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Andrei Gritsan

CMS is a 12,500 metric ton all purpose detector that is being prepared to study 7 or 14 TeV proton-proton collisions at the CERN Large Hadron Collider (LHC). The Standard Model of fundamental particles points to a mysterious component of empty space which gives particles the property of mass. It is called the Higgs particle or field. The Higgs may not be alone, and a number of new fundamental particles may be needed to explain the laws of physics. The Higgs and other new particles are believed to be too heavy to be created at previous accelerators directly. However, the new LHC collider, with the CMS detector, should be capable of producing and detecting them directly.

Project on CMS Tracker Alignment
and Resonance Spin Analysis

This project is supported in part by the U.S. National Science Foundation (grants 0644849, 0758083, 1100862) and Alfred P. Sloan Foundation.

"Spin & alignment" group members at JHU

  • Andrei Gritsan (PI of NSF grant 0644849, co-PI of NSF grant 1100862, since October 2005)
  • Andrew Whitbeck (graduate student, on the project since June 2009)
  • Sara Bolognesi (postdoctoral fellow, on the project since September 2011)

  • Nhan Tran (graduate student, May 2006 - October 2011, [thesis])
  • Alessio Bonato (postdoctoral fellow, May 2008 - August 2011)
  • Zijin Guo (postdoctoral fellow, on CMS project August 2007 - May 2011)
  • Chung Khim Lae (postdoctoral fellow, November 2006 - January 2009)
There are research opportunities for new graduate and undergraduate students as a summer project or during the academic year. Contact Prof. Gritsan or other members of the CMS group at JHU.

Tracker Alignment Project Description

Modern silicon tracking detectors typically have a large number of measuring sensors, and statistical methods can be used to align individual sensors with respect to each other. For CMS there are more than 15,000 sensors which need to be aligned. The goal of the alignment procedure is to obtain six parameters for each independent sensor, these being the three spacial and three rotational parameters. Since 2005 we developed new analysis and modeling techniques and initiated improved procedures for the CMS pixel detector optical survey measurements at FNAL. We developed statistical methods for the alignment of thousands of silicon sensors using the chisq from survey together with tracks and demonstrating their performance within the CMS software framework. Since 2007 we are working on alignment of the first components of the CMS silicon tracker with cosmic tracks. In 2008-2009, the PI was a convener of the CMS tracker alignment group. In 2010-2011 Alessio Bonato is a convener. Understanding the alignment of thousands of silicon sensors, which track particle paths, is necessary to a micron precision and becomes the decisive factor in discovering of new particles.

Results of our group have been discussed in

Alignment of a Giant (March 2010)
[ article in CMS Times]

Alignment of the CMS Silicon Tracker during Commissioning with Cosmic Rays (October 2009)
[ 2010 JINST 5 T03009 ] [ preprint arXiv:0910.2505 [physics.ins-det]]

CMS tracker alignment at the tracker integration facility (April 2009)
[ 2009 JINST 4 T07001] [ preprint arXiv:0904.1220 [physics.ins-det]]

Internal CMS notes [CMS-IN-2009/027] [CMS-IN-2007/012]

Results presented at:
The 2009 Europhysics Conference on High Energy Physics in Krakow (July 2009) [ slides] [ agenda]
3rd LHC alignment workshop in Geneva (June 2009) [ slides] [ agenda]
2nd LHC alignment workshop in Geneva (June 2007) [ slides] [ agenda]
1st LHC alignment workshop in Geneva (September 2006) [ proceedings in CERN-2007-004]

Resonance Analysis Project Description

The group has developed the tools to disentangle complicated angular structures in a broad range of models. This allows analysis of the spin, parity, and fundamental couplings of new particles which may be observed at the LHC, such as signatures of Higgs field, extra dimensions, or new gauge bosons. These studies start with analysis of the known Z boson to two leptons and measure its fundamental couplings to matter by measuring the weak-mixing angle, the only unknown parameter in the standard model which determines the relative couplings. These techniques have direct application to analysis of new potential resonances decaying to two fermions. We have also developed techniques for the search for more complicated di-boson decays of a Higgs or an exotic particle, such as H->ZZ, with subsequent decay to two leptons and two quark jets. This final state is complemented by the golden mode of four leptons in the final state, and our angular analysis provides powerful discrimination tool either against background or among different hypotheses of new physics. The program is designed to extract maximum information possible with the available LHC data, which also provides the tightest possible limit on any model to be excluded, including the limits on the Higgs boson.
Results of our group have been discussed in

The Weak Mixing of Light and Heavy (November 2011)
[ article in CMS Times] [ direct link]; see also an article in [ Fermilab Today]

Measurement of the weak mixing angle with the Drell-Yan process in proton-proton collisions at the LHC (October 2011) [ Phys. Rev. D 84, 112002 (2011) ] [ preprint arXiv:1110.2682 [hep-ex] ]

Search for the standard model Higgs boson in the decay channel H->ZZ->2l2q at CMS (August 2011) [ preprint CMS-PAS-HIG-11-017]

Contributions to Search for a standard model Higgs boson in the decay channel H->zZ->4l (August 2011) [ preprint CMS-PAS-HIG-11-015] and Search for standard model Higgs boson in pp collisions at sqrt{s} = 7 TeV (August 2011) [ preprint CMS-PAS-HIG-11-022]

Measurement of Forward-Backward Asymmetry of Lepton Pairs and the Weak-mixing Angle at CMS (March 2011) [ preprint CMS-EWK-10-011]

Spin determination of single-produced resonances at hadron colliders (January 2010) [ Phys. Rev. D 81, 075022 (2010)] [ preprint arXiv:1001.3396 [hep-ph]]

Internal CMS analysis notes [ CMS-AN-2011-123] [ CMS-AN-2011-100] [ CMS-AN-2011-031] [ CMS-AN-2010-351]

Results presented at:
JHU Physics and Astronomy colloquium (September 2011) [ slides on The Heavy Invisible Light from the Large Hadron Collider ]
JHU particle physics seminar (August 2011) [ slides on Searches for the Higgs boson with CMS at LHC] [agenda]
15th Lomonosov Conference on Elementary Particle Physics in Moscow(August 2011) [ slides on Searches for the Higgs boson with the CMS Experiment] [agenda]
LHC Working Group on Precision Electroweak Measurements in Geneva (April 2011) [ slides on Measurement of weak mixing angle at CMS] [agenda]
MCTP Spring Symposium on Higgs Boson Physics at Ann Arbor, Michigan (May 2010) [ slides on Spin Determination of Single-Produced Resonances at Hadron Colliders] [agenda]
The Power of Spin Correlations: from B-decays to Higgs and Beyond at the LHC (April-May 2010) seminars at [FNAL], [LBNL], [SLAC]
Spin determination of single-produced resonances at LHC (March 2010) [ seminar at UMD/JHU] [ listing]

See also a generator program developed at JHU for spin analysis of a resonance production and decay to a di-boson final state.