status of diffractive physics at dØ run ii

$: Status of Diffractive Physics at DØ Run II$
Low_x 2004 - Prague 1Jorge Barreto

Status of Diffractive Physics at DØ Run II

Status of Diffractive Physics at DØ Run II

Jorge Barreto

Instituto de Física - UFRJ

Rio de Janeiro – RJ - Brazil

Outline

Color Singlet Exchange

Diffractive Z Production

The FPD: Diffractive Scattering

Conclusions


Color Singlet Exchange (Diffraction)Color Singlet Exchange (Diffraction)

The Tevatron collides protons and antiprotons at √s = 1.96 TeV at a crossing rate of 1.7 MHz

About 40% of the total pp cross-section is elastic or diffractive scattering Diffractive processes involve the exchange of a color singlet:

– Quantum numbers of the vacuum – Often referred to as Pomeron exchange

Diffractive studies used to probe nature of the Pomeron

p

I

p

J1

J2

X

X

X

P

Experimental Signature– Rapidity Gap: absence of particles or

energy above threshold in some region of rapidity in detector

– Tagged proton: p or p scattered at small angle from the beam measured in a detector far from the interaction

(pf )

(pi )

(pi )

|t| = (pf – pi)2

= 1 – pf / pi


Measuring Rapidity Gaps at DØ Run II

Measuring Rapidity Gaps at DØ Run II

Use the following detectors to identify rapidity gaps:– Forward Calorimeters– Luminosity Monitors (LM)

VC: 5.2 < |< 5.9

LM: 2.7 < |< 4.4

p p

Forward Calorimeter


CalorimeterCalorimeter

FHEM CHLM

2.7

LMrange

4.4

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

2.6

Esumrange

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

IP


Calorimeter Energy SumCalorimeter Energy Sum

Areas normalized 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

Log10(cell energy sum / GeV):

10 GeV

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

Esum < 10 GeV for current study

Final value will be optimized using full data sample

WORK IN PROGRESS


Inclusive Z→μμ selection:– di-muon (|η|<2) or single muon (|

η|< ~1.6) trigger– 2 muons, pT > 15GeV, opposite

charge– at least one muon isolated in

tracker and calorimeter– cosmics cuts

DØ Run II preliminarySummer 2003

Mμμ (GeV)

Run I publication ”Observation of diffractively produced W and Z bosons in pp Collisions at sqrt(s)=1.8 TeV”, Phys. Lett. B 574, 169 (2003) Nine single diffractive Z→e+e- events. No result in muon channel.

Run II: first search for forward rapidity gaps in Z→μ+μ- events

Search for Z→μμ in DiffractionSearch for Z→μμ in Diffraction


Z Mass of rapidity gap candidatesZ Mass of rapidity gap candidates

Add Esum requirement to define gap

Invariant mass peak consistent with Drell-Yan/Z events

Will be able to compare Z boson kinematics (pT, pz, rapidity)

89.8 ± 0.1 GeV 89.6 ± 1.0 GeV

No Gap GapWORK IN PROGRESS WORK IN PROGRESS


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

Preliminary definition of rapidity gaps at DØ Run II

Study of Z→μ+μ- events with a rapidity gap signature

Current Status– Evidence of Z events with a rapidity

gap signature– Quantitative studies of gap definition,

backgrounds, efficiency in progress

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

outgoing proton side

outgoing anti-proton side

muon

muon

muon

muon


Forward Proton Detector LayoutForward Proton Detector Layout

9 momentum spectrometers each composed of 2 Scintillating fiber detectors housed in (Roman Pots) can be brought close (~6 mm) to the beam.

Reconstruct scattered protons and anti-protons to calculate their momentum fraction and scattering angle– Much better resolution than available with gaps alone

Combine tracks with central high-pT scattering (main detector)

Cover a kinematic region 0 < |t| < 3 GeV2 never before explored at Tevatron energies

Z(m)

D SQ2Q3Q4S A1A2

P1U

P2I

P2O

P1D

p p

D2 D1

233359 3323057

VetoQ4Q3

Q2

|t| = (pf – pi)2

= – 2k2(1 – cos)

~ 2 (small angles)

= 1 – xp = 1 – pf / pi

< 0.05 (diffraction)


FPD Detector SetupFPD Detector Setup

6 layers per detector in 3 planes and a trigger scintillator

U and V at 45 degrees to X, 90 degrees to each other

Layers in a plane offset by ~2/3 fiber. Fibers in each layer of a plane taken together define a segment (0.27mm) used to define hits.

2 detectors in a spectrometer. Hits used to define tracks.

0.8 mm

3.2 mm

1 mm

17

.39 m

m

17.39 mm

UU’

XX’

VV’

Trigger


Detector Hit ResolutionsDetector Hit Resolutions

Starting in January 2004, all 18 detectors regularly inserted (dipoles since February 2003)

Commissioning underway on quadrupoles

Resolutions calculated by the difference of the x value of a hit calculated from u/v segments compared to the x value of the x segment show that most of the detectors are working as expected

WORK IN

PROGRESS


FPD Dipole Data Analysis(Diffraction)

FPD Dipole Data Analysis(Diffraction)

Read out using AFE (Analog Front End) board Trigger minimum of one jet with pT > 25 GeV and North luminosity counters not firing

Harsh multiplicity cut applied on number of segments (1) allowed to fire to help deal with spray background

This correlation is from a small sample

pbar

p halo

pbar halo(0,0)

x

y

beam

D2 D1

D0

WORK IN PROGRESS

X_D1

X_D

2

Y_D1

Y_D

2

WORK IN PROGRESS


Dipole Diffraction AcceptanceDipole Diffraction Acceptance

Fair agreement between data and MC

Simple MC Geometrical Acceptance (14σ from beam)

Data (No Cuts)

flat |t| distribution

WORK IN PROGRESSWORK IN PROGRESS


Dipole Tagged DijetsDipole Tagged Dijets

Comparison of dijet events with (dashed) and without (solid) tags in the dipole detectors– areas normalized to one

Studies underway to calibrate detectors and refine tag definition

WORK IN PROGRESS

WORK IN PROGRESS


SummarySummary

The full FPD system has been installed and is working as designed

Full commissioning studies– Detector alignment and calibration

Initial analysis using FPD data:– Dijets using dipole tags

– Z→ μμ using tags

– (elastics!)

Initial definition of a gap in the calorimeter made

Evidence of Z→ μμ with gap signature found, further work needed to finalize results and interpretation in terms of diffractive physics

p

IP

IP

p


E

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, >1000tagged events expected in Run II

DØ Run II Diffractive TopicsDØ Run II Diffractive Topics

status of diffractive physics at dØ run ii

Documents