Measurement of production cross section of Z boson with associated b-jets and Evaluation of b-jet energy corrections using CMS detector at LHC

13th July 09

Aruna Kumar Nayak Thesis Supervisor : Prof. Tariq Aziz Synopsis Seminar

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 →

ll

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 2

The Standard Model

SM Building blocks The SM is based on SU(3) C Strong : QCD Gluon X SU(2) L X U(1) Electroweak W ± , Z /  Y gauge symmetry SU(2) L X U(1) Y U(1) Q Electroweak Symmetry Breaking (Higgs mechanism), Responsible for generating particle mass 3

The SM : Symmetry Breaking

The potential is of the form The 2 nd 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 : 4

Success of Standard Model

Success :

W, Z were discovered at SPS, CERN in 1980s Tevatron, Fermilab discovered Top quark (the heaviest among all) in 1995 Most 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 5

Is There any New Physics?

    THE SM has quite a few shortcomings, e.g. : The SM is silent about the Gravitational force (the 4 th 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, m top etc. One of the EWK measurements : cross section of Z + b-jets production 6

The large Hadron Collider

~27 KM ring, The LEP tunnel proton-proton collision : 14 TeV CM energy 25 ns bunch crossing : 2808 bunches with ~10 11 protons in a bunch Design luminosity : 10 34 cm -2 s -1 => 100 fb-1/year 7

The Compact Muon Solenoid Detector (CMS)

Design Objectives : Example of few important Higgs discovery modes : H →  H → ZZ → 4 m H → ZZ → 4 e H → ZZ → 2e and 2 m 1) Very good and redundant Muon detection system 2) The best possible measurement of e/  3) Good resolution of hadronic jets and missing transverse energy 4) High quality central tracking

Total weight : 14500 t Diameter : 14.60 m Length : 21.60 m Magnetic Field : 4 Tesla Size of 1 event : 1 MB 100 events / second (stored in tape)

8

Detector Components (I)

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 kA Advantage : 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 strips Pixel : r ~ 10 cm, Particle flux ~ 10 7 /s, size of pixel : 100 m m X 150 m m occupancy : 10 -4 /pixel/bunch crossing spatial resolution : ~10 m m in r  and ~20 m m in r-z Strip : 20 < r < 55 cm, size : 10 cm X 80 m m occupancy : 2-3% / bunch crossing TIB resolution : 23-34 m m in r  and 230 m m in z r > 55 cm, size : 25 cm X 180 m m occupancy : 1% /bunch crossing TOB resolution : 35-52 m m in r  and 530 m m in z TID : 3 disks TEC : 9 disks, 120 cm < z < 180 cm 9

Detector Components (II)

ECAL : Compact, Hermatic, homogeneous, 61200 lead tungstate (PbWO 4 ), X 0 = 0.89 cm, R m = 2.2 cm Fast : 80% light yield within 25 ns Radiation hard : 10 Mrad Barrel (EB) : R in 0 < |  | < 1.479, ~ 129 cm, 36 Super modules Each crystal 0.0174 X 0.0174 (  ,  ), front face ~ 22 X 22 mm 2, Endcap (EE) : Z in L = 230 mm (~25.8 X 0 ) ~ 314 cm, 1.479 < |  | < 3.0 , crystal : 28.6 X 28.6 mm 2, L = 220 mm ( 24.7 X 0 ) Preshower (ES) : 2 layers of Si strip (1.9 mm pitch), behind lead (2X 0 , 3X 0 ) The energy resolution is of the form S : stochastic term, N : noise term, C : constant 10

Detector Components (III)

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  outer 5 towers :  towers, 1.3 < |  | < 3.0, ~ 0.087,  ~ 5 0 , Inner 8 towers :  ~ 0.09-0.35,  ~ 10 0 Forward (HF) : steel/quarz fibre calorimeter. 3.0 < |  | < 5.0, Z in 13  towers ~ 0.175,  ~ 10 0 ~ 11.2 m 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  . 11

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 m m each station : 100 m 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 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. 12

Detector Components (V)

Example of a Level-1 Jet Trigger CMS Trigger : L1 Trigger : Electronics modules e.g. Look up Tables (RAM, ASIPs) L1 Rate : ~25 kHz (at 2X10 33 L1 decision time < 1 m s cm -2 s -1 ) HLT : computer farm, partial reconstruction of physics objects HLT Rate : ~100 Hz 13

Physics Objects Reconstruction : Electrons

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), D in s  < 0.090(barrel), 0.092(endcap), D in < 0.0140(barrel), 0.0275(endcap) < 0.0090(barrel), 0.0105(endcap) H/E : Hadronic to electromagnetic energy deposit ratio.

D in :  difference between the electron supercluster and the electron track D in at vertex :  difference between the electron supercluster and the electron track at vertex 14

Physics Objects Reconstruction : Electrons

Isolation : track isolation S (p T (track)/p T (electron)) 2 < 0.02 (in cone 0.02-0.6, track p T (This isolation criteria is only for Z measurement study) > 1.5 GeV, ) Efficiency calculated by matching MC electron to Reco electron in 0.1 cone Electrons from Z decay 15

Physics Objects Reconstruction : Muons

Reconstructed from the information of Tracker and Muon Chamber Isolation : S p T (tracks) (0.3 cone) < 3 GeV Efficiency calculated by matching MC muon to Reco muon in 0.1 cone Muons from Z decay 16

Physics Objects Reconstruction : Jets

Jets are reconstructed from calorimeter energy using IterativeCone algorithm of cone size 0.5  dependent & p T dependent corrections are used . Reconstruction efficiency of jets Vs generated Jet p T and  for Z + bb events. 17

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

ll

process

CMS PAS EWK-08-001 CMS AN-2008/020 CMS CR-2008/105 (CMS approved result)

 Measurement of Zbb production is an important test of QCD calculation  Background to Higgs discovery channels at LHC, like SM H → ZZ → 4 l , SUSY bb F , F → tt ( mm )  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 1 st 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

s

Cross section and Event generation

Signal

ll

bb (Zbb) :

CompHEP events with p T (b) > 10 GeV, |  |(b) < 10 , m ll > 40 GeV, | were generated and fully simulated in CMS with 100 pb -1  |( l ) < 2.5

calibration and mis-alignment Cross section calculated using MCFM, NLO s PDF : CTEQ6M, scale m R = m F = M Z ( ll bb) = 45.9 pb , l = e, m , t LO cross section calculated using PDF : CTEQ6L1 and same values for scale K (NLO) = 1.51

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 ll cc + n Jets, n>= 0 (Zcc) : Generated using ALPGEN Normalized on NLO s (using MCFM) 13.29 pb, k factor = 1.46 with cuts : p T (c) > 20 GeV, |  |(c) < 5, m ll > 40 GeV ll + n Jets, n >= 2, (Zjj) : Generated using ALPGEN Normalized on NLO s (using MCFM) 714 pb , k factor = 1.02 with cuts : p T (j) > 20 GeV, |  |(j) < 5, m ll > 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.

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 = 10 32 cm -2 s -1

Lepton Selection :

Two high p T , isolated, opposite charged leptons |  |(e) < 2.5

, |  |( m ) < 2.0

, lepton p T > 20 GeV

Jet Selection :

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

b-Jet Tagging

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

b-discriminator of 2 nd highest discriminator jet

Jets are tagged using “Track Counting b-tagging” Which uses the 3-dimentional impact parameter significance , of 3 rd highest significance track, as the b-tagging discriminator i.e. No. track (3D IP significance cut) >= 3 Effective to supress the Z+jets backgrounds.

b-tag efficiency

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

*statistical error bars are not shown

E

T miss

selection

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

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

Type-1 E Tx,y miss = - (E Tx,y calo +

S

jets (E Tx,y corr – E Tx,y raw )) Muon corr. = - (

S

muons (p x,y – E x,y (calo. deposit) )) Effective to supress the tt~+jets backgrounds Cut E T miss < 50 GeV

Event Selection details

Two Leptons, p T > 20 GeV, |  |(e) < 2.5 , |  |( m ) < 2.0

Two or more Jets , E T > 30 GeV , |  | < 2.4 Two b-tagged Jets Missing E T < 50 GeV Initial and final cross sections after all selections

Process Name

Zbb tt~ + jets Z+jets Zcc+jets s

NLO (pb)

46 840 714 13.3

Final

s

(fb)

Electron 176 ± 3.3

Muon 212 ± 3.6

173 ± 9.0

5.5 ± 2.8 4.3 ± 1.63

178 ± 8.7

5.5 ± 3.1

5.1 ± 1.93

* More details for each selection cuts are in backup 25

Expected Measurement for 100 pb

-1

events scaled to 100 pb -1

Purity of b-tagging in Zbb events The 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 → mm final state 27

tt~ background Estimation

Dilepton mass region Signal :

75-105 GeV (Z)

Side band :

0-75 GeV & 105 – above (no Z)

N

Z

(tt) = (

e Z

(tt)/

e noZ

(tt)) X N

noZ

(tt)

D

N

Z

(tt)/N

Z

(tt)= 1/√N

noZ

(tt)

N Z (tt) = expected no. of tt~ events in signal region N noZ (tt) = measured no. of tt~ events out side signal region e Z (tt) = selection efficiency of tt~ in signal region e noZ (tt) = selection efficiency of tt~ outside signal region D N Z (tt) = uncertainty of the expected number of tt~ events in the signal region.

Uncertainty on e Z (tt)/ e noZ (tt) is negligible compared to the statistical uncertainty on N noZ .

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

Systematics

Uncertainty due to Background and double b-tagging.

N Zbb and D N Zbb are determined as follows. N Z before b-tag = N Zjj + N Zcc + N Zbb N Z after b-tag = e l X N Zjj + e c X N Zcc + e b X N Zbb Where, N Z before b-tag = measured number of Z/  * → ll events after all selections except b-tagging under Z mass peak (75-105 GeV). Contribution of tt~ is negligible (~1%). N Z after b-tag = measured number of Z/  * → ll events after all selections including b-tagging with tt~ subtracted N Zjj is unknown number of double b-tagging.

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

(after all selections except b-tagging)

e b , e c , e l 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)

Systematics Contd ......

Reduce the no. of variables to two using the Ratio where is ratio of selection efficiencies Solving the equations The Uncertainties on N Zbb is calculated from uncertainties of N Z after b-tag (uncertainty due to tt~ subtraction),  R and uncertainties on e b , e c , e l

*

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

Total Uncertainty on Measurement

Source of uncertainty

Jet energy scale (JES) Type 1 missing E T scale MC p T jet ,  jet dependence b-tagging of b-jets ( e b ) mistagging of c-jets ( e c ) mistagging of light jets ( e l ) N Z after b-tag due to tt~ subtraction R (Zcc / Zjj)

Value used (%)

7 10 (unclustered E T miss ) + 7 (JES) -10, +0 8 8 7.6

4 5 lepton selections luminosity 0.5

10 

(

s

(Zbb)) (%)

7.6

7.4

-10, +0 16 0.5

0.5

4.6

0.4

0.5

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

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

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

ll

process

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

Why do we need It : b-Jets in final state of many processes at LHC b quark fragmentation function is different than light quark and gluon Production and decay of heavy hadrons in the b-jet Part of the energy will be carried by neutrinos in semi-leptonic decays.

c 1 p xb1 + c 2 p xb2 = -p xZ c 1 p yb1 + c 2 p yb2 = -p yZ c1 = (p yZ p xb2 -p xZ p yb2 ) / (p xb1 p yb2 -p yb1 p xb2 ) c2 = (p yZ p xb1 -p xZ p yb1 ) / (p xb2 p yb1 -p xb1 p yb2 )

c 1 and c 2 are mere scale factors Assumption : Exact p T 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

Applying to Generator level Jets

Ideal : ISR off in PYTHIA ISR Effect The error in direction measurement of one jet affects the other.

C true = E T (jet)/E T (quark) D =  separation between Jet and quark 33

Detector level Jets

Very much similar Selections, 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 with D R > 1.2

Jet veto improves p T balance

E T and



of veto jets

34

Measured p

T

balance between di-b jets and di-leptons

The effect of background on p T balance is small ( < 1 %) (if we fit around the peak)

4th Dec 06 Physics meeting, CMS Week 35

Because of ISR, Z boson and two b quarks are not perfectly balanced in the transverse plane. Jet veto does not reduce completely this effect.

Extraction of energy corrections

When the jet deviates from the original b-quark direction that error propagates in the p T balance equation and gives a wrong correction coefficient

36

Getting the functional form:

4th Dec 06

10 fb -1 “data” 10 fb -1 “data”

Physics meeting, CMS Week

S and S+B points are within ~ 2

s

stat errors

37

How correction function works on bbZ events :

As a first test, the b-jets in the same gg->bbZ process has been corrected using this correction function. The plot shows p T ratio of Z boson to that of combined two b-jets, dashed plot is for uncorrected jets and solid plot is for corrected jets. The correction restores the p T balance and also makes the distribution narrower compared to uncorrected jets

.

4th Dec 06 Physics meeting, CMS Week 38

How correction function works on h->bb in tth, h->bb, W->

l n

events :

4th Dec 06

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

Physics meeting, CMS Week 39

b JES Uncertainty Fit Uncertainty with 10 fb

-1

of data Uncertainty of M

bb

M

bb

= 122.0 ± 8 (syst) GeV

Generated M bb = 120 GeV

4th Dec 06 Physics meeting, CMS Week 40

• • • •

Cosmic Muon Charge Ratio (ongoing)

Cosmic muon Charge ratio : 90% of proton in cosmic ray Production of more p + Shower than p and K . and K + in 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.

Cosmic Muon Charge Ratio (ongoing)

• • • • • • • • •

Muon Selection for Charge Ratio studies

Global muon two Leg,  (downward) < 0 p T (at PCA) > 10 GeV, p T = 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) Example of a cosmic muon passing CMS detector 42

Charge ratio Vs Zenith Angle

p T a measured at PCA from the curvature of two Legs : Zenith angle measured at the entry point (CMS detector surface) 43

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.

Point of measurement Upper Leg • Track propagation The Lower Leg track is propagated to the closest approach to the 1 point (inner most point as convention) of the upper Leg track, using to momentum. st hit SteppingHelixPropagator in opposite Lower Leg • The difference of the measured angle (  , q , zenith angle) at the entry point are studied.

44

MC 10GeV

D  =

Resolution GLB muon

 (Extp Lower Leg) –  (Upper Leg)

Data

Fitted with double gaussian function May be due to difference in magnetic field map

a

(Zenith angle) Resolution GLB muon

Da = a (Extp Lower Leg) – a (Upper Leg)

Data MC 10GeV

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 >= 0 Compatible 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 >= 0 Compatible upper tracker track and upper Standalone muon track Q(lower leg) * Q(upper leg) > 0 . Probe Tag 47

Efficiency from Tag & Probe

Data MC < 2% difference in most of the bins.

48

Jet Plus Tracks performance study using Test Beam 2007 data

CMS AN-2008/111 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

Particle Energy Response : ECAL (7 X 7 crystal ) HCAL (3 X 3 Tower) Without Zero Suppression ECAL Calibration using 100 GeV electrons HCAL Calibration using muon and wire source Jets are made from Charged pions only, by randomly picking 6 pi of 5 GeV, 4 pi of 6 GeV 2 pi of 7 GeV, 1 pi of 8 GeV True Jet Energy : 76 GeV ( pT = 28 GeV, eta = 1.653) Track Correction : for each particle subtract average (EE+HE) response and add true energy. Calo Correction : multiply each Jet energy by True energy / E mean raw

Higgs search at CMS in CPV MSSM Model

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

Because of the suppressed H 1 ZZ coupling, LEP could not exclude the presence of a light Higgs boson at low tan b (~ 3.5 to 10) (LEP Higgs working group, hep-ex/0602042) Because of the suppressed H 1 VV coupling one of the pseudo scalar Higgs state is very light Since there is correlation between the mass of charged Higgs and that of the pseudo-scalar Higgs state in MSSM, => a light charged Higgs, with M H+ < M top .

The traditional decay mode H + -> tn order of magnitude.

is suppressed over an (133 GeV) M(H1) = 51 GeV, M(H+) = 133 GeV, M(top) = 175 GeV F (CP) = 90 o , tan( b ) = 5 (51 GeV) s * 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 Main backgrounds : tt + >= 2jets & ttbb+jets (Ghosh, Godbole, Roy hep-ph/0412193)

p

T

distribution of b-quarks

b-quarks from H 1 are very soft , 36% events have both two b-quarks from H 1 with p T above 20 GeV 51

Quarks distribution in (

, 

) space

D

R between two closest quarks

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.

0.5

52

•

Full Event Reconstruction

Leptonic decayed W was reconstructed from lepton and missing E T . 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 m w ± possible candidates for W . 20 GeV were considered as • 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 D M = sqrt( (m top1 – m top ) 2 where m top1 + (m = 1 b-Jet + 1 W top2 – m top ) 2 + (m W (hadronic) – m W ) 2 ) m top2 m top = 3 b-Jets + 1 W , = 175 GeV, m W = W boson mass. events with m top1 and m top2 within m top ± 30 GeV were selected.

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

Top Mass

54

Results for 30 fb

-1

of data

110 signal events and 203 ± 60 tt + Njets events in 30 fb -1 data : 6.78 < S /



B < 9.2

Systematic uncertainty on tt+jet background = 22.5% Signal significance s

= S/ √(B+

D

B 2 ) = 110 / √(263 + 59 2 ) = 1.8

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

on LO cross section of tt+ ≥2jets is ≥50% M H1 = 51 GeV All 3 possible combination of b-Jet pair out of 3 b-Jets from 2 nd Top The analysis was limited by the unavailability of sufficient background events.

Summary

 The process, Zbb, Z -> ll 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-> ll 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 + -> tn channel was performed with the updated MC datasets for the Physics TDR. 56

Thank You

Trigger Selection for H

+

->

tn

,

t

hadronic decay

CMS IN-2006/008

Level-1 1Tau trigger :

1Tau > 93 GeV

HLT Tau trigger :

HLT MET > 60 GeV + HLT Trk Tau ( pT = 25) For Rate calculation : QCD 30-470 GeV Data Challenge 04 samples m H0 = m H+ = 200 GeV Matching with DAQ TDR results HLT rate : 0.7 Hz (1 Hz in DAQ TDR) * Tables of efficiency and rates are in backup New thresholds to keep L1 rate of 1T Or 2T 3 kHz (with DAQ TDR cuts, it was 3.6 kHz) 58