High Energy Physics Laboratory started under the name of “High energy and cosmic rays” in 1956 when Bulgaria was one of the founding states of the Joint Institute of Nuclear Research, established in Dubna, USSR.
The main topics of our activity are: high energy particle physics with accelerators, physics beyond the Standard Model, search for supersimetry, Higgs particle, discoveries of new states of matter (quark-gluon plasma), searching for new particles and resonances and investigation of their properties and interractions.
We work in the framework of scientific plan of Institute for Nuclear Research and Nuclear energy, approved by Bulgarian Academy of Sciences. Participation of our Laboratory in the scientific programme of CERN, corresponds to integration of Bulgarian scientists into the European research area, as stated in the “Encouragement of Scientific Studies Low” (article 1, part 4, paragraph 3, published in Government newspaper 92/17.10.2003) and it is fully synchronized with basic guidelines of the “National Strategy for Scientific Research” project of Ministry of Education and Science of R Bulgaria.
In the “High energy physics” Laboratory there is 13 staff members - 3 Associate Professors, PhD, 3 Research Scientists PhD, 4 Research Scientists, 1 Engeneer, 2 IT experts. 2 PhD students are involved in the CMS activity of the Laboratory.
Formal and informal bilateral and multilateral co-operation and relations with other research establishments:
• Within the Academy our Laboratory is co-operating with “Nuclear Electronics” Laboratory of INRNE.
• At national level we have a bi-literal co-operation agreement with University of Plovdiv and Sofia University “St.Kliment Ohridski”. Our industrial partners are “Nonferrous Metal Company”, Gara Iskar, Sofia and “Stelmed” CA, Sofia, company for production of aluminium profiles.
• In 1993 Physicists and engineers from “High Energy Physics” Laboratory started work at CERN in the CMS project for experiment at LHC. They were involved in CMS Hadron Calorimeter simulation and beam testing, as well as in the preproduction of the brass plates of about 700 tons for the calorimeter.
• Our participation in CERN activities got à boost in the year 1999, when Bulgaria became the 20th member-state of the Organisation. Since then Bulgaria has joined efforts with the other European countries in building the new powerful accelerator - the Large Hadron Collider LHC and the CMS detector. According to the “Memorandum of Understanding for the Construction for the CMS Detector” signed between Bulgarian Ministry of Education and Science and CERN, 125 RPC RPC chambers were assembled and tested in the “High Energy Physics” Laboratory at INRNE and integrated into the CMS detector. The successful fulfillment of our obligation for production of equipment for the CMS experiment at CERN is performed under cooperation agreements of our Laboratory with FERMILAB (USA), JINR (Dubna, Russia), INFN (Bari, Italy) and CERN (Switzerland) during the period 2002-2008.
• From the beginning of the work on CMS our physicists were taking part in the installation and commissioning of the RPC chambers at CMS, generation and reconstruction of large Monte Carlo data samples for CMS, calibration and validation of the Monte-Carlo simulation and data analysis of the test beam data of the Hadron calorimeter. In the beginning of 2005 in INRNE a GRID-cluster (Tier-3 status ) for work in LCG: ce1.inrne.bas.bg was commissioned and officially certified.
• After LHC starts operation in the 2009-2012 at the beginning the processing of several hundred millions events, registered by the CMS detector, produced by cosmic muon rays at the magnet test and cosmic challenge and cosmic test at four Tesla is completed. This provided opportunity to test the integration of major components of the experiment before lowering them into the underground experimental cavern and important commissioning and operational experience.
• Several million real physical events have been collected at beam energy in the system of center of mass (SCM) 0.9 TeV and 2.36 TeV in successful operation of the LHC collider at the end of 2009 in the CMS detector. The available statistics was good enough for extracting of parameters of the all subdetectors of the CMS and provides his calibration in the real working conditions. Thus the comparison with the test beam data and Monte Carlo data, earlier obtained, shows that the CMS subdetectors overfill project technical specifications such as efficiency, spatial resolution and trigger synchronization.
• In this period we were working on collecting of data and processing of registered events for obtaining of experimental results as well as in the working group DQM (Data Quality Monitoring) of the CMS detector and his maintenance.
More important scientific achievements: The CMS experiment is one of the two experiments proposed to operate in the collider LHC, built at CERN in Geneva, Switzerland. The main results of the work on the CMS project, carried out in the Institute of Nuclear Research and Nuclear Energy of the Bulgarian Academy of Sciences are as follows:
• 125 RB3 Resistive Plate Chambers (RPC) for the experiment CMS were produced and tested in INRNE. This way we have fulfilled our obligation for production of RPC chambers for the CMS. The parameters of the chambers, determined in cosmic ray muon tests, are within the technical specifications for this type of detectors. Required infrastructure for assembly and test with cosmic muons of the Resistive Plate Chambers (RPC) has been established at INRNE, Sofia. The assembly table, test facility and gas system have been installed. The members of the “High Energy Physics” Laboratory were awarded with the “Best experimental investigations in INRNE, BAS” award for the year 2005.
• The chambers were shipped to CERN, Switzerland and our specialists took part in the final installation of the last RPC chambers in the CMS detector. All 480 RPC’s constituting the barrel muon trigger system are already installed and functional tests in situ have been performed. Runs using cosmic muons were carried out in order to check the full data flow chain. These runs achieved the goal of accumulating 300 million cosmic triggers with full magnetic field. After complete installation and commissioning, the detector was closed in time for the first ever LHC beam on 10 September.
• Members of our group, working at FNAL, USA, took part in the work on the calibration of the CMS Hadron Calorimeter and test beam data analysis. They participated also in the activities of “Computing Software and Analysis Challenge 2007”.
• A technical facility based on Grid technology is developed to support CMS distributed analysis. The GRID-cluster in INRNE was permanently operational during 2007-2008 and available for LCG (LHC Computing Grid) work. The grid-specific software was regularly upgraded to meet the LHC requirements. Our specialists contributed to the development at CERN of software for automated installation and configuration of the grid middleware Glite 3.1.
• The latest releases of the CMS software system, CMSSW, are routinely installed in INRNE CMS-computing framework. Monte Carlo studies of Higgs boson production in dijet spectrum of black hole decays at CMS is carried out. Validation of the Monte-Carlo simulation of CMS was performed.
• The physical measurements begun in the period of testing of CMS detector with cosmic rays and continued with collision of two proton beams at beam energy in the system of center of mass (SCM) 0.9, 2.36 and 7 TeV in the CMS detector. For a short period results obtained from the CMS, revised all physics of elementary particles. The masses, branching ratio and cross section of already known particles have been measured and improved results, obtained the last 50 years;
• In the period January – December 2011 High energy Physics Laboratory at INRNE continued his active participation in collecting of data, processing and analysis of registered events for obtaining of experimental results as well as in the working group DQM (Data Quality Monitoring) of the CMS detector dnd his maintenance; LHC collider was work in stable regim with increasing luminosity and at 22 April 2011 set a new world record for beam intensity at a hadron collider when it collided beams with a luminosity of 4.67 x 1032cm-2s-1. This exceeds the previous world record of 4.024 x 1032cm-2s-1, set at the Tevatron collider in 2010. To the end of the year 2011 the collider worked at luminosity 3.54 x 1033cm-2s-1. The collected statistics of 5.2 fb-1 at 91% efficiency have been processed and results are published in several international scientific journals
• The precise measurements for general confirmation of the Standard model have been done. The first results for the seraching of Higgs - bosons and for the testing of new theory for physics beyond Standard model have been obtained. Strategy and policies for future development for High Energy Physics Laboratory: The CMS experiment will operate at the most powerful proton-proton collider LHC at CERN. The principal scientific mission of CMS is to reveal the mechanism of electroweak symmetry breaking responsible for generation of the masses of the particles, which could eventually lead to discovery of a new heavy fundamental particle - the Higgs boson. Also a search will be carried out for manifestations of new physics, such as the “supersymmetry”, which is related to the existence of a set of new particles – partners of the already known ones. Apart from searches for new physics phenomena, the scientific programme of CMS includes various precision measurements in the framework of the Standard Model - the theory, which at present provides the most accurate description of the elementary particles and their interactions.
• After the successful fulfillment of our responsibilities for hardware contribution to the CMS detector, which involved production of RPC-chambers our future work will be oriented to participation in the running of the detector subsystems, data taking and data analysis. Our joint group from the INRNE, BAS and the Plovdiv University envisage to take part in the investigations to register the Higgs boson and in the studies of production of pairs top quark-antiquark.
• The processing of the data from the CMS experiment will extensively rely on using GRID-technologies. To this end, we will develop and extend our GRID-infrastructure. We also plan the equipment in INRNE, used for functional tests of the RPC-chambers during the production phase, to be used to investigate the long-term stability of RPC operation. We will participate in the maintenance of the detector and electronics equipment at LHC at CERN, contributed by INRNE, BAS to CMS.
In 2013 LHC will be upgraded in order to reach luminosity an order of magnitude higher than nominal. We are planning to participate in the R&D of new detectors able to sustain the SLHC environment.
The new agreement between Bulgaria and CERN - “Memorandum of Understanding for Maintenance and Operation of the CMS Detector” (MoU_for_M&O), signed in 2008 (decision 20/22.05.2008 of session of Ministry Council of R Bulgaria), provides the framework for further participation of Bulgarian groups in the CMS research activities. In accordance with the MoU for M&O, the Bulgarian groups are responsible for the maintenance of the detector and electronics equipment contributed by Bulgaria to CMS.

## Scientists

 Member Occupation E-mail Phone Georgi Sultanov Associate Professor, Ph.D. Този имейл адрес е защитен от спам ботове. Трябва да имате пусната JavaScript поддръжка, за да го видите. 5547 Plamen Iaydjiev Associate Professor, Ph.D. - Acting Head of the Laboratory Този имейл адрес е защитен от спам ботове. Трябва да имате пусната JavaScript поддръжка, за да го видите. 5559 Roumyana Hadjiiska Assistant Professor, Ph.D. Този имейл адрес е защитен от спам ботове. Трябва да имате пусната JavaScript поддръжка, за да го видите. Aleksandar Aleksandrov Assistant Professor, Ph.D. Този имейл адрес е защитен от спам ботове. Трябва да имате пусната JavaScript поддръжка, за да го видите. 5542 Stefan Piperov Assistant Professor Този имейл адрес е защитен от спам ботове. Трябва да имате пусната JavaScript поддръжка, за да го видите. 5547 Stefka Stoykova Assistant Professor Този имейл адрес е защитен от спам ботове. Трябва да имате пусната JavaScript поддръжка, за да го видите. 5549 Preslav Konstantinov IT Expert Този имейл адрес е защитен от спам ботове. Трябва да имате пусната JavaScript поддръжка, за да го видите. 5659 Andrey Marinov Researcher Този имейл адрес е защитен от спам ботове. Трябва да имате пусната JavaScript поддръжка, за да го видите. 5547 Gulmira Bakirova Researcher 5542 Milena Misheva Assistant Professor 5542 Mircho Rodozov Researcher Този имейл адрес е защитен от спам ботове. Трябва да имате пусната JavaScript поддръжка, за да го видите. 5542 Nedyalka Chankova-Banzarova Researcher Този имейл адрес е защитен от спам ботове. Трябва да имате пусната JavaScript поддръжка, за да го видите. 5542 Rumen Gushterski Researcher 5542 Mariana Shopova Physicist, Ph.D. Ivan Mihailov Physicist Atanas Monev Worker scientific equipment

## Projects

Experiment CMS in the LHC collider at CERN, Bulgaria, Ministry of Education and Science, contract D01-758/20.12.2008

Advanced European Infrastructures for Detectors at Accelerators AIDA - Capacities â Research Infrastructures FP7-INFRASTRUCTURES-2010-1

## Publications

Experiment Compact Muon Solenoid - CMS at LHC, CERN

1. V.Abramov,et al.Study of Magnetic Field Influence on Hadron Calorimeter Response",Nicl. Instr. and Meth. in Phys. Res. A457,2001.
2. M. Abbrescia…et al. Cosmic rays tests of double-gap resistive plate chambers for the CMS experiment. Nucl. Instrum. Methods A550 (2005) 116-126.
3. The CMS Collaboration. CMS Technical Design Report,Volume II: Physics Performance. J.Phys.G: Nucl.Part.Phys.34(2007) 995.
4. The CMS Collaboration. CMS Physics Technical Design Report: Addendum on High Density QCD with Heavy Ions. J.Phys.G: Nucl.Part.Phys.34(2007) 2307.
5. M. Abbrescia ,et al.Production and quality control of the Barrel RPC chambers of the CMS experiment. Nucl. Phys. Proc. Suppl. 150 290 (2006).
6. M. Abbrescia ,et al HF production in CMS-Resistive Plate Chambers. Nucl. Phys. Proc. Suppl. 158 30 (2006).
7. M. Abbrescia et al Quality control tests for the CMS barrel RPCs. Nucl. Phys. Proc. Suppl. 158 73 (2006).
8. CMS Collaboration. D. Acosta et al. CMS Physics Technical Design Report, Volume 1. Detector Performance and Software. CERN/LHCC 2006-001. CMS TDR 8.1 (2006).
9. G. Bayatian et al. Design, performance and calibration of the CMS forward calorimeter wedges. CERN-CMS-NOTE-2006-044 (2006)
10. CMS Trigger and Data Acquisition Group. W.Adam et al. The CMS high level trigger. Eur.Phys.J.C46605(2006).
11. G.L.Bayatian et al. The CMS Computing Project. Technical Design Report
12. M.Abrescia et al.,The gas monitoring system for the resistive plate chamber detector of the CMS experiment at LHC, Nucl. Phys. Proc. Suppl. 177-178:293-296,(2008)
13. S. Chatarchyan et al,The CMS experiment at the CERN LHC. JINST 3:S08004,2008.
14. M. Abbrescia, et al,First measurements of the performance of the barrel RPC system in CMS. Nucl.Instrum.Meth.A609:114-121,2009.
15. A. Colaleo et al,The compact muon solenoid RPC barrel detector. Nucl.Instrum.Meth.A602:674-678,2009.
16. G. Roselli et al,Resistive plate chamber commissioning and performance in CMS. Nucl.Instrum.Meth.A602:696-699,2009.
17. R. T. Rajan, et al.,A configurable tracking algorithm to detect cosmic muon tracks for the CMS-RPC based technical trigger. Nucl.Instrum.Meth.A602:792-795,2009.
18. S. Chatrchyan, et al,Alignment of the CMS Silicon Tracker during Commissioning with Cosmic Rays. JINST 5:T03009,2010.
19. S. Chatrchyan, et al, Performance and Operation of the CMS Electromagnetic Calorimeter.JINST 5:T03010,2010.
20. S. Chatrchyan et al,Precise Mapping of the Magnetic Field in the CMS Barrel Yoke using Cosmic Rays. JINST 5:T03021,2010.
21. S. Chatrchyan et al,Time Reconstruction and Performance of the CMS Electromagnetic Calorimeter. JINST 5:T03011,2010.
22. S. Chatrchyan et al, Performance Study of the CMS Barrel Resistive Plate Chambers with Cosmic Rays. JINST 5:T03017,2010.
23. S. Chatrchyan et al, Aligning the CMS Muon Chambers with the Muon Alignment System during an Extended Cosmic Ray Run. JINST 5:T03019,2010.
24. S. Chatrchyan et al, CMS Data Processing Workflows during an Extended Cosmic Ray Run. JINST 5:T03006,2010.
25. S. Chatrchyan et al,Commissioning of the CMS Experiment and the Cosmic Run at Four Tesla. JINST 5:T03001,2010.
26. S. Chatrchyan et al,Performance of the CMS Drift Tube Chambers with Cosmic Rays. JINST 5:T03015,2010. 27. S. Chatrchyan et al,Performance of CMS Hadron Calorimeter Timing and Synchronization using Test Beam, Cosmic Ray, and LHC Beam Data. JINST 5:T03013,2010.
28. S. Chatrchyan et al, Identification and Filtering of Uncharacteristic Noise in the CMS Hadron Calorimeter. JINST 5:T03014,2010.
29. S. Chatrchyan et al,Commissioning of the CMS High-Level Trigger with Cosmic Rays. JINST 5:T03005,2010.
30. S. Chatrchyan et al, Performance of the CMS Drift-Tube Local Trigger with Cosmic Rays. JINST 5:T03003,2010.
31. S. Chatrchyan et al, Calibration of the CMS Drift Tube Chambers and Measurement of the Drift Velocity with Cosmic Rays. JINST 5:T03016,2010.
32. S. Chatrchyan et al, Fine Synchronization of the CMS Muon Drift-Tube Local Trigger using Cosmic Rays. JINST 5:T03004,2010.
33. S. Chatrchyan et al, Performance of the CMS Hadron Calorimeter with Cosmic Ray Muons and LHC Beam Data. JINST 5:T03012,2010.
34. S. Chatrchyan et al, Performance of the CMS Cathode Strip Chambers with Cosmic Rays. JINST 5:T03018,2010.
35. S. Chatrchyan et al, Performance of CMS Muon Reconstruction in Cosmic-Ray Events. JINST 5:T03022,2010.
36. S. Chatrchyan,…, P.Iaydjiev,…et al, Commissioning and Performance of the CMS Silicon Strip Tracker with Cosmic Ray Muons. JINST 5:T03008,2010.
37. S. Chatrchyan,…, P.Iaydjiev,…et al, Measurement of the Muon Stopping Power in Lead Tungstate. JINST 5:P03007,2010.
38. S. Chatrchyan,…, P.Iaydjiev,…et al, Performance of the CMS Level-1 Trigger during Commissioning with Cosmic Ray Muons. JINST 5:T03002,2010.
39. S. Chatrchyan,…, P.Iaydjiev,…et al, Commissioning and Performance of the CMS Pixel Tracker with Cosmic Ray Muons. JINST 5:T03007,2010.
40. Vardan Khachatryan et al.Transverse momentum and pseudorapidity distributions of charged hadrons in pp collisions at $\sqrt(s)$ = 0.9 and 2.36 TeV. JHEP 1002:041,2010.
41. M. Abbrescia ,… et al., The gas monitoring system for the resistive plate chamber detector of the CMS experiment at LHC 2008. 4pp. 18th Hadron Collider Physics Symposium 2007 (HCP 2007) 20-26 May 2007, Nucl.Phys.Proc.Suppl.177-178:293-296,2008.
42. Vardan Khachatryan et al. By CMS Collaboration Transverse-momentum and pseudorapidity distributions of charged hadrons in pp collisions at sqrt(s) = 7 TeV. Phys.Rev.Lett.105:022002,2010.
43. M. Abbrescia et al., The gas monitoring system for the resistive plate chamber detector of the CMS experiment at LHC. Nucl.Phys.Proc.Suppl.177-178:293-296,2008.
44. N. Darmenov, et al.,The CMS RPC system overview. AIP Conf.Proc.1203:43-48,2010.
45. V. Khachartyan et al., Search for Dijet Resonances in 7 TeV pp Collisions at CMS. Phys.Rev.Lett.105:211801, 2010.
46. V. Khachartyan et al., Search for Quark Compositeness with the Dijet Centrality Ratio in pp Collisions at vs=7 TeV. Phys.Rev.Lett.105:262001, 2010.
47. V. Khachartyan et al., Observation of Long-Range Near-Side Angular Correlations in Proton-Proton Collisions at the LHC. JHEP 1009:091, 2010.
48. V. Khachartyan et al., First Measurement of Bose-Einstein Correlations in Proton-Proton Collisions at vs=0.9 and 2.36 TeV at the LHC. Phys.Rev.Lett.105:032001, 2010.
49. V. Khachartyan et al., Transverse-momentum and pseudorapidity distributions of charged hadrons in pp collisions at vs = 7 TeV. Phys.Rev.Lett.105:022002, 2010.
50. V. Khachartyan , et al., Measurement of the charge ratio of atmospheric muons with the CMS detector. Phys.Lett.B692:83-104, 2010.
51. V. Khachartyan et al., Transverse momentum and pseudorapidity distributions of charged hadrons in pp collisions at vs = 0.9 and 2.36 TeV. JHEP 1002:041, 2010.
52. V. Khachartyan et al., First Measurement of the Underlying Event Activity at the LHC with vs = 0.9 TeV. Eur.Phys.J.C70:555-572, 2010.
53. V. Khachartyan et al., CMS Tracking Performance Results from early LHC Operation. Eur.Phys.J.C70:1165-1192, 2010.
54. S. Chatrchyan et al., Study of various photomultiplier tubes with muon beams and Cherenkov light produced in electron showers. JINST 5:P06002, 2010.
55. D. Piccolo et al., Resistive plate chambers performance with cosmic rays in the CMS experiment. Nucl.Instrum.Meth.A617:180-182, 2010.
56. S. Chatrchyan et al., Alignment of the CMS Muon System with Cosmic-Ray and Beam-Halo Muons. JINST 5:T03020, 2010.
57. S. Chatrchyan et al., Time Reconstruction and Performance of the CMS Electromagnetic Calorimeter. JINST 5:T03011, 2010.
58. S. Chatrchyan et al., Performance Study of the CMS Barrel Resistive Plate Chambers with Cosmic Rays.JINST 5:T03017, 2010.
59. S. Chatrchyan et al., Aligning the CMS Muon Chambers with the Muon Alignment System during an Extended Cosmic Ray Run. JINST 5:T03019, 2010.
60. S. Chatrchyan et al., CMS Data Processing Workflows during an Extended Cosmic Ray Run. JINST 5:T03006, 2010.
61. S. Chatrchyan et al., Commissioning of the CMS Experiment and the Cosmic Run at Four Tesla. JINST 5:T03001, 2010.
62. S. Chatrchyan et al., Performance of the CMS Drift Tube Chambers with Cosmic Rays. JINST 5:T03015, 2010.
63. S. Chatrchyan et al., Performance of CMS Hadron Calorimeter Timing and Synchronization using Test Beam, Cosmic Ray, and LHC Beam Data. JINST 5:T03013, 2010.
64. S. Chatrchyan et al., Identification and Filtering of Uncharacteristic Noise in the CMS Hadron Calorimeter. JINST 5:T03014, 2010.
65.S.Chatrchyan et al., Commissioning of the CMS High-Level Trigger with Cosmic Rays. JINST 5:T03005, 2010.
66. S. Chatrchyan et al., Performance of the CMS Drift-Tube Local Trigger with Cosmic Rays. JINST 5:T03003, 2010.
67. S. Chatrchyan et al., Calibration of the CMS Drift Tube Chambers and Measurement of the Drift Velocity with Cosmic Rays. JINST 5:T03016, 2010.
68. S. Chatrchyan ,… et al., Fine Synchronization of the CMS Muon Drift-Tube Local Trigger using Cosmic Rays. JINST 5:T03004, 2010.
69. S. Chatrchyan et al., Performance of the CMS Hadron Calorimeter with Cosmic Ray Muons and LHC Beam Data. JINST 5:T03012, 2010.
70. S. Chatrchyan et al., Performance of the CMS Cathode Strip Chambers with Cosmic Rays. JINST 5:T03018, 2010.
71. S. Chatrchyan et al., Performance of CMS Muon Reconstruction in Cosmic-Ray Events. JINST 5:T03022, 2010.
72. S. Chatrchyan et al., Commissioning and Performance of the CMS Silicon Strip Tracker with Cosmic Ray Muons. JINST 5:T03008, 2010.
73. S. Chatrchyan et al., Measurement of the Muon Stopping Power in Lead Tungstate. JINST 5:P03007, 2010.
74. S. Chatrchyan et al., Performance of the CMS Level-1 Trigger during Commissioning with Cosmic Ray Muons. JINST 5:T03002, 2010.
75. S. Chatrchyan et al., Commissioning and Performance of the CMS Pixel Tracker with Cosmic Ray Muons. JINST 5:T03007, 2010.
76. S. Chatrchyan et al., Alignment of the CMS Silicon Tracker during Commissioning with Cosmic Rays. JINST 5:T03009, 2010.
77. S. Chatrchyan et al., Performance and Operation of the CMS Electromagnetic Calorimeter. JINST 5:T03010, 2010.
78. S. Chatrchyan et al., Precise Mapping of the Magnetic Field in the CMS Barrel Yoke using Cosmic Rays. JINST 5:T03021, 2010.
79. S. Chatrchyan et al,Alignment of the CMS Muon System with Cosmic-Ray and Beam-Halo Muons. JINST 5:T03020,2010.
80. S. Chatrchyan et al., Search for Same-Sign Top - Quark Pair Production at vs = 7 TeV and Limits on Flavour Changing Neutral Currents in the Top Sector.JHEP 1108:005, 2011, ISSN 1126-6708, IF=6.049.
81. S. Chatrchyan et al., Search for Light Resonances Decaying into Pairs of Muons as a Signal of New Physics. JHEP 1107:098, 2011, ISSN 1126-6708, IF=6.049.
82. S. Chatrchyan et al., Search for Supersymmetry in Events with b Jets and Missing Transverse Momentum at the LHC.JHEP 1107:113, 2011, ISSN 1126-6708, IF=6.049.
83. S. Chatrchyan et al., Long-range and short - range dihadron angular correlations in central Pb Pb collisions at vs = 2.76 TeV. JHEP 1107:076, 2011, ISSN 1126-6708, IF=6.049.
84. S. Chatrchyan et al., Measurement of W? and Z? production in pp collisions at vs = 7 TeV. Phys.Lett.B701:535-555, 2011, ISSN 0370-2693, IF=5.255.
85. S. Chatrchyan et al., Search for supersymmetry in events with a lepton, a photon and large missing transverse energy in pp collisions at vs = 7 TeV. JHEP 1106:093, 2011, ISSN 1126-6708, IF=6.049.
86. S. Chatrchyan et al., Indications of suppression of excited ? states in PbPb collisions at vs = 2.76 TeV. Phys.Rev.Lett.107:052302, 2011, ISSN 0031-9007, IF=7.621.
87. S. Chatrchyan et al., Measurement of the tt - bar production cross section and the top quark mass in the dilepton channel in pp collisions at vs =7 TeV.JHEP 1107:049, 2011, ISSN 1126-6708, IF=6.049.
88. S. Chatrchyan et al., Search for Neutral MSSM Higgs Bosons Decaying to Tau Pairs in pp Collisions at vs =7 TeV.Phys.Rev.Lett.106:231801, 2011, ISSN 0031-9007, IF=7.621.
89. S. Chatrchyan et al., Measurement of the differential dijet production cross section in proton-proton collisions at vs =7 TeV.Phys.Lett.B700:187-206, 2011, ISSN 0370-2693, IF=5.255.
90. S. Chatrchyan et al., Measurement of the B0 production cross section in pp Collisions at vs = 7 TeV. Phys.Rev.Lett.106:252001, 2011, ISSN 0031-9007, IF=7.621.
91. S. Chatrchyan et al., Search for new physics with same-sign isolated dilepton events with jets and missing transverse energy at the LHC. JHEP 1106:077, 2011, ISSN 1126-6708, IF=6.049.
92. S. Chatrchyan et al., Measurement of the Polarization of W Bosons with Large Transverse Momenta in W + Jets Events at the LHC. Phys.Rev.Lett.107:021802, 2011, ISSN 0031-9007, IF=7.621.
93. S. Chatrchyan et al., Search for a W’ boson decaying to a muon and a neutrino in pp collisions at vs = 7 TeV. Phys.Lett.B701:160-179, 2011, ISSN 0370-2693, IF=5.255.
94. S. Chatrchyan et al., Search for Supersymmetry in pp Collisions at vs = 7 TeV in Events with Two Photons and Missing Transverse Energy. Phys.Rev.Lett.106:211802, 2011, ISSN 0031-9007, IF=7.621.
95. S. Chatrchyan et al., Search for Resonances in the Dilepton Mass Distribution in pp Collisions at vs = 7 TeV.JHEP 1105:093, 2011, ISSN 1126-6708, IF=6.049.
96. S. Chatrchyan et al., Search for Physics Beyond the Standard Model in Opposite Sign Dilepton Events at vs = 7 TeV. JHEP 1106:026, 2011, ISSN 1126-6708, IF=6.049.
97. S. Chatrchyan et al., Measurement of the lepton charge asymmetry in inclusive W production in pp collisions at vs = 7 TeV. JHEP 1104:050, 2011, ISSN 1126-6708, IF=6.049.
98. S. Chatrchyan et al., Search for Large Extra Dimensions in the Diphoton Final State at the Large Hadron Collider. JHEP 1105:085, 2011, ISSN 1126-6708, IF=6.049.
99. V. Khachatryan et al., First Measurement of Hadronic Event Shapes in pp Collisions at vs =7 TeV. Phys.Lett.B699:48-67, 2011, ISSN 0370-2693, IF=5.255.
100. V. Khachatryan et al., Measurement of Dijet Angular Distributions and Search for Quark Compositeness in pp Collisions at vs = 7 TeV. Phys.Rev.Lett.106:201804, 2011, ISSN 0031-9007, IF=7.621.
101. V. Khachatryan et al., Measurement of B anti - B Angular Correlations based on Secondary Vertex Reconstruction at vs =7 TeV. JHEP 1103:136, 2011, ISSN 1126-6708, IF=6.049.
102. V. Khachatryan et al., Strange Particle Production in pp Collisions at vs = 0.9 and 7 TeV. JHEP 1105:064, 2011, ISSN 1126-6708, IF=6.049.
103. S. Chatrchyan et al., Measurement of W+W- Production and Search for the Higgs Boson in pp Collisions at vs = 7 TeV. Phys.Lett.B699:25-47, 2011, ISSN 0370-2693, IF=5.255.
104. S. Chatrchyan et al., Study of Z boson production in PbPb collisions at nucleon - nucleon centre of mass energy = 2.76 TeV. Phys.Rev.Lett.106:212301, 2011, ISSN 0031-9007, IF=7.621.
105. V. Khachatryan et al., Measurement of the B+ Production Cross Section in pp Collisions at vs = 7 TeV. Phys.Rev.Lett.106:112001, 2011, ISSN 0031-9007, IF=7.621.
106. V. Khachatryan et al., Search for Supersymmetry in pp Collisions at 7 TeV in Events with Jets and Missing Transverse Energy. Phys.Lett.B698:196-218, 2011, ISSN 0370-2693, IF=5.255.
107. V. Khachatryan et al., Search for Heavy Stable Charged Particles in pp collisions at vs =7 TeV. JHEP 1103:024, 2011, ISSN 1126-6708, IF=6.049.
108. V. Khachatryan et al., Inclusive b - hadron production cross section with muons in pp collisions at vs = 7 TeV. JHEP 1103:090, 2011, ISSN 1126-6708, IF=6.049.
109. V. Khachatryan et al., Measurement of Bose - Einstein Correlations in pp Collisions at vs =0.9 and 7 TeV. JHEP 1105:029, 2011, ISSN 1126-6708, IF=6.049.
110. V. Khachatryan et al., Dijet Azimuthal Decorrelations in pp Collisions at vs = 7 TeV. Phys.Rev.Lett.106:122003, 2011, ISSN 0031-9007, IF=7.621.
111. V. Khachatryan et al., Measurement of the Isolated Prompt Photon Production Cross Section in ppCollisions at vs = 7 TeV. Phys.Rev.Lett.106:082001, 2011, ISSN 0031-9007, IF=7.621.
112. V. Khachatryan et al., Measurements of Inclusive W and Z Cross Sections in pp Collisions at vs =7 TeV. JHEP 1101:080, 2011, ISSN 1126-6708, IF=6.049.
113. V. Khachatryan et al., Search for Microscopic Black Hole Signatures at the Large Hadron Collider. Phys.Lett.B697:434-453, 2011, ISSN 0370-2693, IF=5.255.
114. V. Khachatryan et al., Search for Pair Production of First - Generation Scalar Leptoquarks in pp Collisions at vs = 7 TeV. Phys.Rev.Lett.106:201802, 2011, ISSN 0031-9007, IF=7.621.
115. V. Khachatryan et al., Search for Pair Production of Second - Generation Scalar Leptoquarks in pp Collisions at vs = 7 TeV. Phys.Rev.Lett.106:201803, 2011, ISSN 0031-9007, IF=7.621.
116. V. Khachatryan et al., Measurement of the Inclusive Upsilon production cross section in pp collisions at vs =7 TeV. Phys.Rev.D83:112004, 2011, ISSN 1550-7998, IF=4.964.
117. V. Khachatryan et al., Search for a heavy gauge boson W’ in the final state with an electron and large missing transverse energy in pp collisions at vs = 7 TeV. Phys.Lett.B698:21-39, 2011, ISSN 0370-2693, IF=5.255.
118. V. Khachatryan et al., Prompt and non - prompt J/psi production in pp collisions at vs = 7 TeV. Eur.Phys.J.C71:1575, 2011, ISSN 1434-6044, IF=3.248.
119. V. Khachatryan et al., Charged particle multiplicities in pp interactions at vs = 0.9, 2.36 and 7 TeV. JHEP 1101:079, 2011, ISSN 1126-6708, IF=6.049.
120. V. Khachatryan et al., Search for Stopped Gluinos in pp collisions at vs = 7 TeV. Phys.Rev.Lett.106:011801, 2011, ISSN 0031-9007, IF=7.621.
121. V. Khachatryan et al., First Measurement of the Cross Section for Top - Quark Pair Production in Proton-Proton Collisions at vs =7 TeV. Phys.Lett.B695:424-443, 2011, ISSN 0370-2693, IF=5.255.
122. S. Chatrchyan et al., Charged particle transverse momentum spectra in pp collisions at sqrt(s) = 0.9 and 7 TeV.JHEP 1108:086,2011, ISSN 1126-6708, IF=6.049.
123. S. Chatrchyan et al., Measurement of the Inclusive Z Cross Section via Decays to Tau Pairs in pp Collisions at vs =7 TeV. JHEP 1108:117,2011, ISSN 1126-6708, IF=6.049.
124. S. Chatrchyan et al., Measurement of the t t-bar production cross section and the top quark mass in the dilepton channel in pp collisions at vs =7 TeV. JHEP 1107:049,2011, ISSN 1126-6708, IF=6.049.
125. S. Chatrchyan et al., Search for First Generation Scalar Leptoquarks in the evjj channel in pp collisions at vs = 7 TeV. Phys.Lett.B703:246-266,2011, ISSN 0370-2693, IF=5.255.
126. S. Chatrchyan et al., Missing transverse energy performance of the CMS detector. JINST 6:P09001,2011, ISSN 1748-0221, IF=3.148.
127. S. Chatrchyan et al., Search for New Physics with a Mono-Jet and Missing Transverse Energy in pp Collisions at vs = 7 TeV. Phys.Rev.Lett.107:201804,2011, ISSN 0031-9007, IF=7.621.
128. S. Chatrchyan et al., Search for New Physics with Jets and Missing Transverse Momentum in pp collisions at vs = 7 TeV. JHEP 1108:155,2011, ISSN 1126-6708, IF=6.049.
129. S. Chatrchyan et al., Measurement of the Strange B Meson Production Cross Section with J/Psi phi Decays in pp Collisions at vs = 7 TeV. Phys.Rev.D84:052008,2011, ISSN 1550-7998, IF=4.964.
130. S. Chatrchyan et al., Measurement of the t-channel single top quark production cross section in pp collisions at vs = 7 TeV. Phys.Rev.Lett.107:091802,2011, ISSN 0031-9007, IF=7.621.
131. S. Chatrchyan et al., Search for Physics Beyond the Standard Model Using Multilepton Signatures in pp Collisions at vs = 7 TeV. Phys.Lett.B704:411-433,2011, ISSN 0370-2693, IF=5.255.
132. S. Chatrchyan et al., Measurement of the Top-antitop Production Cross Section in pp Collisions at vs = 7 TeV using the Kinematic Properties of Events with Leptons and Jets.Eur.Phys.J.C71:1721,2011, ISSN 1434-6044, IF=3.248.
133. S. Chatrchyan et al., Measurement of the Ratio of the 3-jet to 2-jet Cross Sections in pp Collisions at vs = 7 TeV. Phys.Lett.B702:336-354,2011, ISSN 0370-2693, IF=5.255.
134. S. Chatrchyan et al., Dependence on pseudorapidity and centrality of charged hadron production in PbPb collisions at a nucleon-nucleon centre-of-mass energy of 2.76 TeV.JHEP 1108:141,2011, ISSN 1126-6708, IF=6.049.
135. S. Chatrchyan et al., Measurement of the Inclusive Jet Cross Section in pp Collisions at vs = 7 TeV. Phys.Rev.Lett.107:132001,2011, ISSN 0031-9007, IF=7.621.
136. S. Chatrchyan et al., Measurement of the Inclusive W and Z Production Cross Sections in pp Collisions at vs = 7 TeV with the CMS experiment. JHEP 1110:132,2011, ISSN 1126-6708, IF=6.049.
137. S. Chatrchyan et al., Search for Resonances in the Dijet Mass Spectrum from 7 TeV pp Collisions at CMS. Phys.Lett.B704:123-142,2011, ISSN 0370-2693, IF=5.255.
138. S. Chatrchyan et al., Determination of Jet Energy Calibration and Transverse Momentum Resolution in CMS.JINST 6:P11002,2011, ISSN 1748-0221, IF=3.148.
139. S. Chatrchyan et al., Search for Three-Jet Resonances in pp Collisions at vs = 7 TeV. Phys.Rev.Lett.107:101801,2011, ISSN 0031-9007, IF=7.621.
140. S. Chatrchyan et al., Search for supersymmetry in pp collisions at vs = 7 TeV in events with a single lepton, jets, and missing transverse momentum. JHEP 1108:156,2011, ISSN 1126-670, IF=6.0498.
141. S. Chatrchyan et al., A search for excited leptons in pp Collisions at vs = 7 TeV. Phys.Lett.B704:143-162,2011, ISSN 0370-2693, IF=5.255.
142. S. Chatrchyan et al., Measurement of the Underlying Event Activity at the LHC with vs = 7 TeV and Comparison with vs = 0.9 TeV. JHEP 1109:109,2011, ISSN 1126-6708, IF=6.049.
143. S. Chatrchyan et al., Measurement of the t \$\bar{t} Production Cross Section in pp Collisions at 7 TeV in Lepton + Jets Events Using b-quark Jet Identification.Phys.Rev.D84:092004,2011, ISSN 1550-7998, IF=4.964.
144. S. Chatrchyan et al., Measurement of the Differential Cross Section for Isolated Prompt Photon Production in pp Collisions at 7 TeV. Phys.Rev.D84:052011,2011, ISSN 1550-7998, IF=4.964.
145. S. Chatrchyan et al., Measurement of the Drell-Yan Cross Section in pp Collisions at vs = 7 TeV. JHEP 1110:007,2011, ISSN 1126-6708, IF=6.049.
146. S. Chatrchyan et al., Measurement of the weak mixing angle with the Drell-Yan process in proton-proton collisions at the LHC. Phys.Rev.D84:112002,2011, ISSN 1550-7998, IF=4.964.
147. S. Chatrchyan et al., Measurement of energy flow at large pseudorapidities in pp collisions at vs = 0.9 and 7 TeV. JHEP 1111:148,2011, ISSN 1126-6708, IF=6.049.

Other Particle Physics Experiments

Collaboration with nEDM and CryoEDM experiments at ILL, Grenoble, France:

1. D.J.Richardson,J.M.Pendlebury,P.Iaydjiev,W.Mampe,K.Green, "Measurement of the energy dependence of the neutron loss per bounce function on reflection from oil and grease surfaces using monochromatic ultracold neutrons" Nucl.Instr.Meth.in Phys.Res.,A308,1991
2. Y.Chibane,B.R.Heckel,K.Green,P.Iaydjiev,S.N.Ivanov,I.Kilvington, S.K.Lamoreaux,J.M.Pendlebury,N.F.Ramsey,K.F.Smith,"Precision Mercury Magnetometry for large volumes",14 Int.Conf. on Atomic Phys.,Boulder,USA,1994.
3. M.G.D.van der Grinten,J.M.Pendlebury,K.Green,P.G.Harris, P.S.Iaydjiev, "The Search for the Electric Dipole Moment of the Neutron", July 1997,Dubna,Russia,Phys. of Atomic Nuclei,vol.61,8,1998.
4. K.Green,P.G.Harris,P.Iaydjiev,D.J.R.May,J.M.Pendlebury,K.F.Smith, P.Geltenbort,S.Ivanov,"Performance of the Atomic Mercury Magnetometer in the Neutron EDM Experiment",Nucl. Instr. and Meth. in Phys. Res.,A404,1998.
5. V.V.Nesvizhevski, A.V.Strelkov, P.Geltenbort, P.S.Iaydjiev, "Investigation of Storage of Ultracold Neutrons in Traps",The European Phys. Journal, AP 6, 151-154,1999.
6. P.G.Harris,C.A.Baker,K.Green,P.S.Iaydjiev,S.Ivanov,D.J.R.May, J.M.Pendlebury,D.Shiers,K.F.Smith,M.van der Grinten,P.Geltenbort,"A New Experimental Limit on the Electric Dipole Moment of the Neutron", Phys. Rev. Lett.,vol.82,Issue 5,pp.904-907,Feb. 1st 1999.
7. A.V.Strelkov,...,P.Iaydjiev,"Identification of a New Escape Channelfor UCN in Traps",Nucl. Instr. and Meth. in Phys. Res.,A440,2000,695-703.
8. P.G.Harris,...,P.Iaydjiev,"The Neutron EDM Experiment at the ILL",Nucl. Instr. and Meth. in Phys. Res.,A440,2000,479-482.
9. C.A.Baker,...,P.Iaydjiev,...,P.Geltenbort,"Development of Solid State Silicon Devices as Ultra Cold Neutron Detectors",Nucl. Instr. and Meth. in Phys. Res.,A487,2002,511-520.
10. C.A.Baker,...,P.Iaydjiev,...,P.Geltenbort,"Experimental measurement of ultracold neutron production in superfluid 4He",Phys. Lett. A, Vol 308,Issue 1,2003,67-74.
11. C.A.Baker,...,P.Iaydjiev,...,P.Geltenbort,"Development of low temperature solid state detectors for ultracold neutrons within superfluid 4He",Nucl. Instr. and Meth. in phys. Res. A501,2003,517-523.
12. J.M.Pendlebury,...,P.S.Iaydjiev,...,K,F,Smith,"Geometric-phase-induced false electric dipole moment signals for particles in traps", Phys. Rev. A70,032102, 2004.
13. Philip Harris…,P.S.Iaydjiev et al. (EDM Collaboration) The Neutron EDM Experiments at the ILL. SUSY 2005 The 13th International Conference on Supersymmetry and Unification of Fundamental Interactions July 18-23, 2005, IPPP Durham
14. Maurits van der Grinten…P.S.Iaydjiev et al., (EDM Collaboration) The Search for the Neutron Electric Dipole Moment PANIC05 Particles and Nuclei International Conference Santa Fe, NM, October 24-28, 2005
15. Plamen Iaydjiev The Search for Neutron Electric Dipole Moment - present experiment at ILL, Grenoble, and future prospects, CryoEDM experiment and nEDM experiment. Flavours at LHC workshop, CERN, 7-11.11.2005.
16. Maurits Van der Grinten…P.S.Iaydjiev et al., CryoEDM: Neutron Electric Dipole Moment Searches. International Conference on Neutron Scattering, May 3 - 7, 2009 Knoxville, Tennessee
19. C.A.Baker,…,P.Iaydjiev,…. “An improved experimental limit on the electric dipole moment of the neutron.” Physical Review Letters 97 131801 (2006).
20. C.A.Baker,…,P.Iaydjiev,…. Reply to comment on `An Improved experimental limit on the electric dipole moment of the neutron'. Phys.Rev.Lett.98:149102,2007.
21. By CryoEDM Collaboration (M.G.D. van der Grinten,…,P.S.Iaydjiev,… et al.). CryoEDM: A cryogenic experiment to measure the neutron electric dipole moment. Nucl.Instrum.Meth.A611:129-132,2009
22. I. Altarev……P.S.Iaydjiev, et al.Neutron to Mirror-Neutron Oscillations in the Presence of Mirror Magnetic Fields. Phys.Rev.D80:032003,2009.
23. I. Altarev……P.S.Iaydjiev, et al. Test of Lorentz invariance with spin precession of ultracold neutrons. Phys.Rev.Lett.103:081602,2009.
24. C. A. Baker…P.S.Iaydjiev … et al., CryoEDM: a cryogenic experiment to measure the neutron Electric Dipole Moment, 2010 J. Phys.: Conf. Ser. 251 012055 doi: 10.1088/1742-6596/251/1/012055
25. C. A. Baker …P.S.Iaydjiev …et al., New constraints on Lorentz invariance violation from the neutron electric dipole moment, 2010 EPL 92 51001 doi: 10.1209/0295-5075/92/51001

## Gallery

INRNE - Sofia at HCAL - CMS - CERN:

Design (INRNE+Sofia University) and Production and Test of the HCAL prototype:

High Voltage Systems 4 kV and 12 kV for HPD (Laboratory of nuclear electronics at INRNE):

INRNE - Sofia at ECAL - CMS - CERN:

Design (INRNE+CLMPI BAS) and Production and Test of the ECAL prototype:

INRNE - Sofia Laboratory for assembling and test of the 125 RPC (type RB3) for CMS:

Laboratory at INRNE:

Sofia RPC chambers leaving INRNE to CERN:

INRNE - Sofia RPC at CERN:

Test at ISR - CERN:

Installation and Commissioning at Point 5 - CMS cavern:

INRNE's GRID cluster: