determine the relative positions of larger substructures. However, the final alignment accuracy can only be reached with track based algorithms, utilizing distances between measured hits and reconstructed particle trajectories.

Mathematically, the alignment problem corresponds to solving a large system of linear equations: In the case of CMS about 45 000 alignment parameters are needed to describe the corrections to the most sensitive positions and orientations of all detector modules. Studies have shown that the largest challenge to any alignment algorithm is to avoid solutions corresponding to unphysical deformations which  leave the overall quality of the fit unchanged. These modes can be constraint using measurements that link together parts of the detector not hit simultaneously by tracks from the interaction point,  e.g. cosmic muons and tracks from beam-halo events.

Illustration of an elliptical deformation without influence on the overall chi2 if only tracks from the interaction point are utilized.

Alignment precision of the most sensitive coordinate (rphi) for modules in the barrel.

		Submitted by:
Markus Stoye,		Georg Steinbrueck	and	Gero Flucke

One pair of the lasers, including a Nd:YLF pump laser and a tunable Ti:Sapphire laser with dual wavelength.

Light monitoring will play a crucial role in maintaining the energy resolution for the CMS lead tungstate (PWO) crystal calorimeter in situ at LHC. The scintillation mechanism of the PWO crystals is not affected by the radiation, and the loss of crystal's light output is due only to the absorption caused by the radiation induced color centers. The variation of PWO crystal's light output (damage and recovery) will be estimated by using a light monitoring system, which measures the variations of crystal's transmittance.

Histories of the laser pulse energy, FWHM, pulse center timing and corresponding YLF laser pumping current are shown as function of time for a Ti:Sapphire laser running at 440 nm with the software feedback for 2,000 hours. The corresponding histogram distributions are shown at the right.

The Caltech group is responsible for the construction, maintenance and operation of the Light Source and high level Distribution Subsystem (LSDS) for the ECAL monitoring. The LSDS consists of three pairs of lasers (a Nd:YLF pump laser and a tunable Ti:Sapphire laser offering dual wavelength) with corresponding diagnostics, a 3 X 1 optical switch and a 1 X 88 optical switch. Up to four wavelengths (440, 495, 709 and 796 nm) are available by using the 3 X 1 switch. A total of 88 calorimeter elements (72 half barrel Super Modules plus 16 1/4 endcap Dees) will be scanned in half hour in situ at LHC. The primary monitoring wavelength is 440 nm, while the 796 nm infrared (IR) wavelength is used to check electronics chain. The intensity of the laser pulse is adjustable in 1% steps up to 1 mJ, which corresponds to 1.3 TeV equivalent energy deposition in one crystal. In 2006 a software feedback system was implemented so that the stability of the laser pulse intensity and FWHM width are maintained at 3% level with a laser pulse timing jitter of less than 2 ns observed in laser runs lasting for more than 2,000 hours during the ECAL test beam. The dual blue/green laser systems guarantee 100% availability of 440 nm in situ at LHC, even during the laser maintenance.

The Caltech laser team during the 2003 commission at H4. From right to left: optical engineer Dr. Liyuan Zhang, software engineer Dr. Kejun Zhu and David Bailleux.

The Caltech team is lead by Dr. Ren-yuan Zhu with team members of David Bailleux, Dr. Adi Bornheim, Dr. Liyuan Zhang and Dr. Kejun Zhu. The first blue/green laser system was commissioned at the H4 test beam site at CERN in August, 2001. The IR/red laser and the second blue/green systems were commissioned at CERN in August 2003. In March, 2007, a blue/green laser and the IR/red laser will be installed and commissioned in the CMS underground carven at USC55. The other blue/green laser will remain at the H4 test beam site until the end of the tests of the ECAL barrel Super Modules and the endcap Dees.

Submitted by:
Renyuan Zhu	and	David Bailleux

The YB0, the acronym used to represent the central barrel wheel, set the scene of unprecedented attention last week since it is the centerpiece of CMS and houses the heart of the experiment: the magnet and sensitive inner detectors ECAL, HCAL and the tracker. The 1920 tonne object was lowered from the surface hall into the experimental hall on Wednesday Feb 28th amidst a frenzy of media presence as well. We could not afford to go wrong!

The ground moves beneath YB0 and its 11 hour journey begins.

After having worked for over 15 years on this project, Lucien Veillet, Alain Herve and Hubert Gerwig are making sure that there is no snag for the imminent lowering.

YB0 is the heaviest object that has been (and will be) lowered, and even though the heavy lowering gantry was specified around its weight there were some fears of getting some oscillations during the lowering movements, despite the fact that the clearance was of the order of 180 mm or more. In previous cases these oscillations have been of the order of 20 mm with a maximum of 30 mm. Hence three cameras were attached on the vacuum tank to be able to see the choke points where services installed on top of the tank would come very close to the barrier of the "hydrostatic gallery".

Close to the barrier and amply clear of it, as you can see from the TV display of one of the cameras mounted on the vac tank.

In the end everything went extremely smoothly and the oscillations were less than a couple of centimetres.

Enroute towards joining the positive endcap in the cavern.

YB0 makes it safely underground.

The touchdown was greeted by cheers and champagne!

Some relaxing moments after the long day!

The next piece to be lowered is the HB minus, and work has begun in all earnest to keep to the schedule on the other activities.

Submitted by

Archana Sharma

CMS Outreach Meeting during CMS Week

The front cover of the CMS comic-book 4-page bochure

On Friday 2nd March a CMS Outreach meeting took place at CERN. Some of the highlights were the distribution of the new CMS Movie DVD (available from the CMS secretariat) and the 4-page comic-book brochure. The latter is about to be sent for volume printing and should be available, in English, French, German and Italian, by April.

The full agenda, with all presentations, can be found at:

http://indico.cern.ch/conferenceDisplay.py?
confId=13123

In the coming weeks the CMS Times will present some of the Outreach activities; if anyone wishes to get involved in any of these activities please send a message to outreach@cern.ch

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