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PhD Seminar Muhammad Ahmad Quaid-i-Azam University ISLAMABAD Supervisor: Prof. Hafeez Hoorani 1 Date: 24-05-2013

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1. Commissioning of Endcap RPCs of CMS in 2008-2009. 1.A measurement present the relative prompt production rate of c2 and c1 with 4.6 fb -1 of data collected by the CMS experiment at the LHC in pp collision at s = 7 TeV. 2.The two states are measured via their radiative decays, with the photon converting into an e+e- pair for J/ rapidity |y(J/)| 0.5 GeV/c. 3.The measurement is given for six intervals of p T (J/) between 7 and 25 GeV/c. The results are compared to theoretical predictions. Eur. Phys. J. C (2012) 72:2251 2

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Abstract Introduction to Experiment Introduction to LHC Introduction to CMS Commissioning of EndCap RPCs Introduction to RPCs Introduction to Commissoiing HV and LV Gas System DCS, DAQ, Trigger Performance of RPCs in 2010-11 Charmonium Physics Introduction Motivation Charmonium Production Theoretical Potential Model Charmonium Spectrum Other Experiments results Selection Muon pair Selection Converted Photon selection 0 rejection Analysis Dataset and Triggers Conversion Reconstruction Experimental Method Acceptance and Efficiencies Extraction of 1/2 Extraction of N c2 / N c1 from data Systematics Uncertainties Polarization Results Theoretical Comparison Analysis Note Conclusion 3

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Integrated Luminosity: 2010 45 pb -1 @ 7 TeV 2011 6 fb -1 @ 7 TeV 2012 23 fb -1 @ 8 TeV Large Hadron Collider (LHC) Important Design Parameters: Circumference 27 Km Under the surface 100 m CM designed energy 14 TeV Protons/bunch 1.15 10 11 No. of bunches/beam 2808 Design luminosity 10 34 cm -2 s -1 Energy/beam for 2011 3.5 TeV Energy/beam for 2012 4.0 TeV 4

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5 MUON BARREL CALORIMETERS Silicon Microstrips Pixels ECAL Scintillating PbWO 4 Crystals Cathode Strip Chambers (CSC) Resistive Plate Chambers (RPC) Drift Tube Chambers (DT) Resistive Plate Chambers (RPC) SUPERCONDUCTING COIL IRON YOKE TRACKERs MUON ENDCAPS Total weight : 12,500 t Overall diameter : 15 m Overall length : 21.6 m Magnetic field : 4 Tesla HCAL Plastic scintillator copper sandwich

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6 CMS is a general purpose detector. It is possible for CMS to detect the signatures of particles like : e, ,, , jets, b-quarks, . Momentum, charge of tracks and secondary vertices (e.g. from b-quark decays) are measured in central tracker (Silicon layers). Energy and positions of electrons and photons measured in electromagnetic calorimeters. Muons identified and momentum measured in external muon chambers. Neutrinos detected and measured through measurement of missing transverse energy (E T miss ) in calorimeters.

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Resistive plate chambers (RPC) are fast gaseous detectors that provide a muon trigger system parallel with those of the DTs and CSCs. RPC Geometrical view. Barrel and Endcap Number of RPC assembled in Pakistan. 7 Features of RPCs: Gap: 2 mm HV electrodes: 100 m graphite coating Gas pressure: 1 atm Gas mixture: 96.2% C 2 H 2 F 6 (Freon), 3.5% i-C 4 H 10 (iso-butane), 0.3% SF 6 Gas Flow: 0.1 volume/hour Double gap geometry of RPCs improve the efficiency and allows safer operation at higher threshold. It also improve time resolution.

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Commissioning means to ensure that all the service (e.g HV, LV. Gas, cooling, sensors for temperature & humidity and Readout system) needed to operate the chambers are working properly. It also certifies that the performance of our detector is still of the same level as during the production and test phase. Following system needs to be tested for commissioning The performance of RPC detector is based on following parameter: occupancy, efficiency, cluster size, dark current. In total 432 RPCs were commissioned from May, 2008 to June, 2009. 8 For FEB threshold

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To make HV system economical, 24 HV Distribution Boxes were made and tested during commissioning. The two important factors in making DBs were: Time scale Quality Assurance For QA test: dark current is measured for HV upto 15 kV for 24 hours atleast. Total Channels 864 reduced to 216 by using Distribution boxes. Each DB supply HV to 18 RPCs. Acceptable dark current limit = 0.1 m 9 Front: conned with HV module back: supply of RPCs gaps

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10 SY 1527 Main Frame HV Hardware Detail: 01 HV main frame, 01 Mao for HV system, 03 Branch controller, 08 easy crates, 08 fan units, 36 HV boards and 24 HV Distribution boxes. HV Module HV Mao Branch Controller Easy crates

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11 LV System: LV is required to provide digital and analog voltage to Front End Boards (FEB), and Link Board Boxes (LBB). 01 LV main frame, 12 Mao for LV system, 04 Branch controller, 24 easy crates, 24 fan units, 36 LV FEB modules and 24 LV LBB modules. Gas System: RPCs are gaseous detectors. It is important to assure that gas is flowing properly in all chambers. Each Gas sector consist of 6 RPCs. Leak tests were performed for all the sectors. Argon gas were used for the leak testing. Cooling System: Coolant is needed to keep the temperature of electronics in the working range, underneath the electronics there is a metallic copper plate connected to coolant pipes. Coolant leak tests were performed. It is important because in case of cooling water leakage the whole system could be damage.

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Readout starts at FEBs Detector Control System (DCS) was developed to control and monitor the HV/LV applied to the chambers, FEBs and different modules Connectivity test were also performed. Environmental variables e.g. pressure, temperature humidity were also added later on in monitoring system 12 FEBsSignal Cables from RPC To LBB Detector Control System And Current Monitoring Signal Cables from LBB To Control room

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HV Tripping problem of HV channels Some connectors were showing problems in current behavior. These connectors were changed Spikes in HV current Rising in current problem in few channels Due to change in temperature and humidity in the experimental area Due to gas mixture LV Communication problem between the EASY crates and MAO Tripping problem Over current problem Few LV power supplies box showed problem, which were replaced successfully after fixing them. Gas Each end-cap disk was tested for gas leaks Blockage: increase flow rate till blockage is removed Channel swapping problem. Gas Leak: open the connectors and tight Flow cell calibration is done. 13

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Coolant Leaks were found at some joints. The joints were tightened and fixed where required and possible. Readout Signal cable swapping. Threshold setting and calibration. Link board failure: change link board DCS The software was modified completely to display read and control end-cap according to end-cap geometry 14

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Plots for occupancy, cluster size, efficiency 15 Cluster size < 2.5

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16 Working experience on RPCs of CMS Detector. 432 Endcap RPC were fully commissioned during 2008- 2009. Troubleshooting of RPC HV/LV hardware. Gas and Coolant Leakage fixing. Solution of rising current problem: It is concluded that the cavern temperature of RPC must be less than 22.5 degree Celsius to stop rising current problem. RPCs worked efficiently during run 2010-2011-2012, They also has significant role in important discovery of Higgs boson while studding decay H-> 4l.

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c1,c2 J/ + J/ + - Muons detected in Tracker and Muon chambers. e + e - Converted photons detected in Tracker. 17 High mass resolution is needed to separate c1 and c2 particles (m=45.5 MeV), therefore photons reconstructed through pair conversions. Resolution of ECAL can not allow to distinguish the two states.

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Charmonium is a meson which consists of charm and anti-charm. 18

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Production Model: Varity of theoretical models exist for hadronic production of Prompt J/ but they fail to describe simultaneously the J/ differential cross section measurement and polarization measurement at Tevatron. Clean: We measure the ratio of cross sections c2 / c1, where theoretical and experimental uncertainties will cancel out. Photon Reco: c J/ channel is a challenge to reconstruct low pt photons. Extended pT Spectrum: With the current measurement, we improve the sensitivity to theoretical models by extending the J/ pT spectrum beyond the spectra measured by CDF and LHCb. 19

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Quarkonium Production Models: 1. Color Singlet Model (1975) 2. Color Evaporation Model (1977) 3. Color Octet ( NRQCD Model ) (1986) 4.Fragmentation Function Approach (2005) 5.KT Factorization (2001) NRQCD (leading order) Beneke,Kramer PRD 55, 5269 (1997), CDF data Old news: color-octet contributions are important potential problem with polarization data Polarization Cross-section Braaten, Kniehl, Lee PRD 62, 094005 (2000) CDF Run-II data: http://www-cdf.fnal.gov/physics/new/bottom/030327.blessed-jpsixsec/xsec_html/ 20

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21 HERA-B(41.6 GeV) Phys.Rev.D 79, 012001 (2009): ( c2 )/( c1 ) = 1.75 0.7 p T (J/) < 5 GeV/c arXiv:1202.1080 [hep-ex] CDF(1.96 TeV) Phys.Rev.Lett 98, 232001 (2007): ( c2 )/( c1 ) =0.750.03(stat)0.03(syst) range: p T (J/) [4,10] GeV/c p T (J/)>4.0 GeV/c |(J/)|1.0 GeV/c - converted photon LHCb arXiv:1202.1080[hep-ex] range: p T (J/) [2,15] GeV/c 2.0 < y(J/) < 4.5 p T () > 0.65 GeV/c p() > 5 GeV/c - converted photon 21

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CMSSW stable version CMSSW_4_2_3 is used for this analysis. Global tag used: FT_R_42_V13A Total Integrated luminosity = 4.62 fb -1 JSON Files are used according to Run Numbers. In 2011B Datasets Number of events are significantly smaller then 2011A dataset, due to change in Triggers. As in 2011B Trigger favored high pT events.. 22

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Conversion: The Chic photons have very low momentum, pt < 5GeV. They can not reach the ECAL and due to the substantial material budget in the silicon pixel and strip trackers they often convert Into electro-positron pairs. 24

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Any conversion building up a pair which invariant mass falls in the range between 0.11 And 0.15 GeV/c2 is rejected, since it is assumed to originate from a pi0 decay, pi0 yy Each conversion candidate with selection cuts is associated to every other conversion candidate in the event and to every photon reconstructed with electromagnetic calorimeter. 25

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Jpsi selection Prompt Jpsi separation Mu+ u- = 3.0 3.2 GeV Pseudo-proper decay length distribution of Jpsi from the selected Chic candidates. The prompt component is shown in green, The non-prompt component is in lilac and the prompt+non-prompt component in blue. A cut of 30 um to the pseudo-proper decay length shown in red selects the prompt component of Jpsi. 26

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27 The cross section of decay process is measured as: Nobs = Total number of observed events Nbkg = Total number of background events Lint = integrated Luminosity Acc = Geometrical Acceptance = reconstruction efficiency of the decay B = branching ratio Cross section ratio is measured as: where 1 / 2 = (A cc ) c1 / (A cc ) c2 To reduce the finite resolution of the + - pair with the CMS detector, the mass difference spectrum Q is plotted for fitting, where Q = m m + m J/ (PDG). Finally performed unbinned maximum likelihood fit to the Q in various pT ranges of J/ using RooFit to find the numbers of c1 and c2. The Probability Distribution Function (PDF) is used for the unbinned extended maximum likelihood fit is:

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Final yield extracted with a p.d.f. composed of: the parameterized double-sided C-Ball shape from MC for c1, c2 the following functional form for the background p T binsN c1 N c2 7-9618 31315 24 9-111680 49788 37 11-131819 51819 38 13-161767 51851 39 16-201269 43487 30 20-25642 31236 22 28

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Slop = 0.875 0.001 J/ take most of the p T of c with very small difference b/w two states. Photons from c1 have on average a 10% Higher p T w.r.t photons from c2.

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1/13/12Muhammad Ahmad33 N gen generated c1 and c2 particles with Pythia Monte Carlo with |y( c )| 0.5 GeV/c. N reco reconstructed c1 and c2 particles with selections cuts. Difference in 1 and 2 comes from different acceptance for photons from c1 and c2. J/ acceptance is the same for c1 and c2. 33

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34 We studied the stability of N c1 /N c1 as a function of number of primary vertices. 2011A2011B Case 1: Number of vertices in bins up to a given number. [1-2],[1-3],.,[1-16] Case 2: Individual bins. [1-4],[5-6],[7-9],[10-16] No significant trend was found. Results for Run2011A and Run2011B are compatible. As maximum deviation from straight line is not statistically significant, therefore we do not assign a systematic uncertainty due to pileup.

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1/13/12Muhammad Ahmad35 Simulation Sample Size Signal Model Background Model Choice of pT (c) spectrum Tracker material (no significant difference in ratio ) Pileup

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36 Polarization of the c can have a significant impact on the photon spectrum, and therefore on 1 / 2. We dont know anything on the polarization of c at production. There is no preferred polarization axis. We investigate extreme scenarios by studying all possible helicity eigenfunctions in two polarization frames: HX: helicity frame, where the polarization axis is the momentum of the c. CS: Collins-Soper frame, where the polarization axis is the bisector between the momenta of the incoming hadrons in the c rest frame. This prescription should cover adequately our phase space We then quote the ratio between the polarization scenario under consideration and the unpolarized case, and the maximum and minimum deviation

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1/13/12Muhammad Ahmad38 c polarization is unknown therefore it can change significantly the photon spectrum which will affect 1 / 2 (the ratio of efficiencies was measured assuming non polarized c particles.) We study all possible helicity states combinations of c1 and c2 particles in Helicity and Collins-Soper frames. Helicity frame Collins-Soper frame 38

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Ratio of cross sections ratio of cross sections multiplied by branching fractions 39

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Comparison of our measurement with predictions from the k-t factorization. Data are shown with acceptance corrections calculated in the hypothesis that both c1 and c2 are produced with helicity zero in the helicity frame, which is predicted by the theory. Comparison of our measurement with predictions from NRQCD. Since predictions are given in a different kinematical phase space with respect to our measurement, we apply a correction factor derived from Monte Carlo to make the comparison possible. The uncertainty on the correction factors is included as a systematic error in the green area. 40

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45 Tracker Tracker Detector: Pixel (3 layers + 2 discs / side) (4 - 10 cm) (|| < 2.5) TID: Tracker Inner Endcap (3 discs / side) TIB: Tracker Inner Barrel (4 layers) TOB: Tracker Outer Barrel (4 single sided + 2 double sided layers) TEC: Tracker Endcap (9 discs / side)

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