potential for standard model physics with cms at the lhc

Potential for Standard Model physics with CMS at the LHC

Where are we with hard- and software ? From the Tevatron/LEP to the LHC Top quark, EW, QCD, B physics, ... How to search for the Standard Model Higgs ?

Jorgen D’Hondt (Vrije Universiteit Brussel)on behalf of the CMS Collaboration

HEP-EPS Conference, Lisbon, 21-27 July 2005

21st of July 2005 Jorgen D'Hondt (Vrije Universiteit Brussel, CMS Collaboration) 2

The CMS detector : design sketch

76k pieces

16k pieces


The CMS detector : construction progress

Large activities are ongoing to makeprevious sketch into reality

Main underground cavern is ready

Several sub-detector systems are completed or being completed :

Tracker : serious speed-up of production, overall good quality of modules ECAL : ⅔ of barrel crystals delivered, first SuperClusters for endcap made HCAL : assembled, start with electronics integration, calibration ongoing Magnet : completed and succesfully tested for leaks Muons : CSC’s completed, RPC’s being constructed and gradually integrated, 80% of DT’s are completed

Trigger boards are being produced

“ CMS* will be closed and ready for beam on 30 June 2007 ” (T.Virdee, HCP’05 talk)


The CMS detector : becoming a reality

barrel trackersilicon detectors

magnet

muon RPC’s


Example of an Event

IGUANAlow luminosity

SUSY eventpT > 1.0 GeV|| < 2.4


Example of an Event

IGUANAhigh luminosity

SUSY eventpT > 1.0 GeV|| < 2.4


Current status of Simulationand Reconstruction

Still a few years before real data… hence all based on Monte Carlo simulationfirst data expected in 2007

Main generator used : PYTHIA 6.2 does not include many features present in dedicated generators fast simulation : the PYTHIA objects are smeared to mimic the detector the particle interactions are not simulated with GEANT

Results in this presentation: studies based on fast simulation (‘FAMOS’) large efforts have been made to optimize the reconstruction code large Data-Challenge efforts have been made to provide dedicated

GEANT-4 simulation (created ~100M simulated events, ~1Mb/event) in the process of writing a Physics - Technical Design Report with this

accurate simulation and reconstruction tools (expected early 2006) Current results to be digested as an illustration of what can be learned from

CMS data upon arrival


From Tevatron/LEP to LHC

Obtaining orders in magnitude in both the integrated luminosity and the energy, we will collect a huge amount of Standard Model benchmarks channels.

~109 events/10fb-1 W (200 per second)~108 events/10fb-1 Z (50 per second)~107 events/10fb-1 tt (1 per second)

These can be used as control/calibration samples for searches beyond the Standard Model, but can also be used to scrutinize even further the Standard Model.


Top Quark Physics : top quark mass

10 tt pairs per day @ Tevatron 1 tt pair per second @ LHCqq →tt : 85% gg→tt : 87%

width of peak~10 GeV

mt(stat) ~ 300 MeV (10fb-1)

fastsim10fb-1

Most important parameter is the top quark mass (mt), to be estimated with an accuracy of around mt ~ 1 GeV/c2.

Golden channel : semi-leptonic tt →bWbW→blvbqq

Selection via lepton, miss.ET, 4 jets, 2 b-tags (S/B~>20)Top mass from hadronic side t→qqbMain systematics are the jet energy scale

Improve with kinematic fit and more advancedstatistical inference techniques are ongoing.


Top Quark Physics : top quark mass

From t l + J/ + X decays :

→ 100 fb-1 gives after selection ~ 1,000 signal events (S/B > 100) the large mass of the J/ induces a strong correlation with the top mass easier to identify (extremely clean sample) BR(overall in tt) ~ 5.3 x 10-5

no jet related systematics !!

hep-ph/9912320

60

New method : hep-ex/0501043correlate the b transverse decay length with m t

CMS fast simulation

slope


Top Quark Physics : top versus anti-top

Spin correlations the top quark does not loss its spin information before it is decaying into W and b

with A =0.431 (gg) and A = - 0.469 (qQ)

two observables +(-): angle between t(T) direction in the tT c.m. frame and the l+(l-) direction of flight in the t(T) rest frame fit to double differential distribution

result (30fb-1) : A (stat) = 0.035 and A (syst) = 0.028

Measuring the difference between mt and mT

almost all systematics cancel when measuring the difference between both after several years the precision could be around 50 MeV/c2

what we could learn from that ? CPT violation… ? differences between t and T can learn us something about the PDF’s (rapidity

distributions)


Top Quark Physics : single-top-channelNever observed !!

Each channel sensitive to different signals

• heavy W’ → s-channel• FCNC → t-channel• H± → Wt-channel

Also directly related to |Vtb| to percent level(s-channel preferred, t-channel dominated by PDF scale uncertainties of ~10%)


W polarization in top decays

The large top quark mass allows the W boson to be longitudinaly polarized

defined as : angle between lepton (in W rest frame) and W (in top rest frame)Standard Model prediction : f0 = mt

2 / (2 mW2 + mt

2) ~ 0.7 and fR ~ 0 (mb~0)

LH: (1±cos)2

Long: sin2PYTHIA 5.7, 1 year CMSonly W→ev and W→v

Expected uncertainty

stat f0 = 0.023 syst f0 = 0.022

estimation of systematic uncertainties conservativemost of the time limited by the statistical precision of the effect


Gauge Boson Couplings

Direct measurements of vector boson couplings are possible via the cross-section measurements of the processes in which they appear. They test the non-Abelian nature of the Standard Model gauge theory.

Anomalous couplings or new physics can be included in the effective Lagrangian at a fundamental scale .

W

W

pp→Wcross-section

enhanced when anomalous couplings

are present

pt-spectrum of photon sensitive to anomalous couplings (=1.5 TeV)

pt() (GeV)

=0.3, =0

=0, =0

=0, =0.95

Limits @95%CL (=2TeV)

for 100 fb-1 (=2TeV) || < 0.1 || < 0.0009

large improvement for compared to Tevatron

BAUR MC generator

For ZZ and Z couplings both the pT() and the MT(ll) spectrum are sensitive to hi

V (V=Z,) anomalous couplings


Drell-Yan Production of Lepton Pairs

The Drell-Yan process pp→l +l - is a measure for AFB and hence sin2efflept :

LHC reaches much higher masses

Z/

q

q

e-,-

e+,+

inverse of e+e- → qq at LEP

Precision will exceed the magnitude of the EW corrections up to Mll=2 TeV

Rel. exp. uncertainty on ll (in %)

5%

10%

0%

Weak-mixing anglesin2eff

lept can bedetermined to

sin2efflept ~ 0.00014

using forward lepton tagging

main systematic uncertainty is the

knowledge of the PDF’s

can also use sin2efflept to

constrain the PDF’s


Parton Probability Functions

y = pseudorapidity

DGLAP ev

olutio

n

How to find the partons in the colliding protons ?

→ need for precise PDF(x,Q2)

Extrapolate from HERA, but also use the huge LHC data itself

Ratio of W+/W- cross-section is related to u(x)/d(x)

0.1 fb-1 differentiate between several models


Parton Probability Functions

The PDF’s for the heavy quarks can also be measured

Isolated with high pT

+ jet including

Isolated e/ with high pT

+ jet including

Estimate 5-10% accuracy on PDF‘slimited by fragmentation functions

The PDF’s can be determined relative to each other, and therefore depend on the accuracy of the theoretical calculations.

In a similar way the gluon luminosity function can be obtained with a 1% accuracy.


B-physics

The CMS detector allows a rich B-physics program due to its precise tracking and vertexing(but no Particle ID detectors, usually triggers on high-pT objects)

CP violation measurements of Bs oscillations rare decays life-time Bc mesons etc...

Example : (alternative to lepton-tag method) CKM angle via Bd

0→J/ Ks0 in B**±→Bd

0(*) ±

The flavour of B0 is tagged with ±

Expected precision is (sin2)=0.022 (10fb-1) (to be repeated with higher trigger thresholds)

related to angle

after selection

ICHEP’04 : sin(2) = 0.725 ± 0.037

all B-physics studies require a profound knowledge of the detector performance


The SM-like scalar Higgs boson can be observed in several physics channels (depending on its mass mH which is a free

parameter of the model, LEP mH > 114.4 GeV @95%CL)

Standard Model Brout-Englert-Higgs boson

production cross-section decay branching ratios

balance between production rate, decay rate and reconstruction efficiency



H → ZZ* → 4l H → qqH → qq

H → WW* →lvlv ttH → ttbb qqH → qq

mH=130,150,170 mH=130 mH=115

mH=140 mH=115 mH=135

signal

signal signal

signalsignal

signalsignal

signal

100fb-1 100fb-1 60fb-1

30fb-1 30fb-1 30fb-1


Combined discovery potential as a function of mH


zoom in low mass region

WW ZZ

5 at 2 fb-1

at 10 fb-1

at 30 fb-1

At 10 fb-1 full 5 coverage from LEP to 800 GeVLEP limit

5 at 10 fb-1

at 30 fb-1

at 60 fb-1

WW/ZZ


Integrated luminosity needed for 5 discovery as a function of mH


zoom in low mass region

30 fb-1

30 fb-1


Comparing the direct and indirect values of mH

Ultimate test of the Standard Model

To give mt and mW equal weight :mW = 0.7 10-2 mt

Goal of LHC experiments :mt < 1 GeVmW < 15 MeV

mH/mH < 25 %

After a discovery one can use EW measurements to differentiate

between SM or MSSM Higgs bosons


Outlook for CMS activities

First fast-simulation studies (presented)

significant improvement in Standard Model measurements Higgs boson mass range completely covered after 10fb-1

Current progress within the CMS Collaboration

created large amounts of dedicated/realistic simulation large effort in optimizing our reconstruction methods gradually design more advanced analyses techniques start studies on detector calibration/alignment (check influence)

Outlook for the near future

write-up of all the above into a Physics-Technical Design Report this will summarize the physics potential of the experiment in great detail foreseen by December 2005 (Volume-I) and by April 2006 (Volume-II)

thanks to all CMS collaborators who contributed to these Standard Model studies

potential for standard model physics with cms at the lhc

Documents

cms data

cms collaborationexample

standard model physics

standard model higgs

accurate simulation

lhcqq tt

real data

b physics