Aug 22, 2014 - Two collider experiments: H1 and ZEUS. Armen Buniatyan. Feynman-x spectra of forward photons and neutrons at HERA. ISVHECRI-2014. 2 ...
ISVHECRI 2014 Symposium on Very High Energy Cosmic Ray Interactions 18-22 August 2014, CERN
Measurement of Feynman-x spectra of Forward Photons and Neutrons in DIS at HERA Armen Buniatyan
University of Birmingham
H1 Collaboration
arXiv:1404.9201
Eur.Phys.J. C74 (2014) 2915
HERA The first electron-proton collider at DESY Hamburg (1992-2007)
Ee± = 27.6 GeV Ep = 920 GeV Total centre-of-mass energy of collision up to √s ≈ 320 GeV (equivalent to 5 • 1013eV photon on a stationary proton target)
Two collider experiments: H1 and ZEUS
total lumi: 0.5 fb-1 per experiment
Armen Buniatyan
Feynman-x spectra of forward photons and neutrons at HERA
ISVHECRI-2014
2
Deep Inelastic electron-proton Scattering (DIS) at HERA
DIS – a probe of proton structure proton remnant
γ*
current jet
DIS event in H1 detector
e
p
proton electron scattered electron
Armen Buniatyan
Feynman-x spectra of forward photons and neutrons at HERA
ISVHECRI-2014
3
Motivation: Forward Particles in ep interactions DIS
γ*
Significant fraction of ep scattering events contains in the final state an energetic very forward particle, which carries a substantial fraction of the energy of the incoming proton (‘forward’≡proton fragmentation region)
proton remnant
In central (current) region the hard QCD scale is given by Q2 (and/or high pT, mq) ; the proton fragmentation region is non-pQCD regime - essential differences between theory predictions
A better understanding of forward particle production is needed
ep collisions – a clean environment to study the proton fragmentation Measurements very useful for MC model tuning Armen Buniatyan
Feynman-x spectra of forward photons and neutrons at HERA
ISVHECRI-2014
4
Motivation: High Energy Cosmic Ray Physics Shower max vs. CR (lab) Energy arXiv: 0903.3861
The tuning of cosmic ray interaction models crucially depends on the input from the measurements at accelerators
ISR
HERA SPS
LHC
In particular, the forward measurements (baryons, π0 , γ) are of the greatest importance, since the shower development is dominated by the forward, soft interactions. So far, only scarce data on Forward Production at High Energies, e.g. UA5, UA7 (SPS), LHCf at 900 GeV, 7 TeV Armen Buniatyan
Feynman-x spectra of forward photons and neutrons at HERA
ISVHECRI-2014
5
Forward neutron and photon production in ep interaction Energetic forward particles are produced at a very small angles from the fragmentation of proton remnant (e.g. Lund string) or from the exchange mechanism (Pomeron, Reggeon, π,…) pion exchange
proton fragmentation
W
π+ n or γ
Photons - from proton fragmentation (mainly from
π0
t
n
decay)
Neutrons - from proton fragmentation and from pion exchange Q2 =
-q2 =-(k-k‘)2
y = (q·p)/(k·p) W2 =
(q+p)2
photon virtuality inelasticity γ*p
CM energy
long. momentum fraction
x L = En, γ /Ep xF =
p||∗ p
∗ ||max
=
2p||∗ W
Feynman x
(for very forward particles xF ≈ xL) Armen Buniatyan
Feynman-x spectra of forward photons and neutrons at HERA
ISVHECRI-2014
6
H1 Forward Neutron Calorimeter FNC y proton
FNC 106m from IP, measure neutral particles (n,γ) Acceptance limited by beam apertures and detector size
acceptance window θ < 0.75 mrad (η>7.9)
Armen Buniatyan
Feynman-x spectra of forward photons and neutrons at HERA
ISVHECRI-2014
7
Control of energy calibration and linearity check HERA ep data: LER (460 GeV), MER (575 GeV), HER (920 GeV)
n
30.6.2007
γ
Armen Buniatyan
Feynman-x spectra of forward photons and neutrons at HERA
ISVHECRI-2014
8
The phase space of the measurements HERA II period 2006-2007 Luminosity= 131 pb-1 230000 neutron events; 83000 photon events
at high xL, many photon candidates FNC clusters originate from more than one photons; Æ suppress multi-photon events with cut xL
