# Presentation: 570281

## Laura Stiles
University of Kansas
23 August 2008

- Laura Stiles
- University of Kansas
- 23 August 2008

## The Compact Muon Solenoid (CMS) Experiment is one of the 4 large experiments of the Large Hadron Collider (LHC) at CERN

**Notes:**
Detectors that we built are part of the CMS
General Purpose detector to study physics at the multi-TeV scale for PP and HI

## Nearly complete angular coverage allows study of wide range of forward physics

- TOTEM  will measure total cross section + multiplicity detectors in front of ZDC

|  Range | Detector |
| --- | --- |
|  < 2.5 | Tracker and Muon System |
|  < 3 | Electromagnetic (EM) and Hadronic Calorimeters |
| 3 <  < 5 | Two forward Hadronic Calorimeters |
| 5.2 <  < 6.6 | CASTOR: Measures EM and Hadronic Energies |
| | (neutral)|> 8.1 | Zero Degree Calorimeters (ZDC): EM and Hadronic Energies |

**Notes:**
CMS cover wide range of angles from low psuedorapidity range there are tracker and muon systems to the very forward ZDC

## Each ZDC located in TAN absorber

- Identical ZDCs at +/- 140m of the collision point

**Notes:**
These ZDCs will be  able to measure N and photons in PP and HI collisions
-140 m away, after beam dipole magnets
-TAN to protect downstream magnets from synchrotron radiation

## N,

- EM has 5 horizontal towers

- HAD section has 4 longitudinal towers

**N,******

- Tungsten to stop beam:
-  Kinetic energy of N,  produces a shower of charged particles which make Čerenkov light in fibers

**Notes:**
b/c of high rad. Environ. ZDC was designed to be simple and robust, modeled after RHIC ZDCs
-high density W used to get efficient conversion photon to charged particle conversion
-Quartz very rad hard
-EM: fibres directly coupled to PMT then travel +140 m to electronics rack

## Measuring Reaction Centrality

**Measuring Reaction Centrality**
- ZDC measures spectator neutrons of
- 	Heavy Ions

- Heavy Ion Data from RHIC

## Triggering on Ultra-peripheral Collisions (UPC)

- UPCs are electromagnetic collisions of the heavy-ions when passing ~20 fm away from each other

**When V = ~C , flux lines collapse traverse to motion**

**At 90****o**** field is 2750 times stronger  **
- (two Pb ions passing at 20 fm → 2 x 10^20 gauss)

- Interesting photon-nucleus and photon-photon studies accessible

**Notes:**
2. Triggering on ultraperipheral collision
-ultraperipheral physics, PbPb don't make contact, make photon field, 
-when hit, send out photons and really excite other nucleus
-at RHIC factor 100 gain, here bigger bc beam energy is so much higher (30 times higher)

## Diffractive Physics

- Quasi-elastic (aka "diffractive") collisions characterized by:
- (i) forward (leading) proton (surviving the interaction),
- (ii) large rapidity gaps, void of hadronic production.
- TOTEM Roman-Pots can be used to tag forward protons from diffractive interactions
- ZDC can tag or veto (neutral) hadronic activity beyond ~8.1 → very valuable to extend rapidity-gap coverage in CMS

**Notes:**
-another funny collision: diffractive physics when colliding  (protons?) dont hit
-think of proton as wave, c
-exchange a pomeron (similar quant numb as photon)
-TOTEM want to see two scattered protons, make sure that no other particles are emitted; look for rapidity gap
-Two scattered protons, pomerons at 90 deg, nothing else should happen.  People looking everywhere else and say that there is nothing- should be nothing in ZDC; an bounce off each other (proton is particle, has wave properties)

## No injection at LHC → no data except 2006 and 2007 beam tests

- Hadronic Section

- EM Section

**Notes:**
Goal to test performance of ZDC; Test electronics chain
Beam extracted from SPS accelerator at CERN

## EM right

**EM right**
**EM left**

**EM2**

- Resolution agrees with simulation.  A.S.Ayan et al., CMS IN2006/28

**Notes:**
7 test beam energies used from 10 to 150 GeV
At 50 geV, res 12%, signal 2000 -> Gaussian Fits to find resolution
Linearity of response: fitted mean energy/beam energy with 2-3% linear
GEANT simulations

## 300 GeV

**300 GeV**

**21.5%**

**(The energy resolution was obtained by Landau fit)**

**EM Signal**

**Hadronic Signal**

**HAD vs EM**

**Notes:**
Since the total energy is conserved there must be an anticorrelation between the signal in the EM section and the signal in the hadronic section. 
-pions at 150, 200, 300, 350; 
-Factor of 2.6 diff in scale, each channel is 2.6 femptocoulombs

## Right and Left ZDC installed in TAN

- Laser injection system used to debug electronics chain
- Currently, we are working on integrating the ZDC into the CMS system
- Injection of CCW beam September 10th
- ZDC should see photons from beam gas collision

## Luminosity Monitoring

- Van der Meer Scans to obtain relative luminosity measurements
- ZDC information will be used with other LHC detectors

- This was used at RHIC to get measurement to 5%. CMS will use the forward calorimeter, ZDC and other detectors to make a 2% measurement.

## ZDCs help meet very important CMS goals:

- Luminosity (p-p, Pb-Pb),
- Heavy-ions physics (centrality, triggering: UPC, ...),
- Diffractive/forward physics (extended rapidity-gap, ...)
- Beam tests showed acceptable performance
- ZDCs are installed, debugged and being integrated to CMS
- Next step will be LHC beam tuning with aid from ZDC
- One proton beam will be circulating S*eptember 10th*

**Notes:**
* Summary:
" ZDCs help meet physics goals for CMS" ---> " ZDCs help meet very important CMS goals: luminosity (p-p, Pb-Pb), heavy-ions physics (centrality, triggering: MB, UPC, ...), diffractive/forward physics (extended rapidity-gap, ...)"

## Slide 15

## CMS ZDCs are located 10x further from interaction point than RHIC ZDCs, but beam is 30x more energetic at LHC

- CMS ZDC has 9x greater acceptance (3x in Px and 3x in Py)

**Notes:**
BACKUP
Acceptance,
-ZDC same size as RHIC, but ten times further away
-beam is 30 times more energetic than RHIC, so in the center of mass frame, Px and Py momentum: our ZDC is 3 times larger in X dimension and Y dimension
-beam energy more than compensates for distance

## KE=200MeV

**KE=200MeV**

**RHIC   62GeV**
**RHIC 200GeV**
**CMS   5.3TeV**

**P****y **
** ****MeV/c**

**• ****neutron**
**• ****proton**

**Beam crossing angle shifts Px acceptance away from zero**

**Notes:**
Green circle: avg. transverse energy of neutrons
Dots rep. Random dist., Positions of protons and N, fermi energy

## 

****

- Luminosity is proportional to rate of coincidence
- Crossing angle tan()=(Xleft - Xright)/240m
- Average X = Xleft +Xright
- Z of interaction = c* (Tleft - Tright)
- For pHe √S = 100GeV so ZDCs should see something

**X**

- EM section is sensitive to p-p bremsstrahlung with Ephoton>20GeV