# Presentation: 476618

## CMS 2008:2014

**CMS 2008:2014**
** ****Michael Murray**

**Athens,Basel, CERN, Demokritos, Dubna, Ioannina, Kent State, Kiev, Lyon, MIT, Moscow, N. Zealand, Protvino, PSI, Rice, Sofia, Strasbourg, *****Kansas,***** Tbilisi,**
** ****UC Davis, UC Riverside, UI Chicago, U. Iowa, Yerevan, Warsaw**

## Are our projections reliable? 

**“*****There are known knowns. These are things we***
***know that we know. There are known unknowns.***
***That is to say, there are things we know we don't***
***know. But, there are also unknown unknowns.***
***These are things we don't know we don't know.”***
- Donald Rumsfeld  Washington 2002

- “These theories (this talk) ain’t worth a
-  bucket of worm piss”
- Bill Willis CERN Council 1982

**It’s the unexpected stuff that is fun.**

## Muons

**Hadron Calorimeter**

- Cyrostat

- EM

- Tracker

**A Generic Detector**

**17 pp collisions each 25ns = 20% of a PbPb collision**

## What do we want to run?

- The first pp collisions should be  April 2007 and
- PbPb expected one year later. Each year expect
- several weeks of ion beams (106s effective). The
- CERN HI community wants a short exploratory
- run in 2007 Future includes other ion species and
- pA. Start off with surveys of such as  flow, J/ etc.
- We will then move onto statistics limited
- measurements such as, , high pT, jets, and
- correlations of jets with  and Z.

## It is vital to understand pp well

- At RHIC we had
- some idea what to expect but still had to learn pp. At LHC pp √S is 7 times greater than FNAL.

## Measure leptons, hadrons & neutrals 

## Abundant hard probes

**Abundant hard probes**

****

**J/******

## Balancing  or Z0 vs Jets: Quark Energy Loss 

**Balancing ******** or Z****0**** vs Jets: Quark Energy Loss**** **

**Notes:**
Only calorimeter isolation. Pi0 will also be suppressed. Can tracker to suppress background also. 

## Di-muon mass

**J/******

****

_**AA **_
**pp**

****

**J/******

**Energy Density (GeV/fm****3****)**

- m = 50MeV for the ******.**

**Notes:**
J/psi increases by factor of 10 with trigger.

## Jets in the calorimeters: ||<5

- 100 GeV Jet

- PbPb dN/d =5000

## Jet Reconstruction

**Jet E****T ****(GeV)**

******E ****%**

**Eff %**

- 1. Subtract average pileup
- 2. Find jets with sliding window
- 3. Build a cone around Et***max ***
- 4. Recalculate pileup outside the cone
- 5. Recalculate jet energy

***Spatial resolution***:
-  ********** ****= 0.045  ************ ****= 0.051**** **

**Jet Reconstruction**

**Notes:**
Olga will send new plots from Irena.

## Use calorimeters and tracking to  measure V2

******=0.1 ****rad**

**Event plane determination**

- CMS

**Notes:**
Pixel hits is ideal v2., energy dependence of V2, perhapsw V2 J/psi

## Fragmentation & hydrodynamics 

_**dN**_
**d********N****partD**

- Calos cover 14 units of 

## Event by Event Multiplicity (and ET)

**PHOBOS: ****Single Layer ~15000 channels **

**CMS: ****Three Layers **
**~60 Million channels **

****

**dN/d******

- Min pT=26 MeV

## Measure multiplicity on day 1

**Extrapolated to LHC:**
**dN/d********~1400**

## Evidence for Saturation

- _NdAu_
- _N__pp_

## Kinematics at the LHC

**Kinematics at the LHC**

- J/

- Z0

- Saturation

- Gluon density has to
-  saturate at low x

****

- Access to widest range of Q2 and x

## Where do the protons go?

- At RHIC the protons lose about two units of rapidity.

**Rapidity Loss**

**Beam Rapidity**

- CASTOR covers
- 5< <7. This should cover the maximum baryon density

**Notes:**
Start top right data. Peaked is gaussian, black gaussian. Don’t talk about assumptions. Sum = Npart=175

## At zero degrees study energy flow and trigger on ultraperipheral 

**At zero degrees study energy flow and trigger on ultraperipheral**

- ~7*107 J/ and  can be made

**Notes:**
5-70 mbars. PbPb Upsilon cross section is 78-
133  microbarns.

## Fragmentation    of jets

**Fragmentation    of jets**

**A jet covers ~ **
**9000 crystals**

- pTjet

- _dN_
- dpTjet

- _dN_
- dZ

## Physics Goals of CMS 2008:2014

- Observe the _***weakly interacting ***_QGP. This state *may* be characterized by a collapse of directed flow, thermalization of charm and stronger energy loss. Use jets,  resonances Z0 and photons to measure its properties.  Pin down the _***color glass condensate ***_by measuring the saturation scale as a function of rapidity (x) and system size. Be ready for ***unknown unknowns. ***

**Notes:**
Check with anyone who might help?

## Backups

## Si Tracker Performance with Heavy Ions

**6 layers**
**Outer**
**Barrel**

**4 layers**
**Inner**
**Barrel**

**1 Single Detector**

**2 Detectors Back to Back**

- Pixel Layers Crucial for Heavy Ions

## pT Inside a Jet

- 100 GeV

## Heavy Ion Trigger

- Main types of trigger as required by physics:
- multiplicity/centrality:”min-bias”, “central-only”
- high pT probes: muons, jets, photons, quarkonia etc.
- High occupancy but low luminosity !
- many low level trigger objects may be present, but less isolated than in p+p, Level 1 might be difficult for high pT particles
- but we can read most of the events up to High Level Trigger and do partial reconstruction
- HLT for HI needs significant software/simulation effort.

**L1**

**HLT**

## Tracking works well for pT > 1GeV 

## Refinement of RHIC results at the LHC: What lies beyond ?

**Refinement of RHIC results at the LHC: ****What lies beyond ?**

- Many phenomena measured at RHIC have surprisingly simple energy dependence, will this continue at the LHC ?
- Hydrodynamic limit, will it hold?

**dN****ch****/d********/<N****part****>/2**

*Flow*

*Charged particle multiplicity, scaling, limited fragmentation*

## CASTOR and Totem T2

-               **CASTOR**
-          **5.32 **_**<**_** η **_**<**_** 6.86**

- 	       T2 Tracker
**                 ****5.32 **_**<**_** η **_**<**_** 6.****71**

**CASTOR and Totem T2**

- Forward coverage:
- Access to region of relatively high baryon density in HI collisions
- Study diffractive & low-x (<106) Physics in p-p interactions

## ZDC integration with TAN

## Level-1 Trigger

- Fast algorithms: 3 s with coarse local data
- Only Calorimetry and Muon Detectors
- Special purpose hardware (ASICS)
- Centrality with ECAL, HCAL (including HF)
- ZDC for minbias.
- Trigger on e, , jets, Missing ET. Rates steep function of pT thresholds
- AA higher backgrounds

## High Level Trigger (HLT) 

- All event data available:
- Fine data for Calorimetry and Muon Detectors
- Tracker
- Refine triggered object
- Allows to go lower in pT
- Processing time O(s)
- Filtering Farms of commodity processors (Linux)

- L1 in AA has larger backgrounds than in pp due to underlying event.
- Efficiency trigger requires more careful analysis. _HLT can do a better job than L1_.
- HLT to play a greater role in AA

## Illustration Of Online Farm Power: Low pT J/ψ

- Only a small fraction of produced J/ψ are seen in LHC detectors
- E.g. CMS J/ψ→ acceptance 0.1-0.2%, ~O(104) per LHC run
- Detection of low pT J/ψ requires efficient selection of low momentum, forward going muons. Simple hardware L1 dimuon trigger is not sufficient

| L1 trigger | Two  | 60 Hz |
| --- | --- | --- |
| L2 trigger | None | 60 Hz |
| L3 trigger | None | 60 Hz |
| J/ψ pT  |  | >3 GeV/c |

| L1 trigger | Single  | ~2 kHz |
| --- | --- | --- |
| L2 trigger | Re-fit  | 70 Hz |
| L3 trigger | Match tracker | <40 Hz |
| J/ψ pT |  | >1 GeV/c |

**Without online farm (HLT)**

**With online farm (HLT)**

******

**Online farm**

***p******T***

**Online farm**
**Improvement**
**Acceptance x2.5**

## Calorimetric Jet reconstruction

***PILE UP   SUBTRACTION    ALGORITHM***

***Jet spatial resolution***: (**rec****- ********gen****) = 0.032;**  (**rec****- ********gen****) = 0.028**** **
**      ****It is better, than ******,  ** size of tower (0.087 x0.087)**

***  ******Measured jet energy***

***  ******Efficiency,   purity***

***Jet energy resolution***

**Calorimetric Jet reconstruction**

## CMS coverage

## Finding charged tracks

- Occupancy in central Pb+Pb Event:
- 1-3% in Pixel Layers
- Up to 70% in Strip Layers @ dNdy 7000

- Efficiency and fake rates

## Jet fragmentation

**Jet fragmentation**

- Longitudinal momentum fraction z along the thrust axis of a jet:

- pT relative to thrust axis:

- Using ECAL clusters~0 in CMS

- Fragmentation function for 100GeV Jets embedded in dN/dy ~5000 events.
- Use charged particles and electromagnetic clusters