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Measurement of production cross section of Z boson with associated b-jets

andEvaluation of b-jet energy corrections

using CMS detector at LHC

Aruna Kumar Nayak

Thesis Supervisor : Prof. Tariq Aziz

113th July 09 Synopsis Seminar

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Overview Standard Model of Particle Physics The reach of LEP and Tevatron The Large Hadron collider CMS detector Ability of CMS detector : physics objects reconstruction

Cross section measurement of bbZ, Z → process Evaluation of b-jet energy corrections

Study on cosmic muon charge ratio using CRAFT data Jet plus tracks algorithm : performance study using Test beam data Higgs boson search in CP violating MSSM like model

The Standard Model

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The SM is based on SU(3)C X SU(2)L X U(1)Y gauge symmetry Strong : QCD Electroweak Gluon W±, Z /

SU(2)L X U(1)Y U(1)Q

Electroweak Symmetry Breaking (Higgs mechanism), Responsible for generating particle mass

SM Building blocks

The SM : Symmetry Breaking

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The potential is of the form

The 2nd choice does the spontaneous breaking of gauge symmetry

The strength of the interactions of the particles with the Higgs field determines the mass of the particles

e.g. in case of Z boson :

Success of Standard Model

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Success :W, Z were discovered at SPS, CERN in 1980sTevatron, Fermilab discovered Top quark (the heaviest among all) in 1995Most of the SM parameters, like masses and gauge couplings have been measured very precisely at LEP, CERN and matching well with SM predictions

Yet Unknown :The only parameter yet unknown in SM is the mass of Higgs boson : the fundamental ingredient of the model

Limits to the Higgs boson mass :From Experiments : Indirect limit : LEP precision EWK measurements : 191 GeV upper limit (at 95% CL)LEP-II direct limit : 114 GeV lower limit

From Theory : bound from Triviality and Vacuum stability

LEP EWK page

hep-ph/0503172

Is There any New Physics?

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THE SM has quite a few shortcomings, e.g. : The SM is silent about the Gravitational force (the 4th fundamental force) It does not explain the pattern of fermion masses In SM, the higher order corrections to the Higgs boson mass diverges,

unless a fine adjustment of the parameters is performed.

Possible candidates for New Physics : Supersymmetry : predicts the existence of a super partner for each SM

particles (with spin difference ½) , Extra dimension etc…

The LHC can explore all the possibilities upto TeV scale and can answer some of the unknowns. Also precision EWK measurements, mtop etc.

One of the EWK measurements : cross section of Z + b-jets production

The large Hadron Collider

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~27 KM ring, The LEP tunnelproton-proton collision : 14 TeV CM energy25 ns bunch crossing : 2808 bunches with ~1011 protons in a bunchDesign luminosity : 1034 cm-2s-1 => 100 fb-1/year

The Compact Muon Solenoid Detector (CMS)

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Design Objectives :Example of few important Higgs discovery modes : H → H → ZZ → 4 H → ZZ → 4 e H → ZZ → 2e and 2 1)Very good and redundant Muon detection system •The best possible measurement of e/ •Good resolution of hadronic jets and missing transverse energy•High quality central tracking

Total weight : 14500 tDiameter : 14.60 mLength : 21.60 mMagnetic Field : 4 TeslaSize of 1 event : 1 MB100 events / second (stored in tape)

Detector Components (I)

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Magnet : The choice of magnetic field is key to the design of any HEP detector in collider experiments.CMS Magnet : Superconducting Solenoid Field strength : 3.8 Tesla, Length : 13 m, Inner R = 2.95 m operating current : 20 kAAdvantage : Compact and small detector good resolution in inner tracking, good muon momentum resolution

Tracker : Geometry : r ~ 110 cm, L ~ 540 cm, || < 2.4 66 million pixels, 9.6 million silicon stripsPixel : r ~ 10 cm, Particle flux ~ 107/s, size of pixel : 100 m X 150 m occupancy : 10-4 /pixel/bunch crossing spatial resolution : ~10 m in r- and ~20 m in r-zStrip : 20 < r < 55 cm, size : 10 cm X 80 m occupancy : 2-3% / bunch crossing TIB resolution : 23-34 m in r- and 230 m in z r > 55 cm, size : 25 cm X 180 m occupancy : 1% /bunch crossing TOB resolution : 35-52 m in r- and 530 m in z TID : 3 disks TEC : 9 disks, 120 cm < z < 180 cm

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Detector Components (II)ECAL :Compact, Hermatic, homogeneous, 61200 lead tungstate (PbWO4), X0 = 0.89 cm, Rm = 2.2 cm Fast : 80% light yield within 25 nsRadiation hard : 10 Mrad

Barrel (EB) : Rin ~ 129 cm, 36 Super modules0 < || < 1.479, Each crystal 0.0174 X 0.0174 (, ), front face ~ 22 X 22 mm2, L = 230 mm (~25.8 X0)Endcap (EE) : Zin ~ 314 cm, 1.479 < || < 3.0 , crystal : 28.6 X 28.6 mm2, L = 220 mm ( 24.7 X0) Preshower (ES) : 2 layers of Si strip (1.9 mm pitch), behind lead (2X0 , 3X0)

The energy resolution is of the form

S : stochastic term, N : noise term, C : constant

Detector Components (III)

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HCAL : Layers of plastic scintillator tiles, stacked within layers of absorbers (brass). Light read out using WLS fibre. WLS fibres are connected to clear fibres outside the tiles.

Barrel (HB) : 32 towers, || < 1.4, 2304 towers in total 0.087 X 0.087 (, ) , 15 brass plates of 5cm, 2 steel external plates, front scint. plate 9 mm, others 3.7 mm

Eencap (HE) : 14 towers, 1.3 < || < 3.0, outer 5 towers : ~ 0.087, ~ 50 , Inner 8 towers : ~ 0.09-0.35, ~ 100

Forward (HF) : steel/quarz fibre calorimeter. 3.0 < || < 5.0, Zin ~ 11.2 m13 towers ~ 0.175, ~ 100

Outer (HO) : Plastic scintillator, 10 mm, 2 layers in ring 0 separated by an iron absorber of thickness 18 cm, 1 layer each in ring +/- 1,2. towers size same as HB. || < 1.26 . Increases the effective thickness of HCAL to 10 .

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Detector Components (IV)Muon : Drift Tube (barrel), Cathode Strip Chambers (endcap), Resistive Plate Chambers.

Barrel (MB) : || < 1.2, low radiation, low muon rate, low residual magnetic field. 4 station : MB1-MB4, 12 sectors , single point resolution 200 meach station : 100 m precision (1 mrad in direction).

Endcap (ME) : || < 2.4 , high muon rate, higher magnetic field as well. 486 CSCs in 2 endcaps, trapezoidal shape, 6 gas gaps in each chamber, strip resolution 200 m, resolution 10 mrad.

RPC provides fast response (few ns) and good time resolution. But has coarser position resolution w.r.t DT and CSC. Use to identify correct bunch crossing. RPC and DT, CSC provide independent and complementary information for L1 trigger.

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Detector Components (V)CMS Trigger : L1 Trigger : Electronics modules e.g. Look up Tables (RAM, ASIPs) L1 Rate : ~25 kHz (at 2X1033 cm-2s-1) L1 decision time < 1 s

HLT : computer farm, partial reconstruction of physics objects HLT Rate : ~100 Hz

Example of a Level-1 Jet Trigger

Physics Objects Reconstruction : Electrons

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Reconstructed from the information of Tracker and ECAL

Electron Id : Robust (cut based) Electron Id (to discriminate against Jets)

H/E < 0.115(barrel), 0.150(endcap), < 0.0140(barrel), 0.0275(endcap)in < 0.090(barrel), 0.092(endcap), in < 0.0090(barrel), 0.0105(endcap)

H/E : Hadronic to electromagnetic energy deposit ratio.

in : difference between the electron supercluster and the electron track at vertexin : difference between the electron supercluster and the electron track at vertex

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Electrons from Z decay

Isolation : track isolation (pT(track)/pT(electron))2 < 0.02 (in cone 0.02-0.6, track pT > 1.5 GeV, ) (This isolation criteria is only for Z measurement study) Efficiency calculated by matching MC electron to Reco electron in 0.1 cone

Physics Objects Reconstruction : Electrons

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Physics Objects Reconstruction : MuonsReconstructed from the information of Tracker and Muon Chamber Isolation : pT(tracks) (0.3 cone) < 3 GeV Efficiency calculated by matching MC muon to Reco muon in 0.1 cone

Muons from Z decay

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Physics Objects Reconstruction : Jets

Jets are reconstructed from calorimeter energy using IterativeCone algorithm of cone size 0.5 dependent & pT dependent corrections are used.

Reconstruction efficiency of jets Vs generated Jet pT and for Z + bb events.

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Cross section Measurement of pp → Z+bb, Z→ process

Measurement of Zbb production is an important test of QCD calculation

Background to Higgs discovery channels at LHC, like SM H → ZZ → 4, SUSY bb, → ()

bbZ measurement can help reduce the uncertainty in SUSY bbH calculation

Z + 1 b-jet has been measured both at CDF & D0

Z + 2-bjet may be observed for the 1st time

The possibility of observing and measuring the production of Z + 2 b-jet at LHC has been studied aiming at early 100 pb-1 of CMS data at 14 TeV center of mass energy.

Dominant at LHC

~ 15% of bbZ total

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CMS PAS EWK-08-001CMS AN-2008/020CMS CR-2008/105

(CMS approved result)

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Cross section and Event generationSignal bb (Zbb) :

CompHEP events with pT(b) > 10 GeV, ||(b) < 10 , m > 40 GeV, ||() < 2.5were generated and fully simulated in CMS with 100 pb-1 calibration and mis-alignment

Cross section calculated using MCFM, NLO (bb) = 45.9 pb , = e, , PDF : CTEQ6M, scale R = F = MZ

LO cross section calculated using PDF : CTEQ6L1 and same values for scale K (NLO) = 1.51

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Cross section and Event generation

Backgrounds

tt~ + n jets, n >= 0 :Generated using ALPGEN Cross section normalized to NLO inclusive tt~ cross section 840 pb

cc + n Jets, n>= 0 (Zcc) :Generated using ALPGENNormalized on NLO (using MCFM) 13.29 pb, k factor = 1.46 with cuts :pT(c) > 20 GeV, ||(c) < 5, m > 40 GeV

+ n Jets, n >= 2, (Zjj) : Generated using ALPGEN Normalized on NLO (using MCFM) 714 pb , k factor = 1.02 with cuts : pT(j) > 20 GeV, ||(j) < 5, m > 40 GeV

All events are passed through full CMS detector simulation and reconstruction chain,with appropriate alignment and calibration uncertainties corresponding to early 100 pb-1 of integrated luminosity.

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Primary Event selections

Trigger selection : single isolated electron or muon Level-1 threshold 12 GeV, 7 GeV & High-Level threshold 15 GeV, 11 GeV Corresponds to low luminosity period L = 1032cm-2s-1

Lepton Selection : Two high pT, isolated, opposite charged leptons ||(e) < 2.5, ||() < 2.0, lepton pT > 20 GeV

Jet Selection : Two or more jets with corrected ET > 30 GeV , || < 2.4 Jet corrected using Monte Carlo jet energy correction (as described earlier)

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b-Jet TaggingLepton, jet selections + double b-tagging with b-discriminator > 0.

b-discriminator of 2nd highest discriminator jet

Jets are tagged using “Track Counting b-tagging”Which uses the 3-dimentional impact parameter significance , of 3rd highest significance track, as the b-tagging discriminatori.e. No. track (3D IP significance cut) >= 3

Effective to supress the Z+jets backgrounds.

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b-tag efficiency

b-tagging efficiency for b, c, light jetsafter applying cut on b-discriminator > 2.5

23*statistical error bars are not shown

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ETmiss selection

Lepton, jet selections + double b-tagging with b-discriminator > 0

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Missing ET reconstructed from calorimeter and corrected for Jet Energy scale and muons.

Type-1 ETx,ymiss = - (ETx,y

calo + jets(ETx,ycorr – ETx,y

raw))

Muon corr. = - (muons (px,y – Ex,y (calo. deposit)))

Effective to supress the tt~+jets backgroundsCut ET

miss < 50 GeV

Event Selection details

Two Leptons, pT > 20 GeV, ||(e) < 2.5 , ||() < 2.0Two or more Jets , ET > 30 GeV , || < 2.4 Two b-tagged Jets Missing ET < 50 GeV

Initial and final cross sections after all selections

Process Name NLO (pb) Final (fb)

Electron Muon

Zbb 46 176 ± 3.3 212 ± 3.6

tt~ + jets 840 173 ± 9.0 178 ± 8.7

Z+jets 714 5.5 ± 2.8 5.5 ± 3.1

Zcc+jets 13.3 4.3 ± 1.63 5.1 ± 1.93

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*More details for each selection cuts are in backup

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Expected Measurement for 100 pb-1

events scaled to 100 pb-1

Purity of b-tagging in Zbb events

26The points are the result of random selection of exactly 100 pb-1 of data

Expected Measurement for 100 pb-1

Z → ee final state Z → final state

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tt~ background EstimationDilepton mass regionSignal : 75-105 GeV (Z)Side band : 0-75 GeV & 105 – above (no Z)

NZ(tt) = (Z(tt)/noZ(tt)) X NnoZ(tt) NZ(tt)/NZ(tt)= 1/√NnoZ(tt)

NZ(tt) = expected no. of tt~ events in signal region NnoZ(tt) = measured no. of tt~ events out side signal region

Z(tt) = selection efficiency of tt~ in signal regionnoZ(tt) = selection efficiency of tt~ outside signal regionNZ(tt) = uncertainty of the expected number of tt~ events in the signal region.Uncertainty on Z(tt)/noZ(tt) is negligible compared to the statistical uncertainty on

NnoZ.

Assuming side band contains only tt~ background. Other possible backgrounds are negligible

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Systematics Uncertainty due to Background and double b-tagging.

NZbb and NZbb are determined as follows.

NZbefore b-tag = NZjj + NZcc + NZbb

NZafter b-tag = X NZjj + c X NZcc + b X NZbb

Where, NZ

before b-tag = measured number of Z/* → events after all selections except b-tagging under Z mass peak (75-105 GeV). Contribution of tt~ is negligible (~1%). NZ

after b-tag = measured number of Z/* → events after all selections including b-tagging with tt~ subtracted

NZjj is unknown number of +jets (u, d, s, g) events before double b-tagging.NZcc is unknown number of Zcc events before double b-tagging. NZbb is unknown number of Zbb events before double b-tagging.

b, c, are the efficiency of double b-tagging for Zbb, Zcc and Z+jets events ( Ratio of number of events before and after double b-tagging)

(after all selections except b-tagging)

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Systematics Contd ......Reduce the no. of variables to two using the Ratio

where is ratio of selection efficiencies

Solving the equations

The Uncertainties on NZbb is calculated from uncertainties ofNZ

after b-tag (uncertainty due to tt~ subtraction),R and uncertainties on b, c,

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* Calculation of systematics due to JES and MET scale and others are in backup

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Total Uncertainty on Measurement

Total cross section is expected to be measured in 100 pb-1 of data with uncertainty

= +21%, - 25% (syst.) , +/- 15% (stat.)

Source of uncertainty Value used (%) ((Zbb)) (%)Jet energy scale (JES) 7 7.6

Type 1 missing ET scale 10 (unclustered ETmiss) + 7 (JES) 7.4

MC pTjet, jet dependence -10, +0 -10, +0

b-tagging of b-jets (b) 8 16

mistagging of c-jets (c) 8 0.5

mistagging of light jets () 7.6 0.5

NZafter b-tag due to tt~ subtraction 4 4.6

R (Zcc / Zjj) 5 0.4

lepton selections 0.5 0.5

luminosity 10 10

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Evaluation of the b-jet energy corrections from data Evaluation of the b-jet energy corrections from data using bbZ, Z->using bbZ, Z->processprocess

cc11ppxb1 xb1 + c+ c22ppxb2 xb2 = -p= -pxZxZ

cc11ppyb1 yb1 + c+ c22ppyb2 yb2 = -p= -pyZyZ

c1 = (pc1 = (pyZyZppxb2xb2-p-pxZxZppyb2yb2) / (p) / (pxb1xb1ppyb2yb2-p-pyb1yb1ppxb2xb2))

c2 = (pc2 = (pyZyZppxb1xb1-p-pxZxZppyb1yb1) / (p) / (pxb2xb2ppyb1yb1-p-pxb1xb1ppyb2yb2))

CMS Note-2007/014CMS AN-2006/106(CMS approved result)

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Assumption : Exact pT balance in the event (but there is effect of radiated jets) Jets reproduce the parton direction : Effect of detector, Algorithm In Ideal case

It will be exactly 1

c1 and c2 are mere scale factors

Why do we need It :b-Jets in final state of many processes at LHCb quark fragmentation function is different than light quark and gluonProduction and decay of heavy hadrons in the b-jetPart of the energy will be carried by neutrinosin semi-leptonic decays.

Applying to Generator level Jets

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ISR Effect

Ideal : ISR off in PYTHIA

The error in directionmeasurement of one jetaffects the other.

Ctrue = ET(jet)/ET(quark)

= separation between Jet and quark

Detector level Jets

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Very much similarSelections,

10 fb-1 of data(LO cross section used for Zbb sample)

1000 total events after selections

75% signal and 25% background(detail in backup)

Selected events withR > 1.2

Jet veto improvespT balance

ET and of veto jets

4th Dec 06 Physics meeting, CMS Week 35

Measured pMeasured pTT balance between di-b jets and di-leptons balance between di-b jets and di-leptons

The effect of background on pThe effect of background on pTT balance is small ( < 1 %) balance is small ( < 1 %)

(if we fit around the peak)(if we fit around the peak)

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Extraction of energy correctionsExtraction of energy corrections

Because of ISR,Z boson and two b quarks are notperfectly balancedin the transverseplane. Jet veto does not reduce completely this effect.

When the jetdeviates fromthe original b-quarkdirection that error propagates in the pT balance equation and gives a wrong correction coefficient

4th Dec 06 Physics meeting, CMS Week 37

Getting the functional form:Getting the functional form:

S and S+B points are within S and S+B points are within ~ 2 ~ 2 stat errors stat errors

10 fb10 fb-1-1 “data” “data” 10 fb10 fb-1-1 “data” “data”

4th Dec 06 Physics meeting, CMS Week 38

How correction function works on bbZ events :How correction function works on bbZ events :

As a first test, the b-jets in As a first test, the b-jets in the same gg->bbZ processthe same gg->bbZ processhas been corrected using thishas been corrected using thiscorrection function. correction function.

The plot shows pThe plot shows pTT ratio of ratio of

Z boson to that of combined Z boson to that of combined two b-jets, dashed plot is for two b-jets, dashed plot is for uncorrected jets and solid plot uncorrected jets and solid plot is for corrected jets. is for corrected jets.

The correction restores the The correction restores the ppTT balance and also makes balance and also makes

the distribution narrower the distribution narrower compared to uncorrected jetscompared to uncorrected jets.

4th Dec 06 Physics meeting, CMS Week 39

How correction function works on h->bb inHow correction function works on h->bb intth, h->bb, W->tth, h->bb, W-> events : events :

- restore Higgs boson mass to nominal value- restore Higgs boson mass to nominal value- improve resolution by ~ 25 %- improve resolution by ~ 25 %

4th Dec 06 Physics meeting, CMS Week 40

b JES Uncertaintyb JES Uncertainty

Fit Uncertainty withFit Uncertainty with 10 fb10 fb-1-1 of data of data

Uncertainty of MUncertainty of Mbbbb

MMbbbb = 122.0 ± 8 (syst) GeV = 122.0 ± 8 (syst) GeVGenerated MGenerated Mbbbb = 120 GeV = 120 GeV

Cosmic Muon Charge Ratio(ongoing)

• Cosmic muon Charge ratio : 90% of proton in cosmic ray Production of more + and + in Shower than - and -. • Data used : 300 M triggered events

taken last year in CMS : 100 M good events

(tracker used in the run)• Studying cosmic physics is not CMS

aim : not designed for it. • But it helps understanding the

detector by measuring this which has been measured very precisely in earlier dedicated experiments and also confirms CMS capability.

4141

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• Muon Selection for Charge Ratio studies

• Global muon two Leg, < 0 (downward)

• pT (at PCA) > 10 GeV, pT = 1/C (curvature)

C = (1/2)(q1/pT1 + q2/pT2) at Point of Closest Approch (PCA)• Does not share tracker track• No. CSC Hits, TEC Hits = 0• No. of DT Hits (per leg) >= 20 • No. of TOB Hits (per Leg) >= 5• No. of DT SL2 (Z) Hits >= 3• Net q = Sign(q1/pT1 + q2/pT2)

Cosmic Muon Charge Ratio(ongoing)

Example of a cosmic muon passing CMS detector

Charge ratio Vs Zenith Angle

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pT measured at PCA from the curvature of two Legs : Zenith angle measured at the entry point (CMS detector surface)

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Cosmic Muon Angular Resolution(ongoing)

• Muon selection : • 2 Leg Barrel muons (muon) < 0., same track charge for both leg , # of total track hits >= 25, 15 for upper and Lower legs. Track propagation • The Lower Leg track is propagated to the

closest approach to the 1st hit point (inner most point as convention) of the upper Leg track, using SteppingHelixPropagator in opposite to momentum.

• The difference of the measured angle (,

, zenith angle) at the entry point are studied.

Lower Leg

Upper Leg

Point of measurement

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Resolution GLB muon

MC 10GeV

Fitted with double gaussian function

Data

May be due to difference in magnetic field map

=(Extp Lower Leg) – (Upper Leg)

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(Zenith angle) Resolution GLB muon

MC 10GeVData

=(Extp Lower Leg) – (Upper Leg)

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Selection Efficiency from data Using Tag & Probe (ongoing)

Muon Selection Tag Muon : Lower Leg < 0, pT (at PCA) >= 10, no. DT Hits >= 20, no. of TOB Hits >= 5, No. of CSC Hits = 0 , no. of TEC Hits >= 0Compatible lower tracker track and lower Stand alone muon track

Probe Muon : Upper Leg < 0, pT (at PCA) >= 10, no. DT Hits >= 20, no. of TOB Hits >= 5, No. of CSC Hits = 0 , no. of TEC Hits >= 0Compatible upper tracker track and upper Standalone muon track

Q(lower leg) * Q(upper leg) > 0.

Tag

Probe

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Efficiency from Tag & Probe

Data MC

< 2% difference in most of the bins.

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Jet Plus Tracks performance study using Test Beam 2007 dataJet Plus Tracks performance study using Test Beam 2007 data

Particle Energy Response :

ECAL (7 X 7 crystal ) HCAL (3 X 3 Tower)

Without Zero Suppression

ECAL Calibration using 100 GeVelectronsHCAL Calibration using muon and wire source

Jets are made from Charged pionsonly, by randomly picking6 pi of 5 GeV, 4 pi of 6 GeV2 pi of 7 GeV, 1 pi of 8 GeV

True Jet Energy : 76 GeV ( pT = 28 GeV, eta = 1.653)

Track Correction : for each particlesubtract average (EE+HE) responseand add true energy.

Calo Correction : multiply each Jet energy by True energy / Emean

raw

Main JPT steps: subtract average response of “in-calo-cone” tracks from calo jet E and add track momentum.- add momentum of “out-of-calo-cone” tracks (1,2,3 on figure) to jet E

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CMS AN-2008/111

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(LEP Higgs working group, hep-ex/0602042)

Because of the suppressed H1ZZ coupling, LEP could not exclude the presence of a light Higgs boson at low tan (~ 3.5 to 10)

Higgs search at CMS in CPV MSSM Model

Because of the suppressed H1VV coupling one of the pseudo-scalar Higgs state is very lightSince there is correlation between the mass of charged Higgs and that of the pseudo-scalar Higgs state in MSSM, => a light charged Higgs, with MH+< Mtop .The traditional decay mode H+-> is suppressed over an order of magnitude.

(133 GeV)

(51 GeV)

(Ghosh, Godbole, Roy hep-ph/0412193)

M(H1) = 51 GeV, M(H+) = 133 GeV, M(top) = 175 GeV(CP) = 90o, tan() = 5

* BR = 2 * 840 pb * 0.01 (BR(t->bH+) * 0.567 (BR(H+->H1W) * 0.99 (BR(t->bW)) * 0.92 (BR(H1->bb) = 8.675 pb

50Main backgrounds : tt + >= 2jets & ttbb+jets

CMS AN-2008/025arxiv:0803.1154 (hep/ph)(part of 2007 Les houches study)

pT distribution of b-quarksb-quarks from H1 are very soft , 36% events have both two b-quarks from H1 with pT above 20 GeV

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Quarks distribution in () space

The final state of the event consists of 6 quarks and so 6 or more jets.

The two closest quarks in the event fall very close to each other and so it makes difficult to reconstruct 6-jets in the event.

R between two closest quarks

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0.5

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Full Event Reconstruction• Leptonic decayed W was reconstructed from lepton and missing ET. The z-component

of missing energy was calculated using W mass constraint. This yields real solutions in 66% events. Events with imaginary solutions are rejected. There are two possible candidates for each leptonic W.

• Hadronic decayed W was reconstructed from jets not tagged as b-jets. All jet pairs with invariant mass within mw ± 20 GeV were considered as possible

candidates for W.

• Two Tops were reconstructed simultaneously from 4 b-Jets, two leptonic W candidates and N (any number) possible hadronic W candidates. The jets and W were assigned to Tops by minimizing

M = sqrt( (mtop1 – mtop)2 + (mtop2 – mtop)2 + (mW (hadronic) – mW)2 ) where mtop1 = 1 b-Jet + 1 W mtop2 = 3 b-Jets + 1 W , mtop = 175 GeV, mW = W boson mass. events with mtop1 and mtop2 within mtop ± 30 GeV were selected.

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Top Mass

>= 3 jets in top : Wrong combinations+Uncert. In JES and JER

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Results for 30 fb-1 of data110 signal events and 203 ± 60 tt + Njets events in 30 fb-1 data : 6.78 < S / B < 9.2

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Systematic uncertainty on tt+jet background = 22.5%

Signal significance = S/√(B+B2) = 110 / √(263 + 592) = 1.8

The analysis was limited by the unavailability ofsufficient background events.

Large syst. uncert. dut to b-tagging, JES and MET scale

The theoretical uncert.on LO cross sectionof tt+≥2jets is ≥50%

MH1 = 51 GeV

All 3 possible combination of b-Jet pair out of 3 b-Jets from 2nd Top

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Summary The process, Zbb, Z -> has been studied aiming for the first LHC data.

The cross section of this process can be measured with first 100 pb-1 of data within 30% uncertainty .

Zbb, Z-> process provides a data driven technique to evaluate dedicated b-jet energy corrections with higher integrated luminosity.

A study is being carried out for the measurement of Cosmic muon charge

ratio as function of zenith angle

The performance of calorimeter response subtraction method for charge paticles in Jet Plus tracks algorithm has been studied using the Test Beam data (a data driven method which could be used to correct b-jets in Zbb).

Studied the possibility of discovering a light Higgs in CPV MSSM model in higher int. luminosity. The study is limited by the unavailability of large background statistics (large stat. uncert.) and also large systematics. The systematic uncertainty can be reduced with data driven background measurement.

A trigger study for H+ -> channel was performed with the updated MC datasets for the Physics TDR.

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Thank You

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Trigger Selection for H+ -> , hadronic decay

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Level-1 1Tau trigger : 1Tau > 93 GeVHLT Tau trigger : HLT MET > 60 GeV + HLT Trk Tau ( pT = 25)

For Rate calculation : QCD 30-470 GeVData Challenge 04 samples

Matching with DAQ TDR resultsHLT rate : 0.7 Hz (1 Hz in DAQ TDR) New thresholds

to keep L1 rate of 1T Or 2T 3 kHz(with DAQ TDR cuts, it was 3.6 kHz)

* Tables of efficiency and rates are in backup

mH0 = mH+ = 200 GeV

CMS IN-2006/008