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Islamic Republic of Pakistan to become Associate Member State of CERN: CERN Press Release

Geneva 19 December 2014. CERN1 Director General, Rolf Heuer, and the Chairman of the Pakistan Atomic Energy Commission, Ansar Parvez, signed today in Islamabad, in presence of Prime Minister Nawaz Sharif, a document admitting the Islamic Republic of Pakistan to CERN Associate Membership, subject to ratification by the Government of Pakistan.

“Pakistan has been a strong participant in CERN’s endeavours in science and technology since the 1990s,” said Rolf Heuer. “Bringing nations together in a peaceful quest for knowledge and education is one of the most important missions of CERN. Welcoming Pakistan as a new Associate Member State is therefore for our Organization a very significant event and I’m looking forward to enhanced cooperation with Pakistan in the near future.”

“It is indeed a historic day for science in Pakistan. Today’s signing of the agreement is a reward for the collaboration of our scientists, engineers and technicians with CERN over the past two decades,” said Ansar Parvez. “This Membership will bring in its wake multiple opportunities for our young students and for industry to learn and benefit from CERN. To us in Pakistan, science is not just pursuit of knowledge, it is also the basic requirement to help us build our nation.”

The Islamic Republic of Pakistan and CERN signed a Co-operation Agreement in 1994. The signature of several protocols followed this agreement, and Pakistan contributed to building the CMS and ATLAS experiments. Pakistan contributes today to the ALICE, ATLAS, CMS and LHCb experiments and operates a Tier-2 computing centre in the Worldwide LHC Computing Grid that helps to process and analyse the massive amounts of data the experiments generate. Pakistan is also involved in accelerator developments, making it an important partner for CERN.

The Associate Membership of Pakistan will open a new era of cooperation that will strengthen the long-term partnership between CERN and the Pakistani scientific community. Associate Membership will allow Pakistan to participate in the governance of CERN, through attending the meetings of the CERN Council. Moreover, it will allow Pakistani scientists to become members of the CERN staff, and to participate in CERN’s training and career-development programmes. Finally, it will allow Pakistani industry to bid for CERN contracts, thus opening up opportunities for industrial collaboration in areas of advanced technology.

Footnote(s)

1. CERN, the European Organization for Nuclear Research, is the world’s leading laboratory for particle physics. It has its headquarters in Geneva. At present, its Member States are Austria, Belgium, Bulgaria, the Czech Republic, Denmark, Finland, France, Germany, Greece, Hungary, Israel, Italy, the Netherlands, Norway, Poland, Portugal, Slovakia, Spain, Sweden, Switzerland and the United Kingdom. Romania is a Candidate for Accession. Serbia is an Associate Member in the pre-stage to Membership. India, Japan, the Russian Federation, the United States of America, Turkey, the European Union, JINR and UNESCO have Observer Status.

Source : CERN

The mass difference spectrum: the LHCb result shows strong evidence of the existence of two new particles the Xi_b'- (first peak) and Xi_b*- (second peak), with the very high-level confidence of 10 sigma. The black points are the signal sample and the hatched red histogram is a control sample. The blue curve represents a model including the two new particles, fitted to the data. Delta_m is the difference between the mass of the Xi_b0 pi- pair and the sum of the individual masses of the Xi_b0 and pi-.. INSET: Detail of the Xi_b'- region plotted with a finer binning.
Credit: CERN

CERN makes public first data of LHC experiments

CERN1 launched today its Open Data Portal where data from real collision events, produced by the LHC experiments will for the first time be made openly available to all. It is expected that these data will be of high value for the research community, and also be used for education purposes.

”Launching the CERN Open Data Portal is an important step for our Organization. Data from the LHC programme are among the most precious assets of the LHC experiments, that today we start sharing openly with the world. We hope these open data will support and inspire the global research community, including students and citizen scientists,” said CERN Director General Rolf Heuer.

The principle of openness is enshrined in CERN’s founding Convention, and all LHC publications have been published Open Access, free for all to read and re-use. Widening the scope, the LHC collaborations recently approved Open Data policies and will release collision data over the coming years.

The first high-level and analysable collision data openly released come from the CMS experiment and were originally collected in 2010 during the first LHC run. This data set is now publicly available on the CERN Open Data Portal. Open source software to read and analyse the data is also available, together with the corresponding documentation. The CMS collaboration is committed to releasing its data three years after collection, after they have been thoroughly studied by the collaboration.

“This is all new and we are curious to see how the data will be re-used,” said CMS data preservation coordinator Kati Lassila-Perini. “We’ve prepared tools and examples of different levels of complexity from simplified analysis to ready-to-use online applications. We hope these examples will stimulate the creativity of external users.”

 The mass difference spectrum: the LHCb result shows strong evidence of the existence of two new particles the Xi_b'- (first peak) and Xi_b*- (second peak), with the very high-level confidence of 10 sigma. The black points are the signal sample and the hatched red histogram is a control sample. The blue curve represents a model including the two new particles, fitted to the data. Delta_m is the difference between the mass of the Xi_b0 pi- pair and the sum of the individual masses of the Xi_b0 and pi-.. INSET: Detail of the Xi_b'- region plotted with a finer binning. Credit: CERN
The mass difference spectrum: the LHCb result shows strong evidence of the existence of two new particles the Xi_b’- (first peak) and Xi_b*- (second peak), with the very high-level confidence of 10 sigma. The black points are the signal sample and the hatched red histogram is a control sample. The blue curve represents a model including the two new particles, fitted to the data. Delta_m is the difference between the mass of the Xi_b0 pi- pair and the sum of the individual masses of the Xi_b0 and pi-.. INSET: Detail of the Xi_b’- region plotted with a finer binning.
Credit: CERN

In parallel, the CERN Open Data Portal gives access to additional event data sets from the ALICE, ATLAS, CMS and LHCb collaborations, which have been specifically prepared for educational purposes, such as the international masterclasses in particle physics2 benefiting over ten thousand high-school students every year. These resources are accompanied by visualisation tools.

“Our own data policy foresees data preservation and its sharing. We have seen that students are fascinated by being able to analyse LHC data in the past and so, we are very happy to take the first steps and make available some selected data for education” said Silvia Amerio, data preservation coordinator of the LHCb experiment.

“The development of this Open Data Portal represents a first milestone in our mission to serve our users in preserving and sharing their research materials. It will ensure that the data and tools can be accessed and used, now and in the future,” said Tim Smith from CERN’s IT Department.

All data on OpenData.cern.ch are shared under a Creative Commons CC03 public domain dedication; data and software are assigned unique DOI identifiers to make them citable in scientific articles; and software is released under open source licenses. The CERN Open Data Portal is built on the open-source Invenio Digital Library software, which powers other CERN Open Science tools and initiatives.

Further information:

Open data portal

Open data policies

CMS Open Data

 

Footnote(s):

1. CERN, the European Organization for Nuclear Research, is the world’s leading laboratory for particle physics. It has its headquarters in Geneva. At present, its Member States are Austria, Belgium, Bulgaria, the Czech Republic, Denmark, Finland, France, Germany, Greece, Hungary, Israel, Italy, the Netherlands, Norway, Poland, Portugal, Slovakia, Spain, Sweden, Switzerland and the United Kingdom. Romania is a Candidate for Accession. Serbia is an Associate Member in the pre-stage to Membership. India, Japan, the Russian Federation, the United States of America, Turkey, the European Commission and UNESCO have Observer Status.

2. http://www.physicsmasterclasses.org(link is external)

3. http://creativecommons.org/publicdomain/zero/1.0/

Figure 1 (left) Exclusion limits for production of Higgsino production as a function of Higgsino mass and branching fraction. (right) Most sensitive search channel as a function of Higgsino mass and branching fraction. Credit: CERN

Recent results in the search for supersymmetry : CERN CMS

By Frank Wuerthwein, Keith Ulmer and Guillelmo Gomez Ceballos.


Among the leading candidates to describe physics beyond the standard model of particle physics is Supersymmetry, a new symmetry that posits the existence of a partner particle for each known particle in the standard model. Supersymmetry, or “SUSY” as it has come to be known, may help explain the nature of dark matter and the large difference in strength between the fundamental forces of nature. Each year, new experimental results and theoretical developments are reported in the “SUSY” conference series, with the 2014 edition (SUSY2014) happening this week in Manchester, England[1].

Figure 1 (left) Exclusion limits for production of Higgsino production as a function of Higgsino mass and branching fraction. (right) Most sensitive search channel as a function of Higgsino mass and branching fraction. Credit: CERN
Figure 1 (left) Exclusion limits for production of Higgsino production as a function of Higgsino mass and branching fraction. (right) Most sensitive search channel as a function of Higgsino mass and branching fraction. Credit: CERN

Experimental evidence for SUSY has been sought for many years at multiple colliders, including a vast array of search results from the CMS experiment at the Large Hadron Collider at CERN. With data from Run 1 of the LHC collected through the end of 2012, the full set of results thus far has not revealed any striking signs of physics beyond the standard model [2]. New searches presented at SUSY2014 have begun to probe increasingly complicated potential decay chains and to combine multiple searches to access more challenging new physics scenarios. Below we highlight some of the most recent results first presented this summer at SUSY14 and ICHEP 2014 [3].

Figure 2: Exclusion limits versus gluino and neutralino masses for a variety of gluino decay branching fractions from the “razor” search. Credit: CERN
Figure 2: Exclusion limits versus gluino and neutralino masses for a variety of gluino decay branching fractions from the “razor” search. Credit: CERN

Search for new physics in the final states hh, Zh, and ZZ plus MET

After its discovery only two years ago, the Higgs boson is already a powerful tool in the search for new physics. Earlier this year, CMS submitted for publication [4] a set of searches for associate production of W, Higgs, and missing transverse energy (“MET”, indicative of particles escaping the detector). At ICHEP this summer, CMS presented the first combined searches for hh, Zh, and ZZ plus MET. No excess above standard model backgrounds is observed. Figure 1 shows the interpretation of the results in terms of limits on higgsino pair production as a function of the higgsino mass and decay branching fraction. Within the framework of Gauge Mediated Supersymmetry Breaking (GMSB), the neutral higgsino decays to a gravitino and either a higgs or Z boson. The left plot in Figure 1 shows that CMS excludes higgsino production up to ~ 300GeV when the higgsino decays at equal rate to either of these two decays. The right plot in Figure 1 indicates that four different final states dominate the sensitivity in different parts of the 2D parameter space, clearly demonstrating that searches for new physics with one or two higgs bosons in the final state benefit greatly from combining many different decay channels.

Figure 3: Dilepton invariant mass distribution for “same flavor” events, compared to the background prediction from “opposite flavor” events. Credit:CERN
Figure 3: Dilepton invariant mass distribution for “same flavor” events, compared to the background prediction from “opposite flavor” events. Credit:CERN

Search for gluino pair production via the decays to top pairs, bottom pairs, or top and bottom plus MET

Up to now, CMS searches for gluino pair production inspired by “natural SUSY” (i.e. SUSY in which the masses of the SUSY partners are not much higher than those of the Higgs boson) have focused on final states with either four top or four b-quarks plus MET. In contrast, theoretically any combination of MET plus 4 quarks, top or bottom, is well justified. At ICHEP, CMS presented the first complete exploration of sensitivity across the full set of possible final states and branching fractions. Figure 2 shows the corresponding exclusion curves in the gluino vs neutralino mass plane. This search employs the so-called “razor” variables, and its sensitivity is dominated by all-hadronic final states. The more top quarks there are in the final state for a given gluino mass, the less momentum is left for all the decay products, and the harder it is thus to distinguish signal from background. Accordingly, the sensitivity decreases as the number of top quarks per event increases.

Figure 4: MSSMvsSM limit in the MSSM mmod+h scenario. At each mA - tanβpoint a Hypothesis test is performed testing the MSSM (A+H+h+BKG) hypothesis against the SM (hSM+BKG) hypothesis. Credit: CERN
Figure 4: MSSMvsSM limit in the MSSM mmod+h scenario. At each mA – tanβpoint a Hypothesis test is performed testing the MSSM (A+H+h+BKG) hypothesis against the SM (hSM+BKG) hypothesis. Credit: CERN

Searching for SUSY with an “Edge”

The dilepton invariant mass distribution for leptons from the decays χ20 to l+l- χ10, or similar decays via a slepton as an intermediate state, display the striking feature of a kinematic “edge” [5, 6]. As these decays conserve lepton flavor, this edge is present only in same-flavor events, i.e. ee and μμ, and is completely absent in the “opposite flavor” lepton sample, i.e. eμ events. In contrast, backgrounds for which each of the two leptons come from a different W decay, e.g. top pairs, WW, etc., will have identical dilepton distributions for same and opposite flavor. Thus, the eμ sample in data provides a perfect model of the background dilepton mass distribution – modulo effects from the trigger and lepton reconstruction. The kinematic edge is a sufficiently striking signature to reveal new physics even at relatively modest hadronic activity, HT and MET, i.e. in the presence of sizeable top and Z backgrounds.

CMS presented a search for such an “edge” in dilepton events with jets and MET at SUSY2014 using the full 8TeV data sample [7]. Figure 3 overlays the dilepton mass distribution in ee plus μμ (data points), with the corresponding one from eμ (pink histogram). The blue shaded region depicts the systematic error envelope for the background prediction. A small excess is visible below the Z peak. A signal region of 20GeV < mll < 70GeV was chosen before data taking. Within this region, 860 events are observed with an expected standard model background yield of 730 ± 40. The small excess is consistent with a 2.6 sigma fluctuation of the standard model background. For more details see [8].

Search for additional neutral MSSM Higgs bosons in the H→ττ decay channel

Another highlight among the CMS results presented at the SUSY2014 conference is the search for additional neutral Higgs bosons decaying to τ leptons, which is the most promising channel to search for such Higgs bosons in the context of the minimal SUSY extension of the standard model, the MSSM. Following the release of a preliminary result based on the full data set of the 2011/2012 data taking period [8], additional results based on a new interpretation of the data have been presented at this conference for the first time [9]. While the data selection has not changed, extensive work has set the ground for a new interpretation of the data in the context of modern benchmark models. In particular, the new models take into account the presence of the recently discovered Higgs boson with a mass of 125 GeV, as proposed in [10]. Also for the first time the model-dependent exclusion contours as a function of the mass of the CP-odd Higgs boson, A, and the ratio of the vacuum expectation values of the two SUSY Higgs doublets, tanβ, have been derived, taking the presence of the newly discovered Higgs boson properly into account in the test statistic. As recently demonstrated by CMS [11], all observations of the new boson are so far compatible with the SM expectation within ~10% accuracy, which justifies the standard model hypothesis to be the better choice for the test statistic. The hypothesis test now becomes a search based on a model with three Higgs bosons compared against the standard model with only one Higgs boson. Traditional limits, based on the test statistic excluding the Higgs boson from the standard model hypothesis have also been made public on the CMS web-pages [12]. Also made available to the public is an extended database of results based on a model-independent single-resonance search model, which will be extremely valuable to theorists engaged in model building. Figure 1 shows the exclusion contour in a modified mh,max scenario, also referred to as mh,mod+ exploiting the new statistical treatment for the statistical inference.

By Frank Wuerthwein, Keith Ulmer and Guillelmo Gomez Ceballos.


[1] http://www.susy2014.manchester.ac.uk

[2] https://twiki.cern.ch/twiki/bin/view/CMSPublic/PhysicsResultsSUS

[3] http://ichep2014.es

[4] https://twiki.cern.ch/twiki/bin/view/CMSPublic/PhysicsResultsSUS13006

[5] http://cds.cern.ch/record/1194507/files/SUS-09-002-pas.pdf

[6] https://twiki.cern.ch/twiki/bin/view/CMSPublic/PhysicsResultsSUS11011

[7] https://twiki.cern.ch/twiki/bin/view/CMSPublic/PhysicsResultsSUS12019

[8] CMS Collaboration, “Search for Neutral MSSM Higgs Bosons Decaying to Tau Pairs in pp Collisions”, (2013), CMS-PAS-HIG-13-021.

[9] CMS Collaboration, “Search for Neutral MSSM Higgs Bosons Decaying to Tau Pairs in pp Collisions”, to be submitted to JHEP.

[10] M. S. Carena et al, “MSSM Higgs boson searches at the Tevatron and at the LHC: Impact of different benchmark scenarios” Eur. Phy. J C 73, 2552 (2013) (arXiv:hep-ph/0511023).

[11] CMS Collaboration, “Precise determination of the mass of the Higgs boson and studies of the compatibility of its couplings with the standard model”, (2014), CMS-PAS-HIG-14-009.

[12] https://indico.hep.manchester.ac.uk/contributionDisplay.py?contribId=288….

Source: CERN CMS