Measurement of inelastic J/ y and y (2S) photoproduction at HERA

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Measurement of inelastic J/y and y(2S) photoproduction at HERA

A. Bertolin, R. Brugnera

Outline:• short introduction

• differential pT2 cross section in z slices

• differential z cross section in pT slices

• y(2S) to J/y cross sections ratio• momentum flow along the J/y direction• backup slides

ZEUS Week

DESY, 5/9/2012

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inelastic charmonium production at HERA (J/y and y(2S))

other contributions to the signal (decreasing size):

• y(2S) ® J/y (® m m) X decays• J/y from B meson decays• J/y from resolved photon processes

main background sources:

• J/y from the elastic g p scattering

• J/y from proton diffractive dissociationresolved gCS model

z < 0.2

direct gCS model (cc q.n. = J/y q.n.)

0.2 < z < 0.9p-rest frame: z = E(y)/E(g*)

direct gCO model (cc q.n. ¹ J/y q.n.)

this particular diagram 0.2 < z < 0.9

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other contributions to the signal • inelastic y(2S) production:

measure it directly using y(2S) ® m m

can not perform an efficient inclusive reconstruction of the decay y(2S) ® J/y X

y(2S) to J/y cross section ratios will be shown in wide bins of W, z and pT , they are not ideally flat (bins are wide because of the small 2S to 1S cross section ratio)

NOT subtracted (as all other experiments)• charmonium from B meson decays: B production well tested at HERA, much smaller B

cross section than at hadron colliders: overall < 2 % of the J/y are from B meson decays, < 5 % at low z

NOT subtracted

• J/y from resolved g processes (including cC ® J/y g ): not well know in PHP, LO cross section is tiny at HERA: overall < 0.5 %, < 4 % at low z

NOT subtracted

main background sources

• elastic and proton diffractive dissociation: why do we have to discard them ? • can not describe elastic and proton diffractive dissociation using calculations based on

the exchange of a single hard colored parton• explicit request from the theorists

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overall status of the theory

a mess

CS model: • available at LO and NLO (only direct)• more or less ok in PHP, completely wrong in p pbar

NRQCD = CS model + CO model• LO: TERRIBLE … in PHP diverging at low pT and high z, helps in p pbar• NLO direct + resolved: NOW AVAILABLE FOR PHP, will see later on comparison with

our data

kT factorization approach• LO CS model• direct + resolved• high order effects sneaked in via gluon transverse momentum effects

• more or less ok in PHP and p pbar

you should NOT be surprised of inconsistencies / hiccups / … in the theory• this is why it is worth to publish our paper• this is known to theorists … see Quarkinium Working Group WEB page and meetings

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1. Measurement of inelastic J/y photoproduction at HERA DESY 97-147 (July 1997) Zeitschrift f. Physik C76 (1997) 4, 599-612 Alessandro B. PhD thesis + Riccardo B. 94 data

2. Measurements of inelastic J/y and y(2S) photoproduction at HERA DESY-02-163 (September 2002)Europ. Phys. Journal C 27 (2003) 173-188 Alessandro B. + Riccardo B. 96-97 data

3. Measurement of Inelastic J/y Production in Deep Inelastic Scattering at HERADESY-05-071 (May 2005)European Physical Journal C44 (2005) 13-25Alessandro B. + Alexei A. + Igor K. (+ Leonid G. + Riccardo B.) 96-00 data

4. Measurement of J/y helicity distributions in inelastic photoproduction at HERADESY-09-077 (June 2009)JHEP12 (2009) 007Alessandro B. + Riccardo B. HERA I + HERA II

previous ZEUS papers on the same topic

this is why this paper draft is not written like (1) or (2) … tried not to write the same things again and again …

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full details:

Measurement of J/y helicity distributions in inelastic photoproduction at HERA - JHEP12 (2009) 007

http://www-zeus.desy.de/~bertolin/ZEUS_ONLY/inelpsidsdzdpt2/index.html

highlights:• data set: HERA I (114.1 pb-1) + HERA II (354.2 pb-1), please keep in mind the better

performances of CTD FLT and B/R MUON in HERA I w.r.t HERA II • y reconstruction: y ® m m, at least one m must be tagged in B/R MUON and CAL, the

other tagged at least by CAL, |h| < 1.75 (no FMUON), require minimum p/pt to be almost in the plateau region of the R/B MUON detectors …

• (inelastic) events selection: E(FCAL) > 1 GeV, at least 3 central (|h| < 1.75) vertex tracks with pt > 250 MeV

• elastic contribution removed due to E(FCAL) > 1 GeV

• elastic contribution removed due to the requirement of at least 3 central vertex tracks

• proton diffractive dissociation strongly suppressed by E(FCAL) > 1 GeV

• proton diffractive dissociation strongly suppressed by the requirement of at least 3 central vertex tracks

analysis highlights

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MC modeling

signal: • using mostly HERWIG MC• beauty + resolved MC samples for specific cross checks: PYTHIA MC

background:• EPSOFT MC

tuning of the HERWIG (pT) and EPSOFT (pT, W, MX) MC based on data: see backup slides

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proton diffractive dissociation subtraction

diffractive events are generated at z » 1we measure cross sections for z < 0.9the overlap should be ZEROHOWEVER due to the finite z resolution some of the diffractive events are RECONSTRUCTED with z < 0.9

EPSOFT MC generated z

fit the reconstructed z distribution to estimate the amount of diffractive events left after the z < 0.9 cut

for the fit the only change with respect to the nominal analysis is done for the z range:• nominal z range: 0.1 < z < 0.9• z range used for the diffractive fit: 0.3 < z < 1

why ?• we remove 0.1 < z < 0.3 because there is no diffractive yield at low z, instead we observe

a larger non resonant background and expect contributions also from beauty and may be resolved

• we add 0.9 < z < 1 to have more diffractive background and hence more “signal” for the fit

0.9

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data

HERWIG MC

EPSOFT MC

even

t fra

ctio

ns /

bin

shape distorted by the E(FCAL) > 1 GeV and ³ 3 (vertex) tracks requirements

purpose of the fit: fractions of HERWIG MC and EPSOFT MC that best describe the data

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even

ts fr

actio

n / b

in

HERWIG MC component from the fit

MC sumdata

outcome: HERWIG MC fraction for z < 0.9 is 94.7 %

data: stat. errors

MC: no uncertainty; sys. errors, due for example to the hadronic energy resolution, with size comparable to the data stat. errors, NOT shown in the above plot

• in the range 0.3 < z < 0.9, this fit, the result is: 0.947

• in the nominal analysis z range, 0.1 < z < 0.9, the result is: 0.954

• background is small, overall < 5 %

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0.75 < z < 0.9 0.6 < z < 0.75

0.45 < z < 0.6 0.3 < z < 0.45

Alessandro: black

Riccardo: blue

pT2 (and not pT) is the

variable always used

“classical” measurement performed by all mature PHP experiments

60 < W < 240 GeV• W < 60 GeV: too forward,

out of acceptance

• W > 240 GeV: low event yield, large non resonant background

1 < pT2 < 100 GeV2

• pT2 > 1 GeV2: agreed with

the theorists

• pT2 < 100 GeV2: low event

yield …

cross section vs pT2 in z slices

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cross section vs pT2 in z slices

0.1 < z < 0.3 Alessandro: black

Riccardo: blue

two analyses are in very good agreement

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cross section vs z in pT slices

1 < pT < 2 GeV 2 < pT < 3 GeV

3 < pT < 4.5 GeV pT > 4.5 GeV

60 < W < 240 GeVsame as before

0.1 < z < 0.9same as before

0.9

0.90.9

0.9 Alessandro: black

Riccardo: blue


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2S to 1S cross section ratio

basic formulas:

with some algebra:

FULL details:http://www-zeus.desy.de/~bertolin/ZEUS_ONLY/zn-03004/node41.htmlZEUS Note of the HERA I paper

for the HERA I paper we used PDG2002:Data Br1SMu/5.88E-2/,Br2SMu/0.70E-2/,Br2S1S/55.7E-2/today PDG2010:Data Br1SMu/5.93E-2/,Br2SMu/0.77E-2/,Br2S1S/59.5E-2/

PDG2010 ≡Please use this CITATION: K. Nakamura et al. (Particle Data Group), Journal of Physics G37, 075021 (2010) and 2011 partial update for the 2012 edition.

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2S to 1S cross section ratio vs W, z, pT


the phase space is different !yes• W < 190 GeV … above no 2S peak,

remember that the yield decrease as W increases …

• z > 0.55 … below no 2S peak, remember that the yield decrease as z decreases … almost exponentially …

• pT goes to 0 … so we have more statistics, also fine since we have no NLO / kT theory to compare to, the LO CS model only need z < 0.9

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p flow against / along the J/y direction

goal: check if the CS model, as implemented in the LO + PS HERWIG MC, can give a reasonable description of the momentum flow along the J/y direction

reminder:• in the CS model you have only a J/y and a backward “hard” gluon (transverse momentum

conservation in PHP) … so along we expect almost nothing …• in the CO Model you have a J/y with some nearby hadronic activity (“soft” gluons) and a

backward “hard” gluon … some along activity should be visible …

• clearly such an analysis would profit of large J/y pT, like in CMS, but due to the overall status of the theory a qualitative result in PHP would be very valuable anyway (in CMS due to the pT boost the “soft” gluons would become hard ones)

the against momentum flow is studied only “as a cross check”

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only change with respect to the phase space used for the J/y cross section measurements:

• 0.3 < z < 0.9

0.1 < z < 0.3 removed because of the small event yield, yield decrease as z decreases, and of the large amount of non resonant background observed

J/y direction of flight in the lab.

• vertex tracks

• pt(min) > 150 MeV

• | h | < 1.75 (HERA I CTD acceptance)• do not consider the m+ and m- tracks• track and J/y same/opposite hemisphere: p projection along the

J/y gives a positive contribution to Palong/Pagainst• use hemispheres because everybody suspects that the “soft”

gluons will not give well collimated hadrons at HERA• must discard the proton remnants … they have nothing to do with

the momentum flow around the J/y direction … so | h | < 1.75 is quite appropriate !

as discussed with F. Maltoni (UC Louvain, Be)

could have used ZUFOsbut should have used | h | < 1.75 anyway …so the difference between central ZUFOs and central vertex tracks is not so large … we do not see the neutrals but for soft charged hadrons CTD is better than CAL

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• have to measure two distributions: Pagainst and Palong

binning of each distribution: 0. 0.25 0.5 1. 1.5 2. 2.5 3. 4. 5. GeV

• have to measure vs pT

pT bins: 1. 1.4 1.9 2.4 3.4 4.2 10. GeV (bins used for the “inelastic J/y helicity paper”)

expect large statistical errors (like in the helicity paper)

Alessandro’s and Riccardo’s analyses differ in the way the non resonant background is handled (Alessandro: side bands, Riccardo: mass fit) … see previous HFL presentations for more details …

every method has its own advantages and disadvantages … so how does the two methods compare ?

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p flow against/along the J/y: data comparison

two analyses are in very good agreement for data

Alessandro: black

Riccardo: blue

against along

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p flow against/along the J/y: MC comparison

along against

Alessandro: black

Riccardo: pink

along against

two analyses are in very good agreement for MC

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sys. error analysis

1. diffractive background subtraction2. hadronic energy resolution3. BMUI chambers efficiency4. RMUI chambers efficiency5. J/y helicity parameters: l6. J/y helicity parameters: n7. HERWIG MC pT spectrum8. EPSOFT MC MX spectrum9. EPSOFT MC W spectum10. EPSOFT MC pT

2 spectrum11. invariant mass fit12. central vertex track multiplicity cut from 3 to 5

I will show the 12 steps, one by one, for the z differential cross section in pT slices

ALL the rest:http://www-zeus.desy.de/~bertolin/ZEUS_ONLY/inelpsidsdzdpt2/ijphp-sys-120518.pptx / .pdf

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s vs z for different pT slices: diffractive background

• diffractive component quantified by comparing the z(rec.) distribution measured in data with an HERWIG (signal) + EPSOFT (background) MC mixture

• increase / decrease the EPSOFT fraction while keeping a reasonable agreement between data and MC mixture

• redo all calculations

only one bin, at low pt and high z, with cross section variations > ± 5 %

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s vs z for different pT slices: hadronic energy resolution

• z = f (E-Pz(J/y),E-Pz(ZUFO))• using the true J/y kinematic

work out the true E-Pz• decrease or increase the

difference E-Pz(ZUFO) - E-Pz by 20 % event by event


variations < ± 5 %

may be 20 % seems “large” but even with this “large” value the results are stable … 20 % is also the value we used in the previous J/y papershad. energy resolution studies:• jet – jet ET balance in PHP• e’ – hadrons balance in DISnone of them apply to the J/y case

in a recent ZEUS jet paperInclusive-jet Photoproduction at HERA and determination of Alpha_s, Nucl. Phys. B864 (2012), 1-37quote ± 1 %

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s vs z for different pT slices: BMUI chambers efficiency

• efficiency in data computed from two tracks J/y events, known within some statistical uncertainties (due to the finite number of two tracks J/y events)

• data efficiency plugged into the MC at the analysis level (eaze)

• decrease or increase the efficiency for the barrel section, rear section unchanged


variations in the range ± 5 %, the size of the stat. uncertainties on the efficiencies

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s vs z for different pT slices: RMUI chamber efficiency

• efficiency in data computed from two tracks J/y events, known within some statistical uncertainties (due to the finite number of two tracks J/y events)

• data efficiency plugged into the MC at the analysis level (eaze)

• decrease or increase the efficiency for the rear section, barrel section unchanged


variations in the range ± 5 %, the size of the stat. uncertainties on the efficiencies, for z > 0.75variations much smaller for z < 0.75

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• l related to the polar distribution of the m in the J/y rest frame

• l = 0: isotropic• l is weekly dependent on z

and pt• from the ZEUS measurements

(HERA I+II) we know that | l | < 0.5 “everywhere”

• l = ± 0.5 at the event level• redo all calculations

largest sys. error of the analysisunavoidable (even if you go to p p instead of PHP)

s vs z for different pT slices: l helicity parameter

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s vs z for different pT slices: n helicity parameter

• n related to the azimuthal distribution of the m in the J/y rest frame

• n = 0: isotropic• n is weekly dependent on z

and pt• from the ZEUS measurements

(HERA I+II) we know that | n | < 0.5 “everywhere”

• n = ± 0.5 at the event level• redo all calculations

largest sys. error of the analysisunavoidable (even if you go to p p instead of PHP)

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s vs z for different pT slices: HERWIG MC pT spectrum

• the HERWIG MC J/y pt spectrum is reweighted to the data

• can make the MC spectrum harder or softer while keeping a reasonable agreement between data and MC

• additional weight given by exp(a pt2) at the event level


small effectas expected based on the experience with the past papers

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s vs z for different pT slices: EPSOFT MC Mx spectrum

• the EPSOFT MC Mx spectrum can be fitted with the function 1/Mx

• E(FCAL) is the observable mostly sensitive to the Mx spectrum


• additional weight given by 1/Mxa at the event level


small effectMx has a small impact on z(rec) i.e. E-Pz in FCAL is small

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s vs z for different pT slices: EPSOFT MC W spectrum

• the EPSOFT MC Wgp spectrum is flat … unphysical …

• reweight to a linear dependence: observe good agreement between data and MC for 2 tracks events at high z (diffractive background rich region we cut out in the analysis)


• additional weight given by Wa at the event level


small effectW has a small impact on z(rec) with the kinematic of diffractive events

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s vs z for different pT slices: EPSOFT MC pT2

spectrum

• the EPSOFT MC pt2 spectrum was set to -1 and -0.5 at the generation level and the two samples added

• observe good agreement between data and MC for 2 tracks events at high z (diffractive background rich region we cut out in the analysis)


• additional weight given by exp(a pt2) at the event level


small effectsizable only for z > 0.75 at low pt

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s vs z for different pT slices: invariant mass fit

• invariant mass procedure is fitting the non resonant background away from the mass peak with a smooth function

• an invariant mass window is defined for the signal: [2.85,3.3]

• count the events in the window and subtract the integral of the non resonant background function over the signal window

• change the window by ± 50 MeV (both in data and MC)


at most a10 % effect in the low z bins, there the S/B ratio is decreasing with respect to the bins with z > 0.45

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s vs z for different pT slices: central vertex track multiplicity cut from 3 to 5

• ask for at least 5 vertex track, with pt > 125 MeV and | h | < 1.75 and DO NOT consider any diffractive background after this

• redo the analysis

two bins with 20 % variations:• one at high z – pT • one at low z – 2 < pT < 3 GeV

this is testing the diffractive background procedure but also how well the track multiplicity cut is corrected for via MC

it is remarkable that at high z and low pT the difference is < 10 %

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(primary) vertex tracks with:pt > 250 MeV| h | < 1.75

crosses: dataupper histo.: HERWIG + EPSOFT MClower histo.: EPSOFT MC

primary vertex tracks control plot (requested by Olaf, NOT for the paper)

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E(FCAL) control plot (requested by Olaf, NOT for the paper)

crosses: dataupper histo.: HERWIG + EPSOFT MClower histo.: EPSOFT MC

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paper figures: invariant mass plot

a few obvious points: • the paper is not based on just ONE invariant mass fit !• the next figure alone, the control plots figure, needs 15 different invariant mass fits• fig. 1 is just for illustration purposes, to show the overall behavior of the invariant mass

distribution(s) we have• it would be impossible to put in the paper all the invariant mass plots practically used

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paper figures: some control plots

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naive expectation of the LO CS model: flat ratios at 0.25(2)

most of the central values are above 0.25, mild indications that the W - z ratio may not be that flat …

LO CS model «prediction»:s µ Gmm / m3

1S: 3096.6 MeV, 5.93 % x 92.9 keV2S: 3686.0 MeV, 0.77 % x 304 keVcan work out the prediction with a pocket calculator …

paper figures: 2S to 1S cross sections ratios

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paper figures: cross section vs pT2

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paper figures: cross section vs z

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observation on cross sections

• proton diffractive dissociation background is subtracted, this is fundamental for the theorists;

• y(2S) feed down is not subtracted, an inclusive reconstruction of the y(2S) decay would be needed and we do not have it. But the 2S to 1S cross section ratios vs p t W and z are measured. Theorists (should) know how to correct for this. Moreover they never asked us to perform this subtraction;

• J/y from any B hadron decay are not subtracted:

• the ratio between B hadron to J/y to “primary” J/y is much smaller at HERA than at hadron colliders (CDF, D0, CMS, ATLAS)

• theorists never asked us to perform this subtraction

• no PHP experiment up to now has performed this subtraction

• a subtraction based on data is very hard

• the only subtraction we could do would be fully based on MC … likely the theorists could account for this better than us (by adding a beauty component to the QCD predictions)

• we quantify the size of this contribution

• the cross section we quote, the number in nb, is corrected for this effect, as explained in the following slides

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for cross section vs pt2 in z slices

for every Dpt2 bin:

• disregarding any difference in the correction factors (= acceptances) for beauty:

s = N / CH L f.f. BR Dpt2 = s0

• taking explicitly the beauty correction factor (= acceptance) into account:

s = N – Nb / CH L f.f. BR Dpt2 + Nb / Cb L f.f. BR Dpt

2

…

s = s0 [1+(Nb/N)(CH-Cb)/Cb]

J/y from b decay: effect of the quoted number of nb

outcome:

• if Nb/N << 1 s = s0

• if CH=Cb s = s0

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continuous: 0.1 < z < 0.3

dashed: 0.3 < z < 0.45

dotted: 0.45 < z < 0.6

z > 0.6: at the event level negligible

usually < 10 events, 16 at most (low z low pt)

expected number of J/y from b decay (Pythia PHP inclusive beauty sample):

when Nb is largest Nb/N < 16/375 < 0.045

usually Nb/N < 10/400 < 0.025

total number of beauty MC events processed:

22.207.433

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0.3 < z < 0.45:

CH = Cb s = s0

whatever amount of beauty we have in data the number in nb we quote for the cross section is correct

0.1 < z < 0.3:

s = s0 [1+(Nb/N)(CH-Cb)/Cb]

= s0 [1+ 0.25×(Nb/N)]

< s0 [1+ 0.25×0.045] (use largest Nb/N)

< s0 [1+ 1.2 %]


negligible cross section increase (stat. error is > 10 % level)

for z > 0.45 Nb/N is so small that the effect is negligible anyway

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outcome on beauty:

beauty is included in the cross sections and the quoted cross sections, the number of nb, take this contribution properly into account

any theorist can compute the J/y cross section, according to his preferred model, compute the J/y from beauty contribution, according to his preferred model, add the two numbers and compare with our data …

as requested, we added to the paper tables “our” beauty cross numbers, obtained from the Pythia MC …

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paper figures: momentum flow along and against the J/y direction

although this is NOT a cross section measurement try to use a graphical layout similar to fig. 4 to 7, as requested

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conclusions and outlook

the material for the paper has been presented … we have the feeling this is the best we can do keeping in mind the different constraints we have (we are not leaving in a word with an infinite amount of money and time)

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extra slides

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theorists “like” and requested explicitly the s vs z because z is believed to be the key variable in PHPthey “like” and requested explicitly s vs z with pT > (as large as possible) GeVas a consequence in:Measurements of inelastic J/y and y(2S) photoproduction at HERA Europ. Phys. Journal C 27 (2003) 173-188 we provided:• s vs z with pT > 1 GeV• s vs z with pT > 2 GeV

using s vs pT2 in z slices one can build the s vs z with pT

> something … summing the contributions of the appropriate bins … but then for the stat. errors ? do we advise to take the square root of the sum of the squares of the stat. errors of the appropriate bins ?but then for the syst. errors ?

so let’s provide the theorist directly with what they need:• s vs z with pT > 4.5 GeVand add:• s vs z with 1 < pT < 2 GeV• s vs z with 2 < pT < 3 GeV• s vs z with 3 < pT < 4.5 GeVto allow also comparisons between the different ranges

s vs pT2 in z slices and s vs z in pT

slices

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check for Iris A.: Palong, 1 < p T < 1.4 GeVlooks like data > MC everywhere while both should be normalized to 1compare lin / log scale: MC > data in the first bin, MC < data elsewheregraphical artifact

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96/97 pos. data (20718 27889)

mbtake & GLOMU effic.: ok

num97v5.2 HERWIG MC

evtake + mbtake lumi: 38.0 pb-1

98/99 ele. data (30758 32906 )


num98v5.0 HERWIG MC


99/00 pos. data (33125 37715 )


num98v5.0 HERWIG MC


03/04 pos. data (45783 51245)


num03t6.0 HERWIG MC


04/05 ele. data (52258 57123 )


num05t3.0 HERWIG MC


06 ele. data (58207 59947)


num06t4.0 HERWIG MC available


06/07 pos. data before L/MERs (60005 62639)mbtake & GLOMU effic: oknum07t4.1 HERWIG MC availableevtake + mbtake lumi: 137.5 pb-1S (HERA I) = 114.1 pb-1

S (HERA II) = 354.2 pb-1

S (all HERA) = 468.3 pb-1

MC samples produced runlib v2008a.2

last version available

w.r.t. v2007a.2 used previously some

changes occurs for HERA II but the

overall sum stays 354.2 pb-1

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HERWIG MC J/y (direct photon)

HERWIG MC y(2S) (direct photon)

PYTHIA MC J/y (resolved photon)

PYTHIA MC c ® J/y g (resolved photon)

EPSOFT MC J/y

DIPSI MC: muon chamber efficiency in MC

GRAPE MC: muon chamber efficiency in MC

http://www-zeus.desy.de/~bertolin/ZEUS_ONLY/epstapes.html

http://www-zeus.desy.de/~bertolin/ZEUS_ONLY/effictapes.html

http://www-zeus.desy.de/~bertolin/ZEUS_ONLY/resolvedtapes.html

http://www-zeus.desy.de/~bertolin/ZEUS_ONLY/psitapes.html

MC samples produced

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EPSOFT MC vs data

generated parameters:

• Wep / f.f. = Wgp flat

• MX taken from EPSOFT MC of the form (1 / Mx)

• exp (-b pt2), sample with b=0.5 and sample with b=1, mixed with the same weight

only reweighting:

• reweighted to a liner dependence Wgp dependence (Wep / 60)

to compare EPSOFT MC and data:• 60 < W < 240 GeV (as for the nominal analysis)

• 0.9 < z < 1 (0.1 < z < 0.9 for the nominal analysis)

• pt > 0 GeV (pt > 1 GeV for the nominal analysis)

• 2 (vertex) tracks (³ 3 (vertex) tracks for the nominal analysis)

• E(FCAL) > 1 GeV (as for the nominal analysis)

• HERA I + HERA II data

proton diffractive

dissociation is dominant

55

EPSOFT MC vs data

S/B huge

data to MC ratio for W consistent with being flat (A1 consistent with 0)

in the diffractive modeling part of the sys. errors will take care of this little mismatch in pt pt

2

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EPSOFT MC vs data

in the diffractive modeling part of the sys. errors will vary the (1 / MX) dependence and hence the Efcal

EPSOFT MC shape

decay track reaching the m chambers

57

HERWIG MC

based on our past experience the only observable which needs attention is the p t – pt2

distribution

effect on the acceptances is mild, NOT a touchy issue

reweight the HERWIG MC to bring the simulation closer to the data

selected phase space for the reweighing procedure:• 60 < W < 240 GeV (as in the nominal analysis)

• 0.3 < z < 0.9 (avoid 0.1 < z < 0.3 where the signal is small and the non resonant background is large)

• pt > 1 GeV (as for the nominal analysis)

• ³ 5 (vertex) tracks (³ 3 in the nominal analysis)

• E(FACL) > 1 GeV (as for the signal)

• HERA I + HERA II data

proton diffractive

dissociation is negligible

58

HERWIG MC

pt2 reweighting procedure: fit the reconstructed dN/dpt

2 in both data and MC with a suitable function, F(pt

2), weight: ratio of the data to MC function, Fdata (pt2)/FMC (pt

2)

F is arbitrary as long as it describes data and MC

F = A0 + S Am cos(mw pt2) + S Bm cos(mw

pt2)

may be this is not the best possible choice ...

F = P1*(exp(P2*pt2)+P3*exp(P4*pt

2))P2: first slopeP4: second slopeP3: relative weight

04 ele. / 05 data

59

HERWIG MC

96 / 97 98 / 99 99 / 00 03 / 04 04 / 05 06 06 / 07 96 / 97 98 / 99 99 / 00 03 / 04 04 / 05 06 06 / 07

parameters are remarkably stable vs time

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• 60 < W < 240 GeV• 0.3 < z < 0.9• pt > 1 GeV

• ³ 3 (vertex) tracks• E(FACL) > 1 GeV• HERA I + HERA II data

even

ts fr

actio

n / b

inControl plots for the MC mixture

EPSOFT MC

HERWIG and EPSOFT MC predictions are affected by (systematic) uncertainties due, for example, to the hadronic energy reconstruction NOT shown in these plots

even if not too large these uncertainties are of the size of the data stat. errors (HERA I + HERA II data)

in the signal part of the sys. error the W and pt HERWIG MC spectra and the hadronic energy resolution implemented in the MC, E-Pz(rec)-E-Pz(gen), will be varied accordingly

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even

ts fr

actio

n / b

inControl plots for the MC mixture

the uncertainty on the muon chamber efficiency is not shown for the MC histograms, its size is

similar to the data statistical error, this uncertainty will be

included in the signal part of the sys. error

EPSOFT MC

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acceptance corrections

see:Measurement of the neutral current cross section and F_2 structure function for deep inelastic e^+p scattering at HERA ZEUS Collaboration; S. Chekanov et al. The European Physical Journal C 21 (2001) 3, 443-471

9.2 Binning and resolution

definitions of acceptance and puritycorrection factor = acceptance x puritycorrection factor, as obtained from MC, used to correct the data

keep in mind that in the ZEUS HFL group the correction factor is (inappropriately) called acceptance

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ff*BR*Lumi_tot=0.0975*0.0593*468300• ff for 60 < W < 240 GeV and Q2

max=1 GeV2

• BR = ( 5.93 ± 0.06 ) × 10−2

• Lumi_tot = 468.3 pb-1 = 468300 nb-1

PDG read on 27/1/2012Please use this CITATION: K. Nakamura et al. (Particle Data Group), Journal of Physics G37, 075021 (2010) and 2011 partial update for the 2012 edition.

BR(2S) = ( 7.7 ± 0.8 ) × 10−3

BR(2S to 1S+anything) = ( 59.5 ± 0.8 ) × 10−2

Measurement of inelastic J/ y and y (2S) photoproduction at HERA

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