# Presentation: 894969

## Diffraction at DØ

_**Diffraction at D**__**Ø**_

- Andrew Brandt,  U. Texas at Arlington

- Future QCD Workshop
- May 20, 2004
- Fermilab

## Diffraction/Color singlet exchange

-  Exchange of quantum numbers of the vacuum (no charge or color),
-   often referred to as **Pomeron** exchange

-  Single Diffraction

-  search for rapidity gap in forward regions of DØ
-  Luminosity Monitor
-  Calorimeter

-  Elastic Scattering

-  search for intact protons in beam pipe
-  Forward Proton Detector

- proton track

- rapidity gap

- proton track

-  Hard Diffraction (UA8), SD+high PT

## Learning about the Pomeron 

**  ****QCD** is theory of strong interactions, but **40%** of  total cross section is attributable to **Pomeron**  exchange -- not calculable and poorly understood
-    Does it have partonic structure? **Soft? Hard? Super-hard? Quark? Gluon?** Is it universal -- same in  ***ep***  and      ?  Is it the same with and without** ****jet** production?
-   Answer questions in HEP tradition -- collide it with something that you understand to learn  its structure
-    Note:  variables of diffraction are ***t*** (momentum transfer) and  ****** ~ M****2**
-     (fractional momentum loss) with FPD measure
-     without FPD just measure  

## Luminosity Monitor

**Luminosity Monitor (LM)**
-  Scintillating detector
-  2.7 < |η| < 4.4
-  Charge from wedges on one side are summed:  Detector is **on/off** on each side, North and South

## Calorimeter

**FH**

**EM**

**CH**

**LM**

**2.7**
**LM**
**range**
**4.4**

- Cells arranged in layers:
-  electromagnetic (EM)
-  fine hadronic (FH)
-  coarse hadronic (CH)

**2.6**
**Esum**
**range**
**4.1 - 5.3**

-  Sum E of Cells in
-     EM and FH layers
-     above threshold:
-  EEM > 100 MeV
-  EFH > 200 MeV

- Liquid argon/uranium calorimeter

*(Run I: **n*cal = # cal towers with energy above threshold)

## Slide 6

## Hard Color-Singlet Exchange (central gap)

- Count tracks and EM  Calorimeter Towers in || < 1.0

- jet

- jet

- 

- 

- 

-  (ET > 30 GeV, s = 1800 GeV)

**Measured fraction (~1%) rises with initial quark content **:
***Consistent ***with a soft color rearrangement model preferring initial quark states
***Inconsistent*** with two-gluon, photon, or U(1) models

- Measure fraction of  events
- due to color-singlet exchange

** ****Phys. Lett. B 440 189 (1998)**

- Cox+Forshaw + others subsequently
- found ways to flatten BFKL prediction!

## Why study Diffractive W Boson?

## Observation of Diffractive W/Z

**Observed**** clear ****Diffractively produced W and Z****  ****boson**** ****signals**
**Events have typical W/Z characteristics**
**Background from fake W/Z**
**       ****gives negligible change in gap fractions**

** ****Sample****	****         Diffractive                  Probability Background**
**                                           ****All                  Fluctuates to Data **
- Central W	(1.08 + 0.19 - 0.17)%      	         **7.7******
- Forward W	(0.64 + 0.18 - 0.16)%      	      **5.3******
**All W**		(**0.89 + 0.19 – 0.17)%****	****      7.5******
- All Z	        	(1.44 + 0.61 - 0.52)%      	      **4.4******

- ncal

- nL0

**Diffractive W and Z Boson Signals**

- Central electron W

- Forward electron W

- All Z

- ncal

- nL0

- ncal

- nL0

- Phys. Lett. B 574, 169 (2003)

**Notes:**
Partonic models don’t describe the entirety of the data (give more Forward than Central)
Forward W isn’t described well by any normalization.
Soft Color seems to do best, but not evolved enough
CDF was 3.8sig signal, significant existence for Z even with few events

## DØ/CDF Diffractive W Boson Comparison

- CDF {PRL 78 2698 (1997)} measured RW = (1.15 ± 0.55)% for  ||<1.1 where
- RW = Ratio of diffractive/non-diffractive W  (a significance of 3.8)
- This number is corrected for gap acceptance using MC giving 0.81 correction, so uncorrected value is (0.93 ± 0.44)% , consistent with our uncorrected data value:
**We measured (1.08 +0.19 –0.17)%  for |********|<1.1**
- Uncorrected measurements agree, but corrections derived from MC do not...
**Our measured(*) gap acceptance is (21 ± 4)%, so our corrected value is 5.1% !**
**(*) : derived from POMPYT Monte Carlo **
- Comparison of other gap acceptances for central objects from CDF and DØ using 2-D methods adopted by both collaborations:DØ central jets 18% (q) 40%(g)
- CDF central B  22%(q) 37% overall
- CDF J/  29%
**It will be interesting to see Run II diffractive W boson results!**

##    Run II Improvements

- Larger luminosity allows search for rare processes
- Integrated FPD allows accumulation of large hard
-  diffractive data samples
- Measure , t over large kinematic range
- Higher ET  jets allow smaller systematic errors
- Comparing measurements of HSD with track tag vs.
-  gap tag yields new insight into process

## DØ Run II Diffractive Topics

**Soft Diffraction and Elastic Scattering:**
-     Inclusive Single Diffraction
-     Elastic scattering (t dependence)
-     Total Cross Section
-     Centauro Search
-     Inclusive double pomeron
-     Search for glueballs/exotics
-   **Hard Diffraction:**
-     **Diffractive jet**
-     Diffractive b,c ,t , Higgs
-     **Diffractive W/Z**
-     Diffractive photon
-     Other hard diffractive topics
-     **Double Pomeron + jets**
-     Other Hard Double Pomeron  topics

**Rapidity Gaps:**
-     **Central gaps+jets**
-     Double pomeron with gaps
-     Gap tags vs. proton tags

- Topics in **RED **were studied
- with gaps only in Run I

- <100 W boson events in Run I, >1000
- tagged events expected in Run II

- DØ Run II Diffractive Topics

- In this talk highlight diffractive
- Z boson and elastic analysis

## Calorimeter Energy Sum

- Areas are normalised to 1

- empty events

- physics samples

-  Compare 'empty event' sample with physics samples:
-  Empty event sample: random trigger. Veto LM signals and primary vertex,    i.e. mostly empty bunch crossings
-  Physics samples: minimum bias (coincidence in LM), jet and Z→μμ events

- Log(energy sum) on North side:

- 10 GeV

-  Esum cut of 10GeV was chosen  for current study
-  Final value will be optimised  using full data sample

-  Use energy sum to distinguish proton break-up from empty calorimeter:

## Search for diffractive Z→μμ

-  Inclusive Z→μμ sample well understood:

-  2 muons, pT > 15GeV,   opposite charge

-  at least one muon isolated in tracker   and calorimeter

-  anti-cosmics cuts based on tracks:
-  displacement wrt beam
-  acolinearity of two tracks

- Mμμ (GeV)

## Z Mass of rapidity gap candidates

**Z Mass of rapidity gap candidates**

-   Invariant mass confirms    that these are all    Drell-Yann/Z events
-   Will be able to compare    Z boson kinematics    (pT, pz, rapidity)

**WORK IN PROGRESS**

-  Add Esum requirement:

- Gap North &Gap Southcombined

## First step towards gap: LM only

- cosmics shape
- expected from
- inclusive sample

**WORK IN PROGRESS**

**First step towards gap: LM only**

-  Separate the Z sample into four groups according to LM on/off:

-  Expect worst cosmic ray   contamination in sample   with both sides of LM off
-  no evidence of   overwhelming cosmics   background in LM off samples

## Diffractive Z→μμ candidate

**Diffractive Z****→****μμ**** candidate**

- outgoing proton side

- outgoing
- anti-proton side

- muon

- muon

- muon

- muon

## Z→μμ with rapidity gaps: Summary

**Z****→****μμ**** with ****rapidity gaps: Summary**

-  Preliminary definition of rapidity gap at DØ Run II
-  Study of Z→μ+μ- events with a rapidity gap signature   (little or no energy detected in the forward direction)
-  Current status:
-  Evidence of Z events with a rapidity gap signature
-  Quantitative studies of gap definition, backgrounds, efficiency in progress  (effects could be large)
-  No interpretation in terms of diffractive physics possible yet
-  Plans:
-  Measurement of the fraction of diffractively produced Z events
-  Diffractive W→μν, W/Z→electrons, jets and other channels
-  Use tracks from Forward Proton Detector

## Forward Proton Detector

**Forward Proton Detector (FPD)**

-  **Quadrupole Spectrometers**
-  surround the beam: up, down, in, out
-  use **quadrupole magnets** (focus beam)

- - a series of momentum spectrometers that make use of accelerator magnets in conjunction with position detectors along the beam line

-  **Dipole Spectrometer**
-  inside the beam ring   in the horizontal plane
-  use **dipole magnet**  (bends beam)

-  also shown here:** separators** (bring beams   together for collisions)

- A total of 9 spectrometers composed of 18 Roman Pots

## Acceptance

- Dipole acceptance
- better at low |t|,
- large 
- Cross section
- dominated by
- low |t|
- Combination of Q+D gives double
- tagged events, elastics, better alignment, complementary acceptance

- Actual acceptance more limited due to higher halo backgrounds than predicted  by accelerator div.

## Castle Status

- All 6 castles with 18 Roman pots comprising the  FPD were constructed in Brazil, installed in the Tevatron in fall of 2000, and have been functioning as designed.

**A2 Quadrupole castle **
**installed in the beam line.**** **

## FPD Detector Design

**FPD Detector Design**

- 6 planes per detector in 3 frames and a trigger scintillator
- U and V at 45 degrees to X, 90 degrees to each other
- U and V planes have 20 fibers, X planes have 16 fibers
- Planes in a frame offset by ~2/3 fiber
- Each channel filled with four fibers
- 2 detectors in a spectrometer

- 0.8 mm

- 3.2 mm

- 1 mm

- 17.39 mm

- 17.39 mm

- U

- U’

- X

- X’

- V

- V’

- Trigger

## Detector Construction

- At the University of Texas, Arlington (UTA), scintillating and optical fibers were spliced and inserted into the detector frames.

- The cartridge bottom containing the detector is installed in the Roman pot and then the cartridge top with PMT’s is attached.

## Detector Status

-  **In 2001-2002, 10 of the 18 Roman pots were instrumented with detectors.**
-  Funds to add detectors to the remainder of the pots have recently been obtained
**  **from NSF (should acknowledge funding from UTA REP, Texas ARP, DOE,
-   and Fermilab as well).
-  **During the shutdown **
**  ****(Sep-Nov. 2003), the final eight **
**  ****detectors and associated readout **
**  ****electronics were installed.**
**  ****All 18 pots are routinely inserted**
**  ****near the beam.**

**A2 Quadrupole castle with**
**all four detectors installed**

## Elastic Scattering

-  Measure dN/dt for elastic scattering using incomplete FPD:

-  Quadrupole acceptance:
-  t > 0.8 GeV2 (requires sufficient scattering angle to leave beam)
-  all ξ (no longitudinal momentum loss necessary)

-  proton side:
-  quadrupole ‘down’ spectrometer
-  full detector read-out

-  antiproton side:
-  quadrupole ‘up’ spectrometer
-  trigger only

-  Elastic scattering: ξ = 0

## Elastic Data Distributions

- 

**Events are peaked at zero, as expected, with a ****resolution**** of**
- ****** ****= 0.019**

**dN/dt**

******=********p/p**

- Acceptance
- loss

- Residual halo
- contamination

**The fit shows the bins that will be considered for corrected dN/dt**

## Preliminary Elastic Scattering Results

-  The dσ/dt data collected by  different experiments   at different energies
-  A factor of 10-2 must be   applied to each curve
-  New DØ dN/dt distribution  has been normalized by   E710 data
-  Compare slope with model:  Block *et al*, Phys. Rev. D41,  pp 978, 1990.

## Dipole TDC Resolution

**Dipole TDC Resolution**

- Can see bunch structure of both proton and antiproton beam
- Can reject proton halo at dipoles using TDC timing

- D1 TDC

- D2 TDC

- p

- p halo from
- previous
- bunch

## What’s getting done now

- Seven Ph.D. students in diffractive group based at Fermilab+2 remote
- Analyses underway or just getting started on
- Large samples of SD and DPE jet events with gaps, some of which with FPD tracks
- W/Z +gap and/or track (electron and muon channels)
- J/ψ +gap data  (χc )
- Analyses attempt to measure diffractive structure as f(ξ,t) in many channels
- Search for exclusive production in double pomeron to jets  or  χc  (major foci)
- Updating expectations based on current experience
- Improving trigger capabilites to allow selection of double track events in global list
- Working on background reduction
- Quadrupole detector commissioning

**Notes:**
Elastic cross section is used in measurement of luminosity (discrepancy between D0 and CDF)

## What will likely get done

- Special run to map out |t| down to 0.1-0.2 and perhaps measure total cross section (when detectors fully commissioned)
- Inclusive double pomeron/glueball searches, (when trigger is ready)

## What GTeV could/should do in diffraction

- focus on double pomeron topics
- best possible acceptance for low+high mass
- diffractive measurements in regions of phase space without acceptance in Run II, or where statistics insufficient

## Summary and Future Plans

**Early FPD stand-alone analysis shows that detectors work,**
**    ****will result in elastic dN/dt publication (already 1 Ph.D.)**
**FPD now integrated into DØ readout (detectors still work)**
**Commissioning of FPD and trigger in progress**
-  **Tune in next year for first integrated FPD physics results**

**Notes:**
Elastic cross section is used in measurement of luminosity (discrepancy between D0 and CDF)