# Presentation: 497669

## Intnl. Conf. on Particle Physics

**CMS Physics**
**Dan Green**
**Fermilab**

## Higgs Cross Section

**CDF and D0 successfully found the top quark, which has a cross section ~ 10****-10 ****the total cross section.**
**A 500 GeV Higgs has a cross section ratio of  ~ 10****-11****, which requires great rejection power against backgrounds and a high luminosity.**
**Rate = luminosity * cross section**
**LHC has ~ 20 times the luminosity of the Tevatron and 7 times the energy.**

## Outline

**Establish the Standard Model (100 pb****-1****)**
**Minbias, Underlying event**
**Dijets and balance, photon + J**
**B tagging**
** ****Dilepton resonances: ****ψ****, ****Υ****, W, Z – mass scale and resolution**
**Top pairs**
**Tau**
**Look for the new along the way ( 1 fb****-1****)**
**Excited quarks**
**W’, Z’ in dileptons**
**Diphoton gravitons**
**SUSY spectroscopy ( dark matter )**
**Then a jumping off point ( > 10 fb****-1****)**
**Higgs**
**V+V Scattering**
** ......****.**

## Typical Statistics for a 10 TeV Run

**Assume 200 pb****-1****, include acceptance, initial reconstruction and id efficiency**
**Establish Standard Model cross sections and distributions**
**Log ~ 200 pb****-1**** at 10 TeV in 2009. This should be reliable data taking without Physics penalty for masses < 2 TeV**

| min bias | 2 x1013 |
| --- | --- |
| Jet Et>25  | 6 x 1011 |
| Jet Et>140 | 6 x 107 |
| +Jet Et>20 | 6 x 107 |
| W ->l | 600,000 |
| Z -> ll | 60,000 |
| tt-> l4q | 2000 |

## 2009, Rediscover the SM

| L for 1 month run (106 sec) | Integrated L | Trigger | Process | Comments |
| --- | --- | --- | --- | --- |
| 1023 | 100 mb-1 | None
I~ 50 mb | Inelastic
non-diff | Input to tweak Pythia |
| 1024 | 1 b-1 | Setup Jet | Inelastic
non-diff | Calib in azimuth |
| 1025 | 10 b-1 | Jet
(gg) ~ 90 b
(ggg) ~ 6 b | g+g -> g+g
g+g -> g+g+g | Establish JJ cross section |
| 1026 | 100 b-1 | Jet | g+g -> g+g
g+g -> g+g+g | Dijet balance for polar angle – Establish MET |
| 1027 | 1 nb-1 | Jet
Setup Photon
(q) ~ 20 nb | g+g -> g+g
g+g -> g+g+g
q+g -> q+  | Dijet masses > 2 TeV, start discovery search.
J+ calib |

## Minimum Bias Events

**Use dE/dx in the CMS tracking system to do particle identification. Extract the charged particle cross section vs. particle type as a function of y and Pt**
**Useful for overlap to simulate high luminosity pileup.**

## The Underlying Event

**Extrapolation of the UE is uncertain. The UE is crucial for trigger strategy – e.g. lepton isolation. Must tune the CMS Monte Carlo to have a valid representation of the UE**

## Dijet Balance

**Dijet Balance**

**Use azimuthal symmetry for “rings” in y. Use dijet balance for equalizing the rings.**
**We can quickly equalize at “ low Et” until we run out of statistics.**
** **

## Photon + Jet Balance

**Photon + jet balance analysis is ready for data**
**Ready to combine ******** + jet and Z + jet  and extrapolate using the MC**
**Z + jet balance will give valuable confirmation but samples will be small**

## Jets and Dijets

**Establish low Pt cross section, mass distribution and angular distribution. Then look at high mass. Discovery possible very quickly - ~ 3 TeV for 100 pb****-1**

## LHC – 2009 Run, 10-100 pb-1

| L for 1 month run | Integrated L | Trigger | Process | Comments |
| --- | --- | --- | --- | --- |
| 1028 | 10nb-1 | bB ~ 600 nb. Setup – run single electron, muon, photon | g+g -> b+B

          | 900,000 JJ, 6000 bB,
1200 1, 60 2
Establish  jet tag
80 2e and 2 events from  |
| 1029 | 100 nb-1 | Setup dimuon, dielectron
v ~ 10 nb | 
q+Q->W->+v
(D-Y)
        | 
1000   from W-> + v
Lumi – standard candle (look at high Mt tail)
100 2e and 2 events from Υ |
| 1030 | 1 pb-1 | Run dilepton trigger
 ~ 1.5 nb
tT ~ 630 pb | q+Q->Z->+
(D-Y)
g+g->t+T | 1500 dimuons from Z-mass scale, resolution
Lumi- standard candle, high M
600 t + T produced |
| 1031 | 10 pb-1

End of ’07
Pilot Run | Setup, J*MET
q ~ 40 pb
 ~ 24 pb | 
g+q->Z+q->++q
q+Q->+- (tree)

             | 400 Z + J events with Z->dimuons –  Z+J balance, calib
Estimate J + MET ( q + v )
240 diphoton events with M > 60 GeV
6000 t + T
150 Z->tau pairs into dileptons > 8 GeV * MET > 15 GeV |
| 1032 | 100 pb-1 | qQZ ~ 170 pb
qgZg ~ 32 pb

tT ~ 630 pb | g+g->q+Q+Z
g+q->q+g+Z+g | 3000 J+J+Z->vv events, Pt>30
500 J+J+Z->+ events, Pt>30
600 J+J+J+Z->vv events
10000 J+J+J+J++v events |
| 1033 | 1 fb-1 (1% of  design L for 1 yr) End of ’08 Physics Run |  |  | M of dijet in 100000 top events, W->  +v – set Jet energy scale with W mass. Dimuon mass > 1 TeV, start discovery search, diphoton search, SUSY search |

## Heavy Stable Particles?

## B Tagging

**Identify b Jets using Pt relative to jet axis. Tracking alignment crucial.**
**Establish b tagging. Check with top pair events. **

## Psi Production

**Largest cross section resonant dilepton state. Set momentum scale for tracker. Note the cross section scale is nb.**

## Upsilon Calibration – D0

**Cross section * BR about 1 nb. Resolve the spectral peaks? Mass scale correct?**
**Moving to higher P scale.**

## W Production - Muons

**Check W cross section and y distribution. The PDF predictions are quite constrained. Charge asymmetry is a ratio – many efficiencies cancel out. The cross section is ~ 20 nb.**

## W Production - Electrons

## W’ Search

**With SM W in hand, look in BW tail of the W. At 100 pb****-1****, the W’ mass limit is ~ 2 TeV**

## Z Production - Muons

**SM Z – check mass scale, Z resolution, width and FB Asymmetry. Use Z signal for “tag and probe” to get lepton efficiencies.**

## Z Production - Electrons

**The dilepton “tag and probe” – extract data driven efficiencies for leptons – e.g. e trigger efficiency. Backgrounds are small so purity for tagging is very high.**

## Calibration Validation - Photons

**Zee mass peak useful to test “********-symmetry” in EE **
******0**** peak: in EE (insufficient for EB: small energy & opening angle) **
******0************ee (Dalitz): electrons well measured in TK (low pt)**
**************: rate 1/20 of ********0************ but better mass resolution**

- JETET20 – CSA08
- PRELIMINARY

## Z’ Search

**Having established Z decays into dileptons, look in the BW tail of the Z for new physics. At 100 pb****-1**** start to probe the “terascale” – masses ~ 2 TeV.**

## Missing Transverse Energy

**Establish MET with SM processes: e.g. W leptonic decay, Z -> v + v and top decays. When validated use MET as a tool for probing new physics. Use particle flow and tracking information to improve MET resolution by ~ 2x.**

## Irreducible SM MET Background

**Z -> v + v is irreducible. Use leptonic Z decay to estimate (low statistics) or use photon as a signal which is dynamically similar to Z.**

## Top - Dileptons

**Establish top pair SM signal in dilepton final state – clean but low statistics. Top has SM “candle” with leptons, jets, MET and b jets.**

## Top – Jets + Leptons + MET

**Check jet energy scale with hadronic decay of the W. Check b tag efficiency with 2 b in final state. Establish MET scale.**

## Z Decay to Tau Pairs - Collinear

**                                                 **
**                                                                 **

**SM “candle” for tau – third generation lepton important in many BSM scenarios.**
**Assume collinear neutrinos. Then have 2 Eqs in 2 unknowns. Must cut on determinant**
**|det|>0.005 is ~ 70% efficient after cuts on Pt of the leptons and MET.**

## Di-lepton Search for Z -> 

**Having established clean electron, muon and tau “objects” a look at di-lepton masses can be taken with some confidence. The top pair background dominates the dilepton mass spectrum at high masses - SUSY****.**

**Tevatron**

## CDF - Diphotons

**Mass spectrum explored to ~ 300 GeV. Large increase in mass reach at the LHC****.**

-       COMPHEP – tree diagrams

## Di-photons at High Mass

**Gravity couples to all mass “democratically”. Therefore look at rare processes with SM weak couplings. LHC will be in new territory by 100 pb****-1****.**

## SUSY  MSSM Mass Spectrum

**Why SUSY?**
**GUT Mass scale - unification works with SUSY**
**Improved Weinberg angle prediction**
**p decay rate slowed consistent with present limits.**
**Mass hierarchy  protected Planck/EW**
**Dark matter candidate**
**String connections, local SUSY and gravity.**

**MSSM has ~ SM light h and ~ mass degenerate H,A. LSP is a neutralino. Squarks and gluinos are heavy, sleptons are light.**

## GUT and Evolution of 

**SUSY particles intervene at masses ~ (100,1000) GeV. The modified loop running improves the convergence at the GUT mass.**

**M****GUT**** = 2 x 10****16**** GeV and 1*****/************GUT***** ~ 24**

## SUSY Cross Sections

**The SUSY cross sections for squarks and gluinos are large because they have strong couplings. R parity means cascade decays to LSP. Simplest signature is  jets and MET, independent of specific SUSY model.**
**Dimensionally**
****** ****~ ********s****2****/(2M)****2 **
**or ~ 1 pb  for M = 1 TeV.**

## SUSY and 2009 Run

**Energy is important. Quickly surpass Tevatron discovery reach**.

## Getting to the Terascale

**Very early for SUSY CMS will exceed the CDF/D0 mass reach –  for strongly produced squark/gluino even in 2009 at 100 pb****-1****.**

## Sparticle Cascades

**Use SUSY cascades to the stable LSP to sort out the new spectroscopy.**
**Decay chain used is :**
**Final state is**

## SUSY Reconstruction 

**Mass of         from MET, then others from observed decay products.  Earliest searches are with jets + MET, semi-inclusive. Here use dilepton end point? Note plots are for 1 year at 10% of design luminosity.**

## SUSY Signatures

**The gluino pair production cascade decays to jets + leptons + missing Et. Gluino is a Majoran, like sign ~ same sign for dileptons**
**The gaugino pairs cascade decay to missing Et + 3 leptons which is a very clean signature, but with smaller cross section **

## Dilepton Kinematic Edges

**Edges give mass information. Signals for 1 fb****-1****. Use flavor of lepton and charge pairing to extract signal (Majorana)**

## Cosmology and CMS

**The universe is flat and composed largely of dark energy (73%) and dark matter (22 %). What are they? We understand only about 5% of the Universe by weight !**

## Dark Matter ?

**There is no SM candidate. Can we produce DM in CMS? Is it the SUSY LSP? Searches at LHC, in direct (recoil) measures and in annihilations (e.g. GLAST) may find new aspects of DM**

## Dark Matter and SUSY

**Boltzmann Eq. Freezout of relic when annihilation rate ~ expansion rate.**

**Neutralino annihilation rate into quark pairs. A weakly interacting particle with a mass (100, 1000) GeV has the correct relic density to be dark matter. Thus DM ( lensing, rotation curves), plus cosmology (thermal relic) implies a weakly interacting, TeV scale stable (R parity) object. Can we be more incisive? What is the thermally averaged annihilation cross section times velocity?**

## Dark Matter and SUSY

**It may be a big hint that a SUSY LSP with a mass O(TeV) with a weak cross section (neutralino ?) decouples from the Big Bang expansion to give roughly the correct relic density to be “dark matter”. The hope is then to produce and detect dark matter at the LHC. The memory of the Big Bang is stored in the vacuum waiting to be reignited at the LHC.**

**SUSY = dark matter?**

## LEP,CDF D0 Data Indicate Light Higgs – 2009 and Beyond

**W         t        W**

**b**

**W        H        W**

**W**

**Quantum mechanics: traces of higher mass states are seen in radiative corrections due to virtual quantum loops, e.g. Lamb shift in atomic spectrum due to virtual e pairs. Note sign – fermion, boson (Quantum Amplitude – phase matters) - SUSY. Data indicates light Higgs.**

## Early Physics Reach - 2009

**CMS was designed to find the SM Higgs boson at design luminosity in less than 1 year ( 100 fb****-1****).**

## Is There a Quark-Gluon Plasma?

**The LHC and CMS offer a ~ 35 fold increase in C.M. energy for heavy ion collisions w.r.t. RHIC. Will that allow the formation of a true plasma?**

## Summary

**CMS is ready for data taking in 2009**
**We will first re-establish the Standard Model through a variety of “standard candles”. **
**While doing this we will make multiple searches for new Physics at a scale ~ 2 TeV.**
**At higher luminosities ( > 2009?) the exploration of the TeV scale**** ****will become even wider and more inclusive. **

## SUSY – Squark/Gluino Mass “Reach”

**SUSY – Squark/Gluino Mass “Reach”**

**WMAP**

**1 year at 1/10 design luminosity.**
**SUSY discovery would happen quickly.**

## Region explored for Low Mass SUSY

## SUSY - Discovery

- backgrounds

- SUSY
- 600 GeV
-  squark

**Assuming a conserved SUSY quantum number, the lightest SUSY particle (LSP) is stable. A neutral weakly interacting LSP escapes the detector. Dramatic event signatures ( cascade to LSP -> jets + Missing Et) and large cross section mean we will discover SUSY quickly, if it exists.**

**Notes:**
So, as I said in the introduction, the other question that the LHC was designed to adress about the standard model is whether supersymmetry is the reason the higgs can be light.  I for one hope it is, because not only is SUSY theoretically beautiful, but it provides the kind of dramatic event signatures that are a real pleasure for an experimentalist to analyze.  For example, even a simple variable such as the scalar sum of the PT of the neutrinos and jets gives good discrimination between signal and background.

## Sparticle Masses

**Sparticle Masses**

- Sequential
- 2-body decay:  edge in M*ll*

**10 fb****-1**

**An example of the kind of analysis done, from 1 year at 1/10****th**** design luminosity.**

**Notes:**
By a year, we’ll be doing sophisticated analyses to identify and measure the masses of the lighter sparticles.  Here is an example of an analysis that uses the mass distributions from di-lepton events to get a jacobian whose leading edge is related to the mass of the second lightest neutralino.  Events with two different types of leptons are used to estimate the background distribution, which is subtracted.  

## Heavy Stable Particles

**Use tracker with dE/dx vs. P and TOF. Also have a TOF measure in the Muon subsystem. Plots shown for a 500 GeV SUSY top.**

## Production of SUSY Particles at LHC is dominated by gluinos and squarks
The production is followed by a SUSY+SM cascade.

**The production is followed by a SUSY+SM cascade.**

**SUSY Cascades**