Diffractive Physics

E

Andrew Brandt, U. Texas at Arlington

DØ Physics WorkshopJuly 30, 2004Fermilab

A1U A2U

P2DP1D

P

Pbar

LMVC

Focus on mature analyses:1) Diffractive Z2) Elastic Scattering

Search for diffractive Z→μμ

DØ Run II preliminarySummer 2003

• Inclusive Z→μμ sample well understood:

• 2 muons, pT > 15GeV, opposite charge• at least one muon isolated in tracker and calorimeter• cosmic rejection

• RunI 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.

• RunII: first search for forward rapidity gaps in Z→μ+μ- events (Tamsin Edwards)

Mμμ (GeV)

Gap Definition: Luminosity Monitor

North(η<0)

South(η>0)

pp

• LM is 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 Run II LM

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:

Gap Definition: Calorimeter

Z Mass Comparison

• Invariant mass for gap events looks like standardZ sample• Will be able to compare Z boson kinematics (pT, pz, rapidity)

• Add Esum<10 GeV requirement to LM gap samples:

NoGAP

OneGAP

6

Problem: Run Dependent Esum

Two different run rangesshow different noise distributions;forward noise study in progress

7

Z→μμ + 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• No interpretation in terms of diffractive physics possible yet

• Plans:

• Understand run dependent effects• Measurement of the fraction of diffractively produced Z events; properties of gap candidate events• Diffractive W→μν, W/Z→electrons, jets and other channels • Use tracks from Forward Proton Detector

Elastic Scattering

A2U A1U

P2DP1D

p

pp

P

• Measure dN/dt for elastic scattering using early stand-alone FPD data:

• Quadrupole acceptance: • t > 0.8 GeV2 (requires sufficient scattering angle to leave beam envelope)• 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 (no momentum lost by beam particle)

veto on LM and VETO counters, early time hits (halo tracks)

Preliminary Elastic 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.

This analysis based on Jorge Molina’s thesis:first FPD Ph D

Fall 2003 shutdown survey data (points A+B) made available by accelerator in March shows offsets of up to 0.7 cm! Required rewriting of MC to separate separators,reanalysis of acceptance.

Separator plates

ACCEPTANCEACCEPTANCEThe acceptance for the PD spectrometer:

Before sep correction: After sep correction:

Much better high-t acceptance (previously high-t data thoughtto be halo)

CORRELATION OF AU-PDCORRELATION OF AU-PDWhen the correlations are introduced, the acceptance is reduced, beginning at higher values of |t| due to the positions reached by the AU pots

Separator corrected

Noacc.for low t !

Which acceptanceto use?

Note that triggeris based only on scintillator hits anddominated by halo spray(only 2% real tracks), so low-t data is presumablysingle arm elastics, high-tdouble arm elastics

Elastic Summary

• Re-evaluating acceptance and backgrounds

• Will decide soon if sufficient confidence in results to publish

• Silver lining: nearly 100% of effort directly transferable to new analyses

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

Diffractive Topics and Students!

New student, Vlatislav Hynek (Czech), working on forward diffractive jets

Student

Year

Institute Advisor Subject

Tamsin Edwards

2004

Manchester B. Cox Diffractive Z production using gaps

Ana Carolina de Jesus

2007

Rio A. Santoro Heavy Flavor production in diffraction

Helena Malbouisson

2007

Rio A. Santoro Diffractive dijet structure function

Luis Mendoza

2007

Bogotá C. Avila Diffractive W, Z

James Monk

2006

Manchester B. Cox Double Pomeron+jets

Renata Rodrigues

2007

Rio A. Santoro Elastic/Diffractive/Double Pomeron

Michael Strang

2004ish

UTA A. Brandt Diffractive jets tagged with FPD

• Start with a list of all global physics runs for which the FPD pots are inserted that have not been declared bad by another sub-detector group

• Filter out interesting triggers (from diffractive POV) on a run by run basis

• With p17, FPD information is in TMB so everything will be done with QCD_analyze

• Current Status– Final merging of pre-Nov 03 data underway– post-Nov 03 stripping started

Extract raw fpd fiber information fromraw (pre-Nov 03), DST (post-Nov 03)

put in a root tree

Use QCD_analyze to extract all other information from TMBs and put in a root tree

(using fixtmb2 version)

Sort tree by event number Sort tree by event number

Clone QCD tree, add matching FPD branch, compare each entry in trees

for matching event numbers and output to a merged tree for analysis

Diffractive Data Samples

New UTA post-doc DuncanBrown leading diffractiveanalysis group