Recent results of the CMS experiment QFTHEP2015 The 22 th International Workshop on High Energy...

Recent results of the CMS experiment

QFTHEP2015The 22th International Workshop on High Energy Physics and Quantum

Field Theory, Samara (Russian Federation)

Dr. Bora Akgün – Rice University(on behalf of CMS Collaboration)

Recent Results of the CMS Experiment - [email protected]

2

Outline

25 June 2015

• CMS - Data Collection• Selected Results• Vector Bosons – arXiv:1505.06520, arXiv:1503.05467• Quarkonia – PRL 114 (2015) 191802, arXiv:1501.07750• Rare Decays – Nature 522 (2015) 68• Top Physics – arXiv:1505.04480• SUSY – arXiv:1502.06031• Exotica – arXiv:1502.04994• What to expect from Run2 and beyond

• Summary


3

CMS Detector

25 June 2015


4

Data Collection

25 June 2015

• Results presented in this talk have been produced with LHC Run-1 data collected by CMS experiment

• CMS Public Results twiki• https://twiki.cern.ch/twiki/bin/view/CMSPublic/PhysicsResults

https://twiki.cern.ch/twiki/bin/view/CMSPublic/PhysicsResults









5

CMS Standard Model Summary Plot

25 June 2015

Great agreement btw theory and measurements


6

Vector Bosons

25 June 2015

• W and Z can be measured very accurately through their leptonic decays, photon energies precisely measured in the electromagnetic calorimeter

• Z and photons used for calibration of jets, Z used as a candle to determine lepton efficiencies

• Vector boson plus jets are major backgrounds in beyond standard model searches and excellent testing ground for QCD NLO predictions

• Diboson processes (ZZ and γγ) are major SM backgrounds for Higgs measurements

• WZ and ZZ w/ Zνν major contribution to backgrounds in searches w/ large missing transverse energy (e.g. SUSY)


7

Z+jets / Photon+jets

25 June 2015

Z+jets

Photon+jets

• V+jets are major backgrounds in beyond standard model searches and excellent testing ground for QCD NLO predictions

arXiv:1505.06520

njet≥1


8

Z+jets / Photon+jets

25 June 2015

• The ratio of Z + jets to γ + jets• Both simulations reproduce the shape

of the ratio better than the individual distributions in all selections

arXiv:1505.06520

njet≥1

njet≥2


9

Production cross-section for ZZllνν

25 June 2015

• ZZllνν production cross section measured • Using a profile likelihood fit to the reduced-ET

miss • Main backgrounds

• DY, WZ, WW,W+jets,top• σ(ppZZ) = 5.2+1.5

-1.4(stat)+1.4-1.1(syst)±0.2(lumi)pb at 7 TeV

• σ(ppZZ) = 6.9+0.8-0.8(stat)+1.8

-1.4(syst)±0.3(lumi)pb at 8 TeV

• Theory calculations w/ NLO QCD and NLO EW

• σ(ppZZ) = 6.2+0.3-0.2 at 7 TeV

• σ(ppZZ) = 7.6+0.3-0.3 at 8 TeV

arXiv:1503.05467


10

Production cross-section for ZZllνν

25 June 2015

• ZZγ and ZZZ expected to be null at the tree level• Enhancement in ZZ production rate compared to SM indicate the existence

of anomalous boson couplings

arXiv:1503.05467

• No observation of new physics stringent limits on the relevant Anomalous Triple Gauge Coupling (ATGC) parameters


11

Charmonium spectrum

25 June 2015

cross sections and polarizations

cross section ratio

observation, cross section

observation with > 5σ


12

Prompt ψ(ns) cross-sections

25 June 2015

• Yields are corrected for efficiency and acceptance on an event-by-event basis

PRL 114 (2015) 191802


13

Prompt ψ(ns) cross-sections

25 June 2015

• Yields are corrected for efficiency and acceptance on an event-by-event basis

• Four polarization scenarios are considered • PT reach is extended compared to previous measurements • FKLSW band is obtained in a fit to previous data w/ essentially PT <

30 GeV and extrapolated to higher PT values

PRL 114 (2015) 191802

un-polarized scenario

un-polarized scenario


14

Bottomonium spectrum

25 June 2015

cross sections and polarizations cross section ratio


15

ϒ(ns) differential cross-sections

25 June 2015

• Acceptance calculated w/ polarization values measured by CMS (PRL 110 (2013) 081802)

• PT reach is extended compared to previous measurements

arXiv:1501.07750

ϒ(2S), ϒ(3S) scaled by 0.1, 0.01, respectively

NRQCD


16

ϒ(ns) production ratios

25 June 2015

arXiv:1501.07750

• Exponential fit – 10 < PT < 20 GeV• Power-law fit – PT >20 GeV• Change in ratios occur at the same PT range

in which dσ/dPT also changes behavior


17

BS0μ+μ- and B0μ+μ-

25 June 2015

• SM predicts small branching fractions for BS0μ+μ- and B0μ+μ-

• Direct flavor-changing neutral currents not possible in SM, theories beyond SM predict larger branching fractions

Nature 522 (2015) 68


18

First observation - BS0μ+μ- (CMS

& LHCb)

25 June 2015

• Weighted distribution of dimoun mass-spectrum, superimposed in a combined fit• First observation of BS

0μ+μ- (6.2σ) and evidence for B0μ+μ- (3.2σ)

Nature 522 (2015) 68


19

Combined result - BS0μ+μ- (CMS

& LHCb)

25 June 2015

• Likelihood in BS0μ+μ- vs B0μ+μ- branching ratio plane

• BR: BS0μ+μ- = 2.8+0.7

-0.6 * 10-9 (0.76+0.20-0.18 * SM)

• BR: B0μ+μ- = 3.9+1.6-1.4 * 10-10 (3.7+1.6

-1.4 * SM)

Nature 522 (2015) 68


20

Top mass measurements

25 June 2015

• The most massive particle known to date

• Very short lifetime shorter than hadronization timescale

• The only elementary high mass particle that has color• EWK, QCD and flavor physics

• Combined top mass using all CMS Run-1 data• 172.38±0.10(stat.) ±0.65(syst.) GeV


21

ttbar production cross-section at 7/8TeV

25 June 2015

• ttbar production cross-section measured w/ different channels at 7 and 8 TeV

• ttbar is a major background for many processes


22

ttbar differential measurements

25 June 2015

• MC generators predict harder dilepton mass and lepton PT spectrum than observed in data• Powheg+Herwig6 provide a satisfactory agreement • 8 TeV results are input for future MC tuning

arXiv:1505.04480


23

SUSY searches

25 June 2015

• SUSY, popular BSM theories• Solves the hierarchy

problem• Provides a suitable

dark matter candidate• SUSY corrections

allow for high energy unification of strong and electroweak couplings

• Searches involve typically the presence of large missing transverse energy and multijets


24

SUSY search w/ two leptons, jets and ET

miss

25 June 2015

arXiv:1502.06031

• The invariant mass distribution of the two-lepton system can exhibit an excess that increases with the di-lepton mass, followed by a sharp decrease, if the two leptons originate from the decay of a neutral particle decayed from a bottom squark-antisquark production

1. Mass difference btw Χ20 and Χ1

0 fixed to 70 GeV

2. Mass of the slepton chosen to lie halfway btw the masses of Χ2

0 and Χ10

• Lepton pair from the decay of an o-shell Z boson from gluino pair production

1

2

3

3.


25


miss

25 June 2015

Mll> 20 GeVNjets ≥ 2

arXiv:1502.06031

Low mass significance: 2.6σNo evidence for a statistically

significant signal


26


miss: setting limits

25 June 2015

arXiv:1502.06031


27

Exotica: Narrow high-mass resonance decaying to Z and H

25 June 2015

arXiv:1502.04994• A search for a highly massive ( ≥ 0.8TeV) and narrow

resonance decaying to Z and H bosons that decay in turn to merged dijet and ττ final states• τ decaying leptonically and hadronically

• Advanced reconstruction techniques in boosted topology• Main backgrounds (simulated in MC)• Z+jets/W+jets• Ttbar, single-t• ZZ,WW,QCD

• Main source of uncertainty: limited MC statistics for signal efficiencies and background estimation


28

Exotica: Narrow high-mass resonance decaying to Z and H

25 June 2015

arXiv:1502.04994

• From a combination of all possible decay modes of the τ leptons, production cross sections in [0.9-27.8fb] depending on the resonance mass [0.8-2.5TeV], are excluded at a 95% CL


29

What have we been doing lately?

25 June 2015

• Finishing analyses w/ 2012 data • Many results and publications (≥400), more to come..

• Long Shutdown (LS) – 1: 2013-2015• Fixes and upgrades to CMS detector

• Pixel detector taken out, misbehaving channels (~5%) fixed and installed back to CMS• w/ an additional part - pilot system w/ upgrade

electronics and readout• Muon detectors

• New stations (CSC/RPC) to complete redundancy, new electronics for triggering

• Narrower beampipe• Preparation for upgrade pixel detector in 2017

• Re-commissioning of the detector for Run-2


30

Detector Improvements for Run 2

25 June 2015

Muons• Completion of forward detector

• 4th layer in ME• RPCs to |η|=4

Tracker • at -200C• Pixel Pilot System

New Beam pipe


31

13 TeV Collisons

25 June 2015

• June 3rd: First collisions at the new center of mass energy


32

LHC plan for 2015

25 June 2015


33

What to expect in Run-2?

25 June 2015

• EW & Quarkonia• Improve on precision w/ higher statistics

• Top• Increase mass precisions w/ better jet energy scale

systematic uncertainties• Use boosted reconstruction techniques to perform

differential cross-section measurements• Improve precision on ttZ, ttW, ttH cross-sections

• Higgs• Look for deviations from SM w/ higher precision

• SUSY• Discovery?

• ??


34

Summary

25 June 2015

• Only a small portion of results out of the rich long list of measurements performed by CMS

• In general predictions provide a good description of data• CMS is ready for Run-2 data taking (already started)• Sophisticated reconstruction techniques, analysis tools,

analysis methodologies and interpretation approaches have been developed and matured during the previous years

• Exciting times ahead of us

Date post:	03-Jan-2016
Category:	Documents
Upload:	hollie-sullivan
View:	214 times
Download:	0 times

Recent results of the CMS experiment QFTHEP2015 The 22 th International Workshop on High Energy...

Documents