PhD Seminar Muhammad Ahmad Quaid-i-Azam University ISLAMABAD
Supervisor: Prof. Hafeez Hoorani 1 Date: 24-05-2013
Slide 2
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
Slide 3
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
Slide 4
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
Slide 5
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
Slide 6
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.
Slide 7
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.
Slide 8
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
Slide 9
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
Slide 10
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
Slide 11
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.
Slide 12
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
Slide 13
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
Slide 14
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
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.
Slide 17
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.
Slide 18
Charmonium is a meson which consists of charm and anti-charm.
18
Slide 19
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
Slide 20
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
Slide 21
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
Slide 22
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
Slide 23
23
Slide 24
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
Slide 25
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
Slide 26
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
Slide 27
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:
Slide 28
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
Slide 29
29
Slide 30
30
Slide 31
31
Slide 32
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.
Slide 33
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
Slide 34
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.
Slide 35
1/13/12Muhammad Ahmad35 Simulation Sample Size Signal Model
Background Model Choice of pT (c) spectrum Tracker material (no
significant difference in ratio ) Pileup
Slide 36
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
Slide 37
37
Slide 38
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
Slide 39
Ratio of cross sections ratio of cross sections multiplied by
branching fractions 39
Slide 40
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